An analytical method for determining the loading on connections in heating and cooling during a fire

This paper presents a proposed analytical method for calculating the mechanical loading on a beam column connection in fire. The behavior of connections in fire has received considerable interest over the last decade since it is well known and demonstrated experimentally that composite steel concrete construction is able to adopt alternative load bearing mechanisms in fire as a result of large displacements. This global behavior is different from behavior which is studied in standard furnace testing and places additional loads on the supporting structure which must be able to support elements which are effectively 'hanging' in tension as opposed to supporting the load through shear and bending, as at ambient. First, this paper explores the mechanisms which lead to time varying mechanical loading on a beam / column connection in fire. Then a simple method for calculating a loading envelope of the connection is proposed. The analytical method is derived from fundamental principles of structural behavior at high temperatures and is a development of previous work published by the authors elsewhere. New developments presented include a discussion of the mechanisms which govern the response of composite structures during cooling following a fire and inclusion of these in the analytical model. The analytical method is then compared with the results of finite element analyses and is shown to compare favorably