SHEAR FAILURE OF TWO-SPAN CONTINUOUS PRESTRESSED CONCRETE BEAMS WITHOUT WEB REINFORCEMENT

SHEAR FAILURE OF TWO-SPAN CONTINUOUS PRESTRESSED CONCRETE BEAMS WITHOUT WEB REINFORCEMENT By ISSAC ZEKARIA, University of Manchester, England SYNOPSIS Tests were made on 12 two-span continuous prestressed concrete beams of rectangular section without web reinforcement and without un-tensioned steel. Linearly transformed concordant cables were used, and all beams were post-tensioned and grouted. It was shown by the present tests that such beams can fail in shear before the beam develops its full flexural strength. The mode and mechanism of such failures are described, and compared with flexure failures. The validity of the elastic equations used in computing the principal stresses in concrete was checked experimentally, but these equations were found to fall short of describing precisely, or fully, the actual behaviour of the beams. They were, thus, found unsuitable as criteria for predicting the mode of failure. Test results suggested that there is some degree of interaction between shear and bending, i.e., an increase in bending at a section reduces its shear-carrying capacity. Analysis of the factors influencing shear failure in continuous prestressed concrete beams is presented, and a new concept, the Shear Susceptibility Number, is introduced the magnitude of which throws light on the vulnerability of a continuous beam to shear failures, and on the behaviour of the beam at failure. In addition, the difference in the internal behaviour of beams failing in shear and flexure is outlined by measurements of the variation of principal strains and the orientation of principal axes with loads in beams having high and low values of shear susceptibility number. INTRODUCTION The prediction of shear failure and the load at which such failure will take place is very important, and it becomes particularly so if we are to base our design on ultimate strength and load factor rather than on working stresses and a factor of safety. The importance of the study of shear failure in reinforced and prestressed concrete beams has long been recognized by engineers, but the study of the problem in prestressed concrete has started only recently. The literature available deals, in fact, with only one or two series of tests carried out on simply supported beams.' The present tests are believed to be the first attempt ever made to investigate the problem of shear failure in continuous prestressed concrete beams. 10 PCI Journal

SHEAR FAILURE OF TWO-SPAN CONTINUOUS PRESTRESSED CONCRETE BEAMS WITHOUT WEB REINFORCEMENT

Documents

shear failure

reinforced concrete

beams

untensioned steel

flexural strength