Pre- and post-cracking torsion in prestressed concrete beams: experimental study

Abstract

Experimental cracking-twist data on torsional concrete beams display significant variations due to the difficulty of measuring small twists during torsion tests of concrete beams. A recent torsion experiment on large reinforced concrete (RC) beam specimens developed a new method that was able to accurately measure small twists before and around cracking. In the current study, the test method was extended to torsion experiments on prestressed concrete (PSC) beam specimens. In addition to addressing the issue of small-twist measurement, the new method also improved other aspects, such as precise measurement and examination of prestressing forces and prestress transfer, and the testing of relatively large specimens with medium to high prestressing levels. This paper describes the test apparatus and method, presents the experimental results of six PSC beam specimens, and discusses and compares the experimental results. The experimental cracking torques Tcr,Test are compared with the Tcr,RC values calculated using a rational formula for RC members. It was found that the Tcr,Test/Tcr,RC ratio for solid PSC beams increases almost linearly with increasing prestress ratio (fpc/f′c) when fpc/f′c is in the range of approximately 0·09 to 0·16, and asymptotically approaches an upper limit of 1·80 when fpc/f′c exceeds 0·16.