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Alaska Building

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Monty Hart,

In my opinion, a relative rigidity analysis should be done in both
directions. A tributary area check should be done in the transverse
direction to compare the demands. Compartment analysis of three sided
sub-units is not rational. The horizontal diaphragms have considerable
displacement control capacity parallel to the longitudinal open fronts. I
have used UBC Standards section 23-2 to estimate horizontal diaphragm
deflection of an open front by taking a value of twice the cantilever
projection for the equivalent simple span. Any use of gypsum board or
plaster for resistance to distributed demands should be avoided. These
materials degrade rapidly during ground shaking and many similar configured
apartments in the Los Angeles area have had unacceptable damage in past
earthquakes. I would not combine the stiffness of a steel moment frame with
a long sheathed hallway wall in a rigidity analysis. The present system you
have inherited should be able to be substantiated.

Michael Krakower SE
Arcadia, CA.