§4.[B2] Loads, Load Combinations, and Nominal Strengths

Where standard provision load combinations are referred to (such as in Section 4.1 in regard to the applicable building code), RAM Frame will use the current load combinations from the standard provision mode. The engineer is responsible for ensuring that an appropriate set of loads and combinations are defined in the standard provision mode prior to switching to special seismic mode and performing a code check. Amplified Seismic load combinations as referenced in section 4.1 are generated within this mode.

For member code checks of SCBF and BRBF column frame types using the AISC 341-10 code, a set of generated load combinations independent of the user generated combinations are evaluated. The set of combinations use (+ 1.0 Emh) for LRFD and (+ 0.7 Emh) for the ASD code as the seismic term in combinations with the analyzed gravity load cases. Where transient loads exist in an ASD combination, (+ 0.525 Emh) is applied. Emh is determined using the analysis conditions specified in Section F2.3 and F4.3 of AISC 341-10 for SCBF and BRBF columns respectively.

For member code checks of SCBF and BRBF column frame types using the AISC 341-16 code, a set of generated load combinations independent of the user generated combinations are evaluated. The set of combinations use (+ 1.0 Ecl) for LRFD and (+ 0.7 Ecl) for the ASD code as the seismic term in combinations with the analyzed gravity load cases. Where transient loads exist in an ASD combination, (+ 0.525 Ecl) is applied. Ecl is determined using the analysis conditions specified in Section F2.3 and F4.3 of AISC 341-16 for SCBF and BRBF columns respectively.

Note: It is recommended that generated seismic combinations are created to ensure that correct parameters (Sds etc.) are used. For models without generated seismic load combinations (where only custom seismic load combinations are defined), combinations are internally generated assuming the default template values.

The provisions of AISC 2005 and AISC 2010 are written for consistency with load combinations given in ASCE 7 and IBC (ICC 2006 and ICC 2009). While AISC 341-05 refers to the applicable building code as the source of the load combinations they should be consistent with the codes above to be applicable to the design provisions. Refer to Sections C4 and B2, respectively, in the commentaries of the AISC 2005, AISC 2010 and AISC 2016 specifications for more information.

Nominal strengths are based on the following specifications:

ANSI/AISC 360-16, Specification for Structural Steel Buildings (July 7, 2016), published by the American Institute of Steel Construction in Steel Construction Manual (15th Edition).
ANSI/AISC 360-10, Specification for Structural Steel Buildings (June 22, 2010), published by the American Institute of Steel Construction in Steel Construction Manual (14th Edition).
ANSI/AISC 360-05, Specification for Structural Steel Buildings (March 9, 2005), published by the American Institute of Steel Construction in Steel Construction Manual (13th Edition).