Performance of plastic hinge in a two-span continuous rectangular cross-section beam prestressed with unbonded tendons under concentrated load at mid span

It is common to use continuous unbonded pre stressed concrete (UPC) beams for the one-way concrete floors systems. Fewer studies have been made on the redistribution of internal forces in unbonded prestressed concrete continuous beams. Experiments on sixteen two-span rectangular cross-section concrete beams prestressed with unbonded tendons are reported here, in which the global reinforcement index in critical section above inner support, tensioning control coefficient, prestressing degree in critical section, the span to section depth ratio, and the ratios of global reinforcement indices at critical sections of mid-span and over inner support locations are the main testing parameters. Design of testing beams, test scheme, phenomena and determination of normal section load-bearing capacity are presented. The emphasis is placed on the appearance and development of plastic hinges above inner support in continuous rectangular cross-section concrete beams prestressed with unbonded tendons. Formula is proposed for calculating the equivalent length of plastic zone above inner support in correspondence with load type. The results may serve as a basis for moment modulation coefficient with relative plastic rotation as the independent variable.