ASCE 7 combinations

The combination generator ships two standards. EN 1990 is one; ASCE 7 is the other, and it produces the combinations the AISC 360 module expects. A project can hold both (a Eurocode job can carry an ASCE set for comparison), and a new combination starts on the standard of the project's national code family.

Two philosophies, two sets

ASCE 7-22 defines its combinations in two sections of Chapter 2, for two design methods:

A third, smaller set, the service-level combinations of the serviceability appendix (Appendix C, Commentary CC.2.2), is generated for deflection and drift checks, with the serviceability wind taken as $0.42W$ — roughly a 10-year wind — unless you set another ratio.

The two sets are not interchangeable on the load side. The AISC module lets you choose LRFD or ASD as a parameter on the check, and both routes use the same nominal strengths; the difference is entirely in what is compared with what.

The LRFD set

With $D$ dead, $L$ floor live, $L_r$ roof live, $S$ snow, $R$ rain, $W$ wind and $E$ earthquake:

Each "or" is a separate combination: rule 2 with roof live, rule 2 with snow, rule 2 with rain. That is why a set with all three roof actions defined grows quickly, and a set without them is short.

The ASD set

The 0.75 factor on rules 4, 6 and 9 is the standard's allowance for the improbability of two variable actions peaking together: the ASD equivalent of a ψ factor.

The factors are fields

As with the Eurocode generator, the LRFD factors (1.4, 1.2, 0.9, 1.6 on $L$ and on the roof actions, 1.0 on $W$ and $E$, and the companion $L$) are editable fields on the generator, not constants compiled into the app, and so are the service-level wind and snow factors. The ASD factors (0.6, 0.7, 0.75) are fixed. The fields matter for three provisions:

• The 0.5 live load exception. §2.3.1 allows the companion $L$ in rules 3, 4 and 6 to be taken as $0.5L$ where $L$ is at most 100 psf (about 4.8 kN/m²) and the occupancy is not a garage or a place of public assembly. It is a value you set, not a branch to work around.
• Wind. The $1.0W$ factor assumes wind speeds from the strength-level maps. A project working from older service-level wind data uses $1.6W$ and $0.8W$ in the earlier form of the rules. Change the field, and say so in the report.
• Earthquake. The $1.0E$ factor is a field like the others. The standard defines $E$ from horizontal and vertical components ($E_h$, $E_v=0.2S_{DS}D$); the generator takes $E$ as one action, the static-equivalent seismic case your model carries. Put $E_v$ into that case, or drop it where the standard permits, and say which in the report.

Mapping your load groups

The generator applies the rules to the load groups you defined. It does not guess which case is which:

Reading the generated set

The same discipline as for Eurocode combinations:

Pairing with the design check

Point the AISC 360 check at the LRFD set with the LRFD method selected, or at the ASD set with ASD. The check runs every combination it is given and reports the governing one with the clause and the substituted formula, as the Eurocode module does. Deflection and drift go against the serviceability set, with the limits from the project specification.

Related

Automatic combinations covers the EN 1990 rules and the partial factor tables; Envelopes covers getting the governing value out of either set; National annexes explains the United States entry in the project's code family list, where the design method replaces ${\gamma }_M$.