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The long accepted test procedure for determining the fire endurance of floor and roof assemblies, as described in ASTM Standard Methods of Fire Tests of Building Construction and Materials (Designation: E 119), is being questioned seriously. Skepticism has developed because the performance under fire exposure of structural members and assemblies has not corresponded with anticipated performance based on established properties of materials at elevated temperatures. The difference between predicted results and actual results is attributed to the test procedures used to implement provisions in the Standard which require restraint of the test specimen and imposition of loads to develop working stresses. Restraint of the test specimen has contributed so substantially to the performance that normal structural criteria such as deflection and collapse appear to be of limited value in judging fire endurance.
Research projects have established that significant improvement is brought about by the presence of restraint during fire tests. Individual steel beams have resisted collapse in fire tests for a 25 percent longer time when tested under restraint as compared with simply supported tests. Concrete members have shown in excess of 400 percent increase in fire resistance in comparative tests.
Certain constructions employing continuity and cantilevered sections have shown improved fire resistance as compared with simply supported structures.
Various revisions of the criteria in ASTM Methods E 119 have been proposed. Each of these, developed in 1964, 1965, 1967, 1968, and 1969, provided partial solutions. With the exception of the 1969 proposal, which is before ASTM Committee E-5 at this writing, some features of each proposal have been criticized. The concepts of these proposals are examined in this paper, with a summary of the prevailing views. The impact on future designs of building construction for fire resistance and on the costs of building construction are so great as to make any changes in criteria a most important and difficult decision.
fire tests, fire endurance, fire resistance, restraint, building construction, temperature criteria, evaluation, tests
Bono, J A
Managering engineer, Underwriters' Laboratories, Inc., Northbrook, Ill.