Cause Analysis Of Cracking Of Simply Supported Box Girder Bridge Experimental Study On Reinforcement Effect Of CFRP

In recent years,China's economy has entered a period of rapid development,and the infrastructure of bridge engineering has also been continuously developing.Among them,simple-supported beam structure is simple in force,not affected by bearing displacement and other factors.It can be applied to many geological conditions,easy to assemble construction,easy to manufacture and install,and is the most widely used beam bridge.Although simple-supported box girder has been used for many years and its structure is mature,there are still some unavoidable diseases,among which concrete cracks are particularly prominent.Cracks are closely related to the integrity,stiffness and strength of the bridge itself.If not properly controlled,they will have adverse effects on the bridge structure,and may even cause major safety accidents.In order to better prevent and cure cracks,it is particularly important to analyze the causes of cracks in simple-supported box girder bridges.It can not only provide theoretical basis for the design,construction and reinforcement of simple-supported box girders,but also avoid unnecessary cracks to the greatest extent.It has great practical significance.Based on Zhangjiaba Middle Bridge,this paper analyses the causes of cracking of simply supported beam bridges,summarizes the corresponding reinforcement methods for concrete cracking,carries out finite element analysis of the whole structure and load tests before and after reinforcement,and compares the results of load tests before and after reinforcement with the mechanical effects.The analysis and research of science.The concrete contents and conclusions are as follows:(1)The causes of cracking of simply supported girder bridges are analyzed,including cracks caused by load,cracks caused by temperature change and insufficient strength of concrete,and corresponding strengthening methods are summarized for concrete cracking,including enlarging section method of members,bonding steel plate method,bonding fiber composite material method,external prestressing reinforcement method,etc.(2)Using finite element analysis software,structural calculation and analysis of Zhangjiaba Middle Bridge are carried out by finite element method;load tests before and after reinforcement are carried out.The results show that the values of deflection and stress measured points are reduced to varying degrees,indicating that the carbon fiber structure and the original box girder have worked together to participate in the force of the box girder.(3)Comparing and analyzing the data of deflection and stress of steel bar measured points before and after reinforcement.Among them,the average reduction of the deflection of the test points of the left bridge under symmetrical loading is 4.99%,while the average reduction of the deflection of the test points under partial sidewalk loading and partial guardrail loading is 3.44% and 5.47%,respectively.The average reduction of the stress value of the steel bars in the left bridge under symmetrical loading is 3.5%.The average reduction of the stress value of the steel bars in the partial sidewalk loading and the partial guardrail loading is 3.96% and 4.31%,respectively.The average reduction of the deflection value of the steel bars in the right bridge under symmetrical loading is 4.95% and that in the partial sidewalk loading.The average reduction of the deflection of the test points after reinforcement under the loading condition of eccentric guardrail is 2.81% and 3.93%,respectively.The average reduction of the stress at the reinforcement point of the right bridge under symmetrical loading is 9.01%.The average reduction of the stress at the reinforcement point under partial sidewalk loading and partial guardrail loading is 7.55% and 7.14%,respectively.In summary,this paper takes Zhangjiaba Middle Bridge as the engineering support,and aiming at the cracks at the bottom of the beams after its completion,analyses the complex causes of the cracks in the simply supported beams,and proposes the use of carbon fiber reinforcement.The load tests before and after the reinforcement show that the stiffness and strength of the bridge have been improved to a certain extent,and the stress and deflection tests have been carried out.The bearing capacity of Zhangjiaba Middle Bridge meets the design requirements.