Bracing of thin walled steel box columns during pumping of wet concrete in tall buildings

Abstract

This paper considers the bracing of thin walled steel box columns during the wet concrete pumping procedure for the construction of concrete filled columns in a tall building. The wet concrete exerts a hydrostatic pressure in addition to the axial loads from floor construction on the column cross-section and this causes excessive lateral deflections. For economical construction the steel component plates of the column are required to be minimized in thickness and thus an effective bracing strategy is required to be developed to restrain these deformations. The bracing system presented is similar to that employed for formwork of rectangular reinforced concrete columns and has been used on various tall buildings throughout the world being particularly germane to steel columns which are composed of flat faceted plates such as rectangular and triangular sections. The analysis presented herein uses a linear folded plate finite element method developed elsewhere to study the effects of wet concrete being pumped into steel columns. The main parameters which are found to influence the results are the boundary conditions, column width and plate thickness and the number of braces provided between floor levels. A design example is given and further research, including experimental calibration, is then outlined.