INVESTIGATION INTO DUCTILE BEHAVIOUR OF CONFINED 'PLAIN AND FIBRE REINFORCED CONCRETE COLUMNS

Abstract

Ductility is an important issue particularly in HSC columns under seismic loading. This can be achieved by providing proper confining reinforcement in potential plastic hinge regions of reinforced concrete columns. Although various building codes have specified design equations which can be used to determine the requirement of confining steel in these potential plastic hinge regions, but these equations have some limitations. Most of the equations are valid for normal strength concrete only. Further these design equations do not incorporate all the factors affecting the requirement of the confining steel in potential plastic hinge regions of reinforced concrete columns such as curvature ductility demand, axial load level, mechanical reinforcement ratio, yield strength of lateral steel and grade of concrete. Thus there is an immediate need to develop some design equations for ductile design of columns which can include all these factors and can be used for both normal and high strength concrete. In this thesis an attempt has been made to derive such design equations for requirement of confining reinforcement in potential plastic hinge regions of reinforced concrete columns for ductile behaviour of columns. The design equations are based on an extensive moment curvature study of reinforced concrete columns. The moment curvature results are verified with the already established experimental results. These design equations can be applied to both the normal and high strength concrete columns and also to both the normal and high strength steel reinforcement. The design equations are compared with the already established equations and a good comparison was observed. Design charts have also been prepared so as to make design simple and easy. Further the use of fibres in high strength concrete columns is also proposed so as to reduce the spacing of ties to avoid congestion especially near beam column joints. Equations which can assess toughness based on the percentage of fibres and volumetric ratio of confining steel in columns have also been derived.