Full-scale model tests were carried out on a 30 m span prestressed concrete box girder and a 20 m span prestressed concrete hollow slab. Failure models were prestressed reinforcement tensile failure and crashing of ro...Full-scale model tests were carried out on a 30 m span prestressed concrete box girder and a 20 m span prestressed concrete hollow slab. Failure models were prestressed reinforcement tensile failure and crashing of roof concrete, respectively. The ductility indexes of the box girder and hollow slab were 1.99 and 1.23, respectively, according to the energy viewpoint. Based on the horizontal section hypothesis, the nonlinear computation procedure was established using the limited banding law, and it could carry out the entire performance analysis including the unloading, mainly focusing on the ways to achieve the unloading curves computation through stress-strain, moment-curvature and load-displacement curves. Through the procedure, parameters that influence on the bearing capacity, deformation performance and ductility of the structures were analyzed. Those parameters were quantity of prestressed reinforcement and tension coefficients of prestressed reinforcement. From the analysis, some useful conclusions can be obtained.展开更多
Tests of 4 simply supported unbonded prestressed truss concrete composite beams encased with circular steel tube were carried out. It is found that the ratio of the stress increment of the unbonded tendon to that of t...Tests of 4 simply supported unbonded prestressed truss concrete composite beams encased with circular steel tube were carried out. It is found that the ratio of the stress increment of the unbonded tendon to that of the tensile steel tube is 0.252 during the using stage,and the average crack space of beams depends on the ratio of the sum of the bottom chord steel tube's outside diameter and the secondary bottom chord steel tube's section area to the effective tensile concrete area. The coefficient of uneven crack distribution is 1.68 and the formula for the calculation of crack width is established. Test results indicate that the ultimate stress increment of unbonded tendon in the beams decreases in linearity with the increase of the composite reinforcement index β0. The pure bending region of beams accords with the plane section assumption from loading to failure. The calculation formula of ultimate stress increment of the unbonded tendon and the method to calculate the bearing capacity of normal section of beams have been presented. Besides,the method to calculate the stiffness of this sort of beams is brought forward as well.展开更多
Usage of fiber reinforced concrete to replace shear reinforcement has become more common in the precast industry in recent years. In some cases, the use of steel fibers could be problematic because of corrosion, hence...Usage of fiber reinforced concrete to replace shear reinforcement has become more common in the precast industry in recent years. In some cases, the use of steel fibers could be problematic because of corrosion, hence, synthetic material could be a suitable alternative material solution. Thus, it would appear logical to undertake a comparison of these fibers＇ load bearing capacity to determine suitability in each case. In this paper, the bending and the shear tests of four large-scale and prestressed beams made of steel or synthetic fiber reinforced concrete without stirrups are presented. The post-cracking residual tensile strength diagram of the fibers, according to RILEM （International Union of Laboratories and Experts in Construction Materials, Systems and Structures） TC162, is given and the experimental behavior of the fiber solutions is compared. The modified fracture energy method is used to define an advanced material model for the fiber reinforced concrete in the finite element analysis. The numerical calculations and the test results are compared in terms of crack propagation and the loading-deflect＇ion process. As a consequence, both steel and synthetic fibers seem to be good alternatives to replace the stirrups. However, the behavior of each fiber is not the same. The numerical calculation provided a good approximation for the real scale tests.展开更多
基金National Natural Science Foundation of China(No.50678063)
文摘Full-scale model tests were carried out on a 30 m span prestressed concrete box girder and a 20 m span prestressed concrete hollow slab. Failure models were prestressed reinforcement tensile failure and crashing of roof concrete, respectively. The ductility indexes of the box girder and hollow slab were 1.99 and 1.23, respectively, according to the energy viewpoint. Based on the horizontal section hypothesis, the nonlinear computation procedure was established using the limited banding law, and it could carry out the entire performance analysis including the unloading, mainly focusing on the ways to achieve the unloading curves computation through stress-strain, moment-curvature and load-displacement curves. Through the procedure, parameters that influence on the bearing capacity, deformation performance and ductility of the structures were analyzed. Those parameters were quantity of prestressed reinforcement and tension coefficients of prestressed reinforcement. From the analysis, some useful conclusions can be obtained.
文摘Tests of 4 simply supported unbonded prestressed truss concrete composite beams encased with circular steel tube were carried out. It is found that the ratio of the stress increment of the unbonded tendon to that of the tensile steel tube is 0.252 during the using stage,and the average crack space of beams depends on the ratio of the sum of the bottom chord steel tube's outside diameter and the secondary bottom chord steel tube's section area to the effective tensile concrete area. The coefficient of uneven crack distribution is 1.68 and the formula for the calculation of crack width is established. Test results indicate that the ultimate stress increment of unbonded tendon in the beams decreases in linearity with the increase of the composite reinforcement index β0. The pure bending region of beams accords with the plane section assumption from loading to failure. The calculation formula of ultimate stress increment of the unbonded tendon and the method to calculate the bearing capacity of normal section of beams have been presented. Besides,the method to calculate the stiffness of this sort of beams is brought forward as well.
文摘Usage of fiber reinforced concrete to replace shear reinforcement has become more common in the precast industry in recent years. In some cases, the use of steel fibers could be problematic because of corrosion, hence, synthetic material could be a suitable alternative material solution. Thus, it would appear logical to undertake a comparison of these fibers＇ load bearing capacity to determine suitability in each case. In this paper, the bending and the shear tests of four large-scale and prestressed beams made of steel or synthetic fiber reinforced concrete without stirrups are presented. The post-cracking residual tensile strength diagram of the fibers, according to RILEM （International Union of Laboratories and Experts in Construction Materials, Systems and Structures） TC162, is given and the experimental behavior of the fiber solutions is compared. The modified fracture energy method is used to define an advanced material model for the fiber reinforced concrete in the finite element analysis. The numerical calculations and the test results are compared in terms of crack propagation and the loading-deflect＇ion process. As a consequence, both steel and synthetic fibers seem to be good alternatives to replace the stirrups. However, the behavior of each fiber is not the same. The numerical calculation provided a good approximation for the real scale tests.
