MECHANICAL PROPERTIES OF GYPSUM BOARD AT ELEVATED TEMPERATURES
Gypsum board is a common fire barrier used in house and general building construction. Recently, evaluation of the collapses of the World Trade Center Towers highlighted the potential role and failure of gypsum board in containing the fires and resisting damage. The use of gypsum board as primary fire protection of light-flame wood or steel construction is ubiquitous. Yet knowledge of the common engineering mechanical properties of this construction product is nearly nonexistent. Gypsum board is used in a prescriptive manner with little or no rational design. Summarized here are the results of a study examining the mechanical properties of Type X gypsum board at elevated temperatures. These properties are needed to contemplate the engineering design of gypsum board fire barriers. Tests were undertaken with a small oven within a test machine measuring mass loss, shrinkage, bending strength and modulus of elasticity at elevated temperatures to 400°C. The research showsthat shrinkage and calcination of the gypsum board appear complete between 20 to 30 minutes of exposure at a uniform 400°C. Only after complete calcination, where all moisture is driven off, does the bending strength approach 0. Strength appeared to decrease linearly with increasing temperature. Mass loss and modulus of elasticity exhibited similar trends with the greatest decreases occurring from 100°C to 200°C followed by more gradual decrease to 400°C. The surface paper plays significant stiffening and strengthening roles up to 60 minutes at temperatures as high as 200°C.
Structural Design for Fire Safety
Fire safety in buildings - overview: fire safety objectives process of fire development conceptual framework for fire safety fire resistance controlling fire spread building construction for fire safety. Fire and heat - overview: fuels combustion fire initiation burning objects t-squared fires pre-flashover design fires heat transfer. Room fires - overview: pre-flashover fires flashover post-flashover fires design fires other factors. Fire severity - overview: fire severity and fire resistance fire severity standard fire equivalent fire severity. Fire resistance - overview: fire resistance assessing fire resistance fire-resistance tests approved fire-resistance ratings fire resistance by calculation fire resistance of assemblies. Design of structures exposed to fire - overview: structural design at normal temperatures structural design in fire conditions material properties in fire design of individual members exposed to fire design of structural assemblies exposed to fire. Steel structures: overview: behaviour of steel structures in fire fire-resistance ratings steel temperatures protection systems mechanical properties of steel at elevated temperature design of steel members exposed to fire design of steel buildings exposed to fire. Concrete structures - overview: behaviour of concrete structures in fire fire-resistance ratings concrete and reinforcing temperatures mechanical properties of concrete at elevated temperatures design of concrete members exposed to fire composite steel-concrete construction exposed to fire. Timber structures - overview: description of timber construction fire-resistance ratings wood temperatures mechanical properties of wood design concepts for heavy timber exposed to fire design of heavy timber members exposed to fire behaviour of timber connections in fire.
Percussion marks on bone surfaces as a new diagnostic of hominid behaviour
Since stone tool cut marks and carnivore tooth marks were first described systematically on Plio-Pleistocene archaeological bone1,2, bone surface modification has played a prominent role in interpreting early archaeological site formation and hominid behaviour3–15. Here we introduce a new class of bone surface modification, which we call percussion marks. Percussion marks were produced during experimental breakage of marrow bones, and occur as pits or grooves impressed on a bone's surface by natural protrusions on the granitic hammerstone and anvil used. Although percussion marks can superficially mimic carnivore tooth marks, they nonetheless are closely associated with hammerstone impact notches and show consistent micromorphological features which distinguish them from tooth marks and other classes of bone surface modification. Given indications of prehistoric hammer-stone breakage of marrow bones1,7, an awareness of percussion marks is critical for accurately identifying the biological agents of bone modification at archaeological sites and provides a new diagnostic of carcass processing by hominids.