POSTCRACKING STIFFNESS OF REINFORCED CONCRETE BEAMS IN TORSION AND BENDING

THEORETICAL EXPRESSIONS FOR THE POSTRCRACKING STIFFNESS OF RECTANGULAR REINFORCED CONCRETE BEAMS IN TORSION AND BENDING ARE DESCRIBED AND SIMPLIFIED. THEY ARE BASED ON A SPACE TRUSS MODEL. IT IS SHOWN THAT THE POSTRCRACKING TORSIONAL STIFFNESS IS NOT GREATLY INFLUENCED BY BENDING WHILE THE POSTCRACKING FLEXURAL STIFFNESS DEPENDS ON THE AMOUNT OF TORSION. REALIZING THAT THE DROP IN TORSIONAL STIFFNESS AFTER CRACKING IS GREATER THAN THE DROP IN FLEXURAL STIFFNESS, THE TORSIONAL MOMENTS AFTER CRACKING WILL BE SMALLER IN MANY CASES THAN THE ONES PREDICTED BY THE UNCRACKED STIFFNESS VALUES. THE TORSIONAL REINFORCEMENT MAY THUS BE REDUCED BY MEANS OF THE TOOLS PROVIDED IN THIS PAPER. /ACI/