Analysis and experimental research on load-bearing behavior of grouted-round-steel-tube truss-prestressed concrete continuous beam

In order to investigate the plastic redistribution of internal forces in encased grouted-round-steel-tube truss-prestressed concrete continuous beams, three encased grouted-round-steel-tube truss-prestressed concrete continuous beams were tested. Six simulated beams were also studied using nonlinear numerical analysis. The two ultimate limit states used for design and evaluation and the plastic redistribution of internal forces in the test beams are discussed in this paper. According to the results, the encased grouted-round-steel-tube truss-prestressed concrete continuous beams reach the limit state of the cross sectional bearing capacity when the loads begin to decrease and the displacement begin to increase rapidly on any span. The plastic redistribution of internal forces and moment modulation process mostly take place during the plastic hinge rotation at the middle support. Base on the results of the nonlinear M-φ analysis of cross section using strip layer method, the experimental results and the numerical analysis results, the formulae for calculating the stress increment in non-bonded tendons under the service stage and the two ultimate limit states are established. The plastic hinge lengths on both sides of the middle support under the two ultimate limit states are measured, which are used to obtain the formula for estimating the equivalent plastic hinge length by regression analysis. In addition, the formulae for computing the internal force redistribution coefficients Δ under the two ultimate limit states are proposed. For the formula corresponding to the ultimate limit state for design, the independent variables are the reinforcement indices βo,i and βo,m at the cross section at the middle support and the controlling cross section at the mid-span respectively. For the formula corresponding to the ultimate limit state for evaluation, the independent variable is the relative plastic rotation θp of the controlling cross-section at the middle support.