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Re: IBC 2003 Eqn. 16-50

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This is one of the most confusing items in the code and many people have questioned this before. The term 0.2SD is intended to capture the vertical "effect" of the seismic forces on members that resist vertical loads (It is not clear whether this applies to all members or only those that are part of the lateral force resisting system)

For example if you have a beam that is part of a moment frame, when checking the beam for flexural stresses the load 0.2SD gets added to the gravity loads that are resisted by the beam. Or, when checking a shear wall, this load gets added to al the other vertical loads that are acting on the wall and it could either add or subtract from the them. It is not intended to be a vectorial combination of horizontal and vertical forces.

Ben Yousefi, SE
Santa Monica, CA

>>> AGrathwol(--nospam--at) 12/11/03 08:38AM >>>
Equation 16-50 combines lateral seismic loads (QE) with vertical dead loads (D) and calls it "E", that is then to be used as E in the load combinations of Section 1605.
Is the combined E force then assumed to be totally a lateral load or is the equation intended to represent vectorial combination, and not mathematical addition?

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