Metal Building Systems (MBS) are frequently constructed with mezzanines contained in their floor plans. These mezzanines can be heavy and have a significant impact on the seismic design and performance of the MBS. When a mezzanine is attached to the MBS, it is not clear to the designer whether it should be treated as a one- or two-story building. It is also not clear how the seismic forces should be distributed vertically. Validity of common assumptions about mode shapes and the first-mode dominating system response was investigated. A codified design procedure was compared with a simpler procedure commonly used by MBS designers. A parametric study suggests that the current building code procedure for vertical distribution of seismic forces may be inapplicable to the design of MBS moment frames because it does not properly address the unique dynamic characteristics of the system. The parametric study and a recommendation for a design procedure are presented in this paper.
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