NIST Technical Note 1908 

The Use of Demand-to-Capacity 

Indexes for the Iterative Design of 

Rigid Structures for Wind 

Filmon Habte 

Arindam Gan Chowdhury 

Sejun Park 

This publication is available free of charge from:

http://dx.doi.org/10.6028/NIST.TN.1908
NIST Technical Note 1908 

The Use of Demand-to-Capacity 

Indexes for the Iterative Design of 

Rigid Structures for Wind 

Filmon Habte

Arindam Gan Chowdhury 

Department of Civil and Environmental Engineering 

Florida International University, Miami, Florida 

Sejun Park 

Engineering Laboratory 

National Institute of Standards and Technology 

Gaithersburg, MD 20899-7311

This publication is available free of charge from: 

http://dx.doi.org/10.6028/NIST.TN.1908 

February 2016 

U.S. Department of Commerce 

Penny Pritzker, Secretary

National Institute of Standards and Technology 

Willie May, Under Secretary of Commerce for Standards and Technology and Director
Certain commercial entities, equipment, or materials may be identified in this 

 document in order to describe an experimental procedure or concept adequately. 

Such identification is not intended to imply recommendation or endorsement by the 

National Institute of Standards and Technology, nor is it intended to imply that the 

entities, materials, or equipment are necessarily the best available for the purpose. 

National Institute of Standards and Technology Technical Note 1908 

Natl. Inst. Stand. Technol. Tech. Note 1908, 35 pages (February 2016) 

CODEN: NTNOEF 

This publication is available free of charge from: 

http://dx.doi.org/10.6028/NIST.TN.1908
Disclaimers 

(1) The policy of the NIST is to use the International System of Units in its technical

communications. In this document however, works of authors outside NIST are cited which 

describe measurements in certain non-SI units. Thus, it is more practical to include the non-SI 

unit measurements from these references. 

(2) Certain trade names or company products or procedures may be mentioned in the text to

specify adequately the experimental procedure or equipment used. In no case does such 

identification imply recommendation or endorsement by the National Institute of Standards and 

Technology, nor does it imply that the products or procedures are the best available for the 

purpose. 
iii

Abstract 

Estimates of wind effects on rigid buildings by database-assisted design (DAD) methods can be 

more accurate than those based on information available in standards. An upgraded version of 

DAD was developed that streamlines the wind engineering/structural engineering components of 

the design process by allowing the direct computation of Demand-to-Capacity Indexes (DCIs). 

Although the basic procedure described in this report is applicable to any rigid building, the 

focus in this work is on simple buildings with gable roofs, portal frames, and bracing parallel to 

the ridge. The procedure makes use of the two largest building aerodynamics databases available 

worldwide; large simulated extreme wind databases for hurricane- and non-hurricane-prone 

regions; a novel interpolation scheme allowing the design of buildings with dimensions not 

covered in the databases; an effective multiple-points-in-time algorithm for estimating peaks; 

and parameter-free methods for estimating DCIs with specified mean recurrence intervals. In 

addition to a brief description of the procedure, the report contains the following link to the 

software developed for the implementation of the procedure: 

www.nist.gov/wind/DADmetalportalframes. A user’s manual for the software is also included in 

this report. 

Keywords: Aerodynamics; database-assisted design; demand-to-capacity indexes; parameterfree statistics; structural engineering; wind climatology; wind engineering. 
iv

Acknowledgment 

Contributions to this report by D. Yeo, helpful comments and assistance by Joseph A. Main, E. 

Simiu, and N. A. Heckert, and careful review by Prof. Yongwook Kim of the Manhattan College 

are acknowledged with thanks. Filmon Habte gratefully acknowledges the scholarship support 

provided by the Presidential Fellowship (Florida International University, Graduate School). 

Sejun Park served as a Guest Researcher at the Engineering Laboratory of the National Institute 

of Standards and Technology; on leave from the School of Civil and Environmental Engineering, 

Yonsei University, Seoul, South Korea. 
v

Contents 

Abstract.. ....................................................................................................................................... iii

Acknowledgment.......................................................................................................................... iv

Contents.........................................................................................................................................v

List of Figures...............................................................................................................................vi

List of Tables...............................................................................................................................vii

1. Description of the Iterative Design Procedure

- Filmon Habte and Arindam Gan Chowdhury

 1.1. Introduction ........................................................................................................................... 1

 1.2. Description of the Structural System .................................................................................... 2

 1.3. Overview of the Design Procedure ....................................................................................... 3

 1.4. Aerodynamic and Wind Climatological Databases .............................................................. 5

 1.5. Internal Forces and Deflections Induced By Wind with Unit Speed at Eave Height ........... 5

 1.6. DCI Databases ...................................................................................................................... 7

 1.7. Estimation of Peak DCIs and Deflections with Specified MRIs. ......................................... 8

 1.8. Interpolation Procedures ....................................................................................................... 9

 Conclusions ................................................................................................................................ 11

 References .................................................................................................................................. 12

2. USER’S MANUAL

- Filmon Habte and Sejun Park

 2.1. Description of the Graphical User Interface (GUI) ............................................................ 13

 2.2. Building Input File .............................................................................................................. 23

 2.3. Design Output File .............................................................................................................. 24

 2.4. Design Example .................................................................................................................. 26

APPENDIX .................................................................................................................................. 30
vi

List of Figures 

Figure 1. Structural System............................................................................................................. 3

Figure 2: DCI database ................................................................................................................... 8

Figure 3: Frame Design Menu Page ............................................................................................. 13

Figure 4: Enter Building Information ........................................................................................... 14

Figure 5: Input Building Dimensions ........................................................................................... 14

Figure 6: Input Terrain Conditions ............................................................................................... 15

Figure 7: Input Frame Locations................................................................................................... 15

Figure 8: Definition of Frame Locations ...................................................................................... 15

Figure 9: Input Attachment Locations .......................................................................................... 16

Figure 10: Input Frame Supports .................................................................................................. 16

Figure 11: Input Frame Design Parameters .................................................................................. 16

Figure 12: Input Cross-Section Design Parameters ...................................................................... 17

Figure 13: Input Gravity Loads ..................................................................................................... 17

Figure 14: Computation of Time-histories of Responses GUI ..................................................... 19

Figure 15: Select Response Computation Options ....................................................................... 19

Figure 16: Input Sampling Rate Reduction .................................................................................. 19

Figure 17: Output of Time-series of Responses ........................................................................... 20

Figure 18: Design of Frames GUI ................................................................................................ 21

Figure 19: Designed Frame Sections ............................................................................................ 22

Figure 20: Sample Building Input File ......................................................................................... 23

Figure 21: Definition of Attachment Locations ............................................................................ 24

Figure 22: Sample Design Output File ......................................................................................... 25

Figure 23: Definition of Sections in the Design Output File ........................................................ 26
vii

List of Tables 

Table 1: Enter Building Information ............................................................................................. 27

Table 2: Input Design Parameters ................................................................................................. 27

Table 3: Input Gravity Loads ........................................................................................................ 28

Table 4: Output of Designed Frame Sections ............................................................................... 29

Table A1: Variables of the bldg_struct Data-structure ................................................................. 30

Table A2: Variables of TIF_struct Data-structure ........................................................................ 33

Table A3: Variables of the DCI_struct Data-structure ................................................................. 34
1 

1. Description of the Iterative Design Procedure

Filmon Habte and Arindam Gan Chowdhury

1.1 Introduction 

Conventional methods for determining wind loads on main wind force resisting systems 

(MWFRS) of rigid buildings involve the use of tables and plots provided in standards and codes 

(e.g., the Standard on Minimum Design Loads for Buildings and Other Structures [1]). The wind 

loads determined by such methods can differ from wind loads consistent with laboratory 

measurements by amounts found in some cases to exceed 50 % [2]. 

Increased computational power and major advances in pressure measurement capabilities 

led to the development of the database-assisted design (DAD) concept. DAD makes direct use of 

stored pressure time series to calculate wind loads [3]. One of DAD’s useful features is that it 

allows wind effect combinations to be performed objectively via simple algebraic time series 

summations. For example, internal forces in structural members are in general induced by wind 

loads that act in the directions of the two principal axes of the structure, x and y, and are 

therefore imperfectly correlated. Also, cross sections of the MWFRS are simultaneously acted 

upon by bending moments and axial forces that, typically, are also imperfectly correlated. The 

capability to perform rigorously correct combinations of wind effects distinguishes time-domain 

from frequency-domain techniques since, as typically used in wind engineering, the latter do not 

preserve phase relationships and therefore force designers to combine wind effects subjectively. 

The application of the DAD approach to rigid structures has so far been developed primarily 

for frames of simple gable roof buildings [4]. A main purpose of the procedure presented in this 

report is to expand the capabilities of previous work by using time series of Demand-to-Capacity 

Indexes (DCIs, i.e., left-hand sides of the design interaction equation), for structural design 

purposes. As shown in subsequent sections, this eliminates or reduces inaccuracies in the 

representation of wind effects and can result in more effective designs. In spite of its focus on 

frames of simple gable roof buildings, the procedure can, with modest modifications, be adapted 

for use for any rigid buildings, including mid-rise buildings. 

The procedure enables the use of the large, recently developed Tokyo Polytechnic 

University (TPU) database (http://wind.arch.t-kougei.ac.jp/system/eng/contents/code/tpu), which 

was shown in [5] to result in response estimates comparable to those based on the National 

Institute of Standards and Technology (NIST)/University of Western Ontario (UWO) database 

(http://fris2.nist.gov/winddata). This largely eliminates what, according to the Commentary to 

the ASCE 7-10 Standard, is an important obstacle to the wide use of DAD-based approach in 

engineering practice: the fact that the NIST/UWO database is not sufficiently comprehensive. In 

addition, an updated interpolation routine is included in the procedure, which makes it possible 

to apply the DAD approach to buildings with dimensions and/or roof slopes different from those 

covered in those databases. 
2

Checking the adequacy of the cross section’s design consists of ascertaining that, subject to 

possible serviceability constraints, its DCI is close to and less than unity. If the DCI of a cross 

section does not satisfy this condition, the cross section must be redesigned. The structural 

member properties based on this iteration process may then be used to recalculate the requisite 

influence coefficients and perform checks based on those recalculated values. 

Since different expressions for the DCI apply for different axial loads [see Equation (1)], the 

DCIs depend nonlinearly upon axial load. Therefore, the peak DCIs are not proportional to the 

squares of the wind speeds inducing them. Therefore, for the structure being designed, it is 

necessary to calculate sets of DCIs induced by winds with a sufficient number of directions and 

speeds by accounting for Equation (1). Those sets are referred to as DCI databases. The 

calculations of peak DCI databases use an economical multiple-points-in-time method developed 

in [6]. 

The peak DCI databases are the structure’s responses under wind and gravity loading that 

depend upon the structural system’s configuration, member sizes, and terrain exposure, and are 

independent of the wind climate. The databases are used to estimate peak DCIs with any 

specified mean recurrence intervals (MRIs) by using non-parametric statistics. Since the design 

MRIs specified in [1] are of the order of hundreds or thousands of years, the use of such statistics 

requires that the directional wind speed database be commensurately large. With a view to 

expanding the usefulness of the DAD approach to structural designers, a procedure for 

developing large extratropical wind speed databases was developed by Yeo [7], thus eliminating 

an earlier restriction of wind climatological databases to hurricane data.

The software for the implementation of the procedure is available at

http://www.itl.nit.gov/div898/winds/iterative_design/wind_pressure.htm and 

http://www.nist.gov/el.

1.2 Description of the Structural System

The MWFRS being considered consists of equally spaced moment-resisting steel portal 

frames (with compact flange and web elements) spanning the width of the building (Figure 1). 

Portal frames are the most commonly used structural forms in low-rise industrial buildings, and 

are typically designed using web-tapered members. Roof and wall panels form the exterior 

envelope of the buildings, and are attached to purlins and girts supported by the frames. 
3

Figure 1. Structural System 

The DAD procedure is based on the following assumptions: (1) bracing is provided in the 

planes of the exterior walls parallel to the ridge, hence responses to loads in that direction are not 

considered, (2) the coupling between frames due to the roof diaphragms is neglected, (3) the 

purlins and girts are attached to the frames by hinges, (4) the purlins and girts act as bracings to 

the outer flanges, and the inner flanges are also braced. The following limitations are imposed: 

(1) The taper should be linear or piecewise linear, and (2) the taper slope should typically not 

exceed 15o[8].

1.3 Overview of the Design Procedure

The sizing of the structural members is accomplished via the calculation of their DCIs. The 

final design is achieved when the member DCIs are less than and as close as possible to unity, to 

within specified serviceability and constructability constraints. The calculation of the DCIs 

makes use of the procedures for determining member capacities specified in the American 

Institute of Steel Construction Manual [9] and Steel Design Guide 25: Frame Design Using WebTapered Members [8]. Preliminary investigation of the stability of the frame members showed 

that secondary moments have typically negligible effects on the type of structure being 

considered. However, in order to comply with the AISC’s design for stability requirements, a 

first order analysis method of design was followed. This method, which accounts for geometric 

imperfections, requires that the total member moments be multiplied by an amplifier B1, and that 
4

lateral notional loads be applied in every loading combination. A brief explanation on how the 

first order analysis method was applied is provided in the Appendix. The frame members’ elastic 

in-plane buckling capacity, which is required for computing the axial capacity of the frame 

cross-sections, Pij, where the subscripts i and j identify the frame and the cross section, 

respectively, is computed using the method of successive approximations as described in 

Timoshenko and Gere [10]. The in-plane and out-of-plane buckling capacities were compared 

and the critical ones were selected for calculating the axial capacity of the frame cross sections.

For a given member cross section of a frame subjected to wind loading the DCI is a function 

of the internal forces. Each internal force is in turn a sum of contributions due to gravity loads 

and to wind forces acting along the building’s principal axes. In the particular case of the type of 

structure addressed here the wind forces acting along the axis parallel to the ridge are resisted by 

secondary bracing members; hence the wind force contributions to the DCIs are due only to 

forces normal to the building’s ridge. Time series of DCIs pertaining to axial forces and bending 

moments at cross section j of frame i, denoted by DCIij

PM (t), have the expressions

0.2:

ij P

(t) ij Pr



 























 

X

b

Mij

(t) X

ij M r

ij P

(t) ij Pr

(t) PM

ij DCI

 

9

8

(1)

0.2:

ij P

(t) ij Pr



 























 

X

b

Mij

t

X

ij M r

ij P

t

ij Pr

t

PM

ij DCI

 

( )

2

( )

( )

where Prij(t) and Mrij

X

(t) are time histories of total axial load and in-plane bending moment 

respectively; Pij and Mij are the nominal axial and in-plane flexural strengths of the crosssection;



and 

b



are axial and flexural resistance factors, respectively. The demand-to-capacity 

index for shear forces, DCIij

V (t) at cross section j of frame i is computed as follows

ij Sv

(t) ij Sr

(t) DCIij

V



 (2)

where Srij (t) denotes the time history of the total shear load, Sij is the nominal shear strength of 

cross-section j of frame i, and 

v

is the resistance factor for shear forces. The force time histories 

in Eqs. (1) and (2) are computed as sums of factored load effects due to gravity (which are 

assumed to be constant in time) and wind loads (which are time-varying). Equations (1) maintain 

the phase relationship between the different load effects (i.e., axial and bending moments), hence 

they produce DCIs rigorously commensurate with the actual combined wind effects. 

The preliminary design must start with an informed guess as to the MWFRS’s member sizes 

(i.e., with a preliminary design denoted by Des0), to which there corresponds a set of influence 

coefficients denoted by IC0. The wind loads applied to this preliminary design are taken from the 
5

standard or code being used. In the case of portal frames on which this paper is focused, the 

ASCE 7-10 Standard wind loads can be taken from the Standard’s Chapter 27 or Chapter 28.

The next step is the calculation of the DCIs inherent in the design Des0. The cross sections 

are then modified so that their DCIs are close to unity. This results in a new design, Des1, for 

which the corresponding set of influence coefficients, IC1, and a new set of DCIs are calculated. 

The procedure is repeated until a design Desn is achieved such that the effect of using a new set 

of influence coefficients, ICn+1, is negligible, that is, until the design Desn+1 is in practice 

identical to the design Desn. Next, the procedure is repeated by using, instead of the Standard 

wind loads, the loads based on the time histories of the pressure coefficients taken from the 

aerodynamics database. This results in a design Desn+2, to which there corresponds a set of 

influence coefficients ICn+2 and a new set of DCIs. The cross sections are then modified so that 

the DCIs are close to and less than unity. Typically this will be the final design Desfinal, although 

the user may perform an additional iteration to check that convergence of the DCIs to unity has 

been achieved, to within constructability and serviceability constraints. 

1.4 Aerodynamic and Wind Climatological Databases 

Aerodynamic databases provide the spatio-temporal distribution of wind pressures on 

building surfaces for various wind directions and terrain conditions. They are typically obtained 

from pressures measured in wind tunnels at large numbers of ports on the external and/or internal 

surface of building models. As mentioned earlier, the aerodynamic databases used here are: (1) 

the NIST/UWO database (http://fris2.nist.gov/winddata/), and (2) the Tokyo Polytechnic 

University (TPU) aerodynamics database (http://wind.arch.tkougei.ac.jp/system/eng/contents/code/tpu). To the authors’ knowledge, these are currently the 

two largest public aerodynamic databases. 

Climatological databases typically consist of matrices of recorded or simulated extreme 

wind speeds versus their directions for different locations of interest. The climatological database 

used in this work consisted of estimates of largest hurricane wind speeds generated in [11] using 

Monte Carlo simulations for 16 wind directions and 999 storm events simulated for a large 

number of locations along the Gulf of Mexico and North Atlantic coast 

(http://www.nist.gov/wind). For regions not prone to hurricanes large directional climatological 

databases required for the estimation of wind effects with 300-yr to 3,000-yr MRIs can be 

simulated from available directional wind speed data available on the same site, as shown in [7].

1.5 Internal Forces and Deflections Induced By Wind with Unit Speed at Eave Height

The assumptions and procedures followed in transferring wind loading from pressure taps 

on the exterior building surfaces to structural frames are similar to those used in [4], which 
6

contains detailed descriptions and explanations. The time series of the wind-induced internal 

forces r

w

ij (t,θ) at cross section j of frame i, due to a unit wind speed with direction θ at eave 

height H, is

)

1

2

( ,) 1  C (t,

k

p

k Ai

n

k

t N

w

ij r

k  ij



 (3)

where ρ is air density; N

k

ij is the influence coefficient representing the internal force at cross 

section j of frame i, due to a unit force applied at the k-th point of attachment of a purlin or girt to 

the frame i; and A

k

represents the tributary area of the k-th point; C

k

P(t,θ) is the pressure 

coefficient applicable at the k-th attachment point, associated with a wind speed with direction θ

at height H, calculated as the weighted average of pressure coefficients at taps located inside the 

area A

k

; and n is the number attachment points on frame i. 

For rigid structures, the wind-induced internal forces are proportional to the square of the 

wind speeds. Therefore, the time-series of total internal forces due to gravity and wind loads 

induced by wind with velocity VH,θ from direction θ at height H are

2

,

( , ) ( , )



  H

t V

w

ij r w

f

g

ij r g

t f

ij R   (4)

where r

g

ij is the internal force at cross-section j in frame i due to gravity loads; and fg and fw are 

load combination factors for gravity and wind loads, respectively. Rij (t,θ) represents any of the 

forces in the numerators of Eq. (1) and (2).

Strength design requires considering the following five LRFD load combination cases [1]:

Case 1: 1.4D, 

Case 2: 1.2D + 0.5Lr,

Case 3: 1.2D + 1.6Lr + 0.5W, 

Case 4: 1.2D + 1.0W +0.5Lr, 

Case 5: 0.9D + 1.0W, 

where D, Lr, and W denote dead load, roof live load and wind load, respectively. The dead load 

includes both superimposed dead load and frame self-weight. The superimposed dead load and 

roof live load are assumed to be uniformly distributed on the roof surface; they impose forces on 

the frame through the frame-purlin connections in the vertical downward direction. Self-weights 

are determined by dividing the frames into large number of elements.

Once time histories of total individual internal forces are determined, the estimation of 

combined internal forces associated with the axial forces and bending moments required for DCI 

calculations is performed using the multiple points-in-time (MPIT) approach for estimating peak 

wind effects [6]. In this approach the largest n local peaks (in absolute value) from the time 
7

series of each force or moment are selected first. Next the ordinates at the times of occurrence of 

those n peaks are selected in each of the m – 1 time series to be combined with that force or 

moment, where m is the total number of time series being combined. The combination of internal 

forces is then performed only for the m x n points so selected, rather than for the whole length of 

the time series. The estimated peak of the combined effects is then computed as the largest of the 

m x n combinations. This method significantly reduces the amount of computation required. 

Comparisons of DCIs computed using the entire time-histories of axial and bending moments to 

those calculated using the MPIT method with n = 20 showed that the MPIT approach produces 

highly accurate results [6].

Deflections can be calculated using Eq. 3 in which N

k

ij denotes the influence coefficient 

representing the deflection at cross section j of frame i, due to a unit force applied at the k-th 

point of attachment of a purlin or girt to the frame i.

1.6 DCI Databases

DCI databases are properties of the structure that incorporate its aerodynamic and 

mechanical characteristics at all cross sections of interest, and are independent of the wind 

climate. For rigid structures a DCI database for a member cross section consists of peak DCIs 

corresponding, for each of the incremental wind directions considered, to incremental wind 

speeds within a range that encompasses all speeds of interest. Note that, for member cross 

sections in compression, the DCI induced by a wind speed V is not proportional to the square of 

that wind speed. This is due to the dependence of the axial load capacity Pij upon the buckling 

effects associated with the applied axial load. 

DCI databases are calculated for specified cross sections of all members being designed for 

all the loading combination cases being considered. Loading combinations 1 and 2 include dead 

and live loads only, hence response databases need not be prepared for those combinations. 

However, for each of the remaining loading combinations two sets of response databases are 

computed, one for positive and one for negative internal pressures. Effects of wind-induced 

positive and negative internal pressures are computed using internal pressure coefficients 

specified by the ASCE 7-10 for enclosed, partially enclosed, or open buildings. 

Figure 2 shows the DCI database associated with the axial force and bending moment acting 

on the pinch cross section of the first interior frame in a building with the following dimensions: 

width B = 24.4 m (80 ft), length L = 38.1 m (125 ft), eave height H = 7.3 m (24 ft), roof slope = 

4.8 deg. Frame spacing of 7.62 m (25 ft) was used and the DCI database plot shown is for 

loading combination 0.9D + 1.0W.
8

Figure 2: DCI database

1.7 Estimation of Peak DCIs and Deflections with Specified MRIs. 

Peak DCIs with specified MRIs are obtained by combining the DCI response databases with 

the directional wind speeds of the wind climatological database. The response database provides 

DCI values for all wind directions and wind speeds being considered at discrete increments, e.g., 

15° and 6 m/s (19.7 ft/s). 

The climatological database consists of (i) a p x q matrix (p rows and q columns) of largest 

directional wind speeds Vsθ (the index s = 1, 2... p denotes the storm event and the index θ = 1, 

2... q, e.g., q = 16, denotes the wind direction), and (ii) the mean annual rate of storm occurrence 

λ. It is recommended that, for the precision of the estimates to be acceptable, the number of 

storm events being simulated be p > 3Nλ, where N is the MRI of interest in years [7].

For buildings with known orientation the estimation of the peak DCI with an N-year MRI 

proceeds as follows. In the matrix [Vsθ] each wind velocity Vsθ is replaced by the demand-tocapacity index DCIsθ, corresponding for that cross section to that wind velocity. In the matrix so 

obtained all but the entries maxθ[DCIsθ] are disregarded, since only the largest of the DCIs 

induced in that cross section in any one storm is of interest in design. The vector maxθ[DCIsθ] (s 

= 1, 2, ..., p) so obtained is then rank-ordered. The MRI N of the DCI with rank r is N = (p + 

1)/(r λ) ([12], p. 157-158). The procedure just described accounts for wind directionality effects 

directly, without the intervention of a wind directionality factor, and it yields a physically correct 

estimation of the pressures or forces with an N-year MRI [13]. 

For buildings with unknown orientation the procedure described for the case of buildings 

with known orientation is modified by replacing the wind speeds Vsθ in each row s of the matrix 

[Vsθ] by the largest wind speed regardless of direction, maxθ[Vsθ]. The DCI with an N-year MRI 

obtained following this modification is then multiplied by the directionality reduction factor Kd, 

specified in ASCE 7-10 to be 0.85. This procedure was used in the present work. 
9

The estimation of deflections with specified MRI that account for directionality is performed 

in a manner similar to that described for DCIs. 

1.8 Interpolation Procedures

For DAD to be of practical use, simple and reliable interpolation schemes have to be 

developed that enable the prediction of wind responses for building dimensions intermediate 

between those covered in the available database. Several researchers ([14], [15], [16], [17], [18], 

[19]) have addressed this issue.

Using Reynolds turbulence decomposition, a model was developed in [15] that can 

interpolate between time-series of pressure coefficients Cp,est(t) (Eq. 5). The mean pressure 

coefficients C̅p,est for the building of interest are predicted first. Next, the fluctuations are 

obtained by correcting a reference time series of pressures fluctuations C’p,est (t) via 

multiplication by the ratio of predicted root mean square (RMS) values C͂

p,est to reference RMS

values C͂

p,ref:

p ref C

p est C

t

p ref C p est t C p est C

,

~

,

~

( )

,

'

,

( )

,

 

(5)

In [15] artificial neural network (ANN) models were used which were trained to recognize 

functional relationships between building geometry and flow conditions and pressure coefficients 

to predict mean and RMS values of pressure coefficients for the building of interest. Any other 

method that can accurately predict the mean and RMS of pressure coefficients for the structure 

of interest can also be used.

A procedure was developed in [17] that can, with acceptable accuracy, determine structural 

responses induced by unit wind speeds at eave height from various directions (i.e., Directional 

Influence Factors, or DIFs) in a building with dimensions {dj} not available in the aerodynamic 

database. This is done by interpolation between responses of two or more building models with 

dimensions {dj + Δj

+

} and {dj – Δj

-

}, where Δj

+ ≠ 0 and Δj- ≠ 0 for at least one of the dimensions 

dj. In this procedure, dimensions defining locations of the pressure taps on the models with 

different dimensions (i.e. the dimensions used in the interpolation) are first scaled to match the 

dimensions of the building of interest. They are then used in conjunction with influence 

coefficients of responses computed for building of interest to calculate DIFs with dimensional 

deviations, denoted by . Finally, estimates of the DIFs for the building of interest are 

obtained as weighted averages of the s. The method, explained in [17], produces satisfactory 

results and is relatively simple because interpolation is performed between peaks of structural 

responses instead of pressure coefficients. In an updated version of the procedure developed in 

[17], peak DCIs are calculated for the reference buildings for a sufficient number of wind speeds 

DIF DIF
10

and wind directions. The requisite interpolations are then effected by making use of those peak 

DCIs. 

Based on the approaches used in [15] and [17], a modified interpolation scheme was 

developed. This new interpolation scheme is used to produce time-histories of responses for the 

building of interest from two or more aerodynamic models with different dimensions, and has 

the following three steps:

1. Two or more time histories of structural responses are evaluated by (a) scaling 

dimensions that define the locations of pressure taps in the building models with different 

dimensions to match the dimensions of the structure of interest and (b) using influence 

coefficients obtained for the building of interest. The time histories of responses 

computed using pressures from the model with the least dimensional deviation from the 

building of interest are named the reference response rref (t).

 The mean r̅est and RMS r͂est of the responses for the structure of interest are evaluated as 

weighted averages of the mean and RMS of the response time histories calculated in step 

1, as shown in Eqs. (6).

i

r

i

d

r

b

i

est 







1



,

i

r

i

d

r

b

i

est

~ ~

1











 (6a, 6b)

where

1

1

1































b

i i

d



with

di  di  d0

;

T

R W

i Wi

R

H W

i Wi

H

L W

i Wi

L

W

Wi

di



















0 0 0 0 0 0 0

r̅i and r͂i are mean and RMS of responses computed for building model i used in the

interpolation; di and d0 are normalized vectors of building dimensions of building model i

and the building of interest respectively; b is the total number of building models used for 

interpolation; ||.|| denotes norm operator; and W, L, H, and R represent building width, 

length, height, and roof rise, respectively. It can be seen that more weight is given to the 

models with the least dimensional deviation from the building of interest.

2. Finally, the r̅est and r͂est evaluated in step 2 are used as follows:

ref r

est r

t

ref r

est t rest r

~

~

( )    ( )

(7)

to estimate the required time-series of responses, rest (t). In Eq. (7), fluctuations of the required 

time-series of responses are estimated by rescaling the fluctuations of a reference response r′ref (t) 

using ratios of r͂est to RMS of the reference response (r͂ref). The assumption that fluctuations of 

responses can be obtained by re-scaling from a reference response is reasonable as long as the 

aerodynamics does not change significantly over the range of interpolation.

The fluctuation of the reference response are computed using Eq. (8),
11

ref t r

est t r

ref r

 ( )  ( )  (8)

where rest(t) and r̅ref are the time history and mean of the reference response respectively.

1.9 Conclusions

An upgraded version of DAD was presented that streamlines the wind 

engineering/structural engineering components of the design process by allowing the direct 

computation of the design interaction equation’s left-hand side (i.e. of Demand-to-Capacity 

Indexes, or DCIs) for each of the MWFRS’s cross sections of interest. This computation 

rigorously combines imperfectly correlated time series of wind forces and effects (e.g., forces 

along each of the building’s principal axes; simultaneously acting axial forces and bending 

moments), thus eliminating errors due to subjective estimates of combined effects. While the 

basic approach presented is applicable to any rigid low- or mid-rise buildings, the focus in this 

paper is on simple buildings with gable roofs, portal frames, and bracing parallel to the ridge. In 

addition to the incorporation of DCI-based iterative structural design, useful features include: 

access to the two largest aerodynamics databases available worldwide; use of large simulated 

extreme wind databases for hurricane-prone and non-hurricane-prone regions; an interpolation 

scheme applied to time series, allowing the design of buildings with dimensions not available in 

databases; an effective multiple-points-in-time algorithm for estimating time series peaks; and 

parameter-free methods for estimating DCIs with specified mean recurrence intervals, applicable 

to buildings with known or unknown orientation. 
12

References

[1] ASCE 7-10. Minimum Design Loads for Building and Other Structures. American Society 

of Civil Engineers, Reston, VA; 2010.

[2] Coffman BF, Main JA, Duthinh D, Simiu E. Wind effects on low-rise metal buildings: 

Database-assisted design versus ASCE 7-05 standard estimates. J Struct Eng 2009;

136:744–8.

[3] Simiu E, Sadek F, Whalen TM, Jang S, Lu L-W, Diniz S, et al. Achieving safer and more 

economical buildings through database-assisted, reliability-based design for wind. J Wind 

Eng Ind Aerodyn 2003; 91:1587–611.

[4] Main JA, Fritz WP. Database-assisted design for wind: concepts, software, and examples 

for rigid and flexible buildings. National Institute of Standards and Technology, 

Technology Administration, US Department of Commerce; 2006.

[5] Hagos A, Habte F, Chowdhury AG, Yeo D. Comparisons of Two Wind Tunnel Pressure 

Databases and Partial Validation against Full-Scale Measurements. J Struct Eng 2014; 140.

[6] Yeo D. Multiple Points-In-Time Estimation of Peak Wind Effects on Structures. J Struct 

Eng 2013; 139:462–71.

[7] Yeo D. Generation of large directional wind speed data sets for estimation of wind effects 

with long return periods. J Struct Eng 2014; 140.

[8] Kaehler RC, White DW, Kim YD. Frame design using web-tapered members. American 

Institute of Steel Construction; 2011.

[9] ANSI/AISC. Specification for Structural Steel Buildings. Chicago, Illinois: American 

Institute of Steel Construction; 2010.

[10] Timoshenko S, Gere JM. Theory of elasticity stability. McGraw; 1961.

[11] Batts ME, Simiu E, Russell LR. Hurricane wind speeds in the United States. J Struct Div 

1980; 106:2001–16.

[12] Simiu E. Design of buildings for wind: a guide for ASCE 7-10 standard users and designers 

of special structures. 2nd Edition. Hoboken, New Jersey: John Wiley & Sons, Inc.; 2011.

[13] Habte F, Chowdhury AG, Yeo D, Simiu E. Wind Directionality Factors for Nonhurricane 

and Hurricane-Prone Regions. J Struct Eng 2014.

[14] Chen Y, Kopp GA, Surry D. Prediction of pressure coefficients on roofs of low buildings 

using artificial neural networks. J Wind Eng Ind Aerodyn 2003; 91:423–41.

[15] Chen Y, Kopp GA, Surry D. Interpolation of pressure time series in an aerodynamic 

database for low buildings. J Wind Eng Ind Aerodyn 2003; 91:737–65.

[16] Kopp GA, Chen Y. Database-assisted design of low-rise buildings: aerodynamic 

considerations for a practical interpolation scheme. J Struct Eng 2006; 132:909–17.

[17] Main JA. Interpolation procedures for database-assisted design. Proc 12th Int Conf Wind 

Eng., 2007, p. 1–6.

[18] Masters F, Gurley K, Kopp GA. Multivariate stochastic simulation of wind pressure over 

low-rise structures through linear model interpolation. J Wind Eng Ind Aerodyn 2010;

98:226–35.

[19] Gavalda X, Ferrer-Gener J, Kopp GA, Giralt F. Interpolation of pressure coefficients for 

low-rise buildings of different plan dimensions and roof slopes using artificial neural 

networks. J Wind Eng Ind Aerodyn 2011; 99:658–64.
13

2. User’s Manual

Filmon Habte and Sejun Park

2.1 Description of the Graphical User Interface (GUI)

Launching the windDESIGN software opens a Matlab based Graphical User Interface

(GUI) with the following three interfaces; (i) windDESIGN Menu, (ii) Computation of Time 

History of Responses, and (iii) Design of Frames.

Figure 3: Frame Design Menu Page
14

2.1.1 windDESIGN Menu

The windDESIGN Menu interface (Figure 3) includes the Software Description, Design 

Information and Aerodynamic Database panels. Within the Design Information panel an option 

to whether prepare new building input file or use existing building input file is provided. If the 

“Prepare New Building Input File” option is selected, an interface (Enter Building Information,

Figure 4) will appear that enables preparing a building input file and saving it as commaseparated values (.csv) file format in a user selected folder destination. All the variables required 

in a building input file can be provided through this interface. The building input file can be 

further modified once it has been created and saved. The Enter Building Information interface 

has the following buttons:

□ Input Building Dimensions. This button opens the Input Building Dimensions dialog box 

(Figure 5), wherein the dimensions of the building to be analyzed and number of frames to be 

designed can be defined.

Figure 4: Enter Building Information Figure 5: Input Building Dimensions
15

□ Input Terrain Condition. Roughness of the terrain surrounding the building can be specified 

in the dialog box shown in Figure 6. Two type of terrain roughness can be defined; 

“Open_Country” terrain which corresponds to a roughness length of z0 = 0.03 m (0.1 ft), and 

“Suburban” terrain which corresponds to a roughness length of z0 = 0.3 m (1 ft).

Figure 6: Input Terrain Conditions

□ Input Frame Locations. The along building-length location of each structural frame being 

designed is defined in the dialog box shown in Figure 7. For each frame of interest, its location 

and location of the neighboring frames are specified in the following manner; previous frame, 

frame of interest, subsequent frame as shown in Figure 8.

Figure 7: Input Frame Locations Figure 8: Definition of Frame Locations

□ Input Attachment Locations. The locations at which girts and purlins are attached to the 

frames are defined by specifying the spacing between purlins and between girts in the dialog box 
16

shown in Figure 9. The locations of girts and purlins can be further edited by accessing the 

building input file once it has been saved.

Figure 9: Input Attachment Locations

□ Input Frame Supports. Using the dialog box shown in Figure 10, the support conditions 

(either “pinned” or “fixed”) of the frames can be specified. 

Figure 10: Input Frame Supports

□ Input Steel Design Parameters. In this interface (Figure 11), the yield stress and modulus of 

elasticity of the steel material used are defined.

Figure 11: Input Frame Design Parameters
17

In the Design Information panel of the windDESIGN Menu interface, options for selecting 

and specifying; type of building enclosure (i.e. enclosed Cpi = +/- 0.18, partially enclosed Cpi = 

+/- 0.55, or open Cpi = 0), design parameters and gravity loads are also provided. Pressing the 

“Input Design Parameters” and “Input Gravity Loads” buttons open the dialog boxes shown in 

Figure 12 and Figure 13 respectively. In the dialog box shown in Figure 12, design wind speed 

(i.e. 3 sec gust wind speed at 33ft height according to the ASCE 7), section’s flange width, purlin 

or girt heights, section’s minimum web height, rafter division (i.e. ratio of RS 1 to Rafter length 

in Figure 23), maximum demand-to-capacity index (DCI), and preliminary arbitrary ratios of 

web heights are specified. The type of aerodynamic database to be used (i.e. NIST/UWO 

aerodynamic database or TPU aerodynamic database) is specified in the Aerodynamic Database

panel located at the bottom of the windDESIGN Menu interface.

Figure 12: Input Cross-Section Design 

Parameters

Figure 13: Input Gravity Loads
18

2.1.2 Computation of Time Histories of Responses

Pressing the “Time History of Responses” button at the bottom of the windDESIGN Menu

interface (Figure 3), will open the graphical interface shown in Figure 14. Within this interface;

In the Building Definition panel, users can select a building input file that includes 

dimensions of the building and details of the preliminarily designed members. The location of 

frames within the building, internally computed influence coefficients, and preliminary frame 

designs can be displayed graphically by pressing the Display button. Interpolation Sensitivity 

Factors (sensitivity of interpolated time-histories to different building dimensions) can also be 

adjusted. 

In the Pressure Databases panel, the folder containing the aerodynamic databases to be used 

in computing time-series of responses is selected. The contents of the selected folder will appear 

under the Open Terrain: and/or Suburban Terrain: listings, and the contents of an aerodynamic 

database can be displayed by pressing the Display button under the corresponding terrain. 

Calculation of time-histories of responses is commenced by pressing the Compute Responses

buttons. When the Compute Responses button is pressed, users can activate in the Select 

Response Computation Options dialog box (Figure 15) options for (i) extending building 

directions by exploiting building symmetry, and (ii) reduction of aerodynamic pressure data 

volume by specifying a sampling rate factor defined as a ratio of the original sampling rate to a 

new sampling rate (Figure 16). Once the time-history of responses calculation is completed, the 

user will be prompted to confirm the name and folder destination of the file to be saved.
19

Figure 14: Computation of Time-histories of Responses GUI

Figure 15: Select Response Computation Options Figure 16: Input Sampling Rate 

Reduction

Once the wind-induced time history of responses are computed and saved, the listing of 

available response files in the Time History of Responses panel will be updated. Note that the 

responses computed here are for a wind speed of 1 ft/s at building eave height and are saved in

.mat file format. The computed time histories of responses can be displayed graphically (Figure 
20

17) by pressing the Display button under each listing. The user interface shown in Figure 17 also 

enables saving the time-history of response being displayed in a .csv file format. If results of 

responses from previous calculations are being used, the Pressure Databases panel can be 

skipped by directly selecting the folder containing the time-history of response files/files in the 

Time History of Responses panel. The Select Response Computation Options dialog box (Figure 

15) can also be accessed using the Response Computation Options button in the Time History of 

Responses panel. In the time-history of responses listing, if more than one response output file is 

selected within one terrain, the interpolate button will be visible and interpolation of timehistories of responses can be performed.

Figure 17: Output of Time-series of Responses
21

2.1.3 Design of Frames

Pressing the Design Frames button at the bottom of the interfaces shown in Figure 3 and 

Figure 14 will open the Design of Frames interface (Figure 18). In this interface:

In the Building Definition panel, the building input file can be selected, and the preliminary 

frame design and the influence coefficients of each member can be displayed.

Figure 18: Design of Frames GUI

In the Wind Speeds and Design MRI panel, an option to whether use wind speed from the 

ASCE 7 maps, or climatological databases is provided. If the ASCE 7 option is selected, the 

wind speed specified in the Input cross-section design parameters dialog box (Figure 12) is used 

in design. If the Climatological Databases option is selected, the left side of the panel will be 

active, and the folder containing the wind speed databases, the site location of the building being 

designed, and mean recurrence interval (MRI) can be selected. An option to whether use 

Hurricane or non-Hurricane winds is also provided. The non-Hurricane wind databases contain 

simulated directional wind speeds, average yearly storm recurrence rate, and period of years 

covered, for both thunderstorm and non-thunderstorm types of storm events.
22

In the Design of Frame Members for Selected MRI panel, the time-history of responses to be 

used in design can be selected. Three design cases are available: (1) “Perform Design” with no

option, (2) “Perform Design” with the option of “Additional Design for Shear” option, and (3) 

“Perform Design” with the option of no iteration. The first case is for iterative design of 

members for axial loads and bending moments to obtain DCIPM less than but close to unity. The 

second case add to the first case the additional design of members for shear forces using DCI

V

. 

The final design case calculates without iterations the DCIPM and/or DCI

V

of preliminarily 

designed members provided by users. Once the design procedure is completed, the Designed 

Frame Sections interface shown in Figure 19 will appear. This interface displays the section 

dimensions as well as the DCIPM and DCI

V

results, and provides an option for saving the design 

results in a “.csv” file format.

Figure 19: Designed Frame Sections

After the first design process is completed, the “Re-Design Frames” button in the Design of

Frame Members for Selected MRI panel will be visible. If this button is pressed, the preliminary 

frame designs will be replaced by the new frame sections, new influence coefficients are 

calculated based on the new frame design, and the design process can be repeated again. 
23

2.2 Building Input File 

Building input files can be prepared manually or using the Enter Building Information

interface shown in Figure 4. Once all the required inputs in the Enter Building Information

interface are specified, pressing the Save Building Input File will create a .csv file format 

building input file (Figure 20). All the required keywords (keywords begin with asterisk) except 

*UNITS (which defines the basic units used in the building input file) can be specified through 

Enter Building Information interface. The default units used are ft, lb, and ft/s for length, force 

and wind speed, respectively. The attachment locations and/or other inputs can be further 

modified by accessing the building input file shown in Figure 20. The definition of girt and 

purlin attachments is shown in Figure 21.

Figure 20: Sample Building Input File
24

Figure 21: Definition of Attachment Locations

2.3 Design Output File 

The write design output button at the bottom of the Design Output interface ( Figure 19) 

enables saving the design results in a .csv format output file. The output file additionally 

provides the building information of the building input file, including Building Dimensions, 

Terrain, Frame Locations, and Column Supports. A sample output file is shown in Figure 22, and 

as in the building input file the keywords (key parameters) are indicated by an asterisk. 

*ENCLOUSRE. The type of building opening enclosure used is specified.

*FRAME_DESIGN_PARAMETERS. Here the following parameters which were used in 

performing the design calculations are specified; (i) ASCE 7 based design wind speed (3 sec 

gust at 33 ft.), which is used in the preliminary frame design, and also in performing final 

designs if selected by user, (ii) the minimum web height used in designing the cross-section, 

(iii) yield strength of the steel material, (iv) modulus of elasticity of the steel material, (v) 

flange width, (vi) purlin/girt height, (vii) dead load, (viii) roof live load (ix) rain load, and 

(x) maximum demand-to-capacity index (DCI) used in design.

*FRAME SECTIONS DESIGNED USING ASCE 7-10. Preliminary frame design is 

performed using wind loading from the ASCE 7-10 (Chapter 28). The preliminary section 

properties for 9 cross-sections (Figure 23) across each frame considered are provided under 

this heading. For each cross-section, the flange width and thickness, web height and 

thickness, section area, the strong (x-x) and weak (y-y) axes moment of inertias (I) and 

section modulus (S) are displayed.

*AERODYNAMIC DATABASE USED. The source of aerodynamic database used to 

calculate the time-histories of responses is specified. “National Institute Standards and 

Technology (NIST)” or “Tokyo Polytechnic University (TPU)” will be displayed depending 

on the public database used. 
25

*DESIGN WIND SPEED. Type of wind speed used in performing frame design calculation 

using the DAD method is specified. “Wind Speed from ASCE 7”, “Hurricane Wind 

Speeds”, or “Non-Hurricane Wind Speeds” will be displayed under this keyword depending 

on the type of winds speed used. 

Figure 22: Sample Design Output File
26

*FRAME SECTIONS DESIGNED USING Database-Assisted Design. The final frame 

design using Database-Assisted Design methodology is provided herein. Similar to the 

results of frame designs using ASCE 7-10, section dimensions of 9 cross-sections across 

each frame are given. The final design results also include the final demand-to-capacity 

indexes, DCIPM and DCIV. .

Figure 23: Definition of Sections in the Design Output File

2.4 Design Example

Consider a gable roofed industrial low-rise building. The building is 52.5 ft (16 m) in width 

(B), 78.7 ft (24 m) in length (L), 26.2 ft (8 m) in height (H), and has a roof slope of 14.0 deg (i.e. 

roof rise of 6.54 ft (2 m)). It has web-tapered moment-resisting frames spaced at 17.5 ft (5.33 m), 

and it is required to design the 2nd and 3rd frames. The building is assumed to be located in 

Miami, FL. Note that the software requires the following four main inputs (i) A building input 

file, (ii) design parameters and static loads, (iii) aerodynamic database (NIST or TPU database),

and (iv) climatological database and design wind speed. This design example section provides 

users with a step-by-step explanations of the inputs required for executing the windDESIGN 

program.

windDESIGN Menu page

In this example a new building input file is created. The interface for creating a new 

building input file can be displayed by selecting the “Prepare New Building Input File” option 

in the windDESIGN Menu page (Figure 3). The information shown in Table 1 is then entered. 

The SAVE BUILDING INPUT FILE button (Figure 4) creates an input building file named 
27

“BLDG W=52.5, L=78.7, H=26.2, R=6.6, Suburban.csv” for later use. Once the input building 

file has been saved, the “Use Existing Building Input File” option is selected. 

Table 1: Enter Building Information

Input Building 

Dimensions

Building Width, B (ft) : 52.50

Building Length, L (ft) : 78.70

Building Height, H (ft) : 26.2

Roof Rise, R (ft) : 6.56

Number of Frames to be designed : 2

Input Terrain Conditions : Suburban

Input Frame Locations :

0 17.5 35

17.5 35 52.5

Input Attachment 

Locations

Spacing between girts : 3

Spacing between purlins : 3

Input Frame 

Supports

Frame support – right column : Pinned

Frame support – left column : Pinned

Input Steel Design 

Properties

Yield Stress (ksi) : 50

Modulus of Elasticity (ksi) : 29000

The next step is to specify the building enclosure, design parameters and gravity loads. In 

this example the default building enclosure Enclosed is used, and the information shown in Table 

2 and Table 3 are entered into the Input Design Parameters and Input Gravity Loads dialog 

boxes respectively.

Table 2: Input Design Parameters

Design Wind Speed (ft/s) : 250

Flange Width (ft.) : 0.33

Purlin / Grit Height (ft.) : 0.70833

Minimum web height (ft.) : 0.67

Segment 2 – fractional length (0 to 1) : 0.4

Maximum DCI : 1

Preliminary Ratios Knee to Column Base : 3
28

of Web Heights Pinch to Column Base : 2

Ridge to Column Base : 3

Table 3: Input Gravity Loads

Superimposed Dead Load (psf) : 2

Roof Live Load (psf): 20

Rain Load (psf): 5

In the Aerodynamic Database panel of the windDESIGN Menu page, the TPU Aerodynamic 

Database option is selected. Recall that the NIST/UWO aerodynamic datasets are in .HDF file 

formats while the TPU aerodynamic files are in .mat file formats, the windDESIGN software can 

read both types of files but the appropriate database should be specified in the Aerodynamic 

Database panel.

Computation of Time histories of Responses page

In the Building Definition panel, the BLDG W=52.5, L=78.7, H=26.2, R=6.6, Suburban.csv

building file is selected. This step (i) reads the input building file, (ii) performs design of frames 

sections using wind load from the ASCE 7-10, Chapter 28 (those sections serve as the 

preliminary designs), and (iii) creates a data-structure named bldg_struct which contains building 

input information, design parameters, gravity loads, and preliminary section designs. The 

contents of data-structure bldg_struct are shown in Table A1. The preliminary section designs 

can be viewed by pressing the display button in the Building Definition panel.

A folder containing aerodynamic datasets for the building being designed is selected in the 

Pressure Databases panel. (For this example they can be downloaded from 

http://www.wind.arch.t-kougei.ac.jp/info_center/windpressure/grouplowrise/mainpage.html ).

In this example, time histories of responses are computed for wind directions of 270, 300, 

330 and 360 degrees (orientation of wind direction is shown in Figure 8). The “use symmetry to 

extend wind direction range” option is selected and the sampling rate factor of 2 is used for faster 

computation. Once the calculation is completed, a file named DIF W=52.5, L=78.7, H=26.2, 

R=6.6, Suburban.mat is created and saved. This file consists of a data-structure named 

TIF_struct which contains the computed time-histories of responses and other variables (Table 

A2). 

Design of Frames page
29

In this example hurricane wind speeds are used. The building is assumed to be located in 

Miami, FL (Milepost 1450) and design is performed for Mean Recurrence Interval (MRI) of 700 

years. In the Wind Speeds and Design MRI panel, the climatological databases option is 

selected, and milepost 1450 is selected after browsing to the folder containing the hurricane wind 

speed datasets.

In the Design of Frame Members for Selected MRI panel, the appropriate TIF file is selected

from “suburban” time history of responses listing, and the “Design for Shear” option is also 

selected. Pressing the “Perform Design” button commences the design calculations, and once the 

calculations are completed a data-structure with the designed frame sections and their DCI 

values named DCI_struct is created. The contents of DCI_struct are shown in Table A3.

The final results of section designs with their DCIs are shown in Table 4. The section 

numbers are shown in Figure 23, sections 6 to 9 are omitted from Table 4 because of frame 

symmetry.

Table 4: Output of Designed Frame Sections
30

APPENDIX A

In this appendix, descriptions of the variables existing in the bldg_struct, TIF_struct and 

DCI_struct data-structures are provided. (‘*’ denotes variable description and ‘–’ denotes values 

of the variable for the design example provided above).

Table A1: Variables of the bldg_struct Data-structure

d0 *a vector with the building’s geometric dimensions, [B, L, H, R] in ft.

- [52.5, 78.7, 26.2, 6.56]

Filename * the building input filename

- ‘BLDG W=52.5,L=78.7,H=26.2,R=6.6,Suburban.csv’

pathname * pathname of the building input file

- ‘C:\....’

length_units *length unit

- ‘ft’

force_units *force unit

- ‘lb’

ws_units

*wind speed unit

- ‘ft/s’

terrain * terrain surrounding the building being designed 

- ‘Suburban’

z0 *terrain roughness in feet

- 0.984

frame_coords

*Nf x 3 matrix describing the location of the frames being designed, (Nf 

represents number of frames being designed) 

- [

0 17.5 35

17.5 35 52.5

]

attach_points

*Na x 2 matrix describing the location of each purlin/girt on the frame, (Na 

represents number of attachments) - [face number, location along face]

- [

1 0

1 4.25

: :

]

column support *support system of the left and right columns

- [“pinned”, “pinned”]

frame_design_

parameters

*vector with the user specified design parameters and static loads 

- [design wind speed, minimum web height, yield strength, elasticity, flange 

width, purlin/girt height, dead load, roof live load, rain load, maximum DCI]
31

section_type

*the type of frame cross-section used

- ‘I-Section’

enclosure *the type of building enclosure

- ‘Enclosed’

frame_segments

*6 x 10 matrix of arbitrary pre-preliminary frame section dimensions. The 6 

rows represent the 6 frame segments shown in Figure A1, and the columns 

represent in order: face number, length ratio, flange width at segment start, 

flange thickness at segment start, web height at segment start, web height at 

segment end, web thickness at segment start, flange width at segment end, 

flange thickness at segment end, and web thickness at segment end.

Figure A1: Frame Faces and Segments

- frame_segments:

b2_max

*maximum B2 factor (note that B2 is a factor used to estimate the ratio of the 

second-order analysis drift to its first-order analysis counterpart)

- 1.0021

resp_names

* a vector with all the names of the frame responses 

- [Axial load at column base, Shear at column base, ...]

resp_units

* a vector with all the units of the responses specified in variable resp_names 

variable

- [lb., lb., lb.ft., lb., ...]

frame_resp

*a matrix specifying the location and numerical notation of each response (i.e. 

1-Axial, 2-Shear, and 3-moment). 

- [Face number, location along face, response numerical notation] 

ASCE_designs

* 3 x 10 x Nf, matrix of frame sections designed using wind load from ASCE 

7-10, chapter 28. Nf represents the number of frames designed. The rows 

represent segments 1 to 3 (Figure A1), and the column arrangement is similar 
32

to those used in the frame_segments variable.

- ASCE_designs: 

ASCE_dci

*3 x 3 x Nf, matrix of Demand-to-Capacity indexes (DCI) of the frame 

sections in the ASCE_designs variable. The rows represent the frame 

segments, and the columns represent in order: segment start, segment mid, and 

segment end.

- ASCE_dci:

ASCE_s_dci

*3 x 3 x Nf, matrix of Demand-to-Capacity Indexes for shear, (DCIV) of the 

sections in the ASCE_designs variable. The rows represent the frame 

segments, and the columns represent in order: segment start, segment mid, and 

segment end.

- ASCE_s_dci:
33

Besides variables; d0, resp_names, resp_units, length_units, force_units, ws_units, 

enclosure, terrain, frame_coords, and attach_pts which also exist in the bldg_struct datastructure, TIF_struct also includes the variables shown in Table A2.

Table A2: Variables of TIF_struct Data-structure

d

*a vector with the aerodynamic model’s geometric dimensions [B, L, H, R] in ft.

- [52.5, 78.7, 26.2, 6.6]

TIF_filena

me

*filename of the ‘.mat’ file containing the TIF_struct data structure

- ‘DIF W=52.5,L=78.7,H=26.2,R=6.6, Suburban.mat’

theta_all

*a vector specifying all the wind directions considered, in deg.

- [0; 30; 60; 90; 0; 330; 300; 270;...]

theta

*a vector specifying the unique wind directions considered (if building symmetry is 

not exploited theta would be equal to theta_all), in deg.

- [0; 30; 60; 90; 120; 150; 180; 210; 240; 270; 300; 330]

TS

*Nf x Nt matrix, where Nf represents the number of frames being designed and Nt 

represents the number of unique wind direction (i.e. from variable theta). Each 

element in matrix TS consists of time-histories of responses for a wind speed of 1ft/s 

at eave height. For instance TS [2, 3] consists of time-histories responses for the 

second frame at the third wind direction. 

In this example, TS is a 2 x 12 matrix, and TS [2, 3] consists of time-histories of 

responses for the second frame and wind direction of 60 deg.

TS_Dr *Similar in structure to variable TS, but each element in TS_Dr consists of timehistory of frame sway for a wind speed of 1ft/s at eave height

Pestory

*Nf x Nt matrix, each element in variable Pestory represents frame’s story critical 

buckling strength.

ws

*wind speed conversion factor, 

[hourly wind speed at eave height, 3sec gust at 10 m over open terrain]

- [1, 2.2719]
34

The DCI_struct data-structure contains the following variables; d0, d, resp_names, 

resp_units, length_units, force_units, ws_units, enclosure, terrain, z0, frame_coords, and 

attach_pts which also exist in data structures bldg_struct and/or TIF_struct it also includes the 

variables shown in Table A3.

Table A3: Variables of the DCI_struct Data-structure

Axial_TS

*Nf x Nt matrix, where Nf represent number of frames being designed and Nt 

represents number of wind direction (variable theta). Each element in matrix 

Axial_TS consists of time-history of axial responses at the start, mid, and end of 

frame segments 1 to 3 for a wind speed of 1ft/s at eave height. For instance 

Axial_TS [2, 3] consists of time-history of axial responses for the second frame 

at the third wind direction. 

- In this example, Axial_TS is a 2 x 12 matrix, and Axial_TS [2, 3] consists of 

time-history of axial responses for the second frame and wind direction of 60 

deg.

BM_TS

*similar in structure to variable Axial_TS but variable BM_TS consists of time 

histories of bending moments

Shear_TS

*similar in structure to variable Axial_TS but variable Shear_TS consists of 

time histories of shear load

V_H

*a vector or matrix containing wind speeds used in design 

- In this example, V_H is a 999 x 16 matrix of hurricane wind speeds from 

milepost 1450 (Miami, FL)

mu

*hurricane or storm recurrence rate. This variable is important when 

climatological databases are used 

- 0.56

orientations

*a vector consisting the building orientation considered, in deg.

- [0, 15, 30, ...]

MRI_list

*design mean recurrence interval (MRI), in years

- 700

fr_designed

* 3 x 10 x Nf, matrix of the final designed frame sections. The rows represent 

segments 1 to 3 (Figure A1), and the columns represent the parameters specified 

in the columns of the frame_segments (BLDG_struct) variable.

- fr_designed: 
35

DCI_FINAL

*3 x 3 x Nf, matrix of DCIs of the frame sections in the fr_designed variable. 

The rows represent the frame segments, and the columns represent in order: 

segment start, segment mid, and segment end.

- DCI_FINAL:

DCI_S_FINAL

*3 x 3 x Nf, matrix of DCI

V

s for shear of the sections in the fr_designed 

variable. The rows represent the frame segments, and the columns represent in 

order: segment start, segment mid, and segment end.

- In this example, DCI_S_FINAL: