Transverse Impact of a Horizontal Beam on a Vertical Column

Abstract

The transverse impact of a uniformly translating beam hitting a fixed-fixed column is investigated. Although in-air impact is considered, the study is motivated by water-driven woody debris during flood, storm surge, and tsunami. Hence, the beam (pole) is assumed to be wood, and the column is concrete, steel, or wood. Given the relatively small magnitude of the impact speed in such events, only elastic impact is considered. An analytical solution method is presented, which is also used to verify finite-element results. The results show that the contact force between the pole and the column depends on the local shear deformation in the pole and the column, and hence Timoshenko beam theory is needed. Multiple impacts are considered, and the whole collision event is divided into contact phases and separation phases. It is shown that for all cases the maximum contact force occurs during later contact phases and its value can reach up to 1.5 times the peak force in the first contact phase. The impact duration of the first contact phase depends on the shear wave in the pole or the column according to the mass and wave speed ratios. The total impulse on the pole ranges between 1.5 and 1.8 times the initial momentum of the pole, depending on the stiffness of the column. The energy exchange during the multiple impacts, while it can be complicated, reveals that for relatively stiff columns the sum of the translational kinetic and bending strain energies of the pole constitutes approximately 90% of the total energy. In all cases considered, relatively little net energy has been transmitted to the column at the time of final separation.