Structural Collapse Under Fire Conditions

摘要

Most fire service per-sonnel learn basic building construction early in their careers but little on how to predict structural collapse. However, the newer materials and construction techniques used today, particularly truss systems, are more likely to collapse faster in a fire than traditional materials, thus making it all the more crucial to possess the knowledge to predict structural collapse at an incident scene. Over the past 30 years, construction methods have transitioned from heavy timber, larger steel, and concrete sections to smaller, lighter sections. The wood construction industry transitioned from using heavy timber sections (approximately 12 inches × 30 inches), to rough-sawn lumber, to dimensional lumber, and now to engineered lumber. Engineered lumber is presented in several ways, which may include larger pieces of laminated veneer lumber (LVL) I-joists, and wood trusses. Connection methods vary from glues to metal plate connectors. The larger LVLs and structural glue-laminated timber (known as "glulams") perform similarly to heavy timber. Wood I-joists are constructed of smaller laminated veneer flanges and an oriented strand board (OSB) web. The structural and economic advantages of the truss products have led to a significant increase in their use, especially in residential and light commercial buildings. It is common to find lightweight steel or wood framing in virtually all smaller structures such as nursing homes, hotels, apartments, schools, single-family homes, daycare centers, and small business offices. The Wood Truss Council of America reports that wood truss roof systems are used in more than 60 percent of all new buildings constructed in the United States. When properly installed and unaltered, truss systems are among the strongest structural systems. However, the performance of truss systems is less predictable under fire conditions.