Experimental study of moment redistribution in continuous concrete beams prestressed with unbonded tendons

The moment redistribution in a continuous prestressed concrete beam occurs as a result of a change in the rigidity of a beam and formation of plastic hinges when approaching the failure. Rotation capacity is required to allow for moment redistribution. Four continuous two-span concrete beams prestressed with unbonded tendons were built and loaded up to failure at the laboratory of Civil Engineering in Tampere University. The test beams had different reinforcement ratios in the support area when the degree of prestressing and amount of tension reinforcement in the midspans were kept constant. All test beams were loaded by bending, but one test beam had torsion load in addition to bending. The degree of bending moment redistribution was defined by using nonlinear analysis and equations from the European standard and ACI318, as well as the test results. Moment redistribution clearly occurred on all test beams, and the beams had a high level of deformability.