Construction Cost Premiums for Risk Category IV SMF Buildings

The International Building Code uses Risk Categories to reduce the probability of damage and collapse for certain buildings. One proposal for improving post-earthquake functional recovery is to design more buildings as Risk Category IV. The purpose of the study was to investigate the construction cost premiums for Risk Category IV buildings with steel special moment frames (SMF). Mathematical derivations were used to bound the stiffness and strength amplifications required for Risk Category IV design, accounting for period effects (as buildings are strengthened/stiffened, design loads increase). To complement this mathematical approach, twelve case study SMF buildings were designed with heights ranging from two to sixteen stories. The primary conclusion of the study is that construction cost premiums for drift-governed SMF buildings are an order-of-magnitude greater than for strength-governed buildings. For many strength-governed buildings, the cost premium for Risk Category IV design is around 1% of the total building cost. For drift-governed SMF buildings, the cost premiums for Risk Category IV design are 6-16% of the total building cost, with the greatest premiums for buildings around eight stories. These cost premiums should be considered when evaluating Risk Category IV design as a strategy for improving post-earthquake functional recovery.