The ASD combinations are based on ASCE 7-98, and are given in Section 1605.3, Load combinations using allowable stress design. Basic and Alternate sets of equations are given. The template files are RamSteelIBC2000_ASD.cmb and RamSteelIBC2003_ASD.cmb. The Alternate combinations of 1605.3.2 are not implemented. The Basic load combinations used are those given in Section 1605.3.1:
| D + L + Lr | (Formula 16-9) |
| D + L + Lr + W | (Formula 16-10) |
| D + L + Lr + 0.7E | (Formula 16-10) |
| 0.6D + 0.7E | (Formula 16-12) |
where
|
E
| = | ρQE ± 0.2 SDS D (see Sec. 1617.1.1) |
|
QE
| = | the Seismic force from the analysis. ρ is the Reliability/Redundancy Coefficient as explained in the previous section |
In combinations with two or more cases in addition to Dead Load, those cases may be multiplied by 0.75 (Sec. 1605.3.1.1). When this factor is applied, the 0.7 factor is not applied to E.
Note that when the 0.75 factor is applied to load cases with E, it is also applied to the 0.2SDS term (which becomes 0.15SDS) and that when the 0.7 factor is applied to load cases with E, it is also applied to the 0.2SDS term (which becomes 0.14SDS).
If the Roof Load has been specified as Snow in the Criteria – Live Load Reduction command in the RAM Manager, the user may specify whether to use the full factor (1.0) or the partial factor (0.2) on the Snow load, or disregard the Snow entirely when in combination with seismic forces, as specified in Exception 2 of Section 1605.3.1.
