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QUALITYASSURANCECORNERmeeting and exceeding requirements and expectations

Validating the Results of Structural Engineering SoftwareBy Cliford Schwinger, P.E., SECB and Eric J. Heller, E.I.T.

The previous Quality Assurance Corner articlediscussed the limitations of structural engineeringsoftware. This article discusses methods for validat-ing the results of structural engineering computeranalysis using simple manual calculations.

Engineers use computers because they canperform repetitive analysis and design cal-culations thousands of times faster than ifperformed manually with a calculator and pencil.Obviously, if the wrong data is entered into

the computer, the results will be incorrect.

The purpose of validating a computer gener-ated design with manual computations is toverify that data was entered into the programcorrectly, and that the software is employingrational and valid methodologies for designand analysis.The goal of performing manual calculations

to verify computer generated design is notnecessarily to match the precise design pro-vided by the computer analysis, but rather toget an answer that is comfortably close to thedesign provided by the program.As a general

rule, if uic! manual computations are withinappro"imately#$ percent of the results providedby the software, it is reasonable to assume thatthe computer analysis and design is correct.%owever, if manual computations di&er fromcomputer results by more than '$ percent,then there is a high li!elihood that an errorwas made somewhere. Errors in computer-generated designs are usually the result ofincorrect input, incorrect understanding ofprogram default settings or lac! of under-standing as to how the software wor!s.The (rst thing an engineer should do when

reviewing a computeri)ed design is to stepbac!, loo! at the big picture and as!, *+oesthis ma!e sense Although this might seemso obvious as to not warrant stating, its some-thing that often does not happen. The engineerverifying if a computeri)ed design *ma!essense obviously has to be an engineer withsome level of e"perience. /o structural en-gineering (rm should ever allow a computergenerated design produced by a 0unior level,ine"perienced engineer to leave the o&icewithout a review by a senior level engineer.

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1 Compute the base shear inch direction

using the computer calculatelding

period, T.1 Compare the manually

culated valueto the base shear determined

computer analysis.1 +istribute the load in a

angular loadpattern 2centroid of loading

atedtwo thirds of the building

ght abovethe base3

1 +istribute loads to the laterace-

resisting elements in proportthe

tributary mass around each

ment. 1 Analy)e braced frames, mommes

or shear walls using theportioned

lateral load.The procedures above will

nerally be ac-curate enough for regular shape

ldings ofmoderate height in areas of low

derateseismicity within a level of

curacy that will catch signi(cant errors in amputer analysis.

A common mista!e with compusign of

lateral force-resisting systems isfailure to

consider load path issues whereeral loads

pass through 4oor diaphragmsm one lateral

force-resisting element toother. Figure 2

illustrates a condition where an-of-plane

o&set irregularity in a bracedme transmits

lateral loads into the 4oorphragm. 5hile

many software programs allowor slabs to

be assigned as diaphragms, notprograms

will design the diaphragms.idation of the

computers results in theseuations reuires

recognition of which structuralmbers may

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not have been designed by thetware.

Concusion6alidating computer-generated

uctural de-sign with manual computation

entialand can be accomplished uic!ly

hin an ac-ceptable level of accuracy using

dimentarycalculations. 5hile those

culations may notbe to a level of precision accura

ough fordesign, they are usually accurate

ough to helpengineers spot errors in a

mputer model.7

Cliford Schwinger, P.E., SECa Vice

Presiden a The Har!anou#$s %ing o&

Prussia, P' ofice where he ie (ualiy

'ssurance )anager.He !ayreached a

cschwinger@harmangroup.com

Eric Heller, E.I.T. is a graduaVillano+a

ni+ersiy and is a -esign

gineer a The Har!an "rou#.He !ay *eached a

eheller@harmangroup.com.

endless combinations of strength and (PipeMedic.com) (PileMedic.com)

PLEASE CALL US FOR A FREE EVALUATION BY ONE OF OUR STRUCTURAL

ENGINEERS. (520) 791-7000 OR (866) Q!"#$%!& '782-597

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