Restrained composite columns

Abstract

This Thesis describes the development of an analysis for inelastic columns, with cross-sections composed of one or more materials, loaded with axial load and biaxial moments. The column can have both rotational and directional restraints at its ends. The analysis has been programmed for a computer and subsequently tested against published results for steel columns, reinforced concrete columns, and concrete-encased steel composite columns and shown to give good agreement. A test rig with an axial load capacity of 2MN and capable of testing full-scale columns of any practical length has been designed and built. Columns with elastic and elastic-plastic rotational restraints or, pin-ends or any combination can be tested and column end-moments of up to 50 kNm can be applied through the beams. One important feature of the test rig is sets of crossed knife-edges, which give both major and minor axis rotational freedom and thus allow accurate positioning of the axial load. Eight elastically restrained concrete-encased steel composite no-sway columns have been tested, three with biaxial restraints and loadings, using the rig. The results from the tests have been compared with predictions using the computer program and agreement between the observed and predicted results for ultimate loads, deflections, and end-moments is good. The behaviour of column lengths within rigid-Jointed no-sway frames with both plastically and elastically designed beams has been studied. For the case of a column with elastic restraints design proposals have been checked and shown to be conservative. When the beams are designed plastically it is recommended that a conservative approach should be adopted until further research has been carried out into this topic