An experimental examination of the dynamical behaviour of a strut in a rigidly jointed truss framework

Abstract

The relation between axial load and axial deformation for a strut generally involves an increase of deformation with decreasing load after the maximum load is reached. When a truss containing one or more struts is subjected to dead load, it is possible that equilibrium may be lost temporarily while the structure undergoes a ‘dynamic jump’ to a new position of equilibrium. The dynamic jump phenomenon was analyzed theoretically for a simple truss by Davies & Neal (1959). It was shown that the motion is governed by interchanges between the elastic strain energy stored in the tension members, the work done on the strut, and the kinetic and potential energies of the applied load. The present paper describes an experimental investigation into the dynamic jump phenomenon for the same simple truss system. Predictions concerning the collapse load at which the dynamic jump would occur, and the magnitude of the jump, were made using the energy method together with strut characteristics obtained previously under quasistatic conditions. It was found that the collapse loads could be predicted accurately with the aid of these characteristics. However, in order to determine the magnitude of each jump it was necessary to modify the strut characteristics markedly to allow for the effect of high strain rates during the jump in increasing the load sustained by the struts.