The Behaviour Of Restrained Steel Beam During Heating And Cooling And The Damage Of Beam-to-Column Connection

The aim of fire-resistance design of building structures is to avoid severe damage or collapse during fire attack. Due to the difficulty to determine global stability of a building structure subjected to fire, most Codes and Standards in the world for fire-resistance of structures adopt isolated member capacity checking. By now, there are two fire-resistant design methods of steel structure, the first one is based on experiment, and the second one is based on calculating. However, these two design methods are all for isolated members, not for restrained members in a completed structure. With the progress of recent research on fire-resistance of structures, more and more investigators become doubtful of the effectiveness of these methods, since they have recognized, for example, that the behaviour of a steel beam in a building structure is not the same as that of an isolated beam.In the middle of 1990's, some researchers began to investigate the behaviour of restrained beams in fire conditions. By now, the behaviour of restrained steel beams can be well simulated by FE method, and some theoretical methods have been presented, but there are still some problems needing to be investigated. In this paper, some of the problems are studied, as listed below:(1) In the previous theories of restrained steel beams, because the stress distribution in the model changes abruptly when it yields, the behaviour of restrained beams is not continuous when it changes from elastic to plastic. In this paper, a continuous development model of stress and strain is presented, through which the above problem is solved.(2) The stiffness of beams, which has not been properly studied in the previous researches, makes an important role on the behaviour of restrained steel beams. In this paper, based on the behaviour of a curved beam, the change of the stiffness of restrained steel beams is studied.(3) In fire conditions, local buckling in restrained steel beams may occur, but it has not been studied by previous researchers. In this paper, local buckling of restrained steel beams is investigated, according to elastic-plastic buckling theory.(4) By now, the behaviour of restrained steel beams during cooling has not been investigated. In this paper, this problem is studied through theoretical analysis and experiment. It is shown that tremendous axial tensile force can be induced in restrained steel beam during cooling.(5) In the current design method for beam-to-column connection, the axial tensile force in restrained steel beams is not taken into account, which may lead to the...