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SAP Analysis ,Same Floor Joist, Two Different Results

SAP Analysis ,Same Floor Joist, Two Different Results

SAP Analysis ,Same Floor Joist, Two Different Results

(OP)
SAP is giving two different result of same cold form floor joist as shown below.

In first method top and bottom chord considered as one member but in this case top chord fail but in second method when I break the top chord at intersection points (webbed and top chord member) top chord passes.

Which method is correct? I should break the top and bottom chord at joining point or I should keep the top and bottom chord as one member??

RE: SAP Analysis ,Same Floor Joist, Two Different Results

Sounds to me like SAP is giving two different results to two different problems.
Look at the output for each one and figure out what forces are changing between the two models. Is there an increase in axial force? Shear? Flexure? What portion of the total allowable does each of these forces contribute?
I think you need to understand what SAP is doing before you worry about which answer is correct. Blindly trusting the computer is risky business.

RE: SAP Analysis ,Same Floor Joist, Two Different Results

I believe that treating the top chord as one, continuous member would be more accurate as that better reflects the real world condition. If your joints are concentric and the difference is significant, it probably indicates that your chords are quite stiff flexurally relative to the truss as a whole.

Is the chord failing because it's seeing higher moments or because design parameters such as unbraced length are changing within the software?

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

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