Research And Application On The Reinforcement Of Double Arch Bridge With Extrados Section Enlargement Method

The extrados section enlargement method is a kind of section enlargement method. This method is very convenient, which can be construct directly on extrados; The new added concrete can elongate because of the micro expansion effect of the micro expansion concrete, which can reduce the shrinkage difference between the old and new concrete, at the same time this method is good for the combination of the new and old concrete; The micro expansion effect of the micro expansion concrete will cause the stress redistribution on the reinforced section, which has a obvious unloading effect of the original bridge, which is good for the structure stress. This paper analysis the application of the extrados section enlargement method, the main research contents are shown as follows:(1) Optimization analysis on the scope of reinforcement in extrados section enlargement method. The FE model under different span, rise-span ratio, arch-axis coefficient with different length of the reinforcement are built, then the rule of the internal force of the arch ring with the change of reinforcement length and the best scope of reinforcement are founded by analyzing the characteristics of the vault and extrados influence lines.(2) Analyzing the shrinkage difference between the old and new concrete of the extrados section enlargement method. The shrinkage and micro expansion stress-strain formulas are inferred by the theory of bond beams, then the stiffness coefficient of the arch ring is also calculated.(3) Analyzing a in service double arch bridge with finite element simulation method. First, the comparison of the bridge force condition before and after reinforced is made, which proves that the extrados section enlargement method can achieve good reinforcement effect; Then, the stress caused by the shrinkage of the new added concrete is calculated, stress distribution of the bridge caused by the shrinkage is also founded, also the suggestion of the structure to adapt the stress is given; At last, shrinkage compensating effect of the micro expansion concrete is calculated, which proves that the micro expansion concrete has great ability to compensate the shrinkage, suggestion to the dosage of expanding agent is also given.Extrados section enlargement method has a dominant position in reinforcement method selected of the double arch bridge, also has a very good reference and guidance significance to the reinforcement of the box arch bridge and rigid-framed arch bridge.