Response of the Bond in Reinforced Concrete to High Temperatures

Abstract

Synopsis The effect of high temperutures upon the bond between the steel und concrete in reinforced concrete was examined over a temperature range of 20–750°C. The concrete mix was constant throughout und 16 mm deformed reinforcing bar (Tor bar) was used in most tests. Various parameters were examined including different test conditions and depths of cover. The four test conditions used were: (l) stressed during heating (a steady-state bond stress of 3·70 N/mm2 was applied) and loaded to failure when hot, (2) stressed during heating and loaded to failure when cooled, (3) no applied stress during heating and loaded to failure when hot, and (4) no stress during heating and loaded to failure when cooled. Four different depths of concrete cover (25, 32, 46 und 55 mm) were l for the stressed/residual test condition, but only tht 55 mm cover was used with the other three test conditions. The effect of heat upon the compressive und tensile strength of the concrete was also considered, together with its effect upon the bond performance. Some 16 mm plain bar specimens were used in the tensile strength studies. Introduction When a reinforced concrete structure has been involved in a fire. it is often possible for it to remain standing, because of the good fire-resisting properties of the concrete. This means that. in dealing with such a situation. a choice can be made between reconstruction and reinstatement. Often reinstatement can be the quicker and cheaper alternative. However, before a decision can be made, it is necessar/10 establish whether or not the damaged structure is suitable for such treatment. To do this, its residual capacity for structural performance must be assessed, which requires knowledge of the properties of steel and concrete, and of the bond between them at temperatures experienced in fires.