Spatial Stability Of Concrete-filled Steel Tubular Arches Under Combined Bending And Compression

The concrete-filled steel tubular(CFST)arches have been widely used in China due to their high strength,convenience in construction and attractive appearance.There are more than 300 CFST arches in China and the longest span length has reached to 530 m.The increasing slenderness ratio of the arches and the decreasing width-to-span ratio of the bridges,both of which are induced by the increasing span length of the arch,make the CFST archers more prone to spatial buckling problems.In addition,for the CFST arches without wind braces,the spatial buckling problems are more crucial because their out-ofplane stiffness is much smaller than the in-plane one.Up to date,the available experiments on the spatial stability behavior of CFST arches are quite limited and hence,their mechanical behavior,and failure process have not been well investigated.The available designing equations have quite different prediction results on the ultimate capacity of the CFST arches.In this context,this thesis conducted experiments and finite element analysis(FEA)to investigate the spatial stability of CFST arches under combined bending and axial compression.The main contents include:1)Using the newly invented loading systems with the capability of simulating the non-directional loads provided by the bridge deck,failure tests were carried out on the parabolic CFST arches with single circular cross-sections to investigate their mechanical behavior,failure process and failure mode when subjected to single concentrated load applied at the midspan or subjected to three concentrated loads that evenly distributed along half of the span length.By comparing the displacement measuring results obtained from the LVDTs,the binocular stereo vision and the total station,reliable displacement measurement system was specified for the spatial stability tests on slender CFST arches.The strains of the steel tubes at the arch crown,the springings and at the quarter points of the span length were measured using 45° strain rosette to investigate the confined effects and the influence of the shear stresses on the mechanical performances of the CFST arches.2)The finite element model was built by ABAQUS to investigate the spatial stability behavior of the parabolic CFST arches with single circular cross-section.Analysis were carried out to determine the proper element type,element mesh,geometrical imperfection and concrete constitutive model for the finite element model.The reliability of the finite element model was benchmarked against the test data from this paper.3)Parametric analysis were conducted to investigate the influences of the slenderness ratio,the rise-to-span ratio,the steel ratio,the concrete strength and the steel strength on the stability of the CFST arches under combined compression and bending.Based on the analysis results,the reliability of the available designing equations was evaluated,and new formula were proposed to predict the load resistant capacity for the CFST arches under combined compression and bending by modifying the equivalent moment coefficient from the "Wu and Liu formula".The newly proposed equations had higher prediction accuracy with the mean values for the ratio of the FE results over that from the equations of 0.98~0.99,and with the coefficient of determination of 0.998.