Response of Prestressed Concrete Beams Subjected to Shear and Torsion

Eccentric loading or compatibility conditions can cause beams in buildings to be subjected to significant torsions. Although design procedures for torsion are based on tests of stand-alone members and require closed stirrups to be used as transverse reinforcement, interior girders in beam-and-girder construction are usually integral with floor slabs and reinforced with open stirrups. This paper describes an experimental investigation of two post-tensioned companion specimens, designed to represent interior beams with an integral slab, which were loaded to failure under combined moment, shear, and torsion. The specimens were identical, except one was detailed using open stirrups and the other using closed stirrups. The strength of these members was significantly underpredicted by the ACI 318-19 and CSA A23.3-19 codes, which were, on average, conservative by factors of 3.50 and 2.05, respectively. The specimen detailed with open stirrups did not demonstrate a significantly different torsional response than the specimen containing closed stirrups.

Automated summary

The experimental investigation of interior beams with integral slabs showed that the strength of these members was significantly underestimated by the ACI 318-19 and CSA A23.3-19 codes. Additionally, there was no significant difference in torsional response between specimens detailed with open stirrups and closed stirrups.