Why both chords are positive?

compe_ad · Apr 30, 2024

Hi! I am applying a response spectrum along x direction (RSX). The diaphragm should have the chords shown by black arrow but if I checked the sign of resultant forces both are positive. If I was applying ELF it matches the sign convention. I am not understanding why is this happening for the response spectrum load case?
FYI I am looking these forces to design the chords and collectors.

JoshPlumSE · Apr 30, 2024

In response spectra analysis, the statistical combination of the various modes (thing Square Root Sum of Squares) means that the final combined results will all have positive signs.

That's why you're getting the results that you're getting. For what it's worth, the EQ can go in either direction, so each chord could have positive or negative results. So, the results for each chord is correct... as long as you understand you should use load combinations which has the EQ going in both directions.

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Why both chords are positive?

compe_ad

Civil/Environmental

JoshPlumSE

Structural

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