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As per 12.10.2.1, for Seismic Design Categories C-F, the diaphragm force Fpx along with transfer forces factored by Ω0 , are used for the determination of the shear line force for drag strut and in-plane shear wall anchorage calculations if they are greater than the forces derived from base shear using the Equivalent Lateral Force procedure in 12.8.
Shearwalls applies a proportionality factor between the diaphragm force Fpx and the unfactored design force Fx on the level in question to the seismic loads that were created from building masses and multiplies all loads generated for shear wall design by that factor. These loads along with transfer forces from the level above factored by Ω0, and user-applied loads and forces are then distributed to the shear lines via rigid and flexible diaphragm distribution.
The resulting shear line force represents the contribution of the loads on the level with the drag strut or anchorage. The shear line forces for shear wall design from levels above on the same shear line are then added in as per 12.10.2 ("seismic forces originating in other parts of the structure"), then the maximum of this force and the force used for shear wall design is taken as per 12.10.1.1 ( "but not less than... 12.10-1"). For certain irregular structures, the force is increased by 25% as per 12.3.3.4; see Irregularities.
Refer to seismic design requirements for drag strut forces for the application of the redundancy factor r from ASCE 7 12.3.4 to each of these component forces.
The shear line force used for drag struts and in-plane anchorage is shown in the Collector Forces table of the Design Results output, and can be viewed both Plan View and Elevation view in place of the shear wall design forces by checking a Show/Hide menu item. In Plan view, you must be in the the Loads and Forces action.