Through the experiments of 7 T-section composite beams, steel fiber reinforced self-stressing concrete (SFRSC) as the composite beam in the composite layer was studied under the hogging bending. The tests simulated composite layer tensile strain under the hogging bending of inverted loading composite beams, giving the relationship under the different fatigue stress ratios between fatigue cycles and steel bar's stress range, crack width, stiffness loss and damage, etc., in composite layer. This article established fatigue life equation, and analyzed SFRSC reinforced mechanism to crack width and stiffness loss. The results show that SFRSC as the composite beam concrete has excellent properties of crack resistance and tensile, can reinforce the fatigue crack width and stiffness loss of composite beams, and improve the durability and in normal use of composite beams in the hogging bending zone.
Super-span, reinforced concrete, T-shaped cross-section beams (T-beams) with a service life of more than 30 years are widely used in highway bridges in China. Most of these beams have been retrofitted with glass fiber-reinforced plastic (GFRP) to prevent performance degradation. However, the actual shear performance, ultimate state, and failure mechanism of the existing retrofitted super-span concrete T-beams are currently unclear for many inextricable problems. To fill these gaps, in this study, one super-span concrete T-beam, in service for 31 years and retrofitted with GFRP, was extracted from a highway bridge to conduct shear experimentation in a structural laboratory. To assess the particularity of the specimen, finite element analysis was also conducted using ABAQUS software as a supplement to the shear tests. The failure procedure of the specimen was investigated, and the influence of the loading mode on the shear performance of a super-long and old T-beam was also studied. It is concluded that the failure of the super-span T-beam begins with small cracks at the bottom of the mid-span, rather than a loading point.
The special reinforced concrete composite beam consists of a steel fiber reinforced self-stressing concrete composite layer and a reinforced concrete T-beam, and constructional bars are set up at their bonding interface. Fatigue properties of the composite beam under the action of negative moment were experimentally studied. Through inverted loading mode the load-bearing state of a composite beam was simulated under the action of negative moment. With the ratios of constructional bars being 0, 0.082% and 0.164% respectively as parameters, the effects of constructional bars on the properties of composite beam, such as fatigue life, crack propagation, rigidity loss as well as damage behavior of bonding interface, were studied. The mechanism of the constructional bars on the fatigue properties of the composite beams and the restriction mechanism of crack widths and rigidity loss were analyzed. The test results show that the constructional bars can enhance the shear resistance of the bonding interface between composite layer and old concrete beam and restrict expanding of steel fiber reinforced self-stressing concrete, which are beneficial to synergistic action of composite layer and old concrete beam, to reducing the stress amplitude of bars and the crack width of composite layer, and to increasing the durability and fatigue life of the composite beam.
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