The Finite Element Nonlinear Analysis Of Cracking And Reinforcement For Gravity U-Shaped Skew Abutments

Abutments are the most important substructures of bridges,With the rapid increase of highway traffic volume,more and more abutments became larger in last decades.However, lots of abutments happened to crack during the usage stage or the course of construction.Cracking was common especially for the gravity U-shaped skew abutments which have huge volume.The investigation has been indicated the cracking skew abutments have a common characteristic that the location of the cracks are almost the same,both took place by the joint of forward and long flank wall,thus the same reason induced the cracking of abutments is possible,so researching into the main reason of cracking,taking methods to reinforce the cracking skew abutments and improve the structure of gravity U-shaped skew abutments have became serious problems that need to solve immediately.The paper consist of six chapters .In these chapters,chapter three ,chapter four are kernels. Chapter one is introduction.In this chapter mainly introduce the structure and types of gravity U-shaped abutments,the criterion on it,the traditional calculation method of earth pressure and the current research about the gravity U-shaped abutments cracking problems.In addition, at the end of this chapter there is a simple statement about the tasks of the whole paper.Chapter two mainly introduce the basic theory of finite element method.Both soil and concrete are nonlinear materials, as the stiffness of concrete is obviously larger than soil, so for the sake of making the simulated calculation convenient and saving calculation time, in the paper concrete was assumed as linear material and soil was elastic plastic material which obeys DP yield criterion.How to deliver the earth pressure to abutment shaft, the traditional method is caculating theearth pressure of abutments as that of retaining wall and then putting the pressure directly on the abutments concrete surface,however,the plane calculation can't truly reflect the contact relationship of concrete and soil,so the paper cited the finite element nonlinear contact theory and used the contact analysis system of finite element software Ansys to simulate the space surface-surface contact of concrete and soil,also some contact elements were introduced at length。The contents of chapter three are the kernels of the whole paper .In this chapter the finite element caculated software Ansys was introduced firstly, then give a explicit presentation of some basic parameters selections of abutment shaft concrete and soil behind abutment, such as elastic modulus,Poisson ratio,density and so on which are absolutely necessary through the process of the moodels building.And the selection of surface to surface contact element and enactment of real constants were also introduced in detail.After the preparations,two groups of skew abutments which width was determinate (B=20m,B=25m) and height regulary increased (Height from 10m to 20m,select every one by 2m), another two groups of skew abutments which height was determinate (H=10m,H=15m) and width regulary increased (width from 14m to 26m, select every one by 4m) were simulated with Ansys, otherwise, for the sake of realizing the influence of skew angle on skew abutments,in this chapter skew abutments of different angles of skew (from 60 degree to 90 degree, select every one by 10 degree) were simulated. And of course all the skew abutments dimensionally accorded with criterion. From the stimulation results, earth pressure was confirmed as the main reason of skew abutments cracking.Chapter four is also core of the paper.This chapter introduced several reinforcement methods of cracking skew abutments.The tapered edge,reinforced concrete girder methods were simulated, and got the conclusion: 1 .The skew abutments (Height=12m, Height=14m) with tapered edge, when the tapered edge width increased from 0.5m to 2m, the max1st principal decreased from 13 percent to 39 percent, but it only can be used to the skew abutments under designing or construction. 2. Mounting one or two circles of reinforced concrete girder on the skew abutments model, the max 1st principal decreased obviously, from 20.8 percent to 27.8 percent. It can be applied on cracked skew abutments.In the fifth chapter, the cracked abutment of Jilin-Wuchang highway and railway bridge was analyzed. After field observation and consulting a report written by Communications Science Institute of Jilin province, excluding the reasons of foundation settlement,soil frost heaving,basement lacking intensity leaded to the cracking of abutment. So simulated the abutment by Ansys, the results showed undering the motor vehicle loading,constant loading and earth pressure the emergence of crack on abutment is greatly possible. Then adopted reinforced concrete girder method to reinforce the cracking abutment, the results show the max 1st principal greatly decreased, and compareing with the abutment before reinforcement the max principle decreased 20.8 percent and 27.8 percent. And so it can be used on the reinforcement of the cracked abutment.Chapter six is the last part .This chapter is summarization of the paper and the direction also pointed out for further study.