THE SIZE EFFECT ANALYSIS OF STEEL CONCRETE BOND STRENGTH

Abstract

This report presents a research and study on analysis of size effect on concrete steel bond strength. The utility of reinforced concrete (RC) as a structural material is derived from the combination of concrete that is strong and relatively durable in compression with reinforcing steel that is strong and ductile in tension. Maintaining composite action requires transfer of load between the concrete and steel. When the reinforced concrete is under some applied load, the stresses are developed at the concrete-steel interface. With the mounting loads the capacity of the interface to transmit the stresses starts waning and important prominent displacements occur between steel and concrete. Cracks develop and the structure loses its strength. By general convention, the load capacity of reinforced concrete structures was determined by plastic limit analysis, allowable stress design method and ultimate strength design method in which the material failure criterion is expressed in terms of stress and strain without incorporation of size effect. The compressive stress of concrete or the yielding strength of steel in a reinforced concrete member is considered to remain the same under the standard laboratory and experimental conditions whether it is for a slender member like column or a small element of beam. The size effect represents the deviation from such a prediction. Our goal was to study the changes to the concrete steel bond strength when the member dimensions, size and geometry (i.e. size effect) are taken into account. An experimental and analytical study is carried out as final term project to determine the effect of size on behaviour of RC structures. It is observed, by taking a constant embedment length for a specific size of specimen, that bond strength depends on two parameters; concrete cover and bar diameter. The smaller the concrete cover confinement for a particular diameter of rebar, the smaller is the bond strength. Pull out occurs when the bar diameter is small and splitting occurs when it is large.