Analysis And Prevention Of Web Crack In Early Stage Of Prestressed Continuous Box Girder

Since 1980 s,prestressed concrete box girder Bridges have developed rapidly and become one of the main types of long-span Bridges in China.These Bridges are gradually put into use,load bearing,design and construction problems are gradually exposed,especially cracking problems of different properties are more common,and the web oblique cracks are the most obvious.Based on hongshui river bridge as the research object,this paper analyses the prestressed concrete box girder bridge in the design,construction and operation period of common diseases and influence factors of the hongshui river bridge box girder cantilever web cracks during the construction as the key object of study,mainly for conduct the thorough research to the related issues on web cracks,the main work includes the following several aspects:(1)In hongshui river prestressed concrete continuous box girder bridge as an example,using software Midas/civil space model is established to simulate the actual bridge structure,according to the result of calculation,analysis calculation the bridge bearing capacity limit in normal use limit stress state,stress state and the status of the construction stage of stress state of stress,discuss the web cracking reasons.(2)Summarize the causes of 0#-5# web cracking in the early stage of Hongshuihe Bridge,and take corresponding prevention measures for simulation analysis and real bridge verification.By controlling the construction quality of solid bridge,such as optimizing concrete design mix ratio,adding steel fiber concrete,layered symmetrical pouring,hydration heat preservation,vibration control and other measures;(3)Through comparative analysis of Midas/fea simulation to calculate the stress and temperature changes of each measuring point before and after the hydration heat insulation of Block 0,formulate the insulation scheme to reduce the hydration heat effect;Through the real bridge modeling,the effects of loading ages on shrinkage and creep of 3d,7d and 30 d,and the effects of relative humidity of 40%,70% and 90% on early shrinkage and creep are analyzed,and corresponding curing measures are formulated to prevent and control early shrinkage cracks.(4)Through the comparison of cracking results of 0#-5# blocks and subsequent block sections,the prevention and treatment measures for cracks of Hongshuihe Bridge are verified,the cracking problems of subsequent blocks are effectively avoided,and the web cracking problems in the construction process of long-span prestressed concrete bridge have certain reference value.