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Shear Wall over Girder Truss

Shear Wall over Girder Truss

Shear Wall over Girder Truss

(OP)
We, as the engineer of record for the project, are often required to use walls which are supported by floor (or wall) girders as shear walls for wind loading. As a result we have overturning forces each end of the shear wall which must be supported by the girder. We have been asking the truss engineers to add this load to the truss, both as a positive and negative number due to reversal of wind direction. What we get back from the truss designer varies greatly. Most just enter the load as an uplift on the truss in load case 1. I'm fine with this but want to see the truss run with a positive overturning force as well. Most of the time this positive load should produce the highest stress in the truss in combination with all of the other positive gravity loads. Because it is a wind load, the truss should use ASD load case 5, 6, or 7 along with a 1.6 duration? Not sure how the duration should be used in combination with dead and live loads. I'm curious if you guys could give me some suggestions on how I should have this type of loading run. Let me know if any of this needs further explanation. I would like to develop a form that we submit to the truss designer describing the load (positive and negative), location of loads, and a brief description on how they should enter the load.
Thanks for any info.

RE: Shear Wall over Girder Truss

How are the load tying into the girders?

Sitting on a floor system, where the floor members are hanging on the girder? Or something else?

FWIW - I've never seen wind loads control anything significant on a girder truss. It usually does little except for change the uplift forces at the bearings.

RE: Shear Wall over Girder Truss

(OP)
The walls are typically directly over the girder. So the loading would be directly to the top chord.
We occasionally see overturning loads in the 3-4,000 range which would be both positive and negative. The positive loads (positive being down) will add to the gravity loads and always changes the webbing or plates.

RE: Shear Wall over Girder Truss

Just curious - Are these girders in situations where the top chords are restrained from lateral movement?

I've often been asked to design "wall girders" as part of a wall. I have always refused, unless the top chords were somehow restrained. I seem to have a hard time making people understand the importance of it.

RE: Shear Wall over Girder Truss

(OP)
Yes, they follow the roof or floor sheathing lines, so laterally braced.

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