30 September 1999
f. Unusual features. This portion of the form is to be used to note any unusual structural
features that could adversely affect the seismic response of the building. A brief description of
these adverse features, as evidenced by the building drawings, should be recorded on the form
for use as a basis for the applicable structural modifiers on the Structural Review Score Sheet.
Plan irregularities, for the purpose of this form, include geometric irregularities
(e.g., is the building plan symmetrical, "T" shaped, "L" shaped, or other asymmetrical
configuration?), and obvious irregularities in the apparent rigidity and location of the vertical
lateral-load-resisting elements (e.g., are the shear walls or braced frames symmetrically located
with regard to size and extent?).
Vertical irregularities to be noted in this form include significant setbacks in the plan
configuration of the building from one story to an adjacent story (e.g., a building that has a
"stepped" configuration in elevation), and discontinuities in the vertical lateral-load-resisting
system (e.g., are there shear walls or braced frames in upper stories that are discontinued in the
(3) The floor and roof diaphragms should be visually evaluated for obvious
discontinuities (e.g., are there large stair or elevator openings that significantly impair the
effectiveness of the diaphragm to transmit in-plane story forces to the vertical resisting
elements?). Discontinuities can lead to adverse seismic response, particularly for highly
stressed diaphragms (e.g., diaphragms required to transfer horizontal shear from a
discontinuous vertical element to an offset resisting element).
(4) The presence of a basement should be noted, because an embedded structure
subjected to ground motion generally performs better than one founded on shallow foundations.