IMBSIR 75-790

FY75 Progress Report on Desig

Criteria and Methodology for

Construction of Low- Rise

Buildings to Better Resist

Typhoons and Hurricanes

Contributors:

Richard D. Marshall, Principal Investigator

Noel J. Raufaste, Jr., Project Coordinator

Emil Simiu, Structural Research Engineer

S. George Fattal, Structural Research Engineer

Joseph Kowalski, Building Research Economist

Steven Kliment AIA, Architect, New York City

Gerald Sherwood, Engineer, Forest Products Laboratory, U.S. Forest Service

Thomas Wilkenson, Engineer, Forest Products Laboratory, U.S. Forest Service

Jamilur R. Choudhury, Associate Professor of Civil Engineering,

Bangladesh University of Engineering and Technology, Dacca

Center for Building Technology

Institute for Applied Technology

National Bureau of Standards

Washington, D. C. 20234

November 1 975

Interim (July 1, 1974 through June 30, 1975)

Prepared for The Office of Science and Technology

Agency for International Development

Department of State

Washington, D. C. 20523

Under a Participating Agency Service Agreement (PASA)

No. TA(CE) 04-73

NBSIR 75-7S0

FY75 PROGRESS REPORT ON DESIGN

CRITERIA AND METHODOLOGY FOR

CONSTRUCTION OF LOW-RISE

BUILDINGS TO BETTER RESIST

TYPHOONS AND HURRICANES

Contributors:

Richard D. Marshall, Principal Investigator

Noel J. Raufaste, Jr., Project Coordinator

Emil Simiu, Structural Research Engineer

S. George Fattal, Structural Research Engineer

Joseph Kowalski, Building Research Economist

Steven Kliment AIA, Architect, New York City

Gerald Sherwood, Engineer, Forest Products Laboratory, U.S. Forest Service

Thomas Wilkenson, Engineer, Forest Products Laboratory, U.S. Forest Service

Jamilur R. Choudhury, Associate Professor of Civil Engineering,

Bangladesh University of Engineering and Technology, Dacca

Center for Building Technology

Institute for Applied Technology

National Bureau of Standards

Washington, D. C. 20234

November 1975

Interim (July 1 , 1 974 through June 30, 1 975)

Prepared for The Office of Science and Technology

Agency for International Development

Department of State

Washington, D. C. 20523

Under a Participating Agency Service Agreement (PASA)

No. TA(CE) 04-73

U.S. DEPARTMENT OF COMMERCE, Elliot L. Richardson, Secretary

James A. Baker, III. Under Secretary

Dr. Betsy Ancker-Johnson, Assistant Secretary for Science and Technology

NATIONAL BUREAU OF STANDARDS, Ernest Ambler. Acting Director

TABLE OF CONTENTS

SI CONVERSION FACTORS ± ABSTRACT ±i

INTRODUCTION 1

A. SUMMARY OF PROGRESS FOR FISCAL YEAR 1975 5

Background 5 Activities at the Field Test Sites 6

1) Quezon City Science Garden Weather Station 8

2) Daet Weather Station 8

3) Laoag City Weather Station 9

Activities at the UP Wind Tunnel Facility 1.0 Wind Tunnel Studies 11

Analysis of Climatological Data 12

Other Project-Related Activities 13

Regional Conference 13

Description of Draft Project Outputs 15

1) Basic Wind Speeds 15

2) Design Speeds and Pressure Coefficients 16

3) Masonry Connectors and Timber Fasteners 16

4) Economics of Building Needs 17

5) Socio- Economic and Architectural Considerations ig

Technology Transfer 20

B. EXPECTED PROGRESS THROUGH PROJECT COMPLETION 23

Field Test Sites 23

Wind Tunnel Operations 23
Preparation of Design Criteria 24

Caribbean Regional Conference 24

FISCAL YEAR 1976 PROJECT SCHEDULE 26

APPENDIX A

APPENDIX B

APPENDIX C

APPENDIX D

APPENDIX E

APPENDIX F

.APPENDIX G

.APPENDIX H

Minutes of the 7th-llth Philippine Advisory Committee

Meetings

Low-Rise/Low-Cost Housing and Extreme Wind Related Problems

in Bangladesh

Manila Regional Conference Program

Estimation of Extreme Wind Speeds in the Philippines

A Guide to the Determination of Wind Forces

A Guide for Improved Masonry and Timber Connectors in

Buildings

The Economics of Building Needs: A Methodological Guide

Housing in Extreme Winds
SI CONVERSION FACTORS

This report describes measurements in metric units. It is recommended that the reader assume the responsibility for applying the appropriate

conversion to English units. The United States of America, as a signatory

to the General Conference of Weights and Measures (which gave official

status to the metric SI system of units) , recognizes the International

Standard (SI) units of measurement.

Length

1 meter (m) = 3.281 feet (ft)

Velocity

1 meter per second (m/s) = 3.281 feet per second (f/s)

= 2.237 miles per hour (m/h)
ABSTRACT

The annual progress report presents major NBS accomplishments and

activities during the third phase (FY75) of a forty month project concerned

with developing improved design criteria for low-rise buildings in developing countries to better resist extreme winds. The research study, sponsored

by the Agency for International Development, commenced in March 1973. Two

other progress reports: NBSIR 74-582 FY73 Progress Report (first phase of

the research- -4 months) and NBSIR 74-567 FY74 Progress Report (second phase

of the research- -12 months), document the first 16 month level of effort.

During FY75, 6 major tasks were completed; instrumentation of remaining

two of six test houses, continuation of technician training, analysis of

extreme wind data, development of draft reports describing project results,

participation in regional conferences in Manila and schedule a regional conference in Jamaica during November 1975. During FY76, data collection and

analysis activities will be completed. A final report will be published by

the end of the fiscal year.

Key words: Buildings; codes and standards; housing; hurricanes; low-rise

buildings; natural disaster; structural connections; typhoons;

wind loads.

ii
INTRODUCTION

The FY 7 5 progress report is the third in a series of annual reports

describing the National Bureau of Standards' activities in developing

improved design criteria for low-rise buildings in developing countries to

better resist extreme winds. The research project is sponsored by the

Office of Science and Technology, Agency for International Development

(AID), under a Participating Agency Service Agreement (PASA) No. TA(CE)

04-73.

The report discusses the principal activities and accomplishments

during the period July 1, 1974 through June 30, 1975. Information about

FY73 and FY74 accomplishments are contained in the two National Bureau of

Standards Interagency Reports, NBSIR 74-582 and NBSIR 74-567, Project

Status Reports - Design Criteria and Methodology for Construction of Lowrise Buildings to Better Resist Typhoons and Hurricanes .

The FY73 Project Status Report provides the initial project background and discusses the formation of a Philippine Advisory Committee.

The committee was instrumented in coordinating local project research

activities, selecting field test sites, providing field test buildings

and selecting appropriate personnel to work on the project.

The FY74 Project Status Report covers the instrumentation of test

houses, the training of technical personnel at the field test sites and

the wind tunnel facility, the preliminary analysis of wind load data,

the four-day NBS international workshop on designing for high winds, and

an assessment of the state-of-the-art of wind technology on low-rise buildings.
This report discusses activities performed during FY75 and includes

additional technical information resulting from FY75 activities. Draft

technical outputs are found in the appendices as listed below.

During FY75, six principal tasks were completed. The tasks were:

a. Instrumentation of the fifth and sixth test houses (Quezon City

and Laoag City field sites)

,

b. Continuation of technician training for full-scale data collection and wind tunnel testing,

c. Transfer to the Philippine Advisory Committee of a computer

program developed by NBS to determine extreme wind speeds for

various mean recurrence intervals,

d. Scheduling of a Caribbean regional conference at Kingston,

Jamaica for November 6 and 7, 1975 to disseminate project

results to Caribbean wind-prone countries,

e. Development of draft reports on:

• distribution of extreme winds

• improved design pressure coefficients

© guidelines for timber fasteners and masonry connectors

• economic analysis/housing forecasting methodology

« socio-economic and architectural considerations

f. Dissemination of draft reports at regional conferences in

Manila during May 1975.

The Appendices are:

Appendix A - Minutes of the 7th - 10th Philippine Advisory Committee

Meetings

Appendix B - Low-Rise Low-Cost Housing and Extreme Wind Related

Problems in Bangladesh

2
Appendix C - Manila Regional Conference Program

Appendix D - Estimation of Extreme Wind Speeds in the Philippines

Appendix E - A Guide to the Determination of Wind Forces

Appendix F - A Guide for Improved Masonry and Timber Connectors in

Buildings

Appendix G - The Economics of Building Needs: A Methodological

Guide

Appendix H - Housing in Extreme Winds

3

A. SUNMARY OF PROGRESS FOR FISCAL YEAR 1975

Background

The project originated from the recognition by AID and NBS that

additional research on wind is needed to reduce property losses, human

suffering, disruptions of productive activities, and expenditures for

disaster relief. Information is, needed to supplement the limited amount

of existing data on wind effects on low-rise buildings. Existing wind

load criteria do not make adequate provisions for steady and fluctuating

wind pressures along the edges of roofs and walls where separated flows

occur. Extreme negative pressures (suction) acting on these building

surfaces are one of the primary contributors to building damages. This

research project possesses a potential for reducing building damages

worldwide, as well as in the U.S.

The research centers around field studies (direct measurement of

wind loads on six low-rise buildings at three separate sites in the Philippines) and wind tunnel studies (scale models of the field test buildings

and models of other typical dwelling geometries)

.

The primary purpose of the full-scale field studies and the wind

tunnel model studies is to refine the design pressure coefficients for

low-rise buildings. While a great deal of work on wind loading on tall

buildings has been accomplished during the past 10 years, very little

parallel work has been devoted to buildings having heights less than 10

meters. Investigations of wind damage strongly suggest that coefficients

contained in most current codes and standards do not adequately describe

the wind characteristics near the ground and the pressure distributions

5
on low-rise buildings. Highly localized wind pressures on buildings tend

to be underestimated while overall pressures tend to be overestimated.

This was confirmed from full-scale test results obtained in this program.

Equally important to the understanding of wind pressures on buildings,

is the selection of design wind speeds in geographic areas having a high

frequency of tropical storms. By taking proper account of these frequencies and local terrain effects, it is anticipated that design speeds can

be selected which will accurately reflect the risk of wind damage to buildings. It will thus be possible for the building designer to specify more

realistic design loads (from the NBS improved pressure coefficients) which

should permit buildings to better perform during their expected life.

The reader is referenced to Appendix A, "Minutes of the 7th-10th

Philippine Advisory Committee Meeting," for a review of the Committee's

involvement with this research project.

Activities at the Field Test Sites

Three field test sites (see Fig. 1) were selected for recording wind

load data on buildings. The sites are Quezon City where 3 houses were

instrumented with wind pressure equipment. Laoag City about 500 kilometers

north of Quezon City is the site of two test houses. Daet, about 230 kilometers south east of Quezon City is the location of one test house.

A detailed description of the three field test sites and related instrumentation was presented in the FY74 Progress Report (NBSIR 74-567).

Three site visits were made by NBS personnel during FY75. These occurred

in July and November of 1974 and May of 1975. Although most of the activities conducted during FY75 were of a routine nature (calibration and main6
I I 122

J E 126°E

Figure 1 Building test sites
tenance of test equipment) , several serious problems were encountered which

required component repair or replacement and certain changes in operating

procedures. Summaries of activities at the three sites and the status of

each site as of June 30, 1975, are discussed below:

1) Quezon City, Science Garden Weather Station

This site currently has three test houses which are instrumented with

a total of 19 pressure transducers. A delay in shipment of the third test

house provided by CARE, Inc. , Bangladesh, at this site made it impossible

to complete the instrumentation of the house in FY74. This unit was subsequently instrumented by the NBS team during July, 1974. Minor problems

were encountered with the time code generator and pressure transducer signal

conditioner. These units were either replaced or repaired with no loss of

test data. A more serious problem was encountered in November, 1974, when

a number of pressure lines and signal cables were damaged by rodents which

infested the test site following the clearing of a nearby squatter settlement. Approximately one week of repair work was required. A rodent control

program was initiated.

Approximately eight hours of recordings were obtained during the year.

These data were recorded during a time when significant changes in the wind

exposure occurred with recent construction of tall buildings southeast and

west of the test site. The construction provided an ample opportunity to

collect wind pressure data under differing topographic conditions.

2) Daet Weather Station

The single test building at Daet is currently equipped with 10 pressure

8
transducers. The Daet test site has been relatively free of problems since

the installation of test equipment in March, 1974. A fence was erected in

July to protect the meteorological tower and guy cables from livestock

grazing on the station grounds. Corrosion due to the ocean exposure required

the replacement and painting of a number of tower bolts and cable clamps in

May of 1975. It was necessary to replace most of the exposed flexible pressure tubing at the same time because ultraviolet radiation deteriorated the

tubing. Commercial power at the site has been extremely unreliable over the

past six months which required a change in data recording operating procedure.

Rather than keeping the data system in a "power on" mode, the test equipment

is now turned on only when a tropical storm is known to be approaching the

site. If no commercial power is available, the system is switched over to

the generator which normally supplies the station radar system.

Approximately eight hours of records were obtained during the passage

of Typhoon Bidang in November and Typhoon Andoy in December of 1974. Wind

speeds in excess of 30 m/s (68 m/h) were recorded and wind directions ranged

clockwise from north to southwest.

An additional problem at the Daet test site has been the transfer of

trained personnel to other Philippine Atmospheric Geophysical and Astronomical Services Administration (PAGASA) Stations. This action required NBS

personnel to perform additional training sessions for replacement personnel

during each site visit.

3) Laoag City Weather Station

The two test houses at Laoag City are currently equipped with 10 pressure transducers. Construction of a barrack by the Philippine Air Force has

changed the exposure of the test site to easterly winds.

9
As with the Daet test site, construction of a stock fence and replacement of exposed pressure lines were required at the Laoag City site. A

short circuit in the wind direction data line resulted in the loss of some

data during the passage of Typhoon Aning on November 6, 1974 during which

winds with gusts up to 47 m/s (105 m/h) were recorded at Laoag City. More

recently (June 1975) , two data lines were accidentally cut by a construction

crew. This damage was repaired by the PAGASA. In spite of these problems,

the Laoag City test site has yielded several valuable records on the first

test house, which is adjacent to weather station buildings, and on the

second test house, which was instrumented in July of 1974. Approximately

four hours of valid recordings were obtained this past fiscal year. Test

tapes from Laoag City have not been fully analyzed.

Activities at the University of the Philippines Wind Tunnel Facility

Two building models were tested at the University of the Philippines

Wind Tunnel Facility during FY75. They were a 1:80 scale model of Test

House No. 1 located at the Quezon City site, and a 1:80 scale model of the

RP-US Bayanihan School Building. The house is single story with a plan

dimension of about 6 by 7 meters. The school building is single story and

8 by 18 meters in plan. Tests were conducted to evaluate the performance

of the tunnel and of the characteristics of the simulated atmospheric,

boundary layer in producing pressure fluctuations on building models.

The agreement between model and full-scale indicates that this facility

is entirely suitable for modeling buildings in the lower 10 meters of

the atmospheric boundary layer at scales of 1:80 or smaller.

Following validation of the wind tunnel flow simulation, a model

10
of the AID funded RP-US Bayanihan School Building was tested at the

request of the local AID Mission to determine overall load coefficients

and localized pressure coefficients. The results of these tests were

presented in a draft report which has been reviewed by the AID Manila

Mission, the Philippine government .and other interested parties. The

report is currently being prepared as a final NBS document. Although

the UP Wind Tunnel Facility has been shown to yield satisfactory results

and is fully operational, serious local staffing problems have arisen. A

key technician who had undergone continuous training since the initiation

of wind tunnel operations in November of 1973, left the University in

September, 1974 for an educational opportunity abroad. No satisfactory

replacement has been found. The University also seems relatively disinterested in establishing a viable alternative research facility in the area

of building aerodynamics . Because the University lacks trained staff in

fluid dynamics or aerodynamics, they do not currently have the capability

of conducting wind tunnel tests without NBS supervision. Some interest

has been shown by PAGASA (who have appropriate staff members) in assuming

responsibility for wind tunnel operations; this matter has to be fully

resolved.

Wind Tunnel Studies

Because of the problems outlined above and to keep the project on

schedule, NBS project staff initiated a series of wind tunnel tests at

the Virginia Polytechnic Institute and State University (VP I and SU) using

a flow simulation technique similar to that which was perfected at the UP.

Since VP I and SU's test section was larger than that at the UP (2.14 x

11
2.14 meters square and 5.5 meters long) the scale ration was increased

from 1:80 to 1:70. The tests initiated in April, 1975, have been completed. They cover 32 combinations of roof slope, height-to-width ratio,

length-to-width ratio and size of roof overhang. The test results are

still being analyzed. Preliminary data suggest that additional studies

be conducted on roof slopes near 10 degrees. The wind tunnel test results

and the full-scale test results obtained during previous studies in Montana,

and studies conducted by the Building Research Establishment in England

including research by NBS in the Philippines provided the basic data used

in developing tentative design pressure coefficients. These data were

presented at regional conferences in Manila in May, 1975. These results

are discussed in more detail in a later section and fully reported in Appendix E. It is anticipated that the remaining tests and data analysis can be

completed by the end of December, 1975.

Analysis of Climatological Data

Work continued during FY 7 5 on the analysis of wind speed records in

the Philippines. Several station data series were fitted with extreme

value distributions using a computer program developed at the NBS. This

program is currently being modified for use on the PAGA.SA computer facility

in Quezon City and is expected to become fully operational early in FY76.

Features of this program and preliminary results of the data analysis were

presented at regional conferences at Manila in May. The computer program

is available for use by other wind-prone countries. Additional information

on the estimation of wind speeds may be found in Appendix D.

12
Other Project-Related Activities

On December 25, 1974, Cyclone Tracy passed over the city of Darwin,

Australia, causing almost total destruction of the residential areas of

the city. Because of the widespread use of corrugated galvanized iron

sheet and light timber frames, the behavior of housing in Darwin has a

definite bearing on the development of design criteria for housing in

other tropical regions of the world, particularly those regions having a

high frequency of intense storms. Due to its involvement in wind load

research, the NBS was invited to participate in post-disaster studies of

Darwin and a close liaison is being maintained with Australian research

establishments which are conducting follow- on projects relative to Darwin.

It is anticipated that some of these findings will be incorporated in the

final design criteria.

Regional Conference

As previously mentioned, draft project results were disseminated and

discussed at a regional conference held in Manila, Philippines, on May

16-17, 1975. The purpose of the conference was to provide draft results

to the professional building community from Asian wind-prone countries. The

conference provided the NBS team an opportunity to receive technical feedback as an indicator of project research relevence. This information serving as inputs will assist future data analysis and in developing final

technical reports for the completion of this study. The conference program

is contained in Appendix C.

The first day of the two-day regional conference was devoted to presentation and discussion of technical results. A short description of each

13
presentation is presented in the following section. The second day was

devoted to an open forum. The technical reports are contained in Appendices D - H.

Information transfer between Bangladesh and the project was performed

by Dr. Jamilur R. Choudhury, Professor of Civil Engineering, Bangladesh

University of Engineering and Technology, Dacca. Dr. Choudhury is under

contract with NBS to provide technical inputs relative to the Bay of Bengal

Countries. He presented a paper (based on his latest report to NBS) on

housing, socio-economic aspects, and wind distributions in Bangladesh,

India, Burma and Sri Lanka. This report in Appendix B supplements a previous report (see Appendix D, NBSIR 74-567). Additional information on

socio-economic factors, anticipated housing needs through 1985, and data

on wind speed records and wind damage statistics is discussed. The report

will be submitted separately to the National Technical Information Service

(NTIS).

The conference was scheduled just prior to international conference

(also in Manila) on civil engineering in disaster prevention and control.

The draft project results were presented at this meeting. This provided

an opportunity to discuss the high wind project with another segment of

the international and Philippine professional building community.

This conference was sponsored by the Philippine Institute of Civil

Engineers (PICE) . Approximately 450 professionals from seven countries

attended. Countries represented were the United States, Republic of China

(Taiwan), Philippines, Japan, United Kingdom, Indonesia, and New Zealand.

Proceedings of the conference will be published by the PICE.

The project results were also discussed at the Seventh Joint Meeting

of the U.S. -Japan Panel on Wind and Seismic Effects, May 20-23, 1975 in

Tokyo. On June 17, 1975, the project draft results were presented at an

14
AID- sponsored international disaster preparedness seminar.

Description of Draft Project Outputs

The following is a brief description of the contents of the reports

presented at the conferences. Reports were presented in draft form and

were circulated to all attendees for review and comment. These reports

included in Appendices D -H

x are briefly reviewed in the following paragraphs .

1) Basic Wind Speeds

The report, Estimation of Extreme Wind Speeds in the Philippines , by Dr. Emil Simiu, is found in Appendix D. The report contains a comprehensive review of probabilistic techniques for the analysis of extreme

wind speeds. Corrections of annual extreme speeds for the type of instrumentation used, averaging time, height above ground, and type of exposure

are covered so that homogeneous sets of wind records can be established.

Probabilistic models are then described and are applied to wind records

for several Philippine stations using a computer program developed at the

NBS. The results are compared with design speeds presented in the National

Structural Code of the Philippines.

It is concluded that design speeds currently used in parts of Mindanao

can be reduced while those in use for Northern Luzon and certain coastal

exposures should be increased. Finally, problems related to the estimation of basic wind speeds for very long mean recurrence intervals in tropical storm areas are outlined.

1The reports contained herein were developed for the regional conference

in Kingston, Jamaica held during November 6-7, 1975; the contents contain

additional data analysis subsequent to the Manila and Tokyo conferences.

15
2) Design Speeds and Pressure Coefficients

The report titled, A Guide to the Determination of Wind Forces , by

Dr. R. D. Marshall of the NBS, is found in Appendix E. The report describes the basics of wind flow around buildings and the pressures created

by these flows on building surfaces. Effects of such features as roof

slope, roof overhangs and building openings are also discussed. This

paper refers to material covered in the paper by Dr. Simiu and assumes

that the basic wind speed is known or can be calculated by the designer

.

A procedure for determining the design speed is presented which takes into

account the general terrain roughness, local topographical features,

height of building, expected life of building and acceptable risk of failure.

Once the design speed has been obtained, the mean dynamic pressure

is calculated and pressures acting on walls, roofs and internal portions

of buildings are then determined by use of appropriate pressure coefficients which are tabulated in the paper. Finally, corrections are applied

to the calculated pressure to account for terrain roughness and height of

building. The steps required to calculate pressures and total drag and

uplift forces are summarized and a worked example is presented. It is

intended that this paper form the basis for wind load design standards in

developing countries.

3) Masonry Connectors and Timber Fasteners

The report, A Guide for Improved Masonry and Timber Connectors in

Buildings , was prepared by Dr. S. George Fattal of NBS and Messrs. Gerald

Sherwood and Thomas Wilkenson of the Forest Products Laboratory and is

16
found in Appendix F. The buildings discussed are one and two stories in

height, generally with a gable timber roof covered with corrugated iron

with overhangs of up to 1.5 meters. The chapters on connectors lead off

with an introductory background discussion. They are followed by a section

on buildings damaged by high winds. Examples of wind damages are presented

through use of photographs and an analysis is presented in textual form.

The report also discusses building damages caused by the December 1974

cyclone at Darwin, Australia.

A survey and evaluation of some current masonry practices as used in

the tropics are presented. Local practices, investigation of building

products, and standards compliance are discussed and evaluated with the

aid of photographs of buildings during various stages of construction.

Current masonry practices in the United States are presented. Also,

various types of connectors used in such construction are discussed. This

serves as a reference for improving building practices.

The last section of the report addresses suggested improvements in

masonry construction. The suggestions are based on a review of several

masonry documents, appropriate reports, building codes, specifications,

working drawings and photographs of Philippine houses and post- disaster

surveys of typhoon- damaged buildings.

The chapter on timber fasteners is similar in format to that for

masonry connectors; it presents a general introduction to timber fasteners

and a review of Philippine timber fastener construction practices. Recommendations follow.

4) Economics of Building Needs

The report, The Economics of Building Needs - A Methodological Guide ,

17
by Dr. Joseph Kowalski of NBS, (see Appendix G) serves as a tool to assist

the decision maker in assessing the impact of the development of buildings

to better resist winds on local housing needs. This document leads off

with a review of the economic background of forecasting housing needs.

This is followed by an economic model to forecast housing needs. The report attempts to identify those parameters that define a low-cost house.

This is determined by a simple mathematical procedure based on readily

available data i.e., family income, housing expenditure, and the established

regional poverty line.

5) Socio -Economic and Architectural Considerations

The report, Housing in Extreme Winds , by Steven Kliment, architectural

consultant (see Appendix H) is a review of socio-economic and architectural

aspects of low-rise/low-cost buildings exposed to high winds. The report

is consumer- oriented in nature and is intended for residents, owners, planners and builders of low- cost/low- rise housing in developing countries.

The report addresses the Philippines, Jamaica and Bangladesh. A

general review considers socio-economic conditions prevailing in developing

countries. These conditions include: strong respect for traditional

materials and methods of house construction with a corresponding suspicion

of innovative forms and approaches; a high proportion of rural residents,

remote from new building concepts as well as from post- typhoon/hurricane

relief programs; a rising proportion of urban poor who live in squatter

settlements; a very high ratio of citizens (in a range from 60% to 12%

depending on country) whose incomes are at a level where they cannot afford

housing of any kind- -either on the open market or government- subsidized;

18
and a chronic shortage of capital funds to stimulate or support a national

program of wind-resistant housing construction.

The report reviews approaches for providing assistance in "sites and

services". This concept suggests that squatters and other low income individuals be provided through gift, loan or lease with a site equipped with

water supply, sewerage and electricity, on the condition that the beneficiary

erect and maintain a house upon it. The importance of land from the social

standpoint is stressed. Advantages and limitations of squatter settlements

are discussed.

Suggested solutions include the placement of buildings to exploit

existing land contours and vegetation, and the design of buildings so as to

conform to research recommendations concerning preferred configurations of

roofs, walls, overhangs and openings. In addition, construction techniques

are briefly covered.

Materials that are cheap, strong and locally available are recommended,

and several innovative methods of construction are mentioned. They include

soil that has been stabilized or strengthened by means of asphalt or cement

and indigenous fibers and grasses for possible use as reinforcement for

concrete, adobe and brick. Plastics have been produced using native and

imported raw materials and could serve as an excellent low-cost house once

their configurations become more familiar to the population. At first,

they may be used for clinics, schools and warehouses.

Rural and urban components of population trends for each of the three

countries are reviewed. The greatest projected increase in population will

be in Bangladesh (a rise of 110% by the year 2000) . These percentages

tend to conceal actual numbers; the 86.6 million projected increase in

19
Bangladesh will raise even further the 1970 average population density of

1,361 persons per square mile. The density will be much higher in urban

areas and on rural high ground during the flood season.

Finally, housing characteristics peculiar to each country are summarized through text and in thumbnail sketches, in both architectural terms and

in terms of occupancy characteristics. The socio-economic functions of

family ties and housing needs are reviewed. The community structure, the

economics of housing, the housing characteristics, and the housing programs

are summarized by country.

Technology Transfer

The NBS/AID high wind project results should have an impact on several

key sectors of the local developing country's population- -the professional

community, the government policy-making sectors, and the building user both

owners and tenants.

It is hoped that attendees from the Manila conferences have become

more proficient in applying improved wind technology to low-rise buildings

so they in turn can inform others. NBS has a responsibility to the building tenants and is very concerned about establishing effective methods for

the transfer of technical information. To stimulate the homeowner and

tenants interest to read the final reports; the documents must be made

readily available through concise and graphic descriptions, of technological

issues, the research, the findings, and the conclusions.

The use of brochures, pamphlets and other consumer- oriented material

is an excellent first step in transferring a glimpse of the project. They

serve as "pointers" to technical information and reports. Brochures have

been and are being developed to summarize various aspects of the project.

20
Consumer- oriented information pamphlets for the five draft project

reports were developed in August 1975. These pamphlets contain about five

pages of summarized material. They may be loosely inserted in a folder for

ease of removal or annotation, addition or substitution of information.

The individual folders forming the file package may be circulated individually or together to users in government agencies, the professional

community and individual households within the community.

A movie, another consumer -oriented package, was completed in April

1975. The movie summarizes the high wind research project to date. Through

illustrating the destructive effects of winds on buildings, it informs the

viewers of the NBS field testing activities and the wind tunnel testing program. The movie also uses computer graphics to illustrate the effect of

wind on buildings. This 16 mm color movie is a transfer of information

mechanism aimed at architects, engineers, building officials and students

in both developing and developed countries. The movie is intended to be

both educational and entertaining. Copies of the film are available on

free loan from Association Sterling Films, 600 Grand Avenue, Ridgefield,

New Jersey, 07657. Prints of the film may be purchased for $73.25 from

the National Audiovisual Center (General Services Administration) , Washington, D. C. , 20409.

In addition to these informational tools, and equally important to

the whole concept of information transfer, is establishing an effective

working relationship with the users of the research early in the project.

Through such working relationships, efficient training programs for both

on-site and in the laboratory, provides appropriate continuity through the

project. Such a relationship was established during the past two years.

21
Local Filipinos had responsibilities in the project under the direction of

Drs. Roman Kintanar and Ernesto Tabujara, from the Philippine Weather

Bureau and University of Philippines respectively. The results of these

efforts are significant. These activities provided the first step toward

the preparation of improved wind codes and standards for developing

countries. The Philippine National Building Code is currently undergoing

revision to incorporate new technology which will lead to improved building practices. Section 2.05, Wind Pressures, is scheduled to be revised

by September 1975. Results from this project will be incorporated into

this Section. Also, test data will be made available to the subcommittee

on wind loads of the American National Standards Institute (ANSI) for possible incorporation into American National Standard A58.1-- "Minimum Design

Loads for Buildings and Other Structures".

22
B. EXPECTED PROGRESS THROUGH PROJECT COMPLETION

Field Test Sites

Operation of test equipment at the three field sites will continue

through the 1975 typhoon season (December 1975) . It is quite likely

that data collection will continue beyond December 1975 because PAGASA

has expressed a strong interest in continuing the field activities.

This would be particularly advantageous in the case of the Quezon City

Science Garden site since building construction is rapidly changing the

wind exposure, thus providing a unique opportunity to assess the effects

of urbanization on the local wind environment. There is also a possibility

that instrumentation at the Xaoag City field site can be transfered to a

new barrack building located adjacent to one of the two test houses. The

size and shape of the barrack building is quite similar to typical community

service buildings. This transfer will not be made before December because

considerable information remains to be collected from the two test houses.

Analysis of wind speed and pressure records will continue, using data

recorded to date and data acquired during the current typhoon season. The

basic procedure for calculating wind loads has already been established.

New test results will be used to refine the design pressure coefficients

which have been tabulated in the draft document outlining design procedures

(Appendix E) . It is anticipated that the forthcoming data will be important

in establishing internal pressure coefficients since these coefficients cannot be obtained from wind tunnel tests.

Kind Tunnel Operations

As indicated previously, some serious problems have been encountered

23
with the wind tunnel operation at the University of the Philippines.

Discussions with the Philippine Advisory Committee on this matter will

continue in an effort to obtain local funding and a commitment from the

University of the Philippines to establish an active and continuing wind

tunnel program. Failing this, efforts will be made to transfer this

program to another agency.

The wind tunnel program at the Virginia Polytechnic Institute and

State University will continue. The primary effort will be the analysis

of extreme pressures on various roof geometries. The major portion of

the wind tunnel work has already been completed. However, the data

analysis quite likely will indicate the need for additional tests on

specific roof geometries.

Preparation of Design Criteria

The draft documents covering the selection of design wind speeds and

the calculation of corresponding loads have been prepared with the intent

that they will form the basis for codes and standards in developing countries. This same approach will be followed in preparing the final versions.

Additional information will be included concerning site selection, effect

of clusters of buildings and of extreme wind speeds in the Caribbean. The

final version will also include several illustrative examples and a commentary on the behavior of certain building materials subjected to repeated

loading and missile impact.

Caribbean Regional Conference

A Caribbean regional conference is scheduled for November 6 and 7,

1975 in Kingston, Jamaica. The conference will be similar to that held

24
during May in Manila. The local conference organizer is Mr. Alfrico Adams

of Douet Brown and Adams and Partners, 7 Lismore Avenue, Kingston, Jamaica,

West Indies and a member of the Jamaican Institution of Engineers.

25

C. FISCAL YEAR 1976 PROJECT SCHEDULE

The project schedule for FY76 is presented on the following page.

The schedule may be adjusted to accommodate, to the maximum extent

possible, full-scale and wind tunnel data analysis and publication of

project results.

APPENDIX A

Minutes of the 7th - 11th Philippine

Advisory Committee Meeting

MINUTES of the 7th MEETING of the ADVISORY CXMnlTTEE formed in connection

with the Research on " DEVELOPMENT OF DESIGN CRITERIA AND METHODOLOGY FOR

LOW-RISE/LC«-COST BUILDINGS TO BETTER RESIST EXTREME WINDS."

Held on 6 August 1974 at the National Hydraulic Research Center, College

of Engineering, University of the Philippines, Diliman, Quezon City at

2 p.m.

Present: Dr. Ernesto G. Tabujara, Presiding

Prof. Geronimo V. Manahan, Secretary

Prof. Angel A. Alejandrino

Mr. Manuel C. Bonjoc

Sngr. Ambrosio R. Flores

Col. Alejandro R. Kabiling

Mr. Wellington A. Minoza

Engr. Jose P. Orola

Dr. Josef ina M. Ramos

Col. Manuel R. Rebueno

Col. Alberto R. Sanchez

Engr. Modesto D. Soriano, Jr.

Dr. Richard D. Marshall

Mr. Peter Paul M. Casxrc

Mr, Joaquin 0. Siopcngco

7:01 The Minutes of the 6th Meeting were read and approved. Dr. Tabujara

mentioned that after the November 1973, March and April 1974 Meetings, the membership's attendance in meetings has dwindled. He

further mentioned that the model houses at Daet and Laoag have

been erected and the CaRE House at the Science Garden has been

in full operation.

7:02 After a brief review of the Philippines regarding the wind studies,

Dr. Marshall gave a comprehensive report of activities from March

to August 1974 as follows:

a. Daet House

This model was erected last March 1974. Here, Dr. Marshall's

work has been divided between wind tunnel activities and field

inspections. The building at Daet has a hip roof, the only

one in the whole program. As of July 21, 1974 .it has been

instrumented. He inquired about the possibility of erecting

another building in the site close to the runway after which

instrumentation of the structure can be easily undertaken.

b. Laoag House

The GSIS structure located next to the runway was erected late

March. Problems were encountered on the site. Winds coming

from the southwest are obstructed by the CAA and PAL Buildings.

Furthermore, goats grazing in the area have eaten a portion

of the electric cable necessitating the fencing of the area

around the mast. Presently the building is being used as a
Minutes, 7th Meeting - page 2

residence typifying normal domestic functions. The other

house erected by NHC is in an isolated area and Dr. Marshall

suggested that the other house be furnished with plumbing

facilities so that it can be occupied, too. The house having,

the data system is air-conditioned to control high humidities.

c. Science Garden Site

The first model was erected last September 1973 while the se- cond unit was completed November 1973. These units have

experienced from 3 to 4 hours of tape records due to strong

winds. A third unit, the CARE House, has been instrumented

during the last week of July 1974. This unit has 4 transducers, 3 external, 1 internal. The work on the instrumentation will be completed by the first week of August. Dr, E.G.

Tabujara has the complete technical data on the CARE House,

7:03 Major points discussed on the model houses were:

a. The possibility of having another unit in Daet. Currently

PHHC is not in a position to furnish the building. However,

Col. Rebueno will make a last plea with the PHHC Board.

b. For the possibility of the second house at Daet, Dr. Tabujara

will visit Col. Rebueno to negotiate with PHHC.

7:04 Wind Tunnel Studies:

In Dr. Marshall's opinion, the wind tunnel tests are heading towards a critical stage and graver problems may then *rop-up. The

problem as he sees it is that he has a limited time in the Philippines and is leaving by Monday. Specific problems are:

a. Equipment problem:

Voltage of power supply greatly fluctuates and a number of

equipment malfunctions have been attributed to the variability of the voltage. A voltage regulator has been provided

for the more sensitive instruments.

b. Availability of the DC power is limited for there are other

priority projects that have to be serviced with direct current. In asmuch as data are needed by January 1975 the formulation of design criteria for major building layouts have

to be established early enough to meet planned schedules.

7:05 PaGASA's Minoza mentioned that his agency has a wind tunnel under

construction at the Science Garden, but its specifications are very different from U.P.'s so that PAG^SA's tunnel cannot be used

for the program. The alternative that was reached is £hat Dr.

Marshall and his men will make a day-to-day visit to the tunnel

to maximize available operational time.

It was further mentioned that by the end of the year design engineers can apply and make use of the information and initial
Minutes, 7th Meeting - page 3

results of the study. By November Dr. Marshall may be back in

the Philippines, this time with Mr. Noel Raufaste, Jr.

7:06 Other matters:

a. NBS has informed the committee that the Proceedings of the - recent Workshop are now being printed and each Workshop

participant will be given one copy. A mini-brochure of

the project is also being printed.

b. The Regional Seminar-Workshop slated for spring 1975 at

Bangladesh may' not push through in that country since Dr.

Choudury is on sabbatical leave. The Philippines is again

being considered with Cebu City as the suggested site for

the activity. The objectives of the Seminar-Workshop are:

1. To dessiminate any results arising from the project.

2. To concentrate on what was learned on the progress of

the project, particularly with activities in the Philippines .

3 . To improve on the format of the report before the results

are printed.

4. To assess the overall program and tc see what other directions can be done.

5. To dessiminate the socio-economic data gathered in conjunction with the technical studies.

It was decided that in two months the Advisory Committee will

meet to finally establish whether the Philippines can host

the Regional Seminar-Workshop at Cebu City or any other agreed

site.

c. The NBS wants to receive technical publications from the Philippines-lika a list of engineering and architectural journals,

monthly journals on economics, consumers' price index and cons- truction price index.

Further to this, NBS is also interested in getting information

on connections as well as practices on connectors and anchorages,

d. Mr. Miftoza reported that "Bulletin Today" is preparing an ar- ticle on wind study. He is inviting the members of. the Committee to the PAGaSA's Penthouse on 7 August 1974 at 10:00a.m.

to sit for the reporter's interview.

7:07 The Meeting was adjourned at 3:45 p.m.

(Sgd.) GERONIMO V. MANAHAN (3gd.) ERNESTO G. TaBUJARA

Secretary Chairman
MINUTES of the 8th MEETING of the ADVISORY COMMITTEE formed in connection

with the Research on

" DEVELOPMENT OF IMPROVED DESIGN CRITERIA TO BETTER

RESIST IKE EFFECTS OF DCI'EEME KINDS FOR LOW-RISE BUILDINGS IN DEVELOPING

COUNTRIES"

.

Held on 12. November 1974 at the PaGaSa Penthouse, Development Bank Bldg.,

Quezon Blvd. Ext., Quezon City at 2:30 P.M.

Present:- Dr. Ernesto G. Tabujara, Presiding

Dir. Angol A. Alejandrino

Engr. Cesar a. Caliwara

Mr. Hugo de la Cruz

Engr. Ambrosio R. Flores

Mr. Rodolfo A. de Guzman

Engr. Andres 0. Hizon

Col. Alejandro R. Kabiling

Engr. Octavio A. Kalalo

Adm. Reman L. Kintanar

Engr. Rosaiio A. Mallonga

Dr. Josef ma M. Ramos

Engr. Joaquin 0. Siopongco

Engr. Modesto D. Soriano, Jr.

Mr. William Littlewood

Dr. Richard D. Marshall

Mr. Noel J. Raufaste, Jr.

8:01 The Minutes of the 7th meeting held last August 6, 1974 were read.

Item 7:02-A was corrected by Dr. Marshall in that the proposed

Daet house was not erected, but instead, an existing building was

instrumented for the study. The Minutes were then approved as corrected.

8:02 Dr. Tabujara welcomed Mr. William Littlewood of USAID, Dr. Richard

Marshall and Mr. Noel Raufaste, Jr. Two new members of the Advisory

Committee were introduced; namely, Mr. Hugo de la Cruz and Mr. Rodolfo

de Guzman, both of the PAGASA. Likewise, Mr. Roger Balinong and Miss

Minda Aguilar, BRS' new Research Aides were introduced to the body.

Dr. Tabujara aknowledgec! the dedication to Mrs. Templa on the cover

of the published Proceedings of the Seminar Workshop held at the NSD3

on Nov. 14-17, 1973. He also thanked Mr. Raufaste, Jr. and Dr. Marshall

for their invaluable contribution which included published materials

aside from editing «nd printing the Proceedings.

8:03 Mr. Noel Raufaste, Jr. extended the greetings and best wishes of Dr.

Richard Wright of NBS, He also mentioned that Dr. Marshall and he were very glad to be back in the Philippines. Mr. Raufaste, Jr. then

presented a summary of his findings on the three test sites located

at Laos.:?, Daet, and Quezon City. He said that the complete instrumentation of the houses have been accomplished but there are still

problems with the Wind Tunnel phase of the program. On the whole,

there has b ...n improved efficiency on the job and processing of relevant

data needed for analysis is going smoothly. He also emphasized the
Minutes, Sth Meeting - paa, 2

need for an economic study of Filipino housing conditions so that

benefits that could bo derived from improved design criteria may

be analyzed. With regards to the coming Regional Conference by

mid-next year, he expressed the desire of Dr. Ning of Taiwan to

attend it. Other countries are also interested to participate in

the working sessions.

8:04 Dr. Marshall reviewed the status of the Wind Tunnel Tests; Further

discussions cn thii-rg tests will have to be taken up during the

Regional Conference. He gave a brief summary of the results collected from the test sites since Sept. of 1973. He cited the problems

presently being felt. Most of these have stemmed from the recent

typhoons which have caused seme damage on materials and equipment.

The damage caused in the Q.C. test site apparently was done by rats

eating into the plastic tubing used to protect the wiring system

of the test 'instruments . He passed some parts of the tubing to the

body for inspection. He also gave a report cn the Wind Tunnel results

and stated that they are about six months behind schedule. He re- minded the body that there should be power sharing in order to

facilitate 50% cut from time in order to get back in schedule. Another setback was caused by the departure of one of the trained

technicians assigned to the Wind Tunnel tests. He proposed remedies

and solutions to some of the problems encountered. The Wind Tunnel

needs a new voltage regulator. Dr. Tabujara proposed to convene

engineers in a form of a subcommittee, and the Pa.Gn.SA personnel to

help gather and evaluate data to facilitate analysis and evaluate

the results.

8:05 The body was informed that the following are needed by the NBS:

A . Building Code Standards

.

B. Literature on Housing.

C. Progress Report on the First four months of the

Project for FY 1974. The latter has to be furnished

before Mr. Raufaste, Jr. leaves for abroad on

Nov. 21, 1974. •

8:06 Mr. Littlewood expressed satisfaction for the job being undertaken

considering the social and economic aspects involved. The results

of the findings will not only benefit the Philippines but also

other countries within the typhoon belt such as Bangladesh, Jamaica in the Carribean Area, He commented that this Research

Project is one of. the most successful so far.

8:07. The Committee was unanimous in deciding to host the Regional Conference. It was also decided ;that it is most convenient to hold it

here in Manila or in the Suburbs.

8:08 At his juncture, Sngr. Caliwara informed the body of the International Civil Engineers* Convention slated on May 20-24, 1975.

The theme is"Civil Engineering and Disaster Prevention and Control".

The c:;mittae could make -arrangements whereby there could be

integration of objectives.
Minut- s, 6th Meeting - i-. w 3

6:09 Upon the suggestion of Mr. Littlewood it was agreed that the Regional

Conference will be a back-to-back Meeting, slated for May 16-17, 1975,

One day is for actual dissemination and another day for reconiendat ions

and/for conments.

8:10 Dr. Tabujara appointed a sub-cemmittee of five members to decide on the details of the proposed seminar. The members are Engr. Soriano,

Dr. Ramos, and Mr. de la Cruz. Mr. Eaufaste, Jr. was invited to

attend their Electing on Monday Nov. 18 at 2 p.m. at the GSIS.

8;li During the Regional Conference, a 15 rr.inute colored video presentation

of the activities for the past 18 months will be presented. Part of

this movie wis actually shot during this particular meeting of the

Advisory Committee.

8:12 Mr. Raufastc, Jr. stated that they are still in the process of -making

a study on timber and masonry connectors used in Philippine construction and any information and data regarding this would be highly

appreciated. Mr. Raufaste, Jr. also stated their interest re- garding economic studies of Filipino houses and housing needs in

the Philippines between 1980-85; also to develop definitions of

certain terms such as "Low-Cost house" or "Low-Rise Building".

8:13 Before adjourning, Dr. Tabujara thanked Dr. Reman Kintanar and the

PAGASA for hosting this 8th Meeting. The Meeting was adjourned at

4:30 P.M.

{Sgd. ) Geronimo V. Manahan

Secretary

(Sgd.) Ernesto G. Tabujara

Chairman

d by

:

U.\. v * .ch'ia
SsIilUTES of the 9th KEETIHG of the ADVISORY COMMITTEE forned in

connection with the Pesearch on "DISVSLGEKSfiT 07 DESIGN CRITERIA

APT :-3?:;CO0LCGY 70S LOJ-CCGT/LOU-EISE BUIL3I8GS TO 33TTSB pecig:

IDG'

Zeld on 12 -.ec ember 1974- at the National Hydraulic Research

Center Conference uooa , Coll©£0 of ^.n^n^e^ns, : IJj t , Diliman,

;u ;^jn . City 7 at . 2i30 P.M.

Present: Dr. Truest o S. Tabujara, Presiding

Mr. Catalino P. Arafiies

Engr. Ambrosio R„ 71 ores Dean Aurelio T« Juguilon

Prof. Geronimo V. Ilanahan * Engr. Jose P. Qrcla

Dr. Josefina H. Pamos

Dngr. Joaquin G. Ciopongco

Engr. Modesto D. Coriano, Jr.

Mr. P.uben Pucae (representing Cel. M. Pebueno)

Mr. Peter Paul Castro

Mr. Samuel P. Cor an

9: CI The Minutes of the previous meeting were read. Consents

and corrections included: Mr. P. de Guzman cited Item

8:04, 11th line; as improperly phrased. He made the ne- cessary suggestion for improvement and the new statement

was re-phrased as follows: "There was a b'C^o cut on the

schedule". The Minutes were then approved as corrected*

9:32 Dr. Tabu jar a introduced Mr. Ruben Bucas who represented

Col. Pebueno. be also welcomed the six Pagasa members of

the Committee.

9:03 Dr. Tabujara mentioned that the- Cub-committee Meeting was

held at Culo Hotel to tresh out details for the forthcoming

Pegional Conference on May. The Meeting was hosted by Dngr

Jr. .

9:04 An updated list of members of the Advisory Committee was distributed. Mr. de Guzman made corrections on the designations of his colleagues.

9:05 Dngr. Ciopongco suggested that Hiss Lydia Tansinsin of

Y.ZZ3 be invited to be member of the Advisory Committee.

Mr. Arafiies recalled that Sen* Tings or. had expressed interest to be represented in the Advisory Committee.

9:06 Dr. Tabujara stated that the primary purpose of the 'Meeting

was to f ol low-through Item G:07 of the previous Meeting.

He said that the Tody is committed to host the Pegional
Minutes, 9th Meeting — page 2

Conference, tie then presented the tentative program propared by the Prograia sub-committee for further comments

,

and/or revisions for final approval. (Gee attached)

9:07 Tfar. Hugo de la Crua informed the body that Dr. Kintanar

will not be available on Kay LZ and 17 r 1975» The keynote address has to be delivered by s onebody else. Dean

Juinio*s naae was suggested by. Sngr* Soriano* Jr* This

was approved uhaniaously.

9:08 The Project Background and Summary will be presented by

Dr.. Tabujara. . Another suggestion on the program was the

inclusion of a local group to discuss Structural Connection Details together with Dr. E. Pfrang. Suggested names

were: Jose I-'Ia.. de Castro, Fiorello Estuar and Romeo Sstafiero. Engr. Flores was, requested to prepare handouts

for his part in the prograia.

9:0© As suggested by Dean Juguilon, the time for Registration

should start at. 8:00 a.ra. instead of 8:30 and the rest o£

the schedule is as follows

J

International Conference on the Rossimi nation of Project

Results of the Research, on "Development of Improved Design

Criteria to Better Resist, the Effects of Extreme "/inds

for Low-Rise. Buildings in Developing Countries"

TENTATIVE PROGRAM

Friday, Lay 16 1 1975

Part. A: Opening Ceromony

Raster of Ceremonies: Director Angel A. Alejandrino

8:00 -Registration ;> ,

9:00 Philippine Rational Anthen

Keynote Address Dean Alfredo L« Juinio

Project Background and

Summary Dr. Ernesto G. Tabujara

Part B:- Presentation of Results " %

9:30 Distribution - of Extreme

Uinds Rr. Rodolfo A. de Gusman

10:00 Break
Ilinutes, 9tb Meeting - page 3

ID: 30 Draft Criteria for

".."inc. Loading Dr. uicbard 3. ilarsfeall

li:2C Structural Connection

Details and Improved

Architectural Practices .... Mr. 'Joel J. Icaufaste, Jr.

12:00 L U NX E

2:00 Dconoaic Analysis and

oocio-Iconomic Considerations . , . = , . * . r.. Kr. Noel J. Paufaste^ Jr.

2:30 Information Transfer: e -

: hr» Noel J* Ianfast e, Jr.

3:15 Ireak

3:45 Iffects of Research on lay of Bengal Countries .... Ir. Jamilur P.. Ghoudhury

4:15 implementation of Results .« Ingr. Aabrosio 3« ?1 ores

' 3ngr. Andres. 0. lis on

4:45 Social lour

aturdagi lay 17, 1975

Part C: Discussions

Master of Ceremonies: Ingr. Joaquin 0. Ciopongco

9:00 Panel Discussion Dr. Richard D. Marshall

;lr. Noel J. Paufastcj Jr.

•Ir. I-odcifo A, de Guzman

Sngr. Inbrosio I. 71 ores

Ingr. A"odes to I. Coriano, J

10:30 Break

11: CO General Discussion by Participants

11:45 Closing Remarks and

Future Projections •»•••.••• Dr. Drnesto G. labuiara

ir. Noel J* Daufaste', Jr.

12:00 LUNCH

2:00 Field Trip to PA3AGA

Ccience Cardan ..-.•*». °-o«o.«° Col. Alberto E. SancheZj

- * Marshal

3:30 R sfreshuan is
Minutes t 9th Meeting — page. 4

9:10

9x11

Appointment of Committee Chairmen-~sri d Members for each" of

the- t-roHking Committees was made tentatively;

Overall Chairman:

Finance Committee:

Arrangements Committee:

Br. Ernesto G» Tabu jar

a

Engr, Modesto "D, Soriano, Jr», Chairman

Dr. Ernesto G, Tabujara.

Col. Alejandro £, Kabiling

Engr» Joaquin 0, Giopongco •' *

Engr» Jose P# Orola,, Chairman

Engr. Modesto D. Coriano,. Jr.

Enrr. Eosalio A. Hallonga.'

Mr. Catalino P.. Arafilea

Documentation Committee : Sngr. Ambrosio H« Flore®, Co-Chairman

Prof, Geronimo V. Manahan, Co-Chairman

Dean Aurelio T» Juguilon

Mr. Rodolfo A, do Guzman

Reception and \ Hospitality Committee.:

Program and

I nvi t ati on C ommit-tee:

Publicity Committee.:

Col. Alberto ... Sanchez, Chairman

Arch, Cesar E, Concio • Dean Aurelio T, Juguilon

Col. Manuel R, Eobuend

Mr., v/ellington A. Mifioza

I- jr. Manuel C. Bonjoc, Chairman

Engr. Andres 0, Ilizon

Prof. Angel A, Alejandrino

Sngr, Miguel V. Paala

Engr, Octavio A. Kalalc, Chairman

Dr. Ernesto G. Tabujara

Engr. Cesar A, Caliwara

Mr, Hugo de la Cruz

9: 12

There v/erc throe suggested places for the Conference, "he.

GSS, HGD3 and the Population Center. The GSS was finally

prefjprred duo' to its proximity and convenience to most of

the participants. In this connection, tlie help of Engr,

Paala was' to be solicited.

1

rhe 'documentation and Secretariat expenses: will be shouldered

by the NBS as before.

9:13 The- Meeting was adjourned at 3:30 P.M.

(Ggd.) GEROUIMQ V. I-IAKAEAN Secretary

Prepared by:

(Gdg.) Mrs. Cynthia S, Unriquez.

(Sgd.) ERNESTO G. mBUJAEA

Chairman
MINUTES of the IOth MEETING of the ADVISORY CGtfc;IT2E3 formed in

connection with the Research on "DEVELOPMENT OF IEERCV2D DESIGN

CRITERIA TO BETTER RESIST TEE SELECTS 0? EXTREME UTNB5 FOR L0..r- RI3E BUILDINGS IN DEVELOPING COUNTRIES".

Held on March 19, 1975 at the Seminar Room, 4th floor, Iielchor

Eall, University of the Philippines, Dilinan, Queson City at 2:15 P.K

Present: Dr. Ernesto G. Tabujara, Presiding

Prof. Geronino V. Manahan, Secretary

Engr. Modesto D a Soriano, Jr.

Mr. Catalino P. Arafiles:

Mr. Manuel C. Eonjoc

Mr. Hugo de la Cruz

Engr. Amhrosio R. Flores

Mr> Rodolfo A. de Guzman

Engr. Andres 0. Eizon

Col. Alberto R. Sanchez

Engr. Joaquin 0. Siopongco

Mr. Peter Paul M. Castro

Mr. Qanuy Goran

Mr. Bayani Lonotan

10:01 The Minutes of the 9th Meeting were not nineographed on

tine, but was read by Dr. Tabujara. The Minutes was approved as corrected. The Tentative Program for the Regional Conference to be held on May 13-17, 1975 in Manila

was reviewed.

10:02 Dr. Tabujara announced that this nesting was convened to

finalise the plans for the Regional Conference.. The coming

conference is a follow through of the successful November"

1973 7/orkshop. During that year, the Committee had only

two weeks of preparation. In this Regional Conference

Dr. Richard D. Marshall and Mr. Noel J. Raufaste, Jr» will

be presenting two important papers.

10:03 Since the ZZZ auditorium and the IJSD3 Rail will not be

available on May 13, 1975 it was agreed that another place

be chosen, instead of changing the agreed dates. Suggested

places v/ere the Population Center and the v/orld Health Organisation auditorium. However, upon the suggestion of

Engr. Soriano it was: agreed that the GSIS Social Eall would

be a better place to hold the conference especially since^

there is an adjacent canteen and the* hall's maximum seating

capacity is 400 persons. Some nenbers were apprehensive

of the parking conditions in the area. The parking space

problem will be \yorked out by Engr. Soriano* Any other

related problem would be threshed out by the Arrangement's

Committee which shall convene on the 24 March 1975*
Minutes,, 10th Meeting — page. 2

10 : 04 The Chairmen and members of the S ub-C ommi 11ees for this

Regional Conference were road. In addition, Col* Sanchez

was: appointed member of the deception and Hospitality Committee and Mr. Bon joe as Chairman of the Programs Committee.

The Program Coanittee nay work" out plans for a guided tour

for the foreign delegates. Individually,, the Chairmen were

advised to call upon their members to coordinate details

and work out problems.

10:435 The Finance and Arrangement Committees^ would meet on Monday, March 24, 1975 and have luncheon at the office of

Engr. Orola at the GGIS, Manila.- Dr. Tabujara offered to

host the meeting, but Engr, Soriano insisted to do this

instead.

10:0 Dr. Tabujara reported that by ne:rt week, the Tentative

Program, the.Minutes -of the previous meetings as well

as the up-dated list of the- Philippine Advisory Committee

members will, be sent out. To be included as members of

the Philippine Advisory Committee are the representative

of the Civil Aeronautics Administration and Miss Lydia

Tansinsin of NGD3. Gen. Singson had previously recommended

Engr. Salita as one of his representatives.

10:07 Engr. Flores wanted clarification on the meaning of:

"Implementation of Results" as indicated on the Tentative

program. Dr. Tabujara explained that the first phase

of this research ends on January 1976 and how the results

can be used have to be discussed. He also stated that:

the title, is still tentative and can still be made more

explicit.

10:08 On the Tentative Program the phrase ""./here do we go from

here?" could be changed to "Future plans or Programs" or "Projections" as suggested by Ir» Arafiles and Engr. Flores.

10:09 The Meeting was adjourned at 3:30 P.M.

Secretary

(Sgd.) . rarjSTC a. tadujaiil

Chairman

Prepared by:.

(Sgd. ) Mrs* Cynthia S. Enriquez
MINUTES »f the 11th MEETING of the ADVISORY COMMITTEE convened in

connection with the Research on DEVELOPMENT OF IMPROVED DESIGN

CRITERIA FOE LOW-RISE BUILDINGS IN DEVELOPING COUNTRIES TO BETTERRESIST THE EFFECTS OF EXTREME WINDS" .

Held, on May 8, 1975 at the Office of Dir. Rosalio A. Mallonga,

Bureau of Public Works, Quezon City at 2:30 p.m.

Present: Dr. Ernesto G-, Tabujara, Presiding

Prof. Geronimo V, Manahan, Secretary

Prof. Angel A, Alejandrino . Mr. Catallno P. Arafiles

Mr. Manuel C. Bonjoc

Archt. Cesar H. Concio

Engr, Ambrosio B* Flores

Mr. Rodolfo A, de GuzmanCol. Alejandro R. Kabiling

Engr. Jose P. Orola

* Ingr. Miguel V. Paala • *

Engr. Joaquin 0, Siopongco

Engr. Modesto D. Soriano, Jr.

Atty. Jacobo S. de Vera

Engr. Ramon R, Veto

Dr. Richard D. Marshall

' Mr. Noel J. Raufaste, Jr.

Engr. Ieidro Jarabelo, Jr. (Representing Dir. Rosalio

A. Mallonga).

11:01 The Minutes of the previous Meeting was read and approved.

11102 The Tentative Program of the Regional Conference was also

read and reviewed. On the Tentative Program, * Panel Discussion" was changed to "Open Forum" and "Panel Discussion?

Members/1

' to "Discussants" • as suggested by Dean Goncio and

Mr. Arafiles. Dean Conoio also suggested that "General Discussion by Participants" in the Tentative Program be changed

to "Continuation of Open Forum" in order to encourage more

participation. Dr. Tabujara mentioned the difficulties of

getting a keynote speaker. He also mentioned that he has invited Gen. Florencio Medina of the NSDB and in case Gen. Medina is not available, the keynote speaker will be one of the

members of the Phil. Advisory Committee. The Closing Remarks

will be delivered by Mr. Raufaste, Jr. Dr. Tabujara also

announced that the discussants wdll have to prepare a 10-mi- .#

nute; comment and observation. The Program as corrected will

go to press immediately.

11:03 Dr. Tabujara welcomed and introduced to the body two new members from PHHC, Atty. Jacobo de Vera and Engr. Ramon Veto who

took the place of Col. Manuel R. R<=Sueno who had retired. .

11:04 Reports from the different sub-committees were asked by Dr. Ta-
Minutes, 11th Meeting - page 2

bujara. The Reception and Hospitality Ccomittee . informed

the body that during the .mib-ccGE&ittee meeting, they agreed

that the Social Hour will be sponsored by the GSIS. It was

also reported that the envelopes for the Conference are ready*

Dr, Tabujara suggested that the envelopes be printed at the same time with the program. Name plates for participants .are being prepared by Mr. Minoaa'a staff. Engr. Soriano mentioned

that some GSIS girls will help the hospitality sub-committee.

11:05 Engr. Orola, Chairman of the Arrangements Committee reported

that the GSIS Social Hall is airconditioned and with complete

facilities. Another member of the Arrangements Committee,

Engr. Soriano, Jr. , suggested that car stickers- for parking

should be sent out together with the invitations. Banners

to be placed in fx rat of the GSIS Building are also ready.

11:06 The Chairman of the Finance Committee, Engr,. Soriano, Jr.,

reported that a check for ?§00.00 was issued to Mrs. Cynthia

Enriquez as cash advance for, pertinent Conference expenses.

11:07 Mr. Bonjoc of the Program & Invitation Committee informed

the body that most of the participants who are to be invited

are developers. Their addresses in the list in the previ«us

Workshop are incomplete. Dr. Tabujara announced that members

may invite anybody they think is interested in the forthcoming

Regional Conference.

11:08 Dr. Tabujara also informed the body that International Secretariat Services has submitted a quotation of 600.00.

This is composed of 6 stenographers and one Documentation

Specialist, The Publicity Committee expects a press release

regarding this Regional Conference in two newspapers.

11:09 At 3:30 p.m. Mr. Raufaste, Jr. showed a 16mm. movie entitled

"Development of Improved Design Criteria for Low-Rise Buildings

in Developing Countries to Better Resist the Effects of Extreme

Winds" about this research project and informed the group that

one copy of this film will be left with Dr. Tabujara.

11:10 Qr. Marshall announced that the Wind Tunnel activities is behind schedule by approximately one year and he asked the Committee how they may continue Wind Tunnel studies.

lis 11 The funding problem of this activity was cited although Dr.

' Tabujara expressed his appreciation of the value of technology transfer and took responsibility on some short-comings

of the Committee. However, he expressed the Committee's

desire to continue with this very important undertaking and

wanted Dr. Marshall to spell-out areaa& of concern and suggest

a Time Frame of Work.
Minutes. 11th Meeting - page 3

11:12 It was decided that with regards to funding, a project proposal would be submitted to NSDB.

11:13 Engr. Flores suggested:

b)

c)

a) To extend full, scale data with regards to field instrumentation.*

To pinpoint technical gaps in the Wind Tunnel tests.

Establish a center capable of carrying Wind Tunnel

tests in general.

11:14 Mr, Raufaste, Jr. stated that the Committee has now the

necessary equipment and the only missing part is the "per-'

son or persons who*ll press those buttons". According to

Dr. Marshall it would take a year to train such a person and

he can afford to be in the Philippines an aggregate of only

six weeks a year.

11:15 Dr. Tabujara mentioned that this project is indeed more useful and important to us. Filipinos. Engr. Paala also mentioned

that materials emanating from this project were already incorporated in SSS amended Manuals. He also suggested solicitation of funds from private corporations. Dir. Alejandrino

- suggested that a Trust Fund Foundation like the NHRC would be

better,

11:16 Dr. Marshall commended the Pagasa personnel who have worked

closely with him.

11:17 The Meeting was adjourned at 5 p.m. with Dr. Tabujara thanking Dir. Mallonga and nsst. Dir. Isidro Jarabelo, Jr. and

his staff for hosting the Meeting,

» (Sgd. ) GERONIMO V. MANAHAN

Secretary

(Sgd.) ERNESTO G. TABUJARA

Chairman

Prepared by:-

(Sgd.) Mrs. Cynthia S. Enrique

z

APPENDIX B

Low-Rise Low-Cost Housing and Extreme

Wind Related Problems in Bangladesh

LC T 7-iCSE LOW-COSE HOUSING AND EXTREME

WIND RELATED PRO ELMS IN BANGLADESH

Report No. 2

Prepared by

Dr. Jamilur R. Choudhury

Associate Professor of Civil Engineering

Bangladesh University of Engineering and Technology, Dacca.

For

National Bureau of Standards

U.S. Department of Commerce

Y/ashinp-ton D.C.

April 1975

CONTENTS

Pare No.

1 INTRODUCTION 1

1.1 Scope 1

1.2 Limitations 1

2 SOCIO-ECONOMIC FACTORS 2

2.1 Gross Domestic Product 2

2.2 Population 2

2.3 Income Distribution 3

3 URBAN HOUSING 5

3 . 1 General 5 3.2 Types of Urban Houses 6

3.3 Kitchen, "Bathroom and Water Supply 8

3.4 Verandahs and Open Spaces 8

3.5 Floor Area 8

3.6 Rent 10

3 . 7 Urban Housing Demand 1

1

3.8 Urban Housing Development plans 12

4 RURAL HOUSING H

4.1 General U

4.2 Structural Conditions of Rural Houses 14

4.3 Rural Housing Demand 17 4.4 riural Housing Development Plana 17

5 SPECIAL SOCTO-CULTURAL CHARACTERISTICS 18

6 WIND SPEED RECORDS 19

7 'WIND DAMAGE STATISTICS 22

8 SPECIAL PROBLEMS 27

9 CONCLUDING REMARKS * 28

APPENDIX PROBLAMS IN OTHER INDIAN OCEAN COUNTRIES 29

(a) India 29

(b) Burma and Ceylon 3''

LIST 0? REFERENCES 52

1, INTROCTJCTION

1.1 Scope

The first report on "Low-rise Low-cost Housing and Extreme Windrelated Problems in Bangladesh", presented at the International

Workshop held in Manila, Phillipines from November 14-17, 1973, dealt

with the overall housing conditions in the country and gave an outline

of the extreme wind related problems. The present report furnishes

further information on Socio-economic factors, the present conditions

of urban and rural housing, and housing needs for the next ten years.

It also provides data on available wind speed records and wind damage

statistics. Finally, some special problems unique to Bangladesh are

discussed.

1 .2 Limitations

Originally it was intended to include in this report all the &y <~f (Indian Ocean) countries (viz. India, Goylon , Burma and Bangladesh)

facing extreme wind problems. The author's efforts to obtain data

from the first three countries have not been successful. The scope of

this report is therefore limited to Bangladesh only. Some information

regarding the other countries is included in Appendix „
2. SOdO-BCONOMIC FACTORS

2.1 Gross Domestic Product (GDP)

The GDP of "Bangladesh was estimated to be Takas 42.94 billion

(equivalent to US #5.3 billion, at official rate of exchange ) at

the beginning of FY73^ ^ . The contribution of housing to this GDP

was Ta. 2.36 billion or 5.5$ of total. The First Five Year Plan

formulated by the Planning Commission of Bangladesh Government

envisaged a growth of GDP to Ta. 65.42 billion in FY78 with an average

annual rate of growth of 8.8$. The contribution of housing is expected

to go upto Ta. 2.88 billion - increasing at 4.1/6 annually - but its

share in total GDP would be going down to 4.4$. The per capita GDP

is expected to grow from Ta. 580 to Ta. 766 increasing at the rate of

5.7% annually .

2.2 Population

Although a census of population was conducted in early 1974»

the details are yet to be made public. However, various official

and unofficial estimates of the population and rates of growth have

been made. According to official estimates, the present population

( 1) should be around 78 millionv

. The density of population would be

a'oout 1415 persons per square mile.

The estimated rate of natural increase of population in 1973

was about 3$ (with 47 births and 17 deaths per thousand). Inspite

of efforts to popularize family planning programs in the country,

this rate of increase has shown very little change. The Five Year

Plan of the Government, however, assumes that the rate of increase of

* 1 US Dollar = 8.08 Bangladeshi Takas.

** Ail values are calculated at FY73 prices.
3

population will fall by 0.0% every year^ . Using this as a basic,

the projected population in 1 985 will be around 100 million.

2. 3 I ncome distribution

(2) The Urban Housing Surveyv

' carried out in 1970 revealed the

gross inequalities in income distribution among urban households.

Table 1 shows the details of income distribation among the representative sample of 2494 households covered by the survey.

Table 1

Income Distribution in Urban Households

Annual income

in Takas

* Income group

designation

Number of households in the

income group expressed in percent

of total households in the area Dacca

City

Chittagong

City

All urban

areas

Less than 2,400 Low 45.96 37.73 53.89

2,400 - 5,999 Lower middle 29.63 35.96 30.51

6,000 -11,999 Middle 13.65 19.30 10.44

12,000 -23,999 Upper middle 8.03 5.26 3.83

24,000 and

above

" T pper 2.69 1.75 1.33

* This classification into groups is arbitrary.

The survey revealed that at least one-third of the urban households

had income between Ta. 100 to Ta. 200 a month. The average annual

income of a urban household was estimated to be about Ta. 3900.

However, 70^ of the households earned less than this average.
4

F:0 reliable estimate of the income distribution among the rural

population is available. In 19-3-64, the poorest 20^ of the whole

population received ffc of the GDP and the average annual income per

head of the poorest 20fs was (Pakistani)Rupees 157.50 or 6 US cents

per person per day^ ^ . Almost the w

l iole of this income was spent

in buying food.
3.1 G-eneral

Results of a Urban Housing Survey, carried out by the Institute

of Statistical Research and Training, University of Dacca, during

(2) "una to August 1970, nave recently been published ' . The survey

included both urban and potentially urban locations, covering 78

cities, tcwr.s and townships. A sarple of 2500 households was selected

from the 'universe' according to a stratified two-stage random sampling design. The discussion which follows is mainly based on the

results of the above survey. However, the large-scale dislocation

of the whole population during the war of liberation in 1971 and the

subsequent mass influx of rural population intc the large cities,

have changed the housing situation significantly. The peculation of

the cities has greatly increased, in some cases by about 50^. The

number of houses has, however, remained almost constant during these

years. The scarcity and high cost of bailding materials has resalted

in almost a standstill of new private building construction. Most of

the additional urban population, therefore, live in makeshift shacks

in squatter settlements. This has made the housing situation even

v/orse than what it was in 1970, when the Survey was carried out.

Although a housing census was conducted in late 1973, the results are

yet tc be made public. It is expected that a more accurate appraisal

of the deteriorating housing situation may be made when the results

c? the census are available.
6

3.2 Type s of Urban Houses

(2) The survey^ identified six major types of structures used for

urban houses:

Type I All pucca ; floor usually of cement concrete, wall usually

of burnt brick and roof usually of reinforced cement

concrete

.

Type II Floor and wall pucca; corrugated galvanized iron (C.I.)

roofing.

Type III Floor pucca; wall and roof C.I. sheet.

Type IV Floor Kutcha ; wall and roof C.I. s

: ieet.

Type V Floor Kutcha; C.I. sheet roof on walls neither pucca nor

C.I. sheet (e.g. of split bamboo thatch)

and

Type VI Floor "Kutcha: roof and wall Kutcha (i.e. material other

than 'pucca' or C.I. sheet).

Table 2 shows the number of households occupying different types of

houses in urban areas of Bangladesh. As expected, the percentage of

households living in all pucca (Type i) houses increases as the income

level rises. Only Qfc of 'low income group' families live in pucca

houses.

It appears that Type V houses, i.e. with Kutcha floor, C.I. sheet

rcof and walls of various indigenous materials are very popular in all

income groups (see Fig. 2, Report no.1).

louses of Types II, III, IV and V have C.I. sheets as roofing

material and these four types account for about 40$ of all urban houses,

* 'pucca' usually means cement concrete, lime concrete or burnt brick.

'Kutcha' usually means mud, thatched-bamboo etc.
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3.3 Kitchen, Bathroom and ./ater supply

The survey revealed that only ^% of "low income group* households

have regular kitchens, share kitchen with other family, 34^- cook

somewhere inside their house, 14?; cook in the Verandah and others

cook in open spaces outside the house. Only jfc of the households

in the 'low income group' had their own bath room; 8% had no bathroom

at all (own or shared") . They usually take their baths in the rivers

or ponds which commonly have a little space enclosed in split bamboo

thatch for use by womenfolk. The concept of a closed bathroom is

almost non-existent in rural households and is yet to gain popularity

even in the towns of Bangladesh. However, with rising income level,

the households usually have separate bath rooms.

Only 7;> of 'low income group* households had taps for water

supply and 57f used manually operated tube-wells.

3.4 Verandahs and Open Spaces

A Verandah around a house is a common feature in a Bangldeshi

ho\ise. Moreover, it is common to have open spaces around houses

even in urban areas. About two-thirds of the houses of 'low income

group' had open spaces around them, the average area being 280 sq. ft.

and about 41/' had verandahs, the average area being 77.3 sq. ft.

3.5 Floor Area

The average floor area per person of a household (excluding

detached 71. Q. and kitchen) for different income groups is shown

in Table 3.
9

Table 3

Floor Area in Urban Households.

! Income ffrouT) Average floor area per person in square feet

Dacca city Chittagong city All areas

Low 32.08 39.51 37 .55

Lower miadle 43.93 45.13 48.93

raddle 57.59 67.21 63.11

Upper middle 86.37 85.34 90.54

Upper 77.34 102.49 94.41

All groups 47.93 53.03 48.93

The overall average floor area of 43.98 sq. ft. shown above shows

the peer condition of urban housing in Bangladesh.

About 50^ of the surveyed households informed the investigators

that their present accommodation was not sufficient. In Dacca city,

71^' of the households said that they needed additional space. The

survey found that the overall average of the desired norm (existing

space plus the space demanded) of the floor area was 80 sq. ft. per

person. However, this value showed a remarkable variation according

to the income level as shown in Table 4.

Table 4

Desired "norm" of Floor area

Income group

Desired norm of floor area (average) in sq. ft.

Dacca city Chitta#ong city All areas Low 68.3 71.6 68.3

Lower middle 79.3 77.3 79.4

Kiddle 92.0 112.2 97.0

Upper mi 3 die 125.1 112.5 127.9

Upper 113.0 102.5 131.0

All classes 83.6 88.0 30.3
10

Cne interesting feature revealed by the survey was that the desired

norm for Upper middle income group was higher than the Upper income

group, both in Dacca and Chittagong cities.

It may be concluded from data in Table 4 that the 'low income

troup* household, with an average of 5.7 persons per household, needs

about 390 sq. ft. of floor area (excluding kitchen and latrine) on

the average.

3.6 Rent

Cut of 2494 households interviewed, 1077 (43?>) lived in rented

houses. The monthly average rent paid by the 'low income group'

households was only Ta. 12.42. Table 5 shows the rent for all the

income groups. It is seen that the average rent for the 'upper

income group 1 is at most 10;;, of their total income.

Among the total of 1417 households who lived in their own houses,

it was found that 52$ of households of 'low income group* inherited

their houses, 20$ got their houses built and 16?' bought their houses

from others. According to the owners' estimate, the average price

(at the time of procurement) of a house for 'low income group' was

Ta. 7,800.

Table 5 House cents in Urban areas.

Income group Average monthly rent (Takas)

Low 12.42

Lower middle 34.58

Middle 73.31

Upper middle 154.21

Upper 21P-.91

* Rents h^ve gone up by around 1005' during the last three years.
11

3.7 Urban Bousing Demand

The already appalling -urban housing situation is further deteriorating due tc the large-scale migration of landless rural population

into the large cities. This has naturally resulted in an increase in

the number of slum dwellers and squatters. The situation in Dacca

City reached a stage where at least a fifth of the population were

living in slums and squatter sextlements. These were mostly ccncen-

"ra~ei in and around the old railway track (which passed through the

heart cf the city) after it was abar.doned due tc the construction of

a new trac-; by-passing the centre of the city. The Government has

recently evicted these unauthorized settlers and has started resettling a small fraction cf them in the outskirts of the city.

The urban population was estimated to be 2.92 million in 1^61

(5.2- cf total) and around 6 million of total) in 1973. Assuming

that the urban population is increasing at a rate between 6-7f every

year, the urban population in 19S5 would be around 12 million. This

means an increase of 6 million over the 1973 urban population.

During 1961~73» the urban population increase of about 3 million

required the construction of 0.5 million new houses (at the rate cf

6 persons per household^ . But during this period, not more than one

fifth of the requirement was satisfied and there was a backlog of

around 0.4 million houses. By 1925 "the urban population increase

of around 6 million would require the construction of about one million new

houses (assuming the same modest rate of one house for six persons).

It is almost inconceivable hew a poor country like Bangladesh can solve

-his gigantic problem.
12

3. B Urban 'lousing Development Plans

The First Five Year Plan ( 1973 - 1978) of the Government has

recognized the enormity of the problem and has directed its efforts

towards achieving short-term objectives by undertaking the following

(1) pro gram

s

v

:

(i) building of multi-stcried apartment houses within the urban

areas for low and lower middle income groups in the public

sector.

(ii) building of 'minimum shelters' in a planned environment

( iii) development of 'sites and services' schemes through the

Urban Development Agencies and local bodies for building

apartment houses

(iv) organization and financing of Go-operative apartment houses

(v) providing planned environments for temporary settlements

with a view to developing these into proper housing estates

in future

.

(vi) framing adequate legislation and building bye-laws, housing

codes for guiding and controlling the development.

The Government views the construction of multi-storied flats and

'minimum' shelters for the low income groups as the desirable longterm solution especially in view of the extreme scarcity of buildable

urban land. The Five-year Plan envisages two components in the

immediate solution of low income urban housing problem:

(i) multi-storied apartment housing

and (ii) 'nuclear' shelters providing pucca accommodation - of a

basic sort at a much lower unit cost than the apartments.

These will seek to house about 4-0 families per acre in '

shelters within 80 square yards of space.
13

In view of the rising inflation all over the world, Bangladesh,

which has to import a substantial fraction of foodgrain and industrial

raw material requirements, is being forced to spend more and more on

feeding its starving population. This has adversely affected its

housing program discussed above and it is doubtful whether the 115.6

million takas (2.8? of the total public sector outlay of the plan)

allocated to the Housing Sector in the Five-year Plan can be made

available.
14

4. fflJBAL K3USING

4 . 1 General

The population of Bangladesh is predominantly rural with about

69 million people (92^ total) living in roughly 64OOO rural settlements

scattered all over the country.

Very little quantitative information is available on rural

housing except that furnished by the 1960 Housing Census.

4.2 structural Conditions of Rural llouses

A brief description of the structural conditions was given in

Sec. 2.2.2 of the First He port. Table 6 gives further details

regarding the materials used in rural houses. It is felt that

although 15 years have elapsed since the Census was conducted, the

qualitative characteristics of the houses have not chan^-ed significantly.
15

Table 6

(a) Principal Materials used in Roofs of Houses, ( shown as

percentage of total houses in each District)

Principal material used in Roof

District

Cement Baked

Concrete/ Tiles

Baked brick/

Stone

CLE./ A sbe sto s sheets

food

1 . Dacca 1 .

1

2. Chittagong 0.3

3. Dinajpur 0.4

4. Rangpur 0.2

5 . Bogra 0 .

3

6. Zushtia 2.2

7. Ra.ishahi 0.9

3. Fabna 0.4

9. Khulna 4.5

10. Jessore 2.5

1 1 . Bari sal 0.5

12. Myinen- 0.2

singh

13. Faridpur 0.6

14. Sylhet 0.3

15. Comilla 0.4

15. Kcakhali 0.2

17. Chittagong *

iiiii

Tracts

0.1

0.3

0.1

0.4

0.3

0.7

1.1

0.1

1.4

1.5

0.6

0.1

0.7

0.8

0.1

0.2

*

63.1

22.4

11.1

21.3

43.0

26.4

24.7

44.4

9.9

19.2

37.1

33.

0

44.8

20.6

45.8

39.5

2.0

0.3

0.2

0.1

0.2

0.1

0.1

1.5

0.3

0.2

0.5

0.2

0.2

0.2

0.3

0.2

*

Bamboo

Thatch

Mud Others

Thatch

1.2

1.2

0.7

2.6

0.2

0.6

1.4

0.3

0.9

0.5

1.0

1.1

0.6

2.4

1.2

0.9

3.5

29.6

70.6

87.0

74.4

55.4

68.8

71.5

49.0

44.2

70.5

42.8

4.5

4.5

0.4

0.8

0.7

1.1

0.4

A.

2

29.9 53.3

70.7 5.3

33.3

53.5

27.0

7.0

8.9

5.3

9.2

46.9 12.1

75.0 19.5

* Negligible
16

Table 6

(h) principal materials used in ''alls of Houses ( shown as

percentage of total houses in each District)

Principal material used in Palls

Concrete/ Stone Earth/ G.I./ Wood Bamboo Thatched Others

Raked in Kutcha asbestos

brick/

stone

Pud "Bricks sheets ——

1. ".a oca 1.4 0.2 13.3 13.5 1.1 31.2 23.1 16.4

2. Chittagong 0.9 0.2 32.8 0.5 0.5 63.7 1.1 0.4

:>j . Pinajpur 1.1 0.3 41.3 0.3 0.2 36.3 19.7 0.7

4. Pingpur 0.5 0.2 6.7 2.4 0.6 49.8 37.0 2.8

'So ^ra 0.6 0.1 54.9 2.2 1.6 24.3 12.1 4.3

6. P.: ..;'': tia 3.3 0.8 38.8 0.9 0.4 42.2 7.9 5.5

7. Rajshahi 1.4 0.2 53.8 0.4 0.1 25.1 16.2 2.8

D Pabna 0.7 * 2.4 6.5 1.9 22.8 24.6 41.0

9. Khulna 3.0 0.9 30.3 1.7 6.9 21 .9 5.3 30.1

10. Je ssore 3.8 1.0 30.0 1.4 3.9 44.0 3.0 12.7

11. B~risal 0.6 0.1 0.7 14.5 6.6 16.3 34.1 27.2

Py-ensingh 0.3 0.1 3.5 8.6 1.0 29.4 30.4 26.6

13. Faridpur 0.6 * 0.4 11.2 4.0 24.6 27.9 31.3

14. Sylhet 1.4 0.1 2.0 2.9 1.5 28.9 56.8 6.8

15. Comilla 0.8 0.1 4.8 9.8 0.8 27.6 37.5 18.6

16. •"oalchali 0.4 0.1 2.1 3.7 0.5 49.8 28.0 15.4

17. Chittagong 0.1 * 0.8 0.1 98.7 0.2 0.1

Hill

Tracts

* = Pegligible

Source: Census of Pakistan, Vol.9, 1960.
17

4.3 Rural "casing; Demand

It is estimated that the population of Bangladesh in 1935* would

be about 100 million. Of these, a little less than 90^ would still

be living in the rural areas. The rural population would, therefore,

increase by about 20 million during the next ten years, it the modest

rate of 6 person per dwelling unit, this wculd mean the construction

of 3.33 million new rural hemes. It was estimated that 3 million

houses needed replacement due to damage, destruction and natural

dilapidation upto the end of 1-71 . Cut of these about 0.4 million

have been reconstructed with the help of voluntary relief organizations.

Therefore, the total number of rural nouses needed in the next ten

years would be about 6 million.

4 . 4 Rural Mousing Development Plans

The Government plans are only to provide supporting environmental

facilities like drinking water supply and sanitation and to provide

institutional support in the organization of co-operatives at 'I nana 1

(small administrative unit composed of a number of villages' level.

The government envisages the creation of Co-operative Housing Finance

Corporation with an authorized share capital of Ta. 250 million to

marshal! and channel funds for a non-profit housing program. A

principal function of the CEFC will be to mobilize savings through a

network of branches throughout the country. Seventeen model villages

- 5 in the coastal areas and 12 in other regions - are planned to be

built by the Government. Each village wculd be a 400 family nucleated

settlement, the estimated cost (1973) being Ta. 3 million on average.
18

5. SP5CIAL 90GI0-CULTURAL CHARACTERISTICS

(2) The urban housing surveyv revealed that the Bangalees share

baths but rarely share kitchen. Toilet and kitchen are often preferred

by the Banzai ees to be detached from the main house. Taking bath in

community ponds outside the house is quite popular.

Religious factors play an important role in the orientation of

houses. The population of Bangladesh is predominantly Muslim. A

Muslim is supposed to pray five times a day facing the direction of

Mecca (viz. West) and to avoid any confusion regarding direction,

almost all the houses in Bangladesh have sides either in the NorthSouth or East-West direction. A Muslim is not supposed to recline

or lie with his feet pointing towards Mecca - it is, therefore, more

usual to have beds in North-South direction. The sitting arrangement

in a latrine has also to be North-South and never East-West. These

are important considerations in the architectural design of a Banglade sM hou se

.
19

6. -.vr-iD R700ROS

The location of wind-measuring meteorological stations are shown

in - ig. 1. ?our of these are equipped with P.T. anemometers, "taut

these are not capable of measuring wind speeds in excess of 70 mph.

Table 7 shews the available annual maximum wind speed records. Some /7

of these values are based on eye observations of experienced meteorologists. Using the data in Table 7 and applying the Lieblein Fitting

Tec iriique^ , the wind speeds for return periods of 20, 50 and 100

years have been calculated and is shown in Table 8.

Due to insufficient data, it has not been possible to include

(5) the tropical frequency factor . It is hoped that a more detailed

investigation of the meteorological records will throw more light on

their aspect of the problem. Another anomaly in the data supplied is

that some of the readings from anemometers are taken at heights varying

from 37 ft. to 84 ft. above surrounding ground level, whereas other

readings are estimated at ground level. A further drawback of these

records is that some of the values extracted from pen-recorder plots

are probably gust values (of the order of 15 seconds) whereas the

others are estimates of sustained wind speeds. The values tabulated

in Table 8, therefore, only give an idea about the magnitude of the

wind speeds involved. However, before recommending these values for

use in the design of buildings, it is suggested that a more thorough

analysis of existing wind data should be made. The instruments used

in measuring wind speed should also be modernised.
20

Table 7

A nnual Maximum Wind Speed in T.iiles per Hour

Year

Station 1961 1962 1963 1964 1965 1956 1967 1968 1969 1970

Dacca 90 77 78 62 100 74 46 75 90 100

Chittagong 50 61 125 70 72 74 60 66 62 138

Cox'

s

Bazaar

50 51 100 52 131 75 81 75 82 78

Bogra 22 36 32 64 52 59 38 49 41 56

Je ssore 53 44 17 56 52 68 63 40 32 43

I shundi N.A. N.A. N.A. 58 58 62 52 52 63 63

Banisal N.A. N.A. N.A. 35 28 51 58 24 52 60

Sylhet N.A. 46 52 58 73 65 81 69 81

M.A. = data not available

Source: Meteorological and Geophysical Centre, Bangladesh

Meteorological Department, Chittagong.
•Dinajpur

kittVnirhat

, Kangp-

• Anemometer

a Wind finding Radar

Electrical Anemometer

• Bogra

•RajshaM .Serahjganj

• Ishurdi

^aridpur $o

# Joseoro j^hairdpury^ei

• Khulna

^Sa-thkhira^

15

Bazar

Fig. 1 Loo-vtion of VJincU-meacruring Meteorological Stations in;

Ban^I adoah.

1

21

?aMe 6

Wind Speeds for Return Periods of 20 , 50 and 100 years.

Wind Speed in miles per hour for Return Periods of

Station - - - - —

20 years 50 ears 100 years

Dacca 123 140 153

Chittagong 122 140 153

Cox* 3 Bazaar 109 121 131

Bogra 73 84 93

Jessore 86 101 113

Ishurdi 65 67 69

•lari sal • 69 79 87

Sylhet 83 96 103
22

7. \n:r: vava^ ? att"tic3

Table 9 shows the available statistics of damaging- cyclones over

Bangladesh since 1795 • It is extremely difficult to assess the daiaage

to houses, particularly in the rural areas. T'ost of the houses are

blown away by even, moderate storms, attempts have, however, been

made to gather some quantitative data regarding the damage to housing.

Since the cyionic storms are usually accompanied with storm surges,

these data show the combined effect of wind and storm surge daTage.

'etween i960 and 19^6, the total loss to crops, building a lives

and development works was estimated at more than (Pakistani) Rupees

1334 million (equivalent to US % 281 million), or an average of

#40.1 million annually. This was about 1.2$ of the G-NP. Tne total

annual damage including damage other than mentioned above was estimated

at about 2

s of GK? of Bangladesh (then known as Cast Pakistan)^ .

Of the many cyclones which have affected Langlade sh in the recent

past, available quantitative data regarding the most severe cyclones

are discussed below.

TaKLe 10 shows the area and population affected by the 1960 cyclones

(October 9-10 and October 30 - 31) .
23

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25

Table 10

Area, and Fopulation affected "by i960 Cyclones'

* Severely

affected

Moderately

affected

* Slightly

affected Total

Area affected

(sc. miles)

660 1,110 960 2,730

Estimated

population 650,000 1,230,000 1,350,000 3,230, XX)

* By 'severely affected' areas, it is meant that these areas were either covered by the tidal flood or that they were devastated b' r the ravaging winds. In these areas, the number of casualties was very high, and the majority of houses collapsed or were washed

sway. In the ' slightly affected 1 areas, roofs and temporary

structures experienced minor, reparable damages.

The number of houses destroyed in the three affected districts is

giver, in Table 11. The 'slightly affected' areas in table 10 have not

been included in preparing this table.

Table 11

Areas in

District of

Estimated

population

in* 1960

IT umber

dead

Estimated

number of

houses

Houses

Destroyed

Houses

partially

damaged

Noakhali 790,000 4,742 157,000

21 ,100

(13.4^')

96,600

(61.380

Chittagong 840,000 9,163 131,700 26,700 81,200

(44.7*0

3arisal 250 , 000 2,952 50,000 N.A. N.A.

In the areas affected by the cyclone in the districts of Xoakhali and

Chittagong, 14.1-'' of the houses were completely destroyed and 52.5^. of the

houses were partially damaged.
26

There high figures of dama e to housing are attributable partly to

the extremely poor quality of houses themselves, as mentioned in

•Jeo. 4.2. The cost of a house for each family was between Is. 30 and

Hs. 50 and the house consisted of four thin tree or bamboo trunks,

anchored in the floor, on which a number of straw mats or old C.I.

sheet are fixed and which supports a primitive light bamboo grate

and the thatch roof. The houses were of such low quality that the

District Magistrate, Noakhali, estimated the average damage per

house completely destroyed or partially affected at Rs. 62 (U.S. $ 13}

o„ly.< 4>

The November 12-1 3» 1970 cyclone has been termed as the most

destructive in living memory. About 2000 sq. miles, containing a

pre-cyclone population of 1,700,000, v/ere severely affected, *<iccording

to a survey carried out in early 1971^ of the 206,500 houses in the

area, about 85. J' were severely damaged by the cyclone. At least

224,000 persons perished in the cyclone. In the worst-affected offshore island, Manpura, about 98? of the houses were almost completely

destroyed.

According to figures obtained from the Ministry of Relief and

Rehabilitation, Govt, of Bangladesh, about 5 million houses were

damaged due to cyclones and tornadoes during the 14 years from i960

to 1973. The estimated value of the houses was Takas 1188,07 million.

During the same period, floods damaged 2.58 million houses with an

estimated value of Takas 850 million. The detailed statistics is given

in Table 12.
Table 12

Number of Dwelling Houses Damaged due to Cyclones & Tornadoes

I960 - 1973

Year

IJunber of

houses

damaged

Estimated value of

damages to housing

(million takas)

I960

1961

1963

1964

1965

I966

1968

1969

1970

1973

347,700

232,292

443,737

15,644

2,602,004

273,250

6,110

CO , 30

1

639,012

269,031

69.54

106,46

88.75

3.13

520.40

54.65

2.24

13.56

183.01

146.33

Total 4,995,141 1188.07 million Takas

27

6. ffJCIAL FjXmjMS

The rural houses in the coastal areas are usually the worst-hit

"by cyclones. One of the special problems in this region is the

sinailtaneous occurrence of storm surges and high winds. The wave

heights may be 10 - 15 ft. above the ground level. One solution

which has been suggested for minimizing damage to property and lives

is the building of houses on stilts which albw water to flow underneath. In fact, some of the multi-purpose cyclone shelters, planned

to be build in these regions would be two or three storied structures,

supported on H.C. columns with the ground floor left open. The wind

load response of these structures would be different from ordinary

structures, with all t'=e faces, including the bottom one, being exposed

to wind.

The commonly used corrugated galvanized iron sheet roofs perform

poorly as heat insulating material. With the summer temperature around

£0°-90°F, it becomes very uncomfortable to live in such houses. The

houses are therefore built with large number of windows and openings

at eaves level, which results in a highly permeable structure. Moreover, it is common to have Verandahs (about 5 ft. wide covered projections) on at least one side of the house. These projections probably

adversely affect the wind load characteristics of the structure.
28

9 . CON CUT TUNG MARKS

An attempt has been made in this report to discuss the housing

situation in Bangladesh. With the major thrust of the development

efforts directed towards the agricultural sector and related activities,

the planners in Bangladesh accord a low-priority to housing development

sector. It is unlikely that the standard of housing would show any

appreciable improvement in the years to come. It is anticipated that

owner-built houses, with traditional materials like bamboo pests,

bamboo-thatch walls and C.I. sheet roofs would retain their popularity

in the rural sectors while the urban areas, particularly Dacca and

Chittagong City, may have a few 5- storied blocks of small flats for

low-income housing.

The amount of wind damage to houses could be minimized by proper

detailing of the connection of roof structure to the supporting wall

and proper connection of the roofing sheets (usually corrugated galvanized iron) to the roof structure. Proper application of design

criteria developed for construction of low-rise buildings to resist

extreme wind loads would go a long way in minimizing the immense loss

to housing almost every year.
29

raCBLIMS IN CTH K INDIAN OCEAN COUNTRIES

(a) INDIA

(i) Housing

The total population of India, according to the 1971 census, was

547.95 million of which 10-9 million (19.95^) constituted urban dwellers.

Between 1961 and 197 1, the growth rate of population was 24.8^.

According to late 1972 estimates, the total shortage of housing in

(9) rural areas, including huts, was around 72 million dwelling unitsN

.

The urban housing shortage, according to statistics computed in 1965»

was estimated to be around 12 million units. The total requirement of

new dwelling units to be constructed in urban areas during 1961-76

has been estimated at 25 million units inclusive of an estimated 12

to 13 million units required to meet the increase in urban population

during the same period. The Fourth Five Year Plan ( 1 966-7 1) allocated

about Rs. 2420 million to housing (about 1.6j$ of the total public sector

investment). During the First Plan, housing outlay constituted I6f

of the total public sector investment, decreasing to 8fa in the second

plan and 7f in the third plan. This shows that the India planners are

according a very low priority to housing development plans.

(ii) Wind Loads

The 77est Bengal, Orissa and Madras coast, lying on the eastern

side of the peninsula, are often affected by cyclones originating in

the Bay of Bengal.

The Indian Standards Institution has well-defined wind-load codes

( 10) for the design of buildings^ . Figure 2 shows a map of India showing

the basic wind pressures recommended in the design of structures. The

2 formula p = KV has been used in arriving at these pressures, with
K = 0.006, V being1 in Km/hr and p in Kg/m . The code recommends a

2 2

basic wind pressure of 200 Kg/m (40.94 lb/ ft ) along the coastal

belt upto a height of 30 metres above the retarding surface. This is

equivalent to a wind speed of 182.6 Km/hr or 113.5 mph.

The number of severe cyclones which crossed the coasts during

1391 to 1960 is indicated in Fig. 2 by circles in 5° latitude zones.

A severe cyclone has been defined as one in which the wind speed

2

exceeds 89 Km/hour corresponding to a wind pressure of 48 Kg/m .
fcig. 2 Basio Maximum Hind Pressure Map of India » Bxoluding Hinds ef Short

Duration*

Pressures in kg/m*

fc3 200

FAKISTAH

I7SPAL

25°N

kDESH

rrsii

20'

Bay of Bengal

BURMA

todsjBSJr St Fiooba/ Island^

( India)*

The number of severe cyclones which have approached or crossed the

coasts during 1691 to i960 is indioated in oiroleo in 5 latitude sones

( A severe oyclone is one in which the wind speed exceeds 89 km/h)

The influence of a severe cyclone may he taken to extend from the coast

line up to the line demarcating 60 kg/m sons.

* Source j R*f. tO
P:if*. 3 I-asirawn Hind' Pressure I lap of India, Including Uinds of Short

Duration as in Squalls*

For purposes of this rn?.p, a short duration wind is that which lasts only

for a few minutes, Generally Iocs than 5 minutes
31

(b) T: 1'A ir CEYLON

j'rora available records, it appears that cyclone damage to housing

in these two countries is not as severe as that in Bangladesh.

Although approximately one out of ten cyclonic storms that occur

in the "Bay of Bengal strike the Arakan coast of Burma, the presence

of iirakan mountain ranges and the Chin hills near the coast results in

appreciable reduction of wind speeds as the cylcone moves inland. The

maximum wind speed of the cyclones before striking the coast was

estimated to be 70 miles per hour or less. The damage caused by

cyclonic storms was almost negligible when compared to other countries.

However, in 19 39* a cyclonic stor^i orossed the Arakan coast near

Kyaukpyu and caused slight damage, About 300 human lives were lost

in the storm surge. Again in 1943, a storm crossed the Arakan coast

near Akyab causing appreciable damage to crop and structures due to

accompanying floods. The damage was about 13 million Kyats (equivalent

to US #2.1 million)

.

In the last few decades, only two cyclones have affected Ceylon

causing appreciable damage. One was in the early thirties and the

other in December 1964. In the December 1964 cyclone which hit

Trincomalee, the average maximum wind velocity was about 70 m.p.h. with

100 m.p.h. gusts. The cyclone affected a 70 mile wide area. The roofs

(7) of most houses in Trincomalee were blown off. '
32

LI ST 0^ REFERENCES

1. First Five Year Plan (1973-1978), Planning Commission,

S-overnment of the Peoples' Republic of Bangladesh, 1973*

2. Urban Housing Demand Survey in Bangladesh (Research Report),

Institute of Statistical Research and Training, University of

Dacca, 1974.

3. Khan, A.R., 'The Economy of Bangladesh", Oxford University

Press, 1973* pp. 23.

4. Report of Institute of Engineers Sub-committee on Cyclone Disasters

in East T'akistan, Institute of Engineers, Pakistan, 1962 (available

from Institution of Engineers, Bangladesh, Dacca).

5. Kintanar, R.L., Climatology and Wind Related Problems in the

Phillipines, BSS 56, National Bureau of Standards, Washington B.C.,

pp.32.

6. Hussain, S.M., (Deputy Director, Meteorology Directorate, Dacca),

Private Communication.

7. Proceedings of the meeting of '."orking Group of experts on Cyclones,

mC and BCAFI3, Dec. 19 66, Dacca.

8. Sommer, A. and " ; osley, W.H., East Dengal Cyclone of November, 1970,

The Lancet, 13 Hay, 1972.

9. Chandrasekhara, C.S., National Report of India in 'Cne World

Only', Report no. 8, Friedrich Ebert Stiftung, '/.'. Germany.

10. Indian Standard Code of Practice for Structural Safety of Euildin^s;

1972, IS 875-1964, Delhi.
APPENDIX C

Manila Regional Conference

Program

REGIONAL CONFERENCE

on the

Dissemination of Project Results of the Research

on

"Development of Improved Design Criteria for Low-Rise Buildings in Developing Countries

to Better Resist the Effects of Extreme Winds."

Jointly Sponsored

- :

• -

U.S. National Bureau of Standards

U.S. Agency for International Development Mission

in Manila

Philippine Advisory Committee

to be held on May 16 and 17, 197o

at the

GS1S Auditorium

- AiToeeros, St., Manila

(Thi& saves a* an invitation)

R.S.V.P. by Thursday, May 15, 197-") Cynthia — Tel. 97-60-61 Lot. 566

Vivian — Tel. 08-4(5-89 ; 96-11-85

Dr. Taluijava — Tel. 1)9-82-60
Philippine Advisory Committee

Dean ALFREDO L. JUINIO, Honorary Chairman

U.P. College of Engineering

Dr. ERNESTO G. TABUJARA. Chairman

U.P. Building Research Service

Dr. ROMAN L. KINTANAR, Vice-Chairman

Philippine Atmospheric Geophysical and

Astronomical Services Administration

Prof. GERONTMO V. MANAHAN. Executive Secretary

U.P. Building Research Service

Prof. ANGEL A. ALEJANDR1NO, National Hydraulic Research Center

Mr. CATALINO P. ARAFILES, Philippine Atmospheric Geophysical

and Astronomical Service Administration

Mr. MANUEL C. BONJOC. Philippine Atmospheric Geophysical

and Astronomical Service Administration

Engr. CESAR A. CALIWARA. Philippine Association of Civil Engineers

Archt. CESAR H. CONCIO. National Building Code CommitteeMr. HUGO S. DE LA CRUZ. Phil. Atmospheric Geophysical and

Astronomical Services Administration

Engr. AMBROSIO R. FLORES. Philippine Standards Association Mr. RODOLFO A. DE GUZMAN. Philippine Atmospheric Geophysical

and Astronomical Services Administration

Engr. ANDRES O. HIZON. National Society for Seismology and

Earthquake Engineering of the Philippines

Dean AURELIO T. JUGUILON. U.P. College of Architecture

Col. ALEJANDRO R. KABILING. National Housing Corporation

Engr. OCTAVIO A. KALALO. Association of Structural Engineers of the Philippines

Engr. ROSALIO A. MALLONGA. Bureau of Public Works

Mr. WELLINGTON A. MISOZA. Philippine Atmospheric Geophysical

and Astronomical Services Administration

Engr. JOSE P. OROLA, Government Service Insurance System

Engr. MIGUEL V. PAALA, Social Security System

Dr. JOSEFINA M. RAMOS. U.P. Building Research Service

Col. ALBERTO R. SANCHEZ, Land and Housing Development

Corporation

Engr. JOAQUIN O. SIOPON'GCO. National Science Development Board

Engr. MODESTO D. SORIANO. Jr., Government Service Insurance System

Dr. FRANCISCO N. TAMOLANG. National Science Development Board

Gen. GAUDENCIO V. TOBIAS. National Housing Corporation

Atty. JACOBO S. VERA. People's Homesite and Housing Corporation

Engr. RAMON R. VETO. People's Homesite and Housing Corporation

CYNTHIA SEIZORAN ENRIQUEZ. Secretary of the Committee
International Consultants, Delegates and Gutsts

Dr. JAMILUR R. CIIOUDHURY. Assistant Professor, Civil Engineering, Bangladesh University of Engineering & Technology, Dacca, Bangladesh

Mr. RICHARD M. DANGLER, Assistant Director for Capital

Development, U.S. Agency for International Development

Mr. THOMAS E. JOHNSON. Deputy Assistant Director for

Capital Development, U.S. Agency for International

Development "

Mr. WILLIAM LITTLEWOOD, Associate Director, Office of

Science' and Technology, Agency for International Development, Department of State

Dr. RICHARD D. MARSHALL, Center for Building Technology,

National Bureau of Standards

Mr. THOMAS C. NIBLOCK, Director, U.S. Agency for Inter- national Development

Dr. WERNER Y.F. NINGjNational Bureau of Standards, Taipei

Dr. EDWARD 0. PFRANG. Chief, Structures Materials and

Life Safety Division, Center for Building Technology, National Bureau of Standards

Mr. NOEL J. RAUFASTE, JR., Federal Building Program Coordinator, Office of Federal Building Technology, Center

for Building Technology, National Bureau of Standards

Dr. SUDHINDRA NATII SENN. Chief, Typhoon Research Committee, Economic Commission for Asia and the Far East

(ECAFE)

Mr. GUNTER P. STE1TZ, Project Manager, RP-US Bayanihan

School Reconstruction Project, Office of Capital Development, U.S. Agency for International Development
PROGRAM

FRIDAY, MAY 16. 1975

Part A: Opening- Ceremony

Master of Ceremonies Director ANGEL A. ALEJANDRINO

8:00 Registration National Hydraulic Research Center

9:00 Philippine National Anthem

Keynote Address Chairman FLORENCIO A. MEDINA

National Science Development Board

Project Background and

Summary Dr ERNESTO G. TABUJARA

U.P. Building Research Service

Part B: Presentation of Results

9:30 Distribution of Extreme Winds .... Mr, RODOLFO A. DE GUZMAN

Philippine Atmospheric Geophysical

and Astronomical Services Adminis.

tration 10:00 Break

10:30 Draft Criteria for Wind Loading .... Dr. RICHARD D. MARSHALL

U.S. National Bureau of Standards

li:3u Structural Connection Details and Improved Architectural

Practices Mr. NOEL J. RAUFASTE. JR.

U.S. National Bureau of Standards

12:00 LUNCH

Master of Ceremonies Engr. JOSE P. OROLA

Government Service Insurance System

2:C0 Economic Analysis and

Socio-Economic Consideration Mr. NOEL J. RAUFASTE, JR.

U.S. National Bureau of Standards

2:30 Information Transfer Mr. NOEL J. RAUFASTE. JR.

U.S. National Bureau of Standards

3:15 Break

3:45 Effects of Research on Bay

of Bengal Countries Dr. JAMILUR R. CHOUDHURY

4:15 Implementation of Results Engr. AMBROSIO R. FLORES

PHILSA

Engr. ANDRES O. HIZON' NSSEEP

4:45 Social Hour
PROGRAM

SATURDAY, MAY 17, 1975

Part C: Discussions

Master of Ceremonies Engr. JOAQUIN O. SIOPONGCO

National Science Development Board

9:00 Open Forum DISCUSSANTS:

Dr. Richard D. Marshall

Mr. Noel J. Raufaste, Jr. Mr. Rodolfo A. de Guzmaa

Engr. Ambrosio R. Flores Engr. Modesto D. Soriano, Jr. Engr. RoscJio A. Mallongc

10:30 Break

11:00 Continuation of Open Discussion or Future Projections

11.45 Closing Remarks Dean CESAR H. COXCIO

National Building Code Committee

Mr. NOEL J. RAUFASTE. JR. U.S. National Bureau of Standards

12:00 LUNCH

:00 Field Trip to PAGASA

Science Garden Col. ALBERTO R. SANCHEZ

Land Housing & Development

Corporation

Marshal

3:30 Refreshments
CONFERENCE WORKING COMMITTEES

Dr. ERNESTO G. TABUJARA

Overall Chairman

FINANCE

Engr. Modesto D. Soriano, Jr., Chairman

Dr. Ernesto G. Tabujara

Col. Alejandro 11. Kabiling

Engr. Joaquin 0. Siopongco

ARRANGEMENTS

Eil^'i". Jose P. Orola, Chairman

Engv. Modesto 1). Soriano, Jr. Engr. Rosalio A. Maiionga

Mr. Catalino P. Arafiles

DOCUMENTATION

Engr. Ambrosio R. Flores, Cc-Chairman

Prof. Geronimo V. Manahaii, Co-Chairman

Dean Aurelio T. Juguilon

Mr. Rodolfo A. de Guzman

RECEPTION AND HOSPITALITY

Mr. Wellington A. Mihoza, Chairman

Col. Alberto R. Sanchez

Dean Aurelio T. Juguilon

Areht. Cesar II. Concio

PROGRAM AND INVITATION

Mr. Manuel C. Bonjoc, Chairman

Engr. Andres 0. Ilizon

Prof. Angel A. Alejandrino

Engr. Miguel V. Paa'a

PUBLICITY

Engr. Octavio A. Kalalo

Dr. Ernesto G. Tabujara

Engr. Cesar A. Caliwara

Mr. Hugo C. de la Cruz
APPENDIX D

Estimation of Extreme Wind Speeds

in the Philippines

ESTIMATION OF EXTREME WIND

SPEEDS — APPLICATION TO THE PHILIPPINES

by

Emil Simiu

Center for Building Technology

Institute for Applied Technology

National Bureau of Standards

Washington, D.C. 20234

Report Presented at Regional Meeting on Development

of Design Criteria and Methodology for Low-Rise/Low-Cost

Buildings to Better Resist Extreme Winds

ESTIMATION OF EXTREME KIND

SPEEDS — APPLICATION TO TEE PHILIPPINES

by

Emil Simiu

ABSTRACT

Theoretical and practical considerations are presented that are pertinent

to the estimation of probabilistically defined design wind speeds. Results

of the statistical analysis of extreme wind data in the Philippines are presented and interpreted. Recommendations based on these results are made

with regard to the possible redefinition of wind zones, and tentative

conclusions are drawn regarding the adequacy of design wind speeds currently

used in the Philippines.

KEY WORDS: Building Codes; hurricanes; probability distribution functions;

risk; statistical analysis; storms; structural engineering;

tropical storms; wind loads; wind speeds.

ACKNOWLEDGMENTS

The writer wishes to express his indebtedness and appreciation to Dr. Roman L. Kintanar, Mr. Manuel Bonjoc, Mr. Bayani S. Lomotan, Mr. Jesus

E. Calooy, Mr. Leonicio A. Amadore, Mr. Samuel B. Landet and Mr. Daniel

Dimagiba, of the Philippine Atmospheric, Geophysical Astronomical Services

Administration (PAGASA) , for kindly permitting him to use the PAGASA records

and facilities and for their effective and generous help. He also wishes

to thank Dr. R.D. Marshall, of the Center for Building Technology, National

Bureau of Standards and Dr. A.J. Goldman, of the Institute for Basic Standards,

National Bureau of Standards, for useful comments and criticism of this work.

The computer program used herein was developed by Dr. J.J. Filliben, of the

Statistical Engineering Laboratory, National Bureau of Standards.

i
TABLE OF CONTENTS

Abstract i

Acknowledgments a . ±

List of Figures ±±

List of Tables ±±

1. Introduction i

2. Wind Speed Data 3

3. Probabilistic Models of Extreme Wind Speeds 8

4. Assessment of Procedures Based on the n

Annual Highest Speeds

5. Assessment of Procedure Based on the 15

Highest Monthly Speed

6. Statistical Analysis of Extreme Wind Data in 17

the Philippines

7. Interpretation of Results 18

8. Conclusions 22

References .24

LIST OF FIGURES

Figure 1 Ratio, r, of Maximum Probable Wind Speeds Averaged over 30

t seconds to those Averaged over 2 sec. (after Ref. 6)

Figure 2 Quantity 3 31

Figure 3 Probability Plots:

(a) Type II Distribution, y = 2 32

(b) Type I Distribution 33

LIST OF TABLES

Table 1-Suggested Values of Z

q for Various Types of Exposures 6

Table 2-Maximum Annual Winds (1 minute average) 28

Table 3-Station Descriptions and Estimated Extreme Wind Speeds 29

ii
ESTIMATION OF EXTREME WIND SPEEDS — APPLICATION TO THE PHILIPPINES

1, INTRODUCTION

In modern building codes and standards [1, 2] basic design wind

speeds are specified in explicitly probabilistic terms. At any given station a

random variable can be defined, which consists of the largest yearly wind

speed. If the station is one for which wind records over a number of consecutive years are available, then the cumulative distribution function (CDF)

of this random variable may, at least in theory, be estimated to characterize

the probabilistic behavior of the largest yearly wind speeds. The basic design

wind speed is then defined as the speed corresponding to a specified value F of

o the CDF or, equivalently (in view of the relation N = 1/(1-F ), in which N = mean

o recurrence interval) , as the speed corresponding to a specified mean

recurrence interval. For example, the American National Standard A58.1

[1] specifies that a basic design wind speed corresponding to a 50-year

mean recurrence interval (i.e., to a value F

q

of the CDF equal to 0.98,

or to a probability of exceedance of the basic wind speed in any one

year equal to 0.02) be used in designing all permanent structures, except those

structures with an unusually high degree of hazard to life and property

in case of failure, for which a 100-year mean recurrence interval

(F = 0.99) must be used, and structures having no human occupants or

o where there is negligible risk to human life, for which a 25-year mean

recurrence (F^ = 0.96) may be used. A wind speed corresponding to a

N-year recurrence interval is commonly referred to as the N-year wind.

1
The mean recurrence intervals specified by building codes, rather

than being based on a formal risk analysis—which is in practice not

feasible in the present state of the art —are selected in such a manner

as to yield basic wind speeds which, by professional consensus, are

judged to be adequate from a structural safety viewpoint. Nevertheless,

it is generally assumed that adequate probabilistic definitions of

design wind speeds offer, at least in theory, the advantage of insuring a

certain degree of consistency with regard to the effect of the wind

loads upon structural safety. This is true in the sense that, all

relevant factors being equal, if appropriate mean recurrence intervals are

used in design, the probabilities of failure of buildings in different

wind climates will, on the average, be the same.

In the practical application of the probabilistic approach to the

definition of design wind speeds, certain important questions arise.

One such question pertains to the type of probability distribution best

suited for modeling the probabilistic behavior of the extreme winds.

The provisions of the National Building Code of Canada [2] are based

upon the assumption that this behavior is best modeled by a Type I

(Gurobel) distribution. The American National Standard A58.1 [1], on the

other hand, assumes that the appropriate models are Type II (Frechet)

distributions with location parameters equal to zero and with tail

length parameters dependent only upon type of storm. Finally, Thorn [3] has

proposed a model consisting of a mixed probability distribution, the

parameters of which are functions of (a) the frequency of occurrence

of tropical cyclones in the 5° longitude-latitude square under consideration

and (b) the maximum average monthly wind speed recorded at the station

2
investigated. The question' of selecting the most appropriate distribution

is one that deserves close attention: indeed, as indicated

in Refs.4&5, the magnitude of the basic design wind speed may depend

strongly upon the probabilistic model used.

Assuming that the type of probability distribution best suited for

modeling the behavior of the extreme winds is known, a second important

question arises, viz., that of the errors associated with the probabilistic

approach to the definition of design wind speeds. Such errors depend

primarily upon the quality of the data and upon the length of the record

(i.e., the sample size) available for analysis.

These questions will be dealt with in this work, which will also

present results of statistical analyses of wind speed data recorded in

the Philippines. In the light of the material presented herein, possible

approaches will be examined to the definition of extreme wind speeds for

purposes of structural design in the Philippines.

2. WIND SPEED DATA

For the statistical analysis of extreme wind speeds to be meaningful,

the data used in the analysis must be reliable and must constitute an

homogeneous set.

The data may be considered to be reliable if:

-The performance of the instrumentation used for obtaining the data

3
(i.e., the sensor and the recording system) can be determined

to have been adequate. . '

-The sensor was exposed in such a way that it was not influenced

by local flow variations due to the proximity of an obstruction

(e.g., building top, ridge or instrument support).

A set of wind speed data is referred to herein as homogeneous if

all the data belonging to the set may be considered to have been obtained

under identical or equivalent conditions. These conditions are determined

by the following factors, which will be briefly discussed below:

-type of instrumentation used

-averaging time (i.e., whether highest gust, fastest mile, one-minute

average, five-minute average, etc. was recorded),

-height above ground

-roughness of surrounding terrain (exposure)

-in the case of tropical cyclone winds, distance inland from the

coastline.

Type of instrumentation . If, during the period of record, more than

one type of instrument has been employed for obtaining the data, the

various Instrument characteristics (anemometer and recorder) must be

carefully taken into account and the data must be adjusted accordingly.

4
Averaging Time. If various averaging times have been used during

the period of record, the data must be adjusted to a common averaging

time. This can be done using graphs such as those presented in Ref . 6

and included in Fig. 1 in which Z

q is a parameter defining the terrain

roughness (see, for example, Ref. 7).

Height Above Ground . If, during the period of record, the elevation

of the anemometer had been changed, the data must be adjusted to a common

elevation as follows: Let the roughness length and the zero plane displacement be

denoted by Z and Z,, respectively (Z , Z, are parameters which define the rougho a O a ness of terrain, see Ref. 7). The relation between the mean wind speeds U(Z^)

and U(Z_) over horizontal terrain of uniform roughness at elevation Z, and Z 0

above ground, respectively, can be written as

u(zx ) In —± ^

Z

o (1)

U(Z2 ) ln

Z

2 " Z

d

Zo

Suggested values of the roughness length Zq are given in table 1

(see Refs. 7, 8, 9). For example, at Sale, Australia, for terrain

described as open grassland with few trees, at Cardington, England,

for open farmland broken by a few trees and hedge rows, and at Heathrow

Airport in London, Zq

- 0.08m [7, 8]. At Cranfield, England where the

ground upwind of the anemometer is open for a distance of half a mile

across the corner of an airfield, and where neighboring land 'is broken

by small hedged fields, Zq = 0.095 m [10]. It is noted that Eq. 1 is

applicable to mean winds and should not be used to represent the profiles of

peak gusts.
Table 1 - Suggested Values of Z

Q for Various Types of Exposure

Type of Exposure Z (meters)

o

Coastal U • UUJ u . vs.

Open 0.03 - 0.10

Outskirts of towns, suburbs 0.20 -0.30

Centers of towns 0.35 - 0.45

Centers of large cities 0.60 - 0.80

The zero plane displacement may in all cases be assumed to be zero,

except that in cities (or in wooded terrain) 2^ = 0.75 h, where h =

average height of buildings in the surrounding area (or of trees) [7, 11].

Thus, for example, if in open terrain with Z

q = 0.05 m, U(23) = 30 m/s, then

adjustment of this value to the height = 10m, using Eq. 1, gives

In —

U(10)= U(23) = 30 |— = 25.9 m/s.

ln 0^5

It is noted that, in most cases, the roughness parameters Z , Z,

o d

must be estimated subjectively, rather than being determined from

measurements. Good judgment and experience are required to keep the

errors inherent in such estimates within reasonable bounds. In conducting

statistical studies of the extreme winds, it is advisable that for any

particular set of data, an analysis be made of the sensitivity of the results

to possible errors in the estimation of Z and Z,. v o d
In the case of winds associated with large-scale extratropical

storms, the mean wind U(Z) at height Z in terrain of roughness Z , Z,

o d

is related as follows to the mean wind U^(Z^) at height Z^ in terrain of roughness

zd> zdi w

U(Z) -6 D.CZj) -2 (?)

In

Z ol

The quantity, B , may be obtained from Fig. 2, which was developed

in Ref . 8 on the basis of theoretical and experimental work reported

by Csanady [14] and others [15]. (Note that Z < Z .) ol o

Eq. 2 may be applied if the roughness of the terrain is homogeneous

over a horizontal distance from the anemometers of about 100 times the

anemometer elevation [12, 13].

Let, for example, U(Z

1

) = 29m/ s, Z ± = 10m, Zq1

= 0.05m, Zdl

= 0.

The corresponding speed U(Z) at Z = 40m, say, in open terrain of roughness

Z = 0.25m, Z = 0 is

o d

in 40

U(10) = 1.12 x 29 — = 31.1 m/s

where 1.12 is the value of 8 for Z = 0.05m, Z = 0.25m, obtained from

ol o

iig. 2.

7
It is pointed out that, just as in the case of Eq. 1, errors are

inherent in Eq. 2 that are associated with the subjective estimation

of the roughness parameters. Also, recent research suggests that

in the case of tropical cyclone winds Eq. 2 underestimates wind speeds

over built-up terrain, calculated as functions of speeds over open

terrain, by amounts of the order of 15% or more [27].

Distance Inland from the Coastline . The intensity of hurricane or

typhoon winds is a decreasing function of the distance inland from the

coastline. Hurricane wind speeds may be adjusted to a common distance

from the coastline by applying suitable reduction factors. Such

reduction factors have been proposed by Malkin, according to whom

the ratios of peak gusts at 48, 96 and 144 km from the coastline to

peak gusts at the coastline are 0.88, 0.82 and 0.78, respectively [16, 17].

The nature of the variate suggests that an appropriate model of

extreme wind behavior is provided by probability distributions of the

largest values, the general expression for which is [18]:

3. PROBABILISTIC MODELS OF EXTREME WIND SPEEDS

F(v) = exp {-[(v-y)/a] Y

} y < V < 00

—oo < y < oo (3)

0 < a < 00

Y > 0

where v = wind speed, y = location parameter, a = scale paramter,

Y = tail length parameter. Eq. 3 may be regarded as representing

3
a family of distributions, each characterized by a value of the tail

length parameter y. As y becomes larger, the tail of the probability

curve becomes shorter, i.e., the probability of occurrence of

large values of the variate becomes smaller. In particular, as

Y * °°, Eq. 6 may be shown to become

F(v) = exp {-exp [-fc-u) /a] } -« < v < «

-co < y < eo (4)

0 < a < 00

The distributions given by Eqs. 3 and 4 are known as the type II

and the type I distributions of the largest values, respectively.

Two basic procedures for estimating probabilities of occurrence of

extreme winds are currently in use. The first procedure consists in

estimating the parameters of a probability distribution of the largest

values from the series of annual highest wind speeds at the station

considered. This procedure has been applied by various authors as follows:

(a) In Ref. 4, estimates are made of all three parameters, u, a and y

in Eq. 3 , no specific value being assigned a priori to any of these parameters.

(b) In Refs. 19 and 20, the location parameter is assumed to have

the value u = 0. Estimates are then made of the remaining parameters,

a and y. The arbitrary assumption that u = 0 entails a sacrifice in goodness

of fit; the justification for using this assumption is that it makes

possible the application of Lieblein's well-known estimation procedure

9
[21] to obtain values of a and y [19]. However, in view of the recent development of alternative estimation procedures applicable to type II

distributions with y ^ 0 [4], the assumption that u = 0 becomes unnecessary.

(c) Court in the United States [22] ,. Davenport in Canada [23]

and Kintanar in the Philippines [25] have assumed the universality of the type

I distribution, i.e., that the tail length parameter is always Y = 00

•

Estimates are then made of the parameters y and a.

The second procedure assumes the universal validity of the mixed

distribution

-9

F(v) = p Eexp ] + pTexp

[-(J)

^] (5)

proposed by Thorn in Ref. 3. The first and the second term in the sum of

Eq. 5 represent the probabilities that the winds associated with

extratropical storms and with tropical cyclones, respectively, will

not exceed the value, v, in any one year. The scale parameter, a, is

an explicit function of the maximum of the average monthly wind speeds recorded at the station considered. The second parameter of the mixed distribution,

p«pj is an explicit function of the frequency of occurrence of tropical

cyclones in the 5° longitude-latitude square under consideration,

and p = 1 - p T> Thus, in this second procedure, the series of annual

highest winds is not used for estimating distribution parameters.

An assessment of the models described in this section will now be

presented.

10
4. ASSESSMENT OF PROCEDURES

EASED ON THE ANNUAL HIGHEST SPEEDS

To assess the validity of current probabilistic models, statistical

analyses of annual highest speeds were carried out using a computer

program described in Ref . 4. The results of the analyses, which are

reported in detail in Ref. 4, lend credence to the belief that a sufficiently

long record of annual largest speeds will provide an acceptable basis

for probabilistic estimates of the N-year winds — even for large values

of N, such as are of interest in structural safety calculations —

if the following conditions are satisfied. First, the value of opt (y)

for that record is large, say y >_ 40 (opt (y) = value of y [see Eq. 3]

for which the best distribution fit of the largest values is obtained)

.

Second, meteorological information obtained at the station in question,

as well as at nearby stations at which the wind climate is similar,

indicates that winds considerably in excess of those reflected in the

record cannot be expected to occur except at intervals many times

larger than the record length. Wind climates which satisfy these two

conditions will be referred to as well-behaved.

Assuming that the wind speed data are reliable, lower bounds for the

sampling error in the estimation of the N-year winds in a well-behaved climate

may be calculated on the basis of a mathematical result, viz., the

Cramer-Rao relation, which states that for the type I distribution

[see Ref. 18 , p. 282]

11
n

(6)

<3) ^0^0Zi3 ff var 2 (7 ) n

where var (0) , var (d) are the variances of (3 and d, where y and d are

the estimated values of y and a, respectively, obtained by using any

appropriate estimator consistent with basic statistical theory requirements; a is the actual value of the scale parameter and n is the sample

size. Using Eqs. 6 and 7, lower bounds for the standard deviation of the

N-year wind, SD[v(N)], can be approximated as follows. Eq. 4, in which

the parameters y, o are replaced by their estimates y, d , is inverted to

yield

where

v(N) = y - G(lJt)d (8)

G(l-jjj) = -£n[-*n(l-«j)] . (9)

Then

L,2 1/2

SD[v(N)] > {var(y) + [G(l-±)r var(d)} (10)

Eq. 10 is based on the assumption that the error involved in neglecting the

correlation between y and 8 is negligible. The validity of this assumption

was verified by using Monte Carlo simulation techniques.

Since the actual value of a is not known, in practical calculations the

estimated value d is used in Eqs. 6 and 7. For example, the distribution

parameters corresponding to the wind speed data at Davao (n = 24, see Table 2),

12
estimated by using the technique described in Ref. 4, are y = 38.89 km/hr,

a = 9.40 km/hr. It follows from Eq. 8 that v(50) = 75 km/hr and from Eqs. 6,

7, and 10 that SD[v(50)] >_5.18 km/hr. Subsidiary calculations not reported

here have shown that Eq. 10 provides a good indication of the order of magnitud

of the sampling errors.

Wind Climates Characterized by Small Values of opt (y) . Occasionally,

a record obtained in well-behaved wind climates may exhibit small values

of opt (y) ; this will occur if that record contains a wind speed

that corresponds to a large mean recurrence interval. There

are regions, however, in which, as a rule, the statistical analysis of

extreme wind records taken at any one station yields small values of

opt(Y). This is the case if, in the region considered, winds occur

that are meteorologically distinct from, and considerably stronger than

the usual annual extremes. Thus, in the regions where tropical cyclones

occur, opt (y) will in general be small, unless most annual extremes

are associated with tropical cyclone winds. An example of a record

for which Y(°pt) is small is given in Fig. 3a, which represents

the probability plot with y = opt (y) - 2 for the annual extreme

fastest-mile speeds recorded in 1949-73 at the Corpus Christi, Texas, airport

.

For purposes of comparison, the same data have been fitted to a type I

distribution [opt (y) = 00

, or Eq. 4 ]; the fit in this case is seen

to be exceedingly poor, i.e., the plot deviates strongly from a straight

line (Fig. 3b). (As shown in Ref. 4, a measure of the goodness of

fit is given by the extent to which the probability plot correlation

coefficient is close to unity; this coefficient is printed out in

Figs. 3a and 3b .

)

13
To small values of the tail length parameter there frequently

correspond implausibly high values of the estimated speeds for large

recurrence intervals. In the case of the 1912-48 record at Corpus Christi,

for example, opt(y) = 2 and the estimated 5- minute average is 327 mph

(155 m/s) for a 1000-year wind, which is highly unlikely on

meteorological grounds. For 20-year records, the situation may be even

worse: thus, for the 1917-36 Corpus Christi record, which contains an

exceptionally high wind speed due to the 1919 hurricane [22, 24]

opt (y) = 1 and the calculated 1000- year wind is 1952 mph (873 m/s)

[4], a ridiculous result. Also, the situation is not likely to improve

significantly if the record length increases. From a 74-year record,

a plot quite similar to Fig. 3 would presumably be obtained, with twice

as many points similarly dispersed, to which there would correspond a

similar least squares line on probability paper.

It may be stated, consequently, that while in the case of wellbehaved climates it appears reasonable to infer from a good fit of the

probability curve to the data that the tail of the curve adequately

describes the extreme winds, such an inference is not always justified

if opt (y) is small.

It may be argued that one could avoid obtaining unreasonable extreme

values by postulating that the annual largest winds are described by

a probability distribution of the type I, i.e., by assigning the value

Y

= oo t o the tail length parameter. This has been done by Court [22]

and Kintanar [25]. As can be seen in Fig. 4, the corresponding fit may

14
be quite poor. However, the estimated extremes at the distribution tails

will be reduced. The drawback of this approach is that unresonably

low estimated extremes may be obtained. For example, at Key West,

Florida, if all three parameters of Eq. 3 are estimated as in Ref . 4,

to the 1912-48 record there corresponds opt (y) = 3, v(50) = 83 mph

(37 m/s), v(100) = 99 mph (44.2m/s) and v(1000) = 188 mph (84 m/s) -

see Ref. 4. If it is postulated that y

= 00

» then v(50) = 71 mph

(31.7 m/s), v(100) = 77 mph (34.4 m/s) and v(1000) = 97 mph (38.8 m/s)

[4], an unlikely result in view of the high frequency of occurrence of

hurricanes (about 1 in 7 years) at Key West.

It may also be argued that since the estimated extremes resulting

from small values of y (say y <_ 4) may be too large, and those corresponding

to y = 00 may be too small, a probability distribution that might

yield reasonable results is one in which y has an intermediate value,

say 4 <_ y <_ 9. Such an approach has been proposed by Thorn and will now

be examined.

5. ASSESSMENT OF PROCEDURE BASED ON

THE HIGHEST AVERAGE MONTHLY SPEED

The procedure for estimating extreme winds in hurricane-prone regions

on the basis of annual highest winds at a station was seen to have the

following shortcomings. First, because hurricane winds are relatively

rare events, the possibility exists that the available data do not contain

wind speeds associated with major hurricane occurrences and are therefore

15
not representative of the wind climate at the station considered (see

the case of Calapan in Section 7 of this report). Second, in regions

subjected to winds that are meteorologically distinct from, and considerably stronger than the usual annual extremes, implausible estimates

may be obtained.

The model proposed by Thorn [Eq. 5] in Ref. 3 represents an attempt

to eliminate these shortcomings. It can be easily shown by applying the

intermediate value theorem, that if this model is assumed, the estimated

extreme winds may be obtained by inverting an expression of the form:

F(v) = exp[(-v/o-)"Y(v)

]

in which 4.5 < y (v) < 9. If the mean rate of arrival of tropical cyclones

in the region considered is high, then y (v) will be closer to 4.5.

Otherwise, y (v) will be closer to 9; in regions where hurricanes cannot

be expected to occur, Y (v) =9. In order that estimates not be based

upon possibly unrepresentative annual extreme data, Thorn's model does not

make use of annual extreme speeds. Rather, the parameter a is estimated

from the maximum of the average monthly wind speeds on record at the

location considered, presumably a quantity for which the variability is

small.

A few specific cases to which Thorn's model was applied were considered

in Ref. 5, in which it was shown that estimates based on this model do

not appear to be always sufficiently reliable for structural design

purposes. Also, it was shown in the preceding section that the approach

16
which utilizes the series of annual largest speeds may fail in regions

in which hurricanes occur. For such regions, therefore, it may be

that alternative approaches need to be developed. Among such

approaches is one in which estimates of extreme winds are based upon

the following information: ,

- average number of hurricanes affecting the coastal sector considered

(per year)

- probability distribution of hurricane intensitites

- radial dimensions of hurricanes

- dependence of wind speeds upon central pressure and distance from

hurricane center.

This approach appears to provide useful estimates of extreme winds

corresponding to large recurrence intervals - which are of interest in

ultimate strength calculations - and is currently under study at the

National Bureau of Standards.

6. STATISTICAL ANALYSIS OF EXTREME

WIND DATA IN THE PHILIPPINES

Through the courtesy of the Philippine Atmospheric, Geophysical and

Astronomical Services Administration (PAGASA) , 16 sets of data were

obtained consisting of maximum yearly wind speeds recorded during at

least 14 consecutive years. The data for each of the 16 stations are

listed in Table 2. Table 3 includes subjective station descriptions provided

17
by PAGASA personnel and the results of the analysis. In Table 3 are listed

largest values is obtained and = N-year wind based on the type I

distribution, N = mean recurrence interval in years.

The results will be grouped into three classes, according to

the t<rind zone (as defined in Ref . 26) in which the stations considered

are located (Table 3)

.

Zone III . It is noted that for all three Zone III stations listed

in Table 3, opt (y) ~ 00 . It is convenient to adjust the speeds at Davao

and Cagayan de Oro to open terrain exposure. On the basis of the terrain

descriptions of Table 3, if it is assumed Z = 0.30m, Z, = 0, Z , = 0.08m,

o d ol *

Z, - 0, it follows from Eq. 2 that

where U(10), U^(10) are mean speeds above ground in open and town

exposure, respectively. Thus, in Davao and Cagayan de Oro the calculated

50-year mean speeds at 10m above ground in open terrain are 94 km/hr and

76 km/hr. respectively, versus 88 km/hr in Zamboanga. If the corresponding

highest gusts are obtained by multiplying the one-minute means by a

factor of, say, 1.20 (see Fig. 1), the estimated highest 50-yr gusts at

Davao, Cagayan de Oro and Zamboanga are at most 94 x 1.20 = 113 km/hr,

N-year wind based on the distribution for which the best fit of the

7. INTERPRETATION OF RESULTS

uqo) - 0.8

18
i.e., considerably lower than the value specified for design purposes

by the National Structural Code of the Philippines [26] for Zone III,

viz., 153 km/hr. This suggests that the requirements of Ref. 26 regarding

wind loading in the Zone III portion of Mindanao are conservative and

might be somewhat reduced. (It can be easily shown, on the basis of Eq. 2

and Fig. 1, that this statement holds even if it is assumed that the

errors in the estimation of the parameter values Z = 0.30m and Z , = 0.08m

o ol are of the order of as much as 50%.) To validate such a conclusion it would

however be necessary to determine, from long-term records of tropical

cyclone occurrences, that the 1950-73 data at the three stations analyzed

are indeed representative for southern Mindanao.

Zone II . Several difficulties arise in interpreting the results for

the Zone II stations in Table 3. It is noted, first, that the results

obtained at stations in and near Manila (stations 4, 5, 6 in Table 3)

are widely divergent. The discrepancies between the results for Pasay

City and Manila may be due to the different elevations of the respective

anemometers. It may also be conjectured that the discrepancies between

these results and those obtained from the 1902-1940 Manila Central

record are due to differences in the averaging times and in the

exposure, elevation and calibration of the instruments, as well as to

possibly inaccurate estimates of the maximum speed in Manila and

Pasay City in 1970 (200 km/hr, see Table 2).

19
The estimated wind speeds at Bagnio based upon the 1950-73 record

are higher than those obtained from the 1914-40 data. No explanation

is offered for these differences; an investigation into their causes

seems warranted.

The record at Calapan illustrates the limitations of the approach

to the definition of design wind speeds based on the statistical analysis

of the highest annual winds. From the data covering the period 1961-72,

the estimated 50-yr wind based on a Type I distribution is 141 km/hr

[25], versus 209 km/hr, as obtained if the data covering the period

1959-1973 are used (see Table 3) . Since wind loads are proportional to

the square of the wind speeds, the ratio between the respective estimated

wind loads is (209/141)

2 =2.2.

Although the record at Pasay City is best fitted by a type II

distribution with opt (y) = 2, it is unlikely, as noted previously, that

such a distribution correctly describes the behavior of the extreme

winds. This is obvious, particularly in the case of the 1000-yr wind,

which, on physical grounds, could not possibly attain 820 km/hr (Table 3)

The National Structural Code of the Philippines specifies, for

Zone II and elevations under 9.15m, a design wind of 175 km/hr. In the

light of the data shown in Table 2, the value appears to be reasonable.

It will be noted that Tables 2 and 3, and Fig. 13 of Ref. 26, indicate

20
that the extreme speeds and the frequency of occurrence of tropical

cyclones, are considerably higher at Laoag than at Cebu. This suggests

that Zone II could be divided, accordingly, into two subzones, with

wind load requirements higher in the northern than in the southern

subzone

.

Zone I . As indicated previously, if y(°pt) is large, i.e., if the

differences among maximum wind speeds recorded in various years are

large, the probability distributions that best fit the data may not

describe correctly the extreme wind speeds for large recurrence intervals,

The minimum and the maximum winds for the period of record are. at Legaspi,

40 km/hr and 20A km/hr, respectively, and, at Tacloban, 42 km/hr and 194 km/hr,

respectively. In the writer's opinion, the reliability of the N-year wind

estimates obtained at these stat ions for N—50. 100 and 1000 if? tberpfnTP

doubtful. The same comment applies to the estimates for Infanta, where

the record length is quite insufficient (14 years) . The writer therefore

believes that the results of Table 3 should not be used to assess the

adequacy of the design wind speed requirement for Zone I specified in Ref

.

26. Rather, it is reasonable to base such an assessment on a comparison

between wind speeds in Zone I and in areas affected by hurricanes in

the United States. In the light of U.S. experience, it is the opinion

of the writer that from such a comparison it follows that the 200 km/hr

wind speed requirement for Zone I and elevations under 9.15 m is

adequate for structural design purposes.

21
8. CONCLUSIONS

From the analysis of available extreme speed data in the

Philippines, the following conclusions may be drawn:

1. The design wind speeds specified by the National Structural Code

of the Philippines for the Zone III part of Mindanao appear to be conservative and might be somewhat reduced . For this conclusion to be

validated, it would be necessary to determine, from long-term records

of tropical cyclone occurrences, that the data analyzed herein are

representative for southern Mindanao.

2. Methodological difficulties and uncertainties with regard to

the reliability of the data preclude, at this time, the estimation for

Zones II and I of N-year extreme winds that could be used, with a

sufficient degree of confidence, as design values within the framework

of an explicitly probabilistic code.

3. According to the data included herein, Zone II can be

divided into two subzones, with wind load requirements higher in the

northern than in the southern subzone.

4. The data included herein suggest that the wind speed requirement

specified by the National Structural Code of the Philippines for

Zone I is adequate for purposes of structural design, except as noted

below.

5. Higher wind speed values than those specified by the National

Structural Code of the Philippines should be used'—except perhaps in

the Zone III part of Mindanao —in open, and in coastal exposure.

22
6. Improved design criteria for Zones II and I, including possible

redefinitions of these zones, could in the future be achieved by applying

the methodology briefly described at the end of the section "Assessment of

Procedure Based on the Highest Average Monthly Speed". This would require,

in addition to data on the frequency of occurrence of tropical cyclones at

various locations in the Philippines, that the following data be available;

a. Reliable wind speeds, carefully defined with respect to

terrain roughness, averaging time and distance from shore line.

b. Approximate radial dimensions of tropical cyclones.

c. Approximate dependence of tropical cyclone speeds upon minimum

central pressure and distance from storm center.

23
REFERENCES

1. American National Standards Institute, 1972, American National

Standard A58. 1-1972, Building Code Requirements for Minimum Design

Loads in Buildings and Other Structures, 1^72.

2. National Research Council of Canada, Canadian Structural Design Manual , Supplement No. 4 to the National Building Code of Canada, 1970.

3. Thorn, H. C. S . ','Toward a Universal Climatological Extreme Wind Distribution, M P£0£ejedings_, International Research Seminar on Wind Effects on Buildings

and Structures, Vol. I, University of Toronto Press, Toronto, Canada, 1968.

4. Simiu, E. , and Filliben, J. J., Statistical Analysis of Extreme

Winds , National Bureau of Standards , Technical Note 868, Washington, D.C.,

1975.

5. Simiu, E. , and Filliben, J. J "Probabilistic Models of Extreme

Wind Speeds: Uncertainties and Limitations," Proceedings , Fourth

International Conference on Wind Effects on Buildings and Structures,

London, 1975.

6. Sachs, P., Wind Forces in Engineering , Pergamon Press, 1972.

7. Helliwell, N. C.,"Wind Over London',' Proceedings , Third International

Conference of Wind Effects on Building and Structures, Tokyo, Japan, 1971.

8. Simiu, E. , "Logarithmic Profiles and Design Wind Speeds',' Journal

of the Engineering Mechanics Division , ASCE, Vol. 99, No. EM5, Proc,

Paper 10100, October, 1973, pp. 1073-1083.

9. Fichtl, G., and McVehil, G M Longitudinal and Lateral Spectra of

Turbulence in the Atmospheric Boundary Layer , NASA TN D-5584, Washington,

D. C, 1970.

24
10. Harris, R. I . /'Measurements of Wind Structure at Heights up to

598 ft above Ground Level" Proceedings , Symposium on Wind Effects on

Buildings and Structures, Loughborough University of Technology,

Leicestershire, England, 1968.

11. Oliver, H. R. , "Wind Profiles In and Above a Forest Canopy,"

Quarterly Journal of the Royal Meteorological Society , Vol. 97, 1971,

pp. 548-553.

12. Peterson, E. W. , "Modification of Mean Flow and Turbulent Energy

by a Change in Surface Roughness under Conditions of Neutral Stability,"

Quarterly Journal of the Royal Meteorological Society, Vol. 95, 1969,

pp. 569-575.

13. Simiu, E., and Lozier, D. W. , The Buffeting of Tall Structures

by Strong Winds , Building Science Series 74, Center for Buildine Technoloev

National Bureau of Standards, Washington, D. C, October, 1975.

14. Csanady, G. T., "On the Resistance Law of a Turbulent Ekman Layer",

Journal of the Atmospheric Sciences , Vol. 24, Sept., 1967, pp. 467-471.

15. Tennekes, H. , and Lumley, J. L., A First Course in Turbulence ,

The MIT Press, Cambridge, Mass., 1972.

16. Goldman, J. L. and Ushijima, T. , "Decrease in Maximum Hurricane

Winds after Landfall," Journal of the Structural Division, ASCE, Vol. 100,

No STI, Proc. Paper 10295 , January, 1974, pp. 129-141.

17. Malkin, W. "Filling and Intensity Changes in Hurricanes over Land,"

National Hurricane Research Project , Vol. 34, 1959.

18. Johnson, N. L., and Kotz, S., Continuous Univariate Distributions » Vol.

1, Wiley, New York, 1970.

25
19. Thorn, H. C. S . , "Distributions of Extreme Winds in the United States5

,'

Journal of the Structural Division , ASCE, Vol. 86, No. ST4, Proc. Paper

2433, April 1960, pp. 11-24.

20. Thorn, H. C. S.,"Kew Distributions of Extreme Winds in the United

States'" Journal of the Structural Division , ASCE, Vol. 94, No. ST7,

Proc. Paper 6038, July, 1968, pp. 1787-1801.

21. Lieblein, J.

,

Method of Analyzing Extreme Value Data , National

Advisory Committee for Aeronautics, Technical Note 3053, Washington,

B. C. , 1954.

22. Court, A.yWind Extremes as Design Factors V Journal of the Franklin

Institute, Vol. 256, July 1953, pp. 39-55.

23. Davenport, A.G., "The Dependence of Wind Loads upon Meteorological Parameters,

Proceedings , International Research Seminar on Wind Effects on Buildings and

Structures, Vol, I, University of Toronto Press, Toronto, Canada, 1968.

24. Sugg, A. L., Pardue, L. G., Carrodus , R. L., Memorable Hurricanes

of the United States , National Weather Service, Southern Region, N0AA

Technical Memorandum NWS SR-56, Fort Worth, Texas, 1971.

25. Kintanar, R. L Climatology and Wind-Related Problems in the

Philippines',' Development of Improved Design Criteria to Better Resist

the Effects of Extreme Winds for Low-Rise Buildings in Developing

Countries , Building Science Series 56, National Bureau of Standards,

Washington, D. C, 1974.

26. National Structural Code of the Philippines , Section 206, in:

Development of Improved Design Criteria to Better Resist the Effects

of Extreme Winds for Low-Rise Buildings in Developing Countries , Building Science Series 56, National Bureau of Standards, Washington,

D. C, 1974.

26

uSCOMM-NBS-DC
27. Patel, V.C., and Nash, J.F., Numerical Study of the Hurricane Boundary

Layer Mean Wind Profile , Report prepared for the National Bureau of Standards

by Sybucon, Inc., June, 1974.

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33

APPENDIX E

A Guide to the Determination of

Wind Forces

A GUIDE TO THE

DETERMINATION OF WIND FORCES

by

R.D. Marshall

Center for Building Technology

Institute for Applied Technology

National Bureau of Standards

Washington, D.C. 20234

Report Presented At Regional Meeting on Development

f Design Criteria and Methodology for Low-Rise/Low-Cost

Buildings to Better Resist Extreme Winds
List of Figures

Figure 1 Typical Flow Pattern and Surface Pressures

Figure 2 Vortices Along Edge of Roof

Figure 3 Areas of Intense Suctions

Figure 4 Typical Record of Hind Speed and Surface Pressure

List of Tables

Table I Mean Recurrence Interval

Table II Relationships Between Risk of Occurrence, Mean Recurrence Interval and Expected

Life of Building

Table III Pressure Coefficients for Walls of Rectangular Buildings

Table IV Pressure Coefficients for Roofs of Rectangular Buildings

Table V Internal Pressure Coefficients for Rectangular Buildings

Table VI Correction Factors for Height of Building
A GUIDE TO TEE

DETERMINATION OF WIND FORCES

TABLE OF CONTENTS

Pagj

1.0 INTRODUCTION 1

2.0 AERODYNAMICS OF BUILDINGS 1

2.1 Typical Wind Flow Around Buildings i 2.2 Effect of Roof Slope 2

2.3 Roof Overhangs 2

3.0 DESIGN WIND SPEED 2

3.1 Mean Recurrence Interval 2 3.2 RisV Factor 3

3.3 Averaging Time and Peak Wind Speed 3

4.0 DESIGN PRESSURES 3

4.1 dynamic Pressure 3

4.2 Mean and Fluctuating Components of Pressure 3

4.3 Pressure Coefficients 4

4.3.1 Pressures on Extended Areas 4

4.3.2 Pressures on Localized Areas 4

4.3.3 Internal Pressures 5 4.4 Correction Factor for Height of Building 5

5.0 PROCEDURE FOR CALCULATING WIND FORCES 5

6.0 PEFEEENCES 6

7 . 0 ACKNOWLEDGEMENTS

APPENDICES

A. TABLES

B. ILLUSTRATIVE EXAMPLE
ABSTRACT

This paper briefly describes sense of the more common flow mechanisms which create wind

pressures on low-rise buildings and the effects of building geometry on these pressures.

It is assumed that the basic wind speeds are known and a procedure is outlined for

calculating design wind speeds which incorporates the expected life of the structure, the mean recurrence interval, and the wind speed averaging time. Pressure coefficients are tabulated for various height-to-width ratios and roof slopes. The steps required to calculate pressures and total drag and uplift forces are summarized and an illustrative

example is presented.
DETERMINATION OF WIND FORCFS

1.0 INTRODUCTION

This paper deals with the nature of wind flow around buildings, the pressures generated

by wind and the determination of forces acting on building elements as well as on the overall structure. It is assumed that buildings designed in accordance with the procedures outlined in the following sections and the tables in Appendix A do not exceed 10 meters in

height or 50 meters in plan dimension and have a height to width ratio (h/w) not exceeding

four.

2.0 AERODYNAMICS OF BUILDINGS

The flow of wind around buildings is an extremely complex process and cannot be completely

described by simple rules or mathematical formulae. Wide variations in building size and

shape, type of wind exposure, local topography and the random nature of wind all tend to complicate the problem. Only by direct observation of full scale situations or by resorting

to properly conducted wind-tunnel tests can the characteristics of these flows be established.

In spite of these complications, guidance can be provided by considering some typical flow

situations.

2.1 Typical Wind Flow Around Buildings

A typical flow situation is illustrated in Figure 1 where the wind is blowing face-on to a building with a gable roof. The flow slows down or decelerates as it approaches the building, creating a positive pressure on the windward face. Blockage created by the building

causes this flow to spill around the corners and over the roof. The flow separates (becomes

detached from the surface of the building) at these points and the pressure drops below

atmospheric pressure, creating a negative pressure or suction on the endwalls and on certain

portions of the roof.

Fig. 1 Typical Flow Pattern and Surface Pressures

A large low-pressure region of retarded flow is created downwind of the building. This

region, called the wake, creates a suction on the leeward wall and leeward side of the roof.

The pressures are neither uniform nor steady due to the turbulent character of the oncoming

wind and varying size and shape of the wake. However, it has been established that the

patterns of wind flow around bluff bodies such as the building in Figure 1 do not change

appreciably with a change in wind speed.

This allows dimensionless pressure coefficients (to be discussed later) determined for one wind speed to be applied to all wind speeds. In general, the wind pressure is a maximum

near the center of the windward wall and drops off rapidly near the corners. Pressures on

the side or endwalls are also nonuniform, the most intense suctions occurring just downstream

of the windward corners.

1
2.2 Effect of Roof Slope

The pressures acting on a roof are highly dependent upon the slope of the roof, generally

being positive over the windward portion for slopes greater than 30 degrees. For slopes

less than 30 degrees, the windward slope can be subjected to severe suctions which reach a maximum at a slope of approximately 10 degrees. Under extreme wind conditions, -these

suctions can be of sufficient intensity to overcome the dead weight of the building, thus

requiring a positive tiedown or anchorage system extending from the roof to the foundation

to prevent loss of the roof system or uplift of the entire building.

Intense suctions are likely to occur along the edges of roofs and along ridge lines due to separation or detachment of the flow at these points. For certain combinations of roof slope

and wind direction, a conical vortex can be developed along the windward edges of the roof as shown in Figure 2. This is a "rolling up" of the flow into a helical pattern with very

high speeds and, consequently, very intense suctions. If not adequately provided for in the

design, these vortices along the edges of the roof can cause local failures of the roofing

; often leading to complete loss of the roof. Areas where intense suctions can be expected

are shown in Figure 3.

Figure 2 Vortices Along Edge of Roof

Areas where high suctions must be allowed for on the cladding

Figure 3 Areas of Intense Suctions

2 . 3 Roof Overhangs

In calculating the total uplift load on a roof, the pressure acting on the underside of roof

overhangs must also be included. These pressures are usually positive and the resultant

force acts in the same direction as the uplift force due to suction on the top surface of

the roof. Pressures acting on the inside of the building (to be discussed later) can also

contribute to the total uplift force and must likewise be accounted for.

3.0 DESIGN WIND SPEED

Several factors must be considered in selecting a wind speed on which to base the design

loads for a. building or other structure. These include the climatology of the geographic

area, the general terrain roughness, local topographical features, height of the building,

expected life of the building and acceptable level of risk of failure. The assessment of

climatological wind data and the procedure for obtaining basic wind speeds are discussed

in Ref. 1. The selection of the basic wind speed and the determination of modifying factors

to obtain the design wind speed are discussed in the following sections.

3 . 1 Mean Recurrence Interval

The selection of a mean recurrence interval, with which there is associated a certain basic

wind speed, depends upon the intended purpose of a building and the consequences of failure.

The mean recurrence intervals in Table I are recommended for the various classes of structures.

2
3 .2 Risk Factor

There is always a certain risk that wind speeds in excess of the basic wind speed will occur during the expected life of a building. For example the probability that the basic wind

speed associated with a 50-year mean recurrence interval will be exceeded at least once in

50 years is 0.63. The relationship between risk of occurrence during the expected building

life and the mean recurrence interval is given in Table II. It should be noted that the

risk of exceeding the basic wind speed is, in general, not equal to the risk of failure.

3 . 3 Averaging Time and Peak Wind Speed

It is well known that the longer the time interval over which the wind speed is averaged, the

lower the indicated peak wind speed will be. The calculated design loads will thus depend

upon the averaging time used to determine the design wind speeds. In this document, it has

been assumed that all speeds used in pressure and load calculations are based upon an averaging time of 2 seconds. Wind speeds for averaging times other than 2 seconds can be

converted into 2-second average speeds using the procedure described in Ref. 1.

4.0 DESIGN PRESSURES

4 . 1 Dynamic Pressure

When a fluid such as air is brought to rest by impacting on a body, the kinetic energy of

the moving air is converted to a dynamic pressure q, in accordance with the formula

q = 1/2 pU

2 (1)

2 3 where q = N/m , p is the mass density of air in kg/m and U is the free-stream or undisturbed

wind speed in m/s. The mass^density of air varies with temperature and barometric pressure,

having a value of 1.225 kg/m at standard atmospheric conditions. In the case of tropical

storms, the mass density may be 5 to 10 percent lower. However, this is offset somewhat by

the effect of heavy rainfall and the value quoted above should be used for all wind pressure

calculations , i.e.,

q = 0.613 U

2 (2)

4 . 2 Mean and Fluctuating Components of Pressure

As in the case of wind speed, pressures acting on a building are not steady, but fluctuate

in a random manner about some mean value. A typical recording of wind speed and pressure

at a point on the roof of a house is shown in Figure 4. 20

15

10

5

0

WIND SPEED = m/s

10 20 TIME

30

SECONDS

40

200

100

0

-100

-200

PRESSURE = N/m

50 60

Fig. 4 Typical Record of Wind Speed and Surface Pressure

3
A close inspection of Figure 4 reveals the following characteristics:

a) The average or mean pressure is negative (suction)

b) Pressure fluctuations tend to occur in bursts

c) Maximum departures from the mean are in the negative (suction) direction

d) The peak values far exceed the mean value

To quantify these pressures, it is essential that a suf f iciently long time interval be used

to obtain a stable mean, p. The fluctuations are described by their standard deviation or root-mean-square, Prms

> taken about the mean. Finally, the peak pressure fluctuations are described by a peak factor, g, which indicates the number of standard deviations that the

peak pressure deviates from the mean. Thus, the peak pressure can be expressed as

p =p + gp orp.=p-go (3) max r s rm.s rmin v & L rms

It should be noted that the peak factor, g, is a random variable and has a probability

distribution function that depends on the geometry of the building and turbulent structure

of the wind. The values of g are selected so that the associated probabilities of being

exceeded are in line with the expected building life.

4.3 Pressure Coefficients

It is convenient to express pressures acting on the surfaces .of a building in terms of the

dynamic pressure as follows

P

= Cp

q (4)

where Cp is a pressure coefficient whose value depends upon the geometry of the building and

local flow conditions. Pressure coefficients are specified for particular surfaces or elements of a building and, when multiplied by the surface area and dynamic pressure, give the

wind loads acting in a direction normal to those surfaces or elements. The total resultant

forces and moments acting on a building can then be determined by considering the appropriate components of these loads acting on each of the surfaces or elements.

As discussed in the previous section, the instantaneous peak pressure can be expressed in

terms of the mean pressure and a fluctuating component. Since pressure fluctuations are limited in spatial extent, it is necessary to consider the size of the building surface

or element when selecting the pressure coefficient.

4.3.1 Pressures on Extended Areas

For the purpose of determining wind loads acting on sizeable surface areas such as the walls

and roof of a building, the pressure coefficients listed in Tables III and IV should be used

These coefficients have been determined experimentally from measurements taken on full-scale

buildings and from wind-tunnel tests and they represent an upper limit of conditions likely

to occur on the indicated building surfaces.

4.3.2 Pressures on Localized Areas

It is to be expected that the smaller the area considered, the larger the effective peak

pressure will be. In addition, there are certain surface areas where intense suctions occur

as pointed out in sections 2.1 and 2.2. To provide for these cases, pressure coefficients for

localized areas are included in Tables III and IV. These coefficients are for the purpose

of assessing wind loads on local cladding and roofing elements and should not be used to calculate overall loads on buildings. They should be used in conjunction with the internal

pressure coefficients (where appropriate) as described in the following section.

4
4.3.3 Internal Pressures

i

As indicated in section 2.3, the net load or force acting on the roof or walls of a building

depends not only on the external surface pressures, but on the internal pressure as well.

The magnitude of the internal pressure depends upon the building geometry, size and location

of openings, and wind speed and direction. As with external pressures, it is convenient to express internal pressures in terms of the dynamic pressure and a pressure coefficient Cp-j/

These coefficients can be positive or negative as indicated in Table V. The net pressure

acting on a building element is the algebraic sum of the external and internal pressures

P

= q CCp - Cp

.) (5)

Thus a positive internal pressure will increase the loading on those areas of roofs and walls

subjected to external suction.

4 . 4 Correction Factor for Height of Building

The pressure coefficients described above are based on building heights of 10 meters and

peak wind speeds at 10 meters above ground, averaged over 2 seconds. Overall loads calculated

for- buildings appreciably less than 10 meters in height (measured to eaves or parapet) will

thus be overestimated if these coefficients are used without modification. On the other

hand, tributary areas such as doors, windows, cladding and roofing elements will respond co pressure fluctuations with duration times considerably less than 2 seconds. To account for

this, the pressures must be multiplied by the correction factors, R, in Table VI. Thus

the expression for the net pressure acting on a building surface becomes

p = q (C R - C . R.) (6) P Pi l and the force acting normal to a surface of area A is

F = qH

(Cv R - C . R.)A (7) p pi i' v

where R and R_^ are correction factors for external and internal pressures, respectively.

5 . 0 Procedure for Calculating Wind Forces

The procedure for calculating wind forces on a building is summarized in the following steps.

1 . Select the appropriate mean recurrence interval from Table I

2 . Check the associated factor of risk in Table II and select a longer mean recurrence

interval if appropriate.

3 . Determine the basic wind speed for this mean recurrence interval and the appropriate

terrain roughness and type of exposure as outlined in Ref. 1.

4 . Convert the resulting basic wind speed to a 2-second mean speed using the procedure

described in Ref. 1.

5 . Calculate the dynamic pressure q using the expression

q = 0.613 U

2

6. Select the appropriate pressure coefficients from Tables III, IV and V

7 . Select the appropriate correction factors from Table VI

8 . Calculate the pressures from the expressions

p = q C R

P or r p = q(C R-C.R)

P Pi l

5
9. Multiply these pressures by the respective surface areas to obtain the wind forces

10. Sum appropriate components of these forces to obtain net uplift and drag loads.

6.0 REFERENCES

1. Simiu, E., "Estimation of Extreme Wind Speeds in the Philippines." Report

presented at Regional Meeting on Development of Design Criteria and Methodology

for Low-Rise/Low-Cost Buildings to Better Resist Extreme Winds. Kingston, Jamaica,

6-7 November, 1975.

knots

0 10 Lx^j L_

30 40 50 60 _J I I ! I ! L

70 _J L

90 100 110 _J L I I

velocity V

m.p.h. o 10 20 30 40 50 60 70 80 90 100 110 120 130

I I i . . 1 I I L_J 1 I 1 L_J I L_J I ' I I. . I

m/sec.

0 5

I L

10 15 20 25

i

I I I 40 45 J L

50 55 60 _J

lbf/ft' o

I

1 2 3456789 10

I I I

I I I I I I I 20 25 30 35 40I I III

dynamic

pressure

N/rn^

kgf/ rrT

100 200 600 000 1000 1200 1400 1600 1800 2000 _J L_l L_l I i I ; I L—

J

10 20 30 40 50 60 70 80 90 100 120 140 160 180 200 J I I I I I I I I I I I I I I

Conversion chart for wind speed and dynamic pressure head

7.0 ACKNOWLEDGEMENTS

Acknowledgement is made to the Building Research Establishment (UK) for the illustration

used in this document. The writer also wishes to acknowledge useful comments and suggestions

provided by members of the Philippine Advisory Committee and by Emil Simiu of the Center for

Building Technology.

6
APPENDIX A

TABLE I MEAN RECURRENCE INTERVAL

Class of structure Mean recurrence interval

vears All structures other than those set out below 50

Structures which have special post-disaster functions, e.g.

hcspit-ils, communications buildings, etc. 100

1 Structures presenting a low degree of hazard to life and other

property in the case of failure

20

TABLE II RELATIONSHIPS BETWEEN RISK OF OCCURRENCE, MEAN RECURRENCE

INTERVAL AND EXPECTED LIFE OF BUILDING

Desired

Life tire

Risk of exceeding in N years the wind speed corresponding

to the indicated mean recurrence interval

y

Years 0.632 0.50 0.40 0.30 0.20 | 0.10

Mean Recurrence Interval in Years

ilO 10 15 20 29 45 95

i 20 20 29 39 56 90 190

50 50 72 98 140 224 475 aoo 100 144 196 280 448 949

Note: Prom this Table it will be seen that there is a 10% risk that the wind speed

corresponding to a mean recurrence interval of 475 years will be exceeded in a lifetime of 50 years.

7
TABLE III

PRESSURE COEFFICIENTS FOR WALLS OF RECTANGULAR BUILDINGS

Building

Height/Width

Ratio

Building

Length/Width

Ratio

Wind Angle

a (Degrees)

C for Face

P Local

CP A B C D

h/w<0.5

l<|/w<1.5

0

90

1 ! 0.8 -0.5

! -0.6 -0.6

,

-0,

0.8

-0.6

-0.5

-1 . Z

1.5<i/w<4

0

90

0.8 -0.5

-0.4 : -0.4

-0.8

0.8

-0.8

-0.4

-1.3 |

1

!

i

i

0.5<h/w<1.5

1< i/w<1.5

1

0

90

0.8 i -0.5

-0.7 -0.7

i

-0.7

0.8

-0.7

-0.5

————

j -1.4 |

i

|

1.5<«t7w<4

0

90

0.8 i -0.6

-0.4 i -0.4

I

-0.9

0.8

-0.9

-0.3

j -1.4 I

|

1.5<h/w<4

i

<

l<i/w<1.5

0

90

! 0,8 -0.5

-0.8 ; -0.8

-0.8

0.8

-0.8

-0.5

1

i -1.5 j

|

j

i

1.5<i/w<4

i

0

90

1 0.8 ! -0.6

i -0.4 1 -0.4

s

i -0.9

0.8

-0.9

-0.3

! -1.5

1

|

Lesser of h or 0.2w -H 1*^"

J _JL

T

e w —?-]

ELEVATION

i W ->i

PLAN

Notes: 1) h is the height to eaves or parapet, i is the greater plan dimension of the

building and w is the lesser plan dimension.

2) Local C values (last column) should be used in conjunction with correction

factors for overall areas in Table VI.

8
TABLE IV

PRESSURE COEFFICIENTS FOR ROOFS OF RECTANGULAR BUILDINGS

Building

Height/Width

Ratio

,

I Wind Angle Area

a Designation

(Degrees)

, j

Roof Slope

(Degrees)

0

0

1

i n 1 on 25 '

h/w<0.5

EF

GH

0 ' JK

1

-1.0

-0.6

-1.6

-1.4

1 -l.o ; -0.4

-0.6 j -0.8

-1.9 ; -1.9

-14 -2 0 —\ —

*

90

. _ ..

EG j -1.2

FH -0 .

J -2.0

K -1.4

-1.1 1 -1.0

-0.6 | -0.6

-1.8 I -1.8

-14 ! -2.0

1

•

*

0.5<h/w<1.5

o

EF j -1.0

GH j -0.6

J |-1.8

K •

j -1.4

i i

-1.0 j -0.6

-0.6 ! -0.8

-1.8 j -1.8

-1.4 I -2.0

'

i

-0.4

-0.8

-1.8

-1.6 .

i

90

EG -1 .

FH ! -0.6

J ! -1.8

K i, -1.4

-1.1 j -1.0

-0.6 -0.5

-1.8 , -1.6

-1.6 j -1.6

'

!

-0.8

-0.4

-1.6

-1.6

1.5<h/w<4

EF

GH

JK

*

j

I * i ft

j

, 1

j

ft

90

EG

FH

J * K

- —

ft

f

h

il

E G

F H

T

b = lesser of

h or 0.15w

(Typical)

w >| L< w >|

(Extended areas) (Local areas)

ELEVATION PLAN

Notes: 1) The pressure coefficient on the underside of roof overhangs should be taken as that on the adjoining wall surface.

2) Local C values (J and R) should be used in conjunction with correction factors

for ove?all areas in Table VI.

3) * Indicates coefficients unavailable at time of publication.

9
TABLE V

INTERNAL PRESSURE COEFFICIENTS FOR RECTANGULAR BUILDINGS

' Condition —^——^—_—^——

Internal pressure coefficient Cp^

1. Two opposite walls equally permeable, other

walls impermeable:

(a) Wind normal to permeable wall

(b) Wind normal to impermeable wall

+0.3

-0.3

2. Four walls equally permeable -0.3 or +0.2 whichever is the more

severe for combined loadings

3. Dominant opening on one wall, other walls of

equal permeability:

(a) Dominant opening on windward wall, having

a ratio of permeability of windward wall to total permeability of other walls and roofs

subject to external suction, equal to —

2

36 or more

(b) Dominant opening on leeward wall

(c) Dominant opening on side wall

(d) Dominant opening in a roof segment

+0.5

+0.6

+0.8

value of C for leeward external wall

p surface

value of C for side external wall

, P surface

value of C for external surface of

roof segment

Internal pressures developed within an enclosed structure may be positive or negative depending on the position and size of the openings.

In the context of Table V the permeability of a surface is measured by the

total area of openings in the surface under consideration.

The value of C . can be limited or controlled to advantage by deliberate

distribution o?

1permeability in the wall and roof, or by the deliberate provision of a venting device which can serve as a dominant opening at a position

having a suitable external pressure coefficient. An example of such is a ridge

ventilator on a low-pitch roof, and this, under all directions of wind, can reduce the uplift force on the roof.

10

Notes: 1)

2)

3)
TABLE VI

CORRECTION FACTORS (R) FOR HEIGHT OF BUILDING

Terrain

1 Structural System ! Area h<5

———

5<h<10

Smooth

Zo<0.12m

j Overall

Walls Elements

0.85

1.00

• 1.00

1.20

Roofs

Overall

Elements

0. 85

1. G5

1.00

1.25

Internal Pressure 0.85 1.00

Rough

Zo>0.12m

Walls

Overall

Elements

0.75

i 0.90

j

1.00

1.20

Roofs

Overall

Elements

0.75

1 C.95

1

1.00

1.25

Internal Pressure 1 0.75 1.00

Ilotes: 1) The term "Overall" refers to the entire area of a given wall or rcof slope.

2) The term "Elements" refers to roof and cladding elements, doors, windows , etc,

3) The terrain roughness parameter Z must be estimated subjectively. The

following values are suggested for various types of exposure.

r/PE CF EXPOSURE Z (meters)

o Coastal 0.005-0.01

Open 0.02-0.12

Outskirts of towns, suburbs 0.13-0.30

Centers of towns 0.40

11
APPENDIX B

ILLUSTRATIVE EXAMPLE

A housing development is to be located in flat, open country on the outskirts of Zamboanga

and will ultimately consist of several hundred single-family dwellings of quite similar

geometry. The period of construction is anticipated to be from 10 to 15 years. The basic

plan dimensions are 6.2 x 7.5 meters and the height to the eaves is 2.7 meters. The gable

roof has an overhang of 0.7 meters on all sides and a slope of 10 degrees. Openings for

doors and windows are evenly distributed on the exterior walls.

Because the development is to be built over a period of several years, it would not be

appropriate to assume a builtup area in selecting the basic wind speed and flat, open

country will be assumed here.

From Table I, a mean recurrence interval of 50 years is selected and it is considered that

the associated risk of exceeding the basic wind speed (0.632) in Table II is acceptable.

From Ref . 1, the 1-minute average wind speed (N=50) for Zamboanga is 88 km/hr (Type I distribution) . Since this is based on data obtained in open country at 10 meters above

ground, this speed can be converted directly to the design speed. From Ref. 1 the ratio

of the 1-minute speed to the 2-second peak speed is 0.82. Thus the design speed is

U = 88/0.82 = 107.3 km/hr = 29.8 m/s

The dynamic pressure is calculated from Eq. 2

q = 0.613U 2 = 0. 613(29. 8)

2 = 544 N/m2

Wind pressures are next calculated using Eqs. 4-6 and the coefficients presented in Tables

III-VI. Note that

h/w = 2.7/6.2 = 0.44

and

i/w = 7.5/6.2 = 1.21

WALLS

Inspection of Tables III and V reveals that the worst cases are walls A and C with the wind

blowing normal to the ridge. For wall A, Cp = 0.8 and for wall C, Cp = -0,6. The local Cp

is -1.2. The internal pressure coefficients can range from 0.2 to -0.3. Table VI indicates

that the reduction factor is 0.85 for walls and internal pressures and 1.00 for cladding

elements, doors, windows, etc.

For wall A,

p = (544) [0.8-(-0.3)] (0.85)

= 509 N/m2

For wall C,

p = (544) [-0 6-(0.2)](0.85)

= -370 N/m2

For cladding elements, the worst cases are

p = (544) [0.8 - (-0.3) (0.85)]

=574 N/m2

12
and

p = (544) [-0.6 - (0.2)(0.85)]

= -419 N/m2

For local pressures acting on strips of width 0.2w = 1.2 meters at each corner,

p = (544X-1.2 - 0.2)(0.85)

= -647 N/m2

ROOF

Inspection of Table IV reveals that the greatest uplift pressures on extended areas occur

when the wind is blowing along the ridge.

For sections E and G,

p = (544) [-1.1 - (0.2)] (0.85)

= -601 N/m2

For sections F and H,

P = (544) [-0.6 - (0.2)1(0.85)

= -370 N/m2

Pressures acting cr. roofing elements in sections E and G are obtained as follows:

P = (544) [(-1.1) (1.06) - (0.2X0.85)]

= -727 N/m2

and for sections F and E,

P = (544) [(-0.6) (1.06) - (0.2X0.85)]

= -438 N/m2

Localized pressures act on strips of width C.15w = 0.93 meters as shown in Table IV. The

worst case occurs for area J with the wind blowing normal to the ridge. Note that the uplift

pressure under the eaves must also be included.

t p = (544) [-1.9 - (0.8)1(0.85)

= -1248 N/m2

For area K in section F, this negative pressure or suction is slightly less

p = (544) [-1.4 - (0.8)1(0.85)

= -1017 N/m2

Along the ridge (area K) , the localized pressure is

p = (544) [-1.4 - (C. 2)] (0.85)

= -740 N/m2

TOTAL UPLIFT FORCE

The total uplift force on the building is calculated for the wind blowing normal to the ridge

as follows:

Area of one roof slope = [7.5 + (2) (0. 7) ] [6 . 2/ (2C0S 10°) + 0.7]

= (8.9X3.85)

= 34.2 m2

13
Note that areas E, F, G and H include areas J and K when calculating overall loads.

Uplift = (544) (1.0 + 0.6)(34.2)(COS 10°) (0.85) + (544) (6 . 2) (7 . 5) (0. 2) (0.85)

= 24,918 + 4,300

= 29.2 kN

TOTAL DRAG FORCE

The total drag force (neglecting the roof) is calculated as the sum of the loads on the windward

and leeward walls.

Drag = (544)(2.7)(7.5)[0.8 - (-0.5)] (0.85)

= 12.2 kN

COMMENT

The loads calculated above are the loads that can reasonably be expected to occur under the con- ditions stated in the example. They should be considered as the minimum suitable loads for use with stresses and load factors appropriate for the type of structural material used.

For geographical areas exhibiting large variations in annual extreme wind speeds, the basic wind

speed should be selected with caution. The application of probabilistic models of extreme wind

speeds and some of their limitations are discussed in Ref. 1.

USCOMMNBS-OC 14
APPENDIX F

A Guide for Improved Masonry and Timber

Connectors in Buildings

A GUIDE FOR IMPROVED

MASONRY AND TIMBER

CONNECTIONS IN BUILDINGS

by

S. George Fattal

Center for Building Technology

Institute for Applied Technology

National Bureau of Standards

Washington, D.C. 20234

and

G.E. Sherwood, Engineer

T.L. Wilkinson, Engineer

Forest Products Laboratory

Forest Service

U.S. Department of Agriculture

Madison, Wisonsin

Report Presented at Regional Meeting on Development

Design Criteria and Methodology for Low-Rise/Low-Co

Buildings to Better Resist Extreme Winds

Table of Contents

Page

SI Conversion Units ii

Abstract iii

1. Building Systems 1

1.1 Introduction 1 1.2 Roof Systems 1 1.3 Pole Type Construction 2 1.4 Masonry Bearing Wall System 3 1.5 Timber Wall System 3

2. Masonry Connectors 9

2.1 Introduction 9 2.2 Types of Masonry Construction 9 2.3 Analysis of Wind Damaged Buildings 11

2.4 Masonry Construction in Developing Countries 13

2.5 Masonry Practices in the United States 14 2.5.1 Available Masonry Connectors 14 2.5.2 Available Technical Information 16 2.6 Suggested Improvements in Masonry Construction 16

2.6.1 Utilization of Available Connectors 16

2.6.2 Improved Construction Practices in Severe Wind Environment 17

3. Fasteners for Timber Construction in High Wind Areas 46

3.1 Introduction 46

3.2 Available Timber Fasteners 46 3.2.1 Nails, Screws, Bolts, and Lag Screws 46

3.2.2 Timber Connectors 47 3.2.3 Truss Plates 47 3.2.4 Sheet Metal Fasteners and Other Special Devices 48

3.3 Philippine Timber-Related Practices 48

3.3.1 Pole Type 48

3.3.2 Wood-Framed Wall and Roof 49

3.3.3 Masonry Wall 49

3-3.4 Roof Framing 49

3.3.5 Roofing 50

3.3.6 Protection From Wood-Destroying Organisms 50

3.3.7 Summary of Good and Poor Practices 50

3.4 Timber Fasteners Appropriate for Construction in

Developing Areas With High Winds 52

3.4.1 Pole-Type Construction 52

3.4.2 Light Wood-Frame Construction 52 3.4.3 Concrete and Masonry Construction 53

3.4.4 Roof Framing 53

3.4.5 Roofing 53

3.5 Fasteners for Fabrication by Indigenous People 53

3.6 Summary 54

3.7 A Caution 54

Acknowledgements 86

References 87
SI Conversion Units

In view of present accepted practice in this technological area, U. S. customary

units of measurement have been used throughout this report. It should be noted that the

U. S. is a signatory to the General Conference on Weights and Measures which gave officia

status to the metric SI system of units in 1960. Readers interested in making use of the

coherent system of SI units will find conversion factors in ASTM Standard Metric Practice

Guide, ASTM Designation E 380-72 (available from American Society for Testing and Materia

1916 Race Street, Philadelphia, Pennsylvania 19103) . Conversion factors for units used

in this paper are:

Length

1 in = 0.0254* metre

1 ft = 0.3048* metre

Exact Value

ii
ABSTRACT

The National Bureau of Standards (NBS) through this project is developing improved

design criteria for low-rise buildings in developing countries to better resist the

effects of extreme winds. The project is sponsored by the Agency for International

Development (AID)

This report investigates the use of connectors for masonry and timber elements in

low-rise buildings. Connector characteristics and construction details that improve a building's re;p:r.= e :: exireze wind effects are given primary emphasis. Recrr—e:~da.i:ns

include improvements through better utilization of connector technology showing good

feasibility of introduction in developing countries. The building systems considered in

this study fall within the low to moderate cost category.

Key Words: Codes and standards; connectors; fasteners; lowrise buildings; masonry walls

structural design; technology transfer; timber roofs; timber walls; wind effects.

iii

1. BUILDING SYSTEMS

by

S . George Fattal—

1 .1 Introduction

This report discusses the use of connectors in houses and other low-rise buildings

to improve their structural response characteristics under extreme wind conditions. The

report is organized into three main sections. Section 1 presents a general overview of

masonry connectors and timber fasteners. Section 2 is devoted to a detailed discussion

of connectors in building systems using masonry wall construction. Section 3 treats

fasteners used in building of timber wall construction. These two types of buildings are most prevalent in housing for low to middle income occupancy in developing countries

2/ located in wind -prone areas [1] . —

These buildings are typically one or two story detached units which are supported by

a continuous wall footing made of cast concrete or concrete block masonry or, in floodprone areas, by wooden poles embedded in the ground. The roof is commonly characterized

by a pitched timber frame often projecting up to 5 ft beyond the exterior walls, and

topped by corrugated metal cover.

The types of building systems of interest to this study are identified by reference

to figures 1.1 through 1.5, which also serve as key visual reference for locating specific

connector details discussed in the subsequent sections of this report.

1 .2 Roof Systems

Figure 1.1 exhibits the two most commonly used framing systems for the roof: (a) the

truss type and (b) the joist-rafter assembly. The truss type construction employs a series of equally spaced trusses spanning between opposite exterior walls. The corrugated

metal roof cover is attached to a series of longitudinal purlins connecting the trusses

together. The joist-rafter type consists of a system of inclined rafters framing into a ridge beam at the top and attached to ceiling joists spanning between opposite exterior

walls at the bottom. Collar beams attached to the rafters provide stiffness to the roof

in the vertical plane. The close spacing of the rafters permits direct attachment of

roof cover to the rafters thereby eliminating the need to use purlins. — Dr. S. George Fattal is a Structural Research Engineer with the Center for Building

Technology. —2/ Numbers in brackets indicate references listed at the end of this report.

1
The choice of a particular roof system depends on many factors. A joist-rafter

assembly allows better utilization of attic space while the truss system permits prior

assembly of the individual trusses at the shop where quality control is generally better

than in the field. Structurally, both systems can be designed to have the desired

diaphragm capability to transmit lateral wind forces to the appropriate shear walls

(having the same orientation as the wind as in fig. 2.1, ref . [2]). For instance,

diaphragm rigidity can be improved by introducing horizontal cross-bracing in the plane

of the joists and vertical cross-bracing in the longitudinal ridge plane (perpendicular

to the joists) of both systems shown in figure 1.1. A practical but somewhat more expensive alternate to the horizontal bracing would be to provide wood flooring fastened

to the joists in a manner that will insure integral action in the horizontal plane.

The importance of diaphragm action for roof systems in extreme wind regions should

be emphasized in the light of the types of roof and wall failures observed that were attributed to a lack of transverse rigidity of the roofing system, as noted in section 2. The use of timber fasteners for connecting roofing elements is discussed in section 3.

1 . 3 Pole Type Construction

Figure 1.2 shows the structural layout of a pole type construction. The raised

floor protects the house against insect infestation and floods. This type of construction

provides generally a lower cost housing than either masonry or wood frame wall system

since it lends itself more readily to auto-construction (self-help) . It also permits

utilization of less expensive indigenous products such as nondimensioned timber (logs)

for the poles, and cane (i.e. bamboo) framing with rattan or twisted cane connectors as shown in figure 1.3. The figure also illustrates suggestions for adequate joining of

members. The poles should be treated against insect infestation and water penetration

prior to being embedded into the ground. The length of embedment required to resist

wind-induced uplift or overturning and to provide adequate bearing is determined by local

soil conditions. Figure 1.2 shows footing schemes for the poles and for the dimensioned

timber post used as an alternative. Note that shallower embedment will require more

substantial footings for the same level of resistance against wind-induced uplift forces.

The design should also account for the additional uplift forces under the exposed floor.

Since the poles are the main pillars of support for the superstructure, they should

preferably extend to the top and be provided with adequate connections at the roof and at

the floor level. Because of their unsupported length between the raised floor and the

ground, these poles should be proportioned to provide adequate flexural resistance to lateral forces induced by extreme winds. If this is not altogether feasible from a practical design standpoint, vertical cross-bracing made of wood, bamboo or wire cable

should be introduced to tie the poles together below the floor level. Cables and various

2
tiedown straps used in the United States to protect mobile home installations against

extreme winds should also be explored for use in buildings on poles to provide additional

stability against uplift and overturning forces. Information on available tiedown and

3/ anchoring devices may be acquired from the Manufactured Housing Institute. — Design

provisions for mobile home tiedowns are prescribed in Chapter 6 (1974) and appendix D (1975) of ANSI A119.1 [4], and ref. [5] supplies guidelines for their design. Section 3 discusses fasteners used in pole type housing. Supplementary information on pole type

construction and the structural use of bamboo may be acquired by consulting references

[6] and [7]

1 .4 Masonry Bearing Wall System

Figure 1.4 displays the structural layout of a masonry bearing wall building system.

The single wythe walls (defined in section 2.2) are built with hollow concrete masonry

units which permit the passage of vertical reinforcement without the need of additional

wythes. Note that alternate schemes are available for constructing lintels and peripheral

(or collar) bond beams. They are indicated in the same figure for generality and convenient

referencing purposes.

It was noted earlier that the type of masonry discussed in this report is generally

representative of masonry housing construction in developing countries [1] . This makes

it unnecessary to consider diverse masonry systems such as multiple wythe construction

(to permit vertical reinforcing when solid units are used) or masonry veneers and other

non-loadbearing elements. However, Section 2 does consider one additional masonry

system (generally referred to as an "infill frame") which consists of a concrete frame

with masonry filler walls.

1.5 Timber Wall System

r

Figure 1.5 shows a partial view of a timber of "stud" wall system. The studs or "verticals" transmit gravity loads and the vertical component of wind-induced loads which

may be reversible (bearing or uplift) . In addition, the studs provide f lexural resistance

against direct horizontal wind pressure or suction. The diagonals stiffen the walls in

their own planes and increase the capability of the system to resist lateral loads. The

specific fastener details for the stud wall system are discussed in Section 3.

Manufactured Housing Institute, P.O. Box 201, Chantilly, Virginia 22021

3
ROOF. .GUSSET PLATES

PURLIN. .RAFTER UPPER CHORD

DIAGONAL

WEB MEMBERS

-CEILING JOIST LOWER CHORD

(a) TRUSS ROOF SYSTEM

END STUD

RIDGE BOARD

COLLAR BEAM

RAFTER

RAFTER

BLOCK

lb) JOIST-RAFTER ROOF SYSTEM

Figure 1.1 Common roof systems for low-rise buildings.

4
PRESERVATIVE TREATED WOOD POLES

TREATED

POLE TREATED

POLE

8 FT

4«

CONCRETE

FOOTING

J"IMBER OR CONCRETE PAD

_T R E AT E D POLE

5?

U

2 FT BOLT OR LAG

HEAVY

GALVANIZED STRAP

EMBEDDED

POLE

POLE WITH CONCRETE

FOOTING

CONCRETE COLLAR

PERMITS SHALLOWER EMBEDMENT

POLE WITH CONCRETE

FOOTING

Figure 1.2 Pole type construction.

5
Figure 1.3 Miscellaneous bamboo and non-dimensioned

lumber connection details.

6
7
Figure 1.5 Timber wall construction.
2. MASONRY CONNECTORS

by

S. George Fattal

2 . 1 Introduction

This Section discusses the use of masonry connectors in bearing wall construction

for improved structural response under severe wind conditions. The structures considered

are- low-rise buildings (i.e., dwellings, small business stores, community centers,

schools) in developing countries. For the purpose of this section the word "connector"

is used to designate any mechanical device, including reinforcing bars, which can be

effectively used to connect individual masonry walls to the other elements of the system

(walls, columns, beams, partitions, roof or foundation).

The material in this section consists of an introductory discussion giving background

information on masonry construction, exhibits and analyses of buildings damaged by

extreme winds, a survey and evaluation of current masonry practices in developing countries

experiencing high winds, a study of current masonry practices in the United States

relating to high winds and earthquakes with a discussion of various types of masonry

connectors employed in such construction, and general and specific recommendations for

improving high wind response of masonry buildings in developing countries through better

utilization of existing connector technology.

2 . 2 Types of Masonry Construction

Masonry bearing walls used in low-rise buildings in developing countries are commonly

built with hollow concrete masonry units. Figure 2.1 shows some of the common types of

masonry units used in the United States [8] . Although the standard unit shown has 2 cores, 3-core units are also quite common in the United States as in the Philippines and

other developing countries. In running bond construction (vertical joints staggered), it

is somewhat easier to place vertical reinforcement through the 2-core units because the cores are in vertical alignment. They are also more modular than the 3-core units (less

number of shapes and sizes are required in construction) . For additional information,

detailed classifications of concrete masonry are found in ASTM Designations C90, C129,

C140, C145 and C33 [9]

Masonry units are laid in mortar which acts as their binding agent. Prevailing

types of mortar in the United States are cement-line-sand and masonry cement-sand mortars.

Different proportions of the constituents in these types will produce different strength

properties. Standard mortar designations, such as types M, S or N are used for the

appropriate mortar identification according to the range of constituent proportions, by

volume, specificed in ASTM Designation C270 [9]. Types M,S, and N are commonly used

9
for structural masonry applications. Types M or S are specified for high flexural

strength requirements. Various other specifications for mortar and mortar ingredients

are found in ASTM Designations C5, C91, C109, C110, C144 , C157, and C207 [9].

Masonry walls are classified according to type of construction and intended use in

a building. A single wythe wall has one masonry unit in its thickness. A multiple

wythe wall has several masonry units in its thickness. In a composite wall construction,

at least one of the wythes is built with masonry units dissimilar from those in the

neighboring wythes. Multiple wythe walls without cavity are laid contiguously with the

spaces between the wythes, called collar joints , filled with mortar or grout. To insure monolithic action of the assembly, additional bonding is effected by the use of

metal ties laid horizontally in bed mortar across the wythes at periodic intervals

throughout the height of the wall. A cavity wall is identified by a continuous vertical

air space between any two adjacent wythes and by metal ties laid as in composite wall

construction and connecting the two wall sections flanking this space. Reinforced

masonry walls built with solid units are reinforced by placing steel bars, vertically

and/or longitudinally, as needed, in the space between consecutive wythes and by grouting

this space. In hollow block walls, such as those studied in this report, vertical

reinforcement may be placed as needed, through the hollow cores which are then grouted.

The following types of masonry walls are identified by their intended function in a building. A load bearing wall supports the vertical loads above it, in addition to its own weight, with or without the aid of a vertical load-carrying space frame. A nonload bearing wall supports no vertical loads other than its own weight. A shear wall

resists planar forces induced by exterior horizontal loads acting on a building. A curtain wall is a non-load bearing wall, built outside the building frame and not

entirely supported at each floor. A panel wall is a non-load bearing exterior wall

supported at each floor. A partition is a non-load bearing interior space divider which

will function as a shear wall unless isolated along three edges from the rest of the

structure. Veneer is the exterior masonry layer of a two-layer wall system, connected

to the interior layer and/or to the primary load-supporting structure by horizontal

ties. Veneer is generally designed to be non-load bearing. A pier is a masonry wall

segment flanked by two adjacent openings or by an opening and the vertical edge of a wall. A lintel is a wall segment above an opening.

A masonry filler wall or infill wall designates a wall fully enclosed within a structural frame or bounded by two columns and wholly supported at each floor level.

Filler walls may be load bearing or non-load bearing depending on the type of construction.

In the United States, filler walls are generally non-load bearing because they are usually laid after the frame has been erected so that only mortar bond exists at the

interface. Figure 2.2 shows another type of filler wall construction where the walls

are laid first on top of a wall footing, followed by casting of the concrete columns and

10
peripheral bond beam. This scheme permits extension of horizontal and vertical wall

reinforcement into the surrounding frame so that the assembly will act integrally under

superimposed loading. This system is widely used in the Latin American countries and has

shown good performance under severe earthquakes in the past.

The latter type of infill wall construction and the single wythe masonry bearing

wall construction shown in figure 1.4 are the two types of masonry systems considered in

this study.

2 . 3 Analysis of Wind Damaged Buildings

Figures 2.3 to 2.12 exhibit buildings damaged or destroyed by recent hurricanes and

typhoons. The buildings shown in figures 2.3 to 2.5 belong to a group of one-story

structures in Northern Luzon, the Philippines, which either sustained severe damage or collapsed as a result of the November, 1974. These structures consisted of maosnry walls

and wood posts, a pitched roof system of wood trusses, purlins and corrugated iron cover,

and a continuous foundation wall of cast concrete.

Figure 2.5 exhibits a typcial failure of the fasteners connecting the purlins to the

top chords of the trusses. Most of the roofing was "peeled off" in this manner. Portions

of the corrugation iron roofing found on the ground contained the purlins with their

metal wire attachments still in place (figure 3.18). Instability of the trusses, few of

which were still standing, was attributed to the loss of purlins and the absence of other

longitudinal bracing between the trusses. The collapse of the masonry walls as shown in

figure 2.3 was likewise attributed to the loss of lateral support at the roof level.

However, the extent and severity of wall damage is also attributed to the absence of

connections between abutting walls and the ineffectiveness of the vertical anchorage at the base. As indicated in figure 2.4, the only anchorage consisted of steel plates

bolted to the wood posts. Close inspection revealed severe corrosion of these plates,

especially at the ruptured section through the bolt holts (figure 2.4). The masonry

walls in these buildings were non-load bearing as they were stopped short of the roof to provide openings at the top (figure 2.3). Thus the wood posts were the only vertical

loadbearing elements and with the loss of the roof many of the corner posts were tipped

over (figure 2.3).

Figures 2.6 to 2.8 shows single family housing units of concrete masonry bearing

wall construction, located in Central Luzon, the Philippines, that were damaged or destroyed by the November, 1970 typhoon. An inherent weakness of these systems is the

absence of peripheral support of the masonry walls at the top because of a local preference

for large openings at these locations. This practice reduces the effectiveness of the

roof to function as a diaphragm and makes it more susceptible to failure by wind suction

or uplift. As indicated in figure 2.6, most of the roofs of these units were removed by

11
the storm. Inspection of figures 2.7 and 2.8 indicates good quality workmanship was used

in constructing the masonry walls which contained vertical reinforcement in grouted

cores. Note that the nails between the top window frame insert and the wall below or the

peripheral wood joist above were not effective in preventing the masonry wall from caving

in (figure 2.8) or in keeping the inserts from falling down (figure 2.7). In fact, there

is no evidence that any fasteners were used between the wall panel (in the background of

figure 2.7) and the peripheral joist on top which was probably removed together with the

roof by the storm.

Figures 2.9 to 2.12 exhibit structures consisting of different types of masonry wall

systems that sustained severe damage or were destroyed by the December, 1974 cyclone in

Darwin, Australia. These structures represented engineered masonry construction with

respect to the quality of workmanship and adherence to Australian masonry codes and

standards (which are comparable to those in the United States) . The Darwin experience

demonstrated that compliance with current standards does not necessarily produce a structure capable of resisting the estimated 150 mph winds experienced during this storm. However, it does indicate the need to reexamine the existing provisions with the

objective of developing improved design criteria, connection details, and construction

practices in order to mitigate the extent of disaster associated with extreme winds.

A damage study of the Darwin structures reveals some features worthy of note. In figure 2.10, it appears that failure occurred at the fourth bed joint from the top, in

the inner concrete masonry wythe of the double-wythe cavity wall. Since the inner wythe

is the loadbearing component, its failure was probably caused by an outward thrust of the

roof under the action of wind. The tilted position of the inner wythe with its top

leaning against the brick facing indicates the absence of ties between the wythes near

the roof level. The masonry wall in fiugre 2.9 consists of two concrete block wythes

with a cavity in between. The condition of the reinforcement demonstrated the ineffectiveness

the light-gage ties in assisting the integral functioning of the two wythes in out-ofplane flexure.

Figure 2.11 shows an infill wall construction with a steel frame and concrete masonry

filler walls. There is no visual evidence of any reinforcement having been used in the

filler walls. Note the severity of vertical cracking through the wall on the right and

also the separation between the steel column and the wall at the left. It is not possible

to establish by examination of the figure whether there were any connectors between the

steel columns and the filler walls. Figure 2.12 shows the portion of a concrete masonry

wall under the sill of a large window opening that has failed. Note that the top course

was connected to the window frame with anchor straps embedded into the grouted cores. It is likely that failure was caused by the movement of the window frame, prying the top course loose from the rest of the wall.

12
2 .4 Masonry Construction in Developing Countries

The following discussion pertains to masonry buildings representing the types of

construction used in developing countries. Local practices, utilization of building

products, standards compliance, etc., are discussed and evaluated with the aid of exhibits

of buildings at various levels of completion.

Figures 2.13 and 2.14 show two different stages of construction of a single family

house located in Central Luzon, the Philippines. The walls are built with 3-core concrete

block units (some of which may be seen lying on the ground in figure 2.13). The units

are laid in stacked bond to permit placement of reinforcement through the vertically

aligned cores. On the basis of figure 2.14 the quality of masonry construction is deemed

inferior by existing masonry standards. Some of the deficincies noted are: (1) use of

defective units, (2) partially filled and non-uniform mortar joints, (3) insufficient

horizontal reinforcement for stacked bond construction, and (4) insufficient lintel

reinforcement above the openings. It should be pointed out, however, that this system

utilizes a peripheral concrete bond beam cast directly above the lintel course (see

figure 2.13). From the standpoint of overall structural integrity in a severe wind

environment, attention is drawn to the practice of using large roof overhangs which are particularly susceptible to wind damage as they are subjected to a positive pressure from

below and suction from above [2]. A potentially critical condition also exists in the

masonry column supporting a larger overhang at the corner of the landing. Unless substantial

top and bottom anchorage and vertical reinforcement is supplied in the column, which is not likely to be the case, given the limited available core space in the single unit

section, there is a high probability that the column will fail under the impact of windborne missiles and/or uplift forces exerted by the roof in a severe windstorm.

Figure 2.15 shows completed single family houses in another project located in

Central Luzon, the Philippines. Figures 2.16 and 2.17 display the infill wall construction

of a typical unit which is judged to be superior in the overall quality of construction

as well as wind-resistant capacity to that shown in figure 2.13. Structurally sound

features include: (1) the use of running bond (vs. stacked bond) masonry construction

with vertical and horizontal reinforcement, (2) adequate connections between neighboring

elements and (3) the practice of casting the column concrete after completion of the

infill walls. With regard to item (2), note for instance, in figure 2.16, that the

vertical bars extend beyond the top of the column and the walls to provide connection to the roof. A structurally marginal practice identified by reference to figure 2.17 is the manner in which the lintels are built. A wood form is shored at the top to give the

desired height of opening, and the space is filled with broken concrete block remnants

and mortar. After setting, the metal window frame is fitted into the opening. Probably

the window frame is relied upon to carry ;he weight of the lintel above it in addition to

13
any loads transmitted form the roof. It is not known whether any horizontal reinforcement

was placed in the courses above the lintel; none appear to be projecting into the adjacent

corner column.

Another example of reinforced masonry bearing wall construction used in the Central

Luzon area of the Philippines is the house shown in figure 2.18. Although it is quite

similar to the first systems discussed above (figure 2.13), there are some major differences

that make it a more viable system structurally. For instance, the use of lintels cast

integrally with the bond beam (figures 2.20 and 2.21) gives better integrity to the

system. Likewise, the hip roof is essentially a space truss which has a better diaphragm

capability because it is braced in both horizontal directions. Also note that the

amount of reinforcement (figure 2.19) is more substantial, the masonry and workmanship is

of a better quality and better connections are used between the roof and wall elements.

The common inherent weaknesses are: the use of slender columns made by stacking single

units (figure 2.18) and excessive projections of the roof overhangs.

Figure 2.22 shows a house built in Bangladesh by CARE, Inc., consisting of walls and

2/ pilasters built with cinva-ram— masonry units. The wall footings are built wider than

the walls and are raised above ground to protect the house against floodwater. One of

the attributes of this house is its low cost because it lends itself to self-help construction

since the skills needed to produce cinva-ram is minimal. One disadvantage of this construction

is the difficulty of reinforcing it economically. Since cinva-ram units are solid,

double wythe walls are needed for the placement of bars. This can be compensated to a certain extent by using thicker walls built with larger units.

The foregoing case studies, which were based on information gathered from field

surveys of ongoing construction projects, indicate the need for a broader dissemination

of existing literature on building construction practice to the public. The reference

section lists some of this information that is available through local sources such as the Philippine Standards Association [15 to 18], the Association of Structural Engineers

of the Philippines [20], the Philippine Bureau of Standards [13, 14], and the Carribean

Council of Engineering Organizations [27].

2 . 5 Masonry Practices in the United States

2.5.1 Available Masonry Connectors

Among the broad variety of connectors available for use in masonry construction, a significantly large number are utilized for non-structural applications such as for

attachment of facing panels, hangers and miscellaneous appendages. Others are used in

dual wall systems such as cavity walls, wood framing with masonry veneer and two-wythe was ___

Units made by pressing a mixture consisting mostly of clay and some cement into rectangular units which are then dried in the sun.

L4
with reinforced and grouted collar joint. Both of these categories are excluded in this

study since they do not relate to the single wythe bearing wall construction most commonly

used in developing countries.

Figure 2.23 shows a variety of metal anchors used to tie masonry walls to interconnecting

elements. Tiebars come in different sizes and shapes for diverse applications. Where

used to provide lateral support between abutting bearing walls, 1/4-in tiebars with end

hooks are typically placed in alternate courses with the bent ends embedded in cores filled with mortar or grout as illustrated in figure 2.24 (c) . A twisted bar without

end hooks is used to tie floor or roof joists to the concrete masonry bearing surface as shown in figure 2.24 (b) . These joists are supported laterally, at specified intervals,

by the masonry walls of the same orientation, with tiebars as indicated in figure 2.24

(a) . Tiebars used in pairs provide an effective means of anchoring the roof to the

walls. At the top the hooks are lapped and nailed to the rafter or the top chord of the

roof truss. At the bottom, they are embedded in the concrete bond beam or, in the

absence of a concrete bond beam, into the grouted cores of the concrete blocks in the

top course. Steel reinforcing bars can also be used for this purpose. In either case proper care should be exercised to protect exposed metal surfaces against corrosion.

Plain or corrugated dovetail bars shown in figure 2.23(e) and (g) are made of

lighter gage metal than the tiebars and are used to tie masonry walls to concrete walls

or columns. These anchors require special metal duct inserts in the concrete to receive

the dovetail end in interlock. Although dovetail anchors are generally designed for

non-load bearing masonry wall connections, they provide some measure of resistance

against pullout forces. The corrugated dovetail tie with an end hook shown figure 2.23

(f) provides an effective means of anchoring door and window frames to the masonry

walls

Anchor bolts such as the one shown in figure 2.23 (h) are mainly used to connect

wood elements to the masonry. The bent end generally gives more holding power for the same length of embedment than the head of a standard straight bolt. Figure 2.25 illustrates

two anchor bolt applications: (a) anchorage of sill to masonry wall and (b) anchorage

of stud wall to masonry wall. Also consult figures 3.23 and 3.24 which illustrate the use of anchor bolts to connect a stud wall system cast concrete slab footings and

concrete masonry foundation walls.

Figure 2.26 shows reinforcement designed for placement in the horizontal joints of

masonry walls. The two common shapes are the truss and the ladder shown in (a) and (b)

,

respectively. This reinforcement is fabricated from light-gage, cold-drawn steel and

consists of two longitudinal rods welded together by cross rods. Joint reinforcement is

used as a means to avoid or control cracking in masonry walls and to improve their

tensile strength in horizontal flexure.

15
The use of joint reinforcement is strongly recommended in walls of stacked bond

construction which are prone to develop cracking in service along the vertically aligned

mortar joints. A good practice is to use them in alternate courses in stacked bond

construction and in every third course in running bond construction. Special prefabricated

units are also available for continuous reinforcement around corners as in figure 2.26(c)

and (d), and for anchoring abutting walls and partitions as in figure 2.26(e) and (f )

.

There are a large number of manufacturers of masonry connectors. The best source

of obtaining names of manufacturers is The Thomas Register [26] and the best source of

obtaining product information is Sweet's Industrial Consturction Catalog File [3]. The

pertinent data supplied by the manufacturer include descriptions of the available products,

their application, technical data and level of acceptance by building regulatory agencies.

2.5.2 Available Technical Information

The design and construction of masonry buildings are governed by the provisions of

various regulatory documents. Among these, the principal one for concrete masonry is

the NCMA Specification [28] which comes with a Commentary [29] giving the rationale

behind its provisions. The ACI Committee 531 report [30] contains proposed reocmmendations

for concrete masonry structures that have been referenced by Jamaican sources [1] . This

committee is currently preparing a revised code for concrete masonry. Provisions for

maosnry in general, are prescribed in ANSI A41 [31] and the Uniform Building Code [32]

.

Information of a less technical nature is contained in reference [33] published by

NCMA, which provides guidance for vocational training in concrete masonry. NCMA also

published a TEK series [34] which supplies technical information on design, construction

and detailing aspects of concrete masonry.

Experimental and analytical research work on concrete masonry conducted at the

National Bureau of Standards is described in various publications media with the more

recent ones included in the reference list [35 to 39], Additional sources of information

on concrete masonry-related practices are also listed [40 to 46]

.

2 .6 Suggested Improvements in Masonry Construction

2.6.1 Utilization of Available Connectors

Improvements in building construction can be obtained through a better utilization

of ivailable masonry connectors. The methods include the use of tiebars as an expedient means of anchoring masonry walls together as well as to roof and foundation elements.

Bars of 1/8-to 1/4-inch thickness which should be locally available in many developing

16
countries can be bent or twisted to give them the desired configuration by labor-intensive

methods much in the same manner as is employed to hook reinforcing bars in the field.

It was previously noted that connections effected by tiebars may also be accomplished

by using plain or deformed reinforcing bars which are generally more readily available

than tiebars. To be effective, exposed reinforcing bars should be resistant to corrosive

agents. Where used to connect the roof to the masonry walls, reinforcement should have

sufficient embedment in concrete or grout-in-core at the bottom, and should preferably

extend over and around the connecting roof element and be secured on both sides by

straps nailed into the wood.

To provide anchorage between intersecting walls, reinforcing bars formed into a loop or hooked at both ends may be placed in bed mortar for constructions without using

bond beams as indicated in figure 2.27(a) and (b) . Where bond beams are utilized a more

substantial anchorage may be effected by bending and extending the bars into the neighborin

walls as indicated in figure 2.27(c) and (d) . Likewise, walls may be connected to the

foundation by dowels embedded in the footing (bent dowels are preferable) and extending

into the grouted core of the wall and lapping with the vertical reinforcement.

2.6.2 Improved Construction Practices in Severe Wind Environment

Improved structural response in a severe wind environment may be achieved through

practices which have been identified through past records to be more effective during

natural disasters. The more important aspects are:

1. Use of Peripheral bond beam connecting all load-bearing masonry elements together.

Alternate construction schemes include the use of a cast concrete beam and the use

of bond beam masonry units through the top course (figure 1.4). Both schemes

permit placement of horizontal reinforcement to achieve better integrity at the

top. It should also be mentioned that a substantial bond beam relieves the walls

from resisting forces in out-of-plane flexure and supplements the diaphragm rigidity o the roof.

2. Use of appropriate lintels and connections between lintels and the rest of the

walls. Alternate cast-in-place and precase lintels are indicated in figure 1.4. A most effective means of achieving continuity of lintels is to cast them integrally

with the bond beam as indicated in figure 2.20.

3. The need for adequate diaphragm capability of the roof cannot be overemphasized. The

roof system should preferably be braced in both directions to achieve a measure of

diaphragm rigidity which is needed to transmit lateral wind loads to the appropriate

shear walls below.

17
The use of slender vertical elements such as those built with single stacked concrete

masonry units to provide columns for the support of large roof overhangs at reentrant corners or landings should be avoided in a severe wind environment. This restriction

is necessary because these elements are highly susceptible to impact by flying

debris and uplift transmitted from the roof.

Large roof overhangs serve as vehicles for attracting and transmitting higher uplift

forces on to the system and therefore require more substantial construction provisions

against high winds. Considerations such as aesthetics, shading provisions and

social preferences of dwelling environment should be traded off against precticality

of design and increased costs associated with such practices to arrive at a reasonable compromise.

Overall integrity of the system should be assured by providing continuity between

vertical wall reinforcements and the roof and foundation through appropriate

utilization of reinforcing bars and anchor bolts and by providing continuity between

intersecting walls by means of tiebars and/or horizontal reinforcement grouted

within a bond beam course and extending into the neighboring walls and partitions.

The use of infill wall construction in building systems under a severe wind environment

should be encouraged. The masonry infill walls should be laid first on top of a cast concrete wall footing and attached to it by means of dowels lapped a sufficient

distance with the vertical reinforcement placed into the grouted cores of the hollow

blocks. Horizontal and vertical reinforcement should project from the sides and top

of the filler walls to achieve continuity with the surrounding concrete frame which

should be cast last.

18
8x8x8 8x8x8 8x8x16

SASH LINTEL STANDARD LINTEL BOND BEAM

4x8x16 4x8x8 4x8x!2

STANDARD HALF CORNER

Figure 2.1 Concrete masonry units

19
20
Figure 2.3 Collapse of one-story building caused by the

November 1974 typhoon in the Philippines

21
Figure 2.4 Failure of metal anchor -plate in building destroyed

by the November 1974 typhoon in the Philippines.

22
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Single family house showing collapse of roof and exterior

wall during the Philippines typhoon in November, 1970.

25
Figure 2.8 Interior damage of single family house caused by the

November 1970 typhoon in the Philippines

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Figure 2.10 Building of cavity wall construction in Darwin,

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cyclone.

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Figure 2.16 Concrete columns with concrete masonry infill walls being

constructed for single family dwelling occupancy in

Central Luzon, the Philippines.

34
Figure 2.17 Construction of single family housing unit in Central

Luzon, the Philippines, showing, concrete masonry

filler walls and reinforcement of corner column.

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Figure 2.21 Single family housing under construction in Central Luzon

,

the Philippines, showing concrete bond beam detail over openings

39
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40
(h)

Figure 2.23 Various metal anchors: (a), (b) tiebars with end hooks;

(a) tiebar with hook and split hook; (d) tiebar with 90°

twist; (e) corrugated dovetail tie; (f) corrugated tie;

(g) dovetail tie with hook; (h) Anchor bolt.

41
Cross bracing at every wall anchor and at intermediate spacings

as required.

(a)

Floor or

roof joists or beams.

Nail anchors to underside or side of joists. Wall anchors at required intervals emhpHHoH

S S

.h0uld have S PI|( end embedded in mortar joint or end bent down into block core and cor i filled with mortar. Length of anchor should

be sufficient to engage at

least three joists.

(b) Solid unit

Hollow bridging unit

Solid top units in course supporting

floor joists.

Wood joists framing

into masonry wall. Joists to have min. 3" bearing on masonry. Wx'/S" twisted steel plate anchors with one end embedded m horizontal mortar joint

(c)

Place metal lath or wire

l'/4"x'/4"x30" strap mortar or concrete, anchors with 3" right angle bends at each

end, at vertical spacings not exceeding 32" o.c.

Figure 2.24 Application of metal anchor's in masonry construction:

(a) tiebar anchor to wood joists; (b) twisted anchor

connecting wood joist to concrete masonry bearing wall;

(c) tiebar anchor connecting concrete masonry

intersecting walls.

42
Toenail joist to

sill or anchor to

sill with Trip-L-Gnp or

similar anchors

as shown.

Fill hollow cores in course

supporting floor with concrete

or mortar.

Vt" min. dia. anchor bolts extending at least 15" into

filled cells in the masonry

and spaced not more

than 6'-0" o.c. to anchor sill to wall.

Rake out and caulk Metal washer

Double studs W bolts top and

bottom courses and 32 o.c. max.

Place wire screen or metal lath in joint under cores to be filled to prevent filling of cores below.

WOOD STUD WALL

(b)

(a)

7ig-ure 2.25 Application of anchor bolt for masonry connection: (a)

connection of sill plate to concrete masonry bearing wall;

(b) connection of concrete masonry wall to wood stud wall.

43

EXTERIOR WALL BOND BEAM BOND BEAM AT WALL INTERSECTION

(c) (d)

•

' -ft

Figure 2.27 Horizontal reinforcement between intersecting masonry walls

(a) and (b) without bond beams; (c) and (d) with bond beam.

45
3. FASTENERS FOR TIMBER CONSTRUCTION IN HIGH WIND AREAS—

by

G.E. Sherwood and T.L. Wilkinson—

3.1 Introduction

Houses and other low-rise buildings in many tropical areas such as Jamaica, Bangladesh,

and the Philippines are subject to extreme winds several times each year. Failures that occur in buildings or building elements of wood construction usually occur in the fasteners

rather than in the structural members. Buildings that are adequately braced to resist

racking forces, and have each element tied together from foundation to roofing, can resist high winds without structural failures. This section describes and provides

sources for commercially available timber connectors, existing timber-related building

practice in the Philippines, and identification of good and poor timber connector practice.

It also presents recommended practice, including connectors that can be fabricated by

the indigenous people.

3 .2 Available Timber Fasteners

3.2.1 Nails, Screws, Bolts, and Lag Screws

These common mechanical fasteners for wood come in many varieties. A variety of

nails is shown in figure 3.1. Some may be used for several purposes while others are intended for special purposes.

In general, nails resist or transmit smaller loads than screws, and screws resist

or transmit smaller loads than bolts or lag screws. However, because of their smaller

size, more nails can usually be used in a joint. A good source of information of the

design of joints with such fasteners is the National Design Sepcif ication for StressGrade Lumber and Its Fastenings by the National Forest Products Association [47].

There are a large number of manufacturers of such fasteners. The best source for

obtaining names of manufacturers is the Thomas Register of American Manufacturers and

Thomas Register Catalog File [26] . — This work was done in cooperation with the National Bureau of Standards, U.S.

Department of Commerce, Washington, D.C.

—— Messrs G.E. Sherwood and T.L. Wilkinson are engineers with the Forest Products Laboratory,

Forest Service, U.S. Department of Agriculture, maintained at Madison, Wisconsin, in

cooperation with the University of Wisconsin.

46
These manufacturers can provide catalogs which describe the fasteners they manufacture

along with the intended purpose for each.

3.2.2 Timber Connectors

Timber connectors generally refer to split rings, shear plates, and toothed rings

(figures 3.2, 3.3 and 3.4). These are intended primarily for heavy timber (members

larger than 4 inches in thickness) construction and usually result in bulky joints.

Special tools and skills are needed for properly constructed timber connector joints.

Split rings and toothed rings are used for wood-to-wood joints, and shear plates

are used for wood-to-steel joints, and sometimes for wood-to-wood joints. Proper joint

design procedures and loads can be found in ref. [47].

Manufacturers of timber connectors as listed in Thomas Register are as follows:

(1) Simpson Company

1472 Doolittle Drive

San Leandro, California 94577

(2) Woodmack Products, Inc. 852 Aldo Avenue

Santa Clara, California 95050

(3) Timber Engineering Company

5530 Wisconsin Avenue

Washington, D.C. 20015

(4) Kees, F.D., Manufacturing Company

21 High Street

Beatrice, Nebraska 68310

(5) Cleveland Steel Specialty Company

14442 Industrial Avenue, South

Cleveland, Ohio 43228

3.2.3 Truss Plates

These fasteners are made of galvanized sheet metal, usually 20 gage, intended

primarily for use as gussets for light timber (members 2 inches thick) trusses. The

plates may be obtained in many sizes of rectangular shape. Their means of transferring

load vary from the use of nails in punched holes, plugs or barbs of different shapes, to teeth of different shapes and lengths. Figure 3.5 shows some typical plates.

Procedures for designing with these plates are presented in Design Specifications

for Light Metal Plate Connected Wood Trusses by the Truss Plate Institute [48] . This

publication also lists 11 manufacturers which are members of the Truss Plate Institute.

Detailed description of the plates and design loads can be obtained from the

manufacturers

47
3.2.4 Sheet Metal Fasteners and Other Special Devices

These fasteners include such items as joist and beam hangers, framing ancho.rs,

rafter anchors, post anchors, etc., (figure 3.6), which are made of galvanized sheet

metal and which require fastening to the framing with nails or screws.

A Good reference for descriptions and specifications of these fasteners is Products

in Action by the Timber Engineering Company [49]

.

Some of the manufacturers of truss plates also make certain types of special fasteners

for use in framing applications.

3 . 3 Philippine Timber-Related Practices

Timber-related building practices in the Philippines can be divided into three

general categories:

(1) Pole-type construction in which poles are set into the ground to serve as foundation and extend to the roof (figure 3.7).

(2) Concrete slab, perimeter, or pier foundation of concrete or masonry with wall

and roof framing of wood (figure 3.8).

(3) Concrete slab or perimeter foundation supporting masonry or poured concrete

walls, and a wood-frame roof (figure 3.9).

3.3.1 Pole Type

This type of construction is well suited to highwind areas because the major structural

member, the pole, serves as the connecting link between all other structural members.

If the poles are set 4 feet or more into the ground, they serve as anchors for the

building. For long life, all poles must be pressure treated for resistance to decay and

insect attack.

Roof -framing members are either round or sawn timbers. In remote areas, they may

be tied together with strips of bamboo (figure 3.10). This type of connector appears to provide good resistance to wind forces. Nailing is also effective if nails are loaded

laterally rather than in direct withdrawal.

Covering materials for this type of construction are often thatch roofs and walls

of thatch or bamboo. There appears to be no way to assure anchorage of thatch during

high winds (figure 3.11). Wood siding nailed to framing members offers good resistance

to wind, but nails should be corrosion resistant.

48
3.3.2 Wood -Framed Wall and Roof

Wood-framed walls often have a single covering material. It may be applied to the

exterior of the building or set between framing members. Anchor bolts are used to tie

the wall to the foundation. Where the foundation is concrete block, the anchor bolt

should extend through blocks into the footing. If the house is anchored only to the top

concrete block, this block may be pulled from the foundation and moved with the house.

Covering material applied on the outside of the framing (fig. 3.12) protects the

wall framing and connectors from rain. Walls with the covering set into the framing

have a greater potential for trapping water, and thus promoting decay. Anchor bolts on

the outside of the wall are particularly susceptible to trapping water (fig. 3.13).

They can easily be placed on the inside for protection. The type of sill plate shown in

figure 3.13 also traps water. The sill plate should at least be sloped to the outside

so water will drain from it, and the joint with panel materials should be caulked.

Roof framing is either nailed to the top of the wall or secured with sheet metal

connectors. Good nailing should hold down the roof framing, but sheet metal connectors

provide a stronger joint and have less chance of being improperly nailed.

3.3.3 Masonry Wall

One method of tying roof framing to a masonry wall is to pour reinf orced-concrete

columns at all corners and at intermediate locations on long walls. Reinforcement is

tied to the foundation and extends above the columns so that it can be attached to a wood beam which extends completely around the perimeter of the house on top of the

masonry wall. Trusses are sometimes anchored to this beam by metal straps nailed to both members. The metal strap has a 90° twist at its center which weakens it and allows

the nails to be pulled out when anything but a direct uplift force is exerted on the

strap (f ig . 14)

A sheet metal connector that can be nailed to both sides of the rafter and beam

would prevent the type of failure caused by rotation in the single, heavy strap.

3.3.4 Roof Framing

Framing for the roof of any of the types of structures involves use of either

trusses or a raf ter-and-joist system. Trusses are fabricated with metal plate connectors

or bolted joints. In some larger structures, split-ring connectors are used. Trusses

generally are made from an engineered design and under controlled conditions, so they

have less potential for failure than the conventional raf ter-and-joist system.

49
Where rafters are used, some type of collar tie is important to keep the roof

from dividing at the peak (fig. 3.15). Ceiling joists, well nailed or bolted to rafters,

prevent the roof from spreading outward (fig. 3.16).

Purlins are connected to rafters or trusses in several ways. Nailed joints are among the most vulnerable because in this application the nail is loaded in direct

withdrawal. Short 2 by 2's nailed to the purlin and the rafter (fig. 3. 16) provide a stronger joint by loading the nails laterally.

3.3.5 Roofing

The major roofing material in the Philippines is corrugated sheet metal. One

method of tying roofing to purlins is the use of sheet metal straps (fig. 3.17). One

end of the strap is bent at a 90° angle, and that bent portion is riveted to the roofing.

The strap is nailed to the side of the purlin and bent under the purlin. The attachment

of the strap to only one side of the purlin results in an unsymmetrical load so the

strap can be twisted off by wind forces. Two straps riveted to the roofing on both

sides of the purlin and lapped under the purlin, would resist forces due to moment in

the connector.

Figure 3.18 illustrates the effectiveness of having tiedowns symmetrically loaded.

A wire was tied to a nail in the bottom of the purlin, punched through the roofing,

wrapped over the purlin, and tied back to the nail. This tie held well enough that the

purlin-to-rafter connection failed before the roofing connector. However, roof leakage

may be a problem.

3.3.6 Protection From Wood-Destroying Organisms

A key element of good performance of timber connectors is maintenance of the strength

properties of the wood. In many cases where failures have occurred, some deterioration

of the wood is evident (fig. 3.19). Staining is prevalent around many nails and bolts

(fig. 3.20), which reduces decay resistance of the wood. Corrosion of nails also results

in loss of cross section which loosens the nails. In such a humid environment, all

connectors should be corrosion resistant.

3.3.7 Summary of Good and Poor Practices

Design, construction, and maintenance practices are summarized below:

Good Design Practices

Design the building to act as a unit by connecting all components together and

50
anchoring the whole structure to the foundation. Design joints to resist torsion as well as uplift even where it means using connectors in pairs.

Good Construction Practices

The use of engineered trusses fabricated under good quality control assures structural

integrity of the roof framing. Where trusses are not used, collar beams and ceiling

joists must be nailed or bolted to the rafters. Sheet metal connectors provide better

quality control at joints than nails alone.

Pole framing offers a good way of tying componenets together because all major

structural members are connected to the poles. In masonry construction, a reinforcing

rod extending from the footing to the roof provides the required continuous tie.

Good Maintenance Practices

All connectors should be corrosion resistant. Locate connectors where they are protected from rain, and avoid exposed joints which trap water.

Poor Design Practices

Loads should not be concentrated in a small number of connectors. Connectors

applied to only one side of a member can often be twisted off because they have little

resistance to torsional loads.

Poor Construction Practices

Nails loaded in direct withdrawal offer less resistance than laterally loaded

nails. Roof framing that is anchored only to the top course of a block wall may blow

off taking the blocks with it.

Poor Maintenance Practices

The use of connectors that are not corrosion resistant is poor practice in a humid

location. Exposure of connectors to rain provides a place for water to enter the wood

and promote decay. Horizontal members exposed as exterior elements form water traps

which can lead to decay.

51
3 . 4 Timber Fasteners Appropriate for Construction

in Developing Areas With High Winds

3.4.1 Pole-Type Construction

Where poles are set in the ground to serve as the main vertical framing, major

floor and roof framing securely attached to the poles assures the structural integrity

of the building. Round framing members commonly used for indigenous type. of construction

have been successfully tied to the poles with strips of bamboo (fig. 1.3). Sawn timbers

should be bolted to the poles using 3/4-in or larger bolts, depending on the load. If round poles are used with sawn timber framing, notching the pole to provide a wider

bearing surface (fig. 3.21) may be necessary, especially where two members meet end-toend (fig. 3.22).

Siding materials may be boards nailed directly to the framing. Corrosion-resistant

nails are particularly important for this application. Indigenous-type construction

often employs walls of bamboo or thatch. These coverings have served well in many

applications, but are difficult to secure in extreme winds.

3.4.2 Light Wood-Frame Construction

The wood-frame must not only be anchored to the foundation at its base, but must

also provide a continuous tie from the foundation to the roof. Anchorage of wall framing

to a concrete foundation may be accomplished with hooked bolts embedded 8 to 12 inches

in the concrete. A large washer should be used under the nut to spread the load on the

wood framing (fig. 3.23). Where the foundation is concrete block, the anchor bolt

should extend through the block and be anchored in the concrete footing (fig. 3.24).

The exposed end of the anchor bolt should be protected from weather. Were a single

covering material is set into framing, the bolt should be placed on the protected side

of the covering material (fig. 3.25).

The wall must be tied together as well as anchored. Panel-type covering material

nailed to the anchored sill and to the top plate provides this continuous tie. Panel

material nailed to framing completely around its perimeter also provides racking resistance

in the wall. Where siding does not provide such a tie, sheet metal straps can be used

as connectors between plates and vertical framing (fig. 3.26). /

Roof framing is effectively tied to walls with sheet metal brackets (fig. 3.27) or wood cleats (fig. 3.28). Where a ceiling joist-and-rafter system is used, sheet metal

straps nailed to joists and studs (fig. 3.29) provide a good tiedown for roof framing.

In this method, the rafter must be well nailed to the ceiling joists.

/
3.4.3 Concrete and Masonry Construction

Poured concrete posts at corners and intermediate locations in concrete block walls

provide tiedown points for roof framing. Wood plated can be tied down to hooked bolts

in the poured concrete posts or walls. This is the same type of connector shown in

figure 3.23. Roof framing can then be attached to the anchored plate by sheet-metal

brackets or wood cleats as shown in figure 3.27 and 3.28.

3.4.4 Roof Framing

Trusses may be used for roof framing for any of the types of construction that have

been discussed. Connectors may be metal plates for light construction or split-rings

for heavy construction. Split-rings that are tapered in cross section and wedged into

place have the highest load-carrying capacity.

3.4.5 Roofing

Thatch roofs are often used for indigenous construction. The thatch is tied to small poles which are laid on the roof in courses with each course overlapping the one below. Poles are secured by tying them to roof framing with bamboo strips which provide

good resistance to wind loads. However, the thatch itself may blow off in extreme

winds

The predominant roofing material is corrugated, galvanized sheet metal. The usual

roof system consists of purlins (sometimes referred to as roof joists) spanning between

rafters or trusses, and roofing attached to these purlins. The purlins should be tied

to rafters with sheet metal brackets (fig. 3.30) or with wood cleats (fig. 3.31). In either case the tiedowns should be attachable to both sides of the purlin and rafter, so they cannot be twisted off by loads that are not perpendicular to the purlins.

Corrugated roofing is best affixed by a fastener that wraps completely around the

purlin. Two sheet metal straps lapped under the purlin and riveted to the corrugated

roofing on each side of the purlin (fig. 3.32) provide a good connector system that will

resist moment loads which cause failure when a strap is used on only one side.

3 . 5 Fasteners for Fabrication by Indigenous People

Any of the sheet metal straps could be easily fabricated with a minimum of tools. A minimum thickness of 20-gage galvanized sheet metal should be used. A width of 1-1/4

inches and a length of 20 inches would be suitable for many applications (fig. 3.33).

It may be necessary to vary this size for specific applications.

53
Galvanized strap could be fabricated for roofing tiedowns. This strap should be

only about 6 inches long, bent at 90° 1 inch from one end, and have a 1/4-in hole

punched in the 1—in section (fig. 3.34). These straps should be used only in pairs on opposite sides of a purlin. The ends of the straps should be bent under the purlin with

the two straps lapped and nailed to the bottom as well as sides of the purlin.

A multipurpose bracket could be fabricated from 20gage galvanized steel. A suggested

size is given in figure 3.35; however, this could be varied for other standard sizes of

wood framing. Slits cut in the sheet metal permit forming the bracket for a variety of uses

.

Split-ring connectors have been fabricated by cutting 3/4-in wide sections from 3-

in steel pipe, and then cutting the ring at an angle. This connector and present

commercially produced split-ring connectors are shown in figure 3.36. For maximum

strength the ring should be wedged tightly into the circular groove cut in the wood.

Present commercial split-rings cut from steel pipe should have good load-carrying capacity

even though its capacity would be somewhat less than the tapered ring.

Metal plate connectors for truss joints is another possibility for fabrication by

indigenous people. These are usually fabricated from 20-gage galvanized sheet metal.

The sheet metal is punched in a way that produces barbs or teeth at right angles to the

plate. Plates with barbs punched in the pattern shown in figure 37 generally do not maintain optimum strength after expansion and contraction of the wood with moisture

changes over a long period of time. Plates with teeth that penetrate deeper than barbs are less affected by moisture cycling of the wood.

3 . 6 Summary

Wind-resistant construction for wood-frame buildings in developing countries can be

achieved by providing good connectors between all members from foundation to roofing.

All connectors should be corrosion resistant and protected from rain where possible.

Connectors should be designed to resist being twisted off. Where nails are used, connectors

should be a type that load the nails laterally rather than in direct withdrawal.

Sheet metal straps and brackets could easily be fabricated by indigenous people in

developing countries. Such connectors could be fabricated using a minimum of tools and

equipment

.

3 . 7 A Caution

In present tropical cnstruction, the most frequent failure caused by high winds is

the loss of roofs. It should be recognized that improved design which holds the roof

54
securely will ultimately result in the concentration of greater loads in other parts of

the building. Details of wall construction and anchorage to the foundation which have

been adequate when the roof failure relieved the total load on the building, may not be

adequate when the roof remains intact. The building will be subjected to a large overturning

moment as well as to uplift load on walls.

55
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59
60
TECO DU-AL-CLIP

Framing Anchors

Figure 2.6 Some examples of special fasteners made by the Timber

Engineering Company.

61
62
63
64
65

Figure 3.12 Covering material on the outside protects framing and

connectors

57
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75
Figure 3.21 Round pole notched for sawn framing member.
WASHER

SOLE PLATE

A

(k- v.

4 . P toirJ

Figure 5.23 Anchor bolt in concrete a minim-am of 8 inches. Washer

spread load.

WASHER

SOLE PLATE

HEADER PLATE

HIP—CONCRETE BLOCKS

ANCHOR BOLT

GROUT CORES WITH ANCHORS

CONCRETE FOOTING

Figure 3.24 Anchor bolt through concrete block foundation into footing.

11
/

WASHER

SOLE PLATE

. p -b y ^ \

• >

"ANCHOR BOLT

ure 3.25 dneftor boZ-t installed on protected side of wall.

STUD

NAIL STRAP TO STUD

SOLE PLATE

ANCHOR

Figure 3.26 Sheet metal strap tying stud to bottom plate.

78
ROOF FRAMING

METAL BRACKET

DOUBLE TOP PLATES

STUD

Figure Z.2? Sheet- metal bracket for tying roof framing to walls.

WOOD CLEATS

ROOF FRAMING

SIDE NAILING

DOUBLE TOP PLATES

7igure 3.23 Wood cleats nailed to each side of roof framing and to top plates.

79
Figure 3.30 Sheet metal bracket used to connect purlin to rafter.

80
RAFTER

NAIL TO PURLIN

PURLIN

NAIL TO RAFTER

Kgure 3.31 Purlins tied to rafters by wood cleats.

STRAPS RIVETED TO ROOFING

WASHER

PURLIN

STRAPS LAPPED UNDER

PURLIN AND NAILED

Figure 3.32 Two metal straps riveted to corrugated roofing, lapped

wader purlin and nailed to purlin.

81
20 -GAGE GALVANIZED

SHEET METAL

I l

20" t

igure 3.33 Multipurpose strap. Length and width can be varied for

specific applications.

1/4" RIVET AND I" WASHER

ZED STRAP

Figure 3.34 Galvanized sheet metal strap with rivet and washer for tying

down corrugated roofing.

82
BEND LINES

I r

1/2"

ll/2 M

4 5/8'

11/2

4 5/8'

Figure 3.35 Multipurpose bracket fabricated from 20-gage galvanized steel.

Bend either direction at bend lines to form desired bracket.

83
S3osSoa

ftOsso o

to

CO Cu

to&s

ft,

84
85
ACKNOWLEDGEMENTS

The contributions of the following persons are acknowledged:

Noel Raufaste, Jr., Center for Building Technology, for supplying field survey documentation

and for critically reviewing the report.

Deborah Borkman , Cathy Warfield , and Julie Reinhold , Center for Building Technology, for

typing the manuscript.

Thomas Ruschell and L. E. Cattaneo , Center for Building Technology, for organizing and

proofreading the report.

Ricardo Florez , Guest Worker, Center for Building Technology, for his assistance in preparing

figures and for his constructive suggestions.

Steven Kilment , AIA, New York City, for supplying those figures and references relating to pole type construction.

Charles Yancey , Center for Building Technology, for critically reviewing the report.

C.C. Raley , Office of International Relations, for critically reviewing the report.

86
REFERENCES

1. Raufaste N.J., Jr., and Marshall R.D., FY74 Progress Report on Design Criteria and

Methodology for Construction of Low-Rise Buildings to Resist Typhoons and Hurricanes,

NBSIR 74-567, National Bureau of Standards, Washington, D. C, July 1, 1974.

2. William F. Reps and Emil Simiu, Editors, Design, Siting, and Construction of Low-Cost

Housing and Community Buildings to Better Withstand Earthquakes and Windstorms, BSS-48,

National Bureau of Standards, Washington, D. C, January 1974.

3. Sweet's Industrial Construction Catalog File, Sweet's Division, McGraw-Hill Information

Systems Company, New York, N. Y. 10036.

4. Standard for Mobile Homes, ANSI A119. 1-1974, and Appendix D, ANSI A119. 1-1975, American

National Standards Institute, New York, N. Y., 1974.

5. Protecting Mobile Homes from High Winds, TR-75, Defense Civil Preparedness Agency,

Department of Defense, U. S. Army AG Publications Center, Civil Defense Branch, 2800,

Eastern Blvd. (Middle River), Baltimore, Maryland 21220, June 1972.

6. Narajanamurty D., and Mohan D., The Use of Bamboo and Reeds in Building Construction,

No. E.72. IV. 3., United Nations, New York, N. Y.

7. Pole House Construction, prepared for FHA by American Wood Presevers Institute,

McLean, Virginia, 1971.

8. Concrete Masonry Design Manual, Concrete Association, Los Angeles, California, 1955.

9. ASTM Standards, American Society for Testing and Materials, 1916 Race St., Philadelphia,

Pennsylvania 19103.

10. Raufaste N.J., and Marshall R.D., FY 1973 Progress Report on Design Criteria and

Methodology for Construction of Low-Rise Buildings to Better Resist Typhoons and

Hurricanes, NBSIR 74-582, National Bureau of Standards, Washington, D. C, July 2, 1973.

11. Raufaste N.J., Jr., and Marshall R.D., Editors, Development of Improved

Design Criteria for Low-Rise Buildings in Developing Countries to Better Resist the

Effects of Extreme Winds, Building Science Series 56, National Bureau of Standards,

Washington, D. C, October 1974.

12. Housing and Urban Development in the Philippines, USAID/Manila, Philippines, January 1968

13. Amendment No. 1 to Specification for Portland Cement, Philippine Trade Standard 661-01.02

1972. Bureau of Standards, Manila, Philippines.

14. Specification for Portland Cement, Philippine Trade Standard 661-01.02: 1968, Bureau

of Standards, Manila, Philippines.

15. PHILSA, Standard Specification for Glazed Ceramic Tiles and Tile Fittings, PHILSA 1-10-72

Quezon City, Philippines, November 17, 1972.

16. PHILSA, Standard Specification for Philippine Cold Drawn Steel Wire for Concrete

Reinforcement, PHILSA 1-5-71, Quezon City, Philippines, November 17, 1972.

17. PHILSA, Standard Specification for Steel Reinforcement Bar, PHILSA 1-7-71, Quezon City,

Philippines, November 17, 1975.

18. PHILSA (Philippine Standards Association), Standard Specifications for Construction

Lime, PHILSA 1-1-68, Manila, Philippines, March 13, 1968.

87
19. PACE, Masonry, PACE CP 206, Manila, Philippines, January 1965.

20. ASEP (Association of Structural Engineers of the Philippines), Private Practice

of Structural Engineering, Manual of Engineering Practice No. 1, Quezon City,

Philippines, January, 1973,

21. PACE, Private Practice of Civil Engineering, Pace Manual of Engineering Practice No. 1,

Manila, Philippines, December 1960.

22. PACE, Code of Practice for the Design, Fabrication and Erection of Structural Steel

Members with Minimum Thickness of 1/8" for Buildings, PACE CP 205, Manila, Philippines,

January 1968.

23. PACE (Philippine Association of Civil Engineers) , Engineering Standards, PACE CP 200,

Manila, Philippines, January 1965.

24. PACE, Excavations and Foundations, PACE CP 201, Manila, Philippines, January 1965.

25. National Structural Code for Buildings, Association of Structural Engineers of the

Philippines, Philippine Association of Civil Engineers, 1972.

26. Thomas Register of American Manufacturers and Catalog File, Thomas Publishing Company,

One Penn Plaza, New York, N.Y. 10001.

27. Carribean Council of Engineering Organisations, Proceedings of Conference on Unified

Building Code, P.O. Box 122, Kingston 10, Jamaica, W.I.

28. Specification for the Design and Construction of Load-Bearing Concrete Masonry, National

Concrete Masonry Association (NCMA) , P.O. Box 9185, Rosslyn Station, Arlington, VA,

22209.

29. Research Data with Commentary in Support of Specification for the Design and Construction

of Load-Bearing Concrete Masonry, National Concrete Masonry Association, P.O. Box 9185,

Rosslyn Station, Arlington, Virginia 22209.

30. Report on Concrete Masonry Structures-Design and Construction, ACI Committee 531,

American Concrete Institute Journal, May-June, 1970.

31. American Standard Building Code Requirements for Masonry, ANSI A41, Miscellaneous

Publication 211, National Bureau of Standards, Washington, D.C., July, 1954.

32. Uniform Building Code, International Conference of Building Officials, 5360 South

Workman Mill Road, Whittier, California 90601, 1973.

33. Toennies, H. and Merteu, John, E., Concrete Masonry Vocational Training Students'

Manual, National Concrete Masonry Association, P.O. Box 9185, Rosslyn Station,

Arlington, Virginia 22209.

34. NEMA TEK Series, National Concrete Masonry Association, P.O. Box 9185, Rosslyn Station,

Arlington, Virginia 22209.

35. Yokel, F.Y., Mathey, R.G., and Dikkers, R.D., Compressive Strength of Slender Concrete

Masonry Walls, Building Science Series 33, National Bureau of Standards, Washington, D.C.,

December, 1970.

36. Yokel, F.Y., Mathey, R.G., and Dikkers, R.D., Strength of Masonry Walls Under Compression

and Transverse Loads, Building Science Series 34, National Bureau of Standards,

Washington, D.C., March, 1971.

37. Yokel, F.Y., Dikkers, R.D., Strength of Load-Bearing Masonry Walls, Journal of the

Structural Division, ASCE, May, 1971.

88
38. Yokel, F.Y., Stability and Load Capacity of Members with No Tensile Strength,

Journal of the Structural Division, ASCE, July, 1971.

39. Fishburn, Cyrus C, Effect of Mortar Properties on Strength of Masonry, NBS Monograph

36, National Bureau of Standards, Washington, D.C., November, 1961.

40. Dikkers, R. , and Saxer, E.L., Flexural Strength of Plain and Reinforced Concrete

Masonry Walls, National Concrete Masonry Association, Arlington, Virginia, 1957.

41. Livingston, A.R., Mangotich, E., and Dikkers, R., Flexural Strength of Hollow Unit

Concrete Masonry Walls, in the Horizontal Span, National Concrete Masonry

Association, Arlington, Virginia, 1958. (

42. Moss, P.J., and Scrivener, J.C., Concrete Masonry Wall Panel Tests, N.Z. Concrete

Construction, Journal of the New Zealand Portland Cement Association, April, 1968.

43. Scrivener, J.C., Static Racking Tests on Concrete Masonry Walls, International

Conference on Masonry Structural Systems, Austin, Texas, 1967.

44. Amrhein, J.E., Reinforced Masonry Engineering Handbook, Masonry Institute of America,

Los Angeles, California, 1972.

45. Amrhein, J.E., Masonry Design Manual, Masonry Industry Advancement Committee, 1972.

46. Schneider, R.R., Shear in Concrete Masonry Piers, Masonry Research of Los Angeles,

Los Angeles, California, 1969.

47. National Design Specifications for Stress-Grade Lumber and Its Fastenings, National

Forest Products Association, 1619 Massachusetts Avenue, N.W., Washington, D.C. 20036,

April, 1973.

48. Design Specifications for Light Metal Plate Connected Wood Trusses, Truss Plate Institute,

7100 Baltimore Avenue, Suite 200, College Park, Maryland 20760.

49. Products in Action, Timber Engineering Company, 5530 Wisconsin Avenue, Washington, D.C.

20015.

89

APPENDIX G

The Economics of Building Needs

A Methodological Guide

THE ECONOMICS OF HOUSING NEEDS:

A METHODOLOGICAL GUIDE

by

Joseph G. Kowalski

Center for Building Technology

Institute for Applied Technology

National Bureau of Standards

Washington, D.C. 20234

Report Presented at Regional Meeting On Development

of Design Criteria and Methodology for Low-Rise/Low-Cost

Buildings to Better Resist Extreme Winds

PREFACE

This study was conducted by the Building Economics Section to

demonstrate the application of economic analysis to the determination of

housing needs. Dr. Harold Marshall and Ms. Rosalie Ruegg of the Building

Economics Section and Dr. Carl Muehlhause of the Institute for Applied

Technology provided constructive reviews of this paper. Mr. Noel Raufaste,

project coordinator of the Center for Building Technology's project to

develop design criteria and methodologies for low-rise/low-cost buildings

to better resist extreme winds (of which this paper is one input), provided valuable editorial assistance. Those errors which remain are, of

course, my responsibility.

i
ABSTRACT

Housing is probably the single most important consumer good in most

economies. Measuring the size of a region's unmet housing need is a

first step to planning and implementing improvements in housing conditions. This study analyzes the concept of housing needs in an economic

framework. A methodology for estimating and projecting housing needs at

the regional level is developed. The methodology attempts to make

explicit the income redistribution intent which is the core meaning

behind the concept of housing needs.

ii
EXECUTIVE SUMMARY

Determining the size of a region's unmet housing needs is an important first step to planning and enacting public policies and programs

which will improve the condition, size and quality of a country's

housing inventory. The assessment of current and future housing needs

is particularly important in the developing regions of the world where

the twin pressures of population growth and urbanization especially

aggravate the housing problem.

This study develops a basic methodology for estimating and projecting housing needs. Procedures are developed to compare the costs

with the potential income redistribution effects of meeting the housing

need shortfall. This methodology has been designed to be flexible and

adaptable to situations in which housing and demographic data may be

sparse. An extended example is presented which illustrates this methodology.
TABLE OF CONTENTS

Page

PREFACE i

ABSTRACT ii

EXECUTIVE SUMMARY ill

LIST OF FIGURES vi

LIST OF TABLES vi

1. INTRODUCTION 1

1.1 THE NORMATIVE BASIS OF NEEDS ESTIMATES ... 2

1.2 PROJECTING FUTURE HOUSING NEEDS 3

2. A NEEDS ESTIMATION AND PROJECTION METHODOLOGY 5

2.1 ESTIMATION OF CURRENT NEEDS ... 6

2.1.1 DESCRIPTION OF THE HOUSING INVENTORY 8

2.1.1.1 TASK 1: CONSTRUCTION OF A HOUSING

CHARACTERISTICS MATRIX ....... 8

2.1.1.2 TASK 2: CONSTRUCTION OF A POPULATION MATRIX . 10

2.1.1.3 TASK 3: CONSTRUCTION OF A PER CAPITA

(OR PER FAMILY) HOUSING CHARACTERISTICS MATRIX 12

2.1.2 DETERMINING THE HOUSING STANDARD 12

2.1.2.1 TASK 4: SELECTION OF A TARGET CELL(S)

FROM THE PER CAPITA HOUSING CHARACTERISTICS MATRIX ..... 12

2.1.3 DETERMINING THE NEEDS OR SHORTFALL MATRIX ... 13

2.1.3.1 TASK 5: CONSTRUCTION OF A MATRIX OF

RELATIVE HOUSING VALUES AND

RENTS 13

2.1.3.2 TASK 6: CONSTRUCTION OF A QUALITY

DEFLATOR MATRIX 14

2.1.3.3 TASK 7: CELL BY CELL CALCULATION

OF HOUSING NEEDS 15

2.1.3.4 TASK 8: DISTRIBUTION OF HOUSING NEEDS

BY CONSTRUCTION TYPE AND BY INCOME

CLASS 16

iv
Page

2.1.4 CALCULATING THE COST OF MEETING HOUSING

NEEDS 17

2.1.4.1 TASK 9: DEFINITION OF LOW- INCOME

HOUSING 17

2.1.4.2 TASK 10: CONSTRUCTION COST OF A NEW

STANDARD HOUSE; TOTAL ANNUAL PUBLIC

COST DETERMINATION 18

2.1.4.3 TASK 11: , COST EVALUATION OF THE REDISTRIBUTIVE IMPACT ........ 19

2.2 PROJECTING FUTURE HOUSING NEEDS 21

2.2.1 PROJECTING THE HOUSING CHARACTERISTICS

MATRIX . 22

2.2.2 PROJECTING THE POPULATION MATRIX 24

2.2.3 COMBINING THE PROJECTED MATRICES 25

3. AN ILLUSTRATION OF THE NEEDS ESTIMATION METHODOLOGY .... 26

4. THE IMPACT OF A CHANGE IN BUILDING TECHNOLOGY ON HOUSING

NEEDS 38

5. SUMMARY AND RECOMMENDATIONS FOR FURTHER RESEARCH ..... 40

5.1 SUMMARY 40

5.2 RECOMMENDATIONS FOR FURTHER RESEARCH . 40

APPENDIX 1: AN ECONOMIC INTERPRETATION OF HOUSING NEEDS ... 42

APPENDIX 2: DERIVATION OF THE HOUSING STANDARD ... 54

v
LIST OF FIGURES

Figure Page

1.1 The Demand and Supply of Housing 42

1.2 The Demand for Housing Stock and the Demand for

Additions to the Stock 44

1.3 The Housing Market in Equilibrium 45

1.4 The Adjustment of Housing Market to an Increase

in Demand 46

1.5 Consumers' Surplus 47

1.6 Increase in Consumers' Surplus due to a Fall in

Market Price 48

1.7 An Example of the Gains in Consumers' Surplus

Being Greater than Cost — Resulting from a Program Designed to Meet Housing Needs 49

1.8 An Example of the Benefits of Fulfilling Housing

Needs Being Less than the Costs of Meeting those

Needs 51

2.1 The Per Unit Subsidy 54

2.2 Consumers' Surplus Gain 54

LIST OF TABLES

Table Page

2.1 Basic Research Steps in the Calculation of Current

Housing Needs 7

2.2 The Array of Housing Characteristics Required as Input to a Regional Needs Study 9

2.3 Housing Characteristics Matrix 11

2.4 The Cost Effectiveness of Meeting Housing Needs

as a Means of Redistributing Income (Sample

Format) 21

3.1 An Illustrative Housing Characteristics Matrix for

a Hypothetical Urban Region — Renter Occupied

Housing 27

3.2 An Illustrative Population Characteristics Matrix

for a Hypothetical Urban Region — Renter Occupied

Housing 27

vi
Table Page

3.3 An Illustrative Housing Quantity Per Capita Matrix

for a Hypothetical Urban Region — Renter Occupied

Housing 28

3.4 An Illustrative Matrix of Housing Prices for a Hypothetical Urban Region — Renter Occupied Housing 30

3.5 An Illustrative Matrix of Relative Housing Prices for

a Hypothetical Urban Region — Renter Occupied

Housing 30

3.6 An Illustrative Matrix of the Shortfall in Housing

Stock Per Capita Adjusted by Relative Price when

Compared to the Designated Standard or Target 31

3.7 An Illustrative Matrix of Housing Needs for a Hypothetical Urban Region — Renter Occupied Housing 31

3.8 The Real Income Gains of the Occupants of Renter

Occupied Housing Arising from Filling Housing

Needs (Redistribution Effects) 34

3.9 Annualized Net Resource Cost of Implementing re- distribution Effects Associated with Fullfilling

Housing Needs 34

3.10 Cell-by-Cell Ratio of Redistribution Level to Net

Resource Costs of Implementation 35

3.11 Matrix of Housing Needs — Second Iteration 35

3.12 The Real Income Gains of the Occupants of Renter

Occupied Housing Arising from Filling Housing

Needs — Second Iteration 36

3.13 Annualized Net Resource Costs of Implementing

Redistribution Effects — Second Iteration 36

3.14 Cell-by-Cell Ratio of Redistribution Level to Net

Resource Costs of Implementation — Second

Iteration 37

vii

1. INTRODUCTION

The condition, location, size, and quality of the housing inventory

are important elements in the set of factors which describes a country's

standard of living. This is irrespective of the stage of economic

development or the organizational basis of a country's economic system.

Housing is probably the single most important consumer good in most

economies. Housing expense is often the single largest component of a

household's monthly budget. The public attention given housing often

centers around the universal complaint that housing costs too much.

Other problems, slums and squatter settlements, congestion, crime, and

overcrowding become intertwined with and heighten concerns over the

adequacy of an area's housing stock. Miserable housing conditions are

the most visible manifestation of an area's poverty problem.

Such perceptions, if they are to be translated into realistic and

effective public intervention, require accurate assessment and definition of the nature and size of the problems that exist in the housing

area. Providing such measurement is the general purpose of studies of a

country's or region's housing needs or requirements.

The twin pressures of population growth and urbanization are

forcing the developing nations of the world to make careful measure of

their present and future housing needs. Such assessments are an imperative input to the efficient allocation of scarce public resources.

Public housing programs must compete for the public dollar with other

vital social programs.

The purpose of this paper is to clarify some of the issues that are

involved in the measurement of housing need and to provide an implementable housing needs estimation and projection methodology. First we

shall discuss the economic issues involved in housing needs estimation.

Next we shall present in some detail a step-by-step description of the

1
procedures for estimating the current level, and projecting the future

level, of housing needs. A detailed example will illustrate the methodology. Finally we shall discuss the modifications to the methodology

that are implied by the development of a building technology for lowrise/low-cost buildings to better resist extreme winds.

1. 1 The Normative Basis of Needs Estimates

At any particular point in time, a country's or region's housing

need is measured by the number or value of additional units that would

be required to bring the current inventory up to some pre-defined standard of acceptability. Given this definition, the subjective or normative basis of housing "needs" or "requirements" is clear. What is

judged as acceptable housing conditions will vary between countries and

between regions of a country. Differences in the minimally accepted

standard will be influenced by income, methods of construction, climate,

custom, and expectations. Only if the standard of acceptability is

clearly defined and the underlying normative basis for it is widely

agreed upon, will the meaning of the needs estimate be unambiguous and

useful. Often in needs studies the housing standard against which need

is measured is not explicitly stated. Housing needs studies usually

imply their standard through a process of elimination. For example,

often what is done is to examine current housing statistics to identify

the number of housing units which are substandard by some physical

criteria, and then to count or estimate the number of families that are

living in doubled up arrangements. The sum of these components is taken

as the magnitude of unfilled housing needs.

The notion of housing need can be clarified and its subjectivity

modified by examining the economic meaning behind it. By definition

2
an individual is in need if he or she does not have at his or her

disposal an adequate amount of housing stock or housing capital. In

order for the policy maker or reader to judge if the need level is

reasonable an explicit definition of the housing standard or target

level must be stated. A housing need study which only defines situations

in which housing need exists and does not specify the minimum socially

acceptable level that each consumer should have (i.e., how much should

exist) has only fulfilled part of its function.

1. 2 Projecting Future Housing Needs

A housing needs study is concerned with more than the assessment of

the size of the housing gap at present. It also is concerned with

projecting the future position of that gap given certain assumptions

about the path of housing production. Furthermore, a housing needs

study must identify those sectors in the economy which are to receive

the subsidies that are implied in meeting housing needs. These are

difficult research tasks.

To make a projection we must perform three tasks which are at the

conceptual core of a housing needs study. We need to (1) assess the

future standard, which will be influenced by conditions of supply and

demand in the future, (2) to determine the gap between the actual per

capita quantity and the target per capita quantity, and (3) to project

the future size of the population.

In actual practice, it is very difficult, if not impossible, to

obtain accurate projections or forecasts of precisely these constructs,

given the nature of the existing data. In practice, an analyst will

have to rely upon the information that is available. Nevertheless, the

concepts of benefits and costs and the use of an economic model are

useful in defining the nature of the research task and in guiding the

3
specification of a projection methodology. In the next section a

methodology for estimating and projecting housing needs is presented.

The economic conceptual model which guided the development of the

methodology is discussed in Appendix I.
2. A NEEDS ESTIMATION AND PROJECTION METHODOLOGY

Two general research strategies can be used to determine current

and future levels of housing needs. The first may be termed the national approach. In this approach the current and future inadequacies of

the housing inventory are analyzed from a national perspective. A

standard or target is determined and a country's housing stock is measured against this national standard. Usually a governmental housing or

planning agency located in the central government is responsible for

this type of research.

The second basic strategy is a decentralized approach to housing

needs research. This approach requires that regional housing or planning agencies complete housing needs studies for their respective jurisdictions and that the local current and projected levels of housing

needs be summed to obtain the national need.

Let us examine some of the factors supporting the regional or

summation research strategy for the determination of housing needs.

Many of the same arguments used to indicate the inappropriateness of

expecting that some housing standard would be applicable across countries support the view that a single national standard would be inappropriate to apply across the diverse regions within a particular country.

Of course, the problems of a single standard have considerably less

relevance in a country with a high degree of regional homogeneity.

Examples of such countries are rare, however.

The existence of wide regional divergences and variations in culture, weather conditions, levels of income and development, income

distribution, methods and costs of construction, degree of urbanization,

and expected population growth indicates that a decentralized approach

to housing needs determination is appropriate. The regional approach

enables these regional divergences to be reflected in the separate

5
regional determinations of the housing standard or target. This approach is also consistent with the economic reality that housing markets

are not national markets, but local markets. Regional differences would

most easily be reflected in housing standards if the needs projections

are the products or determinations of those most familiar with their

local housing market conditions.

If a coordinated regional or summation approach is to be feasible

several requirements must be met. First, the regional housing needs

studies must follow a consistent needs estimation and projection methodology. Also, it is necessary that overall coordination and planning

remain in some centralized housing or planning agency since the reconcilation and summation of the regional or local needs studies can only be

accomplished at one point. Finally, the separate needs studies should

share common factual assumptions about future population projections.

Again this requires a centrally located research agency to supply the

regional researchers with consistent population and migration projections.

The purpose of this section is to provide one input to the regional

or summation housing needs research strategy, i.e., a basic methodology

of estimating and forecasting housing needs. The methodology is designed to be flexible. It will accommodate data scarcities and can be

implemented by decision makers with minimal background and/or training

in social sciences.

2 . 1 Estimation of Current Needs

Housing needs estimation involves the assessment of the size and

nature of current deficiencies in the housing inventory and the projection of the future inadequacies in the inventory. Dichotomizing

the research task in this way allows us to keep separate two major

issues: (a) how does one calculate the level of housing need at a

6
particular point in time, and (b) what role does projecting population

growth and housing growth play in housing needs estimated for future

years. We shall first concentrate on the question of the determination

of current needs, and look later to the methodological issues involved

in the projection of housing needs in the future.

The calculation of current housing needs involves 11 basic research

steps. These tasks can be apportioned into 4 major areas of investigation or analysis. (See table 2.1) The first major area of analysis

involves the accurate and relevant description of the housing inventory

in detailed statistical terms.

TABLE 2.1

BASIC RESEARCH STEPS IN THE CALCULATION OF CURRENT HOUSING NEEDS

I. Description of the Housing Inventory

Task 1 . Construction of a Housing Characteristics Matrix

Task 2. Construction of a Population Matrix

Task 3. Construction of a Per Capita (per family) Housin;

Characteristics Matrix

II. Determining the Housing Standard

Task 4 . Selection of Target Cell from the Per Capita Housing

Characteristic Matrix

III. Determining the Needs or Shortfall Matrix

Task 5 . Construction of a Matrix of Relative Housing Values

and Rents

Task 6 . Construction of a Quality Deflator Matrix

Task 7 . Cell by Cell Calculation of Housing Needs

Task 8 . Distribution of Housing Needs by Construction Type

and by Income Class

IV. Calculating the Cost of Meeting Housing Needs

Task 9 . Definition of Low-Income Housing

Task 10 . Construction Cost of a New Standard House; Total

Annual Public Cost Determination

Task 11 . Cost Evaluation of the Redistributive Impact

7
The availability and accuracy of the data set will determine the

overall accuracy and detail that is possible in the final needs calculations. The second area of analysis requires the specification of

the housing standard or target. This will be based on inspection of the

data matrix arising out of the first major task area. The third major

research area involves the conversion of the housing matrix into housing

standard equivalents, and the calculation of cell by cell shortfalls of

the housing inventory matrix. Finally, the housing need level has to be

costed, and this total cost can then be subjected to an analysis of its

cost-effectiveness of redistributing income. If the total income redistribution gains of filling housing needs is less (more) than the

implied resource costs, then a new, lower (higher) standard can be chosen

and the housing needs estimates be reiterated.

2.1.1 Description of the Housing Inventory

2.1.1.1 Task 1: Construction of a housing characteristics matrix

The goal of this task is the construction of a data matrix which

has the number of housing units arranged by locational/tenurial/physical

characteristics and cross classified by the income class of the occupants' households. This matrix in effect will divide the housing inventory into a set of mutually exclusive submarkets.

The characteristics of the housing inventory that are of interest

will include the location of the housing units (rural or urban) , the

tenure class of the housing units (owner occupied, renter occupied, or

squatter) , and the physical attributes of the units (construction type

or the soundness of the condition, or the age). Table 2.2 illustrates a

possible array and organization of the housing inventory. The degree of

detailed subclassif ication will be determined, for the most part, by the

adequacy and detail of the available census data. It would be desirable

if data were available to classify the housing inventory in even greater

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detail than indicated by table 2.2. For example, the subcategory of age

could be made a subset of the construction type category. Another

subset of interest, if data were available, would be by condition of

unit, i.e., sound, dilapidating, or deteriorating.

Once the cell totals for an arra}r have been determined, the next

step is to distribute the dwelling unit totals in each cell among income

classes. It may be that a national census will have the regional dwelling unit data already so classified. If not, a method of distribution

is required."'" Ideally, the data in table 2,2 would be extended into a

matrix as seen in table 2.3. Each cell in this matrix will contain a

measure of the number of dwelling units or the total number of rooms.

2.1.1.2 Task 2: Construction of a population matrix

The goal of this task is to construct a population matrix which in

combination with the housing characteristics matrix of task 1 will

enable a cell by cell computation of housing units per capita. The

column and row headings of this matrix will be identical to that of

table 2.3. However, instead of housing unit data comprising the cellular entries, population data is required.

The construction of the population matrix also may require an

estimation or data development procedure. For example, data on the

population size of urban renters may be available but not be distributed

by income class. In this case it would be reasonable to assume that the

Let us assume that the analyst only has available an income distribution by families or households which is cross classfied by urban

or rural and not by any other housing characteristic. Two alternatives

exist in a situation like this. Either the analyst requests and is

able to get an unpublished cross-classification from the census bureau,

or he or she employs some method of interpolating the totals that are

available, among the construction types. Once again there may exist

some description in a related area which will allow the construction of

reasonable distribution procedures.

10
11
total or urban renters could be distributed by income classes according

to tbe national distribution of the urban population among income

classes. The population of rental income class must then be distributed

according to their division among building construction types. Information for determining this distribution by construction types may be

available from tangential sources such as reports, surveys, or documents

containing estimates of family size by income class. Also data may

exist on the extent of "doubling up", two or more families occupying one

dwelling unit, which in turn is related to the physical characteristics

of dwelling units. These data could be combined using specific assumptions in such a way that the analyst would be able to distribute the

population of an income/tenure class among the construction material

categories. No set rules for data development are available because

each country's data contingencies will dictate the kinds of adjustments

which may be required.

2.1.1.3 Task 3: Construction of a per capita (or per

family) housing characteristics matrix

This task is a straighforward division of the elements in housing

characteristics matrix by the population elements determined in task 2.

The result will be a cell by cell (or submarket by submarket) portrayal

of housing quantity per capita, h^ /pop„ . It permits comparisons

between cells of the amount of housing stock or housing service consumed

by each income /housing type submarket of the housing stock.

2.1.2 Determining the Housing Standard

2.1.2.1 Task 4: Selection of a target cell(s) from the

per capita housing characteristics matrix

This task is essentially one of judgment. The analyst must designate a target which represents the minimal socially acceptable level

of housing consumption per capita. This target, or standard, will be

12
relative to the existing conditions in the current inventory. Thus,

initially the analyst can designate one cell in the per capita housing

characteristics matrix as depicting or representing the highest standard

of housing which should be attained by all household units. Separate

standards can be designated for the urban population and rural population.

In effect, the housing needs analyst makes the initial judgment

that the housing quality and per capita quantity represented by one cell

of the per capita housing characteristics is what should be available

for all. It could be, for example, the kind of urban (and rural) owner

occupied housing of mixed construction consumed by the middle income

class. This particular cell(s) of the per capita housing characteristics matrix is (are) designated as the standard or target cell(s). It

becomes the point from which the adequacy or inadequacy of housing

conditions in the region, as portrayed in the other cells of the matrix,

is measured

The advantage of this procedure lies in the clear meaning of the

standard. Designating, say the housing type and per capita quantity of

a particular income class as the standard is unambiguous and allows the

reasonableness or unreasonableness of the standard to be perceived by

the audience of policy makers. The standard represents an implicit

judgment by the housing analysts about the inadequacy of the income

distribution. The remaining tasks of a needs study can be viewed as

translating such an implicit judgment into explicit terms,

2.1.3 Determining the Needs or Shortfall Matrix

2.1.3.1 Task 5: Construction of a matrix of

relative housing values and rents

The entries in housing characteristics matrix represent housing

units which vary widely in quality. Housing is a very complex gotfd with

13
many factors determining the quality of one unit relative to another.

Thus, the units in the different cells of matrix 1 are in a real sense

non-comparable. The purpose of this task and Task 6 is to arrive at a

means by which the quantity units of matrix one can be adjusted for

quality and thus be susceptible to direct comparison.

The simplest and most sensible measure of variation in quality is

recorded in judgments of the market place in its determination of relative price. This means that if quality adjustments are to be made, a

matrix of average housing prices is required. This means that a matrix

comparable to that described in table 3 must be constructed with housing

value (if owner occupied) , and rental values (if renter or squatter

occupied) as the cell entries.

This is a difficult task and will require expertise and knowledge

on the part of the local needs analyst. Because there is wide regional

variation in the structure of housing prices, the completion of this

task is only feasible at the regional level.

Data may be available on housing prices at the local level. Evidence suggests that such data are difficult to locate. Thus, the

housing needs analyst will probably find it necessary to canvass local

expert opinion in order to ascertain the actual structure of housing

market prices. Of course sample survey techniques are more accurate,

but the cost of a special census of current housing prices at the regional level are prohibitive.

2.1.3.2 Task 6: Construction of a quality deflator matrix

The housing price and rental data matrix of task 5 can now be

converted into a matrix of relative values — relative to the value or

rent of the price of housing in the standard or target cell. This will

result in a cell by cell comparison of the price or rent in any particular cell to that of the price of standard housing. In other words, *

14
this task requires that each cell of this matrix of housing prices and

rents be divided by the price or rent of the standard or target unit.

In order that the value cells in the owner-occupied columns be

comparable to those in the renter and squatter-occupied columns, the

housing values in the owner-occupied columns must be converted into

service values or prices. Thus, if a owner-occupied unit has a stock

value of $15,000, it would be necessary to convert this into a gross

rental value of $1,500. This can be done by assuming a gross rent/price

ratio of a given magnitude based on the following equation:

(2) R/P = Vd + V

k + V

v where R/P = the annual gross rental receipts divided by owner occupied

value

,

Vj = the rate of depreciation, maintenance, and repair expenditures ,

= the tax rate on housing services, and

V

v

= the rate of return on housing services.

The rate of return on housing services will be at least as large as the

mortgage rate currently prevailing in the housing finance market.

2.1.3.3 Task 7: Cell by cell calculation

of housing needs

Housing needs now can be computed for each cell. This will result

in a new matrix, the housing needs matrix. The cell-by-cell computation

is relatively straightforward. For each cell we wish to calculate need

level, . . It will be the product of two terms: the per capita shortfall from the designated standard in housing quantity per capita times

the population in that cell. Equation 3 specifies this procedure. The

first term on the right-hand side of equation 3 represents the per

capita shortfall in cell ij

(3) N.. = (S -h. . . D

±J

) x pop..

po Pij

15
where S = per capita quantity observed in the standard cell.

h../pop.. = per capita quantity in cell i j

,

D.. = the deflator value in cell ij

,

pop^j = the population of cell ij

,

For example, let us assume that the income row i represents the $3,000

to $5,000 income class and the housing characteristic column j is urban

rental housing of medium construction. Assume that the standard cell

has an observed per capita quantity ratio of 1/5 while that for cell ij

is 1/8. Also assume that the rental value deflator D^j is 0.70 (calculated in task 6) and that the cell contains a population of 5,000

(calculated in task 2). This data results in a need estimate of 562.5

units (= [0.20 - (0.125 x 0.7)] 5,000). This means that 562.5 units

comparable to standard units would have to be added to the housing stock

of cell ij , either by new construction or in the form of rehabilitation

of existing units, in order to bring housing in that portion of the

housing inventory up to standard. Thus in this cell the 562.5 units of

standard quality plus the 437.5 existing units of standard quality

(437.5 = 0.7 x 625) add up to a final total of 1,000 standard quality

dwelling units. Thus the goal of 0.2 standard units per capita has been

attained

.

2.1.3.4 Task 8: Distribution of housing needs

by construction type and by income class

The matrix approach has the advantage that the distribtuions of

housing needs by income class or by urban/rural and building characteristic will automatically result from the summation of the row entries

and column entries. Some cells, particularly those in the higher income

rows, will probably contain negative entries in the needs matrix. This

16
means that housing in those submarkets surpasses that of the standard."'"

Thus, when summing the rows and columns of the need matrix the negative

entries should be set equal to zero, indicating that no housing need

exists in those submarkets because the housing quantity per capita

exceeds that of the housing standard specified in task 4.

2.1.4 Calculating the Cost of Meeting Housing Needs

2.1.4.1 Task 9: Definition of low-income housing

Defining a low income dwelling unit is equivalent to defining how

much the low income part of the population is willing and able to pay

for the standard house or dwelling unit which has been defined in task

4. Thus, this task is essentially one of determining that price or rent

level which can be afforded by the poorer part of the population.

The income-class, price data of task 5 can be used to accomplish

the analysis of the income and housing price relationship. The data of

task 5 can be inspected to determine the current average price of

housing which is being paid by each income group. If facilities are

available, a simple regression of housing prices (or rents) can be

estimated as a function of income using the data from task 5. Thus, the

estimated relationship

Y

(4) P. = a + a

*

y + e.

i o 1 x where P^ represent housing prices or rent, Y is the measure of income,

and e^ is the residual, can be used to determine what housing price can

be afforded with a given particular family income, Y. Once the lowincome level of income is defined according to the region's definition

of relative poverty, the maximum price of a low income dwelling unit can

be determined by substituting the low-income cutoff in the estimated

"'"A negative entry will arise in equation 3 when S < h . . x D. . pop . .

17
regression and solving for the price or rent level. Any dwelling unit

renting for a higher price or whose market value implies a higher

inputed rent can not be considered as a low- income house. The differential between the maximum price of housing that the poor can afford

and the price of the standard dwelling unit describes the subsidy per

dwelling unit that will be necessary to fill the low-income populations'

housing needs.

2.1.4.2 Task 10: Construction cost of a new

standard house; total annual public cost determination

The result of task 8 is a detailed estimate of the number of new

standard housing units required to bring the housing stock up to the

socially desirable standard. These estimates are categorized two ways:

by income class and by housing type. In order to determine if these

housing needs are worth meeting, or, put differently, to determine if

the housing standard or target has been set too high, an estimate of the

annualized public costs of filling these needs is required.

A housing needs study does not require an elaborate and detailed

cost estimation. Only an order of magnitude estimate of cost is necessary. The cost concept involved is the annual public subsidy required

to supply standard housing to those who can not afford the cost of

standard housing (See task 9) . The additional standard/needed units

will not be supplied by the building community unless the subsidy is

granted since those for whom the housing is intended cannot afford the

standard house at its going market price.

The main capital costs that require estimation are the average unit

costs of land acquisition and development and the average cost of construction of a new unit which is comparable to the standard or target

unit. These total investment costs can then be annualized using an

appropriate length of life and an appropriate interest rate. The

18
difference between these annualized costs and the average yearly rentals

that the poor can afford represents the annual net resource costs which

must be borne by the public sector.

The total size of the annual governmental housing subsidy, the

public cost of meeting housing needs, can now be computed. The total

public cost can be computed either on a cell-by-cell basis and summed or

computed only for each income class and then summed. Within each cell

or for each income class, the total cost will be the product of the

subsidy per unit times the number of needed units which require subsidization .

2.1.4.3. Task 11: Cost evaluation of the

redistributive impact.

The costs discussed above in task 10 have the primary purpose of

attempting to raise the real income levels of that portion of the population residing in housing which is less than standard. Augmenting the

inventory in those housing submarkets where the need is the greatest

will generate real income increases in those submarkets. The real

income increases will accrue to those who will occupy the subsidized

housing. Also of importance will be the impact on real incomes which

will arise because of the price effect that will occur becuase of the

significant increase in the size of the housing stock. A fall in the

price of housing services should occur because of the increase in

supply. This will raise real income levels by reducing rent levels.

Thus the primary effects of fullfilling housing needs are to be found in

the changes in real income of those at the lower end of the income

distribution. The income increases discussed above are in effect transfer payments. This is the case since the lower housing prices while of

benefit to those not owning the stock (the renters) are net losses of

rental receipts to the holders of the stock. The redistribution from

19
the landlord to the tenant (in owner-occupied units the landlord and

tenant are one and the same) is not done costlessly. The costs discussed in task 10 represent the public sectors' administrative or income

redistribution implementation costs. In evaluating the reasonableness

of statements about housing needs the policy makers of the public sector

should be appraised of the cost effectiveness of these implementation

costs since alternative methods of achieving the same level of redistribution may be available. Thus the last task of the needs estimation

methodology is to assess the size of the potential income redistribution

and to identify the gainers and losers in each cell of the housing

characteristic matrix.

The amount of the income increase (redistribution) within any

particular submarket (or cell in the housing characteristic matrix) will

be measured by the gain in consumers' surplus"'" which will arise because

of the fall in the price of housing services due to the increase in the

size of the inventory needed to bring that submarket up to standard.

Thus if the need level in a particular submarket cell has been

computed to be x percent of the existing inventory, one must ask: What

effect will an x percent increase in the size of the inventory have on

housing prices? Answering such a question presumes knowledge of the

2 price elasticity of demand for housing in that particular submarket.

For the moment, assume reliable information about price elasticities is

available. The gain in consumers' surplus can be approximated by the

3 change in price, Ap , times the existing number of standard units, h,

"''For an explanation of consumers' surplus, see Appendix 1.

2 Price elasticity of demand is discussed in more detail in Appendix 2

3The price change will be equal to the product of the percentage

change in quantity Aq/q times the price per unit in that submarket

divided by the price elasticity of demand.

20
plus one-half times Ap times the additions to the inventory (l/2Ap • Ah).

The cell-by-cell calculations of consumers' surplus gains will, when

summed, yield the income redistribution change that would be associated

with attainment of the housing standard and the elimination of housing

needs. This change in the income distribution can then be compared to

the resource costs or implementation costs which have been calculated in

step 10. It may be that the cost effectiveness of redistribution via

the fullfillment of housing needs is competitive with other programatic

approaches. If the housing needs levels and the income redistribution

gains are not cost effective it may be that the housing standard has

been set too high. A reiteration of the needs estimate may be called

for where a lower standard or target has been specified. The implementation costs will be lower and it may be that cost effectiveness will be

increased. A table like Table 2.4 below can be computed as a means of

explicitly presenting these considerations to the policy maker.

TABLE 2.4. THE COST EFFECTIVENESS OF MEETING HOUSING NEEDS

AS A MEANS OF REDISTRIBUTING INCOME (SAMPLE FORMAT)

(1) (2) (3) (5)

STANDARD

HSG

NEED

ESTIMATE

IMPLEMENTATION

COSTS

INCOME

REDISTRIBUTION

AMOUNT

COSTEFFECTIVENESS

(5)= (4)/ (3)

A

B

C

D

2 . 2 Projecting Future Housing Needs

In the context of the needs methodology discussed above, the projection of future housing needs involves applying tasks 1 through 11 to

data which represent values that are expected to exist in the future

21
projection year. Thus, the housing need analyst will be required to

modify the current needs matrices so they contain projected values.

This section discusses ways in which the projections can be feasibly

accomplished.

2.2.1 Projecting the Housing Characteristics Matrix

The problem involved in projecting the housing characteristics

matrix is in finding a set of factors which when multiplied by the

elements in the housing characteristic matrix of the base or current

period yields reasonable projections of the corresponding future values.

If we let the current housing characteristics matrix be denoted by HCC

,

the set of projection factors be denoted by matrix f , and the projected

f r future housing characteristics matrix by HC , then the conversion of HC

to HC^ can be viewed symbolically as the operation of (in matrix notation)

(4) HC

C F HC

(ixj) ' (jxj) (ixj)

Thus, the housing needs analyst must find a reasonable approximation of

F. To further simplify the problem let us assume that F can be a diagonal matrix, i.e., one in which the non-diagonal elements take on zero

values. If this is the case, then an element of F along the main diagonal will be equal to

he . . (5) f, = —-ii • 3 hc C

..

that is, that ratio of any element i from column j of the future housing

characteristics matrix divided by the corresponding i element from

th

column j of the current housing characteristics matrix. This is equivalent to assuming that all the elements of a given column of the current matrix will grow at the same rate. In other words we are assuming

that urban housing of a given tenure and building characteristic type

will increase at the same rate across all income classes. This is not

22
as restrictive an assumption as it may first appear since it is likely

that a particular kind of housing, say owner-occupied of strong construction, or squatter-occupied of light construction, will be concentrated in a few income classes. This assumption will considerably ease

the problem of projection. Without such an assumption, the housing

needs analysts would be required to make separate projection of each

cell of the current housing characteristics matrix.

The diagonal element of the growth factor matrix will be based

on the net rate of growth:

(6) Fj = (1 + g - d.) n

,

where

gj = the projected annual average rate of gross additions to the

housing stock of housing type j

,

d.. = the projected annual average rate of depreciation from the

housing stock of housing type j , and

n = the length of the period in years over which the projection is

to be made.

Thus, the projection problem is essentially one of determining for

each housing type (for each of the columns of the housing characteristics matrix) reasonable estimates of the net growth rate. The net

growth rate is the sum of two rates as seen above. The rate of gross

additions of housing type j can be based on past experience. Annual

data on new construction by building type, location, and tenure class

can serve as the basis for calculating g_. . If a trend is observable in

a time series of g_. , the value of g^. can be modified to reflect projections of that trend. Annual data on losses from the inventory by

housing type may also be available; if not, alternative assumptions

about the deterioration rate can be substituted. For example, different

lengths of life can be assumed which are based on the kind of construction material used in the dwelling unit. Straight-line depreciation can

23
be assumed and the depreciation rate can be calculated as one over the

average length of life of units of a given construction type. Alternatively, an estimate of the projected rate of net additions (na. = g- - d

can be included. This can be based on comparisons of the size of the •

inventory of housing of type j as revealed in the decennial census for

1970 and the census for 1960.

2.2.2 Projecting the Population Matrix

As was the case in the discussion above, the problem is again one

of finding a set of factors by which the base period population matrix

can be multiplied to yield estimates of future population. A workable

approach to determining such factors even where data is extremely

limited is to multiply all the cell entries in the base period population matrix by a factor, G,

(7) G = (1 + p + nmr)

n

where

p = the rate of natural increase in the population

nmr = the net migration rate of the region

n = the length of the period in years over which the projection is

to be made.

Most central governments develop estimates of the projected rate of

natural increase by region. Similarly, they may project nmr by region.

The population projections can be refined. As was the case in the

housing matrix discussed above, a diagonal population growth factor

matrix, PG, can be constructed. For example, the population growth

factor matrix could assume that all cellular entries will grow at the

same rate of natural increase but that the migration rate within a

region will be positive in the urban sectors and negative in the rural

sectors. Further subdivisions are possible. For example, within the

24
urban sector, the migration rate can be adjusted to reflect differences

by tenure class. Specifically, a higher rate can be assumed for squatter occupied housing than for owner occupied or renter occupied housing.

These rates of migration can be based on recent historical experience

and adjusted according to the conditions that are expected to prevail

over the projection period. Special studies may exist which can allow

the analyst to justify the rates of growth that are entered in the

diagonal matrix. The employment of a diagonal growth factor projection

matrix implicitly assumes that the distribution of income will remain

unchanged between the current and future periods.

2.2.3 Combining the Projected Matrices

The above two projection tasks can now be combined and a per capita

housing characteristics matrix can be constructed for a future period.

This step brings us through the analogous task 3 as outlined in section

2.1.1.3. From this point, there are only slight deviations required

from the remaining calculations outlined for current needs. The procedure for selecting a target cell is identical to task 4. Even the

matrix of relative housing values and rents is best left unchanged from

that calculated for current housing needs. This does not mean that no

price changes are expected to occur. Inflation may in fact exert a

large influence on all housing prices. Nevertheless, since our interest

is in real relative prices, the assumption that the matrix of relative

housing prices and rents task 5 applies to the future period avoids the

construction and estimation of simultaneous housing price determination

models. The housing analyst can then proceed with tasks 6 thru 11, and

obtain estimates of housing needs for a future period.

25
3. AN ILLUSTRATION OF THE NEEDS ESTIMATION METHODOLOGY

The purpose of this section is to illustrate the basic logic of the

needs estimation methodology developed in section 2 of this paper. A

numerical example — strictly hypothetical and highly simplified — has

been developed so as to illustrate the iterative nature of the needs

estimation methodology. This section can not be used as a guide for the

data development and forecasting problems that the needs analyst will

encounter. However, if the analyst follows this example through, he or

she will come to grips with the overall strategy of the recommended

methodology and will be in a better position to develop a data acquisition and forecasting strategy consistent with the goals of this methodology.

Table 3.1 categorizes the renter occupied housing stock of a hypothetical urban area into 15 submarkets based on structural characteristics and on the income class of the dwelling units' household occupants.

Since housing needs will presumably be the most pressing in the lower

half of the income distribution, the matrix has a highly aggregated

income class 5 — wherein 50 percent of the renter occupied housing is

located. As can be seen in this illustrative matrix, 20 percent of the

housing stock is of light construction with 86 percent of these building

units falling into income classes 1 through 4.

Table 3.2 contains hypothetical data on the number of people living

in housing of a corresponding construction type and income class.

Income class 5, which contains 38 percent of the population, consumes 50

percent of the housing services produced by the housing stock. The

entries in table 3.1 are then divided by the entries in table 3.2 to

obtain estimates of housing stock per capita for each of the housing

inventory subcategories. (See table 3.3.) The inverses of the cellular

entries in this matrix reveal the population per housing unit within

26
TABLE 3.1

AN ILLUSTRATIVE HOUSING CHARACTERISTICS MATRIX FOR A

HYPOTHETICAL URBAN REGION — RENTER OCCUPIED HOUSING

Dwelling Units Per Housing Category

Income Strong Mixed Light Total

Class (00's) (OO's) (OO's)

Class 19 4 21 34

Class 2 23 12 15 50

Class 3 21 11 27 59

Class 4 38 20 9 67

Class 5 131 67 12 210

Total 222 114 84 420

AN ILLUSTRATIVE POPULATION

HYPOTHETICAL URBAN REGION

Population Per

Income Strong Mixed

Class (OO's) (OO's)

Class 1 78.94 35.71

Class 2 179.69 97.56

Class 3 151.07 84.62

Class 4 193.88 119.76

Class 5 536.89 335.00

Total 1140.47 672.65

Percent 46.5 27.4

,E 3.2

CHARACTERISTICS MATRIX FOR A — RENTER OCCUPIED HOUSING

Housing Category

Light Total Percent

(OO's)

190.91 305.56 12.5

125.00 402.25 16.4

203.01 438.70 17.1

57.69 371.33 15.1

62.50 939.11 38.1

639.11 2452.23

26.1

27
TABLE 3.3

AN ILLUSTRATIVE HOUSING QUANTITY PER CAPITA

MATRIX FOR A HYPOTHETICAL URBAN REGION — RENTER

OCCUPIED HOUSING

Housing Stock Per Capita

Income Strong Mixed Light

Class

Class 1 .114 .112 .110

Class 2 .128 .123 .120

Class 3 .139 .130 .133

Class 4 .196 .167 .156

Class 5 .244 .200 .192

each subcategory of the inventory. For example, housing of light construction which is occupied by households in income class 1 contains an

average of 9.1 persons per unit (1/0.11 = 9.1) whereas housing of strong

construction occupied by persons in households which fall in income

class 5 contains 4.1 persons per unit (1/0.244 = 4.1). Thus there is

considerable variation among the different sectors of the housing stock

in degree of crowding.

After the construction of the per capita housing matrix, the analyst can either arbitrarily or judgmentally designate one of the cells as

the target or standard cell. The analyst asserts that, say, for example, the kind of housing and degree of crowding typified by those units

which are occupied by households in income class 4 and which is constructed of materials of mixed qualities should be the standard level to

which all the population should have access. (This judgment may or may

not be supported by the rest of the analysis. Thus at this point the

analyst is simply setting a standard as a hypothesis.)

28
Table 3.4 contains hypothetical value data in dollars for the mean

yearly rental value of housing in each of the subcategories. The cell

in row 4 column 2 is the designated standard or target cell. Dividing

all the entries in table 3.4 by the rent per unit of the standard cell

yields table 3.5 — the matrix of relative housing prices.

The matrix of relative prices represents a set of deflators to

apply to the stock per capita quantities contained in table 3.2. Using

relative prices as deflators in effect is assuming that the amount of

housing services rendered by a unit is measured by the number of target

or standard equivalents contained in that unit. For example, if the

standard unit has an annual rental value of SI, 000, and if another unit

is valued at S500, then the second unit is equivalent to 0.5 standard

units. Thus multiplying the units per capita in each cell by the corresponding relative value yields a standardized stock per capita figure.

These figures are then subtracted from the standard or target stock per

capita which is given by row 4 column 2 of table 3.3 in order to determine the cell by cell shortfall of stock per capita. (See equation 3 in

section 2.) Table 3.6 contains such shortfall estimates in per capita

terms

To convert the stock per capita shortfall or housing needs estimates into absolute numbers, the positive entries of table 3.6 are

multiplied by the corresponding population estimates of table 3.2. Thus

table 3.7 contains the first iteration of a cell-by-cell calculation of

needs estimates.

This is the critical point of the analysis. The needs estimates

must now be evaluated as to whether or not they are worth meeting. If

not we must lower the standard or target.

Information on the cost of constructing a standard equivalent is

required. Here we shall assume that the standard or target unit can be

29
TABLE 3.4

AN ILLUSTRATIVE MATRIX OF HOUSING PRICES FOR A

HYPOTHETICAL URBAN REGION — RENTER OCCUPIED HOUSING

Matrix of Annual Rental Values

Income Strong Mixed Light

Class

Class 1 830 510 350

Class 2 960 830 500

Class 3 1,120 970 680

Class 4 1,240 1,000 900

Class 5 1,630 1,180 920

TABLE 3.5

AN ILLUSTRATIVE MATRIX OF RELATIVE HOUSING PRICES FOR A

HYPOTHETICAL URBAN REGION — RENTER OCCUPIED HOUSING

Matrix of Relative Prices

Income Strong Mixed Light

Class

Class 1 0.83 0.51 0.35

Class 2 0.96 0.83 0.50

Class 3 1.12 0.97 0.68

Class 4 1.24 1.00 0.90

Class 5 1.63 1.18 0.92

30
TABLE 3.6

AN ILLUSTRATIVE MATRIX OF THE SHORTFALL IN HOUSING STOCK PER

CAPITA ADJUSTED BY RELATIVE PRICE WHEN COMPARED

TO THE DESIGNATED STANDARD OR TARGET

Shortfall in Housing Stock Per Capita

Income Strong Mixed Light

Class

Class 1 0.072 0.110 0.128

Class 2 0.044 0.065 0.107

Class 3 0.011 0.041 0.077

Class 4 — -- 0.027

Class 5

TABLE 3.7

AN ILLUSTRATIVE MATRIX OF HOUSING NEEDS FOR A HYPOTHETICAL

URBAN REGION — RENTER OCCUPIED HOUSING

Matrix of Housing Needs

Income Strong Mixed Light Total Percent

Class (00's) (00's) (00's) Existing

Units

Class 1 5.7 3.9 24.4 34.0 100.0

Class 2 7.9 6.3 13.3 27.5 55.0

Class 3 1.7 3.5 15.6 20.8 35.3

Class 4 -- — 1.6 1.6 2.4

Class 5

Total 15.3 13.7 54.9 83.9 20.0

Percent of

Existing

Units 6.9 12.0 65.4

31
produced for $10,000. (The analyst will require a realistic construction cost estimate and can not rely on assumption as is done in this

example.) This cost can then be converted to an annualized cost of

$1075. 1

A cell-by-cell calculation of redistribution effects must now

ensue. This will require that the analyst make some assumptions about

the impact that adding new units to each subcategory will have on the

market price within each subcategory. Recall that the main category of

impacts to be considered are consumer surplus benefits — as units are

added to the inventory prices will fall on the already existing housing

and those who do not experience a housing subsidy directly are made

better off because less of their income need be spent on housing. (As

price falls more, housing can be consumed within each cell, and housing

stock per capita is increasing)

.

Returning to the problem at hand, let us see what will happen in

terms of real income effects going to renters in the row 1 column 3

cell. The need estimate in this cell calls for an extra 2,440 units.

Currently this cell contains 2,100 units. The current market price of

housing in this cell is $350. If the price elasticity of demand is -1.0

(an x percent change in price will lead to an x percent change in quantity) then increasing quantity by 116 percent (2,440/2,100 = 1.16) would

2 lead to a price decline to zero. Thus consumer surplus gains would

equal 2,100 x $350 + 2,440 x 1/2 x $350 - $1.16 million. These benefits

^-This calculation assumes a 25 year life, a 10% interest rate

and a scrap value of $3,000.

2 Zero is assumed because negative prices are not meaningful.

32
would arise if 2,440 units are produced at an annualized cost of $1,075

and given away to the residents of this housing submarket. The annualized cost of implementing the redistribution of $1.16 million will be

$2.58 million (2,400 x $1,075). Table 3.8 contains the cell-by-cell

computation of redistribution impacts based on a price elasticity of -1.0

The results in table 3.8 show that the aggregated redistribution

effect of meeting the designated target or standard. Table 3.9 contains

the estimates, cell-by-cell, of the annualized cost of administration or

implementation. Table 3.10 computs the cell-by-cell ratio of redistribution level to administration costs.

For a second iteration we set the standard or target as those

housing conditions obtaining in row 3, column 3 (income class 3 of light

construction). Table 3.11 recomputes the matrix of housing needs based

on this new and lower standard or target. Table 3.12 recomputes the

matrix of cell-by-cell redistribution effects and table 3.13 recomputes

the matrix of net resource costs. Let us assume that the housing industry can reproduce this lower quality unit for $6,000 because of

special scale advantages that are associated with producing such units

in large numbers. We shall assume that these units will have a 20 year

life, zero scrap value and that the interest rate is 10 percent. Thus

the gross annualized cost will be $705 per unit, prior to any rental

collections from those occupying the new units. Table 3.13 is based on

the net annualized costs per unit. Again we have assumed in tables 3.11

through 3.14 a price elasticity of -1.0.

This second iteration produces a considerably lower need level and

an annualized net resource cost approximately seven times lower then the

first case. Also the real income gains accruing to the row 1, column 3

cell are only 40 percent lower than those computed under the first

33
TABLE 3.8

THE REAL INCOME GAINS OF THE OCCUPANTS OF RENTER OCCUPIED

HOUSING ARISING FROM FILLING HOUSING NEEDS (REDISTRIBUTION EFFECTS)

Income

Class

Class 1

Class 2

Class 3

Class 4

Class 5

Total

(Millions of Dollars)

Strong Mixed

0.623

0.887

0.198

0.296

0.659

0.393

1.708 1.915

Light

1.16

0.960

1.366

0.157

3.643

Total

2.079

2.506

1.957

0.157

7.266

TABLE 3.9

ANNUALIZED NET RESOURCE COST OF IMPLEMENTING REDISTRIBUTION

EFFECTS ASSOCIATED WITH FULLFILLING HOUSING NEEDS

Income

Class

Class 1

Class 2

Class 3

Class 4

Class 5

Total

Strong

.433

.351

.007

(Millions of Dollars)

Medium

.414

.422

.144

0.791 0.980

Light

2.623

1.354

1.228

0.038

5.243

Total

3.470

2.127

1.379

0.038

7.014

34
TABLE 3.10

CELL-BY-CELL RATIO OF REDISTRIBUTION LEVEL TO

NET RESOURCE COSTS OF IMPLEMENTATION

Income Strong Medium Light Total

Class

Class 1 1.44 0.71 0.44 0.60

Class 2 2.53 1.56 0.71 1.18

Class 3 28.29 2.73 1.11 1.42

Class 4 — — 4.13 4.13

Class 5

Total 2.16 0.51 0.69 1.04

TABLE 3.11

MATRIX OF HOUSING NEEDS — SECOND ITERATION

Income Strong Medium Light Total

Class (00's) (00's) (00's)

Class 1 — 1.8 14.7 16.5

Class 2 — — 5.5 5.5

Class 3

Class 4

Class 5

Totals 0 1.8 20.2 22.0

35
TABLE 3.12

THE REAL INCOME GAINS OF THE OCCUPANTS OF RENTER OCCUPIED

HOUSING ARISING FROM FILLING HOUSING NEEDS - SECOND ITERATION

(Millions of Dollars)

Income Strong Medium Light Total

Class

Class 1 — 0.113 0.695 0.808

Class 2 — -- 0.325 0.325

Class 3

Class 4

Class 5

Total — .113 1.010 1.123

TABLE 3.13

ANNUALIZED NET RESOURCE COSTS OF IMPLEMENTING REDISTRIBUTION

EFFECTS -- SECOND ITERATION

(Millions of Dollars)

Income Strong Medium Light Total

Class

Class 1 — .076 .875 .951

Class 2 — — .210 .210

Class 3

Class 4

Class 5

Total — 0.076 1.085 1.161

36
TABLE 3.14

CELL-BY-CELL RATIO OF REDISTRIBUTION LEVEL TO NET RESOURCE

COSTS OF IMPLEMENTATION — SECOND ITERATION

Income

Class

Strong Medium Light Total

Class 1 1.48 0.79 0.85

Class 2 1.55 1.55

Class 3

Class 4

Class 5

xotal 0.93 0.97

set of assumptions. In that cell the ratio of redistribution gains to

implementation costs has nearly doubled.

Alternative assumptions about demand elasticities could be employed

in further iterations. For example it may be reasonable to assume

greater inelasticity in the lower income classes. This will improve the

redistribution to resource cost ratios because smaller additions to the

stock in those cells will have a greater impact on market price. Thus a

lower standard would, with a lower associated annualized cost of implementation, generate larger income gains. As alternative need estimates

are generated under different assumptions a table like that of table 2.4

can be generated.

This example illustrates that selecting a standard and computing a

level of need will not be an easy matter. Hopefully, even though this

example is incomplete it should serve to give the methodology outlined

in section 2 a degree of concreteness which will highlight the key problems and issues that are involved in needs estimation.

37
4. THE IMPACT OF A CHANGE IN BUILDING TECHNOLOGY ON HOUSING NEEDS

In this section we shall explore the effect that improvements in

building technology will have on the level of housing needs in the

future and we shall discuss ways in which anticipated changes in housing

technology can be incorporated into the housing needs estimation methodology.

A good example of anticipated technology change involves building

technology research which is related to the impact of high winds on low

rise buildings."'" Extreme winds are a primary contribution to building

damage and destruction in some developing countries. For example, in

the Philipp ines between 1948 and 1971 there were 482 typhoons. Similar

experiences with high winds are found in Jamaica and Bangladesh.

If building technology develops methods of construction which are

relatively low-cost and which result in substantial increases in the

ability of low-rise buildings to withstand extreme x^inds there will be

two major economic impacts which could be incorporated into a housing

needs estimate.

First, the units which embody the new technology will have longer

expected lifetimes than those that do not. This will lower the overall

depreciation rate for the existing stock and will result in larger

actual stocks at some future date. Coupled with this technological

factor is a demand factor. Demand for new construction will also increase. This will be so because the lowering of the depreciation rate

will cause a basic shift in the relationship between rental income and

housing value. Longer expected lifetimes results in greater rates of

return to a housing investment. This will result in greater demand for

housing than would have been the case if no technological change had

Any building technology research that leads to buildings more

resistant to natural disasters could be used in this example.

38
occurred. This means that more units will be purchased over time and

that the actual stock of housing anticipated to exist at the future

projection date will be larger. The gap between the desired level of

housing stock and the actual level will be lower. (These effects will

be offset in part if the new technology causes the price of new housing

to increase significantly.)

The growth factor matrix must be judgmentally modified if the new

technology is to be anticipated in the needs projections. The annual

average rate of gross additions will be higher because of the demand

affect discussed above and the annual average rate of depreciation will

be lower because of the increases in exprected building lifetimes. The

actual percentage modifications that need to be made to these two elements will be determined by conditions which differ country by country.

The needs analyst could provide alternative forecasts based on high,

low, or zero building technology change assumptions.

39
5. SUMMARY AND RECOMMENDATIONS FOR FURTHER RESEARCH

5 . 1 Summary

Determining the size of a region's unmet housing needs is an important first step to planning and enacting public policies and programs

which will improve the condition, size, and quality of a country's

housing inventory. The assessment of current and future housing needs

is particularly important in the developing regions of the world where

the twin pressures of population growth and urbanization especially

aggravate the housing problem..

This study has developed a basic methodology of estimating and

projecting housing needs. Procedures have been developed to compare the

costs with the potential redistributive impacts of meeting the housing

need shortfall. This methodology has been designed to be flexible and

adaptable to situations in which housing and demographic data may be

sparse. The methodology is consistent with the economic constructs

which make the concept of housing needs meaningful.

Finally, this study has shown that in countries where natural

disasters such as high winds or earthquakes occur relatively frequently,

the development and adoption of new wind or earthquake-resistant building technology will have a mitigating effect on a region's future

housing need.

5.2 Recommendations for Further Research

^ One of the inputs to this paper's housing needs methodology is

demand for housing information. Housing needs studies could be considerably improved in terms of accuracy and reliability, if reliable

estimates of price elasticities of demand and supply existed at the

regional level. Thus, much work could be done on developing and estimating regional models of housing demand and supply. This is particularly critical in those regions of countries where housing problems

are the most pressing.

40
Further work is needed on understanding, first conceptually, and

secondly, empirically, the market process in squatter settlements. Both

tasks would necessitate special modeling of the squatter settlements as

specialized submarkets of the housing inventory. Parallel empirical

investigations of the economics of squatter settlements would deepen our

understanding of the specific problem areas and work to feed back a

sense of priorities into the conceptual work.

Specific empirical research on the housing market impact cf the

development of new construction methodologies and design criteria could

also be undertaken. Although we have some idea as to the direction of

the effects that extreme wind research will have, more detailed information on the probable impacts of this technology on both the stock

demand for housing and the supply of new housing units would enable

those countries affected by high winds to be more fully appraised of the

benefits of developing such a new technology.

41
APPENDIX I

AN ECONOMIC INTERPRETATION OF HOUSING NEEDS

The needs estimation and projection methodology of section 2 has

been constructed around a basic conceptual framework. This appendix

analyses the economic elements which underlie the notion of housing

"need."

In figure 1, the demand curve for housing is labelled as DD

.

Assume that DD reflects the demand for housing services by a typical

family unit. The total amount of housing stock per family in existence,

the fixed supply of housing, is represented by the vertical line SS.

Assume that each unit of stock renders one unit of housing service. The

intersection of the demand for housing services curve and the fixed

supply determines the current price per unit of housing (P in figure 1)

.

s

I

!

i

l\

1

1

>D

s

I

1

QUANTITY OF HOUSING

SERVICES (STOCK) PER

FAMILY

Figure 1. The demand and supply of housing.

42
Let us assume that quantity of housing per family is measured in

square feet of living space. The equilibrium quantity of housing services (stock) per family, hg, may be less than that which is deemed to

be the minimally socially acceptable amount of housing space per family.

Assume for a moment that h* represents the judgment of that amount

of housing services per family which is minimally acceptable. The total

housing need in this instance will then be (h*-^) x N (number of families) . Of course h* may have been defined to be either larger or

smaller than shown on figure 1. What information could be developed

which would help guide the determination of where the standard ought to

be?

In order to arrive at some conceptual guidelines for determining

the standard from which housing need is to be measured, it is necessary

to discuss the economics of the housing market. The housing market is

composed of two basic markets whose interaction determines housing

prices and the amount and kind of new construction. Economists generally describe housing as a stock-flow market.

First there is the stock aspect of the housing market. Consumers

can be described as having demand for a quantity of housing services

which are associated with a particular size of the housing stock. Such

demand will be dependent upon the market price, the level of income, the

market rate of interest, and a number of other factors. Figure 1 portrays the interaction of demand with the fixed stock supply. In figure

2, flow demand (dd) , the demand' for new construction, is derived from the

demand for housing stock. At the price Pg in figure 2, given the existing

stock of size hg, there exists zero demand for additional units. (See

panel B.) The actual size of the housing stock is in agreement with

consumers' preferences. However, at price P-^, consumers would be

willing to purchase hn units of housing service (stock). Thus, we see

43
Figure 2. The demand for housing stock and the demand for additions to the stock

in panel B that the demand for new construction at price will be h-^

minus h^units. Similarly, if price were F^, consumers would be faced

with too large an inventory of housing stock. At that high a price the

flow demand would be negative, hj minus hg and holders of the stock

would depreciate the stock by undermaintaining the existing inventory.

The housing construction industry responds to the flow-demand for

housing. Since housing construction approximates a competitive market,

little reality is sacrificed if we add to the flow side of the market an

upward sloping supply curve which describes the number of new housing

units that housing producers would be willing to build at each particular service price. (Curve ss in figure 3.)

Figure 3 portrays the stock-flow housing market in equilibrium.

The actual size of the housing stock, h , is such that at the equilibrium price, Pg, the desired stock is equal to the actual stock and the

level of net construction will be zero.

44
Figure 3. The housing market in equilibrium

If we introduce into this balanced equilibrium world a change in

some underlying factor, be it an increase in income, a fall in the rate

of interest, or a change in consumer tastes for more housing, which

causes demand to increase, the service demand function and flow demand

function for housing will both shift up. Graphically, in figure 4, this

would be illustrated by a shift up in demand from D^D^ to ^2^2 anC* "'" n

flow demand from d^d^ to ^2^2' ^1 W&S t^e P rev^- ous equilibrium price.

It will not be maintained in the face of the increased demand. Price

will immediately rise to . The price of housing will fall by the end

of the first period r to P , because of the new construction activity

n

J which is generated in the flow market (panel B of figure 4) . The intersection of d„d„ and the flow supply curve ss determines P . At the new

2 2 rr n

end of period price, P , the housing industry will be producing Ah

units per year. As these units are added to the existing inventory the

flow demand schedule will fall because the housing stock of panel A will

be growing. The size of the stock after the end of the first period

45
NEW CONSTRUCTION

PER PERIOD

STOCK

Figure 4. The adjustment of the housing market to an increase in demand

will be (h„ + Ah) and the flow demand will be shifting down. Eventually, as the stock continues to grow and flow demand continues to fall

the housing market will reattain the long-run equilibrium price of P .

The meaning of "housing needs" can now be put in the perspective of

a stock-flow housing market analysis. Using such an analysis can shed

some light on the issues that are involved in determining the minimally

acceptable standard which is set as the target in a housing needs study.

The obvious principle behind the establishment of a housing standard is

to set a target that is worth filling. Often, in housing needs studies,

the standard is set implicitly without considering the cost of attaining

it. Determining a housing standard is equivalent to the specification

of an amount of income redistribution that ought to take place. Accomplishing a given size of income redistribution will entail real resource

costs. Explicitly identifying the size and beneficiaries of the income

redistribution which is implied by a specific housing standard and
asking how much it will cost in terms of resources will clarify the

tradeoffs that are involved when discussing the concept of housing

needs.

The following discussion provides an approach for determining the

resource costs and income redistribution gains associated with reaching

a target level of the housing stock. Before the redistributive nature

of housing needs can be clearly seen we must consider the notion of the

"benefits" associated with any investment, e.g., housing, which has as

its object the reduction of the cost of a product or service. (Primary

to the notion that a housing "problem" exists is the impression that

housing is too expensive.) In these instances the basic measure of

benefits can be thought of as a measure of "consumers' surplus." In a

market situation (see figure 5), consumers purchase x^ units of goods at

price P^. The dollar costs to consumers for these units is given by the

u

M

PiyW. Consumers Surplus

B

COST

C v— X,

Figure 5. Consumers' Surplus

QUANTITY

area OCBA. The total dollar value to consumers of the OC units can be

measured by the area under the demand curve, OCBD. Thus, consumers

realize a surplus of the amount ABD in their valuation of the x^ units

over their costs. This amount, ABD, is known as consumers' surplus.

47
The benefits to consumers of a fall in the price of a product due to

increased supply can be illustrated in a like manner. In figure 6, if

price falls from to ?2 consumers will realize an addition to their

consumers' surplus of the amount DCBA.

QUAIJTITY

Figure 6. Increase in consumers' surplus due to a fall in market price

Programs which fulfill unmet housing needs are of direct benefit to

those which occupy the new, standard, subsidized housing which has been

built to satisfy the housing need. In addition to these direct beneficiaries, other groups will reap benefits which arise because of increases in consumers' surplus which will occur because of the impact of

the needs fulfillment programs on housing prices."'"

Returning to the stock-flow framework, the fulfillment of housing

needs will result in addition to the stock of housing which will lead to

lower housing prices for the rest of the inventory and corresponding

In addition to the redistribut ive effects which arise because of

changes in consumers' surplus, housing programs may also generate other

benefits. Examples of these are increases in sanitation and subsequent

reductions in ill-health, reduction of density and subsequent lowering

of crime rates, and increases in worker productivity because of the

better housing conditions. These by-products of housing programs may or may not exist. In fact, a new housing program could aggravate crime rates, worsen the sanitation problem, and increase densities. Evaluating these

other non-market benefits can only be done in the context of a specific

housing program. They are not generalizable like the consumers' surplus

effects. Thus, the non-market benefits can not be dealt with in this paper.

48
gains in consumers' surplus. Figure 7 illustrates this process. If we

start off in an equilibrium position at price P in figure 7, but assert

UNITS NEW CONSTRUCTION

OF PER PERIOD

(A) STOCK (B)

Figure 7. An example of the gains in consumers' surplus being greater than costs —

resulting from a program designed to meet housing needs

that the housing stock is not up to the desired standard of h*, in order

to secure h* prices must fall to P-^. Those occupying the existing units

will benefit by an amount of EDBA because of the fall in price from Pg to

P^. This dollar amount of gain can be considered to come at the expense

of the existing owners of the stock since they will experience an equivalent loss in rental income. Thus one effect of realizing h* will be

to redistribute income from one group (landlords) to another group

(tenants). Additionally, area DCB will .also be confered to those

who enter the housing market in response to the fall in price from Pg to Pi."^

^Society need not impose the cost of income distribution only upon

the landlords. General tax revenues can be used to compensate landlords

for their losses.

49
In figure 7 the shaded area in panel A can be thought of as the

amount of income redistribution that is accomplished by attaining h*.

But in order to provide the extra (h*-h) units the housing construction

industry will require that the housing price be Po. The total incremental resource cost of the (h*-h) units will be ?2 x (h*-"h) . Since

igUre 7 the ah ,deri consumers will pay P, , but Tibtf-iPus, ifehe. resource costs which must be met- amount of , P .. 1 - T 1 '• can be tbn„ • by the public sector will be c ^P£ fhS*j)-fgj (h*-h) , (See the shaded area

in panel B of figure 7.) This-"- subsidy...cost, per unit times the extra "

number of units represents the resource costs borne by the public Vector

of achieving the income redistribution effect of ECBA.

, , The income redistribution will arise as these extra units are "added

V tBe f,ubJi ' Sector „U,

' ;

< Bust ,,. . . •to the inventory and a fall in price is dispersed across the rest of the

• n Panel B 0 f fi . ~' '•) (See the s

- occupied inventory. Price wlli'Tall to P.^ given the subsidy, ancl'the

users of the existing stock, will realize a consumers' surplus gain from

the lower prices.

It will not always be the case that the amount of redistribution

will be larger than the public cost of achieving that level of redistribution. Consider figure 8, where the subsidy required, P-^HTP2, is

greater than the gain in consumers' surplus, DCBH. In this case, meeting the current housing need of (h*-h) confers much less in the way of

redistribution change per dollar of resource cost than depicted in

figure 7.

Within the context of this stock-flow model, three factors interact

to determine how expensive the income redistribution associated with a

particular minimal standard or target (specification of h*) will be.

They are: (a) the price elasticity^ of the stock demand for housing,

-'"The elasticity of demand is the ratio of the percentage change in

quantity demanded divided by the percentage change in prices. The

elasticity of supply is the ratio of the percentage change in quantity

supplied divided by the percentage change in price.

50
-

l-l

Pa

Gain in Consumers

Surplus

UNITS

OF

STOCK

Net Resource Cost

(h*-h)

NEW CONSTRUCTION

PER PERIOD

Figure 8. An example of the benefits of fulfilling housing needs being less

than the costs of meeting those needs

(b) the price elasticity of the supply of new construction, and (c)

the relative size (as a percent of the size of the existing inventory)

or the housing needs gap. (See appendix 2 to this paper for a more

detailed discussion of these conditions.) These factors can be manipulated to describe one upper limit of the housing standard. The size

of the housing gap (h*-h) can be expressed as a fraction of the original

size of the housing stock, i.e., as 3 x h where B is a constant multiplier equal to (h*-h)/h. This gap parameter can be used to describe

where a housing standard, h* max. implies net resource costs equal to

the amount of income redistributed. In equation (1), h* max. is the

size of the stock of housing such that any additions to the stock past

h* max will result in a housing needs construction program whose public

sector resource costs are greater than the dollar value of its redistribution impact.

51
(1) h* = h + 3*h max

In this model 3* depends on the ratio of the stock demand price

elasticity of housing tc the price elasticity of new construction

supply. If the standard set in a needs study implies a standard where 6 > 3*,

then the housing standard specifies that achieving $1 of income redistribution entails more than a $1 net resource cost. If 8 < 3* , fulfilling housing needs will result in housing programs where the redistribution gains are greater than the net resource costs which must be borne

by the public sector.

Although it is the case that housing needs studies are bound to

involve normative elements, the discussion above implies that there are

economic factors relating to the real resource costs of redistribution

which can guide the setting of the housing standards. These factors are

rooted in the housing market characteristics of a particular economy.

The first economic characteristic of impact is the price elasticity of

demand. It will depend upon the underlying tastes and preferences of

the consumers in a particular area. It will be influenced by an area's

level of income. Of equal importance is the elasticity of supply. It

also will deoend upon many institutional factors which vary across

economies. The degree of competitiveness in the housing industry, the

level of production technology employed \tfithin a particular country, and

the responsiveness of the housing industry to innovation are three

underlying factors. Nevertheless the desire for greater equity"'" and a

willingness to use the housing market as a tool to increase equity,

fundamentally lies in the hands of the public policy decision makers. A

housing needs study can be used to specify the real resource costs of

"'"Greater equity is concerned with the redistribution of income from

higher income groups in the population to those at the lower end of the

distribution.

52
achieving greater equity. However, other methods are available to the

public sector for income redistribution, e.g., negative income taxes,

food subsidy programs, and the non-enforcement of laws against theft.

The cost effectiveness in redistributing income housing programs must be

compared to these other alternatives.

The income redistribution goals of housing or other welfare-type

programs generally are not examples of potential Pareto^ improvements.

Thus care should be taken not to interpret cost-effectiveness computations as ranking redistribution schemes on the basis of efficiency

grounds. whether or not the equity or redistributive effects of such

programs are justifiable must be decided, not on economic grounds, but

on the views of the policy makers towards the desirability of attaining

a more equitiable distribution of income at some cost to real income.

A potential Pareto improvement is one in which an economic re- arrangement can result in the gainers being able to more than compensate

the losers. In the case of filling housing needs the gainers (the

tenant classes) will not be able to compensate the losers (the landlord

classes) and still remain better off.

53
APPENDIX 2 - Derivation of the Housing Standard

The resource costs borne by the public sector of a housing program

designed to meet the gap in housing needs will be distance AB in figure

1 times the size of the gap, which will be 3 h. Distance AB will be

PS

uo

H

V.

NEW CONSTRUCTION

the sum of the change in price, CB, that moves along the demand curve,

dd, (APd) plus the change in price resulting from moving along supply

curve, SS, distance CA, (AP ) . Thus, the subsidy cost, SC will be

(1) SC = (APd + APs) 6 h

The redistributive effect can be measured as the increment in

consumers surplus under the stock demand. function of Figure 2.

w

uH

o APd

h h*

UNITS OF STOCK

54
It will be the change in price APd times h plus (utilizing straight

line demand curves) 1/2 APd x 8h. Thus the benefits, B, will equal.

(2) B = APdh + 1/2 APd ph

Setting redistribution effects equal to implementation costs, we

can proceed to solve for the value of 3 which can be used to determine

the housing standard at which implementation costs are matched by income

redistribution effects.

(3) (APd + APs) Bh = APdh + 1/2 APdBh

Rewriting (3)^

(4) 2 APdBh + 2APs 6h = 2 APdh + APdBh,

Subtracting APdBh from both sides and dividing by h • APd yields

(5) B + 2B A Ps/

Apd

= 2

j since APd = 3h • ? E

' 1 and APs = Bh ^ , Ed • h Es • h

(where Ed is the price elasticity of demand and Es is price elasticity

of supply) then Equation (5) can be rewritten

(6) 1/2 + |^ = 1/3, Es I which can be rewritten to solve for B

(7) B = 1/2 || - l t

Interpreting equation 7 yields the following conclusions:

the greater the size of the gap between the standard and the

actual size of the inventory, the less likely it will be that the housing needs are worth filling,

knowledge of the degree of price elasticity of stock demand

and flow supply is an important input in the determination of housing

needs,

a combination of very elastic demand and very inelastic supply

will combine to make housing needs not worth filling, and

a combination of inelastic demand and elastic supply combine

to make the filling of housing needs socially profitable.

55

APPENDIX H

Housing in Extreme Winds

Housing

in extreme

winds

A study of the socio-economic and

architectural aspects of low-rise,

low-cost housing in three developing

nations characterized by high wind

conditions

Prepared for the

Office of Federal Building Technology

Center for Building Technology

National Bureau of Standards

Washington, D. C. 20234

By Stephen A. Kliment AIA

663 Fifth Avenue

New York, N.Y. 10022

Report Presented at Regional Meeting on Development

of Design Criteria and Methodology for Low-Rise/Low-Cost

Buildings to Better Resist Extreme Winds

Report

This report reviews the socio-economic and the

architectural aspects of low-cost, low-rise

housing in three developing countries subject

to extreme winds: the Philippines, Jamaica

and Bangladesh.

The information is based on a review of over

30 printed resources (listed on pages 47 - 50)

In addition, the following individuals

kindly contributed useful information and

suggestions

John Edmondson, Paul Campbell (International

Cooperative Housing Development Association)

Wallace Campbell (Foundation for Cooperative

Housing); Ignacio Armillas, Giovanni Carissimo,

Evner Ergun, Alberto Gonzales-Gandolfi,

Rafael Hora-Rubio, Mario Piche and Ludwig

Van Essche (UN Center for Housing, Building

and Planning)

Stephen A. Kliment

June 27, 1975

1
General data/3

Socio-economic factors/4

Housing characteristics/15

Review by count ry/22

The Philippines/23

Jamaica/ 29

Bangladesh/ 35

Conclusions/ 45

References/47

2
General data

3
1361

factors

The safety aspects of low-cost, low-rise

housing have always been at the mercy of

tradition. Cultural patterns, socioeconomic restraints and technical expertise

(or lack of it) can both enhance and be a severe barrier to innovation. Thus, understanding a nation's socio-economic profile,

the characteristics of its housing and its

administration, is a vital matter.

The comparative socio-economic profile as outlined in Table 1 tells us a good deal.

For one thing, all three countries have a very high density of population. It ranges

from 317 persons per sq . mile in the

Philippines to 1,361 per sq. mile in

Bangladesh, one of the highest in the world.

Compare this with the U.S. density of 56 and

the USSR, which has only 26 persons per sq.

mile

.

These figures do not tell us the whole story.

In all three of these developing countries

there is a strong migration from the country

to the cities. The major cities in all

three have teeming squatter towns.

In the Philippines, one person in 16 lives

in squatter towns, which as of 1970 were increasing at the rate of 12 percent a year.

In Jamaica, squatter towns are illegal but

growing

.

—
^

Table 1: COMPARATIVE CHART OF SOCIO-ECONOMIC CHARACTERISTICS

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Over and above all this, the populations have

been rising at a steady rate, from a low of

1,46% per year in Jamaica (which has suffered

emigration of its most skilled workers) to 2.6 percent per year in Bangladesh and

slightly over 3 percent in the Philippines.

Furthermore, even though infant mortality

has been dropping and lifespan rising through

improved health care, citizens in these

countries tend to live less long and this has

led to a very high proportion of youngsters

under 15 years. (For example, in a not

untypical part of Kingston, Jamaica, known

as Delacree Pen, nearly half the population

is under 15)

.

By tradition and necessity this has forced

onto housing such normally distinct functions

as day care, education and play to accommodate

this many youngsters.

•There are other ramifications to these

population patterns. The economics in all

three countries are highly labor intensive,

so that children are in the Philippines, for

example, seen as an economic asset. Family

planning efforts designed to bring population

more in line with food and other resources

run up against this barrier. This is especially

true in rural areas where agriculture is the

main source of income.

Despite city migration, most of the populations

are still classified as rural (68% in Philippines,

90% in Bangladesh, over 60% in Jamaica).

•Several other socio-economic factors stand out

strongly. Foremost is the tremendous over- crowding of available housing. In the

Philippines, average household size is 6 persons. The typical household has only two rooms (in Manila three) . The median number

of persons in a room in the Philippines is

2.7. In Bangladesh, the average number is

3.2. It is common for several generations

(so called "extended families") to make up a single household.

©There are these other factors: shortage of

funds, markets not large enough to stimulate

economics of scale in prefabricated construction, undeveloped transportation and

distribution systems, a shortage of skilled

labor and, by and large, low standards of

workmanship

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Another factor is the resistance by the

population to certain construction materials

and systems. Adobe blocks are not considered

"noble" when compared with brick or stone

in many countries.

An experiment carried out in Peru some years

ago using igloo-shaped houses made of

polyurethane were rejected because families were unhappy with the lack of corner areas where one could put "things out of the way",

predictably bad interior acoustics, and a lack of normally defined property lines in

which to fence in animals. They were

eventually abandoned

Most families cannot afford housing on the

open market and in many cases not even housing subsidized by the government. With

some exceptions, private housing is better

so far as wind resistance is concerned, but

those who cannot afford housing of any kind

range from 65% in the Philippines, 67% in

Jamaica up to a high of 72% in Bangladesh.

Consequently, the very poor must fall back

on government public housing programs

(which are modest in all three countries)

or build their own housing according to demonstrably unsound wind-resistant

principles

©•"Uncontrolled settlements'

"Uncontrolled settlements", a term which

covers "bustees", squatter towns, and

"transitional communities", have come in for

sharp comment as to their socio-economic

merit in developing countries. Following

is a summary of arguments for and against

this complex phenomenon:

•Contributions to a sound urbanization

process.* (Ref. 15)

1. They provide migrants with housing at

rents they can afford

2. They serve as a reception center for

migrants, helping them to adapt to

urban life

Within their own society they are a source of jobs in small-scale and

marginal enterprises

7
They provide accommodation at a reasonable

distance from sources of jobs in the

adjoining town or city.

The communal organizations provide support

during unemployment and other difficult

times (a study by a Presidential Council

on the Squatters of Manila, the Philippines,

found, in a squatter community of 2,625

families, 29 organizations, with 65% of

family heads interviewed belonging to at

least one organization — Ref. 16).

They encourage (and reward) small-scale

private enterprise in the field of squatter

housing.

In many cases, they provide their own security system of a caliber that

Government would find very costly to furnish.

•Limitation

Some planning professionals question the

merits of uncontrolled settlements, due

to the public health, educational, family

health care, circulation and other problems

which these settlements find hard to solve.

The absence of "sites and services" aggravates these conditions.

#Six fallacies

Several fallacies of thought have arisen around

the squatter town problem:

1. "The more you improve squatter settlements , the more migrants you attract."

Response : Social and economic stimuli

will continue to attract immigrants to urban areas no matter what the living

conditions

.

8

" '!

i
2 . "Improvements in rural areas can significantly reduce urbanization." (Ref. 17)

O Response : "Without urbanization and

industrialization, there is little

prospect of rural development. The

real question is: T how is it possible to

prevent the exchange of rural poverty for

urban misery?'"

3. "Population control measures can substantially effect urbanization in this century."

O Response : "...The average age of migrants

to urban areas generally falls between

20 and 30 ... Therefore, most of those

who will migrate between now and the end

of this century are already born. An

immediate and decisive decline in the

birthrate would not affect the migrant

population until the 1990' s ..."

4. "Decentralization of urban growth will

reduce problems of urbanization." (Ref. 17)

O Response : "Large scale capital investment

in a number of rural areas designated as growth centers, may tend to attract

imigrants to relatively small towns which,

at least in the short and medium term,

would (lack) the financial and staff resources for providing community

services, and otherwise dealing with a rapidly growing population."

5. "Squatter settlements are home largely

for rural and uneducated groups."

(Ref. 17)

O Response : Squatter settlements vary

widely. Residents of some are close to their rural backgrounds. In others,

there is a notable proportion of

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6. "Nearly all squatter town inhabitants are multi-nember families."

professionals, such as engineers and

doctors

9
Q Response : Ref. 18 indicates that the

ratio of single person families is high

(in Bangladesh: 15% in Dacca to as high

as 29% in the more industrialized

Chittagong) . This is seen as an undesirable trend from a sociological viewpoint. •# Sites and services

A policy that is becoming more and more accepted is to focus on improving squatter

settlements. This is done by providing so called "site and services" . Land, water

supply, electric power and waste disposal

are provided. Better structures come along

with appropriate help as the settlement

becomes more established. This way, selfhelp is stimulated.

"Sites and services" implicitly recognizes

that squatter settlements can be viable

economically, and that their main problem is

to keep to a minimum their sanitary, educational

and other negative aspects.

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•Types of "sites and services"

Following are four forms of "sites and

services" (Ref. 19)

:

1. Subdivide land alone — only an unimproved

building lot is provided

2. Subdivide land and instal basic public

utilities and some community facilities

3. Subdivide land with a full complement of

public utilities and community facilities

4. Install a combination of public utilities

and community facilities in existing

residential areas

An interesting variation on the above are the

so-called "poles" of India. An entire downtown block owned by the Government is leased

to a private individual or company, which

then rents space to transient occupants. The

block is entered only through a guarded

gate, with rent collected weekedly. Temporary

10
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structures inside the walls serve newly

arrived migrants who are close to day work

and temporary job sources, and have the

opportunity of acquiring more permanent

jobs and housing.

Hierarchy of public utility services

As the "sites and services" concept evolves,

a hierarchy has emerged among the public

utility services a government may provide.

In the top category are water supply and

waste removal, since lack of purity in the

one and improper location and design of the

other are the primary causes of disease and

mortality in squatter settlements.

Water and waste lines, if possible linked

to a sanitary core, constitute a minimum

.standard

Into the second category fall such utilities

as electricity and public lighting, sidewalks

and paved roads, gas and telephones.

Public utilities make up one of three

components of the "sites and services"

concept. The other two are community

facilities (or access to them) and the land

itself.

•The importance of land

From a public health standpoint, proper water

and sanitary systems are supreme. From

a social standpoint, the security of land

is supreme. Most families, given technical

assistance, will find a way to erect a dwelling, so long as they can count on security of

land

To bring down the cost of land to the occupant,

a variety of arrangements is possible. An

approach tried in Jamaica offers a 40 year

leasehold on land at a modest rental; this is

renewable for 40 years more. The lessee is

responsible for erecting housing and paying

for utilities. The only subsidy is in the

form of technical assistance.

11
®User requirements

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Research into user requirements on low cost

housing can help evolve designs that are not

only adequate technically but also meet socio

economic needs. Clearly, as most current

designs do not meet proper wind-resistant

criteria, new designs, quite possibly using

unfamiliar building materials and methods,

will have to be used. As there is no hard

data on user acceptance of such designs,

this information must be sought out.

Mrs. Tarja Cronberg (Ref. 1) uses these sources of information: statistics of the

country's population (death rate, size of

families, average income, etc.); interviews

with local builders, architects, and con- struction workers; and observation.

She. divides the information into two classes: user characteristics , and user activities .

Under user characteristics, she determines

the users' typical physiological and

psychological characteristics, plus such

socio-economic characteristics as family

size and structure, mobility, identification

with a particular ethnic, religious or geographic group, and educational background.

Under user activities, Mrs. Cronberg identifies 9 headings:

O Sleeping O Recreation/play

O Food preparation O Social (receiving of

O Storage guests, etc.)

O Personal sanitation O Identif ication/partici

O Work pation

OLearning and orientation

She now feels that more information is needed

in four areas: O Health standards in existing environments.

O Need for personal space and privacy in

overcrowded housing.

O Social activities in the neighborhood and

community

.

O Activities of specific groups such as children.

12 •:.
This determination, done with aid of local

experts, is clearly important in arriving at

a clear, objective set of criteria of how

families in a given milieu are likely to

respond to innovative, wind-resistant

design that is new or unfamiliar.

•Acceptance and rejection

K^A^frfats art- rej eeAcm*

,

The Cronberg study also indicates that

innovative housing designs and new materials

are widely accepted in the Philippines, even by low income owners. This is true especially where the owner is able to make small

individual changes on his house after he moves in. Most practicing architects and

engineers in the country are said to accept new materials which have the needed properties

and do not cost too much.

The opposite has been the experience in Peru.

Peru is not a part of this report, but is a useful object of study nevertheless. New

construction materials always run into a strong initial period of rejection, and

only a few have survived this reaction and

kept a place in the market (Ref . 1).

Examples of this rejection include:

OA hollow block based on a Swiss patent

and made up of mineralized vegetable

fibers encased in cement.

OA panel-sized product made of expanded

gyp sum

O Corrugated sheets of glass fiber and

polyvinyl chloride (PVC) . Plastic

bathtubs and basins.

O Sprayed polyurethane igloos developed in

Germany for use after an earthquake (as

discussed earlier)

The few construction materials (other than

indigenous materials) that are broadly accepted ar corrugated sheets of galvanized steel or asbestos

cement. The former, despite poor thermal

and acoustical properties, are popular

because they are strong, do not weigh much,

and can be easily and cheaply transported

on the backs of mules. The latter, though

superior in thermal and acoustic terms, are quite fragile, and the resulting higher

breakage also drives up costs.

13
•Attitudes to pref abrication

Another Peruvian study with clear lessons for

other developing countries is a 1962 survey

of public attitudes towards prefabricated

housing. It was carried out by students at ' the Architecture Department of the National

University of Engineering.

Consumer interest was found to be low because

prefabricated houses cost only a little less

than brick and concrete houses and a good

deal more than adobe houses; they looked too

«v » i u I uniform; and the public did not really

i rtriQ Dk"'^' appreciate the savings inherent in the shorter

[&€>lC' construction time.

5.7/

2.8/

!

As for builders, they found that a restricted

market led to high sales costs; financing was

difficult; and complex transportation sharply

raised construction costs outside the

immediate area of Lima.

Housing economics

Housing approaches in developing countries

have been critized on two grounds.

First, because housing deficits are computed

without taking into account the values or preferences of those to be housed. Secondly,

because the traditional solutions to

housing deficits have turned out to be well

beyond current capital investment rates.

Even in countries that anticipate a high rate

of growth, the competing demands of agriculture, industry, and other programs reduce

the funds available for housing to a level far

beloxj needs (according to a report by William

F. Reps, Ref. 1).

In the Philippines, for example, demand for new dwellings would require a capital investment about 5.7 percent of the gross national

product; in fact, in 1967 only 2.8 percent

was so invested. As a result, slums and

squatter towns grew - 10% of the population

of Manila and 30% of the population of key

GzplteJL 0+Ks$h«uJr \aT8vJU, other cities lived in squatter areas,

fi /( iuvV^ d^Mj^-d^ Yet the "sites and services" solution referred

to earlier has been found desirable, especially

in the Philippines, where self help (known as "bayanihan") is widely accepted in the

building of dwellings. It is discussed in

greater detail later in this report.

14
Housing

characteristics

Four ingredients of housing are discussed.

These are: siting, design, construction

methods, and materials.

Siting

With the relatively primitive wind risk maps,

little regard has been given to the placement of houses in relation to danger. Good

site location or orientation linked to local

terrain and natural cover can be, but

usually has not been, determined from historical wind data. This data provides the

frequency, velocity and direction of the

prevailing winds, especially in their extreme

form. Hence, windstorm damage can be cut

back a great deal by placing buildings so they are protected by hills, stands of trees

and other natural elements.

Design

Windstorm resistance can be notably improved

by various simple measures. These include

horizontal bracing of certain types of roofs

over houses made of adobe masonry and other

small unit construction; a more rational

disposition of openings in bearing walls;

reinforcement of critical areas of a building

subject to being overstressed ; and the

strengthening of connections at joints.

15
fUk<\h Surfaces y 'btit&atix fa-ant ifcionS

eternal prMSurg-*?

All this may not be enough. Special studies

on how turbulence in a storm is distributed

are required.

It is possible to make buildings more wind

resistant by improving connection details, by

learning more about the effects of wind

loading on buildings, and by avoiding shapes

or arrangements of buildings in groups so as not to cause undesirable aerodynamic effects.

For this, theoretical as well as experimental

wind model study research is currently being

conducted as part of this project's research

activities

.

Certain design elements can be very unfavorable. Sharp edges, low-pitched roofs, large

overhangs and improper grouping of buildings

will cause problems. Textures, too, are important. According to R. M. Aynsley

(Ref. 1), the aerodynamic behavior of

buildings can be improved by providing rough

surfaces or ribs on the exteriors of walls.

Grass roofs have allegedly served to relieve

pressures, as have smooth transitions

between planes of a house.

Unfortunately, the internal pressures

developed in buildings with openings are usually not considered in design. Roof

failures have been caused by wind which

penetrated the structure and pressed up on the roof from beneath.

Certain configurations (such as cylinders),

or igloo-type structures, are far more

stable than box-like structures, but in the

few places where they have been tried the

cultural attitudes of the population caused

them to be abandoned.

In Bangladesh, a revolutionary type of

design has been tried, using materials and

shapes new to the country. These are integrated roof and wall elements, made up

of units consisting of polyester resin, and

jute. They have performed well in winds

but their final social acceptance is still

unknown.
Construction technique

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In developing countries, it is often hard to

separate design from construction. By and

large, typical characteristics can be

summarized as follows:

•Foundations: Load transmission to soil

becomes less critical since low-rise dwelling

of one or two stories do not generate a high

dead load. Where flooding is not common,

rectangular footings of plain or reinforced

concrete or gravel are used.

In flood-prone areas houses may be built on stilts (e.g. bamboo) driven into the ground

to the appropriate depth. Mat footings are sometimes used on unfavorable soil.

•Walls: Walls are either structural or non- structural. When non-structural, they merely

serve as an in-fill for a frame and their

constribution to the overall structural

resistance of a building to wind pressure

should be minimal.

Structural walls of wood, concrete, burnt

clay or soil-cement composition are the most

common in low-cost housing construction.

Walls are either monolithic or small unit

masonry type, where units are layed in

staggered courses, usually in beds of mortar.

Clay brick and title, adobe brick and

concrete block are the most common masonry

units. Quality control in making these units

as well as the mixing of the masonry mortar

bed, can make or break the structural

strength of the total wall.

Wind stresses on walls are either out-ofplane bending or in- plane stresses Outof-plane pressures (when wind acts directly

at right angles to a wall) cause deflection

and eventually failure. Tornadoes common

in Bangladesh have pressure drops so strong

and sudden as to cause an actual explosive

action of the wall.

17
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In-plane stresses are developed in walls which

act as shear-resisting elements within the

building, the plane being parallel to the

wind direction.

Moreover, incorrectly planned wall openings

may be critical, especially at corners. In

any case, conditions where two walls intersect

or between walls and foundation or walls and

roof, require special design due to the high

stresses at those joints.

#Roofs: Roof pitch is an important design

element for good wind resistance. The magnitude of positive or negative wind pressures

on roof surfaces is directly related to roof

pitch. Wind affects roofs in two ways,

direct and indirect.

Direct local effects are made up of high

positive pressures (or suction) over local areas of the roofs. This may lead to

damage to roofing — whether shingles, tiles,

corrugated sheets, etc. Overhangs, common

for sun protection, are especially liable

to wind damage, as they undergo positive

pressure from below and suction from above.

Indirect effects occur when wind loads are transferred to lateral walls, causing

stresses. If this mix of pressures on the

roof is strong enough, the capacity of the

connections will be exceeded and the roof will

be lifted off. This brings additional danger

since every roof has a structural role as a horizontal diaphragm. This transmits windloads from the front to the side walls. If

a roof is off, both frontal and lateral walls

may collapse.

Flat roofs (especially with overhangs) are more subject to wind damage than roofs with

a steeper pitch.

® Prefabrication

Any method that will produce housing more

effectively must, at least in its first

phase, make the best use of available local

labor. And the choice and control of the

dwelling environment resulting from any

industralized housing must not conflict with

individual uses, traditional preferences

and outlook.

18
In the Philippines, few companies make

prefabricated components; included are private firms producing wall panels and

roof trusses, and a government firm

which makes lightweight concrete panels.

Filipino builders are said to recognize the

savings which prefabrication offers, and

feel they can make it work. Their problems

at present are lack of adequate financing

and too small a volume.

In Bangladesh, reinforced concrete shell

roofs in a shape of a hyperbolic paraboloid

have been used, using one inch pre-cast

reinforced concrete elements, with concrete

connections made on site.

In Jamaica, the most common form of industralized construction consists of large

precast concrete panel systems. Wall and

roof panels are lifted and assembled by

crane. Other forms of pref abrication in

Jamaica use precast posts combined with

precast; concrete or timber beams, with

concrete infill "boards" between posts.

Materials

of tau**t*j

or $6*m -

The most commonly used materials of

construction are those that are found

plentiful locally and require little or no sophisticated equipment to convert into

building materials. In Bangladesh 90% of

rural houses (and 90% of Bangalis live in

the country) are made of bamboo, thatch and

mud. Two out of three houses use the same materials for roofs. Only 1 percent of these

houses have walls of concrete, baked brick

or stone, and these are mostly staff

quarters built by the government. The

remaining roofs are of galvanized

corrugated iron or corrugated asbestos

cement sheets. In its cities, only some

27% of housing is considered "permanent

and semi-permanent."

19
Following are other common materials used in

the three nations:

Soil : Natural earth is about the most

common material used. Sun-dried adobe

bricks have been the basic masonry units

for low-cost housing. These bricks are often untreated against penetration by

water. More recently adobe brick has

been stabilized by the addition of

asphalt. This boosts the durability

and water-repellent properties and is a major breakthrough. The social acceptance,

however, of adobe, stabilized or not,

is still not high.

Wood : Wood, while popular, easy to handle, versatile and strong in tension,

is not everywhere available. It is useful as a framing material. When not

available in milled, dimensioned form, it

is replaced by non-dimensioned lumber —

as cane, bamboo, palms and thatch for

structural enclosure and roofing purposes.

Cane, bamboo or split wood are often used

to reinforce adobe masonry. Major drawbacks are moisture, fire and insect

infestation. Chemical preservatives which

can be produced in developing countries

can prevent this kind of danger and

deterioration. Also, chipboard products

are used for walls and ceilings.

Concrete : Where sand, cement, water and

various additives are plentiful,

concrete is a logical and widespread

local building material. Weak in tension,

it can be reinforced by a local material

such as bamboo as well as by costlier

imported steels and fiber glass. Concrete

reinforced with a wire mesh and known

as ferro-cement has been used with very

little supervision in some countries, and

the materials needed are cheap and usually

readily available.

#d. Brick and concrete block masonry are

common.,

#e . Steel : As a capi tal-iptensive material,

steel is rarer. Its most common use is

as a roofing material (in the form of

corrugated sheets of galvanized steel or

20
aluminum) , and to a small extent as connectors for bolting and anchoring the

various structural elements.

Plastics : Plastics are a highly adaptable

material. Depending on the choice of

components, they can be tailor-made to adapt to most structural and enclosure

needs of housing. Not enough is known

about the weathering properties of

plastics in outdoor use (as compared

to traditional materials) , especially in

tropical areas such as those in this

study. Use is most advanced in the

Philippines, which also is one of the

chief plastics producing countries in the

Far East. They use native as well as imported raw materials and processing

machinery. Several important tests

underway in Bangladesh are described

later in this report.

Still, plastics are resisted as a new

and unfamiliar material. Solid-seeming

and demonstrably durable materials are preferred. Plastics are likely to be more widely accepted in the future as they penetrate the private, for-profit

housing market and non-housing uses such

as clinics and schools. They can then be

observed and their performance seen by

those who presently must rely on housing

provided by their governments or through

their own labors.

Indigenous fibers , such as palm leaves,

coconut husks and peanut shells have

served as filler materials in spaces

between structural supports or between

roof rafters; and grasses such as jute and

hemp can be used as reinforcement for

concrete or adobe masonry.
The preceding chapter described the overall

picture of housing in the three countries

of the Philippines, Jamaica and Bangladesh

in terms of socio-economic profile and

physical housing characteristics. The three

sections that follow are based in greater

detail on documents developed specifically

to describe conditions in each of these

three countries. In this sense, this

chapter should be seen as an extension of

the preceding one.

22
The Philippines

The Philippines is said to have the highest

frequency of tropical storms in the world.

Average annual frequency is 20.

Filipinos have always depended on water

(whether river or salt) for food, transportation and for watering their fields.

This is still the pattern in rural areas. This attachment to low land and water

logged areas led to a unique type of

dwelling, with a raised floor on stilts.

Communal activities centered around the

houses of the village elders, who also were religious and judicial officials.

This organization has today been formalized

into the barrio, which is the lowest

political unit of government.

•The Filipino family and its housing needs

The family is the strongest unit of society.

Typical of the family system is bilateral

kinship. This is extended often as far as the third or fourth cousins. Families with

at least three generations are common. In

times of crises, family members are expected

to share board and shelter with less fortunate

members, especially parents in old age and

widowed relatives with children. The family

acts as the economic unit in rural and urban

areas. Children are seen as economic assets.

A large family is regarded as a means to social security.

23
#The community

The term "barangay" exists to define this

conscious sense of belonging. It is a pattern

into which the activities of the family units ' are woven. Extended families exist not only

in the country but also in cities. Their

percentage in low income areas around Manila

is said to reach 55 percent. Family size

ranges from 7 to 11 in these cases, with at

least 18 percent made up of 9 members or more.

Only 12 percent of urban families can afford

housing in the open market; 23 percent can afford home ownership provided they receive

long-term financing at low interest rates.

The remainder cannot afford adequate shelter

even at reduced rates.

Ranking cities in the Philippines have between

10 and 45 percent of their populations in

slums or in squatter areas; the national

average is 5 to 6 percent. Filipino squatters

are not said to be shiftless people, but well

motivated and resourceful.

A study made by Jaime Laya, Remedios Balbin

and Romulo Neri of the Agno-Leveriza

squatters area of Manila (Ref . 10, part H)

paints a grim physical picture. Eight

hundred dwellings are crammed into two city

blocks behind a prosperous seeming facade of

solid apartments and houses. Most structures

are of one or two rooms, without running water

or toilet. 11.5% of surveyed heads of household were unemployed, compared to a 1969

national average of 7.3%.

Yet the study team noted little active discontent; rather, they found an attitude of

initiative, of moving on by one's own effort

and enterprise. Education level was relatively

high (7.1 years of schooling on average for

heads of household, more than needed for the

jobs they hold), and income level varied

widely, from destitute all the way to families with a refrigerator, television set

and telephone service.

Another study, by Mary R. Hollnsteiner

(Ref. 10, part I) confirmed a sense of excitement among squatter families after they left

a dull rural existence and moved towards

24
economic opportunity in the city. One

recommendation of this study, which looked

into options for relocating Manila squatters, was to weigh with care any plan for moving

families off to a site too remote from urban

job opportunities.

The estimated annual need for urban housing

alone averages 100,000 units — to accommodate

population increase, new family formations

and replacement of squatter dwellings. The

cost of land is high and this has a direct

effect on the high cost of adequate housing.

In addition, wholesale and consumer product

prices grew sharply between 1970 and 1973.

The average increase for all commodities was

25 percent; for most construction materials

the figure was 40 to 60 percent.

This does not jibe with other, more optimistic

reports which indicate that materials and

skilled labor for conventional construction

methods are said to be fairly available. The

cost of delivering materials is reported low

because production is spread throughout the

country.

•Economic aspects

Only 12 percent of the population (with annual

family income over $1490 — U.S. dollar

equivalent based on exchange rate of the

Philippine peso as of August 9, 1974) can afford housing on the open market. (Ref . 10,

part A)

23 percent can afford to own a house if

offered long term cheap financing with modest

land, development and construction cost ($596

to $1489 annual income range)

The rest cannot afford shelter at any cost.

Investment in housing rose from 2.8 percent

of GNP in 1967 to 4.0 percent in the early

1970' s. But to meet the country's housing

need of some 470,000 units per year, an allocation of 5.7% be required.

Yet the Filipino economy as measured by its

GNP has risen at an average annual rate of

6.6 percent from 1968 to 1973. Average per

capita income ($130 in 1970) also rose, and

is expected to double in the next 10 to 15

years

\ 125/1

I 1 60/1

Pno-S of cvwfcifucDon wafcemk

katfc v\<m twicfi. a,s v*Mck 06

alL otter coiwModtUe^

25
The amount a family can afford for housing

varies chiefly with its income and location

along with other lesser factors. For example,

according to a study by Sixto L. Roxas III

(Ref . 10, part F) , a family with an annual

income of $300 can afford a house 1.3 times

its income, or $390. At an annual income of

$450, it can afford a house of 1.8 times

its income, or $805. This sets certain

numerical limits on the cost of low income

housing

.

In addition, income varies in different

regions of the country, with families in

urban areas outside of Manila having a higher pattern of income than Manila and

rural areas (Ref. 10, part F) . All these

economic aspects are important in determining

realistic parameters for the design and

construction of low-cost, wind-resistant

housing.

U7*

(Housing characteristics

Some key housing characteristics are shown

in Table 2. Note sharp differences between

statistics for metropolitan Manila and for

the Philippines as a whole. They are based

on surveys by the Bureau of the Census and

Statistics and by the Population Institute

National Demographic Survey, They give

little idea of the actual condition of the

dwellings themselves.

Population trends

Table 3 shows the results for the Philippines of a world-wide survey conducted by the

United Nations to identify population trends.

The information is updated through June 1974;

population figures are broken down by urban

and rural, and indicate rates of increase.

Figures for 5-year periods from 1975 to 20^0

are given.

26
^

Table 2: KEY HOUSING CHARACTERISTICS IN THE PHILIPPINES (Ref. 2)

Part 1. TYPE OF DWELLING UNITS BY STRUCTURE (PERCENT)

Type Metro Manila Philippines

Single Family Dwelling

Duplex

Accessoria

Apartment

Barong-Barong (shack)

Commercial Building

Other or No Response

57.6

5.5

15.1

8.1

4.4

1.0

8.3

78.9

4.1

2.3

1.1

5.4

1.3

6.9

Part 2. NUMBER OF ROOMS IN HOUSEHOLD EXCLUDING BATHROOM AND TOILET

(PERCENT)

Metro Manila Philippines

One Room

Two Rooms

Three Rooms

Four Rooms

Five Rooms

Six Rooms

Seven Rooms

Eight or More Rooms

No Response

11.3

22.5

23.1

19.8

8.0

3.8

1.3

1.6

8.7

14.1

28.4

25.7

14.3

6.5

2.6

0.8

0.6

7.0

Part 3. DENSITY (PERSONS PER ROOM) WITHIN HOUSEHOLD (PERCENT)

Type Metro Manila Philippines

Less than one person

per room 5.1 6.1

1.00 to 1.99 persons

per room 27.8 27.4

2.00 to 2.99 persons

per room 26.5 25.4

3.00 to 3.99 persons

per room 14.1 13.7

4.00 to 4.99 persons

per room 7.7 7.7

5.00 to 5.99 persons

per room 4.2 3.7

6.00 to 6.99 persons

per room 1.5 2.8

7.00 to 7.99 persons

per room 1.8 1.7

8 or more persons per room 2.7 4.5

No Response 8.7 7.0

27
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28
Jamaica

• Socio-economic aspects

Virtually all Jamaican housing built by the

private sector today falls outside the

definition of low-income housing, that is,

the cost of house plus a developed site must

be under $5,500 (U.S.). Whereas 350 to 450

sq. feet is said to be a minimum standard

for social housing in developing countries,

a more attainable standard for people with

no fixed income brings this closer to 200 sq

feet. In such cases, provision is usually

made for the owner to extend the house at some future date.

Traditionally, urban low-income housing has

been in the form of high-density apartments

terrace houses or small groups of houses

closely clustered around a communal yard.

Detached houses have been more typical of

middle income groups, and have become the

goal of upwardly-mobile low-income groups.

Over the past 10 to 15 years, this has

caused developers of low-cost housing , in

order to keep prices down, to erect

groupings of closely spaced, single-story

detached units on tiny lots.

Oddly enough, a middle income trend back

to apartment living is seen as encouraging

a similar trend among low income groups;

these may now be more likely to accept

multi-story and terraced housing, with its more efficient use of limited land and resources

29
A useful if not totally representative

picture emerges from a survey of housing

conditions in the Delacree Pen district of

Kingston (Ref. 8). Delacree Pen is the site

of an urban renewal project. The survey

disclosed among other things that:

O Of the 4,935 households, 68 percent lived

in one room; 18 percent in 2 rooms and

8 percent in three rooms. The most common household size was from 5 to 7 (24 percent)

;

37 percent were of one or two persons, and

11 percent had eight or more members.

A notable feature of a Delacree Park urban

housing project (located in the Delacree

Pen District) is its character as a housing

cooperative. Such a cooperative, established

with government, World Bank or other subsidies,

is a useful vehicle for erecting housing, in

the construction and maintenance of which the

occupants have a strong social and economic stake.

Eventually some 350 units will be built in

Delacree, in the form of wind-resistant

2-story garden apartments arranged in clusters

of six. The program has been well-received —

both in its social and its economic context

(90 units have been built to date)

.

Occupfif^e^

#f

5o%

One difficulty has been adherence to occupancy

standards — a common problem in developing

countries. Delacree Park units, which have

a living room and 2 bedrooms, may house up

to six people, according to government standards of two to a room. In practice, families

sometimes have as many as 7 children; conse- quently the government, knowing it cannot

afford to subsidize such supplemental spaces,

will permit its occupancy standard to be

exceeded by up to 50%.

By and large, cooperatives are now an accepted method for erecting housing in

Jamaica. The Jamaican Ministry of Housing

has created a Division of Cooperatives and

Condominia to coordinate this effort.

30
^

Table 4: KEY HOUSING CHARACTERISTICS IN JAMAICA (Ref. 4)

Part 1: DISTRIBUTION OF DWELLINGS BY TYPE OF TENURE (PERCENT)

Type of Tenure Total Urban Rural

Owned 52.4 29.7 70.8

Leased 2.5 3.9 1.4

Rented 36.5 59.9 17.6

Rent-free 7.9 5.8 9.6

Squatter 0.4 0.5 0.3

Other 0.3 0.3 0.3

Total 100.0 100.0 100.0

Part 2: DWELLINGS CLASSIFIED BY TYPE

Type of Dwelling Number Percent

Separate house 327,656 78.0

Flat /Apartment 67,083 16.0

Barracks 3,223 0.8

Out-Room 4,069 1.0

Part of Commercial Building 11,765 2.8

Other Private 3,886 0.9

Other 2,477 0.5

Total Dwellings 420,159 100.0

Part 3: PERCENTAGE DISTRIBUTION OF DWELLINGS BY NUMBER OF ROOMS

of Rooms Total Urban Rural

1 32.7 42.3 24.9

2 26.3 19.6 31.7

3 16.1 11.7 19.7

4 8.5 7.5 9.3

5 5.3 5.9 4.9

6 2.8 3.3 2.4

7 2.6 3.4 1,9

8 or more 5.8 6.3 5.3

Total 100.0 100.0 100.0

31
i

ft&iter

•Housing characteristics

(See also Table 4

)

Jamaicans by and large prefer concrete houses

and do not like houses made of light-weight

materials, unless forced to do so for

financial reasons (Ref. 4). Until recently

there has been a bias against precast concrete

houses (especially those of thin crosssection) but this is disappearing.

The most popular material among all income

groups is hollow concrete block masonry.

Physically, low cost housing in Jamaica

falls into six types (Ref. 4).

01. Wattle and daub (4%)

:

Until the 1930's

rural owners built most low-cost houses in

this fashion. The framework of wooden posts

and beams, with sticks interwoven horizontally

between the posts, was the wattle. This was

daubed inside and out with mud from available

clay, to create solid walls. The roofs were

pitched and made of a thatch made from

bundles of dried leaves and tied in place.

02 . Timber stud and horizontal boarding

(36 . 9%) : Roofs were pitched, made of timber

rafters covered with corrugated iron sheets

or wooden shingles.

03. Brick or concrete nog (11.8%): Like the

preceding, these are typical of urban areas. Wood studs receive a brick or concrete infill

or "nog" and are covered with a lime or cement

plaster. Houses are usually raised two or three feet above ground.

43.4% of Jamaican housing is concrete-based:

04. Hollow concrete masonry: Blocks are manufactured locally: cavities are filled

with concrete during construction, and steel

bars are added to reinforce against wind and

earthquake. Poured in-place reinforced

concrete stiffener columns should be included

in panels over 16 feet long, but are often

omitted in low-cost housing. Reinforced

concrete belt beams are used to cap walls at

roof levels.

3.
05 . Large-panel precast-concrete systems : Single panels can extend to the full length

and height of a unit. Wall and roof panels

are lifted by crane and connected by welding

at matching steel inserts. (These systems

are not strictly speaking "low-cost" but

could be if one steps up volume of production

and accepts a lower standard of finishes)

06. Small-unit precast concrete systems : Precast concrete posts are combined with

precast concrete or timber beams, with an

infill of concrete "boards".

Remaining housing is of brick or stone.

•Housing programs

Except for the 20 percent of needed units

supplied or aided by the government (Ref . 5),

there is presently no machinery for providing

housing for the very bottom of the income

scale. The mechanism used is either the

continuing growth of shanty towns or the

creeping subdivision of existing houses to

accommodate new households.

On the other hand, the government now has

underway a "site and services" project

which selects land; provides an "infrastructure" of utilities; a minimum

core unit; certain community facilities such

as a school; possibility of employment and

skill training.

Families with an annual income of less than

$1650 (U.S. equivalent) are eligible (Ref. 4).

The goal is to provide 6,000 serviced lots in

the next three years. Lots are to be available in three options:

Owith connections for electricity, watersupply and sewerage, plus materials for a toilet-kitchen-shower core unit.

Othe same, but with a built core unit, plus

materials for shelter and enclosure for

the rest of the house.

Othe same as the preceding, but with the

core-unit and shelter being built, and

materials only provided for enclosure of

the rest of the house.

33
Serviced lots are to be owned on a leasehold

basis, and loans for materials will be

provided through credit unions.

Although the main focus of the Jamaican

government is on "sites and services,"

there are other government programs. These

consist of a mix of government-built housing

for sale or lease (1970-1975 goal: 3,125

units); owner-occupied, government subsidized

units (3,600 units); rural housing projects

(4,880 units); indigent housing built on

land owned by recipient (2,250 units); urban

renewal projects focused on Kingston

(4,876 units); plus assistance furnished

to housing cooperatives (Ref. 4). • Wind patterns

Despite the frequency of hurricanes in the

Caribbean, direct hits on Jamaica are few

when compared with the number of tropical

storms which pass within 150 miles of the

island (Ref. 4).

On the other hand, near misses are often

accompanied by flood-rains which cause much damage. Records made between 1886 and

1967 show that the paths of 19 hurricanes

and tropical storms passed directly over Jamaica and those of 98 (48 of them having

hurricane force winds) passed within 150

miles of the island (Ref. 4). About one- third of the latter brought about flooding

and damage.

• •Population trends

Table 3 s hows the results for Jamaica of a world-wide survey conducted by the United

Nations to identify population trends. The

information is updated through June 1974.

Population figures are broken down by urban

and rural, and indicate rates of increase.

Figures for 5-year periods from 1975 to 2000 are given.

2MIL.

AW

34
xooo

Bangladesh

•Socio-economic aspects

•Population trends

Table 3 shows the results for Bangladesh of

a world-wide survey conducted by the United

Nations in an effort to identify shifting

population patterns. The information is

updated through June 1974. Population figures

are boken down by urban and rural, and

indicate rates of increase. Figures for

5-year periods from 1975 to 2000 are given.

Bangladesh, a nation with one of the highest

population densities in the world, is also

troubled by these additional dilemmas:

O Steady population growth has forced

families to live on land that is

increasingly substandard and subject

to wind-induced flooding.

O Periodic flooding of low-lying land

further increases density -- from about

1400 per sq . mile to a temporary

40,000 per sq. mile in coastal storm

regions, as families flee to land left dry.

O The partition of 1947 left the higher

land, with its supply of solid con- struction materials such as stone and

timber, on the Indian side of the

boundary, while the Bangali population

on the treeless alluvial plain was

left with few resources for protection.

Measured by gross domestic product, Bangladesh

is one of the world's poorest countries. 90

percent of the population is rural, and

industrial output accounts for only 9 percent

of the gross domestic product (mostly jute

processing). (Ref . 9)

35
The last housing census was done in 1960;

results from a new housing census are imminent. As Table 1 shows, the average

number of rooms in 1960 per household was

1.77. 53 percent of householders lived in

single room dwellings , and the average

density of occupancy was 3.2 persons per room.

In the case of 31 percent of the population,

five persons or more share a room. Clearly,

any damage from intense windstorms risks

major casualties to a population as densely

crowded as this.

The rural population lives in the patriarchal

family compound. When sons marry, a new

room is erected for the new household on the same field as the parents, next to the

parents' house. Thus, houses occupied by

families that are paternally related are grouped together. These clusters provide

shelter to families numbering as many as 40

members; even higher figures are common. Houses are usually surrounded by dense trees

and other tropical vegetation.

•Attitudes to disaster

A report prepared after the disastrous

November 1970 cyclone (Ref. 22) reveals an interesting set of attitudes. 57 families

of various economic levels in the community

of Galachipa were surveyed. Dr. Aminul Islam

who compared attitudes after the May 1965 and

November 1970 storms, found that;

After 1965 no family wanted to move,

though many families rebuilt their

houses using higher plinths and

stronger posts

After 1970 only 5 families wanted to move; 56 still lived on the site of

their old home

38 families were still living more than

1 mile from a "pucca" (well-built)

structure that could shelter them in a storm

14 were living over 3 miles from a pucca

structure

19 families needed a boat to reach a pucca structure

36
O Only 24 families would spend their money

first on housing. The others'

priorities : 1) food 2) cattle

The majority said that if they had the money

they would build one small pucca house,

rather than several kutchas (or low quality

houses) or corrugated iron (CI) houses.

In sum, the survey found the families

fatalistic and pessimistic over protection

measures

fa*vtl^ compound"

J. hfeujtfacjc

4. Worsted

6. G>wshe4

•Rural housing must be seen as part of

agricultural system

Bangali villagers see housing as part of

their agricultural system, rather than as a building discipline as in the West. Thus,

house building and repair is seasonal, like

other farm activities. It helps relieve

unemployment. Villagers will grow building

materials for houses on their own land.

A tree, for example, will serve as a fruitbearer, windbreaker and fuel, until needed

as a building material.

Similarly, a man's jute and the earth itself

serve him both for agriculture and for

building.

Due to the climate, the bamboo "kutcha" house

(described below) itself decays over a 10-year

cycle, if not destroyed by a storm before then.

Any program for housing that ignores these

rural attitudes risks failure.

•Housing patterns

O Rural : The rural population is divided

into land owners and landless laborers.

One out of five villagers is landless.

The average land owning villager has 1.5 acres and usually rents another acre from

well-to-do villagers. Houses tend to be

scattered throughout the village.

Rural houses are known as "kutcha" or raw structure, with a plinth made of mud, and

walls and roofs of bamboo, straw and

leaves. These houses need to be maintained

constantly and seldom provide safe shelter

37
Typist rural acvM:

ivitrU bamboo.

CQcriAqa.t&tL iron root •

t

against rain and wind. 90% of rural houses

are built this way. Only about one in a hundred has walls of concrete, baked brick

or stone. About one house in three has

roofing made of corrugated galvanized iron

or asbestos cement.

Q Urban : As 72 percent of the urban population can't afford to pay rent for even the

cheapest housing, they live largely in flimsy

shacks, mostly in so-called "bustees" and

squatter settlements. This housing is made

of bamboo, often consisting of a piece of woven split bamboo fencing bent in the shape

of a semi-circle, Headroom is low and

occupants spend most of their time outdoors.

Even moderate winds blow these houses away

despite efforts to hold them down by putting

counterweights on roofs.

The stronger urban houses are mostly made

of burnt clay brick walls, with flat

reinforced concrete roofs. As the walls

are usually 10 inches thick, gravity

usually precludes failure through wind

stresses. Failures occur largely due to substandard mortar or poor workmanship.

No damage to the flat roofs has been

reported, except in cases of projecting

sunshades

.

• What happens to the houses

In the 1970 storm, it was the wind that

caused initial housing destruction; the

storm surge accounted for people and animal

casualties

.

OHere is how the materials fared (Ref. 22):

Material Condition

Thatch

Bamboo matting

Wood or bamboo

supports

CI sheet

5 in. brick

10 in brick

Destroyed or lost

Usually destroyed or lost

Broken, recovered,

reusable

Damaged, in part reusable

Destroyed. If preserved,

hard to reuse

Intact if concrete roof

38
A small Buddhist community builds sturdier

houses, but partial losses after a storm

often cost more than it costs to replace

a kutcha house.

Middle and upper income rural families use

CI sheet and wood. These resist wind and

water if well-built. If not, owners can retrieve their materials and rebuild, unless

the materials are scattered by flood waters.

ty&/> <!> turfy

}

• Other types of housing

O So-called CARE types (named after the

U.S. relief organization) use soil cement

blocks and corrugated iron sheets for roofs.

Units roughly the size of an American concrete

block are made in a simple-to-use machine

which compresses a mixture of 90 percent

non-saline soil and 10 percent cement to

make about 300 blocks a day. A typical

house requires some 1200 blocks. The essence is selfhelp, as a minimum of skilled

labor is needed to put up this kind of house.

The key to wind safety is to properly anchor

the roof to the block walls. This type of

structure is very popular in the country.

CARE has also developed a new composite

building material, made of pulp from the core of the jute plant, jute cloth and a plastic resin for binder and facing. This

seeks to combine a locally plentiful

material (jute) with synthetic binders which

can be manufacturered into panels by domestic

industry.

Several variations of material and configuration have been formulated for laboratory

testing, prototype construction and wind

testing of full-scale units.

Four prototypes have been developed so far.

These are:

1. A pie-shaped, domed structure made of

a 3/4 in. compressed jute-waste board faced

with polyester resin and glass. Public

reaction was good until the facing was identified as plastic, for plastic vas identified

in the public mind with a brand of cheap and

brittle crockery. Those who acknowledged

the strength of the plastic nevertheless

39
(% fee t«n"tfc S^>«- ot

faulted the house for its roundish dome-like

shape. This made partitioning difficult and

made it unsuitable for low-income families —

especially the 80 percent Muslim families

with their tradition of isolating women in one part of the house.

2. A self-supporting house, rectangular in

plan and with an elliptical roof profile,

with curved panels made of the same combination of synthetic resin and jute. No

component was to weigh more than 100 lbs.,

so it could be easily managed by two men.

It was designed to resemble traditional house shapes,

3. A structure using the above materials

but geared for use in larger, non-residential buildings.

4. A structure designed to substitute the

jute/plastic material for the traditional

thatch or corrugated metal roof and its

customary wood or bamboo support rafters.

The new roof of this prototype was designed

to fit over either traditional or new walls.

These four prototypes can be anchored

directly to the soil or to standard

perimeter footing foundations.

Many of these prototypes have been used for

other than residential purposes, and as such

have been very popular. These uses have

included a medical operating theater,

dispensary and office. From a socio-economic

view, this is seen as a useful lesson, in

that citizens of Bangladesh can get to know

the structures in a service role without

having to accept them suddenly into their

personal lives as homes.

Two additional CARE prototypes of more

traditional appearance were developed in the

United States using a panel made of a jute

reinforced polyester core and a fiber glass

reinforced polyester facing. The 10 ft. x

20 ft. two room units successfully passed severe simulated wind and water tests. (Ref . 14).

O Reinforced concrete shell roofs of

hyperbolic paraboloid shape have been used

for industrial and suburban housing. The

roof is anchored to the supporting brick

walls by means of half inch mild steel bars

at the corners.

40
••Housing programs

The 1971 war of independence left about 2 million families homeless. Sizeable housing

rehabilitation and reconstruction efforts

are now under way in rural areas. • The Delta Housing Program

Beginning in 1972, a rural cooperative housing

scheme got underway in the Delta area, a coastal strip of 4000 sq. miles with 4,270,000

bitants. Its main features have been:

Erection of 7500 10 ft X 20 ft soil-cement

block houses on burnt-brick foundations

to withstand severe flooding and substantial cyclonic winds.

A cooperative plan under which farmers

and fishermen undertake to repay 50%

of the cost of the house out of

agricultural income to their local

cooperative society. These societies

are linked into a complex cooperative

system known as the Integrated Rural

Development Program (IRDP) . (The other

50% of cost is subsidized)

One aim is to reduce the villager's

concern about the annual fate of his

house, and thus to attend more to long

range agricultural planning and

development; and, further, to reduce

his (and the government's) repair

expenditures after every cyclone

season

The program, its successes and limitations

are described in more detail in Ref. 23 • Siting

Creation of either artificial barriers or embankments in low-lying areas (so as to either shield houses or raise them above mean high flood levels) has been proposed

0

o

Oufk 4*iCkotriL- to

K/vffc U^- nrd<? O

41
as part of any new wind and flood protection

program.

It was found, for example, that Dutch "polder"

type barriers have protected many houses in

recent storms. Even when the water breached

the barriers and caused flooding, it did not

destroy the houses.

«1

j

By and large, raised embankments or platforms

are thought a better approach. A semiprivate shelter system based on this concept

is discussed in Ref. 22. Its main features

are

:

Build a platform 8 ft above mean high tide

level. Over it, erect a small (60 sq . ft.)

"pucca" quality shelter house (10 in. brick)

with a flat roof (behind a parapet) 13 ft.

above this platform (includes a 3 ft.

plinth)

.

Now a man, woman or child standing on

such a roof platform would be at least

24 ft above mean high tide level, and

this is said to be protection against even the worst onslaught of a storm surge.

Each 'bari' or community would be

responsible for building and maintaining

such a shelter, the interior of which

could serve as storage.

O

o

p

"*W "t St

WwJL Ztowtr lurvu&fcvt\ cL ^sb^-JLiZ &4 *****

• Nucleus housing

Widening the concept of "nucleus" housing has been

proposed. A basic, small, wind-secure house

(such as the soil-cement CARE house) could

serve as a starting point for adding space

horizontally or vertically to the taste of

the owner or tenant. Open, bamboo-andthatch lean-to additions have, indeed, been

created in some localities. In others, soilcement blocks have been plastered to better

resist wind, floods and temperature extremes.

Occasionally, a second and even a third story

are added.

42
•Materials

Since villagers are inclined by their socioeconomic priorities to put food and cattle

ownership before housing, a plan is

proposed in Ref . 22 to ensure building

materials delivery. Its main features are:

Mips j^k* S6^v~» -

O Government subsidies should be in the

form of materials not funds

The government should set. -up local

technical assistance units which would

help with organized harvesting of wood;

introduce mechanized milling to ensure tighter fit; show how to cultivate

plants that are sources of building

materials (such as the Nipa palm which

is semi-aquatic and does not displace

food growing and grazing land) ; and

provide seedlings.

Clay is plentful in Bangladesh, and

there is a 1000-year old tradition

of burnt brick construction. Crushed,

it can replace the imported cement in

concrete. It is useful as a foundation

and, in enough thickness, (10 in) better

resists extreme winds.

O

O The making and use of cement-soil block

has been discussed elsewhere in this

report and in the base report. • Wind and flood patterns

The most common sources of wind in Bangladesh

are the cyclonic typhoons, tornadoes and

norwesters. Damage is not only from wind

pressures but from heavy rain and storm surges

or high walls of water. Thus, the cyclone of

November 12, 1970 caused storm surges some 25

feet high; nearly 100 percent of the kutchas

and semi-permanent houses were demolished in

the area of the storm. The coastal areas of

the country are the most vulnerable to cyclonic storms. , Tornadoes are the most destructive storms.

They usually happen on land during the warm

season in flat areas, with few natural

barriers to hinder them. 200 mph winds are

common, but maximum wind speeds up to 500

mph have been estimated by some experts.

43
6 Storm surge

The storm surge that accompanies cyclones in

coastal Bangladesh usually moves inland at

about storm speed (5-25 mph) . Its mean

depth over a particular site is determined

by 5 variables, two of which are manvariable (Ref . 22 ) :

1. Severity of storm (this determines

height of water over normal sea level)

2. Level of daily sea tide at time storm

strikes

Land configuration and wind direction

(these reinforce or impede rise of water)

Elevation of site (natural plus build-up)

Distance from sea or major inlet (land,

trees and other vegetation resist flow)

.

The last two items are man-variable, and

should be linked to nature-variables in site

planning, design and construction policy.

i Storm warning systems

The huge death rate of the November 1970

cyclone was due in part to a new warning

system unfamiliar to the coastal villagers.

Since then, the new "danger — great danger"

warning scale has been supplemented with

a preparedness system under which 10

volunteers per "bari", each equipped with

signals, lights, etc., are linked by radio

to Red Cross central HQ in Dacca, which

receives and disseminates the latest storm

information.

There are also specially trained local

relief teams. (Ref. 24)

44
Conclusions

A clearcut picture of problems, needs and

solutions emerges from the diverse research

reports, surveys and statistics that served

as a basis for this report:

•As to the socio-economic aspects of designing

wind-resistant low-rise low-cost housing, the

cultural characteristics and financial

capacity of low-income groups must be taken

into account along with the technical

criteria if sound solutions are to stand

the test of widespread acceptance.

This does not mean that new, stronger and

less costly materials and construction

techniques must blindly imitate traditional

forms and processes. Nor, on the other

hand, should these ignore the long traditions

of indigenous building in the three

countries of this report. • One emerging result of new low-cost housing

tests in Bangladesh bears watching. The

interim use of new prototypes for other than

residential use , in a highly visible way as clinics and community offices, points up a viable way of exposing new forms and

materials to prospective users before they

must take the big cultural step and live

in them as families.

•Similarly, the so-called "sites and services"

approach, if tailored closely to the

characteristics and outlooks of the

communities involved, can capitalize on the

proven initiative, ingenuity and hardiness

of squatter and similar families. This will

help overcome the chronic barriers of

insufficient financial and material resources

in developing countries.

45
•Closely allied with the thinking behind "sites

and services" is the wisdom of gearing

innovations in materials or method to the

relatively plentiful labor supply in most

developing countries.

©This does not preclude prefabrication, but

places new focus on the need to identify,

produce, adapt or combine cheap local

substances made from natural earth, trees

and plants. Bamboo, various kinds of soil,

as well as jute, hemp, cane, split trees,

straw, peanut shells and coconut husks

are among materials that have been combined

with manufactured substances such as cement,

plastics and metals to produce inexpensive,

sturdy building materials. • How the building blocks are assembled is one

of the major touchstones for stable, wind

and water damage resistant houses. The

chief caveats are adequate anchorage of

roofing materials and trusses (if any) to

walls. Structural design of roof members,

splices and joints must accommodate high

wind velocities. Anchorage of houses to the

ground must be designed to prevent overturning; and wall openings must be placed to

avoid weakening the structure at vital

points and to prevent wind from entering and

exerting interior upward pressure on the

roof

.

Similarly, design features such as roof

pitch and overhangs must observe latest

findings on positive and negative wind

pressure distribution.

•Proper placement of houses in groups as well

as to accommodate prevailing wind direction

and land features will always raise the wind

damage resistance of houses. This should be

one of the first criteria to observe when

planning houses in areas subject to extreme

wind.

46
References

Many or the following studies and reports contain additional references,

varying from two or three to as many as seventy five.

(1)

" Design, Siting and Construction of Low-Cost Housing and Community

Buildings to Better Withstand Earthquakes and Windstorms," William F. Reps

and Eiail Simiu, editors. National Bureau of Standards, US Department of

Commerce, 1974. 133 pp., ill.

(2) "Socio-Zconomic and Architectural Considerations in Housing, " by Geronimo

V. Manahan and Josefina M. Ramos, Building Research Service, University

of the Philippines. 1973. 11 pp. Report prepared for International

Workshop on Development of Design Criteria and Methodology for Low-Rise

Low-Cost Buildings to better Resist Extreme Winds, held in Manila 14-17

November 1973.

(3) "Research Study of the So cic-Economic Aspects cf Low-Cost Housing in the

Philippines

. " Progress report prepared for National Bureau of Standards,

US Department of Commerce. 1972.

(4) "Low-Cost Housing and Extreme Wind-Related Problems in Jamaica" , by A. D. Adams, consulting engineer. 1973. 25 pp., ill. A two-part report

prepared for the National Bureau of Standards.

(5) "Economic Survey1 ', by National Planning Agency, Jamaica. 1972.

(6) "The Geography of Jamaica, " by Jamaica Information Service. 1972. Unpaged.

(7) "The People of Jamaica," by Jamaica Information Service. 1972.

(8) "Survey of "Housing Conditions in Delacree Pen." Continuous Social and

Demographic Survey Unit, Jamaica. 1969.

(9) "Tirst ?ve~crt or. Lew-Rise, lew-Cost Housing ar.c Extreme Wind-Related

Problems in Bangladesh, " by Dr. Jamilur R. Chowdhury , Department of

Engineering, Bangladesh University of Engineering and Technology. November

1973. 31 pp. ill. Prepared for National Bureau of Standards, US Department

of Commerce.

(1C > "Housing or, zr.a P;.ilir r ir.es " Preparatory materials for the Conference

on Housing. National Economic and Development Authority, Philippines. 1973.

(11) "Design of Low-Cost Housing and Community Facilities, Vol. 1: Climate

and House Design ," by Otto Koenigsberger , Carl Mahoney and Martin Evans.

United Nations. 1971. 93pp., ill.

47
(12) "Report of the International Seminar on Low-Cost Construction Resistant

to Earthquakes and Hurricanes. " United Nations. 1971. 59pp.

(13) "Special Report on Techniques of Aided Self-help Housing — some examples of U.S. and overseas experience," by Ervan Bueneman. Office

of International Affairs, HUD, 1973. 24pp.

(14) "Major Breakthrough in Low-Cost Plastic Housing using Jute-reinforced

Polyesters: the CARE/Winf ield/Bangladesh House," by Armand and Barbara

Winfield. Proceedings, 29th Annual Technical Conference, Reinforced

Plastics/Composites Institute, Society of Plastics Industry, Inc., 1974.

(15) "Housing for the Lowest Income Groups: the Calcutta Experience, ' 1 by K. C. Rosser, Ekistics Magazine, February 1971.

(16) "Report on Slum and Squatter Problems in Metropolitan Manila", by

Presidential Coordinating Council for Housing and Urban Development,

Manila, Office of the President, 1968.

(17) "Rehabilitation of Transitional Urban Settlements" , UNESCO, Committee

on Housing, Building and Planning, Report of the Secretary General,

E/C. 6/115, 17 August 1971. 39pp + appendices.

(18) "Chittagong Region and Metropolitan Chittagong: Proposals for Development" , by B.A.W. Trevallion in collaboration with the Chittagong Development

Authority, 1967. 209pp.

(19) "Sites and Services Programs: the Experience and the Potential", by

the International Bank for Reconstruction and Development in collaboration

with the United Nations. Human Settlements , a publication issued by the

Center for Housing, Building and Planning, United Nations. October 1972.

(20) "Urban Area Problems: Housing, Slums and Uncontrolled Settlements,

Recreation and Tourism," Human Settlements , January 1972.

(21) "Housing Through Cooperatives and Other Non-profit Associations" , Human Settlements , January 1974.

(22)

; ' UN Reconstruction and Relief in Bangladesh Following the

1970 Coastal Storm", end of tour report by Daniel C. Dunham,

Team Leader, Relief and Reconstruction Team, UN Development Program, Dacca. 1971. Unpublished.

This excellent report, referred to several times in the

text, also includes a bibliography, from which the following

items have been drawn:

(a) " Cyclone and Storm Surge Destruction", Report and

Recommendation on Cyclone Shelter Construction

by D.C. Dunham, USAID . Dacca. June 1965, designs,

photos, estimates. 30 pp.

48
(b) "Human Adjustments to Cyclone Hazards" , by Aminul

Islam, a case study of Char Jabbar. Dacca. Univ.

of Dacca, Dept. of Geography. 1970. 26 pp.

(c)

" Survey of 1971 Cyclone - Affected Region of Bangladesh" , by Drs. Sommer & llosley, US AID . 1971, maps,

charts, tables. 15 pp.

(d)

'"Handbook of Construction17

, Department of Democracy

and Local Government (by Peace Corps) Dacca, 1965.

Charts and drawings . 106 pp

(e) ' Report on Experimental House Types for Cyclone

Affected Areas of E. Pakistan' , Pakistan Government

Housing, Building and Res. Center, Dacca. 1971,

photos, estimates. 20 pp.

(f)

' Houses Can Resist Hurricanes ", by US Forest Service,

Madison, Wisconsin, USF Products Laboratory, 1965. 18 pp.

(g)

'' Social Grouping in Rural E. Pakistan", by Robert

Glasse. SEATO Cholera Research Lab. Dacca. 1965. Tables,

bibliography . 8 pp.

(23) "Ine Delta Housing Program -- Bangladesh 1972-1974 — An

Experiment in Rural Housing", prepared by Frank Sullivan

(ICDHA) for UN Commission for Asia and the Far East. 1974.

Unpublished. 10 pp.

(24)

'' Cyclones in 3angladesh", Dacca newspaper article dated

13 November 1973, by Ellen Sattar.

(25)

" Improvement of Slums and Uncontrolled Settlements ",

Report of Interregional Seminar, Medellin, Columbia, 15

February - 1 I'arch 1970. United Nations Publication,

Sales No. E71.IV.6. 203 pp. $4.50.

(26)

" Bibliography "

, Bangladesh Academy for Rural Development,

Comilla, Bangladesh. 1972. 28 pp.

(27)

"' Self-help Practices in Housing: Selected Case Studies ",

UN Dept. of Economic and Social Affairs, No. E73.IV.15.

129 pp. $5.00.

Report reviews 5 case studies from Africa and Latin

America. Instructive, especially the case of Cali,

Colombia, where families were given materials and technical assistance and sold a developed lot, which had to be repaid in 20 years.

(28)

"Hope for Improvement of Slum-Squatter Areas "', by Clarence

Shubert, Newsbriefs of Foundation for Cooperative Housing,

Washington, D.C. Aug. -Sept. 19 74.

49
( (29) " 7500 Housing Units Near Completion in Rural Bangladesh" , ICDHA Profile , December 1974. Newsletter published by

International Cooperative Housing Development Association,

( Washington, D.C.

(30)

" Building Research in Jamaica", a proposal for program and

staffing, by Ole Dybbroe. Scientific Research Council,

i Building Research Unit, Kingston. 1966. 23 pp. + appendices.

Good statement of research needs, both as to materials and

their acceptance.

(31)

::Kousing Construction in Hurricane-prone Areas", by Herbert

S. Saffir, PE. Prepared for Interregional Seminar on LowCost Construction Resistant to Earthquakes and Hurricanes,

Skopje, Yugoslavia. 1971. No. ESA/HBP /AC. 6/2. 71 pp.

A good, simply written treatise, but solutions are geared

to more advanced technologies (such as S. Florida) than to

those of developing countries. Contains details, examples

and design computations. Proposes a 5-point scale for

measuring hurricane intensity.

USCOMM-NBS DC 50
NBS-1UA (REV. 7-731

U.S. DEPT. OF COMM. |. PUBLICATION OR R K FOR T NO. 2. Gov't Accession BIBLIOGRAPHIC DATA No. shfft NBSIR 75-790

3. Recipient's Accession No.

4. TITLE AND SUBTITLE

FY75 PROGRESS REPORT ON DESIGN CRITERIA AND METHODOLOGY FOR

CONSTRUCTION OF LOW-RISE BUILDINGS TO BETTER RESIST TYPHOONS

AND HURRICANES

5. Publication Date November 1975

6. Performing Organization Code

7. AUTHOR! S) Ma.rsn.aii, Kicnaru u., Kaurasre, i\oei J.

8. Performing Organ. Report No. vrpCTD 7C 7Qf1 IVdoIK /b-/yu

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project . Task Work Unit No. Center for Bldg. Tech.

11. Contract/Grant No. PASA No. TA(CE) 04-73

12. Sponsoring Organization Name and Complete Address (Street, City, State, ZIP)

United States Agency for International Development

Department of State

Washington, D.C. 20523

13. Type of Report & Period Covered Final FY75

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

16. ABSTRACT (A 200-word or Jess (actual summary of most significant information. If document includes a significant bibliography or literature survey, mention it here.) This report represents the major accomplishments conducted during the third phase

(FY75) of a three year project to develop improved design criteria for low-rise buildings in developing countries to better resist extreme winds. The research study

sponsored by the Agency for International Development commenced in March 1973. Two

other reports were prepared; NBSIR 74-582 FY73 Progress Report (first phase of the

research--4 months) and NBSIR 74-567 FY74 Progress Report (second phase of the re- search- -12 months). During FY75, 6 major tasks were completed (instrumentation of

fifth and sixth of six test houses to collect full scale field wind data, continuation of technician training at the field sites and at the wind tunnel facility, analyzed of extreme wind data, development of draft improved design criteria reports,

participation in regional conferences in Manila and scheduling of regional dissemination of project results conference in Jamaica for November 1975) . Research activities

will be completed in December 1975. A final report will be published by the end of

FY76.

17. KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name; separated by semicolons

)

Buildings; codes and standards; housing; hurricanes; low-rise buildings;

natural disaster; structural connections; typhoons; wind loads.

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