Analysis On The Cause Of Cracks Of A Cap Beam And Study On Reinforcement Measures

It is a common engineering problem that bridge cracks appear.The analysis of the formation process and mechanism of bridge cracks is conducive to the proposal of reasonable bridge reinforcement scheme,which is of great significance to the development of transportation in China.Previous studies on cracks were all from a macro perspective,which could not reflect the process from generation to expansion of cracks effectively.In this paper,the numerical test of cracking of concrete random aggregate model was carried out.Based on the test,the relationship between damage variables and strain of concrete is deduced and the influence of aggregate parameters and mortar parameters of the model on the macroscopic mechanical properties of concrete is studied.On this basis,combined with the engineering problems of cracks in the cap beam of CheChengLu viaduct,the causes of cracks are analyzed from mesoscopic view,and the cap beam model without damage and with damage are established for verification.Three kinds of reinforcement schemes are put forward to solve the problem of cracks in the cap beam of the CheChengLu viaduct.The main results of this paper are as follows:(1)By uniaxial tensile simulation of the random aggregate model,the stress-strain curve of the model was obtained.By analyzing the stress-strain curve of the model,the relationship between the damage variable and the strain is obtained.This relation can be used for damage analysis of concrete in practical situation.(2)The effects of aggregate and mortar on the macroscopic properties of concrete were studied.The research on concrete random aggregate model with different aggregate parameters shows that the spatial distribution of concrete aggregate has no significant influence on the elastic modulus and the limit value of tensile strength of concrete.When the aggregate size of concrete increases,the ultimate tensile strength of concrete decreases significantly while the elastic modulus increases slightly.The research on random aggregate model of concrete with different mortar parameters shows that when the tensile strength of mortar increases,the ultimate tensile strength of concrete increases significantly,and the elastic modulus of concrete increases slightly.When the elastic modulus of mortar is increased,the ultimate tensile strength and elastic modulus of concrete are improved significantly.(3)To test the bridge performance,load test was carried out on the CheChengLu viaduct.And it was found that there were several vertical cracks in the cap beam of CheChengLu viaduct.Combined with the conclusion of concrete numerical model test in the mesoscopic level,the factors affecting the crack generation of the cap beam are analyzed,and it is believed that external factors(increase of external load)and internal factors(weakening of concrete material parameters)lead to the decrease of concrete tensile strength and elastic modulus,which leads to the large number of cracks in the cap beam finally.This paper deduces the damage state of the cap beam of CheChengLu viaduct,establishes the cap beam model without damage and with damage,and verifies the correctness of the hypothesis by comparing the cracks of the two models with the cracks of actual situation.The influence of concrete composition on cracking of the cap beam is discussed.(4)For carcks on the cap beam of CheChengLu ciaduct,three different reinforcement schemes are put forward,which are pasted steel plate method,pasted CFRP method and prestressed CFRP reinforcement method.The characteristics of each reinforcement scheme are analyzed and discussed from the aspects of stress,technology and economy.Finally,from the perspective of preventing crack propagation,it is concluded that the prestressed CFRP reinforcement method is more suitable for the cap beam of CheChengLu viaduct.(5)It is innovative to combine the microscopic numerical analysis of concrete with the macroscopic material properties and apply the research results to bridge reinforcement.