Experimental investigation of behaviour of axially restrained steel beams in fire

The growing use of unprotected or partially protected steelwork in buildings has caused a lively debate regarding the safety of this form of construction. A good deal of recent research has been concentrated in this direction and has indicated that steel members have a substantial inherent ability to resist fire so that additional fire protection can be either reduced or eliminated completely. A performance-based philosophy also extends the study into the effect of structural continuity. However, thermal expansion during the heating phase or contraction during the cooling phase of most beams is likely to be restrained by adjacent parts of the whole frame or sub-frame assembly. This has not been properly addressed before. A research project was funded to study theoretically and experimentally the effect of restraint on beams in the event of fire. This paper describes the experimental programme that was completed recently in the Fire Laboratory at Manchester. A new test furnace has been built in which an unprotected or partially protected steel beam can be tested under load while it is restrained between two columns in a structure similar to a rugby goal post. Two different types of beam-to-column connection were examined while the whole sub-frame assembly was subjected to various levels of loading. Additional horizontal restraints were applied at the level of the beam in order to simulate the restraining effect of adjacent parts of the complete frame. The experimental programme was particularly concerned with the effect of the axial restraint on eventual catenary action, which may be able to prevent the beam's deflections from running-away at very high temperatures. (C) 2002 Elsevier Science Ltd. All rights reserved.