How do I obtain collector forces within a floor diaphragm?

Answer: The collector forces within a floor diaphragm may be measured through the following process:

Define a semi-rigid diaphragm, then apply diaphragm forces, as shown in Figure 1:

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Figure 1 - Apply diaphragm forces
For a given load case, display any stress or shell force, as shown in Figure 2:

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Figure 2 - Display stress or shell force
Where maximum chord forces are expected, draw or define a section cut, as shown in Figure 3:

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Figure 3 - Maximum chord forces
Moments about the Z-axis represent in-plane moments. Ensure that the resultant-force angle is zero, then select Refresh, as shown in Figure 4:

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Figure 4 - In-plane moment
Compression and tension chord forces are then given as the value of each Z-axis moment divided by slab width, as shown in Figure 5:

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Figure 5 - Compression and tension chord forces
For shear and collector forces located at the connection between the diaphragm and a shear wall, draw or define a section cut next to the support which follows the wall direction, as shown in Figure 6:

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Figure 6 - Shear and collector forces
Again, ensure that the resultant-force angle is zero, and refresh as necessary. Given this example model, the shear/collector force, which is presented in F2, is 2559 lbs., as shown in Figure 7:

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Figure 7 - Shear and collector forces

Diaphragm forces