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## The Third Most Collapse-Resistant Building The third most collapse-resistant building is made of Class 3 ordinary construction, or the standard brick and wood joist. These buildings are generally more prone to burn-through than collapse, especially under normal floor-load limits. This means the...

## The Third Most Collapse-Resistant Building The third most collapse-resistant building is made of Class 3 ordinary construction, or the standard brick and wood joist. These buildings are generally more prone to burn-through than collapse, especially under normal floor-load limits. This means the floor or roof sheathing above burns through long before the floor joists fail. It is unlikely that firefighters would be working on the falling surface, although they may be working below, unaware of the conditions overhead. These conditions can be shielded by hung ceilings or obscured by smoke or fire. A distinct danger in this type of construction is the imposition of unusually high floor loads, such as may be found in a plumbing supply warehouse, and any concentrated loads, such as from roof-mounted air conditioners and signs ($fig. 22-5$). These concentrated loads can result in early failure of localized areas without advance warning. Anyone discovering such loads should immediately report them to the officer in charge, who should order interior forces out of that area and the area below until the stability of the floor or roof has been assured. As with heavy-timber buildings, imposition of lateral loads on walls (e.g., from collapses of floors or roofs) can cause the walls to fail ($fig. 22-6$). However, and not to those types of buildings that, even though meeting the technical definition of wood frame, use lightweight truss-construction methods instead. For the purposes of collapse resistance, a special category containing all lightweight and truss-construction methods should be considered ($fig. 22-7$).