MBMA 96load Combinations

Section 9  LOAD COMBINATIONS 9.1 ALLOWABLE STRESS DESIGN 9.1.1 Non-Seismic Load Combinations--The loads listed herein shall be considered to act in the following combinations, whichever produce the most unfavorable effects on the building or structural member concerned: (a) (b) (c) (d) (e) (f) (g) (h)

D+L D+S D+A D+W D+S+A D + .5W + A D + S + .5W D + .5S + W

where, D = L = S = W= A =

Building dead load plus applicable collateral loads Roof live loads Roof snow loads Wind loads Auxiliary loads (e.g. Crane Loads)

NOTES: (1) For multi-story buildings, or buildings with mezzanines, floor live loads shall be combined with the dead loads including specified collateral loads or with loading combinations (a) through (h), if the result is more severe. (2) Roof snow loads in loading combination (e) shall be: Zero when the roof snow load (pf) is less than or equal to 13 psf; 0.5S when pf is greater than 13 psf, but less than 31 psf; 0.75S when pf is equal to or greater than 31 psf. (3) It is not appropriate to include most collateral loads in combinations that involve wind uplift. (4) Allowable stresses may be increased by 1/3 for loading combinations (d), (f), (g), and (h). 9.1.2 Seismic Load Combinations--The following load combinations are used for combinations involving seismic forces and are used in conjunction with increases in allowable stresses as prescribed in AISC Seismic Provisions for Structural Steel Buildings (Ref B5.12). The applicable seismic load combinations are:

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(a) [(1.1 + 0.5 Av) × Dead] + [(0.5) × Floor Live] + [(R) × Roof Snow] + Seismic (b) [(0.9 - 0.5Av) × Dead] + Seismic where, R = 0 for ground snow < 30 psf. R = 0.2 for ground snow ≥ 30 psf. NOTES: (1) The coefficient on Floor Live must be 1.0 for garages, places of public assembly or when the Floor Live Load is greater than 100 psf. (2) If the building contains a crane, for load combination (b), the dead load shall include the total weight of the crane, including bridge with end trucks and hoist with trolley. (3) One-third increase of allowable stresses shall not be used with seismic load combinations. Specific to the design, AISC Seismic Provisions for Structural Steel Buildings (Ref B5.12) specifies that the allowable stresses be multiplied by 1.7 to convert to equivalent nominal strengths. These nominal strengths for compression, flexure, tension, and other cases are then multiplied by the appropriate resistance factors as detailed in AISC Seismic Provisions for Structural Steel Buildings (Ref B5.12) to arrive at the design strengths to be used with the load combinations involving seismic design. 9.2 LOAD AND RESISTANCE FACTOR DESIGN The required strength of the building and its elements shall be determined from the appropriate critical combinations of factored loads as follows: (a) (b) (c) (d) (e) (f)

1.4D 1.2D + 0.5(L or S) 1.2D + 1.6(L or S) + 0.8W 1.2D + 1.3W + 0.5(L or S) 1.2D ± E + 0.2S 0.9D ± (1.3W or 1.0E)

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