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User-input dead loads are to be manually calculated from distribution of area loads from floors and roofs to line loads on walls. It is also possible to specify the load supported by walls and/or the wall self-weight and have the program generate these loads.
Load Combination Factor
Forces used in hold-down design are factored by the counteracting dead load factor of 0.6 D from combination 7 in ASCE 2.4.1 for wind design, and combination 10 from 2.4.5 for seismic design. The calculation of forces for compression design at the other end of the segment uses a factor of 1.0 D from load combinations 5 and 8, respectively.
For wind design, the same combinations are used when calculating the forces used for hold-down displacement. For seismic design, strength (LRFD) combinations are used with a factor of 0.9 for hold-down displacement and 1.2 for the crushing component of deflection at the other end. These are from ASCE 7 2.3.6, combinations 7 and 6, respectively.
Building Masses vs Dead Loads
IMPORTANT: The generation of building masses for seismic load generation does not affect the value of dead loads on shear lines for hold-down force calculations. Because Shearwalls does not at present have a gravity load distribution system to determine which elements support the building mass of the floors, it is necessary to apply the dead loads directly on the wall lines as line loads resulting from the area and loads on roofs and floors. This can be done manually on each shearline, or you can generate dead loads on the shear lines using the wall self-weights and supported weights you have assigned to each wall or shearline.