The Local Stress Analysis Of Continuous PC Box Girder And Strut-and-Tie Design Method

The phenomenon of web and anchorage zone cracks of continuous PC boxgirder is fairly common and has influenced the bridge's safety and durability. Thisdissertation intends to find the cause of cracks phenomenon from stress disturbedzone design methods. So three dimensions solid element FEM models were built andthe regularity of box girder's stress was analyzed. Base on the contrast of stressobtained by solid element FEM analysis and beam element FEM analysis respectively, box girder was divided into stress regular region(B) and disturbed region(D). Andthen, the Strut-and-Tie method is proposed to conduct the analysis and design for PCbox girder's stress disturbed zone. To obtain above objective, the main works of thisdissertation are described as follows.●The comparison between Chinese reinforced concrete and prestressedconcrete specifications and foreign reinforced concrete and prestressedconcrete specifications was made. The main contrast clauses includeconcrete stress limitation, the specifications of temperature loads, sheardesign methods and anchorage zone. The differences between code fordesign of highway reinforced concrete and prestressed concrete bridges andculverts of China and other codes were contrasted. The compatibility of allkinds of concrete stress limitations specified by Chinese code for design ofhighway reinforced concrete and prestressed concrete bridges and culverts(2004) was analyzed.●Summarizing of strut-and-tie study state, bases on the principle of minimumcomplementary potential energy, propose to take quantity of deviation ofcomplementary potential energy as the evaluating indicator of the rationalityof strut-and-tie models and its feasibility was verified by two examples.●In order to avoid the compression failure of concrete strut happens beforethe failure of stirrup yield, the relations of minimum angle, between start and tie, with ratio of stirrup reinforcement, the yield strength of stirrupreinforcement, the compress strength of concrete.●Takes a continuous PC box girder bridge as an example, the web stress wasanalyzed and contrasted through solid element three dimensions model andbeam element plane model respectively. Base on the analysis results, proposto use strut-and-tie models to analyze the disturbed regions.●The local region stress analysis was conducted of continuous PC boxgirder's end anchorage zone and middle anchorage zone. Bases on theregulation of local stress, the strut-and-tie models used to analyze anchoragezone were built.●Bases on the analysis of the mechanism of inverse key-stone caused by topand bottom longitudinal overlapping cables, take two continuous PC boxgirder bridges as examples, the strut-and-tie used to analyze the verticaltension force caused by top and bottom longitudinal overlapping cableswere given and strut-and-tie analysis was conducted. The designingattentions were pointed out.●For different standpoints of longitudinal cable layout types, the theoryanalysis of different longitudinal cable layout types' merits and faults wasdone. And then, the analysis, which consider the influence of prestressinglose and overload factors, was conducted too.