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BUILDING SCIENCE SERIES

fiTMi?}TM?*''°S * TECH R.I.C. 56

f ""proved Design Criteria

to Better Resistthe Effects of Extreme Winds

for Low-Rise Buildings in Developing Countries

U.S. DEPARTMENT OF COMMERCE / National Bureau of Standards
The Building Science Series ^Yo.

I'he Building .Sciciico Series disseminates technical information developed at the National Bureau of Standards on

liuilding materials, components, systems, and whole structures. The Series presents research results, test methods, and performance criteria related to the structural and environmental functions and the durability and safety charac^terisUcs of building elements and systems. These publications, similar in style and content to the NBS Building Materials and Structures Reports <1938-59),

are directed toward the manufacturing, design, construction, and research segments of the building industry, standards organizations, and officials responsible for building codes. The material for this Series originates principally in the Center for Building Technology of the NBS Institute

for Applied Technology. The publications are divided into three general groups: Building Systems and Processes;

Health, Safety and Comfort; and Structures and Materials. For further information regarding these publications

please contact the Scientific and Professional Liaison Section, Center for Building Technology, Institute for Applied Technology. National Bureau of Standards, Washington, D.C. 20234.

I See mailing list announcement on last page l
NOV V 1374

Development of Improved Design Criteria

for Low-Rise Buildings in Developing Countries

to Better Resist the Effects of Extreme Winds

Proceedings of a Workshop held at the

Dr. Paulino J. Garcia Memorial Hall

National Science Development Board

Manila, Philippines

November 14-17, 1973

Edited by

Noel J. Raufaste, Jr., and

Richard D. Marshall

Center for Building Technology

National Bureau of Standards

Washington, D. C. 20234

Sponsored by

The United States Agency for International Development

U. S. Department of State The Philippine Advisory Committee

formed in conjunction with the above project

and

The U. So National Bureau of Standards

U.S. DEPARTMENT OF COMMERCE, Frederick B. Dent, Secretary

NATIONAL BUREAU OF STANDARDS, Richard W. Roberts, Director

Issued October 1974
Library of Congress Catalog Card Number: 74- 600158

\

National Bureau of Standards Building Science Series 56

Mat. Bur. Stand. (U.S.), BIdg. Sci Ser. 56, 171 pages (Oct. 1974)

CODEN: BSSIMBV

U.S. GOVERNMENT PRINTING OFFICE

WASHINGTON: 1974

For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402

(Order by SD Catalog No. CI 3.29/2: 561 . Price $2.35
3

Dedicated

to the memory of

Mrs. Magdalena A. Templa

whose enthusiasm and dedication to the

improvement of technology made this workshop possible.

ABSTRACT

An International Workshop held in Manila, Philippines, on November 14-17, 1973, addressed the state-of-the-art in mitigating building damages from winds. The workshop was jointly

sponsored by the United States Agency for International Development (USAID) , the Philippine

Advisory Committee (formed in conjunction with this research project), and the U. S. National Bureau of Standards (NBS) . This report presents the proceedings derived from the

workshop. The proceedings present recommendations, the workshop program, five reports, and

nine technical articles. The technical articles addressed four primary topics which were

used to guide subsequent workshop discussions. The topics addressed were; wind and aerodynamics, structural related technology, socio-economic and architectural considerations, and

codes and standards

.

The results of the workshop will serve a twofold purpose. The first suggests improved building practices for developing countries. This was accomplished through the development of

recommendations designed to upgrade to a minimum acceptable level design criteria for lowrise buildings. The second involves integrating appropriate workshop information into the

overall three-year AID sponsored research project to develop improved design criteria for

low-rise buildings in developing countries to better resist the effects of extreme winds.

Key words: Codas and standards; Information transfer; Low-rise buildings; Pressure transducers; Socio-economic; Structural design; Technology implementation; Wind effects; Wind

loads

.

V

CONTENTS

Introduction 1

Workshop Recommendations ^

Recoiranendation 1 - Communication and Exchange of Information 3 Recommendation 2 - Manuals of Accepted Practice 3 Recommendation 3 - Land Use Planning 3 Recommendation 4 - Collection and Dissemination of Wind Data A Recommendation 5 - Wind Observation Stations 4 Recommendation 6 - Structural Loading 4 Recommendation 7 - Roofing and Cladding Loads 4 Recommendation 8 - Unusual Building Shapes 4 Recommendation 9 - Maintenance 5 Recommendation 10 - Post Disaster Surveys 5 Recommendation 11 - Licensing of Professionals 5 Recommendation 12 - Student Education 5 Recommendation 13 - Continuing Education 5 Recommendation 14 - Wind Research Center 6

Appendix A - Workshop Program 7

Appendix B - Presentations and Technical Papers 17

Remarks by T. C. Nib lock .... ••••••••••••••••••••••••••••••••••#• ift Introductory Reiuarks^by A. L. Juinlo I!!!! j^g Background of Study by N. J. Raufaste, Jr

Summary of Accomplishments by E. G. Tabujara 2^

Climatology and Wind Related Problems In the Philippines by

R. L. Kintanar 2 8 Aerodynamics of Structures and Wind Tunnel Modeling by

R. D. Marshall ^3

Remarks by A. A. Alejandrlno y -j Some Problems in the Analysis of Lateral Wind Force Resisting

Systems by J. Ma. de Castro 73

Socio-Economic and Architectural Considerations in Housing

by G. V. Manahan, and J. M. Ramos

Lessons Learned from Post Wind Disaster Investigations by

E. 0. Pfrang

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

In Bangladesh by J. R. Choudhury -1^02 Remarks by W. Woudenberg 121

Low-Cost Housing and Extreme-Wind-Related Problems in Jamaica

by A. D. Adams 123

Wind Pressure Provisions of the National Building Code Republic

of the Philippines by A. R. Flores 140

Standardization in the Philippines Today by A. R. Flores 2.53 Wind Research in the United Kingdom by K. J. Eaton j^^g

Appendix C - Units of measure and SI conversion factors . 160

vli

DEVELOPMENT OF IMPROVED DESIGN CRITERIA FOR

LOW-RISE BUILDINGS IN DEVELOPING COUNTRIES

TO BETTER RESIST THE EFFECTS OF EXTREME

WINDS

(Proceedings of a Workshop)

Edited by

Richard D. Marshall and Noel J. Raufaste, Jr.

INTRODUCTION

The Philippines experienced more than 140"'" tropical storms between 1965 and 1971. These

storms cause many hundreds of deaths and many hundreds of millions of dollars of property

damage. In 1970, for example, when the Philippines were lashed by four disastrous typhoons

and 17 tropical storms, the death toll ran over 1,000. But wind-caused death and destruction

are not confined to the Philippines; similar losses are inflicted on the Indian Ocean countries, the Northern Caribbean islands, and the United States.

The problem of extreme winds and their effects on buildings is obviously one of considerable

magnitude. It is a problem abetted by a lack of information about acceptable building practices and a lack of knowledge concerning the effects of winds on buildings.

Several conferences, workshops and seminars on extreme winds and their effects on buildings

and structures were conducted during the past decade. One national workshop was sponsored by

The National Bureau of Standards (NBS) . This workshop, conducted in 1972 at Boulder, Colorado, centered on current building practices, reviewed disaster mitigation activities and presented recommendations for improvements.

While significant advances have been made in the assessment of wind loads on. buildings , much

remains to be done, particularly in the area of low-rise buildings which have not had the

research attention that has been accorded tall structures.

The United States Agency for International Development (USAID) , being aware of this problem,

requested NBS to develop improved design criteria for low-cost/low-rise buildings in developing countries to better withstand the effects of extreme winds. Accordingly, one objective

of the project is to assess the state-of-the-art of low-cost building technology. To accomplish this, a workshop was held with those individuals concerned with improving building design criteria (research workers, engineers and design professionals).

This workshop was conducted during November 14-17, 1973, at the Dr. Paulino J. Garcia Memorial Hall, National Science Development Board, Manila. Four current state-of-the-art themes

covering climatology and aerodynamics, structural engineering, socio-economic and architectural considerations, and codes and standards were discussed.

The first two workshop days were devoted to presentations of technical papers. During the

afternoon of the first day, a visit was scheduled to the field test site at the Philippine

Atmospheric Geophysical and Astronomical Services Administration (PAGASA) Science Garden in

Quezon City where pressure measurements are being conducted on full-scale houses. Nine

papers were presented during the technical sessions with time reserved for discussions. The

third day was devoted to subcommittee working sessions and the resulting recommendations

were presented and discussed on the fourth day.

1 Research Study of the Socio-Economic Aspects of Low-Cost Housing in the Philippines.

Progress Report, Sycip, Gores, Velayo, and Co. CPA, Manila, Philippines, March 1972.

1
Approximately 140 individuals from five countries attended the workshop. This document,

which constitutes the proceedings of the workshop, includes recommendations for improved

building practices, the opening ceremonies, and five reports and nine technical articles

prepared by the National Bureau of Standards, the Philippine Advisory Committee, delegates

from Bangladesh and Jamaica, and the Building Research Establishment (U.K.) are Included.

The workshop program is attached as Appendix A.

The oral reports and technical papers, both of which were reviewed by the authors subsequent

to the workshop, follow the recommendations which stem from the workshop.

2
WORKSHOP RECOMMENDATIONS

The recommendations contained herein represent the consensus of the International Workshop

attendees. They do not, however, constitute any individual endorsement by any one participant or organization.

It was the intent of the workshop to identify deficiencies in data gathering procedures,

wind effects on buildings and building practices. The purpose of the recommendations is to upgrade, to a minimum acceptable level, design criteria for low-cost buildings, and finally,

to suggest improvements in the building processes.

RECOMMENDATION 1 - COMMUNICATION AND EXCHANGE

OF INFORMATION

A NATIONAL FOCAL POINT SHOULD BE ESTABLISHED IN DEVELOPING COUNTRIES TO PROMOTE COMMUNICATION

BETWEEN METEOROLOGISTS AND CLIMATOLOGISTS , THE

DESIGN PROFESSION, REGULATORY OFFICIALS AND

BUILDING AUTHORITIES ON MATTERS CONCERNING THE

DESIGN OF BUILDINGS TO RESIST WIND FORCES.

The interdisciplinary nature of wind effects on buildings requires close communication and

cooperation between individuals in several areas of science and technology. This can best

be accomplished through the establishment of a national focal point, such as a wind research

center, where the needs of the design profession are identified and the collection of wind

data can be directed to meet the needs.

RECOMMENDATION 2 - MANUALS OF ACCEPTED PRACTICE

MANUALS OF ACCEPTED BUILDING PRACTICE SHOULD BE

FORMULATED BY COMMITTEES REPRESENTING APPROPRIATE

SCIENTIFIC AND PROFESSIONAL ORGANIZATIONS, AND

SHOULD INCLUDE STANDARD DETAILS OF CONVENTIONAL

BUILDING SYSTEMS.

Manuals of accepted practice should demonstrate and explain in a manner acceptable to both

practicing professionals and laymen, the design provisions and details necessary to ensure

the satisfactory performance of buildings subjected to anticipated loads. The manuals should

contain both textual and pictorial step-by-step instructions for the proper construction of

buildings. The version intended for the layman should be formatted so that the reader can understand the instructions and requirements without professional assistance. The manuals

should be revised as new information becomes available.

RECOMMENDATION 3 - LAND USE PLANNING

A COMPREHENSIVE PROGRAM ON IMPROVED LAND USE

PLANNING SHOULD BE ESTABLISHED TO REDUCE THE

DAMAGE POTENTIAL OF EXTREME WINDS AND HEAVY

RAINFALL

.

An effective system for improving land use planning should be implemented by appropriate,

qualified professionals, and should include the participation of government agencies, and

private and professional groups involved with building design, construction and financing.

3
RECOMMENDATION 4 - COLLECTION AND DISSEMINATION

OF WIND DATA

METEOROLOGICAL AGENCIES AND RELATED GROUPS SHOULD

BE ENCOURAGED TO COLLECT MEAN HOURLY WIND SPEED

AND PEAK GUST DATA AND DISSEMINATE THIS INFORMATION TO PRIVATE AND GOVERNMENTAL GROUPS INVOLVED

WITH BUILDING DESIGN AND CONSTRUCTION.

Weather observation stations in most countries record wind speeds averaged over a lO-minute

period at the hour of observation. For design purposes, wind speeds averaged over a period

of 1-hour are more convenient, provided that information on the peak gust within the hour is

also known.

RECOMMENDATION 5 - WIND OBSERVATION STATIONS

THE METEOROLOGICAL SERVICES IN DEVELOPING COUNTRIES WHICH REGULARLY EXPERIENCE HURRICANES OR

TYPHOONS SHOULD TAKE THE LEAD IN IMPROVING THE

DISTRIBUTION, DENSITY AND SITING OF WIND OBSERVATION STATIONS.

Wind observation stations are usually located at airfields to provide for needs of the aviation industry. Consideration should be given to the collection of wind data in urban areas

and areas having a potential for development. Selection of future station sites should be

aimed at improving the geographic definition of design wind speeds.

RECOMMENDATION 6 - STRUCTURAL LOADING

STRUCTURAL DESIGN FOR WIND LOADS SHOULD TAKE INTO

ACCOUNT THE LOCAL WIND CLIMATE AND THE EFFECTS OF

SURROUNDING TERRAIN AND NEIGHBORING STRUCTURES ON

THE CHARACTERISTICS OF SURFACE WINDS.

The characteristics of surface winds, such as mean speed, variation of speed with height,

and intensity of turbulence, can be drastically altered by local surface features and neighboring buildings. Basic design speeds should be adjusted to account for these effects.

RECOMMENDATION 7 - ROOFING AND CLADDING LOADS

THE DESIGN OF ROOFING AND CLADDING ELEMENTS SHOULD

TAKE INTO CONSIDERATION THE EFFECT OF LOCAL PRESSURE FLUCTUATIONS NEAR THE CORNERS OF WALLS, ALONG

THE EDGES OF ROOFS AND UNDER EAVES.

The intensity of localized pressure fluctuations can far exceed the mean pressures used to design the overall structure. If not properly accounted for, these fluctuations can cause

local failures which rapidly lead to complete failure of the structure.

RECOMMENDATION 8 - UNUSUAL BUILDING SHAPES

BUILDINGS HAVING UNUSUAL SHAPES AND STRUCTURAL

CHARACTERISTICS THAT ARE NOT COVERED BY RECOGNIZED CODES OF PRACTICE SHOULD BE SUBJECTED TO

APPROPRIATE WIND TUNNEL MODEL STUDIES.

It Is neither practical nor possible to cover all possible building shapes when specifying

design wind pressures. Because of the complex nature of building aerodynamics, it Is not

generally possible to predict these pressures by theory or intuition and one must resort to

wind tunnel tests In which the building and surface winds are properly modeled.

4
RECOMMENDATION 9 - MAINTENANCE

BUILDINGS SHOULD BE DESIGNED SO THAT ROUTINE

PREVENTATIVE MAINTENANCE CAN BE PERFORMED WITHOUT UNDUE DIFFICULTY.

Buildings and building components exposed to extreme winds are subject to damage or dlsplace-

' ment. Buildings should be designed In such a manner that Inspectors may check and maintain

the building without undue difficulty. Such checks should be performed periodically and

prior to the hurricane or typhoon season. Whenever possible, minimum maintenance materials

should be used.

RECOMMENDATION 10 - POST DISASTER SURVEYS

PROVISION SHOULD BE MADE FOR CONDUCTING POST

DISASTER SURVEYS BY APPROPRIATE GOVERNMENT AND

PRIVATE GROUPS.

Post-disaster surveys provide extremely useful Information on the adequacy of building code

provisions, construction practices and building performance. The engineering community

should develop plans and procedures to collect such Information, Interpret It, and disseminate their findings.

RECOMMENDATION 11 - LICENSING OF PROFESSIONALS

ARCHITECTS AND ENGINEERS ENTRUSTED WITH BUILDING

DESIGN AND CONSTRUCTION SUPERVISION SHOULD BE

LICENSED BY AN APPROPRIATE PROFESSIONAL LICENSING

BOARD.

The licensing board should establish rules and regulations that provide consistent requirements for the licensing of all architects and engineers. These licensed professionals should

assure that future buildings be designed to comply with the minimum wind loading requirements.

It Is essential to the sucessful Implementation of Improved building practices that architects and engineers be familiar with these requirements.

RECOMMENDATION 12 - STUDENT EDUCATION

THE PROFESSIONAL SOCIETIES SHOULD WORK CLOSELY

WITH COLLEGES AND UNIVERSITIES TO DEVELOP COURSES

OF STUDY FOR ENGINEERING AND ARCHITECTURAL STUDENTS RELATED TO THE EFFECTS OF WIND ON BUILDINGS.

It Is essential that Information on Improving building designs to better resist extreme winds

be made available to architectural and engineering students. This can be accomplished

through seminars, workshops and formal courses.

RECOMMENDATION 13 - CONTINUING EDUCATION

PROGRAMS OF CONTINUING EDUCATION SHOULD BE

DEVELOPED AND IMPLEMENTED FOR INDIVIDUALS

INVOLVED IN THE DESIGN AND CONSTRUCTION OF

BUILDINGS

.

5
Continuing education programs can improve the current state-of-knowledge of design professionals, regulatory officials, and builders. Such programs may take the form of workshops, seminars, formal training courses, brochures and technical journals.

RECOMMENDATION 14 - WIND RESEARCH CENTER

A WIND RESEARCH CENTER SHOULD BE ESTABLISHED AND

SUPPORTED BY APPROPRIATE ORGANIZATIONS TO STUDY

THE EFFECTS OF WINDS ON BUILDINGS.

Since many of the problems associated with the design of buildings to resist wind loads are

luiique to each country, the establishment of a research capability is essential to keep pace

with changing conditions. Such a center would not only carry on research, but would also

serve as a link with institutions in developed countries involved in similar work.

6
APPENDIX A

WORKSHOP PROGRAM

7
APPENDIX A

INTERNATIONAL WORKSHOP PROGRAM

on the

"Development of Improved Design Criteria

for Low-Rise Buildings in Developing

Countries to Better Resist the Effects

of Extreme Winds"

Jointly Sponsored

by

U.S. National Bureau of Standards

U.S. Agency for International Development

The Philippine Advisory Committee

November 14 to 17, 1973

at the

Dr. Paulino J. Garcia Memorial Hall

National Science Development Board (NSDB)

Herran, Manila

8
PHILIPPINE ADVISORY COMMITTEE

Dean ALFREDO L. JUINIO, Honorary Chairman

U.P. College of Engineering

Dr. ERNESTO G. TABUJARA, Chairman

U.P. Building Research Service

Prof. GERONIMO V. MANAHAN, Executive Secretary

U.P. Building Research Service

Prof. ANGEL A. ALEJANDRINO, National Hydraulic Research Center

Mr. CATALINO P. ARAFILES , Philippine Atmospheric Geophysical and

Astronomical Services Administration

Mr. MANUEL C. BONJOC, Philippine Atmospheric Geophysical and

Astronomical Services Administration

Engr. CESAR A. CALIWARA, Philippine Association of Civil Engineers

Arch. CESAR H. CONCIO, National Building Code Committee

Mr. ROMEO C. CORDOBA, National Science Development Board

Engr. AMBROSIO R. FLORES , Philippine Standards Association

Engr. ANDRES 0. 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

Dr. ROMAN L. KINTANAR, Philippine Atmospheric Geophysical and

Astronomical Services Administration

Engr. ROSALIO A. MALLONGA, Bureau of Public Works

Mr. WELLINGTON A. MINOZA, 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. MANUEL R. REBUENO, People's Homesite and Housing Corporation

Col. ALBERTO R. SANCHEZ, Land and Housing Development Corporation

Engr. MODESTO D. SORIANO, JR., Government Service Insurance System

Mrs. MAGDALENA A. TEMPLA, National Science Development Board

Gen. GAUDENCIO V. TOBIAS, National Housing Corporation

CYNTHIA SENORAN ENRIQUEZ, Secretary of the Committee

9
INTERNATIONAL CONSULTANTS, DELEGATES AND GUESTS

Mr. ALFRICO D. ADAMS, Partner, Douet, Brown, Adams and Associates, Engineers, Kingston, Jamaica

Dr. JAMILUR R. CHOUDHURY, Assistant Professor, Civil Engineering, Bangladesh University of Engineering & Technology, Dacca, Bangladesh

Dr. KEITH J. EATON, Senior Research Officer, Building Research Establishment, United Kingdom

Mr. THOMAS E. JOHNSON, Deputy Assistant Director for Capital Development,

U.S. Agency for International Development

Mr. WILLIAM C. LARSON, 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, Structural Research Engineer, Center for Building

Technology, Institute for Applied Technology, National Bureau of

Standards

Mr. THOMAS C. NIBLOCK, Director, U.S. Agency for International Development,

Mission to the Philippines

Dr. EDWARD 0. PFRANG, Chief, Structures Materials and Life Safety Division,

Center for Building Technology, Institute for Applied Technology,

National Bureau of Standards

Mr. NOEL J. RAUFASTE, JR., Federal Building Program Coordinator, Office

of Federal Building Technology, Center for Building Technology,

Institute for Applied Technology, National Bureau of Standards

Mr. GUNTER P. STEITZ, Project Manager, RP-US Bayanihan School Reconstruction Project, Office of Capital Development, U.S. Agency for

International Development

Mr. WILLIAM WOUDENBERG, Designer, CARE, Inc, Dacca, Bangladesh

10
Master of Ceremonies

8:45

9:30 Philippine National Anthem

9:35 Welcome Remarks

9:45 Introductory Remarks

10:00 Background of Study

Master of Ceremonies and Marshal

1:30 Aerodynamics of Structures

and Wind Tunnel Modelling

2:30

3:30 Introduction to Wind

Measuring Equipment

3:45 Visit Experimental House

WORKSHOP PROGRAM

Wednesday, November 14, 1973

Engr. Cesar A. Caliwara

Philippine Association of Civil

Engineers

Mr. Thomas C. Niblock,

Director, USAID Mission, Manila

Dean Alfredo L. Juinio

U.P. College of Engineering

Mr. Noel J. Raufaste, Jr. National Bureau of Standards

Dr. Ernesto G. Tabujara

U.P Research Building Service

Dr. Roman L. Kintanar, PAGASA

Col. Alberto R. Sanchez, Land

and Housing Development Corp.

Dr. Richard D. Marshall

National Bureau of Standards

and

Prof. Angel A. Alejandrino

National Hydraulic Research

Center

Dr. Richard D. Marshall,

National Bureau of Standards

Registration

10:30 Summary of Local Accomplishments

10:45 Break

11:00 Climatology and Wind

Related Problems

12:00 Lunch - Courtesy of Marsteel

Corporation

Visit to the Science Garden Center of the PAGASA

5:00 Social Hour - Courtesy of PAGASA

11
WORKSHOP PROGRAM

Thursday, November 15, 1973

Master of Ceremonies Gen. Gaudencio V. Tobias

National Housing Corporation

9:00 Some Problems in the

Analysis of Lateral Wind

Load Resisting Systems

9:45 Soclo-Economic and Architectural

Considerations in

Low-Cost Housing

10:30 Break

10:45 Lessons Learned from Post Wind

Disaster Investigations

Prof. Jose Ma. de Castro

U.P. College of Engineering

Dr. Josefina M. Ramos and

Prof. Geronimo V. Manahan

U.P. Building Research Service

Dr. Edward 0. Pfrang,

National Bureau of Standards

11:30 Lunch - Courtesy of:

Association of Structural Engineers of the Philippines, National

Society for Seismology and Earthquake Engineering of the Philippines,

Philippine Association of Civil Engineers

Master of Ceremonies Engr. Jose P. Orola

Government Service Insurance

System

1:00 Technical Paper Dr. Jamilur Choudhury,

Bangladesh

2:00 Technical Paper Mr. Alfrico D. Adams

Consulting Engineer, Jamaica

3 : 00 Break

3:15 Codes and Standards Engr. Ambrosio R. Flores

Philippine Standards Assn.

Dr. Keith J. Eaton

Building Research Establishment

4:00 Wind Research in the

United Kingdom

4:45 Conclusion

12
WORKSHOP PROGRAM

Friday, Noveinber 16, 1973

Workshop Session Coordinators Prof. Angel A. Alejandrino

Mr. Noel J. Raufaste, Jr.

Co-Chalrmen Rapporteur

9:00 Workshop

Sessions A. Dr. Richard D. Marshall

Mr. Catalino P. Arafiles

Dr. Angel A. Alejandrino, NHRC

B. Dr. Keith J. Eaton

Engr. Andres 0. Hlzon

Engr. Rosallo A. Mallonga, BPW

C. Mr. Noel J. Raufaste Jr. Dean Aurello T. Jugullon

Col. Manuel R. Rebueno, PHHC

D. Dr. Edward 0. Pfrang

Engr. Octavlo A. Kalalo

Engr. Miguel V. Paala, SSS

10:30 Break

12:00 Lunch - Courtesy of

Engr. Cesar A. Callwara

Engr. Romeo S. Caparros

Engr. Octavlo A. Kalalo

Dr. Florello R. Estuar

Engr. Lauro M. Cruz

Engr. Angel Lazaro, Jr.

1:30 Continue Workshop Sessions

3:00 Break

4:30 Conclusion

13
WORKSHOP PROGRAM

Master of Ceremonies, .Arch. Cesar H. Concio

National Building Code

Committee

9:00 Presentations and

Discussions

11:45 Closing Ceremony

12:00 Lunch - Courtesy of Weldon Construction Corporation

6:00 Coctails - Architectural Centre Club

Makati, Rizal

Courtesy of

:

B. F. Homes Incorporated

and

Philippine Shares Corporation

Coffee Breaks - Courtesy of:

Saturday, November 17, 1973

Co-chairmen of Sessions

Mr. Noel J. Raufaste, Jr. National Bureau of Standards

and

Dr. Ernesto G. Tabujara,

U.P. Building Research Service

California Sales Corporation

Commonwealth Foods

Getz Bros, and Co. Republic Flour Mills

American International Dairy Co. Standard Brands of the Philippines

14
WORKSHOP SUBCOMMITTEES

Dr. Ernesto G. Tabujara

Overall Chairman

FINANCE

Mrs. Magdalena A. Templa, Chairman

Dr. Ernesto G. Tabujara

Engr. Modesto D. Soriano, Jr. Col. Alejandro R. Kabiling

Engr. Miguel V. Paala

RECEPTION AND HOSPITALITY

Arch. Cesar H. Concio, Chairman

Dr. Richard D. Marshall

Dr. Josef ina M. Ramos

Prof. Geronimo V. Manahan

Engr. Cesar A. Caliwara

Col. Alberto R. Sanchez

TECHNICAL PAPERS AND DOCUMENTATION

Engr. Ambrosio R. Floras, Co-Chairman

Dr. Josefina M. Ramos, Co-Chairman

Mr. Noel J. Raufaste, Jr.

ARRANGEMENTS

Engr. Jose P. Orola, Chairman

Mr. Noel J. Raufaste, Jr. Engr. Modesto D. Soriano, Jr. Mr. Catalino P. Arafiles

Engr. Rosalio A. Mallonga

SECURITY

Col. Manuel R. Rebueno

PROGRAM, INVITATION AND PUBLICITY

Engr. Octavio A. Kalalo, Chairman

Dr. Ernesto G. Tabujara

Engr. Andres 0. Hizon

15

APPENDIX B

Report Presentations and Technical Papers

17
WELCOME REMARKS

by

Thomas C. Niblock

Director, U. S. Agency for International Development

Mission, Philippines

Ladies and Gentlemen

:

I would like to congratulate the planners who made this conference possible. One of the

problems which has faced planners providing foreign assistance is that of assuring that the

benefits of such assistance accrue to the poor. Many critics have asserted that one of the

major failings of foreign aid is that the benefits go primarily to the rich. They see slums

growing, that the poorest farmers have benefitted little from increased agricultural production, etc. Consequently, some Members of Congress and others despair of supporting foreign

assistance.

Certainly, one of the problems most difficult in this typhoon-prone country is that of

providing wind-resistant shelter at a cost which the average person can afford. What you

will be discussing is a very relevant topic not only because it is addressed to a technical

problem of the profession, but because the target of this work is the underprivileged group

in the community. I think that if this seminar can provide us a significant step forward in

improving low-cost housing programs, a tremendous need throughout the developing world, it

will have made a significant contribution.

The. U.S. Government has had a program for many years which has provided investment guaranty to institutions wishing to invest in housing projects in other countries. Large sums

of money are available from U.S. savings institutions, some of which are available for transfer on a loan basis to the developing countries. These funds have assisted in some measure

the improvement of housing programs in North America. But the terms and conditions on which

these funds have been available are such that they have gone largely to the middle class.

If you can make a contribution in improving the technology, types of materials, the designs,

or whatever for low-cost housing, there is the potential of funds to finance such housing.

For the first time in 10 years I expect to see passed shortly a new Foreign Assistance

Bill. This new bill emphasizes the necessity to find ways and means to have more relevance

for the poor people in the world. No longer is it adequate to provide economic assistance

without concern as to whom the primary beneficiaries will be within a country. This new bill

provides us with an opportunity and with a challenge. We must find ways to exploit the

opportunity and to address the challenge. Certainly the subject you have chosen is one of

great relevance in light of this new legislation.

It is for this reason that I am particularly anxious to encourage this group and others

to deliberate and discuss ways of achieving greater benefits for the poor with the use of

foreign assistance. With you here, I am looking forward to a fruitful conference.

18
INTRODUCTORY REMARKS

by

Alfredo L. Juinio

DEAN, College of Engineering, University of Philippines

Director Nib lock. Dr. Tabujara, distinguished guests from overseas, my esteemed colleagues in the profession—and I see my mentors — ladies and gentlemen: In a way this is

like a homecoming. I have been out of step for sometime now and I feel lost. I am glad of

this opportunity to be able to be with you once more. Now I am in my own element. First of

all, I want to do my job as the Honorary Chairman.

To our guests, especially those from overseas, welcome. I hope you are enjoying your

stay here.

I wish to congratulate the organizers of this International Workshop for bringing together engineers, scientists and researchers, who are all very much interested in the study

of extreme winds as they relate to the design of buildings.

Mr. Niblock of course has very ably explained to you why this is very important to this

country. I refer to the emphasis placed on low-rise/low-cost buildings. After all, it

is said that the Philippines suffers from the great frequency of strong winds — destructive

typhoons. With respect to the designing of buildings and houses this Workshop can do a lot

in solving this problem which affects a great bulk of our people, more than 95 per cent of our people.

As far as I can recall, this may indeed be the first serious cooperative effort to seek

local design criteria, particularly for low-rise, low-cost buildings.

Before this seminar I remember when I was actively teaching that we used textbooks

printed overseas. We can see now how the data on wind velocities printed then differ from

actual figures. I remember too that in the Greater Manila area the effects of strong winds

differ where roofs of rich homes blew up while humble hovels stayed put. We can see from

that that we know so little and that we have to extend what we know. That is why we are glad about the approach being done to this project at this time.

The effects of typhoons which visit the country every year easily makes the Philippines

a convenient natural laboratory. I remember that two years ago we were hit by about 23 typhoons. Dr. Kintanar, correct me if I am wrong. I think we are being hit by 17 or 19 typhoons of varying degrees every year. This makes the Philippines a fertile ground for research.

In this regard, I am fully aware that our PAGASA, the former Weather Bureau, has collected throughout these years an enormous amount of wind data. I believe. Dr. Kintanar can elaborate on this later.

Unfortunately, in the past we suffered from one common deficiency — we did not have

enough funds to collate these data. And these have not been properly nor adequately correlated with engineering applications so as to be readily useful to engineers, architects,

designers and builders. I think we can make further progress if we begin with the data

collected by Dr. Kintanar who has collected these over the years.

With the advent of more sophisticated pressure devices and related recording equipment,

the much desired correlation among important parameters can now be done quite conveniently.

The more one gets exposed to this might and fury of the forces of nature, the more healthy

respect he develops for them.

I am reminded of the time when we were flying over Central Luzon. We wanted to see the

conditions in Central Luzon during one of those times. But when we saw the situation, the

might of the wind and water forces — we told the pilot: "We place our lives in your hands."

We went back. I think that is something we do not appreciate until we realize or see the

destructive might of these forces of nature.

19
Admittedly, there is still no substitute for fullscale tests if done extensively. The enormous amount of wind information already collected will be very useful for building con- struction or building design. However, this kind of investigation can indeed prove very

expensive. It is with this thought in mind that this study plans to include wind tunnel

tests to complement actual field results. The project is planned for three years and we

wish it can be accelerated. However, we can all be confident that whatever recommendations

may come out of the study will be arrived at in accordance with scientific and refined

methods

.

A fact which must be appreciated is that the Advisory Committee is composed of experts

in their own right representing various government and private entities, as well as professional organizations.

Some two years ago when this project was talked about, I was approached to express my

feelings about it . I remember that one of the compelling reasons given by the organizers

was how we can effectively organize all sectors — academicians, active contractors, builders, designers, architects, engineers and everybody concerned with buildings.

At this time I am glad to report to you — I express my feeling — that this can be

done. And this can be done because there is a common interest in all of these people.

Their enthusiasm and support serve to encourage and inspire us all. It vindicates a feeling I have expressed many times before that such cooperative effort is indeed feasible.

We are grateful to our friends from the U.S. National Bureau of Standards and the USAID

for making available to us valuable and modem equipment without which this research cannot

be as meaningful as it is intended to be.

On our part, we hasten to assure our colleagues that we will contribute whatever skill

and knowhow we can muster until we shall have attained our objectives. We pray for and look

forward to the success of this undertaking with the sobering thought that we all have so much to learn. Thank you.

20
BACKGROUND OF STUDY

by

Noel J. Raufaste Jr. Center for Building Technology, Institute for Applied Technology,

National Bureau of Standards, Washington, D. C. 202 34

Thank you, Mr. Caliwara, Dean Juinio, Mr. Nib lock, Dr. Tabujara, ladies and gentlemen,

good morning. It is a privilege for us to be here and to participate in this Workshop and

to work with so many distinguished attendees.

I would like to thank you for being here this morning. I very much appreciate your

attendance. I should especially like to welcome the new members of the Philippine Advisory

Committee and all nonmembers attending this Workshop this morning and for the ensuing three

and a half days. We are proud and happy to have you associated with us, and we promise to

do whatever we can to make your attendance at this Workshop a meaningful one.

This morning I would like to summarize with you the direction which we are going and,

with some careful focusing and delineation as with the aid of a telephoto lens, give you a glimpse of the activities that lie ahead and what needs to be done. First of all, in order

to perhaps develop a little better appreciation of why we are here and what we are doing,

let me quickly review with you who we are and present to you a background of the activities

associated with this project.

The National Bureau of Standards, located in Washington, D. C. , provides technical resources to all federal agencies and to state and local agencies. We also provide support to private industry, universities and the general public through our role as the federal laboratory. We do not develop new products, materials or systems nor do we compare or rank

competitive products. We are, however, engaged in developing improved technology, and in

our case for building related activities, and in the dissemination of such technology. As

such we are actively involved in testing material products, developing standardized test

procedures, designing new instrumentation for improved testing, and developing materials and

component specifications

.

The National Bureau of Standards has recently completed a two-year research project in

which many of you participated. This project was sponsored by USAID to provide initial research and analysis on the design, siting and construction of low-cost buildings to better

resist earthquakes and windstorms. This project evaluated the potential of applying improved housing technology to mitigate earthquake and extreme wind damages to buildings in

developing countries. In addition, we evaluated relevant socio-economic and cultural constraints which could affect current and new technology. This project recommended that additional research in extreme winds has a potential for very high payoffs.

I would like to introduce the project sponsor, Mr. William Littlewood from USAID.

This is one of several projects within the National Bureau of Standards overall program

in building practices for disaster mitigation.

The recommendations from the previously mentioned project were based on such factors

as: (1) building failures due to extreme winds in the Philippines and other developing

countries represent annual losses of many millions of dollars and hundreds and even thousands of lost lives. We all know the after-effects of the 1970 typhoons in the Philippines.

This problem requires immediate attention. (2) A more complete data bank exists about extreme winds and their effects on tall buildings; however, little wind data currently exists

on low-rise buildings.

Also, there is considerable evidence to indicate that existing codes do not make provision for steady and fluctuating wind pressures along the edges of roofs and walls where

separated flows occur. These regions of extremely low pressures, coupled with high uplift

pressures under overhanging eaves, constitute an example of one building area in need of improved design criteria. This topic will be discussed by Dr. Marshall. The above are only

examples of some of the background leading up to initiating this research.

21
Thus, the objective of this project is to develop improved design criteria for low-cost/

low-rise (10 meters and under), houses, school buildings community centers to better resist

the effects of extreme winds (130-140) knots) in developing countries, and to transfer this

Information in a form suitable for implementation by most individuals in highwind countries.

Because the Philippines experience the highest incidence of high winds, this nation can serve

as a natural laboratory for extreme wind research.

Our project was formally started in February of 1973. Early in the project we identified interested organizations and agencies, universities, and other groups from the Philippines, Bangladesh, Jamaica, and third party countries to participate in and direct major

project tasks. This was performed during April and May of 1973.

Examples of such participation from the Philippines include the Philippine Atmospheric,

Geophysical and Astronomical Services Administration which has donated parcels of land at their sites for the construction of full scale test houses. The University of the Philippines

will perform wind tunnel testing and the National Housing Corporation has constructed the

first test houses at the PAGASA's site in Quezon City. We will visit this house later in

the afternoon.

In addition, we identified Dr. Choudhury from the Bangladesh University of Science and

Technology, Dacca, to represent his country and the selected Indian Ocean countries in

assisting us with his experiences and expertise in providing us with climatological , socioeconomical and structural related data. Mr. William Woudenberg from CARE, Inc., Bangladesh,

will also discuss related topics about his low-cost house. Mr. Adams from Douet, Brown, and

Adams and Associates, an engineering consulting firm in Kingston, Jamaica, will represent

Jamaica and the Northern Caribbean Islands in collecting data and sharing his experiences

and expertise with us. Dr. Keith Eaton, Senior Research Officer from Building Research

Establishment in the United Kingdom, has gracefully accepted an invitation to be with us.

During the summer months we assembled and tested our first data acquisition system for our test site No . 1 . We transported this system to the Philippines during our second visit

in September where we instrumented one test house at test site No. 1 in the Greater Manila

Area. And as I mentioned before, we will visit this house later on this afternoon.

The curve in Figure 1 represents the mean monthly frequency of tropical storms in the

Philippines. This information is from Dr. Kintanar's publication entitled "Tropical Cyclones for 1970." Our thanks go to Dr. Kintanar and his staff for this information. As

you can see, this curve oscillates for a period of two and one-half years, the length of our project. It oscillates from an average of about 3.5 storms per month in the late summer to less than one-half storm in late winter. The activities above the horizontal axis represent

full scale tests of our buildings. The first of seven houses was instrumented with wind

measuring equipment in September and the last is scheduled to take place in June, 1974.

The activities below the horizontal line indicate the schedule for wind tunnel tests. As you see, initial wind tunnel modeling has been performed by the Colorado State University

under the direction of the National Bureau of Standards and will be transferred to the University of the Philippines Aerodynamic Laboratory next week by Dr. Marshall. This transfer

will permit Professor Alejandrino to commence his wind tunnel testing program using a scale

model of 1 to 80 of the actual full scale field test buildings. Such testing will provide a correlation of information collected in the field with that collected in the tunnel. It will provide us with additional knowledge to optimize the physical placement of the pressure

transducers (wind measuring equipment) on the full scale test house. The other two horizontal bars represent further refinements in the University of the Philippines wind tunnel testing program.

Figure 2 illustrates the wind measuring equipment on our test house at the Science Garden site. Note the pressure transducers on the roof. There are six on the roof, two mounted on the exterior walls, and one special transducer mounted on an inside wall to measure

internal pressures.

The data collected by the pressure transducers are recorded by a 14-channel tape re- corder located in an air-conditioned building adjacent to the test house. The data acquisition equipment under normal conditions is operated with commercial power. However it has

back-up power through batteries should commercial power fail during a storm. 22
FULL SCALE TESTS WIND TESTING ACTIVITIES

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M AM i J rA S 70 N D J F M A M'J 1 A SONDJ FMAMJJASONOJI

-FY 73 FYH,

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•FY 75

INTERMEDIATE WSHD

TUNNEL TESTWG

•FY 78

PHEIMINARY WIND FUNNEL TESTING iili III

FINAL SERIES WWO TUNNEL TESTING

WWO TUNNEL TESTS

Figure 2. Test House No. 1, Quezon City Test Site

23
In addition to instrumenting a test house in September, we also selected a second of

three field test sites to record wind effects on buildings. This site is also owned by the

PAGASA which contributed greatly in identifying appropriate locations.

This is a very brief summary of the background of our activities. This leads me to ask

why we are here today. This Workshop is the first major step toward coordinating the technical planning and organizing the associated activities to improve design criteria for lowcost/low-rise buildings. What we are all doing today and for two and a half additional days

is to learn more about each other professionally, to share with each other information we already know and, more importantly, to jointly identify areas and data gaps which when filled

will bear fruit in a relatively barren desert. We want to develop conclusions and recommendations about where we should go from this point in time. Viewed another way, we are assessing the state-of-the-art in mitigating damages to low-cost/low-rise buildings from extreme

winds. As you can see from your program, our Workshop is divided into four major categories:

the first is Climatology and Wind Related Problems; the second deals with Structural Related

Technology; the third involves Socio-Econoraic Aspects of Low-Cost Buildings with emphasis

placed on housing; and the fourth centers around Building Codes and Standards.

These categories are addressed initially by technical papers. On Friday, we will break

into four groups, each group representing one of the major subject categories where we will

discuss our respective topic and develop conclusions and recommendations based upon each

member's background and experiences and from information presented during this meeting. On

Saturday morning the conclusions and recommendations will be presented. Later in the year a proceedings report will be prepared from the information assembled during this Workshop. I think at this point you may be wondering what is the end product going to be and who will

use it. Well, this is also one of the purposes of bur Workshop. Mr. Niblock in his presentation suggested that we not forget the importance of implementation.

The implementation aspect of this project must satisfy the requirements of technical

and non-technical users. The first group will be able to understand technical documents.

An example of one such document presenting technical information is our American

National Standard A 58. 1-Building Code Requirements for Minimum Design Loads in Building and

Other Structures . This document is used by those individuals engaged in preparing and administering local building codes. A similar appropriate document will be prepared at the

end of this project. But, what about the man-in-the-f ield? What is he going to use to improve his building construction methods?

The National Bureau of Standards prepared in cooperation with the Ad Hoc Committee on Fuel Conservation, Office of the Special Assistant to the President for Consumer Affairs, a brochure entitled, "7 Ways to Reduce Fuel Consumption in Household Heating Through Energy

Conservation." In this brochure we presented in a simple and straightforward manner ways we

could reduce fuel consumption. For example, we suggested that if the homeowner insulated

his home with the minimum recommended thickness of insulation he could reduce his heating

bill by approximately 15 per cent. In addition, the costs associated with installing the

insulation could pay for itself due to the reduced heating bill in about ten years. While

we are not concerned with insulation in this project, a similar format could be prepared to illustrate for example, improved building connection details to better resist extreme winds.

I hope that what has been presented so far today has given you a little better impression of the overall scope of work and has answered some of your questions. I have addressed

myself specifically to the background and general areas associated with our two and a half

year research project. Those who follow me will deal more specifically with the topics of our Workshop

.

We hope that all of you will be curious during the ensuing days. We also hope that you

communicate whenever you feel others may benefit as well as you. As you know, communication

is a two-way process and this roomfull of individuals with a broad range of specialized

skills is a place where questions must be asked and answers communicated — your answers to

us and ours to you. For the next three and a half days we will be engaged as curious people

working together in this meeting place. After the three and a half days are over, we will

leave. But if our meeting is a successful one, if we really do communicate with one another,

I believe you all will continue to look for answers, arising out of apparent data gaps dis24
cussed during the next few days and the newly discovered data gaps popping up after this meeting asking new questions, looking for new answers and coTnmunicating them to the Philippine

Advisory Committee and to the staff of the National Bureau of Standards. Thank you.

25
SUMMARY OF LOCAL ACCOMPLISHMENTS

by

Ernesto G. Tabujara

Professor of Civil Engineering, University of Philippines,

Quezon City, Philippines

Dean Juinio, Mr. Raufaste, our guests, colleagues and friends. When the Program Committee requested me to render a summary of local accomplishments, I immediately accepted the

assignment because I felt it would be very easy. I was sure that even if I did not say anything, the word "accomplishment" alone was enough to indicate that some things had been done.

I will not try to deny that some measure of accomplishment have indeed been done, and I hope

you will allow me to enumerate briefly these activities.

The previous speaker, Mr. Noel Raufaste, gave us a comprehensive account of the background of the research from the standpoint of the U.S. National Bureau of Standards, which

originally developed the proposal. What Noel failed to mention — and this he may not be in

a position to know — is that as far as the local point of view is concerned, our involvement actually started at a dormitory cafeteria at Honolulu, Hawaii, almost a year ago. At

that time, Mr. Bill Littlewood, Associate Director, Agency for International Development

based in Washington, D. C. and Dr. Ed Pfrang, Chief of the Structures, Materials and Life

Safety Division of the U.S. National Bureau of Standards suggested to Dean Juinio and myself

to have lunch together so that we could discuss a very Interesting research proposal. It did not take these two gentlemen long to convince Dean Juinio and me that the project was

indeed a laudable one and we knew right then and there that it would draw the interest of our colleagues in the Philippines.

I would like to think that the very first local accomplishment was made when Dean Juinio

committed the University of the Philippines Building Research Service to this endeavor — and

to think that such local accomplishment was actually consumated at Honolulu, a foreign country. The four of us who are all here today are very happy to see that the research project

we talked about is now on its way to full implementation.

The second milestone in the local effort was the formation of the Advisory Committee

which held its organizational meeting on April 27, 1973. We were very glad to bring together experts in their respective fields to compose this body — and this alone is quite an accomplishment. The response from the Government and the private sectors was spontaneous,

and as it turned out, 25 scientists, engineers and researchers representing 11 government

entities, four professional organizations and two private groups, made up the total membership of this Advisory Committee.

Since its formation, the Committee has met on several ocassions to come up with important recommendations and decisions as these pertain to local conditions affecting the study.

In accordance with a reasonable timetable, the Committee decided on the construction of

experimental houses which would be fully instrumented for wind pressure readings. For con- venience and expediency, the Science Garden of the PAGASA (formerly Weather Bureau) at

Quezon City was selected as the first test site, where we hope to construct three houses for

experimentation purposes

.

This particular site was preferred because of the gesture of Administrator Roman L. Kintanar when he committed three small parcels of land as well as limited services of PAGASA

technicians to double as observers. This move led to a mutual effect in that PAGASA technicians, in turn, assigned at the Science Garden suddenly found themselves with a new home.

I am happy to report that the National Housing Corporation donated the first house,

which together with the installation of the measuring and recording apparatus, may be con- sidered the third milestone in this collaborative effort.

You will also be interested to learn that all equipment worked perfectly during the

visits of Typhoons Luming and Narsing sometime last month, and this is a tribute to two

things: (1) the meticulous checks made on the equipment at the National Bureau of Standards

in Washington, D. C, prior to shipping these over, and (2) the excellent know-how and capability of Dr. Richard D. Marshall who almost single-handedly installed all the equipment on 26
the first house. Although General Gaudencio V. Tobias and Colonel Alejandro R. Kabiling of

the National Housing Corporation would humbly refuse to confirm that their product is the

best low-cost house for one's money, I get it from reliable sources that the direct costs

of this donation amounted to some 10,000 pesos.

The fourth milestone is the current construction of the second house located near the

first one. This 12,000 peso committment by the Land and Housing Development Corporation,

ably represented in the Advisory Committee by Colonel Alberto Sanchez, differs from the first

one in that the roof slope has been made steeper, the ridge line oriented at right angles to

the ridge line of that of the first house, and we are still hoping to use lightweight concrete — called porous concrete — instead of the popular fiberboard for the exterior walls.

Unfortunately, the gasoline shortage has caught up with the construction of the house and

deliveries of various materials have become most difficult, causing an unforseen delay in

its completion. However, we are still optimistic, that we will have the house ready for Dr. Marshall and his assistants immediately after this Workshop is over. We will all have the

chance to see for ourselves these phases of the research during the visit to the site scheduled for this afternoon.

The Advisory Committee appreciates the desire of the National Bureau of Standards to supply and make available for our use thousands of dollars worth of equipment and related

measuring and recording devices. Details of the formal transfer of the equipment, which are

to be donated to the Philippine Government through the Advisory Committee, are being worked

out. The PAGASA and the National Hydraulic Research Center have acceptec^ the responsibility

to act as custodians for the devices used in full-scale tests and those for the wind tunnel

experiments, respectively.

The Advisory Committee has drawn up line-budget proposals for support of this program

as our counterpart. Some more details will have to be clarified before we can realize tangible and favorable results, but in the meantime, I am happy to say that the Committee was

able to solicit substantial logistical aid from industry, from professional organizations

and from concerned individuals. As a matter of fact, the financial assistance given by these

quarters is perhaps the greatest accomplishment of the Advisory Committee to date — for

without this help sponsoring this International Workshop would not have been possible. In behalf of the Advisory Committee, other activities of the Advisory Committee for the near

future include

:

1. Selection of Daet , Camarines Norte as the second test site,

with a view of constructing two experimental houses at the PAGASA'

s

weather station there.

2. Consideration of three choices for the third test site. This

location will have to be decided shortly after the Workshop.

3. Committment of the construction of four houses at these two

additional sites. The People's Homesite and Housing Corporation has

announced their donation of two houses at one test site, while the

Government Service Insurance System has promised to construct the other

two at the third site.

4. Informed the staff of the National Hydraulic Research Center

of the start of the preliminary wind tunnel testing which will complement field observations.

5. Alerted possible end-users of the results of this research by

agreeing to make available any useful findings even if these have not

been formally released.

The above summary reflects the enthusiasm of each and every member of the Advisory

Committee. It has been my pleasure to be a part of this undertaking. We now all look forward to a very fruitful research. Thank you.

27
CLIMATOLOGY AND WIND RELATED

PROBLEMS IN THE PHILIPPINES

by

Roman L . Kintanar

Director, Philippine Atmospheric, Geophysical and Astronomical

Services Administration (PAGASA) , Quezon City, Philippines

ABSTRACT

This paper attempts to synthesize climatological information particularly wind data into

a form which would be most useful to engineers and designers of building and/or low-cost

housing in the Philippines or in similarly situated tropical countries.

The first portion summarizes the climatic controls and resulting wind systems which

dominate the country for each particular season of the year. It also gives statistical information on transient systems which give rise to very strong wind speeds experienced in the

country. In particular, the frequency distribution of tropical cyclones for various parts

of the country have been determined and incorporated in the analysis of extreme wind values.

The main portion of the paper deals with the statistical analysis of extreme maximum

wind speeds based on one minute sustained maximum winds observed at a standard anemometer

height of 10 meters above the ground. The wind data are extracted from all available records

at the Philippine Meteorological Service covering periods ranging from 12 to 21 years.

Employing the statistical theory by Gumbel (1,2) and the fitting technique of Lieblein

as discussed by Thom (9) , a table was prepared giving the annual maximum wind speeds at cer- tain specified recurrence intervals for 19 representative stations in the Philippines.

Finally, it is suggested that for estimating maximum wind speeds at levels higher than

the standard anemometer height of 10 meters, the logarithmic relation of wind speed with

height may be employed.

INTRODUCTION

This paper puts together Philippine climatological data particularly wind observations

into a form most useful to engineers and designers of buildings. It should be mentioned

that this work is done without any joint action between the author and a design-engineer.

A climatological information is a form of information derived from the historical meteorological parameters by some statistical means. Its importance has proved useful in the

solution of agricultural, industrial, and management problems in general. In particular,

the planning of an engineering design requires such form of information. This type of information, called a climatological design value, will assure with a given probability level

that an engineering system will adequately meet a set of prescribed design requirements.

The choice of analysis for this type of information is a problem of the climatologist , while

the assignment of a probability level and other design requirements are that of the engineer.

However, the choice of the meteorological variable and its relationship to the design is a joint problem of both.

Other in design problems, the climatological variable of interest is the wind velocity.

The prevailing trajectory of winds helps the designer in determining the proper orientation

of the designed structures. For this purpose, a brief discussion on the climatic controls

and resulting wind systems which dominate the country is presented. Likewise, the monthly

charts of the wind systems' streamlines are shown.

With reference to the strength of the designed structures, the variable of interest is

the extreme maximum wind speeds as suggested by several authors (2,3,4,12,15,16). This

arises from the fact that if a designed structure can withstand the highest value in a year,

it can likewise withstand all other values in a year. The method of analysis used is the

statistical theory of extreme values by Gumbel (1) . This theory has been widely employed by

Gumbel(2) himself, Shellard '3 ,4) in Great Britain and in the United Kingdom, Kintanar(5) in

the Philippines, Okubo(13) ...a Japan, and Thom(16) in the United States of America. This

28
theory is likewise applicable to hydrometeorological analysis of extreme values. LiriosC?)

and Ferraris (8) have used the same theory in the analysis of maximum rainfall amounts in

Barbados and in the Philippines, respectively.

The Lieblein technique as described rigorously by Thom(9) is used in fitting the double

exponential probability function. This method is quite simple and convenient. It is quite

j accurate as compared to the other methods discussed by Lowery et al(lO). The maximum likelihood method is best and accurate, but the procedure is quite complex and tedious.

The data analyzed consist of one-minute-maximum wind speeds from all available records

( of the Philippines, Atmospheric, Geophysical, and Astronomical Services Administration.

The length of records ranges from a minimum of 12 years to a maximum of 21 years.

Subsequently, maximum wind speeds that are likely to be equalled or exceeded at certain

specified recurrence intervals are obtained. However, corrections may be applied to the

I above results due to other factors such as the frequency of tropical cyclones and the location and height of the design in question. The recurrence of maximum wind speeds are most

' likely in places where tropical cyclones are most frequent. Thus, a simple linear relationship is used to express maximum wind speeds as function of the tropical cyclone frequency

j in different places in the Philippines. This idea was set first by Hizon et al (11) but

I which however is not quite elaborate. On the other hand, the wind profile in the vertical

II as found out by Orlenko(12) varies exponentially with height depending upon the roughness

characteristics of the ground. Hence, the logarithmic method of estimating the maximum

wind speeds at some levels above the ground is utilized. The values of the roughness parameter employed for places considered in this study is likewise that of Orlenko(12). The

power law used by Hizon et al (11) and Okubo(13) may likewise be applicable but, this method

gives no separate values of the roughness characteristics of the ground between towns and

cities. In other words, the logarithmic method is more appropriate in this study.

A table of factors in obtaining the maximum wind speeds at different places like towns

and cities and at different levels above the ground is presented. The overall results of

this study may therefore enable the engineer or designer of buildings to design his structure on the basis of meteorologically calculated risks.

A REVIEW OF PHILIPPINE CLIMATIC CONTROLS

The climate of the Philippines as presented by Flores et al(14) based on the classification of Koppen, Coronas, and Hernandez shows varied types of climates from place to place.

The regional variations of climates are attributed to the climatic controls which act in

various intensities and in different combinations producing changes in the climatic elements

observed in that region. These climatic controls are: wind systems, tropical cyclones,

semi-permanent cyclones and anticyclones, ocean currents, thunderstorms, geography and

topography, and linear systems. The following is a discussion of each of the above cited

climatic controls:

a) Wind Systems Affecting the Philippines

The climate of the Philippines is largely controlled by the wind systems affecting the

Philippines as a result of the seasonal differential heating of neighboring continents and

oceans. The major types of wind systems that affect the country at different seasons of the

year are:

1) The Southwest Monsoon

This air stream is sometimes called the southwesterlies . It originates as Indian Ocean

Trades from the Indian Ocean Anticyclone during the Southern Hemisphere Winter. On its

journey northward, it is deflected to the right in the Northern Hemisphere as it crosses the

equator reaching the country as a Southwesterly air stream. It is of considerable depth,

often extending from the earth's surface up to 10 km. The surface trajectory is shown in

Figures 6 to 9 based on the 21- year records. This air stream affects the country as early

as the month of June. It attains its maximum intensity in August and gradually recedes in

the later part of September. In some occasions, it may blow in surges and persists up to

the later part of October. Heavy rainfall concentrated along the western coastal areas of

the country during, the period from June to September is caused by this air mass. 29
2) The Northeast Monsoon

This air mass is sometimes called the Northers or Winter Monsoon. It originates in the

cold intense Asiatic Winter Anticyclone and spirals outward across Japan towards the Northwestern Pacific Ocean. It finally reaches the country as a Northeasterly air stream. It starts affecting the Philippines during the later part of October, attains its maximum intensity in January and gradually recedes in the later part of April. The tralectorv of this

air stream is shown in Figures 1,2,3,4,10,11, and 12. This air stream is rather shallow

extending rarely to 2 1/2 km. The temperature inversion layer of this air stream is moderate

at about 1 1/2 km. This air stream is responsible for the relatively cold weather spell and

heavy rainfall along eastern coastal regions of the country during the winter season of the

year

.

3) The North Pacific Trades

This air stream comes from the North Pacific Anticyclone arriving in the Philippines

generally from the north and east directions. It blows domlnantly during the months of

April, May and October (see Figure 5). It usually overlies the Northeast Monsoon air mass

over the eastern sections of the country. It is distinctively the warmest air mass that

affects the country. Its convective activity may result to the formation of fair weather

cumulus and stratocumulus clouds owing to the presence of dry layers above it. At times,

showers may result from a towering cumulus developed by this air mass.

4) The South Pacific Trades

This air stream originates from the South Pacific Anticyclone in the Southern Hemisphere. It veers to the right upon crossing the equator and reaches the Philippines as a southwesterly flow during July. It is warm and quite moist at low levels and relatively dry

at upper levels. It is difficult to distinguish this air stream from that of the Southwest

Monsoon air mass because their characteristics are almost similar. These air streams differ

only on the height of their subsidence layers. The south Pacific Trades has Its inversion

layer at about 11/2 kilometers while that of the Southwest Monsoon is at about 4 kilometers

high from the surface.

b) Tropical Cyclones

Tropical cyclones influence the behavior of other climate elements to a certain degree.

They are responsible for the maximum values of wind speeds, torrential rainfall, and minimal

atmospheric pressures observed in different parts of the country. They contribute largely

to the rainfall from June to December.

The Philippines is a country considered to have the greatest frequency of tropical cyclones in the world. In general, these cyclones are destructive to life and property. A

survey of damages inflicted by these cyclones in the Philippines for a period from 1948 and

1971 showed an annual average of 960 casualties and an estimated yearly loss to property

worth 67.8 million pesos. During this period of study a total of 483 tropical cyclones

formed-in or entered into the Philippine Area of Responsibility. Out of this nunber, about

42% touched or crossed the Philippine Archipelago.

The tropical cyclone season in the country generally covers the period from June to December, although the rest of the year is not entirely free from these cyclones. Table

7 shows the monthly and annual frequency of these cyclones. Figure 21 shows the histogram

of these cyclones while Figure 13 shows the mean percent frequency in different parts of the

country. These cyclones follow widely variable tracks in the vicinity of the Philippines

moving at an average speed of 6 meters/second. They usually affect the country from 1 to 7 days depending upon their trajectory characteristics.

c) Other Climatic Controls

1) Semi-Permanent Cyclones and Anticyclones

The climate of the Philippines is controlled to a certain degree by the location and

intensity of nearby semi-permanent cyclones and anticyclones. They are responsible for the

30
evolution of air streams and ocean currents affecting the country at different seasons of

the year. The large anticyclone centered off Siberia is responsible for the evolution of

the Northeast Monsoon while that one located over the Indian Ocean is responsible for the

evolution of the Southwest Monsoon air mass.

2) Ocean Currents

The ocean current affecting the country is the North Equatorial current moving westerly

across the North Pacific Ocean. This current splits into Northward and Southward branches

upon reaching eastern coastal areas of the archipelago. The Northward bound current becomes

the Korushio Current while the Southward bound current flows along the east coast of Southem Visayas and Mindanao, recurves to the east and becomes the Equatorical Counter Current.

Motions of ocean currents are attributed to the difference in insolation the ocean received

and due to the driving effect of winds upon contact with the surface layers. The temperature at the surface of the sea in the vicinity of the country is relatively high. Thus, air

passing over the warm sea surface becomes impregnated with water vapor.

3) Thunderstorms

Thunderstorms are relatively small scale and short period disturbances as compared to tropical cyclones. They are usually triggered by the presence of the moist and unstable air

streams coupled with orographic lifting. They affect the country practically all months of

the year.

4) Geography and Topography

The country is made up of approximately 7000 islands which are grouped into three regions namely: Luzon Region, Visayas Region and Mindanao Region. The islands are mostly

oriented north to south and completely surrounded by large bodies of water. Luzon, the

largest island, consists of several mountain ranges of more than 500 meters high. The

Sierra Madre Mountains are located along the eastern coast of Northern and Central Luzon.

The Ilocos Ranges are located along the Western coast of Northern Luzon, while the Cordillera Ranges lie between the Sierra Madre and the Ilocos Ranges. The Zambales Ranges are situated along the western coast of Central Luzon. Most of the bigger islands of the

Visayas also have 500 meter elevations or more are situated in western, central and eastern

portions of the island. These topographical features may serve as the orographic obstacles

to the air streams affecting the country. Figure 22 shows the geographical and main topographical features of the Philippines.

5) Linear Systems

The Philippines is also affected by fronts, the intertropical convergence zone, and

easterly waves which are referred to as linear systems. The behavior of each of these

systems is as follows:

(a) Fronts

Frontal systems affect the northern portion of the country during the winter season

only. They are oriented west-southwest to east-northeast cutting across the island of Luzon

during January. The diffused tail ends of these systems move as far south as Mindanao.

These fronts are considered as the interfaces between the Northeast Monsoon and the North

Pacific Trades. Coupled with topographic effects, they are responsible for the portion of

rainfall and cloudiness over the country where they are oriented.

(b) Intertropical Convergence Zone

This zone is also known by such names as intertropical front, eqiaatorial trough, doldrum belt, etc. It is a relatively low pressure zone which serves as the zone of discontinuity between the Northern and Southern Hemisphere air streams. It starts affecting the

southern portion of the country during May, oriented generally from east to west and moving

northwards. It is at the northern tip of the country during the month of July and well to the South during November. The variations of the position from day to day are quite large

and disorganized. Over this zone the weather is quite disturbed consisting of widespread

cloudiness, occassional precipitation, and moderate to strong surface winds.

31
(c) Easterly Waves

These are wavelike perturbations embedded in the easterly current which move from east

to west. They affect the country with varying intensities being more frequent during the summer months. These waves are accompanied by cloudiness and precipitation usually along

the orographic obstacles on the eastern coastal portions of the country.

ANALYSIS OF THE EXTREME ANNUAL WIND SPEEDS

a) The Theory of Extreme Values

A series of extreme values of wind speeds can be represented by a Fisher-Tippett Type I probability function which is given as:

P{x)= Exp(-Exp-(-!^) (1)

where P(x) is the probability that any of the N extremes will be less than x. Taking the

double logarithm on both sides of the above equation and expressing P(x) as a function of

the recurrence interval, T, which in turn is also expressed as the reciprocal of the probability of non-exceedence , that is,

(2) I l-P(x)

Then expressing for x, equation (1) becomes:

x=cc-/3 LiX.^^) (3)

where x depends upon the recurrence interval, T and the parameters of the initial distribution CC and f3 • The method of fitting the above function needs only priori value of T and

the estimates of the parameters OC andyQ.

b) The Lieblein Fitting Technique

This method of fitting the double exponential theory involves maintaining carefully the

original time order series and subgrouping them into a maximum of five or six variables each.

These variables in each subgroup are then arranged in order of increasing magnitude such

that the whole series will form into a matrix denoted by x. . where i = 1,2,3, k, denotes

the number of subgroups and j = l,2,3,....m, denotes the number of variables in each subgroup. Thus, if N = 30, k = 5, and m = 6. This would appear as in Table 1. Each column of x in Table 1 is first summed up to obtain S.i. These values are multiplied by the corresponding values of a. , found in Table 2, the Table of Order Statistics Weights. The results

will be summed up again horizontally to obtain the row sum 2 a. ,S. as indicated in the

table. Next, the S.. are again multiplied by the corresponding valnes of b.j likewise found

in Table 2, and summed up again horizontally to obtain another row sum 2b.jS.j . Thus,

the estimates of cC and y3 are as follows:

<**=t|,°-1S., (4)

Equations (4) and (5) are then substituted in equation (3) to get the estimates of x at certain priori values of the recurrence interval, T.

In cases where there are still remainders in the subgrouping of five or six variables

each, the remainders will be treated separately. Suppose N = 33 instead of previously 30

variables for the whole series, the last three values of the sample climatological series is

then formed into an additional subgroup of m' = 3. These values are likewise arranged in

32
"l2 "l3 "ll+ "15 "16

22 23 24 25 26

^31 "32 "33 "3I1 "35 "36

"Ul ^li2 "1.3 "U5 "U6

"51 "52 "53 "5U "55 "56

S-i S<>2 S.^ S.^ S.g

3.»^

11 22 33 k k 55 66 "^^^'jS'j

b.^ b.3 b.j^ b.^ b.g

b.^S.^ b.^S.^ b^^S^^ b.j^S.j^ bo^ S.^ b.gS.g =S.jS.^

Table 1

m

1

"•1 "•2 x.3 "•5

2 .91637

- 0 72135

.08363

.72135

3 065632

- 06305I+ .25571

.25582

.08797

.371+73

1| .51100

- 055862

.26391+ .08590

.15368

.22392

.07138

.21+880

5 .U1893

- .50313

.2I1628 .00653

.16761

.1301+5 .10882.18166

.05835

.18I+I18

6 .3551+5 - ,1+5928

0255I+9 -.03599

.16562

0 07319

0 12105

.12673

.08352

.11+953

a.

b.'

a.

a*.

13.'

a.

.01+887 a. al+581 a.

Table 2 - Table of Statistics Weights (after Lieblein^

33
order of increasing magnitude. Hence, it would appear as in Table 3. Following a similar

procedure as in the earlier paragraph, the final estimates of flC and ^ , will be

^**=^|,b.jS.j + ^'|b.jS.]

1=1

(6)

(7)

Equations (6) and (7) are likewise substituted in equation (3) to obtain the quantile values

of X.

Table 3 X6I ^62 >^63

a.2 0-3

^62 ^63

b.2 b.3

b.gXgg b.jXgj

D a.i X

J 6j

2 b.;xJ* 6j

The results of the above procedures as actually applied to all available records of the one- minute-maximum sustained wind speeds are presented in Table 4. The above-cited result yields

maximum wind speeds at certain specified recurrence intervals for different places in the

Philippines as indicated therein. The effective height of these computed maximum wind speeds

is at 10 meters since, records of wind data used in the proceeding analysis are observed at the standard anemometer height of 10 meters above the ground.

Estimates of maximum wind speeds for places in the Philippines other than those indicated in Table 4 can be obtained by interpolation from the isolines of computed maximum wind

speeds drawn in as shown on Figures 14 to 19 in the appendix. Isolines of the average maximum wind speeds for places considered in this study are likewise drawn in as shown in Figure 20 for reference purposes. However, these charts should be used with great caution as values interpolated therein may need considerable adjustment from the topography of a place.

c) Correction to the Maximum Wind Estimate Using the Tropical Cyclone

Frequency Factor

Maximum sustained wind speeds observed in different parts of the Philippines are mostly

caused by tropical cyclones. The frequency of tropical cyclone occurrences varies throughout the archipelago from 40% in Northern Luzon down to slightly near zero percent in Mindanao

as shown in Figure 13. In other words, in those areas where tropical cyclone occurrences

are more frequent it is more likely that the chance of the recurring maximum wind speeds

will be higher. Hence, it appears that a frequency factor from these cyclones for safety of

the design may likewise be considered in this type of climatological information.

Perhaps the cost of the design may substantially increase considering that there are

< still non-meteorological factors to be considered; but this author believes it is reasonable

to take into account the tropical cyclone frequency factor. The values of this factor, denoted by ft, for different places in the Philippines are shown in Table 5. These factors

are evaluated from Figure 13 which are based on the 24-year period of tropical cyclone frequency study in different places in the Philippines.

34
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35
To obtain the maximum wind speeds where the frequency factor is considered, equation

(8) can be used. This is given as

U = Ut (1 + ft)

where U is the desired wind st>eed, U is the maximum wind speeds at certain recurrence intervals found in Table 4, and f^ is Ihe frequency factor for tropical cyclones presented in

Table 5. The above expression is only a simple estimate using linear relationship between

plapoc in t'llP Frequency

PVi 1 1 i nvi "1 n p Factor, f^^

± • V J. gctii 0.25

Z • LiUCeila. 0. 15

^ Tin-Fant"SJ 0. 15

H* UaSlgUITan

D# ijega.spi uity

0. 15

0. 15

0. 15

0.15

10. Baguio City 0.15

11. Cagayan de Oro City 0.05

12. Cebu City 0.15

13. Davao City 0.05

14. Iloilo City 0.15

15. Tacloban City 0.25

16. Manila 0.15

17. Pasay City 0.15

18. Quezon City 0.15

19. Zamboanga City 0.05

20. Laoag City 0.35

Table 5 - Tropical Cyclone frequency factor in different places in the Philippines.

the ma"ximum wind speeds and the frequency of tropical cyclones occurrences. But, a more

rigorous and more accurate method may be made by the use of regression analysis.

d) Estimates of Maximum Wind Speeds in the Vertical

Designs of tall buildings especially in large towns and cities require climatological

information in rationalizing the risk of failure of the design at these places and heights

above the ground. Thus, it appears necessary to evaluate the design wind speeds at these

areas. It should be mentioned that records of maximxam wind speeds in the Philippines higher

than the standard anemometer level are nil. The profile of wind velocity in the vertical

varies exponentially. Hence, it is possible to estimate the wind speeds in the vertical.

Considering the aerodynamic aspects of winds near the ground, the velocity-height relationship formula which is referred to as the logarithmic law provides a means of estimating

winds speeds higher than the standard height of 10 meters. This logarithmic law is given as i«Z/Zo

U7/U|o=-s Z — '0 iUZ,o/Zo (9)

where: Uj. is the desired wind speed at any height, Z U|o is the wind speed observed at anemometer (10 meters) level

Z is the height at which wind speed is desired

Z|o is the height at standard anemometer level (10 meters)

Zg is the roughness characteristic of the ground

36
For large towns and cities, the roughness parameter as found out by Orlenko(12) is 100

centimeters and 200 centimeters respectively. These values are used to evaluate the right

side of equation (9). The results are shown in Table 6.

Height above

the ground

Towns Cities

15 meters 1.18 1.25

20 meters 1.30 1.43

25 meters 1.40 1.57

50 meters 1.67 1.94

Table 6 - Computed values of In Z/Z„-rln Z-„/Z

The values presented in Table 6 may be used to estimate the maximum wind speeds at levels and places indicated therein. These values serve as factors to be multiplied to the

values of maximum wind speeds shown in Table 4 to obtain the design wind speeds. Suppose a design is desired at 50 meters high in Baguio City and that the lifetime of the design will

be up to 50 years, the climatological factor for such design will be based on the maximum

wind speeds of 155 knots or roughly 80 meters per second wind speed.

5. Conclusions and Recommendations for Further Studies

This study was based on the well-known methods of statistical analysis for building

design purposes as discussed in the earlier paragraph. Therefore, the results obtained can

be used operationally in the design of all types of buildings situated in the Philippines,

provided the limitations in the use of the data are noted and taken into consideration.

It should be mentioned that the use of simple estimated linear relationship between the

maximxim wind speeds and that of the tropical cyclone frequency may be sufficiently accurate, but the quantitative analysis or approach by the use of regression technique is highly

recommended. It is likewise recommended that the actual profile of strong winds in the

vertical and the actual values of local roughness characteristics of the ground be determined for this country.

The future plan of this author is to conduct further research along this line so that

problems which may lead to a design not achieved due to some climatological causes may be

eased.

37
ACKNOWLEDGEMENT

preparation of tables and figures <;„eM.i

^is valuable assistance in the and Mr. B. Lo.ota„ for readJn^rthis l"ic1lpj?"'= " c/:i:S:ces,

38

i

I
BIBLIOGRAPHY

1. Gumbel, E. J. 1958, Statistics of Extremes. Columbia University

Press, New York.

2. Gumbel, E. J. 1954. Statistical Theory of Extreme Values and Some

Practical Applications. App. Math, Ser. U.S.

Bureau of Standard.

3. Shellard, H. C. 1958. Extreme Wind Speeds over Great Britain and

Northern Ireland, Reprinted from Met. Magazine,

Vol. 87, p. 257-265.

4. Shellard, H. C. 1962. Extreme Wind Speeds over the United Kingdom

for periods Ending 1959. Reprinted from Met.

Magazine. Vol. 91 p. 39-47.

5. Kintanar, R. L. 1971. An Analysis of Annual Maximum Wind Speeds in

the Philippines. UNESCO, Manila.

6. Thorn, H. C. S. 1970. Application of Climatological Analysis to Engineering Design Data. Building Climatology. WMO

No. 255. Tech. Note No. 109 p. 233-234.

7. Lirios, J. F. 1969. Rainfall Intensity-Duration-Frequency Maps for

Kingston and St. Andrew, Jamaica. Carribbean

8. Ferraris, C. C. 1971. An Analysis of Rainfall and Floods in the Pampanga River Basin. Master's Thesis. University

of the Philippines, Philippines.

9. Thom, H. C. S. 1966. Some Methods of Climatological Analysis. WMO

No. 199. Tech. Note No. 81 p. 22-28.

10. Lowery, N. D. and Nash, J. E. 1970. A comparison of Methods of Fitting the Double Exponential Distribution. Jour,

of Hydrology. Vol. 10, No. 3 p. 259-273.

11. Hizon, 0. and Castro, J. 1971. Recommended Design Loads for Wind in

the Philippines. UNESCO Manila.

12. Orlenko, L. R. 1968. Wind and Its Technical Aspects. Building Climatology. Tech. Note No. 109. p. 38-51.

13. Okubo, T. 1971. Wind Effects on Buildings and Structures. UNESCO,

Manila.

14. Flores, J. F. and Balagot, V. F. 1970. Climate of the Philippines.

World Survey of Climatology. Vol. 8. p. 159-213.

15. Hounam, C. E. 1968. The Meteorological Factor in Design. Building

Climatology. Vol. 1, Tech. Note No. 109. p. 218-

220.

16. Janssen, H. W. 1968. Climate in Relation to Housing and Its Environment. Building Climatology. Vol I, Tech. Note

No. 109. p. 214-215.

39
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40
Fig, 1 Prevailing Surface Wind Streamlines (Bold Lines) and Isotachs

(Broken Lines -knots)

41
FEBRUARY

Fig. 2 Prevailing Surface Wind Streamlines (Bold Lines) and Isotachs

(Broken Lines-^knots

)

42
MARCH

Fig. 3 Prevailing Surface Wind Streamlines (Bold Lines) and Isotachs

(Broken Lines-knots)

43
APRIL

Fig. 4 Prevailing Surface Wind Streamlines (Bold Lines) and Isotachs

( Broken Lines-knots

)

44
MAY

Fig. 5 Prevailing Surface Wind Streamlines (Bold Lines) and Isotachs

(Broken Lines-knots)

45
JUNE

II9«» 120® I2I® I22« 123® I240 125® 126®

Fig. 6 Prevailing Surface Wind Streamlines (Bold Lines) and Isotachs

(Broken Lines-knots)

46
JULY

II9» I20«» 121® 122® 123® 124® 125® 126®

Fig. 7 Prevailing Surface Wind Streamlines (Bold Lines) and Isotachs

(Broken Lines-knots)

47
AUGUST

II90 120* 121® 122® 123® 124® 125® 126®

Fig. 8 Prevailing Surface Wind Streamlines (Bold Lines) and Isotachs

( Broken Lines -knots

)

48
SEPTEMBER

€ 4

1190 |20» IZI* IZZ* 123" I240 I25*' 126®

Fig. 9 Prevailing Surface Wind Streamlines (Bold Lines) and Isotachs

(Broken Lines -knots)

49
OCTOBER

119* 120* I2I"» 122® I23'> 124° 125° 126*

Fig. 10 Prevailing Surface Wind Streamlines (Bold Lines) and Isotachs

( Broken Lines -knots

)

50
Fig. 11 Prevailing Surface Wind Streamlines (Bold Lines) and Isotachs

(Broken Lines-knots)

51
DECEMBER

8

Fig. 12 Prevailing Surface Wind Streamlines (Bold Lines) and Isotachs

(Broken Lines-knots)

52
Figo 13 Mean percentage frequencies of tropical cyclone passage in the

different parts of the Philippines

53
Fig. 14 Isolines of Annual }Jla.x, Wind Speeds at 10 Years Return Period

54
Fig. 15 Isolines of Annual Hfex. Wind Speeds at 15 Years Return Period

55
Fig. 16 Isolines of Aimual I.lax. Winds Speeds at 20 Years Return Period

56
Fig. 17 Isolines of Annual Max. Wind Speeds at 25 Years Return Period

57
Fig. 18 Isolines of Annual Max. Wind Speeds at 50 Years Return Period

58
Fig. 19 Isolines of Aimual Max. Wind Speeds at 75 Years Ret\irn Period

59
Fig. 20 Average Annual Maximum Wind Speeds

60

62
AERODYNAMICS OF STRUCTURES AND WIND TUNNEL

MODELING

by

Richard D. Marshall

Center for Building Technology, Institute for Applied Technology,

National Bureau of Standards, Washington, D. C. 20234

This afternoon I would like to get into some of the technical aspects of the program

and what people in other countries have been doing with the problem of wind effects on buildings and structures. But I think, in view of the fact that we had a very delightful lunch

just a few minutes ago and because it is fairly warm in here, I find it better to reduce the

scope of this presentation so that I won't put you all to sleep.

I would like to talk in terms of a flow chart in discussing the general problem of wind

effects (Fig. 1). I think this is a rather convenient way to bring all of the aspects together. It is an interdisciplinary problem that involves many people of different backgrounds. In fact, that is probably the main reason why we find ourselves somewhat late In developing criteria to insure the satisfactory design of buildings to resist wind. We have

climatologists , aerodynamicists , and structural engineers involved. I suppose that actually

one of the most difficult problems to overcome has been one of communication rather than

those of a more technical nature. But basically what is involved here is to take the climatology for the area in which the building site is located and the terrain of the area —

that is, the surrounding buildings, hills and trees, and establish the properties of the

wind for which we are designing. These properties include such things as the mean velocity

profiles and intensity of turbulence. As you all know, the wind speed increases with height

above ground, up to a certain level which we call the geostrophic level. However, we generally do not use the wind speed at that level as a basic measure or basic reference for

wind speed. Rather, as Dr. Kintanar pointed out this morning, we take the lO-meter height.

This is pretty much standard, and although it might not be the best choice, it is one that

has won universal acceptance — and it is doubtful that we shall cease to use it in the near

future

.

The next item is to determine how the wind is going to influence the structure and for

this we must know something about the building geometry. In the case of tall structures, we

must also have some information about its dynamic characteristics. The wind tends to make

the structure vibrate or oscillate — and if the oscillations reach significant amplitudes,

they can modify the wind field around the building.

I would like to confine this discussion to those cases where elastic properties are not

important; to low-rise structures where building geometry is of primary importance. Knowing

the building geometry and the properties of the wind, we can develop what is called an effective aerodynamic input. Ideally, we would like a mathematical model that could be entered

into a computer; I say "ideally" because the nature of the problem is far from ideal. We

could then enter the pertinent information and come up with design loads. While this is

certainly a possibility in the future, we are not at that point with our present level of

technology.

We have some theories that we can use on various parts of the problem, but we currently

have no comprehensive theory that will carry us down to the lower boxes in this diagram. To

do that, we have to resort to other techniques, particularly analogue techniques such as wind tunnel models or by measurements on full scale structures. And, of course, that is

what I intend to address today.

We can think of the wind tunnel model as essentially constituting an analogue computer.

We simulate, at a reasonable scale, all of the phenomena that are relevant to the problem,

make the appropriate measurements, and by means of laws of similitude, scale this information up to the full scale case. Once we have the aerodynamic input, the next step would be

a typical application of design, including the frame, the cladding, and the other elements

such as windows and roofing elements.

63
Finally, we would certainly want to give some thought to the wind environment created

by placing the building at a given site. For low- rise buildings, this is not the important

consideration that it is for tall structures. Very tall structures tend to bring wind speeds

at higher levels down to street level — and we introduce rather severe gustiness in the

pedestrian areas.

It is quite convenient to treat wind pressures in terms of dimensionless coefficients.

Thus, for the pressure at a given point on a structure, we have the free-stream dynamic

pressure at 10 meters (q) — times an exposure factor, C , that takes into account the nature

of the terrain, the height at which you are designing a particular element of a building —

whether it is 10 meters or 100 meters, a gust effect factor, C , that accounts for the turbulence of the oncoming wind and the local flow conditions cauied by the building itself

and, finally, a dimensionless coefficient, C . These coefficients are combined in the form

p = q C C C . P The t^o factors that really concern us here are the last two — C and C . In general,

we have no theoretical techniques to predict these coefficients. Thes§ are ditermined by

measurement, either by means of a wind tunnel model or a full scale structure. If we take

the approach of a wind tunnel model, there are certain requirements that we should satisfy

before we can expect any kind of realistic results. We refer to these as similarity parameters. And here I have listed what are probably the four most important parameters that

have to be satisfied or should be satisfied if we are going to conduct a model study of an engineering structure in a wind tunnel (Fig. 2) using air as a fluid.

We have geometric similarity , which includes neighboring buildings, dynamic similarity , and thermal similarity . Dynamic similarity is important if we are modeling relatively flexible structures. Thermal similarity is important in those cases where we have an unstable

thermal stratification. Fortunately, for most strong wind conditions, and these are the ones we want to model in the tunnel, we are able to neglect thermal stratification because

of the very strong mixing in the vertical direction. And finally, the boundary condition

similarity , which includes such things as the general terrain roughness and the turbulence

in the oncoming flow. To satisfy this similarity, we model in the wind tunnel all the sur- rounding area and topographical features that have an influence on the wind speeds at the

building site.

Perhaps I ought to say a word or two about the source of some of the coefficients that we find in existing codes and standards. I believe that most of the coefficients in use today, except for those codes that have only recently been revised, can be traced back to

two primary documents - the Swiss Building Code and, particularly in the United States, the

ASCE task committee report on wind forces on structures. Most of those coefficients were

obtained by using unrealistic wind tunnel techniques. A building model was simply placed in a wind tunnel and the pressures were measured and reduced to dimensionless coefficients. No

attempt was made to simulate the boundary layer profile, that is, the change in wind speed

with height. Nor was any attempt made to simulate the natural turbulence or gustiness of

the wind. And finally, the pressures themselves were measured in a rather arbitrary way.

The instrumentation available at the time was not capable of measuring fluctuating

pressures. So, the pressures that were measured were generally just mean pressures. In other words, they did not give a true picture of what was happening to the structure. The

philosophy, of wind loading, of course, has greatly changed in the last 10 to 15 years. We

certainly realize now that this approach was not satisfactory. In some cases the results

are somewhat conservative, but there are just as many cases where they are on the unsafe

side. So, there is quite a bit of activity now in a number of countries to develop techniques, wind tunnel techniques, that will insure the reliability of the information gained

from wind tunnel modeling.

This is a picture of the NRC V/STOL tunnel at the National Aeronautics Establishment in

Ottawa (Fig. 3). It is an enormous tunnel, approximately 10 meters square and some 30 meters

long at the test section. We happen to be looking upstream, and this is a model of a downtown portion of Montreal. The scale is 1:400 and the flow is established by a number of

spires across the tunnel at the entrance of the test section to initially generate a sheared flow. Following the spires, there are some roughness elements that are representative of

the city of Montreal between the spires and the model, and they tend to generate turbulence

of a scale and intensity that corresponds to the full scale case. I want to emphasize here

64
very strongly that the spires themselves would not induce a proper flow. It takes both the

spires and the roughness elements.

This is another wind tunnel model study, using essentially the same technique (Fig. 4);

I believe this is a 1 to 600 scale. This particular tunnel is located at Monash University

(Australia). It has a 2-meter square test section with a length of approximately 15 meters.

Obviously, there is quite a bit of sophisticated instrumentation needed to make the

measurements, but I shall go into this subject this afternoon when we visit the field test

site.

Here we have some typical mean velocity profiles that were obtained in a wind tunnel

for two classes of roughness, and they show two rather interesting things (Fig. 5). First

of all, the agreement between the experimental data and the theoretical variation of wind

speed with height, following the power law, is quite good. Certainly, one can argue that a power law is not a good approximation of the mean velocity profile. In fact, it has no theoretical basis whatsoever and one might argue that the log law is a better approach. My

only comment here would be that the power law is somewhat simpler to use, and it does seem

to work. The other interesting thing about this is that it gives you some feel for the difference in velocity profiles for different surface roughnesses. They are all plotted on a non-dimensional scale at the bottom — that is, the local mean velocity divided by the wind

speed at the top of the boundary layer. You see that for the grassland case we reach the

top of the boundary layer much faster than we do over an urban area. So that all matters

being equal, the wind speeds are lower for rougher surfaces at a given height. This is

somewhat offset by the fact that the gustiness is higher in an urban area.

Wind tunnel modeling is a very powerful tool. The only problem is that no matter how

hard we try and no matter how ingenious we are, we simply cannot satisfy all of the similarity parameters simultaneously. There is simply no way to do it. So, we are forced to resort to full-scale measurements, mainly to confirm the validity of the wind tunnel results.

And that, by and large, is the strongest argument for doing full-scale studies. Of course,

there are other arguments if we get into those cases where we have dynamic response of the

structure. We have to model the structure both geometrically and dynamically, and that

again is not an easy matter.

This is an aerial view of a test site at Great Falls, Montana, where we have in the

past conducted full scale studies on two houses (Fig. 6). The area is rather interesting in

that we have quite different exposures, depending on the wind direction. If the wind is

coming from the top of the picture, it is rather open country. If it comes up from the

bottom left hand side, we have a number of 2-story buildings upstream and the flow properties are going to be significantly different. Subsequent to the full scale studies, we conducted some preliminary wind tunnel studies and attempted to correlate the two sets of

data with some success. I will get back to this in a moment.

This is a detailed plan of the immediate area around the test house, the test house

being on the left (Fig. 7). There are similar houses in the immediate area. All of these

houses were modeled in the wind tunnel.

The next figure (Fig. 8) will give you some idea of the geometry of the structure. It

is what we in the United States refer to as a ranch style house. It is rather low, only

some 2.6 meters to the eaves, and the roof pitch is quite flat. In the upper right comer

are the locations of the transducers that were used in both model and full scale.

The model scale that we used was 1:50, which is rather unconventional. We were forced

to that by the fact that a scale of 1:200 or 1:400 would have resulted in a minuscule model,

and there wotild be absolutely no way to get the pressure transducers into the model. We are now looking at non-dimensional velocity spectra obtained from full scale and from the wind

tunnel model (Fig. 9). The straight lines on either side represent the slopes of a theoretical expression for the velocity spectrum.

Here we have a couple of pressure spectra (Fig. 10). Again, in model and full scale

for a typical point on the roof.

65
Another measure of the similitude is the coherence function which indicates how the

pressure fluctuations correlate with each other at two points for different frequencies (Fig.

11). I believe the separation distance for this case was some 4 meters.

This next slide shows the time history of a typical record, say, of pressure at a point

on the roof (Fig. 12). Obviously this is a random process. You can't predict ahead of time,

on the basis of what has happened, what the pressure will be. It's changing in some unknown

manner. But the fact that it is random allows us to make some rather educated statements

about it . In fact , we depend on the data being random to come up with some parameters , some coefficients to be used in design. And in this, it is convenient to make some definitions.

Of particular Interest are the mean, the root-mean-square and the peak values.

If you will recall, in the original expression that I gave you, we had three factors

that I said we were interested in. Two of them must be determined entirely by experimental

measurement — C and C . We can express C in terms of a peak factor g, a fluctuating

pressure coefficient C ^, and a mean pressure coefficient C . I have indicated here ihac ve

define the peak factor^g, which is simply the maximum pressure minus the mean pressure, divided by the standard deviation. In other words, it is the peak excursion from the mean over

a given zero crossing interval. And finally, I have expressed this in terms of the aean

pressure coefficient and a size reduction factor, R. C = 1 + 1.5 (1 + i C pt) R

' P One of the assumptions that we have to make here is that the fluctuating pressure

coefficient can be expressed in terms of the mean pressure coefficient. If this is true, it

essentially cuts our work in half, because we can deal then with only one pressure

coefficient for a given point. The justification for doing this is the subject of the next

slide (Fig. 13).

Here we have a plot of the fluctuating pressure coefficients versus the mean pressure

coefficients for full scale data. We have obtained a quite similar plot for the wind

tunnel data. This indicates that by constructing an envelope for these points, and granted

they are rather scattered, there is some relationship between the fluctuating pressures and

the mean pressures. From a theoretical point of view, I am certainly at a loss to justify

this. Nonetheless, the full scale measurements do give us reason to believe that this is a workable approach to the development of a gust factor.

Well, that is really about all I have to say at this time. And I believe that with the

visit to the Science Garden this afternoon, we will have a chance to go into some of this in more detail.

In closing, I would like to announce that Dr. Keith Eaton of the Building Research

Station will be speaking in place of Mr. Kramer tomorrow afternoon. He also is involved in some very interesting full-scale measurements and wind tunnel model studies. He has

consented to give us a presentation tomorrow. I am sure that he will get into some areas

that I haven't covered today and we are very fortunate in having him here.

I would now like to call on Prof. Alejandrino to continue with this segment of the

program. He will discuss some features of the university wind tunnel facility. Thank you.

66
SIMILARITY PARAMETERS

GEOMETRIC SIMILARITY

DYNAMIC SIMILARITY

THERMAL SIMILARITY

BOUNDARY CONDITION SIMILARITY

Fig. 2 Similarity Parameters

67
National Aeronautics Establishment Wind Tunnel, Canada

Fig. 4- Monash University Wind Tunnel, Australia

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68
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76
REMARKS

by

Angel A. Alejandrino

Director, National Hydraulic Research Center,

University of Philippines, Quezon City, Philippines

As Noel pointed out this morning, this project of ours on wind effects, a complementary

portion of the full scale tests on the building is the model investigation in the wind

tunnel. My own contribution to the workshop at this stage, since our work has not yet

started, is to commit the personnel and facilities of our research organization.

We must admit, however, that the bulk of our work is on hydraulic model testing, and we

have very limited experience along wind tunnel investigation. There is always a first,

however, and for which we are willing and very enthusiastic about this project. We hope

that the transfer of experience in hydraulic model testing would be of help in the wind

tunnel tests. After all, water and air exhibit some common properties of fluids in general.

Our wind tunnel at the Hydraulic Center has a 4 feet by 4 feet test section, 12 feet

long. As Dick has pointed out, this is in the marginal size. But since this is available

at this time, the tests will be conducted there. The tunnel proper is constructed of wood

and plywood panels with transparent glass windows in the test section. We are able to achieve wind velocities to about 75 feet per second by means of a 60-inch axial flow fan

whose speed is controlled by a direct current motor. The instrumentation for this project,

consisting of among the latest in sophisticated measuring equipment — which, as Dick

pointed out, he would like to have himself - is being provided for by the National Bureau of

Standards through U.S. AID. With the expert guidance of Dick, we are quite confident of

attaining the desired results of this project.

Another factor which should work in our favor is in the unique managerial structure of our research organization. What follows, therefore. Ladies and Gentlemen, is a word from

our sponsors.

The National Hydraulic Research Center is recent. It has been organized about the past

three months only. It is a unit of the University of the Philippines under the management

of a private, non-profit organization — the U.P. Engineering Research and Development

Foundation, Inc. This unique arrangement enables us to respond quickly and effectively to

the challenging demands of research since we are able to avoid the many bureaucratic

constraints of a government organization.

Although this structure is quite recent, the nucleus of our personnel and facilities,

however, have been drawn from the Hydraulics Laboratory of the University of the Philippines

where we have conducted hydraulic studies for the past 20 years.

With this project, we shall be expanding our research capability - and that hopefully

by the next workshop, we should be able to convey more information on the results of our investigation rather than on the promise and propaganda we have presented. Thank you.

77
SOME PROBLEMS IN THE ANALYSIS OF LATERAL WIND FORCE

RESISTING SYSTEMS

by

Jose Ma. de Castro

Associate Professor of C.E.,

University of the Philippines, Quezon City, Philippines

Consulting Engineer, Geotechnics Philippines, Inc. and DCCD Engineering Corporation

1. INTRODUCTION

The conventional design process for structures is divided into several phases:

1. The determination of an equivalent static lateral force

system to replace the dynamic effects of the wind;

2. The analysis of the structure under the action of this

force system, of the vertical loads, and such appropriate

loading conditions;

3. The proportioning of the individual members of the structure (design) to resist, with the requisite margin of

safety and acceptable magnitudes of deformations, all

pertinent force system combinations; and,

4. When necessary, re-analysis and redesign of the structure

when initial guesses as to member sizes prove to be too

much in error

.

This paper will not cover the first topic, even though it may well be the most

important phase, since other papers in this workshop will discuss this aspect extensively.

Attention will be devoted solely to the second phase and such aspects of the thirii

phase as directly affect analysis in order to emphasize two points, first, that the analysis

of a structure, particularly of a tall structure, is far from being a cut-and dried

procedure, and second, that many problems and even uncertainties are present in currently

(1973) available methods of analysis. Nothing original is presented herein. However, this

paper is written in the belief that there is need to collect in one place a discussion of

the many problems that have been encountered in the analysis of structures, of the

different means proposed to overcome them, and the references available in the Philippines

where the interested structural engineer can obtain more detailed discussion than is

possible in this paper of the foregoing.

For lack of a definition as to what constitutes a "low-rise" structure, the author

arbitrarily set any structure below 20 stories as a low-rise structure; 20 to 50 stories as medium-rise; and above 50 stories as high-rise. This is consistent with the relative

necessity for the use of shear walls in resisting lateral loads as governed by the number of

stories suggested by Khan (KHAN, 1967) for the purposes of this paper.

With respect to the definition of "low-cost", the author would prefer not to even attempt one because the rapid changes of prices of construction material currently (1973)

obtaining would make any estimate academic.

2. BEAM AND COLUMN STRUCTURES

This lateral load resisting system is by far the one for which the greatest number of

methods of analysis is available. The different methods may be broken up into two major

groups: manual and digital computer methods.

Most manual methods are usually restricted to planar rigid frames. Those methods which

can be made to yield adequately accurate results, such as the traditional moment

distribution, become too laborious to be practical when used for large structural systems,

78
even in plane rigid frames. Approximate methods such as the portal method, the cantilever

nethod, the Factor method, (MORRIS and WILBUR, 1960) etc., which are still being used in

this country can also yiel(J acceptable, albeit approximate, results provided that the

assumptions on which they are based are reasonably well satisfied. The author of this

paper knows of only one manual method for analyzing a three dimensional, rectangular rigid

frame (PCA, 1954). This method makes the assumption, the method then derives formulas from

which a convenient tabulation based-solution will yield end moments for each member of each

floor due to the imposed lateral load including torsion due to any eccentricity between the

lateral load resultant and the computed center of rigidity. All the foregoing manual

methods are severely restricted in that calculation of displacements are very tedious. This

computation of displacements is now receiving much attention particularly in tall structures

(CHEN and ROBERTSON, 1972) because human comfort is affected by their magnitude. Another

factor which may severely restrict the use of manual methods based on planar frame analysis

is the requirement of new building codes of an analysis for torsion even for nominally

symmetric structures.

It is the considered opinion of the author therefore, that for meaningful results to be

obtained in structural analysis, both for internal forces and deformations, a digital

computer solution is an absolute necessity.

Fortunately, there are a large number of digital computer installations in existence in

the Philippines although only three, as far as the author knows, have the necessary software

(programs) for structural analysis. These are:

1. The computer Center of the University of the Philippines,

2. The Data Center Services of IBM Philippines, and,

3. The Computer Services Center (of the Meralco Securities

group of companies).

From the point of view of software there are two types, the general type which can handle any type of structure; truss, grid, rigid frame; whether planar or three-dimensional;

and, the special type which can handle only one type of structure.

The general type of program package is available in all three computer installations

and is the MIT-developed STRESS (Structural Engineering Systems Solver) program (FENVES, et

al, 1964). Since the size of the core memory is the major factor limiting the size of the

problem that can be handled and since the computers in the foregoing installations are of

different sizes and mode]^ not to mention different types, it is best for the potential user

to consult the particular installation as to the maximum structure size that may be handled

using stress.

The special type of programs, being restricted to specific kinds of structures, can handle a much larger-sized structure than STRESS. The author knows of only two and these

are both at the U.P. Computer Center and were developed by Dr. Salvador F. Reyes (REYES,

1973) to analyze planar, rectangular rigid frames (program named CE550020) and

three-dimensional, rectangular rigid frames (program named EQANAL)

.

All the digital computer methods yield displacements as well as internal forces.

The foregoing discussion has made one tacit assumption that only first-order effects

are of importance and that secondary effects are negligible. These secondary effects are

due to stability effects (moments due to column axial loads, P, acting over lateral sway

displacements, D; i.e., P x D) and to axial shortening of columns (due to axial forces in

columns or temperature differentials between adjacent columns) which if unequal induce

additional fixed end moments in beams Fig. 1. Several studies (GRUNDY and WATHEN, 1971;

FINTEL and KHAN, 1965: KHAN and FINTEL, 1966; KHAN and FINTEL, 1968; WEIDLINGER, 1964) have

shown that these are not negligible particularly for tall buildings. All the references

cited discuss either necessary modifications in the stiffness matrix of the individual

member or the approximate methods to be used to account for these secondary effects.

However, existing digital computer programs, those mentioned in particular, can be used in

79
iterative fashion to account for these effects which are non-linear in nature. In the case

of axial load effects and temperature differentials beiween ^oluians, the axial length

changes can be calculated from the first-order solution. The necessary fixed-end moments in

the beams can be calculated by then multiplying the axial load in the particular column by

the sway displacement between the ends Fig. 1. These fixed-end moments than can be input into

the computer program and another analysis run. Examination of the changes in the final moments and displacements due the secondary effects can then be made and a decision made as to whether further recalculations need to be made. These are then superposed on the firstorder analysis. The procedure is relatively rapid in convergence and does not require, except

for unusually proportioned structures, as a maximum, more than four cycles. Grundy and

Wathen recommend as a matter of routine the use of the second order analysis even for medium

rise structures specifically for stability effects.

3. TUBE STRUCTURES

This lateral force resisting system is characterised by a single, cantilever resisting

system for lateral loads. There are different types of tube systems currently in use.

Tube Structures of the Shear Core Type

The first type consists of a central core, usually the elevator and utilities shafts,

made up of shear wall assemblies. This has become quite popular in particular in

conjunction with slipform construction where the central core is constructed first and the

floors then constructed in such a way that they are supported jointly by the core and ties

which are in turn suspended from a supporting member at the top of the core. Fig. 2.

The analysis of the bending moments, shear and axial forces for this lateral force

resisting system is very simple since it becomes merely the analysis of a cantilever once

the lateral forces are determined.

The distribution of bending and shear stresses, in combination with the normal

component due to axial force, among the different elements is an entirely different matter.

It is this regard that many uncertainties exist

.

The core which is made up of shear wall assemblies is essentially a thin-wall

structure. Structural steel textbooks (McGUIRE, 1968 and TALL, et al, 1964) indicate that

for a given aspect ratio (i.e., the ratio of the lesser dimension of a rectangular panel to its thickness) , elastic buckling will take place when the compressive stress reaches the

critical stress. Proportions of shear wall elements and the compressive stress in practice

are such that plate buckling could take place. However, in one of the studies on shear wall

assemblies (BRETTLE, 1971) mention is made of other research involving actual experiments on thin-walled, reinforced concrete, closed tubes of typical shear wall proportions showed that no buckling took place and instead failure compressive stress of the order of 0.85f' to f

were attained depending upon the amount of reinforcement used. Whether these results are typical is still an open question.

Another uncertainty is how much of the flange elements of a core assembly is effective

in view of shear lag. Some designers locally use the rules for effective flange widths of

Tee-beams specified by the ACI (ACI318-71). No theoretical or experimental justification of

the practice is known to the author.

In view of mandatory analysis for torsion now required by most codes, warping of

cross-sections of core elements needs to be taken into account. Again, from structural

steel textbooks, a non-circular thin-wall section will warp under torsion but will undergo

no longitudinal stressing for as long as freedom to warp at every section is provided. In the case of a shear-core assembly, its attachment to what normally is a massive foundation

prevents warping at this end. As a result longitudinal stresses will take place. The

magnitude of these stresses will vary from that, where the beam elements spanning the

openings in the core structure are so flexible that the behavior is that of an open tube, to that of a closed tube, when the beam elements are infinite in stiffness. Fig. 3 shows the

deformations in the neighborhood of a core structure. A study using Vlasov's theory for

torsion of members made up of thin-wall elements (TARANATH and STAFFORD-SMITH, 1973) shows

80
that normal stresses due to warping are of the same order of magnitude as the primary

bending stresses and should, therefore, always be taken into account. This study derives

some formulas which can be used for calculating these longitudinal stresses. Methods of

taking into account the stiffening elements of the floor bridging the openings are also

given. It is interesting to note that the presence of beam or slabs bridging these openings

can produce a significant reduction in longitudinal stresses. Another investigation (TSO and

BISWAS, 1973) using the continuous connection techniques derives a 5th order linear differential equation which when solved with the appropriate boundary conditions yields for a general

three-dimensional shear wall assembly, the deflections and rotations along the height of the

structure as well as the effect of axial deformations.

A fourth uncertainty is: should the analysis of a core be based on the uncracked state

of the wall elements (a state in which the core is at its stiffest) or should they be based

on the cracked state (a state in which the core is least stiff) considering that at one time

or another in the lifetime of the structure the lateral loads can conceivably reach values

which will produce an excursion of the structure into the cracked state. This is

particularly important when one considers the associated problem: if the stiffest state is

used, the deflections which may be critical will be understated; on the other hand when the

most flexible state is used, the deflections may be overstated. In either case one's judgment is distorted and unnecessary measured may be taken in the design.

! A number of other problems for this type of lateral load resisting system exist but

! will be discussed in conjunction with the frame-shear wall system where these problems occur

i more frequently and are more serious in nature.

! Framed-Tube Structures

This lateral load resisting system is of fairly recent vintage but has been applied to what is now the world's tallest structure at 1454 ft. above ground level, the Sears Roebuck

j Building in Chicago (Iyengar, 1973). Complicating matters in reinforced concrete is that

repeated excursions into the inelastic range which can take place throughout the loading

I history of the structure can lead to an increasingly degraded resistance of the component

t elements of the structure. Whether a modified limit analysis similar to that of structural

I steel taking this into account can be developed or not remains to be seen. A typical plan

of this structure is shown in Fig. 4. One will note immediately that although for practical

j purposes this is essentially a conventional frame structure, spacings of columns are much

. closer than in ordinary rigid frames. Also stiff spandrel beams are used. The columns and

j the spandrels then form a rigid exterior grid which is designed to exist the entire lateral

I load. This explains the use of the term "framed tube". The behavior of the tube system has

been described (KHAN and AMIN, 1973) as consisting of two resistances: a resistance to

,1 overturning which results in compression and tension in the columns and a resistance to the

shear from the lateral load which is provided by frame action by the two sides of the

building parallel to the direction of the lateral load, Fig. 4. Because these frames are

not solid webs, considerable shear lag takes place and distribution of compressive forces in

the columns is non-uniform. Khan and Amin in their paper have proposed an equivalent

' "channel flange" to account for this and have provided influence charts which are of

I sufficient scope to allow a reasonably accurate preliminary design. The final analysis of

' such a system needs to be done by computer. This constitutes a considerable problem because

of the number of joints resulting from the configuration which will require a large

computer. The reference listed in the foregoing presents a means of approximating the

full-sized building into one with fewer floors to fit available computers but which still

|)j attains sufficient accuracy for final design purposes.

: Other variations of this system exist. Among them is the use of a shear core system

inside the building so that in effect the whole structure is a tube within a framed type.

I I Another variation is to subdivide the interior or the building into sections by interior

ll columns spaced at the same distances as the exterior columns so that the whole system

I

j becomes a system of "bundled" framed tubes,

Ii The use of the framed tube has not yet been tried in the Philippines perhaps primarily

because existing computer facilities do not have the size of core memory to handle the

j structure without too much approximating.

81
4. SHEAR WALL STRUCTURES

This category is by far the most popular in the Philippines and if one were to judge

from the number of papers in existence is also the most popular in the world. Several

subtypes are found in this system.

Shear Wall Systems

In most apartment and residential structures where the partitions walls are fixed in

identical locations from floor to floor, the walls themselves become the load bearing, as well as lateral force resisting elements.

As long as the walls are solid without any openings, the analysis is straightforward

but is complicated only by the problem of what effective width of the slabs are to be used

in the frame analysis. Some proposals have been made, ranging from the whole span (BARNARD

and SCHWAIGHOFER, 1967) to variable effective widths depending upon properties of slabs and

walls (QADEER and STAFFORD SMITH,, 1969). To date, this remains a problem (DERECHO, 1973).

When walls have openings then the problem becomes more difficult. Actually, the

existing computer programs can be used for the analysis (SCHWAIGHOFER and MINORS, 1969) by

considering the component walls and the beams spanning the opening as a wide column rigid

frame with the individual centerlines of the walls and the beams defining the centerline of

the equivalent frame; by considering the cross-sectional properties of the walls as the

cross-sectional properties of the equivalent columns; and, finally, by using the

cross-sectional properties of the central portion of the beams as the cross-sectional

properties of the central portion of the equivalent beams but now using an infinitely rigid

portion of the ends of the equivalent beams framing into the walls. There is some divided

opinion on how much is to be considered infinitely ri^id. Originally, the whole portion

starting from the intersection with the face of the wall up to the centerline of the wall

was so considered. However, recent work (MICHAEL, 1967) has shown that this is not correct.

A rigorous method is proposed along with an acceptably accurate simplication of assuming the

infinitely rigid portion to start within the wall an amount equal to 1/4 the beam depth

beyond the intersection of the beam and the wall at ends intersecting the wall.

The only drawback in using the computer solution directly is that one has to guess the

initial properties of the walls and the connecting beams. If the guesses are grossly in error, the continual iterative use of the computer can be quite expensive. So there is

need for a rapid manual method that can be used to arrive at a preliminary solution sufficiently close to the final one so as to minimize the number of computer runs to arrive at

the final design.

The best known of the manual methods is the technique known variously as the continuum

method, the continuous connection technique, Rosman's method, etc. The method originally

credited to Chitty has been elaborated on by Beck (BECK, 1962), Rosman (ROSMAN, 1965) and by I Coull and Choudhury (COUL and CHOUDHURY, 1967a and COULL and CHOUDHURY, 1967b). The method

essentially consists of substituting of the connecting beams spanning the openings between

the walls with a continuous medium with an equivalent stiffness per unit of height to that

of the beams. A whole series of papers showing how different loading conditions can be

handled using different conditions of supports are available (in addition to the foregoing

cited references; COULL, A., 1973, COULL, A. and ADAMS, 1973; COULL and IRWIN, 1969; COULL

and IRWIN, 1972; COULL and IRWIN, 1973, COULL and PURI, 1968; GLUCK J., 1969; GLUCK, J.,

1970; MacLEOD, I., 1970; PAULAY , T., 1970). This procedure yields the normal and shear

stresses in the walls, their deflections and rotations as well as the shears and therefore

moments in the connecting beams.

Frame-Shear Wall Systems

Quite apart from the previous type of shear wall system is the combination of shear

walls with rigid frames.

Here the primary problem is the analysis of the proportion of the shear that is

resisted by the frame and that by the wall. Fig. 5a shows pattern of a shear wall resisting

lateral loads alone. But when both are combined. Fig. 5c, the deflection pattern of each

82
component system is different from that when each resists its own share alone. Thus it Is absolutely necessary to analyze the systems in combination if meaningful results are to be

obtained

.

The analysis can be performed by any of the computer programs now available in the

Philippines (STRESS and the Reyes programs). The major limitation is the maximum size of

structure that c an be handled because of the size of the computers available. One way

around the problem is to find a substitute frame which results in a smaller size problem but

which can represent the original structure adequately. Several approaches to the problem

are available (WYNHOVEN and ADAMS, 1972; BAZANT and CHRISTENSEN, 1973). While perhaps no exact substitute frame can be found, for practical purposes, that indicated by the quoted

references can be used.

Again, a computer solution can be very expensive if used in the iterative procedure to arrive at an optimum final design. Some convenient manual procedures using either formulas

(HEIDEBRECHT and STAFFORD-SMITH , 1973, MacLEOD, 1970b) or charts (KHAN and SBAROUNIS, 1964) are available which allow the structural engineer to guess at an initial solution analyzed

by these methods and revise as many times as necessary until the frame shear wall system is

judged to- be sufficiently close to the final after which a computer solution can be used.

In all of the previous discussion, it has been tacitlv assumed that the walls are all

in the same plane as the frame to which it is connected. When shear wall assemblies are connected to two or more frames, then the problem of modelling the system becomes very

difficult. All the problems discussed under tube structures of the shear core type along

with the problems discussed under frame-shear wall systems come into play primary of which

is the adequate representation of the assembly of the shear core elements. Perhaps a modification of Tso's method (TSO and BISWAS, 1973) which is slightly more convenient to handle than that of Taranath (TARANATH and STAFFORD-SMITH, 1973) could be used in developing

a stiffness matrix for the assembly before use in a standard computer program.

Another serious problem common to all of the lateral load resisting systems so far

discussed has been the assumption that floor slabs will act as rigid diaphragms. A

I computer-based solution which includes in-plane deformations of slabs is available

(GODLBERG, 1967). Inclusion of this effect can increase the size of the problem to be

. handled and can be limited by existing computer facilities but may be necessary since errors

I in the frame analysis can be serious particularly when shear walls or lateral load resisting

systems in use are of the same order of magnitude in stiffness as the slabs.

A serious problem that is not even mentioned in most papers is that of providing

adequate foundation anchorage for the lateral load resisting system. This is particularly

' true when the system resists a major portion of the lateral load while at the same time is

; supporting a very minor fraction of the vertical load. This normally requires very stiff

I foundation beams in the order of magnitude of that of the components of the system. It is

thus necessary to analyze footing tie beams as part of the frame in order to take into

account automatically the effect of the stiffnesses of these tie beams rather than make some arbitrary assumptions as to the fixity of the lateral load resisting system at the

foundation levels. The two Reyes programs have provisions for this as well as for including

i elastic resistance of the footing-soil system.

One and Two Story Structures

I

I In the Philippines, one- and two-story structures are usually not specifically analyzed

for lateral loading. The resistance to lateral loads is assumed to be there and is taken

for granted to be adequate.

Structures of this type rely on diaphragm action to provide the lateral resistance to

I wind action. Fig. 6. For a great majority of cases, the use of sophisticated computer-based

' analysis is not justified. There exists, however, a manual method of calculation based on

; principles of strength of materials (BENJAMIN, 1959 and BENJAMIN and WILLIAMS, 1958a) which

' is very convenient for use and can handle openings in walls such as doors and windows.

I Although not completely rigorous because compatibility conditions are not fully satisfied,

the technique is very attractive due to ease of application and to acceptable accuracy.

83
Diaphragm action can be provided in a number of ways. Walls made of brick, concrete

hollow block properly reinforced, thin precast concrete panels, infilled frames (reinforced

concrete columns and beams with space surrounded by them filled with masonry) , plywood

walls, wall studs and lintel beams sheathed, etc.

Theoretical and experimental studies on the strength of diaphragms made of brick

(BENJAMIN and WILLIAMS, 1958b), reinforced concrete walls (BENJAMIN and WILLIAMS, 1959), and

Infilled walls (STAFFORD SMITH, 1967) are available.. A design "manual" for timber and ' plywood diaphragm construction is also available (AMERICAN PLYWOOD ASSOCIATION, 1957).

Actual field experience on behavior of timber and plywood diaphragms have been recorded

(AMERICAN PLYWOOD ASSOCIATION, 1964) and show that this method of resisting lateral loads is

extremely good.

The computational procedures of the foregoing reference^ can be used immediately

without any modifications. However, there is need for more research locally to develop

allowable values for use in design. Two cases in point may be cited. Take the infilled

frame diaphragm system. Stafford Smith has shown that the infill panel between the

reinforced concrete columns and beams can be represented fairly well by an equivalent

diagonal strut having a thickness similar to that of the infill itself. The width of this

in the plane of the panel is variable and is influenced by the stiffness of the framing

members relative to that of the infill, which in turn is affected by the proportions of the

panel. The strength of the panel, whether failure is by diagonal cracking or by crushing is

also influenced by these factors. While the properties of brick and reinforced concrete

have been discussed by Benjamin and Williams and by Stafford Smith, no counterpart studies

on Crete hollow block masonry are known to be available locally by the author. Considering

that concrete hollow block masonry is the most popular material, next perhaps only to wood,

for one- and two-story structures in the Philippines, the need for such data is immediately

obvious. In the case of plywood diaphragms, their resistance is shown by the design

"manual" of the American Plywood Association to be dependent upon the thickness of the

plywood panels, the nail spacing at the plywood panel edges and to some degree on the width

of the wood framing members. Again no comparable data on Philippine plywood diaphragms is

knovm by the author to be available locally.

While it may be argued that it is conservative to disregard the effects of infills and

plywood panels on the strength of the structure and to let the primary members be designed

to handle the entire lateral force, it is obvious that economy can result if these

contributions are taken into account. Also, since diaphragms are very much stiffer than the

frames made up of columns and beams, it may well be that under the action of lateral forcgs

,

these diaphragms can so change the distribution of lateral forces among the resisting

elements, that the actual distribution may be sufficiently different from that assumed in

the analysis to be dangerous.

One Final Problem

Conventional design is based on the idea that if the worst combination of the working

load multiplied by a certain load factor is ever reached, the structure fails. Structural

design in steel recognizes other possible modes of failure (NEAL, 1956 and SUIDAN and

EUBANKS, 1973): incremental collapse, alternating plasticity and fatigue. A start along

those lines has been made in reinforced concrete the predominate structural material in the

Philippines

.

5. CONCLUDING REMARKS

The problem raised in this paper can be divided into two broad categories, regardless

of the type of lateral-load resisting system in use. All of these are indicated as fruitful

areas for further study.

The first category is the need for simplified models of the different systems: (1)

those that can be used manually, to arrive at a sufficiently accurate preliminary design and

(2) those that can accurately reduce the size of the problem to fit existing and

foreseeable computer systems for the Philippines.

The second category of problems is how to design individual component elements so that

the assumptions made in the analysis as to their behavior can be realized.

84
A final note is that except for a few papers, no general analysis of structures in an

I actual dynamic situation has been carried out for the lateral load resisting systems

mentioned. As has been borne out by experience the dynamic behavior of structures is very

different and often disastrously so from the static behavior used as the basis for design.

On the note that so much more needs to be studied, the paper is closed.

I

I

85
Section A-A

Figo 1 Secondary Effects on

Columns

Fig. 2 Typical Shear Core System

Legend

:

(l^ Deflected Shape, Only Primary

Effects Considered

Deflected Shape, 1st Iteration

Including Secondary Effects

(f) Final Deflected Shape

86
Axial stress in column due to true

cantilever action

Actual axial stress due to shear lag effect

JUUUULIUUuuuuuuuuuuuuuuuuL

c

c

c

Tnnnnnnnnnnnnnnnnnnnnnnnnnr

Fig. 4 Framed Tube

Action

t

WIND

FORCE

(c)

Fig. 5 Deflection Patterns of

Different Systems

87
Fig. 6 Distribution of Lateral Loads on a One-Story Building

88
REFERENCES

i American Plywood Association, Basic Facts About Plywood Diaphragms, 1957, Form No. 57-220B

I American Plywood Association, Report From Anchorage, 1964, Form No. 64-300

' Barnard, P. R. and Schwai ghof er , J., "The Interaction of Shear Walls Connected Solely Through

) Salbs", Tall Buildings, Pergamon, 1967

Bazant, Z. P. and Christensen, M., "Continuous Approximation of Large Regular Frameworks and

the Problem of a Substitute Frame", Response of Multi-story Structures to Lateral Forces,

SP 36, ACI, 1973

Beck, H., "Contribution to the Analysis of Coupled Shear Walls", Jrni of the ACI. Proc. V. 59, No. 8, Aug. 1962

Benjamin, J. R., Statically Indeterminate Structures, McGraw-Hill, 1969

Benjamin, J. R. and Williams, H. A., "Behavior of One-Story Reinforced Concrete Shear Walls

Containing Openings", Jrnl. of the ACI, Proc. Vol. 55, 1958-59

Benjamin, J. R. and Williams, H. A., "The Behavior of One-Story Brick Shear Walls", Jrnl. of

the ST Pi v., ASCE, V. 84, No. ST4, July 1958

Benjamin, J. R. and Williams, H. A., "Behavior of Reinforced Concrete Shear Walls", Trans.

ASCE. V. 124, 1959

Brettle, H. J., Ultimate Strength Design of Reinforced Concrete Lift Walls and Building Core

Walls in Compression and Biaxial Bending", Uniciv Report R-68, University of New South

Wales, Austrailia, Aug. 1971

Chen, P. W. and Robertsong L. E., "Human Perception Thresholds of Horizontal Motions", Jrnl

.

' of the ST Div.

,

ASCE, Vol 98, No. ST8, Aug. 1972, Proc. Paper 9142

Coull, A., "Distribution of Shear Form in Coupled Shear Wall Structures", Response of Multistory Concrete Structures to Lateral Loads, SP 36, ACI, 1973

Coull, A. and Choudhury, J. R,, "Stresses and Deflections in Coupled Shear Walls", Jrnl . of

the ACI, Proc. V. 64, No. 2, Feb. 1967

Coull, A. and Choudhury, J. R., "Analysis of Coupled Shear Walls", Jrnl . of the ACI

,

Proc.

V. 64, No. 9, Sept. 1967

i Coull, A. and Irwin, A. W. , "Design of Connecting Beams in Coupled Shear Wall Structures",

I Jrnl. of the ACI, Proc. V. 66, March 1969

j Coull, A. and Irwin, A. W. , "Model Investigations of Shear Wall Structures", Jrnl . of the

ST Div. . ASCE, Vol. 98, No. ST6, Proc. Paper 8936, June 1972

' Coull, A. and Irwin, A. W., "Torsional Analysis of Multi-Story Shear Wall Structures",

Analysis of Structural Systems for Torsion, SP 36, ACI, 1973

Coull, A. and Puri , R. D., "Analysis of Pierced Shear Walls", Jrnl . of the ST Div.

,

ASCE,

) Vol. 94, STI, 1968

I Derecho, A., "Frames and Frame-Shear Wall Systems", Response of Multi-Story Structures to

I Lateral Loads, SP 36, ACI, 1973

I Fenves, S., Logcher, R. D., Mauch, S. P. and Reinshmidt, K, F., STRESS: A User's Manual

,

II M.I.T., 1964

j Fintel, M. and Khan, F. R. , "Effects of Column Exposure in Tall Structures - Temperature

Variations and their Effects", Jrnl . of the ACI, Proc. V. 62, No. 12, Dec. 1965

I Gluck, J., "Lateral Load Analysis of Multi-Story Structures Comprised of Shear Walls with

' Sudden Changes in Stiffness", Jrnl. of the ACI, Proc. V. 66, Sept. 1969

Gluck, J., "Lateral Load Analysis of Irregular Shear Wall Multi-Story Structures", Jrnl . of

the ACI, Proc. V. 67, July 1970

Goldberg, J. E., "Analysis of Multi-Story Buildings Considering Shear Wall and Floor Deformations", Tall Buildings, Pergamon, 1967

Grundy, P. and Wathen, G. R., Frame-Shear Wall Interaction, Report No. 7/1971, Monash University, Australia, 1971

Heidebrecht, A. and Stafford-Smith, B., "Approximate Analysis of Tall Wall -Frame Structures",

Jrnl. of the ST Div., ASCE, Vol. 99, ST 2, Proc. Paper 9550 Feb. 1973

Iyengar, S. H., "Structural System for Two Ultra High-Rise Structures", Pre-print of paper

submitted to the Australian and New Zealand Conference on the Planning and Design of

Tall Buildings, Aug. 1973

Khan, F. R,, "On Some Special Problems of Analysis and Design of Shear Wall Structures",

Tall Buildings, Pergamon, 1967

j Khan, F. R. and Amin, N. R., "Analysis and Design of Framed Tube Structures for Tall Concrete

I Buildings", The Structural Engineer, March 1973, V. 51, No. 3 Khan, F. R. and Fintel, M., "Effects of Column Exposure in Tall Structures - Design Considerations and Field Observations of Buildings", Jrnl . of the ACI

,

Proc. V. 65, No. 2,

I Feb. 1968

89

i
MacLeod, Iain, "Connected Shear Walls of Uniform Width", Jrnl . of the AC I, Proc. Vol. 67,

May 1970

MacLeod, Iain, Shear Wall -Frame Interaction - a Design Aid, Engineering Bulletin 066. OLD,

Portland Cement Association, 1970

McGuire, W., Steel Structures, Prentice-Hall, 1968

Neal, B., The Plastic Methods of Analysis, Wiley, 1965

Norris, C. H. and Wilbur, J. B., Elementary Structural Analysis, 2nd Ed., 1960, McGraw-Hill

Paulay, T. , "An Elasto-Plastic Analysis of Coupled Shear Walls", Jrnl. of the ACI. Proc. V. 67, Nov. 1970

PCA, Continuity in Concrete Building Frames, 4th Ed., 1954, Portland Cement Association

Qadeer, A. and Stafford-Smith, B., "The Bending Stiffness of Slabs Connecting Shear Walls",

Jrnl . of the ACI. Proc. V. 66, No. 6, June 1969

Reyes, S. F., Notes on the Computer Analysis of Multi -Story Buildings, Association of Structural Engineers of the Philippines, 1973

Rosman, Riko, "Approximate Analysis of Shear Walls Subject to Lateral Loads", Jrnl . of the

ACI, Proc. V. 61, No. 6, June 1964

Schwaighofer , J. and Minoys, H., "Analysis of Shear Walls Using Standard Computer Programs",

Jrnl. of the ACI, Proc. V. 66, Dec. 1969

Stafford Smith, B., "The Composite Behavior of Infilled Frames", Tall Buildings, Perqamon,

1967

Suidan, M. T. and Eubanks, R. A., "Cumulative Fatigue Damage in Seismic Structures", Jrnl

.

of the ST Div.. ASCE, Vol. 99, No. ST5, Proc. Paper No. 9759, May 1973

Tall, Lambert Ed., Structural Steel Design, Ronald, 1964

Taranath, B. S. and Stafford-Smith, B., "Torsion Analysis of Shear Core Structures", Analysis

of Structural Systems for Torsion, SP 35, American Concrete Institute, 1973

Tso, W. K. and Biswas, J. K. , "General Analysis of Non-Planar Coupled Shear Walls", Jrnl . of

the ST Div., ASCE, Vol., 99, No. ST3, Proc. Paper 9604, March 1972

Weidlinger, P., "Temperature Stresses in Tall Reinforced Concrete Buildings", Civil Engineering, ASCE, Aug. 1963

Wynhoven, J. H. and Adams, P. F., "Analysis of Three-Dimensional Structure", Jrnl . of the

ST Div.. ASCE, V. 98, No. STI, Proc. Paper No. 8643, Jan. 1972

J

90
SOCIO-ECONOMIC AND ARCHITECTURAL

CONSIDERATIONS IN HOUSING

by

Geronimo V. Manahan

and

Josefina M. Ramos

Building Research Service, University of Philippines,

Quezon City, Philippines

1. Housing Is Not Mere Shelter

It is in the home and its physical environment where the broadest range of man's

existence is fulfilled. It is also in the home where the largest part of his experiences

are made. The house therefore becomes the physical shell upon which the basic

socio-economic need of man and his family is met.

The World Health Organization (1) defines "shelter" as an enclosed environment in which

man finds protection against the elements, is safe and secure from hostile forces and can function with greater vigor, more efficiency and increased comfort and satisfaction, and in

j which he can safeguard his possessions and be assured of privacy for himself and his family.

On the same subject the WHO refers to "housing" as the "residential environment",

' "neighborhood" or the physical structures that man uses for shelter including the environs

' upon which the structures are disposed. This shall also include all necessary services,

facilities, equipment and devices needed or desired for the physical a.ud mental health as well as the social well-being of the individual and his family.

Clearly housing is not merely shelter, nor is it only the physical entity. It is more

of a complex process involving various aspects and tasks like research, health, planning,

architecture, engineering, economics, culture and social relations as well as the political

and behavioral sciences. These are so inter-related and inter-twined that they become

difficult to analyze in isolation. It is patent to state that since housing comprises a number of facilities, services and utilities which a family takes advantage of as its link

to the community and eventually to the region, the more relevant approach for the

development of housing is through community planning, design and management.

Inherent in the proper approach to the socio-economic considerations of housing is a study of the basic social elements and how these interact in the socio-cultural mileu upon

which they survive

.

2. The Filipino Family and Its Housing Needs

In most cultures, the basic unit of social organization is the family. In the

Philippines, it is considered the strongest unit of society. In order to determine the

housing needs of the present Filipino family, it is important to know, at the outset, what

constitutes the Filipino family.

The Filipino family system is generally characterized by bilateral kinship which is

extended to include not only families of both parents but also other blood relatives, often

as far as the third or fourth cousins. It is, therefore, not unusual to find families with

at least three generations

.

To help one's relatives is also an obligation that is expected not only of the family

but the society as a whole. This means that in time of crisis, one is expected to share

his roof or his meal with the less fortunate members of his family. He is dutibound to extend support to his parents in their old age or to a widowed sister and her children.

The Filipino family also serves as the economic unit in the rural areas, as well as in

the urban areas. Children are regarded as "economic asset", and a large family is

considered as a means of achieving social security.

91
A community has been described as the simplest first grouping beyond the family. In the Philippines the community grouping has been recognized as the springboard for local

unity. The "barangay" has been formalized to systematize the conscious sense of belonging

or "we" feeling. This social grouping has shown its positive uses during times of crisis

where community mobilization is of importance. In its physical sense a residential neighborhood is not an aggregate of houses but is a system or pattern into which the family unit

with its occupations, specializations and activities is woven. The neighborhood or his

community is the grouping besides the family into which the individual is inducted into

social life.

An examination of families in any community will reveal great differences in the family

composition as to the number of persons, age, or nature of membership within the family.

Wliile national figures indicate that about 80 per cent of all families are nuclear families,

several studies reveal a different picture. (2) In a survey of selected low- income areas around Metropolitan Manila, the percentage of extended families, embracing parents, in-laws,

married children, and other kinsmen, varies from 42 to 55 per cent. (3) This is an evidence that a relatively large number of extended families exists in the urban sector.

The same survey shows that family size ranges from 7 to 11 with at least 18 per cent

consisting of 9 or more members.

Another important consideration in housing is the economic nature of the family, for

the most important factor that affects the choice of housing is the income of the family. A

general rule of thumb tells us that a family should spend no more than one-fifth of its

monthly income for rent, or no more than twice its yearly income to purchase a house. This

rule may not be easily adaptable if we consider the general economic situation of the

Filipino family. It is an unusual case that as income increases, the proportion of income

spent on housing decreases. How many urban families can afford to spend 20 per cent of

their monthly income to get decent housing at minimum price? Housing experts and economists

estimate that only 14 per cent of urban families can afford housing in the open market; 36

percent can afford home ownership provided they are extended long-term financing at reasonable interest rates; and the rest—50 per cent — cannot afford adequate shelter even

at reduced rates

.

This general housing situation reflects the way the underprivileged Filipino family is

housed. Housing statistics shows that ranking cities in the Philippines have from 10 to 45

percent of their populations either in slums or in squatter areas, although the national

average is only about 5 to 6 per cent.

In a research study made of Metropolitan Manila in 1972 (4) some 85% of the low wage

earners had basic economic problems. The families either had no jobs or not enough income.

This poor earning capacity has spawned other dysfunctions for living like malnutrition, ill

health and environmental health hazards. The low-income had limited personal and community

resources like low education and low levels of urban skills. This is expected since most of

the low wage earners are mostly new migrants from the rural countryside.

On the positive side is that their resourcefulness is unlimited, and they can rely

upon themselves in solving their present predicaments. This is fully substantiated by the

findings of Hollnsteiner (5) in her study of Magsaysay Village. They are generally

optimistic and they want to work and improve their family's level of living. Contrary to common belief that squatters are a thieving, shiftness, dangerous slum dweller, they are a manifestation of an economically deprived social structure where rising expectation

motivates them to try their luck where probabilities of success are great.

Generally housing the urban poor is not of renewal and upgrading the conditions , of the

shelter. It is more of strategies of how to arrive at a system where urban poverty,

deprivation and miseducation can be eliminated.

The general housing shortage will give us a wider picture of the situation. The yearly

need of urban housing in the Philippines averages 100,000 units. This need includes the

provision of housing due to population increase, new family formations, and replacement of

slum and squatter houses. An interesting phenomenon is that while the population in general

increases at the rate of 3.01 per cent per year, the squatter population increases at the

rate of 12 per cent. The effects of poor housing conditions to the social and economic life

of the family need not be elaborated.

92
Another major factor that affects the family housing need is the high cost of land and

building materials. The cost of land is coupled with the problem of lack of available land

for development within the urban areas. In many cities, the cost of land has also affected

I the cost of rental.

A marked increase in wholesale and consumer price indices occurred within the last two

or three years. Although the average increase for all commodities is only about 25 per

cent, the cost of most construction -materials increased by 40 to 60 per cent.

The foregoing discussions have shown the various socio-economic factors affecting the

provision of housing for Filipino families. Through an understanding of these factors lies

the desirability of any design for housing, whether architectural and structural.

j Man always expresses his social and economic aspirations through the physical

improvements he places in the environment. This is greatly manifested particularly in the

[ domestic structures that shelter his family.

3. Housing Characteristics

How are families in the Philippines housed? There are several ways by which dwelling

units may be classified. The Bureau of the Census and Statistics classifies dwelling units

j into the following categories: ownership, type of structure, type of construction

I materials, and type of drinking water, lighting, cooking and toilet facilities. (6) In addition to these, the Population Institute National Demographic Survey (7) includes the

I number of rooms occupied per household, density (persons per room), type of refrigerating

method and lot ownership. Using the latest available data Tables 1 to 10 in Annex A show

! some general housing characteristics.

These statistics alone do not, of course, reflect a wide perspective of the housing

j situation. The accuracy of the data is even subject to scrutiny. For one thing, not any of

these data give the actual condition of the dwelling themselves, except the barong-barongs , which comprise only 4.4 and 5.4 per cent in Metropolitan Manila and the Philippines,

j respectively.

! 4. The Right to Housing

j Because housing brings into focus the social, economic and aesthetic aims and needs of

,j a country, it is considered a major government responsibility. The housing activity takes

I place within a legal framework delineated by the Constitution of the land together with

1 other laws of the country. Santiago (8) states that in the Philippines, while there are no

l! explicit declaration of the right to housing, there are enough provisions which show that • the right is amply recognized. She further states: "Aside from such Constitutional

provisions concerning the right of a person to property; the right against arbitrary

\ deprivation of property; right to security within their houses; liberty of abode and travel,

j there is the newly incorporated provision in the 1973 Philippine Constitution which declares

I that: 'The State shall establish, maintain, and ensure adequate social services in the

I field of education, health, housing , employment, welfare and social security to guarantee

i the enjoyment by the people of a decent standard of living."

j 5. Occupancy Schemes of Urban Public Housing in the Philippines

I

I Occupancy schemes in urban public housing in the country are: tenant,

' tenant -purchasers , purchase, hire-purchase or mortgage. (9)

Tenant occupancy refers to rental housing wherein the dwelling units are leased to eligible applicants. A tenant-landlord relationship exists between the occupant and the

housing agency. The tenant is obliged to pay rentals fixed on the basis of the residual of

I capital and recurring cost minus subsidies given by government.

The "tenant -purchase" or "rent-to-own" scheme is where the tenant is given the right to ownership if he pays rent for a certain length of time. Discount adjustments are occasionally made for early payments. The tenants who would have occupied their dwelling

units continuously for a certain number of years and have faithfully observed the conditions

93
of lease have the option to purchase their dwelling units and lots at the appraised value at

the time of the offer to purchase.

The purchase type of public housing outright ly awards the units from the start of their

occupancy. The purchases are obliged to pay monthly installments for a period of years

after which they shall become the absolute owners of their dwellings and the lots on which

they are erected.

The hire-purchase scheme have awardees who are required to deposit with the housing

agency a lump sum, the amount of which is a proportion of the capital cost or subsidy.

Interests on the deposit are credited to the awardee until he earns the right to own the

property. The right normally comes upon completing the installment payments within a specified period. Until such payments are completed, the occupant is considered a lessee.

The required period to earn ownership is reduced if the occupants pay the full cost of the

house under certain stipulated conditions. The PHHC has not implemented this scheme to

date.

As a mortagagor-mortgagee , the financing by the agency is considered a loan to the

awardee. Ujitil the loan is fully repaid by the occupant the property is mortgaged. Many of

the occupants of PHHC housing projects have mortgaged their house and lot to government

financial institutions. The homeowners who are either members of GSIS or SSS mortgage their

property to secure loans for financing the improvements of their dwellings.

An integrated social development scheme where housing is used as a component for

development is being studied by some entities. The project aims to utilize the integrated

approach for increasing the resources of the household and for increasing the confidence of

the community to manage its own activities. Some aspects of this scheme are:

1. A financing-construction package that will deliver

dwelling units of acceptable standards at a price

affordable by the worker assuming the income maximization component of the project produces expected

results

.

2. A social services staff as part of the management

group of the housing complex to assist the resident

community and to provide opportunities for acquiring

the capability for managing the housing complex itself, the industrial and commercial components, the

community affairs and programs, as well as their own family and business affairs.

3. An income generating component in the project that

will offer the opportunity to members of resident

families to augment the breadwinner's income through

employment right at the housing site.

6. Roots of Settlement Forms in the Philippines

Archeological findings indicate that Stone Age settlements in the Philippines were

small and scattered. The settlements were located by the sea or by rivers and other bodies

of water. It was important for the inhabitants to pick settlements with riverine or coastal

orientations for they depended so much on water for their livelihood. They made use of

water for transportation, as a source of their food, and for watering their fields. This is

still the situation in the rural areas of the country.

The attachment of the Filipinos to the low-lands and water-logged areas caused the

development of a unique type of dwelling that is typical in Southeast Asia. This had very

strong indications of environmental adjustments. A drive along the roads of any provincial

town away from Manila will show the array of regional variations of the typical rural

dwelling. It has a raised floor on stilts. This dwelling type appeared in the area some

6500 to 5500 years ago. The choice of materials and designs reflect the adaptations to

tropical living. Sixteenth century communities in the Philippines were formed essentially

94
by independent households based on extended kinship structures. The size of a community

would not be much larger or smaller than the barrios found in today's agrarian settlements.

Association would normally be based on political, social and economic activities as well as on ritual obligations and ethnic attributes.

The Pre-Spanish community was called a barangay , after the name of the boat used by

Southeast Asian migrants. There were no public buildings upon which community life can

focus

.

The communal activities normally clustered around the houses of the village elders who were also the religious and judicial functionaries. The major affairs of the village

generally rested in the hands of the chieftain. Today the same community organization has

been formalized into a barrio, the smallest political unit of local government.

One always asks why are there no stone structures or buildings of worship in

pre-Spanish Filipino settlements. Authorities have cited numerous reasons, but cogent are:

a. The Philippines was in a marginal position in relation

to Chinese or Indian centers of culture, thus receiving

no direct impact.

b. There was no strong political or religious structure

which can capably direct the erection of massive edifices.

c. The people had impermanent settlement for they had a shifting form of agriculture.

d. Religion was centered on kinship groups called anitos

and ceremonies were conducted in abodes of religious

functionaries

.

7. Conclusions and Recommendations

In the development of criteria for the study of the effects of high velocity winds on low-rise structures the following considerations have to be taken:

1. The long tradition of indigenous building can help in

the development of concepts towards architectural adoptations in a harse environment. This subject could form

part of tropical design which is offered in architectural

schools

.

2. Cultural practices and beliefs of the people should be a parameter in the design of their shelters. It is not

merely economics and technology that should be considered,

but also the sociological and psychological implications

of space. This is particularly important in the rural

areas where building beliefs border towards fantasy.

3. Environmental design and landscaping approaches may in

the over-all analysis give better benefits in finding ways

to optimize resistance of structures to harse winds. The

proper grouping and siting of structures can assist in

the development of wind shields. Similarly, the proper

application of landscaping can develop windbreaks which

can help minimize the harse effects of gusts.

4. The systematic analysis of building component not only

for resisting harse winds but also other environmental

elements should be the approach in the development of

the study program.

95
ANNEX A

Table 1. Type of Dwelling Units by Structure (Percent )

Type Metro Manila Philippines

Single Family Dwelling 57.6 78.9

Duplex 5.5 i+.l Accessoria 15.1 2.3

Apartment 8.1 1.1

Barong-Barong h,h 3.^

Commercial Building 1,0 1.3

Other or No Response 8.3 6.9

Table 2. Nxomber of Rooms in Household Excluding Bath- room and Toilet (Percent)

Tjrpe Metro Manila Philippines

One Room 11.3 lh,l

Two Rooms 22.5 2d.k

Three Rooms 23.1 25.7

Four Rooms 19.8 lk.3

Five Rooms 8.0 6.5

Six Rooms 3.8 2.6

Seven Rooms 1.3 0.8

Eight or More Rooms 1.6 0.6

No Response 8.7 7.0

Table 3. Type of Toilet Facilities for Household (Percent

Type Metro Manila Philippines

Flush Toilet kk.k 10.

1

Antipolo 29.1 l6.1

Pail 3.3 3.5

Open Pit h.9 30.7

Surface or None k.6 30.7

Public Toilet 5.8 1.6

No Response 7.9 6.8

Table k. Type of Cooking Fuel Used by Household (Percent)

Type Metro Manila Philippines

Electricity 17.5 2.5

Gas (piped or tanked) l6.3 3.8

Kerosene 8.9

Wood 13.0 77.6

Others 0.2 0.6

No Response 7.9 6.7

96
Table ^« Lighting Facilities of the Household (Percent )

Type Metro Manila Philippines

Electricity 88.7 22.2

Kerosene 3.3 69.7

Oil 0.2 0.8

Others 0.1 0.6

No Response 7.6 6.7

Table 6. Type of Refrigerating Method in Household (Percent )

Type Metro Manila Philippines

Electricity 26.0 h.k

Petroleum 0.0 1.1

Ice Box 2,1 1.0

None 6U.0 86.8

No Response 7.9 6.7

Table 7» Source of Drinking Water for Household (Percent )

Metro Manila Philippines

Private Faucet Waterworks 63.0 10.2

Private Pump or Artesian

Well 7.2 l6.9

Public Faucet Waterworks 19.2 ll+.l Public Pump or Artesian'

Well 2.8 13.8

Spring 0.0 8.3

River or Stream 0.0 h.6

Rain 0.0 2.3

Well 0.0 23.0

Other or No Response 7.8 6.9

Table 8. House Ownership (Percent .

Type

Owned

Rented

Rent-Free

No Response

Metro Manila

i+3.3 5.5

7.9

Philippines

81.3

6.7

5.3

6.7

97
Table 9» Lot Ownership (Percent )

Tjrpe Metro Manila Philippines

Owned 2I4.3 50.0

Rented hl.h 15.2

Rent-Free 20.

U

28.1

No Response 7.9 6.7

Table 10. Density (Persons per Room) Within Household (Pe

Tjrpe Metro Manila Philippines

(Less than one person

;per room 5.1 6.1

1.00 to 1.99 persons

per room 27.8 27.

U

2.00 to 2.99 persons

per room 26.5 25. i+ 3.00 to 3.99 persons

per room Ik.l 13.7

h.OO to it. 99 persons

per room 7.7 7.7

5.00 to 5.99 persons

per room h,2 3.7

6.00 to 6.99 persons

per room 1.5 2.8

T.OO to 7.99 persons

per room 1.8 1.7

8 or more persons per room 2.7

No Response 8.7 7.0

98
LESSONS LEARNED FROM POST WIND DISASTER INVESTIGATIONS

by

Edward 0. Pfrang

Chief, Structures, Materials and Safety Division

Center for Building Technology

Institute for Applied Technology

National Bureau of Standards

Washington, D, C. 20234

I wish to depart completely from the paper which I prepared for this morning's seminar

after viewing your construction methods and your type of housing. Rather than talk about

the subject of my prepared paper I thought it would be more useful to talk about lessons in

housing that we learned in the United States after observing natural disasters and the

resulting wreckage.

We will view a series of slides which were taken after certain hurricanes struck the

U.S. Gulf Coast. One of the most interesting lessons about hurricanes is that we are getting the same lesson over and over again. So, it is about time that the knowledge we learn, in seminars like this, is put into practice.

One of the simplest lessons one learns after visiting the site of a hurricane, re- gardless of whether the buildings involved are low-rise or high-rise or low-cost or highcost, is that it is not the individual members of the structure that cause problems. Very

rarely does one find failure in a structural member per se . It is almost invariably the

connection details which give the trouble.

To illustrate, let me relate our findings in post-hurricane investigation involving the

two-pole type house, a house that is popular in our coastal regions for two reasons: 1) the

additional comfort one gets by having air circulation along the house; and 2) the fact that

water passes under the house and all we are faced with in terms of forces on the house

itself are the wind effects themselves.

In some instances we have found such houses in reasonably good shape after being subjected to hurricanes. But sometimes we found only the poles remaining. The reason for

this is that the tension ties-the proper bolting of the house to the poles-were missing.

What was the cost difference of two similar vacation pole type houses in the same seashore neighborhood, one of which was blown away while the other survived? Frankly,

the owners of the houses spent exactly the same, although the contractor spent a little more effort on the one house. But we have the same type of house. Certainly we need to tie the frame to the supports at the various junctures. We need adequate ties at the

point where the poles themselves are connected to the ground.

In the United States, we established some standard building details to prevent losses

as described above. The value of establishing the standard details is that one can simplify

the whole design procedure for the house. One does not have to worry about details that we know are workable.

Secondly, and probably even more important, is the enforcement official of the building

regulation system. In the United States he is not a highly trained individual. He does

not have an engineering degree. He is generally a former carpenter, or other craftsman.

If we change the details very frequently his job will be much more difficult. This way

he knows that by referencing the standard, he will need a 5-inch bolt for a certain situation. Economically this is a more feasible approach than trying to be sophisticated about

constructing a building.

Next, we must tie down roofing materials and properly connect the truss or the rafters

to the walls of the building. We should use details which are clean, simple, and where

there is a straight-line transfer of load. Usually, you start getting structural problems

as you tend toward indirect lines of load transfer. Clean, straightforward details are also

preferable from the standpoint of enforcement and inspection. We have tables available

which indicate for example, the capacity of a specific connection detail in terms of the

99
load it can transfer. We know the size of nails to be used and, the number of nails. Thus,

the inspector can simply count nails to see that they are there. In essence, we have a very simple enforcement job.

Frequently used to tie down rafters are standard sheet metal connectors. The manufacturers of these provide test data with a suitable factor of safety. Usually for a connector,

we use a fairly high factor of safety on the order of about 4, sometimes as high as 8. This

factor of safety is possibly a little on the conservative side. But again, it provides for

a simple inspection procedure and it is a nice straight line of load transfer.

Next, if we have sheathing on the building, we can use the sheathing as a mechanism for

transferring that load into the shear plate. So, we can carry that load very simply straight

on down. If we don't have sheathing, if we have a panelized type of system, pre-fabricated

,

something of that sort, more likely than not we would tend to use strapping connectors to tie it to the shear plate. The shear plate in turn must be bolted to the footing. Again, we have standard details for this-to tie down into the footing and carry that load down to

a point where the building can stand up.

I have observed that here in the Philippines your buildings tend to use about the same

type of concrete block construction details as used in the U.S. But details must be attended

to.

The message that I am trying to convey today is that you. must have quality control in

the construction phase through adequate inspection.

Another problem that we continually encounter is deterioration. Wood, for example,

will decay if not properly protected and connectors will pull loose from wood members. In the United States, we recommend the use of ^ treated wood, something that is decay-resistant.

I have seen, since I arrived in the Philippines, some cases that I would be concerned about.

You might be getting into problems of this nature. I have seen tension devices that were

in a situation where they would probably get water around them and yet they were not galvanized; they were not protected. I would be quite concerned about this problem.

We have found design errors in our post-disaster investigations, too. We found a very plush restaurant where cost was obviously no object. But what did they forget to do?

Adequate connectors to hold the building together. They skimped on the bolts that were

needed. So, we don't have to talk about high-cost construction or low-cost construction.

These tension details that give us so much trouble are, by and large, very inexpensive

items. They are common sense details, practical sort of details that we as professionals

should be making sure are incorporated buildings.

Now, there has been some discussion earlier about the importance of shear walls in

the shear resistance or the diaphragm action of houses. We find that in our buildings in

the United States this is what we should call non-problem. However, what is happening in

the United States is that we are running short of plywood which is normally used in the

shear walls. So, we are replacing that plywood. More of the sheathing material we use in our house construction is now a composition board made up of vegetable fibers stabilized with

a binder. In a typical house, even in a hurricane-prone region, we use 4 feet by 8 feet

sheets of plywood only at the corners of the building; the rest of the building will have

composition board material. We find that we are not getting into trouble with the diaphragm

action or the shear resistance of these buildings. If we do get into trouble, it is invariably that we have inadequate nailing or connection of the plywood to the rest of the

frame. We don't get the sheets of plywood buckling, we don't get them breaking. It just

does not seem to be that serious.

We keep getting the same lessons and these are: to tie together our buildings; to be

certain of our quality control, of our building inspection to watch out for deterioration;

to watch out for those things that are frequently overlooked because they are so simple.

Finally, I would like to mention this publication. Building Practices for Disaster

Mitigation which I will leave at the front of the room for the rest of the day. This is

the result of a conference that was sponsored by the National Bureau of Standards and the

National Science Foundation in the United States. We have sent copies of this report to 100
you during a previous trip. They are available in the university library, but some of

you may not have visited the library. What this report does in essence, is establishes a national blueprint or plan for the United States with regard to building practices for

disaster mitigation. It addresses both the seismic and the wind aspects. I think that you

might find this to be a useful document for your own planning here in the Philippines. Unfortunately, we do not have enough copies to make them available to all of you, but we could

probably spare about a dozen copies. So, if those of you that have a real priority interest

in this report would leave your names with me, particularly if you would be willing to share

them with others, I would be very happy to make this available to you.

Thank you.

101
LOW- RISE LOW-COST HOUSING AND EXTREME WIND RELATED PROBLEMS IN BANGLADESH

by

Jamilur R. Choudhury

Associate Professor Civil Engineering, Bangladesh University

of Engineering and Technology, Dacca, Bangladesh

ABSTRACT

The report deals with the present housing conditions and extreme wind related problems in

Bangladesh. Bangladesh, with a population of about 75 million in an area of 55,130 square

miles, has one of the largest densities of population in the world. The housing conditions

are one of the poorest in the world . The problems are made all the more acute due to natural calamities - a third of the country is subject to annual floods and the coastal

areas are ravaged by periodic cyclones.

Most of the houses in rural areas are 'kutcha' ('non-permanent') structures, whose plinth is

made of mud and whose walls and roofs are built of bamboo, grass, straw and reeds. These

houses often do not provide a safe shelter against rain and storms. The stronger type of

houses in rural areas use corrugated galvanized iron sheets supported on bamboo or timber

framing. No special care is taken to anchor the roof to the walls or foundations.

According to the last housing census (1960), the average number of rooms per household was

1.77 and a majority of households (53%) were single room dwellin;^s. It is estimated that

the figures remain virtually the same today.

The conditions of urban houses are no better. The well-to-do class live in buildings with

reinforced concrete flat roofs support on brick masonry walls. With increasing

urbanization, squatter settlements are increasing and most of these slum dwellers live in

almost sub-human conditions.

Extreme winds occur in Bangladesh in three different forms: (i) the Norwesters, (ii)

Cyclonic storms and (iii) tornadoes. Norwesters are violent thunderstorms occurring between

March and May. They originate over land and marshy areas and occur mostly in the central

and eastern districts. The distribution of Norwester squalls in the months of March, April,

May and June are shown in maps. The maximum wind velocities in Norwesters are around 80

mph

.

Cyclonic storms originating in the Bay of Bengal very often hit the coastal areas of

Bangladesh. They are most frequent in the month of October. Usually accompanied with storm

surges, often up to 40 ft. in depth, they cause serious damage to human lives, cattle, houses

and other properties. One of the severest cyclones devastated the coastal areas of

Bangladesh in November, 1970. Wind speeds up to 150 mph have been recorded in recent

cyclones. The C. I. sheet roofs of houses are usually blown away, but the damage to brick

masonry walls and R. C. roofs is not severe.

Tornadoes, the most destructive of all storms, occur in the central and eastern regions.

The outskirts of Dacca c^'ty were devastated by a tornado in April, 1969. The wind speed

causing damage was estimated to be in excess of 150 mph.

Most of the 'permanent' houses with sloping roofs used to be designed according to a wind

pressure derived from the formula p = 0.003 v2 where p is the pressure in Ibs/sft and V is

the design wind speed in mph. A common value of V used in designs is 100 mph. Suction and

lift forces were completely ignored. In recent years, either the B.S. Code No. 3 (Chapter

V) , 1952 or the A.S.C.E. recommendations (1936) is being used. These recognize the effect

of slope of roof on the pressure distribution. Depending on the angle of inclination,

either suction or pressure may be created on the windward side, whereas the leeward side is

always under suction. There is no Code of Building Practice specifying the different design

loads but after recent experiences of cyclonic disasters, some designers use an uplift

pressure of 25 Ibs/sq. ft. in designing the anchor elements for roof structures in lowrise

buildings

.

102
1. INTRODUCTION

General

Bangladesh is one of the youngest nations in the world. Formerly known as East Pakistan, it

emerged as an independent nation after a short but violent war of liberation lasting about

nine months from March 1971 to December 1971.

Geographically, it is located on the north-east of the South Asian Sub-Continent between

20°30' and 26°45' North latitude and 88° and 92° 56' East longitude. The total area is

55,130 square miles. Almost the whole of the country is a network of rivers, constituting

the delta of three of the world's biggest rivers - the Brahmaputra, the Ganges and the

Meghna

.

The country is surrounded on the west, north and north-east by India, on the south-east by

Burma and on the south by the Bay of Bengal.

Population

The present population is about 75 million. With an average of about 1360 persons per

square mile, Bangladesh has one of the largest densities of population in the world. The

annual net rate of population increase in Bangladesh was estimated to be 2.6 per cent in

1961. By the end of the present decade the population is expected to be about 95 million.

Economy

Bangladesh is one of the poorest countries in the world. The Gross Domestic Product

I (constant factor cost at 1959/60 prices) was about 4.57 billion dollars* in FY 1970.

I The economy of Bangladesh is traditionally and predominantly agricultural. About 90% of the

I population is rural and about 80% of these are engaged in agriculture. Agricultural output

l| accounts for about 55% of the GDP. The per-capita real income is about $64 (at the official

exchange rate), a figure which has remained almost constant since mid-sixties. Total industrial output accounts for only 9% of the GDP out of which jute processing and manufacture

is the major component.

2. THE HOUSING PROBLEM

1 Introduction

I The last housing census was conducted in 1960. Arrangements for a population and housing

census in Bangladesh have been completed and the census data collection should be completed

by the beginning of 1974. In the absence of up-to-date reliable data, most of the following

discussion is based on the results of 1960 census. The basic characteristics of house

types, structural conditions, occupancy, etc. have not changed significantly during the last

decade.

In 1960, there were about 9.60 million residential houses in Bangladesh. The average number

of rooms per household was 1.77. A majority of households (53%) lived in single-room

dwellings and the average density of occupancy was 3.2 persons/room. Table 1 gives the

number of households classified according to number of rooms:

* The figures quoted are unofficial estimates

103
Table 1

Number of Houses of Different Sizes*

(Figures in thousands)

Number of Number of rooms households

of all sizes 1 2 3 4 5 6 7 8 9 10

9603 5166 2652 1063 443 161 65 28 13 6 7

Five or more persons share a room in case of 31% of the population, 4 persons in case of 13%

of the population and 3 persons in case of 21% of the population.

The poor housing conditions of the general populace is evident from the above figures.

Rural Housing

The bulk of the rural population of about 67.5 million belong to the poorest income group.

Since the majority of this population depend on agriculture as their means of livelihood,

the distribution of agricultural land holding has a marked effect on the pattern of rural

housing.

The rural population may be broadly classified into two groups: (a) land-owners, and (b)

landless laborers. It is estimated that about one-fifth of the villagers are landless, who

work mainly as field hands or laborers in various projects. Out of the gross area of 55,130

square miles, about 25 million acres (70.8% of the gross area) is cultivable. The average

land owning villager possesses only 1.5 acres. He usually rents another acre from

well-«to-do villagers and therefore cultivates 2.5 acres. This area is usually fragmented

into ten or more plots, some of which may be a mile or more away from the homestead. The

houses, in general tend to be scattered throughout the village.

Most of the rural population in Bangladesh live on the patriarchal family pattern. Peasants

usually establish their households on their own fields. When the sons get married, their

wives move in with them, and a new house (or room) is erected for them, on the same field,

next to the parents' house. As a consequence, houses occupied by families paternally

related are grouped together. The clusters of houses normally provide shelter to families

of relatives numbering 20 - 40 members, but higher figures are not infrequent. The groups

of houses are usually surrounded by dense tropical vegetation and trees. Fig. 1 shows the

layout of a typical rural house. The central courtyard is the centre of almost all family

activities

.

Dwelling Units

Most of the houses in rural areas are 'kutcha' (which literally means raw) structure, whose

plinth is made of mud and whose walls and roofs are built of bamboo, grass, straw and reeds.

These houses require constant maintenance and often do not provide a safe shelter against

rain and storm.

According to the last census report (1960), there were 9.13 million residential dwelling

houses in rural areas of Bangladesh. The increase in number of rural houses between 1950

and 1960 was about 10%. Assuming the same rate of growth the number of houses in 1970

should have been about 10 million.

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

104
Structural Conditions of Rural Houses

According to 1960 census data, about 90% of the total rural houses are made of bamboo,

thatch and mud, and 64.5% of the houses use the same material for roofs. Walls of concrete,

baked bricks or stone are used in only 1% of the total number of houses. These are mostly

the staff quarters built by the government. An average of 34% of the houses have C.I.

(Galvanized corrugated iron) sheets or corrugated asbestos cement sheets as roofing

materials

.

Urban Housing

The conditions of dwelling units in urban areas are no better than those in rural areas. A

vast majority (72%) of the urban population cannot afford to pay the rent for even the

cheapest form of acceptable housing. They have, therefore, to live in makeshift shacks and

huts. These distressing conditions under which the low income families live present a problem which is seemingly beyond solution. The total number of urban dwelling units,

according to 1960 census, was about 471,000 and it is estimated that there were about

520,000 units in 1970. Approximately 27% of the houses are permanent and semi-permanent in

character, the rest being temporary and unclassified. Quite a large fraction of the urban

population live in the 'bustees' and squatter settlements in the larger towns and cities.

They live in bamboo shacks, often consisting of a piece of plaited split-bamboo fencing bent

in the shape of a semi-circle. The headroom in such houses being low, their occupants spend

most of their time under the open sky, taking shelter under the shacks only in case of rain

and during night. The houses are blown away even by moderate winds, despite efforts to hold

them down by putting counterweights like bricks on top of the roofs. The government is

making efforts to rehabilitate these squatters and has already built 4500 semi-permanent one-room houses on the outskirts of Dacca city.

Common Types of Houses

A very common type of construction used for rural houses is shown in Fig. 2. The roof

j consists of C.I. sheets screwed to timber purlins, usually about 2" x 2" section. The load

bearing skeleton consists of bamboo posts. The walls are of bamboo fencing consisting of

; split bamboo woven diagonally. Galvanized steel wire is used in joining the different

I pieces. These houses are never designed from the structural point of view, and are usually

I built by local craftsmen, the owner sometimes providing unskilled labor.

A stronger type of construction used for low-cost housing projects on the outskirts of Dacca

by the Housing Directorate of the Government uses brick walls with C.I. sheet roofing (Fig.

3). The C.I. sheet roof is anchored down to the wall through 1/8" x 1" x 5" twisted steel

I clamps and 1/2" diameter 'holding down' bolts. These bolts are about 2 ft. long with a 4"

square 1/8" thick mild steel plate welded at the bottom end embedded ,in the brick masonry.*

The stronger houses in urban areas are mostly made of burnt clay brick masonry walls with

sand cement mortar (usually 10" thick for buildings up to 2 stories high) with reinforced

I concrete roofs. The roofs are almost invariably horizontal. In the design of such

I buildings, no account is taken of the wind forces. The walls being much thicker than

i| necessary from gravity load considerations, even extreme winds do not produce stresses large

j enough to produce failure. Most of the buildings of this type which have suffered damage

i due to cyclones were either made of sub-standard quality mortar or the workmanship was poor.

No damage to R.C. roofs have been reported. In the island of Manpura, one of the worstj affected areas of the November 1970 cyclone, the only R.C. elements which suffered damages

1 were 'sunshades' which were about 2" thick, 1' -9" projections above window level. These

[ failures might have been caused by uplift wind pressure or the pressure generated by storm

I surges

.

* Source: Housing Directorate, Government of Bangladesh.

105
Some New Types of Houses

In recent years, efforts have been made by different relief agencies as well as Government

departments to evolve new type of houses to better resist the natural calamities. Some of

these use traditional materials like C.I. sheet roofing whereas others are completely new in

concept

.

A very popular type of structure called CARE type houses (after the U.S. relief

organization Co-operative for American Relief Everywhere) uses soil cemfent blocks for walls

and C.I. sheets for roofs. The primary emphasis is on promoting housing on 'self-help'

basis, a minimum of skilled labor being necessary for its construction. However, the

problem of properly anchoring the C.I. sheet roofs to the wall still remains.

Hyperbolic paraboloid reinforced concrete shell roofs have been used in both industrial

housing and suburban housing. One system uses 1" thick precast R.C. elements with in-situ

concrete interconnection. The roof is anchored to the supporting brick walls through 1/2"

M.S. bars at the corners. Cast-in-place hyperbolic paraboloid shell roofs have also been

used in a recently constructed industrial housing project in Jessore.

CARE is experimenting with a revolutionary type of house design. Both the shape and the

materials used are completely new in Bangladesh. The integrated roof and wall element is

semi-elliptic in shape and is made of pre-formed elements of polyester resin, jute and

polyurethane . These elements are anchored to the underlying soil and their performance in severe winds -has so far been satisfactory.

Current Housing Programmes

Bangladesh had the misfortune of suffering two disastrous natural calamities in 1970. In August 1970, flood waters destroyed about 80,000 rural houses completely; moreover about

224,000 houses were partially damaged. In the severe cyclonic storm of November 12, 1970,

about 100,000 houses were completely destroyed. The liberation struggle of 1971 left about

2 million families homeless. Attention of international relief agencies and humanitarian

organizations were naturally focussed on Bangladesh after this series of destructions.

Sizeable housing rehabilitation and reconstruction efforts are now underway in rural areas.

The Government of Bangladesh through its Rural Housing Rehabilitation Project envisaged -the

construction of 155,000 semi-pucca rural houses and 21,000 pucca houses in the coastal areas

in 1972-73. The Government has also undertaken construction of 2-storied cyclone shelters

in coastal areas which will also serve as community centres, schools, dispensaries and

post-offices

.

Table 2 shows the summary of housing programmes undertaken by the different relief agencies

during the last two years

:

Table 2

Housing Programme of Different Relief

Organizations in Bangladesh*

Name of Organization

Number of Houses

Target

up to 1972-73

Construction

up to August 1972

1. CARE 12,500 5,600

2. CONCERN 2,000 50

3. R. K. MISSION 1,500 1,000

4. BERRS 45,220 24,003

5, CORR 300,000 185,260

6. Uncle Erik's Children Help 31 31

7. Service Civil International 925 135

8. SAWS 2,730 200

106
9. AUSTEARS 2,668 ' 2,668

10. Baptist Mission 1,494 1,264

11. Danish Association for International Cooperation 125 15

12. EFICOR 581 95

13. ICRC 991 991

14. RDRS 15,060 2,960

15. Salvation Army 2,331 1,081

16. IPS 1,000

17. BVSC 5,000

18. BRAC 1,000

Total 395,156 225,153

3. EXTREME WIND RELATED PROBLEMS

Types

Extreme winds affecting houses in Bangladesh may be classified into three categories:

(a) The Norwesters (Kalbaishakis '

)

(b) Cyclonic Storms, and

(c) Tornadoes

The Norwesters

Norwesters are violent thunder-storms and occur during premonsoon months, i.e. March to May.

They are most frequent in the month of April (which corresponds to Baishak, the first month

of the Bengali calendar - hence the name 'Kalbaishaki' ) . They originate over land and

marshy areas and occur mostly in the central and eastern districts.

In a study of Norwester squalls over Dacca, it was observed that before the onset of a Norwester, the prevailing surface wind was southerly or south-westerly but with the onset of

the squall, a sudden shift to the west, south-west and even south-east was observed.

Some of the Norwesters originate from West Bengal and Chotanagpur in India and move in a north-west to south-east direction. Another category of Norwesters originate from Assam in

India to the north of Dacca and move more or less in a southerly direction.

The distribution of Norwester squalls over different areas in the months of March-June are shown in Figs. 4,5,6 and 7.* It is observed that in the month of March, an area around

Dacca and north-east of Dacca has the highest concentration of squalls. In the month of

April, the March cell expands in area and another cell near Sylhet near the north-eastern

boundary starts developing. In the month of May, three cells are observed:

(a) the Dacca Cell well expanded,

(b) a cell near Pabna and around, possibly extending to Calcutta in

India; and

(c) Sylhet cell in the north-east becoming prominent.

* Source: Report on the National Workshop on Low-cost and Co-operative Housing in Bangladesh, Nov. 29 - Dec. 5, 1972, Prepared by International Co-operative Housing

Development Association.

107
In the month of June, only two cells are observed, both with considerably reduced frequency

distribution. These are the decaying Dacca and Pabna cells.

The maximum wind velocities encountered in case of Norwesters is in the region of 40 - 80

miles per hour.

Cyclonic Storms

Storm Tracks and Frequency

The south-west monsoons, over which the entire agricultural production of Bangladesh is

dependent, is ushered in pulsations, through the agencies of 'depressions' and cyclonic

storms. High winds with frequent squalls, heavy rain and storm surges are the destructive

agencies of a cyclonic storm.

A study of the storm tracks in the Bay of Bengal between 1891-1923 reveals that the cyclones

may originate anywhere in the Bay of Bengal and then travel either North-west towards the

Madras coast in India or North and North-easterly towards the head of the Bay. The Bay of

Bengal is practically free of cyclonic storms in the months of January, February and March.

In the months of April and May, Bangladesh has occassionally been struck by cyclones

affecting the Cox's Bazar coast and the area East of Barisal. During the monsoon months of

June, July and August, cyclonic storms are frequent but of moderate intensity and they do

not affect Bangladesh; they form at the head of the Bay of Bengal and travel in West and

North-westerly direction to the Orissa and West Bengal coast in India. Cyclonic hazard is

greatest in Bangladesh in the period starting from September and ending in December.

Cyclones are then most frequent and severe and may attack any of the coastal areas at Madras

and West Bengal in India, Bangladesh and Burma.

Table 3 shows the frequencies of cyclonic storms and depressions in the Bay of Bengal at

different periods of a year. Although more depressions were formed in the months of July,

August and September, the number of cyclonic storms was much higher in the month of October.

Table 3*

Frequencies of Cyclonic Storms and

Depressions in the Bay of Bengal

(19A8-1960)

Month Depressions Storms

Total nos

:

Total nos:

January 1 0

February 1 0

March 0 0

April 3 0

May 6 5 June 11 0

July 19 2 August 19 2 September 21 5 October 12 10

November 2 5 December 3 2

The total number of cyclonic storms by decades is given in Table 4.

* Source: The Climatology of East Pakistan by M. A. Quadir, Govt, of East Pakistan

Publication, 1962.

108
Table 4*

Total number of cyclonic storms in

Bangladesh

(1890 - 1959)

1 RQO- . Do or whicb 9Z were reported devastating

1900-1909 : 65 of which 0 were reported devastating

1910--1919 : 48 of which 1 was reported devastating

1920-1929 : 77 of which 3 were reported devastating

1930--1939 : 81 of which 8 were reported devastating

1940--1949 : 89 of which 4 were reported devastating

1950-1959 : 76 of which 0 were reported devastating

Disastrous Cyclones of the Past

Coastal regions of Barisal and Noakhali districts have been subject to severe cyclones and

destructive storm surges in the past. In such severe cyclones, thousands of human lives and

cattle were lost, houses and crops worth millions of Takas were destroyed. Some of the more

severe cyclones of the past 400 years are mentioned below:

(a) Cyclone of 1584 : The cyclone hit the districts of Barisal and Patuakhali. There was a huge storm surge and nearly 200,000 people perished

in the calamity.

(b) Cyclone of 1797 : The cyclone affected the islands south of Noakhali and

has been described as the "most destructive".

(c) Cyclone of 1822 : Unlike other cyclones, which generally occur in October,

a great cyclonic storm ravaged the southern areas of Barisal, Patuakhali

and the islands of Hatiya on June 6-8, 1822. In the district of Barisal

alone about 72,000 people were killed.

(d) Cyclone of 1876 : The coastal districts of Barisal, Patuakhali, Noakhali

and Chittagong were hit by a cyclone on October 31, - Nov 1, 1876.

Storm surges up to 40 feet deep have been reported from the coastal

areas. A total of 215,000 people were probably drowned. This represented 20% of the population of the affected areas.

(e) Cyclones of 1960 ; After a comparatively quiet period in the first

half of the century, two severe cyclones hit the coastal regions of

Barisal, Noakhali and Chittagong in October 1960. The cyclones

occurred in quick succession - the first one on October 9-10 and the

second on October 30-31. The areas affected by both the cyclones were

almost the same in both the cyclones.

A maximum wind speed of about 140 mph was reported from Chittagong

port

.

* Source: Op. Cit.

109
(f) Cyclone of 1970 ; The cyclone of 12th November 1970 is the most disastrous in recent times. It affected the southern regions of Barisal,

Patuakhali, Noakhali and the islands of Hatiya and Manpura. The

accompanying storm surges were upto about 25 feet in height. Almost

100% of the kutcha and semi-permanent houses were destroyed in the

affected areas. The extent of damage indicates that the maximum

wind speed was more than 120 mph

.

Probable Areas of Attack by Cyclonic Storms in Bangladesh

The coastal areas of Bangladesh are the most vulnerable to cyclonic storms originating in

the Bay of Bengal. The southern parts of Barisal, Patuakhali, Noakhali and Khulna districts

and the western coast of Chittagong have suffered extensive damages in recent cyclones. The

severest damage is caused in the off-shore islands of Hatiya, Sandwip and Manpura, which are often completely inundated by storm surges accompanying the cyclones. Areas of Dacca and

Comllla districts are also affected but the intensity is less severe than in the southern

regions

.

Fig. 8 shows the probable storm tracks in different parts of the year and Fig. 9 shows the

track of a typical cyclonic storm with maximum wind velocities in different regions.

Tornadoes

Tornadoes are the most destructive of all storms. They generally occur on land during the warm season of the year in flat areas, where there are few topographical barriers to impede

their movement. The approaching storm may be recognized by a dark funnel-shaped cloud whose

small portion extends downwards to the earth's surface. Usually such storms cover a narrow

path of up to about half a mile in width and their force is spent in 20 to 100 miles of

travel. The major flow of the air in motion at ground level during a tornado is basically

circular and translational at the same time. The average translation speed is about 50 mph

but the peripheral wind velocities are much higher. In 1961, the Task Committee on Wind

Forces of the American Society of Civil Engineers concluded that the peripheral velocities

would be in excess of 300 mph. However, maximum wind speeds up to about 500 mph have been

estimated by some authors.

One of the severest tornadoes in recent memory hit the outskirts of Dacca city in April

1969. A textile mill at Demra, about 10 miles from Dacca, built of brick masonry walls with

C.I. sheet roofing on steel trusses was completely destroyed. It is estimated that the

maximum wind speed in the tornado was in excess of 150 mph.

4. PRESENT DESIGN CRITERIA

Most of the existing houses in Bangladesh have never been designed from a structural point

of view, but their form and use of various materials have evolved over decades of experience

and tradition.

For permanent and semi- permanent structures, a very popular form of construction uses steel

trusses or timber trusses as the load carrying element of the roof. Corrugated galvanized

iron sheets are commonly used as covering although in some cases corrugated asbestos cement

sheets are used.

The trusses are designed to withstand wind forces which were usually calculated in the,

following way

:

If V is the speed of wind in mph for which the structure is to be designed, the pressure p in lbs/ft^ is taken to be

p = 0.003

110
Duchemin's formula for sloping roofs was then used to calculate the component of wind force

normal to roof surface

p - 2 Sin (j) " 1-Sin^ ' where (J; is the angle of inclination of the roof with the horizontal.

Use of the above formula implies that wind forces act only on the windward slope of a roof

and ignores the effect of suction in the leeward slope.

However, most of the structures designed to withstand wind forces calculated from the

above formula with a wind speed of 100 - 120 mph have withstood the forces generated by severe cyclones. It is worth noting that no account is taken of vertical uplift forces

which may be generated by the cyclone

.

Current design practice, however, uses a more realistic pressure distribution. In the

absence of a unified code of building practice in Bangladesh most of the 'permanent'

buildings are designed either according to the British Standards Code of Practice No. 3 (Chapter V) 1952 or according to American Society of Civil Engineers report on Wind Loading

(1936)

.

The B.S. Code recognizes the influence of roof slope as well as the height to width ratio of

the building and the recommendations are based on results of wind tunnel tests on scale

models carried out at the National Physical Laboratory.

The A.S.C.E. recommendations give wind pressures for a given wind velocity with the angle of

inclination of the roof as the only variable

.

2 The velocity pressure is taken as q = 0.002558 V where q is in lbs. /sq.ft. and V is in

mph

.

The leeward slope is assumed to be subject to a suction of 0,6 q for all slopes whereas the

windward slope pressure (or suction forces) are given by the following expressions:

4) « 20°

20° £ (|) <^ 30°

20° ± ^ < 60°

^ > 60°

p = -0.7q

p = (0.07 4) -2.10)q

p = (0.03 (t> -0.90)q

p = 0.90q

(Positive values of p mean pressure and negative values mean suction)

The above pressures and suction forces are assumed to act in a direction perpendicular to the surfaces on which they act

.

The internal pressures developed in buildings with openings are not usually considered in

the design of such structures.

The most commonly used slope for pitched roof is 4 span to 1 height or 2:1 slope. This

gives an inclination of 26.5°. Both the windward and leeward slopes, will, therefore, be

subject to suction forces. This calls for secured fixing of the rafters to the walls and

the covering sheets to the rafters. A wall plate runs on the top of the walls parallel to the ridge and rafters are generally nailed to it. The roofs usually have projections at the eaves to ensure that the rainwater from the roof does not drip down the walls. The presence

of these projections may alter the distribution of wind pressure on the roof and there is a possibility of increase in the suction force due to these projections.

It has been observed in recent cyclones that most of the failures of roofs were due to the

wind having gone inside, pressed from underneath and lifted up the roofs.

Ill
Fig. 1 Lay-out of a typical Rural house

112
"cm

bamboo post

12"

MAIN ROOM

9-0 xlO-6

-window

10-6"

12-6

HOUSE PLAN

Scale= l/4" = r-0"

0 - - - m

bamboo fencing

-roof line

12"

Fig. 2 Details of a typical Rural house with bamboo.

J) 113
Fig. 3 Details of a typical low cost house with brick walls

114
Fig. 4 Area distribution of norwester squalls (r.feirch) (Figures indicate total no. during the period 1955-61)

115
116
117
BANGLADESH

0 25 50

Miles

5 or more

g. 7 Area distribution of norwester squalls (June)

(Figures indicate total no. during the period 1955-61)

118
119
BANGLADESH

ittagon^

Area wind force more than iOO miles per hour

Wind of hurricane force 80-100 miles per hour

Wind of gale force 40-55 miles per hour

Fig. 9 Typical cyclone in Bangladesh (9th Kfey, 1961

)

120
REMARKS

by

William Woudenberg

CARE, Inc , Dacca, Bangladesh

Good afternoon, ladies and gentlemen. As Dr. Choudhury has mentioned I have been

actively involved in housing in Bangladesh. In the past three years we have contributed

approximately 15,000 units which are located mostly in the southern area of Bangladesh. Our

primary interests are in certain regions in which Dr. Choudhury described as most prone to strong cyclonic conditions that prevail in the area. One thing we found is that as we proceed to other regions, the problem of building masonry houses becomes rather formidable.

For that reason then, we have decided to investigate the use of other materials.

I have set up a small shop outside of Dacca where we have experiments with various

approaches to this problem. Some of the disciplines involved are the availability of

materials. There exists practically no stones in Bangladesh and bricks are very expensive.

The supply of wood is becoming increasingly scarse and the price per cubic ft. of wood

almost approaches the price of steel. In fact, in recent purchases for wood, we have to get

government priority before we could buy.

So for that reason, the only material that we find easily available and we could use is

jute which Bangladesh is supplying the world. I decided on a configuration of jute

saturated with polyester resin. In 1971, the first four houses were built and we decided

that a circular configuration would give the best resistance to violent winds. We developed

that in exploring the use of these houses in the villages. The circular configuration

proved to be quite unsatisfactory, however, for their social customs. They are primarily

Moslems and in the villages the privacy of the women is very important and the circular area

made the delineation of the living area quite difficult. For this reason, we changed to a rectangular configuration, although we still hold on to the curved shape which gave so much

strength to the first prototype.

I have a few pictures here that describe the different models. This is the second house

we built (Fig. 1). This is an example of a one family residence. It is 14 feet in width,

22 feet in length and it costs approximately $300 - with about 50% hard currency and 50% local

currency. It is extremely light in weight. It can be transported very easily and it can be

floated for ease of transport in river areas. This particular one has already withstood

storms that Dr. Choudhury described and it seems that there is no ill effects on them. This

particular building, because of its configuration, can lead to a lot of different shapes by

adding sectional structures. This unit can be made to any length, in 3 foot increments to accommodate perhaps warehousing, etc.

This slide shows the veranda. Verandas in Bangladesh are extremely important because

if a man wants to invite you to his home for tea it is very important to give you the

hospitality of the house. He cannot bring you inside because you would invade the privacy

of his wife.

We have a large house constructed of segments from the one shown previously (Fig. 1)

and it illustrates that this material can accommodate the needs of larger buildings. This

house is 33 ft in width, A4 ft in length and 22 ft high and cost approximately $1 per square

foot. It can be brought to the site and assembled perhaps within one week at most.

All these materials are manufactured in Bangladesh.

We have a scale model or the building and the specimen or the insulation used. The

insulation serves as a filler for the fiber glass and further strengthens the material. It serves as an insulation and its serviceability is very important. It can be used either

with a foundation or without a foundation.

One very important thing I forgot to mention is that we hope to be able to deliver one unit to Manila at the early part of next year.

Thank you.

121
122
LOW-COST HOUSING AND EXTREME-WIND-RELATED PROBLEMS

IN JAMAICA

by

A. D. Adams

Partner, Douet Brown Adams Associates,

Consulting Engineers, Kingston, Jamaica

1. Scope

This report presents an outline of low-cost housing and low-rise building-related problems

of Jamaica and data gaps both in the design (e.g. structural systems, connection details,

design loads, etc.) and construction phases. It identifies the related socio-economic

considerations as they effect the design of structures. It presents also, a discussion of

extreme-wind-related problems as found in Jamaica.

Due to the shortage of time mentioned, the practice and problems mentioned in this paper are based on Jamaica only and does not include other Northern Caribbean Islands.

2. Limitations and Assumptions

General

This is the first of two reports. It is intended to present information of a more general

nature here and to present more detailed information and substantiating data in the second

report. This is partly necessary because of the short time that was available for

developing this report.

In addition, there is a lack of technical reports on the effects of past occurrences of

extreme wind in Jamaica. For aspects connected with the observed effects of extreme wind,

some reliance has had to be placed on newspaper reports and photographs and other records

and papers. Not all of these sources are engineering-oriented, hence they have been

interpreted with some caution.

Data Gaps in Design and Construction

For identifying data gaps in design and construction, the author has mainly drawn on his own experience as a consulting engineer and his association with other engineers in Jamaica.

This means that data gaps are indicated where information may conceivably exist, but is not

known by or readily available to, the majority of Jamaican engineers. The second report

will, of course, re-examine any statements made in the first.

Socio-Economic Considerations

For socio-economic considerations, statistics and economic analysis are based on government

reports unless stated otherwise.

Observations on social and sociological aspects are often subjective but where supported by

other reports or studies, this is noted by reference to the sources.

3 . Common Low-Cost Housing Systems in Jamaica

A Look at the Past

As examination of common housing systems in Jamaica should perhaps be preceded by a historical look at 'low-cost' housing as it existed before the advent of modern

industrialized buildings and building materials. This seems even more relevant when it is

considered that at the time of the last severe hurricane in 1951, most houses were of

'early' construction as described below:

In the rural areas, most 'early low-cost' houses (say up to the

1930 's) were constructed by peasant owners, using techniques

described as "wattle and daub" (See Fig. 1). This consisted of

123
COIMON LOW-COST HOUSING SYSTEMS IN JAUtAICA CONTD.

A Look at the Past.

Thatch Roof /Timber Post

/Wattle

\ tH V

T—

r

PART ELEVATION

OF WATTLE

Fig. 1 WATTLE AND DAUB

Early Low-Cost Housing Construction in Jamaica

124
a wooden skeleton frame of posts planted in the ground, tied at eaves level with wooden beams and with sticks interwoven horizontally between the posts, to form the "wattle". This "wattle"

was "daubed" both inside and out with mud formed from readily

available clay, to create solid walls. Roofs were of pitched

wooden framing and battens. The roof covering was generally

formed of 'thatch', made from bundles of dried leaves of certain

plants, tied in place.

In urban areas, houses were mainly of timber studs with lapped horizontal boarding to walls (See Fig. 2). Roofing was of pitched timber rafters with corrugated iron sheets or wooden shingles, either on battens with a thin suspended ceiling, or in boardsheathing

without a ceiling.

As a variation in some cases and also as a further development as time passed, many

houses in the urban areas came to be built of brick-nog or concrete-nog construction (See

Fig. 3). This consisted of masonry or concrete in-fill between the studs and a rendering of

lime or cement plaster. A feature of both types was that in most cases houses were elevated

at least 2 or 3 ft. above ground on concrete or masonry piers or sleeper walls.

Hollow-Concrete Masonry Construction (See Fig. 4)

The introduction of the hollow-concrete block as a cheap masonry unit for walls, marked the

development of the first major construction method using locally manufactured components as

a basic building material for low-cost houses.

Selected vertical cavities in concrete blocks are usually filled with concrete during

construction and vertical and horizontal steel bars are introduced as reinforcement to resist earthquake and wind effects. Poured-in-place reinforced concrete stiff ener-columns

are generally introduced in unrestrained panels of wall exceeding about 16 ft. However, for

low-cost housing, these stiffeners are often omitted and both cavity infill and

reinforcement are generally restricted to corners and edges of openings. Reinforced

concrete belt beams are based to cap walls at roof level.

Roofing Systems are of various types and include poured-in-place reinforced concrete slabs,

and battens on timber joists covered with aluminum sheeting or wooden shingles. Foundations

are of strip-footing type.

Large Panel Precast Concrete Systems (See Fig. 5)

These consist of full size concrete wall panels, with the largest panels being as large as

the full length of the housing unit in one direction and the full story height in the

other

.

In the most common local system of this type, wall and roof panels are lifted and assembled

by crane and connected by welding at matching steel inserts. Overall thicknesses of wall

units vary from 3" to 6" but ribbed panels are often used for the thicker units with

rectangular panel thicknesses of as little as 1 1/2" between ribs.

Roof waterproofing is usually of a bituminous compound or waterproofing felt.

Small Unit Precast Concrete Systems (See Fig. 6)

These consist mainly of precast concrete posts and precast concrete or timber beams with

concrete in-fill "boards" between posts.

Timber Systems (See Fig. 7)

These are mainly of timber studs and 1" thick horizontal boarding on both internal and

external wall surfaces. Roofs are generally of timber framing and aluminum sheeting.

125
COWON LOW-COST HOUSING SYSTBtS IN JAIMICA CONTD.

A Look at the Past

Fig. 2 TDffiER STUD AND BOARDING

Early Low Cost Housing

Construction in Jamaica.

126
COmON LOW-COST HOUSING SYSTEMS IN JAJyIAICA CONTD.

A Look at the Past

Timber rafter

Brick nog

Ground level

Corrugated

sheeting

Wooden joist

Concrete stud column

Wooden

^beam

Wooden

-^stud

NConcrete

nog or brick no

(rendere

Fig. 3 BRICK NOG AND CONCRETE NOG

EARLY LOW COST HOUSING

CONSTRUCTION IN JAJ/IAICA

127
COMTOM LOW-COST HOUSING SYSTBtS IN JAJtAICA CONTD.

Hollow-Concrete I^Aasonry Construction

Aluminum sheeting or shingles (wooden)

laid on 3"x l" laths

Timber rofter

R.C. Belt beam

C. Lintel

Panel door

-Hollow concrete masonry

Terrozo Tiles.

Metal or gloss louvre window

/ ^^Ground level

Continuous strip foundationMild steel Hollow Concrete ^fasonry

Construction

The most common construction

method in Jamaica

concrete

R.C. strip foundation

Poured stiffener columns are often used

in more expensive houses

cement mortar

PART SECTION A-A

128
COmON LOW-COST HOUSING SYSTET.IS IH JAIMICA COMTD.

Fig. 5 LARGE PANEL PRECAST CONCRETE SYSTB<I

The most established, fully prefabricated

Housing System in Jamaica.

129
COMMON LOW-COST HOUSING SYSTMiS IN JMmCA CONTD.

Felt on precast concrete boarding or oluminum sheeting on timber battens

Precast or timber rofters

Precast concrete or timber beams

4 square concrete

Precast columns ^

4'-0"CRS.

I I

Precast concrete boarding- 1-1/2" thick units

r h-i

1'' ' I

Fig. 6 SIAALL UNIT PRECAST CONCRETE SYSTEIVt

NOTE

Government Owner occupier

Scheme Uses Timber Beams and Rafters.

Roofing are generally of timber framing with aluminum

sheeting. In some cases, precast concrete Joists and "boarding"

are utilized with felt waterproofing.

130
COMMON LOW-COST HOUSING SYSTEMS IN JAJMICA CONTD.

Timber Systems

Timber rafter

-Wooden beam

-Timber stud

Aluminum sheeting on

' 3"x I" laths

Boarding on both sides

'of stud

Wooden floor

X

-.zzzzd

Wooden joist

Concrete stub column

Ground level

Zl

Fig. 7 TDjIBER SYSTB^

STUD AND LAPPED BOARDED WALLS

These houses are usually elevated on piers or sleeper

walls at least 2 ft. to 3 ft. above ground and provided with

a flooring of timber joists and boarding.

131
Other Lightweight Systems

Apart from timber boarded systems, other lightweight systems have been proposed and

promoted, particularly by commercial or manufacturing interests. These types generally

utilize a stud system either of tin or aluminum. Some of the boarding materials proposed so

far are : -

(a) Particle board consisting of cane fibre (bagasse) bonded

by a resin.

(b) Thermo-wall panels consisting of bagasse and gypsum bonded

by a resin.

However, to date, very little if any houses and certainly no large scale developments have

been done using such lightweight systems.

Other Low-Rise Buildings

For buildings under 3 stories and requiring substantial external walls or partitions, filled

hollow-concrete masonry is the most popular construction method in Jamaica. This is usually

in conjunction with poured-in-place reinforced concrete floor slabs. Roofs are either R.C.

slab or timber framing with aluminum sheeting.

For office and commercial buildings and for low-rise buildings above 3 stories, the most

popular construction system is cast-in-place reinforced concrete slabs and frames. Less

popular variations are for slabs, composite pretensioned/reinforced concrete or post-tensioned slabs, and for frames, steel skeleton or R.C. shear wall construction.

4 . Problems and Data Gaps in Design and Construction of Low-Cost Housing

Local Building Regulations

Most of the building regulations now legally in force in Jamaica, were first passed in the

early 1900 's. Despite a number of amendments of individual sections, the official building

laws are out of date and far behind modern building design and construction technology.

There has been a tacit acknowledgement of this by most local authorities and today a lot more observance is made of a Proposed Draft Building Regulations - 1971 than of the original

regulations. These Draft Regulations issued by the Kingston and St. Andrew Corporation

(which administers the affairs of the Capital City) is not yet available to the general

public, but is well known to the initiated such as Engineers, Architects and Builders.

These regulations have been mainly based on the series of British Standards and British

Standard Codes of Practice dealing with the design and construction of buildings. This is

due to the fact that, so far, Jamaica has not had the financial or man-power resources,

which would be needed to undertake the intensive study and research necessary to produce a comprehensive set of truly indigenous codes of practice.

One consequence of this has been a lack of detailed guidance in regulations on special local

phenomena, such as earthquakes and extreme winds. There is, therefore, a lack of uniformity

in the treatment of these design problems by Jamaican Engineers. The most popular

resource has been to turn to areas such as the United States with its areas of similar

naturally occuring phenomena e.g. to the Structural Engineers Association of California for

earthquake design.

An encouraging development in this area, has been the efforts of the Engineering

Institutions in the Commonwealth Caribbean Area (CEO) to cooperate in developing

individually, separate sections of a comprehensive building code, which would eventually be

compiled to serve the entire Commonwealth Caribbean region.

One such effort by the Barbados Association of Professional Engineers, has produced "Wind

Loads for Structural Design" Draft Code of Practice - August 1970. This too, was largely

modelled on a British Code of Practice BSCP3 Chapter V: Part 2: 1970: Wind Loads, with

respect to design lift of buildings, topography, ground roughness, building size and height

132
above ground. However, most importantly, it proposed basic wind speeds for various islands

in the region, based on analysis of local wind data.

Local examination of this code has raised one or two unresolved points; namely, the size of

hurricane gusts for the proposed averaging times and modifications to wind speed factors

which allow for variations in return period. Nevertheless, although the document is not yet

widely used by practicing engineers in Jamaica, it should represent the most reliable

guidance on basic wind speeds in the region for design purposes.

Structural Systems

Difficulties common to all construction methods will be dealt

but problems and data gaps associated with various structural

under their individual headings.

Hollow-Concrete Block Masonry

For the more usual single-story buildings involved in low-cost housing construction, load

stresses are usually quite low, so that the tendency has been to design in accordance with

certain nominal rules set down in regulations to ensure minimum standards. The provision of

reinforcement, belt beams, poured stiffener columns and the filling of selected block

cavities to improve earthquake performance, goes even further towards increasing factors of

safety under wind and vertical loads.

For low-rise buildings with more highly stressed wall elements, local regulations provide

little guidance for a rational working stress design except to state in the draft

regulations 1 that "allowable working compressive stresses in masonry walls shall not exceed — 100 lb. per sq. in. gross area in the case of hollow concrete blocks" and to specify a minimum crushing strength on gross area at 28 days, of 750 lb. per sq. in. For such

buildings, therefore, the practice has been to design in accordance with foreign standards

such as the American Concrete Institute Report of Committee No. 531 or British Standard

Code of Practice No. III. These standards are, of course, not applicable in every respect

to entrenched local practice. As a result, the local Institution of Engineers is at present

engaged in preparing recommendations for the design and construction of this type of

building.

One area of uncertainty, unresolved to date, is the necessity for a maximum spacing of

poured-in-place R.C. stiffener columns and their effects in enhancing the strength of the

masonry walls under vertical loads or wind and earthquake loads.

Large Panel Precast Concrete Systems

Although there are foreign standards and design codes 3,4 which give general guidance on precast concrete work, there are no comprehensive codes which cover the various types and

combinations of precast assembly systems and connections. However, these systems are generally mass produced and are usually manufactured by large, highly organized building

concerns. For this reason, they are also usually designed and supervised by qualified

engineers and architects. Nevertheless, there is a great need to develop standards for the use of local authorities and design engineers.

Among the specific items which can be solved only by individual engineering judgment at present are : -

(a) The design of welded metal connections with bar anchorages

to achieve ductility;

(b) Joint waterproofing and the avoidance of rain penetration

in 'flat' thin section, precast concrete roofs;

(c) The design of welded metal connections with bar anchorages,

subjected to combined shear and tension forces.

with further in this report

systems are best discussed

133
Small Unit Precast Systems

These fall in a somewhat different category from the large panel systems. Although mass production is usually necessary for economic reasons, in this case erection does not demand

large lifting equipment.

This lends itself well to the erection of small numbers of houses in scattered locations.

The Jamaican Ministry of Housing in its "Owner Occupier Scheme" has been erecting a few

hundred of these annually for the last ten years.

The main problem with such units is the design of robust joints for members of such small

dimensions. Where all members are precast, connections between posts and beams are generally made by half -lapped and dowelled joints. Boarding is usually slotted into place

along vertical grooves in posts. This would generally provide doubtful overall lateral

stability under wind or earthquake shears, so that great reliance has to be placed on the

embedment of the posts in deep concrete footings.

I Where timber beams are provided with concrete posts, connection is provided by bolted

U-shaped mild steel straps.

Timber Systems

Local draft regulations provide for the design of timber buildings using some cross-referencing to British Standard Code of Practice No. 112.

Formerly, the problem with timber was poor durability due to rot and decay in our sub-tropical conditions. This problem has been largely solved by the use of modern

pressure-applied preservatives^

.

Recognized local practice is to provide straps at roof and floor levels to resist the

uplifting effects of extreme wind, but this is not explicitly mentioned in the local draft

regulations

.

Other Lightweight Systems

As mentioned before, there have been too few examples of the use of resin bonded cane (or

wood) fiber for external work to provide an assessment. The patent-holders and

manufacturers claim the following attributes : -

(1) Dense surfaces

(2) Termite and rot resistance

(3) High Water repellence

(4) High screw and nail holding properties.

In the constant search for very cheap housing systems, these materials represent attractive

possibilities because of their lightness and consequent cheaper construction cost. However,

the local government authorities and engineers in general, are still uncertain of the

durability, strength, stiffness, weather-resistance and fire-resistance of these materials.

Data on the performance and capabilities of these materials is limited and very restricted

in circulation. They consist mainly of laboratory tests commissioned by the manufacturers

themselves. As would be expected, there is no mention of these materials in the available

codes of practice or regulations for the design of buildings. In the present situation,

there is a natural reluctance on the part of our understandably conservative government

authorities, to approve such designs, even where submissions are made by qualified engineers.

134
General Comments on Lightweight Roofing

The greatest single problem in the wind resistance of buildings in Jamaica is in connection

with lightweight roofs. This was very evident from newspaper reports^^ of damage resulting

from the last severe hurricane in August, 1951. The damage usually falls into two

categories : -

(a) Stripping of roofs due to inadequate fixings to roof

coverings (particularly of metal sheeted type)

(b) The lifting and removal or destruction of complete roof

assemblies due to inadequate holding-down force at tops

of walls

.

Since the 1951 event, general building practice has been improved e.g. to provide fasteners

with large heads and/or washers and to provide mild steel "hurricane straps" tying rafters

to walls.

Design codes and local regulations give no explicit instructions for these provisions so that design is not done on a rational basis except where an engineer is engaged. At present

the majority of houses (excepting large housing schemes) are done without the use of

engineers so that such provisions are detailed nominally.

5. Socio-Economic Considerations in Design

Definition of Low-Cost Housing

The classification "low-cost housing" refers to different cost categories in different

countries. Furthermore, in each particular country, the cost category can vary drastically

with time as inflation pushes up the cost of construction.

The current definition of "low-income" housing in Jamaica, including land, on a developed

site, is a house, the cost of which must be under J$5,000 (US$5, 500)11. This implies a construction cost by the author's estimate of J$2,300 (US$2,530). Virtually all housing

being built by the private sector today can be safd to fall outside of this category. Up

to the present time, therefore, low-cost housing can be described as government-built or government -financed housing.

Corresponding space requirements of 350 - 450 squa:re feet have been quoted for "proper

minimum standard, small housing units" as an international standard for minimum social

housing in developing countries. However, this is not envisaged as an attainable standard

for people with no fixed income and here in Jamaica, such houses reach a minimum of 200

square feet

.

It should be noted that for the smaller houses, space and provision are almost invariably

made for future extension by the owner.

Corresponding Income Group for Low-Cost Housing

This is, of course, determined by the ability to make downpajmients and mortgage repayments

for privately-financed houses (usually 20 year mortgage) . Even amongst the least costlv

estates built by private enterprise, the down-payments effectively eliminate those earning

much less than J$30 (US$33) per week or J$l,560 (US$1,723) yearly. Government-housing,

however, is within the financial capabilities of persons with two-thirds that income in the

urban areas and in some types of schemes even less in rural areas^^.

Annual Figures for Construction of Low-Cost Units

In the following table is some figures for low-cost housing units completed by the Ministry

of Housing^ or under Government Mortgage Insurance Scheme.

135
SOCIO-ECONOMIC CONSIDERATIONS IN DESIGN CONTD.

Annual Figures for Construction of Low-Cost Units

TABLE 1

SCJTOffi STRUCTURAL

CATEGORY

NO. OF UNITS COIIPLETED UNDER

CONSTRUCTION

1970 1971 1972

AT 31st DEC,

1972

Government

Housing

Scheme

HollowConcrete

Block

rfesonry

453 422 836

Slum

Clearance

and

Rehousing

- do - - 63 22 570

Owner/

Occupier

Small

Section

Precast

Cone. Units 380 253 37

Farm

Housing - do - 287 91

Indigent

Housing Timber 26 187 354 94

^Mortgage

Insurance

Scheme

( Inspection

only)

Large

Panel

Precast

Concrete

Figs.

not

available

427 378

Figures

not

Available

* Approximately 700 houses annually in this category have been

built by the private sector during the last 10 years. However,

few of these could be defined as 'low-cost ' 5,15^

136
Housing-Purchase Preferences In Construction Materials

There Is a well established preference In Jamaica for concrete houses-*-^. There Is a considerable consumer resistance, for Instance, against the purchase of houses made of

lightweight material financial restrictions make this unavoidable.

A similar prejudice exist against precast concrete houses (especially those of thin section)

but to a far lesser extent and this prejudice is rapidly disappearing. Hollow concrete

block masonry remains the most popular material for all Income groups.

6. Discussion of Extreme-Wlnd-Related Problems

General

Jamaica enjoys the unwelcome distinction of being In an area of frequent hurricanes and also

being In an active earthquake belt. A more rational approach to design against both

phenomena has developed over the past 20 years; the general conclusion has developed that

where construction. Is In concrete, provisions to create good earthquake resistance will

tend to produce adequate wind-resistant buildings.

This Is mainly for single story residential construction, where it Is assumed that stability

against overturning will hardly be a problem, but that Instead, the main concern Is local

suctions and pressures. This Is mainly true where both walls and roofs are in concrete,

but Is certainly not true of the very popular lightweight roofing used In such construction.

In the case of total lightweight construction, such as timber, wind is, of course, critical

and Jamaica has experienced wide-spread damage in the past when this was not fully

recognized. Where adequate fastenings and holding-down devices have been provided,

buildings have performed well both here and in other adjoining Islands.

Another minimizing factor in the effect of hurricanes on Jamaica, is an effective hurricane

tracking and warning service, administered by the Meteorological Office, Jamaica. In the

hurricane season, the public is constantly reminded of the necessary precautions and this

minimizes greatly the effect of any hurricanes.

Summary

The following is a summary of extreme-wind-related problems which require attention or further examination:

(a) Wind Loads: Determination of gust sizes in hurricanes.

(b) Hollow-Concrete Block Masonry: Necessity for and effects of

poured stiffener columns.

(c) Large Panel Precast Concrete Systems:

(I) The design of welded metal connections with bar

anchorages to achieve ductility.

(II) Joint waterproofing and the avoidance of rain

penetration in flat thin-section, precast concrete

roofs.

(ill) The design of welded metal connections with bar

anchorages, subjected to combined shear and tension

forces.

(d) Timber Systems : Simple minimum requirements for providing

resistance against uplift.

137
(e) Other Lightweight Systems:

(i) Durability

(ii) Strength and stiffness

(iii) Weather Resistance

(iv) Fire Resistance

(f) Light Roofing Systems

(1) Effectiveness of fasteners in resisting uplift forces

on metal sheets.

(ii) Simple rules for minimum provision in preventing uplift

of overall roof system.

138
List of References

1. Kingston and St. Andrew Corporation

Draft Building Regulations - 1971

Part 2 - Structural Requirements.

2. Wind Loads For Structural Design

Draft Code of Practice - August 1970

by Barbados Association of Professional Engineers.

3. Minimum Requirements For Thin Section Precast Concrete

Construction (ACT - 525 - 63)

.

4. British Standard Code of Practice No. 116 - 1965

The Structural Use of Precast Concrete

5. Economic Survey, Jamaica - 1971 and 1972

6. "The Return of Timber" by N. A. Goldson and

"Wood Preservation - the Wolmanising Process" by

D. Henderson from - The Master-builder Vol. 7; No. 2; 1968 (Jamaica)

7. "Esso turns Sugar Cane Waste into Particle Board"

Master-builder Vol. 7; No. 2; 1968

9. "Breakthrough in Housing: Prospect seen for $130M

annually from bagasse" - Public Opinion February 23, 1973

(Jamaica)

10. "Daily Gleaner (Hurricane Special)" August 19, 1951

Jamaica.

11. "Cross Section of Jamaican Housing"

The Jamaica Daily News, Real Estate Section,

November 4, 1973 Page 6.

12. "Industrialization the only Possibility - A House

Programme for a Developing Country" by J. Bietry,

The Master-builder No. 3; 1967 (Jamaica) Page 6

13. A National Physical Plan for Jamaica 19 70 - 1990.

October 1971 United Nations Special Fund Project

"Assistance in Physical Development Planning".

14. Jamaica Architect, Issue 8: 1971 - "Housing"

15. "Genesis of a Jamaican Building System" by A. J. Benghiat

The Master-builder, December 1966 and May 1967 (Jamiaica) .

16. "Good Building Practice Prevents Hurricane Damage - A Report on the Effects of Hurricane "Betsy" on Nassau - 1965" by J. M. Wint

.

Scientific Research Council - SRC Technical Report 2; 1966 (Jamaica)

.

17 . "Hurricane Precaution for Tropical Buildings"

by J. M. Wint, Scientific Research Council (Jamaica).

18. "Concrete Masonry Structures - Design and Construction",

Journal of the American Concrete Institute, May 1970

and June 1970.

139
WIND PRESSURE PROVISIONS

OF THE NATIONAL BUILDING CODE

REPUBLIC OF THE PHILIPPINES

by

Ambrosio R. Flores

President, Philippine Standards Association,

Consulting-Structural Engineer, Quezon City, Philippines

SYNOPSIS

The Philippines lies in an area subjected frequently to typhoons, the most severe ones usually occurring during the months of October and November. The tremendous losses of life

and property due to three successive typhoons in 1970 prompted the Philippine Government to review existing regulations and formulate new ones to avoid repetition in future typhoons.

The help of relevant International Institutions with facilities and expertise like UNESCO

was sought by the government, so as to produce a National Building Code incorporating the

best practice in design and construction of buildings and structures to withstand WIND

FORCES

.

1. Introduction

It was an invisible, violent lady named "YOLING" that broke her temper on November 19,

1970 and blew up the roofs of many of our low buildings, residences, schools and industrial

plants, broke the window glazings and vision panels, toppled power transmission and

telephone poles, television towers and signboards, disrupting communications and causing

blackouts

.

For more than half a century, we were contented and felt safe using the WIND- PROVISIONS

of the Building Ordinances of the City of Manila specifying the use of 30 pounds per square

foot pressure, on a vertical plane surface for all structures, regardless of their

geometrical forms, locations, ground topography and presence of vegetation and man-made improvements. But in 1970, the Philippines was the victim of three Typhoon musketeers of

death

:

SENING on the middle of October wrought havoc over the Bicol Area; TITANG on the last

week of October smothered Mindanao and the West Visayas ; YOLING hit the Greater Manila Area

in November. It seemed like a well-planned military strategic attack. Add all the losses

and deaths caused by these typhoons to that of the Earthquakes of April 7, 1970, and that of

August 2, 1968, and you have more than One Billion Pesos worth of property. Something must

be done to minimize the tremendous loss of property and human lives. One of the avenues is to review our Building Regulations and relevant aspects of direction and control.

2. Building Code Background

The oldest Building Ordinance to cover the consideration of Wind in the design of

structures is that of the City o5 Manila which dates back to the early years of the

twentieth century during the American occupation of the islands. This has been followed in

other cities and the same one followed by the Bureau of Public Works.

The Code required the use of 30 pounds per square foot of wind pressure against a vertical plane surface of the structure. On inclined surfaces, the Duchemin'a Formula was

the only guide which is obsolete today.

Then on November 11, 1950, pursuant to Executive Order No. 367 of the President of the

Philippines, a Building Code Committee was created to prepare a "Basic Building Code" under

the National Planning Commission. The Committee was composed of ranking Engineers and

Architects in both the public and private sector. The final draft was sent to Malacanang

for approval in 1954, but it died a natural death. However, the Code Provisions was an improvement over that of the City of Manila.

140
The pertxnent provisions on WIND LOADS are quoted hereunder:

"Sec. 209 (c) . The Wind Pressure on vertical plane surfaces shall

be taken at not less than 20 pounds per square foot for the

portions less than forty (40) feet above the ground and at 30

pounds per square foot for portions more than forty (40) feet

above ground."

"Sec. 209 (e) . Where it shall appear that an isolated building or structure may be exposed to the full force of the wind throughout its entire height and width, the pressure upon the vertical

surfaces thus exposed shall be taken at not less than thirty

(30) pounds per square foot."

"Sec. 209 (g) . On roofs having a rise more than four (4) inches

per foot of run the wind pressure normal to the surface be

taken as two (2) pounds per square foot for each inch of rise

on one foot when the rise exceeds twelve (12) inches per foot."

Note that nothing is mentioned about negative pressure or better understood as SUCTION,

so that it is also obsolete as of now.

3 . The Present National Building Code

Time passes on bringing with it not only changes in science and technology but also

calamities and disasters that result in human misery. The August 2, 1968 Earthquake, which

caused the collapse of the Ruby Tower killing more than 322 persons, injuring more than 300,

and damaged more than 30 buildings, triggered the formulation of the New National Building

Code through the initiative of Senators Gil J. Puyat and Helena Z. Benitez. Thirty (30)

representatives of Architectural and Engineering professions. City Engineers and Fire Chiefs

of the Metropolitan Manila area sat in continuing workshops to produce the National Building

Code. The result is R.A. No. 6542 which establishes the purposes of the Code and the

creation of a joint Building and Environmental Planning and Standards Commission to supervise the implementation.

The WIND PRESSURE provisions were formulated by making reference to the Uniform

Building Code, 1967, of the U.S.A., American Society of Civil Engineers Transactions, the

ALJ Structural Standards of Japan, and the Building Code of Switzerland, all of which are supposed to embody the results of the latest scientific researches and studies.

The astounding losses due to the Typhoons SENING, TITANG and YOLING, all within a period of less than two months in 1970 moved the Philippine Government to request the

UNITED NATIONS EDUCATION, SCIENTIFIC AND CULTURAL ORGANIZATION (UNESCO) to send a team "to

study at first-hand the nature and extent of the damage caused, in consultation with the

authorities, to formulate recommendations for action designed to prevent or reduce damage to buildings and structures in the event of the future typhoons".

Accordingly, Messrs. S. Mackly, C. Finney and T. Okubo were commissioned as a team

which arrived on December 1, 1970. They spent two (2) weeks for the survey and

investigations with the help and guidance of our local government officials. Their report

was submitted on May, 1971.

For the benefit of those who do not have access to this report, a concise excerpt of

the relevant observations are given below:

"5.3 LOW-RISE DOMESTIC BUILDINGS - small houses of one or twostories

a) Poor attention to structural and roofing details to resist

wind effects, not necessarily the effect of higher velocities.

b) False economy in construction.

141
c) Lcfw-pitched roofs, cantilevered to a considerable degree

beyond the exterior walls to form large awnings."

"5.5 PRE-FABRIGATED BUILDINGS - School Houses

The Marcos Type 1 (Post 1969) with Z-Section columns and rafters, and

channel purlins as well as the Marcos Type 2 (Pre 1969) with double

steel channel columns , channel rafters and purlins were damaged due

to "the inadequacy of lateral bracing to withstand the racking action

of wind ----- inadequate anchorage of the portal-frame column

based into the supporting piers or footings with poor quality concrete

- - - -. As a result, under the lateral wind forces, the end-portal

unsupported and severely distorted portion of the roof structure re- sulting in longitudinal racking of the building as a whole and buckling of several portal legs along its length.

In a case of the ARMY Type (3) and (4) the nature and the amount of

damage was erratic in character and depended very, much on the quality

of workmanship displayed in the construction - - - - . What should be

inferred is that good building construction results from a combination of adequate design and good-quality workmanship."

"5.7 DAMAGE TO ROOFS

In the Philippines, the vast majority of the buildings are built with

roofs having very flat slopes , with the result that the full roof area is exposed to negative pressure or suction. In view of the type

and quality of roof construction generally used (light-gauge galvanized corrugated-metal sheeting, corrugated asbestos or aluminum alloy

sheeting) fastened to either timber or steel purlins which are supported in turn, on timber or steel rafters, this leaves them particularly vulnerable to damages from wind attack."

"6. GENERAL CONCLUSIONS AND RECOMMENDATIONS

"6.4 EDUCATION AND TRAINING

(1) UNESCO, in collaboration with the Government of the Philippines

should sponsor a National Seminar on "Design of Buildings and

Structures to resist Typhoon Winds" to be held in Manila at an early date. Such seminar should be essentially practical

in its outlook and should cater for the building as a whole,

embracing architects, structural engineers, building inspectors, meteorologists and building contractors. Topics for

discussion might include:

a) nature and characteristics of natural wind;

b) its effect on buildings and structures;

c) selection of suitable design criteria;

d) exposure factors and local sheltering effects;

e) likely damage patterns in relation to specific types of

buildings and structures;

f) structural design and detailing to avoid such damage;

g) relative costs of improving design and detailing of buildings to resist wind damage; and

h) design of glazing to resist wind forces."

142
Acting on the above UNESCO Teams' recommendations, the UNESCO National Commission of

the Philippines organized a Regional Seminar sponsored by the UNESCO Field Science Office

for South East Asia in cooperation with the World Meteorological Organization.

4. Regional Seminar on "Wind Effects on Buildings and Structures"

In this Seminar, I presented a paper on "Design Methods for Wind Effects on Buildings

and Structures" wherein I presented the following causes of failures as a result of my

personal occular inspection of failures of various types of structures:

1. Inadequate Structural Design of

anchorage

.

members, splices, joints and

2. Poor quality or substitution of materials

.

3. Poor construction methods.

4. Lack of supervision.

5. Lack of periodic inspection and maintenance

.

Lack of properly designed details for splices, joints and connections leaving the

supposedly "simply" job to the Fieldman resulted in miserable failures. Substitution of

rolled steel sections with built-up members with poor welding and inaccurate alignments and

warping caused collapse of towers and signboards in addition to inadequate horizontal and

diagonal members to resist torsion. Use of inferior grade and defective lumber as well as anchorage details without the proper analytical designs caused failure and collapse of roof

trusses. Lack of supervision was revealed by uprooted members exposing crude anchorages or excessive sagging. Lack of maintenance and periodic inspection resulted in deteriorated

members due to weathering. Billboards over roofs when these were not considered in the

original designs caused overloads - a fault of the Owners for allowing dealers to advertise

their products "without the necessary professional design and responsibility to save on the

expense.

Revision of the National Structural Building Code

The National Building Code was revised in its presentation by separating the

Engineering Sections as a separate Volume entitled "The National Structural Code for

Buildings" to which the National Building Code makes reference. In this manner, the design

criteria and methods of design can be revised periodically as may be required by advances or developments of science and technology without going through the grind of legislative

processes. This was made possible by the joint action of the Association of Structural

Engineers of the Philippines (ASEP) and the Philippine Association of Civil Engineers

(PACE)

.

The Impact of Typhoon YOLING on its effects on various structures led to the revision

of the UNIT PRESSURES due to WIND by increasing the values by 50 kilograms per square meter

or 10 pounds per square foot in all areas under ZONES I, II & III.

The various Professionals who formulated the National Building Code are open-minded and

receptive to valid proposals for a more realistic code justified by scientific study and

research. What we have now represents our best thinking and judgment. A Building Code to serve its purpose must be dynamic

.

The "National Structural Code for Buildings" was approved on June 23, 1972, while the

"National Building Code of the Philippines" was enacted without Executive Signature on August 26, 1972. The Presidential Decree No. 1081 Declaring Martial Law on September 21,

1972 has affected its proper implementation.

Included herewith is a Copy of the WIND PRESSURE provisions of the National Structural

Code for Buildings as approved on June 23, 1972.

143
Finally, let us all cooperate to bring out the best results in this Seminar where

preparations were made within a short time. We look forward to a continuing session after more data are secured and analyzed and reduced to actual applications in design and

construction.

BIBLIOGRAPHY

:

1. UNESCO - "Philippines - The Typhoons of October and November,

1970", by S. Mackey, C. Finney, and T. Okubo - May 1971.

2. A. R. FLORES - Design Methods for Wind Effect on Buildings and

Structures" - UNESCO Seminar - 22-26 November, 1971.

3. National Structural Code for Buildings - Approved 23, June, 1972.

144
NATIONAL STRUCTURAL CODE OF THE PHILIPPINES

WIND PRESSURE

APPROVED August 26, 1972

145
National Structural Code of the Philippines

Section 2.06 : Wind Pressure

(a) General. Buildings or structures shall be designed to withstand the minimum

horizontal and uplift pressures set forth in Fig. No. 2.06-C to E and this Section allowing

for wind from any direction. The wind pressure set forth in Fig. No. 2.06-C to E are minimum values and shall be adjusted by the Building Officials for areas subjected to higher

wind pressures. When the form factor, as determined by wind tunnel tests or other

recognized methods, indicates vertical or horizontal loads of lesser or greater severity

than those produced by the loads herein specified, the structure may be designed

accordingly

.

(b) Horizontal Wind Pressure. For purposes of design, the wind pressure shall be

taken upon the gross area of the vertical projection of that portion of the building or structure measured above the average level of the adjoining ground.

(c) Uplift Wind Pressure. Roofs of all enclosed buildings shall be designed and

constructed to withstand pressures acting upward normal to the surface equal to

three-fourths of the values set forth in the calculations below Fig. No. 2.06-E for the

height zone under consideration. An enclosed building shall be defined as a building

enclosed at the perimeter with solid exterior walls. Openings are permitted in the solid

exterior wall provided they are glazed or protected with door assemblies. Roofs of

unenclosed buildings, roof overhangs, architectural projections, eaves, canopies, cornices,

marques, or similar structures unenclosed on one or more sides shall be designed and

constructed to withstand upward pressures equal to one and one-fourth times those values set forth in the Tabulations below Fig. No. 2.06-B.

The upward pressures shall be assumed to act over the entire roof area.

(d) Anchorage Requirements. Adequate anchorage of the roof to walls and columns, and

of walls and columns to the foundations to resist overturning, uplift, and sliding, shall be

provided in all cases.

(e) Moment of Stability. The ovei turning moment calculated from the wind pressure

shall in no case exceed two-thirds of the dead load resisting moment. The wieght of earth

superimposed over footings may be used to calculate the dead load resisting moment.

(f) Combined Wind and Live Loads. For the purpose of determining stresses all

vertical design loads except the roof live load and crane loads shall be considered as acting simultaneously with the wind pressure.

146
ERRA MADRE MOUNTAIN RANGE

ZONE I FIGURE NO. 2.06-B

ZONE III

V= 200 KPH= 125 Wn

p= 300 ksm= 60 psf, h above 100'

p= 250 ksm= 50 psf, h 30' to 100'

p= 200 ksm= AO psf, h 0' to 30'

ZONE II V= 175 KPH= 108' WE

p= 250 ksm=

p= 200 ksm=

p= 150 ksm=

50 psf, h above 100'

AO psf, h 30' to 100'

30 psf, h 0' to 30'

V= 153 KPH= 96 W}{

p= 200 ksm= 40 psf, h above 100'

p= 150 ksm= 30 psf, h 30' to 100'

p= 100 ksni= 20 psf, h 0' to 30'

LEGEND : KPH= Kilometers per Hour

Wti= Mies per Hour

ksm= Kilograms per Square Meter

psf= Pounds per Square Foot

REGOMvffiNDED WIND PRESSURE PER SQUARE LtETER OR PER SQUARE FOOT

OF VERTICAL PROJECTIONS

147
Vertical plane surfaces

Type of structure in closed form.

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.

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7-rTT77-TT77-7

:o.4

•rrTT7-rT-rTyT7

(6) (7)

f5

0.8

1:0.4 z:

^j&-0^0.5 <n 0.5 0.5 «n 0.5

r 7 7/ /// 77 f / ^ /

0.8 10.4 i:

T77 -rr

:;o.4 //^///////

(8) (9) :io)

0.8 1; *0.4 0.8: -7- -7:

*0.4

(11)

TTT-r-rT-rT-rrTTTy-rr

(12)

In case the roof surface forms an arc, changes in pressure may "be assumed at the

quarter points of the arc.

Fig. No. 2.06-C

148
In case of wind in direction

of side wall girders.

Type of structure

in open form,,

/////// / / /

(ill) -e- IN DEGREES In case slope of roof

has intermediate value,

interpolate by straightline method.

Self-supporting

shed

;i5)

0.7

77^7?

(17)

110°,

0.7

(18)

Lattice

structures

,

3 3- — =iS!^H^

:2o) (21) (22) (23) (21+) The ahove figures indicate cross-section of latticed beams and columns. For area acted on by wind pressure, the projected area of the latticed member on the plane

nonnal to the indicated directiolLof wind pressure shall be taken.

0

Circular, Polygonal

structures such as Chimney, Gas Tank, etc. Circular

(25)

Octagonal

(26)

Hexagonal

(27)

Fig. No. 2.06-D

149
uoipns

d

d

tod

CMd

sjnssajd

d d d

00o

b 'ainssejd ojujDu^p pod louojpojj

Fig. 2.06-E

150
L = Length of Arch Rib

Wind Load Distribution which may be used for

Parabolic Arch Ribs of H Approximately 0.55

b

Fig. 2.06-F

151
RECTANGULAR PLAN WITH FLAT ROOF

H

0.9

-0.80 for H/B - 2.5 -0.70 for H/B = 1.00 -0.50 for H/B0.25

ttttttttt

-77777T777T7TT77y

A/B D/C

ELEVATION

o

to O

If) S«> "TT d d o

' ttttlttl

6 Side wall

A Side wall iilillll

0.80 PLAN

L -

l! = Length of arch rib

Fig. 2.06-G

152
Standardization in the Philippines Today

by

Ambrosio R. Flores*

Standardization of industrial products and consumer goods in the Philippines today is way

behind other developed countries, like U.S., Japan and Germany. As a developing country, we

still lean on them for guidance. The tremendous challenge to us, scientists and

technocrats, is serious, yet how often do we hear someone say that we have one of the

highest proportion of professionals per capita and that we are one of the heaviest exporters

of Engineers of various disciplines. Doctors and Nurses to other countries?

There is a gap somewhere between the government institutions and the relevant private

institutions as regards Standardization. Unless such link is furnished by government

initiative and thereafter implemented with adequate organization and logistics, our present

situation will continue to move with turtle speed.

For the proper understanding of everyone. Standardization, in general, is the act of setting

up certain standards, specifications, or regulations covering dimensions, weights,

proportions or compositions, characteristics or qualities to serve as models or criteria for

evaluation to achieve uniformity and quality within tolerable limits of variation in raw materials or finished goods.

As early as 1901, the Bureau of Science was established and served as a states symbol in the

Far East. In the same year. Great Britain started to move towards Standardization, being

the first industrialized nation in the world, but it was only after the first World War when

other European nations followed from 1918 to 1928, while others followed even during the

Depression period after 1930. The Philippine Government created a Committee on Standardization in 1936 under the Division of Purchase and Supply of the Department of

Finance with a very limited scope covering government requirements. Then on June 20, 1964,

R.A. 1109, the Division of Standards under the Bureau of Commerce was converted into the

present Bureau of Standards. This marked the beginning of a serious attitude towards

Standardization. Its objective was to prepare standards for products used by the

government, for expert and local consumption.

To develop the scientific research and technological phases, the National Science Board was erected by R.A. 1808 on August, 1956. The implementing agencies are the NIST (National

Institute of Science and Technology) and the PAEC (Philippine Atomic Energy Commission)

.

Well and good. However, the NIST and PAEC are most concerned with researches, although the

Test and Standards Laboratory of the NIST accepts tests from any party. Still the arm for

producing Standards and Specifications is very weak.

There are other offices which produce their own standards relevant to their own functions

such as the Bureau of Supply coordination under the Department of General Services; Armed

Forces of the Philippines; Forest Production Research Institutes; Food and Drug

Administration under the Department of Health; Materials Testing Laboratory of the Bureau of

the Public Highways; Metallurgical Laboratory Services Division of the Bureau of Mines.

Add to the above the Testing and Research Laboratories of Industrial Firms and

Manufacturers. All the above offices that formulate their own specifications and standards,

including PHILSA, form a heterogeneous group that should be under one Administrative Control

to prevent confusion due to overlapping of activities and to expedite the production of more

standards

.

* Consulting Civil - Structural Engineer, F. ASCE, NSSEEP, ASEP, PACE, PHILSA

153
The need for coordination is, therefore, obvious. PHILSA has for its Membership on a "voluntary basis."

Sustaining Members ------------3

Company Members ------------- -32

Associate Members ------------4

Individual Members -----------82

Life Term Members ------------7

There are: 24 Technical Committees,

61 Sectional Committees , and

51 Working Groups

As of today, PHILSA has been patiently and persistently engaged itself in the formulation of

Standards as reflected in the following as of 1972:

Number of Specifications Published ----- 35

Number of Specifications being Printed - - - 10

Number of Specifications approved by

the Board for Printing ---------- H

Number of Specifications approved by

the Board of Review ----------- n

Number of Specifications under discussion

by Technical Committees --------- 117

Considering that PHILSA was founded in 1955 by the leading technocrats then, the

accomplishment seems low and the progress leaves much to be desired. However, let us look

at the leading world organization for Standardization like the ISO (International

Organization for Standardization) , It has 70 Nation Members and the Bureau of Standards

celebrated ISO's Standards day last October 17, 1972.

It has published 2,000 International Standards, 1,330 of which were published during the

last four (4) years. The above data furnished by no other than Mr. Olle Stures, Secretary

General of ISO, means that ISO has only prepared 1-1/8 Specifications per year per nation,

against PHILSA' s two (2) Specifications per year. Again, ISO has 1,200 Committees in the 70

Countries or 1.7 Committees per nation against PHILSA's 24 Technical Committees, PHILSA

seems to move faster than ISO.

The scope of work is very broad and time consuming considering that there are about 150,000

Standards in the whole world that must be harmonized as to their uses and functions. And

there are at present seven (7) sets of National Standards that are similar to ISO in their

basic format, namely, U.S., England, Germany, France, Sweden, Japan, and Russia.

The Philippines, a comparatively new member of ISO, therefore, has a long way to go to be at par with the leading developed nations. We are trying to adopt International Standards,

but modified to suit our local conditions, because of lack of logistics by way of financing,

the lack of personal and national discipline to refuse and condemn substandard products and consumer goods through publicity, common action, and refusal to buy or entertain inferior

commodities, the enforcement of the observation of standards will be a failure.

Standardization and quality control are the prime requisites for reducing costs to maximize

production and increase exportation. If we lack those factors, the progress of the country

will be consequently small. When we except substandard or inferior articles because of

154
lower prices we are in effect subsidizing mediocrity, that will lead to less production,

lack of competition to upgrade quality and finally, less gross national production.

Adoption of the Metric System

It is relevant to mention here the "Presidential Decree No. 187 prescribing the use of the

Metric System of Weights and measures as the Standard measurement for all products,

commodities, materials, utilities and services and in all business and legal transactions

that the Metric System shall be fully adopted in all sectors throughout the Philippines by

Jan. 1, 1975." To implement this he created the "Metric System Board" composed of the Top

Government Officials composed of:

Sec. of Trade as Chairman

Sec . of Finance

Sec. of Agriculture and Natural Resources

Sec. of Public Works, Transportation and Commiinication

Sec. of Education

Sec. of Justice

Chairman, National Science and Development Board

The Department Undersecretaries and the Board Vice-Chairman concerned

shall serve as alternates.

PHILSA, being a Private Organization was appointed as Member of the Advisory Board and

Technical Committees.

There is also a need for an Organization, be it a Semi- Government or Government in

character, to coordinate, administer, formulate or enforce such Standards prepared by the

various bodies, public and private, mentioned above, with the objective of promoting and

developing^ our national economy, similar to the practice in Japan, which make her the second

best industrialized nation in the world today.

Let us hope that the New Society under the aegis of the Martial Law can change the present

status from a gloomy, frustrating atmosphere to one with clear and orderly direction and

implementation. PHILSA will do its best to continue the good work it has done and is ever ready to cooperate with other bodies of similar objectives.

155
WIND RESEARCH IN THE UNITED KINGDOM

by

Keith J, Eaton

Building Research Establishment, Department of

the Environment, Gerston, Watford, United Kingdom

First of all, ladies and gentlemen, I should like to thank the Workshop for inviting me

to participate here, because for sometime now we have been working on wind loads. For the

last two or three years, we have been working on a joint project, with the staff of NBS, on wind loads on low-rise buildings.

When I arrived here yesterday, I was asked to talk about this subject. I have prepared

some slides, and I would like to give you some idea of what we are doing in the United

Kingdom.

To start with I would like to show you a short film. This will run for only about nine

minutes. And I will discuss this a little bit further afterwards,

( Showing of the film.

)

I would like to spend a little time on the points that were made towards the end of the

film.

The gap in our knowledge was caused by the lack of information on wind pressure, on loads on low-rise buildings. In the United Kingdom in 1968 there was a great deal of

controversy because we increased the loads on low-rise buildings.

We had no reliable information on which to base this and so we started full scale

measurements on the estate of houses that you just saw.

I would like to show some slides and talk about these houses a little more.

( Showing of slides )

The houses on the screen are located in the Southeast of England, at Aylesbury — the

several houses in the estate there, as well as the experimental building in the field.

Here, ( Indicating) we have another view from the southwest; from this direction you are looking at the open field. We got the present distribution of isolated buildings in this

•

situation

.

We started constructing the experimental building. This is a steel-framed building

with timber cladding. Of course, we had a trial erection back at the B.R.S. The buildings

constructed were on six load cells at ground level. And, likewise, with the structure shown

in this film, another six loads cells up at this level. Now you see it in its 2-story

configuration. We also have the possibility of reducing this to 1-story or even adding a 3rd story. At the moment this seems a remote possibility as we have to leave this site

sometime next year. There is a possibility that we might move to some other location.

In its finished configuration as you saw in the film, we have this variable pitched

roof on top. This slide also shows the fixed anemometer mounts, the anemometers being at 10

meters; the other main anemometers are at 5 meters and 3 meters. In addition, we have a couple of other special anemometers in there, but they are not part of the main network.

Now I could just briefly say something about our thinking behind this change of roof

pitch. What we wanted to do was get as near to a multi-geometric building, the same sort of

situation that is easy to undertake in a wind tunnel — as near to the situation as we

could. We devised this roof which can vary between 5-degree and 45-degree pitch. So once

the wind blows, we will take a record, say, for 20 minutes. Then it takes about five or ten minutes to change the roof pitch to any other angle we so desire. Before the wind

conditions have changed appreciably, why, we essentially get the same wind speed and

direction. We change the pitch, then take another record for another 20 minutes, and we

carry on like that as long as the wind is blowing.

156
You can see we can get quite a range of aspect ratios and overall shapes of buildings,

and we are already finding some completely different pressure distributions over the roof

and on the walls as well with the different roof pitches. You can see the locations of the

pressure transducers. They are all over the four walls and both roof surfaces. They are larger diaphragm transducers than those we saw yesterday. They are about 120 milimeters in

diameter. We set these flush with the surface of the building, so that then we are measuring the pressure integrated over that area.

These were designed at the Building Research Station some 10 or 12 years ago. The idea

of having a large diaphragm like that was to give a cladding load representative of the

loading over that sort of size of cladding, and yet at the same time be manageable to install in buildings. There is one other feature that this slide illustrates — and that is

the slats or louvers which are on all four walls. The building is a sealed structure, but

we do have a facility to open these openings to a known degree so that we can introduce

various values for permeability in the walls and also in the roof of the structure. This

will affect the measurement of internal pressures and, hence, the differential loading on

the different parts of the structure. And from looking at some of the damage photographs

this morning, it is this internal pressure which often causes us so many problems.

(Another slide) It is a very similar set up with transducers, as we said yesterday,

with solenoid valves, inside the building. This is the back of the transducer. As Dick

said, he copied this idea from us. We didn't patent it, unfortunately. This gives us a zero position at the beginning of each record automatically, zeroing the pressure on the

outside of the transducer, with a tapping point just at the side of it.

We can't record on all 130 channels at the same time. This has cost us enough in the

first place. We can accommodate 96 channels, and we have to select the channels that we are recording on. At the current time I have finished most of the work on the houses in the

estate. When I say, "finished," I have the various wind directions and speeds that I am likely to get — and I removed a lot of the transducers on the houses. I am now

concentrating in much more detail on the experimental building itself.

( Another slide. ) This is the recording room inside the experimental building. All

these tape recorders are switched on automatically when the wind exceeds a preset level, or we can go there and switch them on manually. And this is the control panel that does all

the switching, operates all the solenoid valves, puts on zero and calibration pulses, prints

out the time of day. And then we have an inhibit switch down here just to give us a cooling-doxm period before it switches on again. We again test the strength of the wind

before we would switch on.

To say a little bit more about the houses, these are pretty traditional local authority

houses in the U.K. — brick cross-wall, timber stud frames on the windward and leeward

faces, built-in terraces, 22 1/2- degree pitch roofs, individual clay tiles. This is quite

typical in the U.K., quite a bit heavier than other forms of roofing, but we still lose many

tiles due to wind damage, particularly if they are not clipped, and most of these are just

laid in place, relying on their dead weight on the battens to hold them down.

(Another slide. ) This was the estate you saw modelled in the wind tunnel on the film,

and one little interesting factor has come out of that straightaway. There are garden sheds

in the back gardens of these houses, and in front of the houses you can see some carports.

In the first set of tests I did, I modelled all these — and then I repeated the tests,

taking these garden sheds, carports and the fences, taking these away from the model; and

this had quite a tremendous difference or quite a tremendous effect on the wind loads, the

pressure distribution on these windward row of houses here.

The effect is that these garden sheds are already raising the on-coming flow over this

windward terrace and tending to reduce the pressures on the windward wall. In the absence

of these, then the pressures on the windward wall increase considerably. And certainly,

when you compare the pressure distributions going into the estate — because you will

remember we have parallel rows of houses — it is this windward row which receives the

greatest loading; and the rest of the half a dozen parallel rows, going back into the

estate, in general had just a bit of turbulent suction and received very little loading.

157
This then raises other problems. You could possibly design sheltered houses for lower wind

loads. But then if you take down that shelter sometime in the future, you will get

problems

.

What we have elected to do on these houses is to install our transducers in dummy roof

tiles rather than put them on the outside of the house as Dick Marshall does; and we had

quite a bit of water leakage here and the mastic compounds smeared all over the place. But

we just took the roof tiles out and put in fiber glass tiles in place of them. We also had

some troubles on these particular roofs, with grit washing down the roof from these concrete

tiles and getting into that narrow gap there around the diaphragm and causing some sticking.

So we had to open that annular gap so that we could wash it. We washed it out easily, and we had no trouble since then

.

( Another slide .) And this is the sort of configuration in the walls of the houses

where we just install the box, once the houses were being constructed, to take the

transducer. This is the .trouble with this sort of installation. We have to get in once the

houses are being constructed — and this poses quite a problem, knocking holes in buildings

later on. And this is why there are many good points to be said for having these screw-on

discs on the outside of buildings. They are certainly not restricted so much in the way

where you can put them.

This house in particular is on the southwest corner of the estate and receives a lot

of direct winds. So on this roof we installed 10 transducers — I think it is six on this

side and four on the other side — and we are looking at the distribution across that roof

in some detail.

You will notice that in these houses there is very little eaves overhang, compared with

the other slides that you will be looking at this week — and we copied these on the

experimental building. But one thing we are going to do this winter is extend the

eaves-overhang on the experimental building so that we can get some pressure measurements

underneath and on top of that — and this will give us some more results which we can compare with the work here.

Within the loft space of this house, as I have already indicated, it is important to measure the internal pressure. The underside of those clay tiles are lined with a felt

roofing liner. So we have two membranes of variable permeability. And I am measuring the

internal pressure in here with respect to my assigned reference pressure — and I am also

measuring the pressure at the intermediate space between the roof tiles and the under-tile

felting. That is causing us some problems as well, but I won't go into that now.

The other aspect of this work is looking at wind speeds in between the houses . But

going back to the code of practice, this was the big area where we had very little

information. The Meteorological Office in our country — and probably in many other

countries as well — measures wind speeds down to 10 meters or 10 meters above the level of

obstructions. So if it is in the middle of a city, they would probably put an anemometer

upon a mast on top of a building. They took the attitude that below that level, below the

general level of obstructions, if engineers put those obstructions up, they could measure

the wind speeds themselves. Hence, this wind speed unit which we now have at BRE.

We have this vehicle with a mast on it, and this can extend up to 20 meters height in

total. We see it at 10 meters. In fact, in that photograph, there is one anemometer on the

top there at 10 meters, another one at five meters. If you put it up to 20 meters, we in

fact keep them at 5-meter intervals. So we have 20, 15, 10 and 5. And we record for about

10 minutes at a time — and at the same time, we compare the measurements with simultaneous

measurements taken with a similar mast out in the open country. So that we are getting the

velocity ratio between our open country measurements — either the same as that which the

Met office provides us with or we are getting reduction factors; not always reduction

factors, becuase sometimes we are getting increased speeds within the built-up area. Then we will compare these sites in between houses, in narrow gaps where we get a lot of

channeling.

And in fact, since we started this work, we have increased the number of anemometers;

and we have two more on the small tripods — and we set these at 1-1/2 meters. We have

158
taken this as a standard height for an average human being. It is sort of this height and

the sort of level at which we get effects on pedestrians in built-up areas. This isn't

directly relevant to loading problems ;• but once we have taken the measurements, we can provide information for our colleagues in the environmental division. So we get a complete

idea of the velocities in built-up areas, compared to those in the open country.

All this information, as I have said — the pressure measurements and the load

measurements on the experimental building, the velocity measurements in between houses in

urban areas — will eventually provide us — well, not too long I hope — with information

for the next revision of the British Code of Practice. Perhaps, I can just digress there

and say that two or three people from various countries this week have not heard of the 1972

version of our Code of Practice. I regret to say that Bangladesh is still using the 1952

version which is very much out of date. And also, I want to put the record straight that we

are entirely using SI units for the last four or five years and I think this is quite general in structrual engineering and meteorology in our country. So I hope I haven't

mentioned anything unusual while I am speaking. We are revising this as I said during the

next three or four years and we hope to improve the data in the next few years.

Just one other aspect of the work of the Research Establishment that I would like to mention, and this concerns the investigation of wind damage whenever we get strong winds

such as tornadoes as we do get quite frequently, although not in the same experience as you

get out here. We do investigate the damage to try to get some of the answers to the problems. Now, I don't have to show the slides on this because I think you have seen identical

slides this morning and as I said these slides are almost identical to yours and that we have the same problems.

We have been battling on these problems for years and we run educational seminars with

archittiCts , designers, engineers and so on in our country. We hope we have been winning

slowly. There are, however, some people who are not aware of the problems - students in

j colleges and other engineers and so on who can help in getting the message across.

j BRE has produced this slide package. This consists of some 40 slides which we sell, I

' think, for about $15. So we put the slides in there, translate your notes on wind damage,

wind flow on buildings and solar instruments. This works well in our country and we hope

ll this will help and will find interests particularly to students where this knowledge will

jl help in their background when they become future engineers, we hope, and will save them a lot of travel time in the future.

I Thank you very much.
APPENDIX C

Units of Measure and SI Conversion Factors

Thi's workshop proceedings describes measurements in both U.S. customary units and metric

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) unit of measurement.

The reader should use the appropriate conversion factor (presented below) when converting from one system of units to another.

LENGTH

Metric

1 milimeter (mm) = 0.039 inch (in)

1 centimeter (cm) = 0.394 inch (in)

; 1 meter (m) = 3.281 feet (ft)

1 kilometer (km) _= 0.622 mile (mi)

U.S.

1 inch (in) = 2.540 centi-meters (cm) or 25.4 milimeters (mm)

1 foot (ft) = 0.305 meter (m)

1 mile (mi) = 1.608 kilometers (km)

AREA

Metric

1 square meter (m^) = 10.753 square feet (ft^)

1 square kilometer (km^) = 0.387 square mile (mi2)

1 hectare (ha) = 2.471 acres

U.S.

1 square foot (ft ) = 0.093 square meter (m^)

1 square mile (mi^) = 2.586 square kilometers (km^)

^ 2 1 acre = 0.405 hectare (ha) or 4.046 meters (m )

VELOCITY

Metric

1 meter per second (m/s) = 3.279 feet p^r second (fps)

1 kilometer per hour (k/h) = 0.278 meter per second (m/s) or 0.622 mile per hour (mph)

1 knot (kn) = 0.514 meter per second (m/s) or 1.150 miles per hour (mph)

U.S.

1 foot per second (fps) = 0.305 meter per second (m/s)

1 mile per hour (mph) = 0.447 meter per second (m/s) or 1.608 kilometers per hour (k/h)

PRESSURE

1 pound per square inch (psi) = 6895 newtons per meter^ (N/m^)

1 pound per square foot (psf) = 47.88 newtons per meter^ (N/m^)

160
NBS-114A (REV. 7-73)

U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET

. IHIHI.K ATION OR RI'PORT NO. NBS BSS-562. (lov'i At e ( -s .s i oil No.

3. Rec ipicm *.s Acccs.sion No.

4. TITLE AND SUBTlTLli

Development of Improved Design Criteria for

Low-Rise Buildings in Developing Countries to Better

Resist the Effects of Extreme Winds, (proceedings of

workshop) .

5. I 'ubi ic ill ion Date October 1974

6. Performing Organization ( odi

7. AUTHOR(S) Noel J. Raufaste, Jr., Richard D.Marshall 8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Ta.sk/Work Unit No. i:enter for Bldg. Technology

11. Contract /Grant No. 'ASA 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.

13, Type of Report & Period Covered Interim CT1973

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

Library of Congress Catalog Card Number: 74-600158

16. ABSTRACT (A 200-word or /ess factual summary ol most si^ificant mformation. If document includes a significant bibliography or literature survey, mention it here.)

An International Workshop held in Manila, Philippines, on November 14-17, 1973, addressed the state-of-the-art in mitigating building damages from winds. The workshop was jointly

sponsored by the United States Agency for International Development (USAID) , the Philippine

Advisory Committee (formed in conjunction with this research project), and the U. S. National Bureau of Standards (NBS). This report presents the proceedings derived from the workshop. The proceedings present recommendations, the workshop program, five reports, and nine technical articles. The technical articles addressed four primary topics which were

used to guide subsequent workshop discussions. The topics addressed were; wind and aerodynamics, structural related technology, socio-economic and architectural considerations, and codes and standards.

The results of the workshop will serve a twofold purpose. The first suggests improved building practices for developing countries. This was accomplished through the development of recommendations designed to upgrade to a minimum acceptable level design criteria for low- rise buildings. The second involves integrating appropriate workshop inf onnation into the overall three-year AID sponsored research project to develop improved design criteria for low-rise buildings in developing countries to better resist the effects of extreme winds.

Key words: Codes and standards; Information transfer; Low-rise buildings; Pressure trans- ducers; Socio-economic; Structural design; Technology implementation; Wind effects; Wind

loads.

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systems. Short numerical tables. Issued quarterly. Annual subscription: Domestic, $9.00; Foreign, $11.25. DIMENSIONS/NBS (formerly Technical News Bulletin) —This monthly magazine is published to inform

scientists, engineers, businessmen, industry, teachers,

students, and consumers of the latest advances in science and technology, with primary emphasis on the work at NBS. DIMENSIONS/NBS highlights and reviews such

issues as energy research, fire protection, building- technology, metric conversion, pollution abatement,

health and safety, and consumer product performance.

In addition, DIMENSIONS/NBS reports the results of Bureau programs in measurement standards and techniques, properties of matter and materials, engineering standards and services, instrumentation, and automatic

data processing. Annual subscription: Domestic, $6,50; foreign, $8.25.

NOMPERIODICALS Monographs—Major contributions to the technical liter- ature on various subjects related to the Bureau's scientific and technical activities. Handbooks—Recommended codes of engineering and

industrial practice (including safety codes) developed

in cooperation with interested industries, professional

organizations, and regulatory bodies. Special Publications—Include proceedings of high-level national and international conferences sponsored by

NBS, precision measurement and calibration volumes,

NBS annual reports, and other special publications

appropriate to this grouping such as wall charts and

bibliographies.

Applied Mathematics Series—Mathematical tables, manuals, and studies of special interest to physicists, engineers, chemists, biologists, mathematicians, computer programmers, and others engaged in scientific and technical work.

National Standard Reference Data Series—Provides

quantitative data on the physical and chemical properties of materials, compiled from the world's literature and critically evaluated. Developed under a world-wide program coordinated by NBS. Program under authority

of National Standard "Data Act (Public Law 90-396). See also Section 1.2.3.

Building Science Series—Disseminates technical infor- mation developed at the Bureau on building materials, components, systems, and whole structures. The series presents research results, test methods, and performance criteria related to the structural and environmental functions and the durability and safety characteristics of building elements and systems. Technical Notes—Studies or reports which are complete

in themselves but restrictive in their treatment of a

subject. Analogous to monographs but not so comprehensive in scope or definitive in treatment of the subject area. Often serve as a vehicle for final reports of work performed at NBS under the sponsorship of other government agencies.

Voluntary Product Standards—Developed under pro- cedures published by the Department of Commerce in Part 10, Title 15, of the Code of Federal Regulations.

The purpose of the standards is to establish nationally

recognized requirements for products, and to provide

all concerned interests with a basis for common under- standing of the characteristics of the products. The

National Bureau of Standards administers the Voluntary Product Standards program as a supplement to the activities of the private sector standardizing

organizations. Federal Information Processing Standards Publications (FIPS PUBS) —Publications in this series collectively constitute the Federal Information Processing Standards Register. The purpose of the Register is to serve

as the official source of information in the Federal Gov- ernment regarding standards issued by NBS pursuant

to the Federal Property and Administrative Services Act of 1949 as amended. Public Law 89-306 (79 Stat. 1127), and as implemented by Executive Order 11717

(38 FR 12316, dated May 11, 1973) and Part 6 of Title 15 CFR (Code 6f Federal Regulations). FIPS PUBS

will include approved Federal information processing standards information of general interest, and a complete index of relevant standards publications. Consumer Information Series—Practical information, based on NBS research and experience, covering areas

of interest to the consumer. Easily understandable language and illustrations provide useful background

knowledge for shopping in today's technological

marketplace.

NBS Interagency Reports—A special series of interim

or final reports on work performed by NBS for outside sponsors (both government and non-government). In general, initial distribution is handled by the sponsor;

public distribution is by the National Technical Infor- mation Service (Springfield, Va. 22151) in paper copy

or microfiche form. Order NBS publications (except Bibliographic Subscription Services) from: Superintendent of Documents, Government Printing Office, Washington, D.C. 20402. BIBLIOGRAPHIC SUBSCRIPTION SERVICES

The following current-awareness and literature-survey

bibliographies are issued periodically by the Bureau:

Cryogenic Data Center Current Awareness Service

(Publications and Reports of Interest in. Cryogenics).

A literature survey issued weekly. Annual subscription: Domestic, $20.00; foreign, $25.00. Liquefied Natural Gas. A literature survey issued quarterly. Annual subscription: $20.00. Superconducting Devices and Materials. A literature survey issued quarterly. Annual subscription: $20.00. Send subscription orders and remittances for the preceding bibliographic services to the U.S. Department

of Commerce, National Technical Information Ser\'-

ice, Springfield, Va. 22151. Electromagnetic Metrology Current Awareness Service (Abstracts of Selected Articles on Measurement

Techniques and Standards of Electromagnetic Quantities from D-C to Millimeter-Wave Frequencies).

Issued monthly. Annual subscription: $100.00 (Special rates for multi-subscriptions). Send subscription order and remittance to the Electromagnetic Metrol- ogy Information Center, Electromagnetics Division, National Bureau of Standards, Boulder, Colo. 80302.
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