Analysis On Causes Of The Box Girder Crack At 1/4 Section Of A Continuous Rigid Frame Bridge

With the development of transportation infrastructure,large span prestressed concrete continuous rigid frame bridge has been widely used.Because of the design theory and construction quality or other reasons,Partially prestressed continuous rigid frame bridge appears box girder cracking phenomena during the construction or completion operations,especially web crack is more serious.Cracks appears frequently hampered the continuous rigid frame bridge better development,also has a negative impact on the safety of the bridge structure,durability and service life.The project rely on an actual Yangtze River Bridge,analyzes the reasons of the continuous Rigid Girder Bridge web cracks,also raises some measures to prevent cracks occurring.In this paper,a large number of documents is checked out,on the existing research results,analyzes the web cracks causes of the prestressed concrete continuous rigid frame bridge.Then through space finite element software MIDAS / CIVIL establishes the full bridge model checks the whole bridge the web box girder stress state.Use the MIDAS / FEA establishes the local three-dimensional solid model of the three blocks near the bridge L / 4 cross-section,analyzes the partial stress state of the box girder webs.Fully considers the impact of various factors on crack.Focus on the influence of the temperature difference between inside and outside the box and the adjacent block segments age differences on web cracking.At the same time relies on the structure of the bridge box girder web-site investigation to validate the accuracy of the analysis result that the finite element model calculated.For the reasons of web cracks,proposes certain measures to prevent cracks.This paper shows the finite element model calculating and analysising results:(1)The stress checking of the web of box girder can satisfy the standard allowable value of the whole bridge model,the overall temperature of the whole bridge and the vertical temperature gradient have little effect on the cracking of the web.The model on the full bridge crack of box beam web analysis is not accurate enough.(2)The local model analysis shows that the individual load has little effect on the crack of web plate,the combination of several single load conditions can be seen that the influence of the temperature difference between the web and the inside and outside of the web on the stress state of the web is larger.(3)The construction causes the interval time between two blocks,and the post casting block section is subjected to the contraction of the upper part of the interface.At the interface of principal tensile stress with the increase of the two blocks of different ages and larger,more than ultimate tensile strength will produce cracks in the webs,but a combination of the temperature difference between inside and outside of the web makes web principal tensile stress greater,which is the bridge box beam web cracking of the main reasons.