LATERAL FORCE DESIGN

SOFTWARE FOR WIND AND SEISMIC LOADS PER IBC 2003 AND ASCE 7-02

by

Xin Wang

A Thesis Presented to the FACULTY OF THE SCHOOL OF ARCHITECTURE

UNIVERSITY OF SOUTHERN CALIFORNIA In Partial Fulfillment of the

Requirements for the Degree MASTER OF BUILDING SCIENCE

May 2004

Copyright 2004 Xin Wang

CHAPTER 5

SOFTWARE DESIGN FOR WIND AND SEISMIC LOADS

5.1. Scope of the Software

Since building codes have evolved from simple to very complex, computers

are broadly used by designers in practice. Quite a few software packages have been

developed to help structural engineers design for wind and seismic forces.

Code Search Excel Spreadsheet (Fig. 5.1) was developed by Struware. This

software can calculate lateral loads based on several building codes including IBC

(2000 or 2003) and ASCE 7 (1998 or 2002). It utilizes Excel spreadsheet and the

information for generating lateral loads can be input or selected. Another software,

Wind Load on Structures 2002, was designed by Standards Design Group. It can

generate wind loads based on ASCE 7-98 or ASCE 7-02.

More applications can be found for determining wind and seismic loads based

on building codes. They are designed for structural engineers and require that users

be familiar with building codes. Because building code theory is not consistently

taught in architectural schools, they are not easy to use for students of architecture.

This thesis presents a software, LATERAL FORCE DESIGN (LFD), designed

to teach students of architecture building code theory of determining wind and

seismic loads. The software is based on IBC 2003 and ASCE 7-02. While teaching

the main concepts and procedures of determining wind and seismic loads, the

software can compute: wind base shear, distribution per level of wind pressure,

force, shear and overturning moment on main wind-force resisting systems of

enclosed and partially enclosed rigid buildings of all heights, seismic base shear,

distribution per level of seismic force, shear and overturning moment.

Fig. 5.1 A screenshot of input module of Code Search Excel Spreadsheet developed by Struware (no date)

There are two main goals in the design software. First, the application is a

teaching tool. It should lead users through the whole application and provide brief

and clear descriptions for all the input, output and intermediate entities.

Wherever possible, images shall be used to convey the idea in visual format. One

picture is worth a thousand words.

The application is also a computing tool. It should allow users to input

relevant parameters in determining wind and seismic forces for common structures,

and then give the output in an easy-to-understand way. The application is not meant

to have industrial strength but more for teaching purpose, thus it should streamline

some complex formula and conditions into simple ways for users to understand

computing procedures.

5.2. Software Structure

Window-based C# is chosen as the computer programming language. Because

the design software is quite complex by considering its scope, divide and conquer

strategy is used in designing the whole application. In computer terms, it is called

object oriented programming paradigm. Basically what it does is to separate the

functionalities of an application into small parts, each part can do a particular job

well, then connect them together whenever it is needed. In this way, most parts can

be reused in different other parts of the system.

The software can run in Windows. It consists of 4 components, help, input,

computation and output. Fig. 5.2 shows the software structure and flow sequence.

The design of help is to demonstrate the software as a teaching tool. It

includes tutorial and input instructions. Tutorial gives users the information

including the scope of the software, the instructions how to use the software, and

building code theory used in the software. Tutorial can be entered at the beginning

of the software or from Tutorial menu in the software design screen. It can run

independently from the main application.

Input is to collect information to generate wind or seismic loads. It is

divided into 4 parts including building information, dimension, wind-related

information, and seismic-related information.

LFD - Introduction

LFD - Main screen

LFD - Tutorial

LFD Input Output

Building info

Dimension

Wind info

Occupancy category

LFRS

Number of levels

Exposure category

Fundamental period

Wind speed

Seismic info

S1, Ss

Site Class

R value

Wind outputSeismic output

Wind pressure

Wind force

Wind shear

Wind overturn moment

Seismic overturn moment

Seismic force

Seismic shear

Exit LFD

Note: Red arrows show LFD flow sequence.

Fig. 5.2 Software structure and flow sequence

Each part of input is represented with a tab page. On each tab, the input is

given step by step. The input is on the left, and its explanations are in the textbox to

the right. After finishing input, the user can proceed by clicking next button or go

back by clicking back button whenever any change needs to be made.

The tab of Building Info (Fig. 5.3) is collecting the building information for

generating wind or seismic loads. There are 3 entries in the order of occupancy

category, lateral-force resisting systems and the number of levels.

The tab of Dimension (Fig. 5.4) is also to collect the building information. It

allows users to draw diaphragm geometry, input height and dead load at each level.

The input instructions are provided for each entry. The building summary gives the

user a report of all the entries so far and let the users check the correctness of the

input information.

Fig. 5.3 A sample of Building Info input

The tab of Wind Info (Fig. 5.5) includes the information only for generating

wind loads. There are 3 entries including rigidity, wind speed and exposure

category. The tab of Seismic Info (Fig. 5.6) is used to generate seismic loads only.

There are 3 entries including S1 and SS, site class and response modification

coefficient R.

Input flexibility is provided to the user. Input menu lists all the entries

associated with each tab. In this way, the user can easily access one particular entry.

It is designed for advanced users or saved projects when some changes are needed.

Fig. 5.4 A sample of Dimension input

Fig. 5.5 A sample of Wind Info input

Input is in the layer of User Interface (UI). All the UI related functionalities of

LFD are implemented in Windows Forms, the standard Windows application

interface. The images or text in color are used to make the UI more interactive and

clear to the user. Default values are given and also warnings when input is out of the

range of the application capacity.

Fig. 5.6 A sample of Seismic Info input

The users input through the UI layer, then the values for each entry are

recorded in the application. The computing logic is based on the theory in Chapter 3

and 4. The flow of data follows input -> process (either wind or seismic processing)

-> output paths.

The output of wind or seismic loads is displayed on separate tabs. The

computation is executed by clicking computation button on each tab. The wind

loads on each orthogonal direction are listed in the separate Table (Fig. 5.7).

Because the seismic loads at each orthogonal direction are equal, they are listed in

one Table. Wind and seismic loads can be display graphically by right clicking in

the Output Table to select the output values.

Fig. 5.7 A sample of Wind Output

If shear wall systems are selected as lateral-force resisting systems, overall

length per level of shear walls can be displayed by clicking shear wall generation

button on the tab of wind or seismic output. The values of shear wall length at each

level are listed in the output Table (Fig. 5.8). If the user does not specify the

allowable shear stress, default values will be used for the computation.

The computing theory of determining wind and seismic loads can be accessed

by clicking each data in the output Tables. If the data is clicked, a new form appears

to provide the information such as the formula, factors in the formula and their

explanations. The question marks are used to explain some factors when more

computations are involved.

The software has the menus including file, input, tutorial, print and help. File

menu includes the common functions for managing the file, such as new, open, save,

save as, and exit. Input menu provides the entries associated with each input tab.

Tutorial menu allows the user to access Tutorial while the design screen is in use.

This software can not send data to the printer. Print menu suggests the user to use

print screen button on the keyboard, then paste the screen into another application

such as Microsoft Word or Adobe Photoshop to print. Help menu includes about and

flow chart. Flow chart provides the software flow sequence that helps the user

navigate in the software.

Fig.5.8 A sample of shear wall output form

5.3. Sample Structures

This section includes the general procedure of using this software, sample

structures and their brief explanations.

Since the software is implemented in C#, which is one programming language

in the Microsoft .Net Framework programming language family. To run .Net

applications, .Net framework is required. The framework is installed on Windows

XP by default. To run in other operating systems such as Windows 2000, it is

required to install the .Net framework first. The .Net framework can be downloaded

from www.microsoft.com for free.

The software, LATERAL FORCE DESIGN, does not need complicated

installation. To run it, just copy and paste the whole folder to a location on the hard

disk, then double click the executable in Windows Explorer.

The first page (Fig. 5.9) of the application appears including the software title,

general scope of the software, the information of the author, the advisors and school.

The user can click continue button to go to the next page.

The next screen (Fig 5.10) displays the scope of the software, computing

theory and the selections to read Tutorial or start to use the software.

If the user clicks Tutorial, the main menu of Tutorial provides several

selections for the user to proceed. The user can click each selection to read through

the whole content by clicking back or next button or clicking main menu button to go

back to the main menu of Tutorial. The user can click exit button to exit Tutorial.

Its sample structures are listed from Fig. 5.11 to Fig. 5.13.

Fig. 5.9 A sample of the software open page

Fig. 5.10 A sample of the software introduction page

Fig. 5.11 A sample of the tutorial main menu

Fig. 5.12 A sample of the software scope in the tutorial

Fig. 5.13 A sample of how to use the tutorial in the tutorial

If the user clicks design button, the main screen of the application appears. On

each tab, the step-by-step input is provided to the left and its instruction is to the

right. The sample structures of the input tabs are listed below.

Fig. 5.14 A sample of the first input in Building Info tab

Fig. 5.15 A sample of the second input in Building Info tab

Fig. 5.16 A sample of the third input in Building Info tab

Fig. 5.17 A sample of an input in Wind Info tab

Fig. 5.18 A sample of an input in Seismic Info tab

After the user inputs all the information for generating wind or seismic loads,

the user can click wind or seismic output tab, then click computation button on each

tab. Its sample structures are listed from Fig. 5.19 to Fig. 5.22.

Fig. 5.19 A sample of wind output

Fig. 5.20 A sample of graphic wind overturn moment

Fig. 5.21 A sample of seismic output

Fig. 5.22 A sample of a pop-up form by clicking the data in the seismic output Table

BIBLIOGRAPHY

Ambrose, J. and Vergun, D., 1995. Simplified Building Design For Wind and Earthquake Forces. 3rd ed. New York: John Wiley & Sons, Inc. Amrhein, J., 1994. Masonry Design Handbook. Masonry Institute of America. Anon. (no date). What is Richter Magnitude [online]. Available from: http://www.seismo.unr.edu/ftp/pub/louie/class/100/magnitude.html [Accessed 4 May 2004]. Arnold, c. and Reitherman, R., 1982. Building Configuration and Seismic Design, John Wiley & Son ATC/SEAOC Joint Venture. (no date). Building Safety and Earthquakes Part A: Earthquake Shaking and Building Response [online]. Available from: http://www.atcouncil.org/pdfs/bp1a.pdf [Accessed 4 December 2003]. ATC/SEAOC Joint Venture. (no date). Building Safety and Earthquakes Part B: Earthquake Forces in Buildings [online]. Available from: http://www.atcouncil.org/pdfs/bp1b.pdf [Accessed 4 December 2003]. ATC/SEAOC Joint Venture. (no date). Building Safety and Earthquakes Part C: Earthquake Resisting Systems [online]. Available from: http://www.atcouncil.org/pdfs/bp1c.pdf [Accessed 4 December 2003]. ATC/SEAOC Joint Venture. (no date). Building Safety and Earthquakes Part D: the Seismic Load Path [online]. Available from: http://www.atcouncil.org/pdfs/bp1d.pdf [Accessed 4 December 2003]. Bachmann, H. (2003). Seismic Conceptual Design of Buildings Basic principles for engineers, architects, building owners, and authorities [online]. Available from: http://www.bwg.admin.ch [Accessed 4 December 2003]. CBTC. (no date). CBTC Shear Wall Basics [online]. Available from: http://www.mcvicker.com/vwall/page001.htm#A1 [Accessed 4 May 2003].

Gibbs, T. (2003). Conceptual Design to Resist Earthquakes [online]. Available from: http://www.disaster.info.desastres.net/LIDERES/english/jamaica/presentations/TonyGibbs_ConceptualDesigntoResistEarthquakes.doc [Accessed 4 January 2004]. ICC, 2002. International Building Code 2003. Illinois: International Code Council, Inc. MCEER. (no date). How do Earthquakes Affect Buildings [online]. Available from: http://mceer.buffalo.edu/infoservice/faqs/eqaffect.asp [Accessed 4 January 2004]. MCEER. (no date). How do Buildings Respond to Earthquakes [online]. Available from: http://mceer.buffalo.edu/infoservice/faqs/brespons.asp [Accessed 4 January 2004]. MCEER. (no date). What are Earthquake Magnitude and Intensity [online]. Available from: http://www.mceer.buffalo.edu/infoservice/faqs/howmeasr.asp [Accessed 4 January 2004]. Pakiser L. and Shedlock K. (no date). What Causes Earthquakes [online]. Available from: http://www.mceer.buffalo.edu/infoservice/faqs/how.asp [Accessed 4 January 2004]. Pittack, L. and Blas, J. (2000). Wind Load Design Analysis: ASCE7-98 [online]. 2000+ EngineeRunner Inc. Available from: http://www.geocities.com/lpittack/cae614proj.html [Accessed 4 January 2004]. Professional Publications. (no date). Lateral Forces Earthquakes [online]. Available from: http://216.239.57.104/search?q=cache:pleyxwlVWsIJ:ppi2pass.com/catalog/servlet/MyPpi_fl_Errata-ARES5ch14.pdf+lateral+forces+-+earthquakes&hl=en [Accessed 4 January 2004]. Schierle, G. G., 2003. Northridge Earthquake Field Investigations: Statistical Analysis of Wood-frame Damage. CUREE Publication No. W-09 Schierle, G. G., 2001. Woodframe Project Case Studies. CUREE Publication No. W-04

Schierle, G. G., 1993. Quality Control in Seismic Resistant Construction. National Science Foundation Report Schierle, G. G., 2002. Northridge Earthquake: Residential Wood Structure Damage. Yokohama, Japan: Proceedings, Structural Engineers World Congress (SEWC). Schierle, G. G., 2002. Northridge Earthquake Field Investigations: Statistical Analysis of Woodframe Damage. Boston: Proceedings, 7th National Conference on Earthquake Engineering. Schierle G. G., 2002. Northridge Earthquake Field Investigations: Damage to Residential Woodframe Projects. Denver: Proceedings, ASCE Structures Congress. Schierle, G. and Vergun D., 1999. Northridge Earthquake Damage Testing. Proceedings, UCSD Workshop Schierle G. G., 1996. Quality Control in Seismic Design and Construction. New York: Journal of Performance of Constructed Facilities, American Society of Civil Engineers. Schierle G. G., 1994. Quality Control for Seismic Safety. LA Architect (cover page) Schierle G. G., 1994. Computer Aided Seismic Design. Journal of Architectural and Planning Research. SEI, 2003. SEI/ASCE 7-02 Minimum Design Loads for Buildings and Other Structures. Virginia: the American Society of Civil Engineers. S. K. Ghosh Associates, no date. CodeMaster 2000 IBC. Standard Design Group. (no date). Wind Loads on Structures 2002 [online]. Available from: http://www.standardsdesign.com/WLS/2002/2002.htm [Accessed 10 March 2004]. Struware. (no date). Code Search Excel Spreadsheet [online]. Available from: http://www.struware.com/prod01.htm [Accessed 10 March 2004]. Structures & Codes Institute, no date. CodeMaster.

USGS. (no date). Earthquakes, Faults, Plate Tectonics, Earth Structure [online]. Available from: http://earthquake.usgs.gov/faq/plates.html [Accessed 10 February 2004]. Wind Effects Committee. (2004). The ASCE/SEI Wind Effects Booklet [online]. Available from: http://www.seiwec.net/mb/ [Accessed 4 February 2004]. Sells, C., 2004. Windows Forms Programming in C#. 1st ed. Boston: Addison-Wesley.