Analysis of the effect of load application eccentricity on the stiffness of supports consisting of stack of elements

Silesian University of Technology, Faculty of Civil Engineering, 44-100 Gliwice, ul. Akademicka 5, Poland

^* Corresponding author: krzysztof.gromysz@polsl.pl

Abstract

During the removal of building deflections, temporary supports, consisting of a stack of repeatable elements, are used. Hydraulic jacks which force the vertical displacement of the building are used, as well. Depending on the phase of deflection removal, the entire weight of the building, or part thereof, is rested on temporary supports. As a consequence of inaccuracies in the installation of a stack of elements, the building weight is transmitted onto supports in an eccentric manner. In addition, the supports are loaded with horizontal forces. The forces result from the wind load, from kinematic excitations of non-axially installed jacks, from 2nd order deformations of supports and from exceptional loads. Deformations in the vertical direction, with a positive sign, occur due to the activity of the eccentric load and horizontal forces in the supports. However, the unbounded hexagonal elements forming the stack are unable to transmit the tensile stresses. As a consequence, the stiffness of the supports depends on the load. The stiffness of temporary supports in the horizontal direction was analysed considering the existence of unintended eccentricity and the horizontal load. A support model was defined for this purpose, whose material does not transmit tensile stresses. It was shown that the scheme of the support is changing depending on the application eccentricity of the vertical load and on the horizontal load value. Eight schemes were distinguished, which may be executed by a support. It was found that if the eccentricity and the horizontal load value are increased, this will decrease the support stiffness. This stiffness varies from zero, when a rocker arm is the support scheme, to the maximum value that is corresponding to the stiffness of cantilever rod. The analysis is limited to stocky supports by assuming that the load is much smaller than critical. Moreover, the influence of the support’s vertex displacement on the eccentricity was not taken into account.