DETERMINATION OF RESTRAINT FORCES FOR STEEL STRUTS.

Abstract

In design, it is generally assumed that the restraint force for struts has a constant value, regardless of the end conditions of the strut and the stiffness and location of the restraint Furthermore, BS 5950: Part 1 (Clause 4.7.1.2) recommends that the force in a restraint for struts (other than those forming the flanges of lattice girders), is equal to 1% of the compressive force in the strut. It is also recommended in Eurocode 3: Part 1.1 (Clause 5.2.4.4) that the restraint force is equivalent to a uniformly distributed load of q (- compressive force / (50 x length of strut)). And for a single restraint anywhere along the strut this will give a restraint force of 1% of the compressive force in the strut This paper deals with the determination of the force induced in the restraint for struts subjected to an axial load and having various end conditions. The restraint which is located at various points along the strut is assumed to act as a spring having a specified stiffness. The mathematical model of the strut, which incorporates the equivalent out of straightness imperfection, was solved and the results obtained show that the restraint force can exceed the 1% value depending on the location and stiffness of the restraint and the end conditions of the strut.