New Criteria for Fire Endurance Tests

Abstract

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.

Rectification of “restrained vs unrestrained”

“…Essentially, the 1969 proposed revisions recommend that beam and floor/roof assembly tests be performed under restrained conditions and unrestrained classifications be derived on the basis of application of temperature limitations during restrained tests. Revealingly, this same proposal acknowledged that correlating restraint conditions of a furnace test to that present in actual building construction is a daunting task …”

“…9 To address the impact of end restraint on the results of standard fire tests of floor and roof assemblies, several revisions were proposed to the governing ASTM committee in 1964, 1965, 1967, 1968, and 1969 for adoption in the ASTM E119 standard. 10 These proposals stemmed from the observation that the results from fire tests on structural assemblies tested under identical configurations, protection schemes, and temperature conditions varied considerably from test to test. 11 Development of a varying degree of applied restraint against thermal expansion in standard fire tests was assumed to be the main reason for such variations 12 .…”

“…Revealingly, this same proposal acknowledged that correlating restraint conditions of a furnace test to that present in actual building construction is a daunting task. 10 In its first appearance in ASTM E119-71, guidance on restraint classification was provided in an appendix to the standard, §A4. This restraint classification guidance remains in an appendix, now §X3, and the language remains largely unchanged.…”