FLEXURAL BEHAVIOR OF BEAMS REINFORCED WITH STEEL BARS EXCEEDING THE NOMINAL YIELD STRENGTH

Abstract

IF STEEL MANUFACTURES USUALLY ALWAYS COMPLY WITH THE MINIMUM CODE SPECIFICATIONS, THE NOMINAL YIELD STRENGTH OF REBAR CAN HOWEVER BE SIGNIFICANTLY EXCEEDED IN MANY COUNTRIES, DEPENDING ON THE STEEL MANUFACTURING PROCESSES. SUCH AN INCREASE IN YIELD STRENGTH CAN HAVE NEGATIVE EFFECTS ON THE FLEXURAL BEHAVIOR OF BEAMS DESIGNED AS TENSION CONTROLLED, AND REDUCE THEIR DUCTILITY, AN ESSENTIAL PROPERTY IN SEISMIC RESISTING STRUCTURES. AN EXPERIMENTAL AND ANALYTICAL STUDY OF THE FLEXURAL BEHAVIOR OF RC BEAMS WAS CONDUCTED THROUGH THE INVESTIGATION OF THE MOMENT-CURVATURE RELATIONSHIPS AND THE ULTIMATE STEEL STRAINS. THE MAIN VARIABLE WAS THE LEVEL OF THE ACTUAL STEEL YIELD STRESS AS COMPARED TO THE NOMINAL VALUE. IT WAS FOUND THAT UNEXPECTEDLY HIGH VALUES OF STEEL YIELD STRESS REDUCE THE BEAM DUCTILITY AND VIOLATE THE TENSION-CONTROL CONDITION WHICH WAS EN-FORCED IN THE DESIGN STAGE. APPROPRIATE DESIGN CORRECTIONS ARE PRO-POSED TO ACCOUNT FOR HIGH YIELD STRESS VALUES IN ORDER TO ACHIEVE THE DESIRED DUCTILITY OF BEAMS WHILE MAINTAINING THE MOMENT CAPACITIES.