47.5 MB - The Whole Building Design Guide

Figure 3-105:Several walls at this schoolcollapsed. Windows werelocated above a nonload-bearingmasonrywall. Hurricane Katrina(Mississippi, 2005)3.6.1 Structural SystemsAs discussed in Section 3.1.4.1, roof decks on many facilities designedprior to the 1982 edition of the SBC and UBC and the1987 edition of the NBC are very susceptible to failure. Poorly attacheddecks that are not upgraded are susceptible to blow-off, asshown in Figure 3-106. Decks constructed of cementitious woodfiber,gypsum, and lightweight insulating concrete over formboards were commonly used on buildings built in the 1950s and1960s. In that era, these types of decks typically had very limiteduplift resistance due to weak connections to the support structure.Steel deck attachment is frequently not adequate because ofan inadequate number of welds, or welds of poor quality. Olderbuildings with overhangs are particularly susceptible to blow-off, asshown in Figure 3-107, because older codes provided inadequateuplift criteria.3-134 MAKING CRITICAL FACILITIES SAFE FROM High Wind