Experimental And Theoretical Research On Torsional Behavior Of CFRP Strengthened Reinforced Concrete Box Beams Subjected To Combined Action

Box beam is widely used in various bridge structures, such as double lane highway bridge, railway bridge, curved beam bridge and cable-stayed bridge with mid or large span. It is a typical structural member suffered bending moment, shear force and torque at the same time. Under the influences of inadequate design and natural condition, even because of serious damages due to earthquake, impact and surcharge using, some bridges were in need of being strengthened effectively due to the deficiency of torsional strength. In this dissertation, a systematic study on the experiment and theory of torsional behavior of CFRP (Carbon Fiber Reinforced Polymer) strengthened reinforced concrete box beams subjected to combined action of bending moment, shear force and torque were studied, which provided an important theoretical and technical reference for the further research and design work. The following creativity work and achievements are included,(1) The failure tests of four reinforced concrete box beams strengthened with CFRP subjected to monotonic combined action and the failure tests of four reinforced concrete box beams strengthened with CFRP subjected to monotonic bending moment, shear force and cyclic torque were progressed. The results of the research stated that, the torsional strengths of reinforced concrete box beams were enlarged obviously and the stiffness of them were expanded and the deformation behavior and hysteresis behavior of them were amplified obviously. A simple restoring force model was put forward to simulate the dynamic torsional behavior of CFRP strengthened reinforced concrete box beams subjected to monotonic bending moment, shear force and cyclic torque(2) Based on the modified diagonal compression field theory considering softening of the concrete, a new mathematical model for torsional behavior of CFRP strengthened reinforced concrete box beams subjected to combined action was developed. The calculation formulae and the corresponding computer program in FORTRAN were deduced, by which the numerical investigation on the torsion behavior of four CFRP strengthened reinforced concrete box beams subjected to combined action was performed.(3) Based on the experimental research, a reasonable 3-D finite element model wasestablished and the non-linear finite element analysis was preformed to study the torsional behavior of CFRP strengthened reinforced concrete box beams subjected to combined action. The comparisons of the calculated results with the experimental results indicated that, the finite element method performed in this study could predict accurately the torsional behavior of CFRP strengthened reinforced concrete box beam subjected to combined action. Further investigation was conducted with respects to the shear-torque behavior of CFRP strengthened reinforced concrete box beams. The dimensionless correlation of shear and torque strengths of CFRP strengthened reinforced concrete box beams subjected to combined action was explored, which behaved diagonal linearity .(4) The calculation expressions of the bending moment capacity, the shear capacity and the torque capacity of CFRP strengthened reinforced concrete box beam were derived. Based on the bending moment, shear and torque correlation equations of CFRP strengthened reinforced concrete box beams subjected to combined action, the design method for the torsional strength of CFRP strengthened box beams subjected to combined action was proposed..