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Force transfer walls allow for light gauge steel straps to transfer tensile forces around openings, and blocking to transfer compressive forces, so that the sheathing above and below the opening contributes to shear wall resistance.
Design of the force transfer walls in Shearwalls follows what is known as the Diekmann method, as presented in APA T555, Design for Force Transfer Around Openings (FTAO). The program also conforms to Special Design Provisions for Wind and Seismic (SDPWS) 4.3.4.4 and 4.3.5.2, and is subject to the limitations therein. Refer also to Sheathing Layout for considerations that designers must adhere to for the Diekmann method to be valid.
In the Diekmann method, shear forces are developed in each wall "pier", defined by the rectangular areas:
A central pier is defined by the top of the highest opening and the bottom of the lowest one. Shearwalls a choice in how this distance is defined when there are openings of different sizes on the wall, refer to the Force-transfer Wall Continuous Strap design setting.
Shear forces are distributed to piers in force-transfer walls as described in Force Distribution within Force-Transfer Walls, and the program determines the critical case of pier force / aspect ratio factor for any pier in the wall (including corner and opening piers with a factor of 1.0) and designs the wall for that case.
Refer also to Force-Transfer Wall Hold-down Forces, Deflection of Force-Transfer Walls, Force-Transfer Strap/Blocking Forces, and Drag Strut Forces in Force-Transfer Walls