An earlier exploratory study on the effects of restraint of thermal expansion on the fire resistance of prestressed concrete showed that for similar specimens, made of normal weight concrete, maximum thermal thrust was a function of the allowed linear expansion. In the present study, data were obtained for three additional groups of specimens: lightweight prestressed, lightweight reinforced, and normal weight reinforced. A method is presented for estimating the maximum thermal thrust that occurs during a fire test of a concrete floor, roof, or beam. Results of 12 fire tests of restrained concrete flexural members indicate that the method predicts the maximum thrust within about 15 percent. The method is applicable to specimens restrained both longitudinally and laterally as well as those restrained in only one direction. The method underestimates thrust for specimens with embedded underfloor ducts and overestimates thrust for specimens partly insulated from direct contact with the fire. In all 43 fire tests the specimens supported their loads considerably longer than would have been anticipated for either simply supported or fully restrained conditions.
The contemporary high rise building with its central air conditioning system and high content of synthetic materials presents a potentially higher fire and smoke hazard than those erected prior to 1950. The fire penetration and the transportation of fire, hot gases, noxious fumes and smoke through the duct system is an important factor affecting the designers' and building code concept of compartmentalization and life safety of occupants. Since air ducts penetrate fire barriers, the duct materials, the flexible connectors between the ducts, and the terminal units are all important elements that can affect the actual fire endurance of the fire barrier. Flexible connectors made of four different materials (aluminum, galvanized steel, glass fiber and woven glass fiber) and two attachment techniques were subjected to fire tests which conformed to the Standard Method of Fire Tests for Building Constructions and Materials, ASTM E 119. The results show that in order to maintain the integrity of a fire barrier penetrated by a duct or flexible connector, the duct and connector must maintain their integrity for the period of the fire exposure, the connectors must remain tightly attached to the duct, and the penetrations through the fire barrier must be suitably blocked (fire stopped) at the edge of i the opening. The tests also showed that rubber and plastic components in the terminal units can produce significant amounts of irritating smoke which can spread into the room and hence to other parts of the buildings.
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