Study On Flexural Behaviour Of Horizontally Curved I-Girder With Round Concrete-Filled Tubular Flange

With the further development of transportation and urban construction,curved girders have been widely used.When the vertical load is applied,curved girders are not only deformed by bending but also by torsional deformation due to the initial curvature.Furthermore,conventional I-girders are regarded as an ‘open’ section member,and their torsional stiffness is much less and stability problem is prominent.The concrete-filled tubular flange girder(CFTFG)is a composite structure which replaces the flat-plate flange of the conventional I-girder with concrete-filled tubular.It combines the advantages of conventional I-girder,namely,convenient design,manufacture,detection and large torsional rigidity of box-girder,and is more suitable for curved girder bridge system.So far,there is no systematic research on the basic mechanical behaviours of curved CFTFG.Therefore,it is of great practical significance and value to investigate the flexural behaviour of curved concrete-filled tubular flange girder.In this thesis,the flexural behaviour of individual curved round concrete-filled tubular flange girders(CRCFTFGs)under concentrated load at mid-span was investigated experimentally and numerically.Firstly,two CRCFTFG specimens and one conventional curved I-girder(CIG)specimen were considered in this study.One of the CRCFTFGs specimens was designed with a pair of transverse stiffeners at mid-span while the other had arranged seven pairs of transverse stiffeners uniformly along the span of the girder,which were denoted CRCFTFG-1 and CRCFTFG-2 respectively.A special rolling track device was designed to ensure that the load was in the vertical direction during the test.In the experiment,the failure mechanism of three specimens and the development of strain and displacement with the vertical load at certain critical positions were measured and analysed in detail.Experimental results have shown that increasing the number of transverse stiffeners could economically and effectively avoid web distortion and significantly enhance the load carrying capacity of CRCFTFGs.Compared with the corresponding CIG,the load carrying capacity of CRCFTFGs was 6.3 times,the lateral displacement was 45.6% less than that of CIG,and the cross-sectional rotation was only60.3% of CIG.Moreover,the finite element(FE)models of CRCFTFGs and CIG in the cylindrical coordinate system were established by using the FE software ABAQUS.The nonlinear buckling analysis of the FE model was carried out considering the material nonlinearity and geometric nonlinearity.The results of FE and test were compared in three aspects:failure mode,load carrying capacity and load-displacement curve.It was found that the FE failure modes were in good agreement with the test failure modes,the maximum error of load carrying capacity between them was 9%,and the load-displacement curve of their were in good agreement,indicating that the FE model can effectively simulate the flexural behaviour of CRCFTFGs and CIG under the concentrated load.Based on the verified FE method,a parametric study was conducted.This task is carried out to investigate the influence of initial geometric imperfections,web distortion and material strength on the load carrying capacity of CRCFTFGs.In addition,a massive number of FE analysis of CRCFTFGs with different spans and centre angles were carried out.On this basis,the calculation formula of load carrying capacity of CRCFTFGs considering the effect of curvature was proposed.The calculation formula was compared with the FE and the test results,and it was indicated that the agreement was good.