Boundary beams load

[rittz]

I believe it can be assumed that shear walls of equal construction do share the shear from a rigid diaphragm in proportion to their lengths. Does the addition of a partial interior shear wall have any effect on the tension load on the boundary chord? See attached sketch example.

 

[msquared48]

Two things:

1. You are listing a rigid diaphragm (concrete or metal deck) where the forces seen by the individual shear walls are NOT directly related to their lengths, but to their flexibility, or tendency to deflect. If this were a flexible diaphragm, you would be correct. and..

2. The introduction of an interior shear wall will break up the diaphragm into two smaller ones, and alter the chord forces seen at the exterior walls - i.e., lessen these forces.


Mike McCann
MMC Engineering

 

[BAretired]

The addition of a partial shear wall tends to reduce the deflection of the roof diaphragm which would otherwise occur at that location. How much is dependent on the deformation of the roof diaphragm as well as the end walls. The added partial wall would tend to carry more shear per unit length

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than the end walls.

BA

 

[BONILL]

rittz,

If by equal construction you mean equal material and thickness (which would mean that their rigidity per unit length is the same) then yes, the shear at each shearwall would be proportional to their lengths.

In order for the interior shearwall to be effective, you would need to provide a collector element though, to transfer the forces from one side of the diaphragm to the shearwall.

In terms of the tension in the boundary chord, it would certainly be different with the interior wall. Your diaphragm would basically be a inifinitely stiff beam supported by springs (the shearwalls), each with it's specific k value. The span moments resulting from this idealization must be divided by the lever arm of the boundary chords (in your case least dimension of builiding) to obtain the boundary chord forces(T = M/d).

Don't forget the oversrength factor when designing the boundary chord elements, as well as the diaphragm collector and it's connection to the shearwall.