Stiffness test in lateral direction of temporary wooden building supports

Abstract

Temporary supports consisting of a jack, a stack of wooden cubic elements and a iron plate are used during the removal of buildings deflections by uneven raising. Where the weight of a building is rested on temporary supports with a considerable length, unintentional displacements of buildings in the horizontal direction are seen. The displacements are connected with supports deformations caused by horizontal forces acting on the building part being raised. Non-vertically installed jacks, being part of the supports, are the most frequent reason for the occurrence of such forces. The jacks are not vertical due to deformations in the stack of wooden elements, upon which they are rested. In such case, the stiffness of temporary supports is essential for the safety of the deflection removal process. Laboratory tests of temporary supports were carried out and they showed that their stiffness, understood as a horizontal force divided by a displacement in the acting direction of the force, is not constant. The stiffness of supports is decreasing as the displacement amplitude grows. A considerable decrease in supports stiffness was experienced when positive longitudinal deformations occurred in the cross section of the support elements. As a result, the unconnected elements of the supports were unable to transmit positive stresses of this number. For the investigated range of loads, the deformations of the material of the supports elements were elastic. Inelastic forces were however generated along the contact points of the elements forming part of the supports, and such forces were responsible for creating a hysteresis loop and energy dissipation by the supports. The system, when a full load-unload cycle was applied, was returning to the initial position. Higher values of the energy dissipation coefficient correspond to higher values of a displacement amplitude.