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## Building Collapse Buildings that have the greatest resistance to collapse are Class 1 fireproof buildings with fire resistance ratings up to 4 hours. These structures are designed using a skeletal framework made from either poured concrete or steel I-beams. In these buildings, the collapse is of...

## Building Collapse Buildings that have the greatest resistance to collapse are Class 1 fireproof buildings with fire resistance ratings up to 4 hours. These structures are designed using a skeletal framework made from either poured concrete or steel I-beams. In these buildings, the collapse is often localized. The ceiling concrete may spall or several I-beams may sag, but usually, the load remains in place. When these structures are exposed to a fire, they are designed to provide enough resistance for evacuation and fire control. The collapse of WTC1, 2, and 7 show how the lightweight modern construction materials used in many buildings might not provide sufficient time for a long evacuation, as well as a long descent before the building collapses. ## Windsor Fire The Windsor Building, a 32 story building in Madrid, Spain, was nearly completely destroyed by a severe fire in February 2005. Though most of the steel frame collapsed, the building remained in place after the concrete core remained standing despite the failure of the upper 12 floors. The core was constructed from reinforced concrete. The outer floor sections were constructed with medium-weight steel, and the exterior walls were partially load bearing. The most dangerous condition in Class 1 buildings occurs under poured in place concrete buildings.