Techno Press

Steel and Composite Structures   Volume 1, Number 4, December 2001, pages 427-440
Performance of steel beams at elevated temperatures under the effect of axial restraints
T.C.H. Liu and J.M. Davies

Abstract     [Full Text]
    The growing use of unprotected or partially protected steelwork in buildings has caused a livelyrndebate regarding the safety of this form of construction. A good deal of recent research has indicated that steelrnmembers have a substantial inherent ability to resist fire so that additional fire protection can be either reducedrnor eliminated completely. A performance based philosophy also extends the study into the effect of structuralrncontinuity and the performance of the whole structural totality. As part of the structural system, thermalrnexpansion during the heating phase or contraction during the cooling phase in most beams is likely to bernrestrained by adjacent parts of the whole system or sub-frame assembly due to compartmentation. This has notrnbeen properly addressed before. This paper describes an experimental programme in which unprotected steelrnbeams were tested under load while it is restrained between two columns and additional horizontal restraintsrnwith particular concern on the effect of catenary action in the beams when subjected to large deflection at veryrnhigh temperature. This paper also presents a three-dimensional mathematical modelling, based on the finiternelement method, of the series of fire tests on the part-frame. The complete analysis starts with an evaluation ofrntemperature distribution in the structure at various time levels. It is followed by a detail 3-D finite elementrnanalysis on its structural response as a result of the changing temperature distribution. The principal part of thernanalysis makes use of an existing finite element package FEAST. The effect of columns being fire-protectedrnand the beam being axially restrained has been modelled adequately in terms of their thermal and structuralrnresponses. The consequence of the beam being restrained is that the axial force in the restrained beam starts asrna compression, which increases gradually up to a point when the material has deteriorated to such a level thatrnthe beam deflects excessively. The axial compression force drops rapidly and changes into a tension forcernleading to a catenary action, which slows down the beam deflection from running away. Design engineers willrnbe benefited with the consideration of the catenary action.
Key Words
    fire engineering; fire resistance; steel beams; fire tests; with resiseants; fire element analysis; catenary action.
T. C. H. L i u and J.M. Davies, Manchester School of Engineering, Oxford Road, Manchester, M13 9PL, UK

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