Study And Application On Strengthening And Widening Of Simply-supported Reinforced Concrete T-Beam Bridge

Part of the active-duty simply-supported Reinforced Concrete T-beam bridges are suffering from the problem of insufficient bearing or traffic capacity because of the traffic volume skyrocketing. The bridge bottleneck effect restricts the economic development to a certain extent. Strengthening and widening those old bridges with reasonable method in order to improve their bearing and traffic capacity, in the meanwhile, making full use of designed service lifespan of them will exert far-reaching practical significances.This paper based on an actual project of strengthening and widening of an old bridge, presented a reconstruction method which combined the methods of section conversion strengthening and cantilever widening. It studied the method's feasibility and effectiveness in the following aspects:(1) It carried out a reduced-scale model test relied on the prototype of actual project girder before and after reconstructing.The test compared the load reaction of reinforced and unreinforced model beam under static load, simulated the test process using the general finite element program ABAQUS, and evaluated the reinforcement effect by comparing the test figure with the simulation results. The comparison shows that the ultimate bearing capacity improved by 71.2%, torsional stiffness increased by 8 times, and stress level significantly lowered under the same load degree after strengthening. The reinforcement effect was remarkable overall;(2) Form the concrete strain distribution along the beam height in the model test, we noticed that the plane cross-section assumption was not accurately satisfied, and one of the analyzed possible reason is the shear lag effect of box girder. Based on the variation principle of elasticity mechanics, by assuming the quadratic parabolic longitudinal displacement differential function of flangeslab, it deduced the analytical solution of shear lag of box girder, and compared it with the finite element simulation results. Analyzed the main influence parameter of shear lag based on the finite element method, the result indicates that the width-span ratio is the dominate influence parameter. By extracting the stress distribution data of ANSYS spatial finite element model, the paper calculated the effective flange width coefficient under different width-span ratio, and compared them with the current bridge specification, it shows that the specification gives a conservative result. The paper suggests adapting the specification result when conducting reinforcement design.(3) After determining of the effective flange width, we can equivalently simplify the transformed single-box and multi-cell section to a I-beam section. Considered the secondary stress characteristics of bridge reinforcement under initial load, it deduced the 3 kinds of bending reinforcing ultimate failure modes and their corresponding bearing capacity calculation formula. The paper put forward the necessity of shear strengthening at the meantime, and presented some strengthening design suggestions on the principles of engineering economy.(4) Finally, relied on the actual project as an example, the paper introduced the construction process and critical technology of strengthening and widening combination reconstruction, as well as reconstruction monitoring and the confirmatory field load test after completion. It could be used as a reference to the similar projects in the condition of lacking relevant construction experience.