Study On Torsion Performance Of Composite Box Girders With Corrugated Steel Webs

As a new type of steel-concrete composite structure,the composite box girders with corrugated steel webs(CBGCSWs)exhibit many advantages,e.g.,light self-weight,complete avoidance of web cracking,high material utilization efficiency,good economical effect and attractive appearance.Therefore,this type of structure has wide application prospect.So far,systematic research have been carried out to investigate the flexural performance,shear performance,shear-lag effect and shear connector of the CBGCSWs.However,the research regarding the torsional behavior of CBGCSWs is insufficient.In fact,the CBGCSWs are more highly influenced by torsion than conventional concrete box girders by replacing the concrete webs with corrugated steel webs(CSWs).In this paper,the torsion performance,including the rigid torsion and distortion,of CBGCSWs are systematically investigated through theoretical derivation,numerical simulation and experimental test,and the main research results can be drawn as follows:(1)The distortion calculation theory of non-prismatic CBGCSWs under eccentric loads is established.By taking the distortional angle as the unknown,the governing differential equation for distortion of non-prismatic CBGCSWs under eccentric loads was derived.Then,the governing differential equation is solved by combining the beam on elastic foundation(BEF)method and the Newmark method.The applicability and accuracy of the proposed distortion calculation theory is validated by numerical examples using the finite element method.(2)A diaphragm spacing equation is developed for determining the diaphragm spacing of non-prismatic CBGCSWs.Based on the distortion calculation theory proposed in this paper,the relationships between different design parameters and the magnitude of distortion effect for non-prismatic CBGCSWs are investigated.Based on the data of parametric analyses,a recommended equation for diaphragm spacing is obtained using a multiple nonlinear regression analysis.(3)The improved softened membrane model for torsion(ISMMT)is established for predicting the mechanical behavior of PCCBGCSWs under pure torsion.Based on the softened membrane theory(SMMT)for reinforced concrete members under pure torsion,a series of equations are derived from equilibrium and compatibility conditions and constitutive relationships of the materials of prestressed concrete composite box girders with corrugated steel webs(PCCBGCSWs)by considering its structural feature.The solution algorithms,including a general algorithm for the entire torsional process and a simplified algorithm for the stage when both steel bars,the prestressing steel and the CSWs are in the elastic state are presented to solve all the equations.The torque-twist curves of eight PCCBGCSW specimens subjected to pure torsion obtained from the experiment agree well with those calculated by the ISMMT,which demonstrates the feasibility of the proposed theoretical model.(4)The pure torsion test of a PCCBGCSW specimen has been conducted.The torque-twist curve and the entire strain evolution in components of the specimen are obtained from the test.The comparisons between the theoretical results calculated by the ISMMT and those from the experiment and the precise nonlinear finite element(FE)model indicate that the ISMMT not only can predict the torque-twist curve of the PCCBGCSWs under pure torsion,but also can accurately predict the entire stress evolution in components of the PCCBGCSWs,including the concrete flanges,CSWs,prestressing steels,and steel bars,during loading.(5)The mechanical performance of a PCCBGCSW with bottom steel plate under pure torsion has been investigated.By replacing the bottom concrete flange of the conventional PCCBGCSWs with the steel plate stiffened with longitudinal ribs,a PCCBGCSW with bottom steel plate is designed.Based on the precise nonlinear FE models established using ABAQUS software,the mechanical properties and economic indexes of the conventional PCCBGCSW and the PCCBGCSW with bottom steel plate under pure torsion are compared comprehensively.The results show that both the mechanical performance under pure torsion and the economic benefit of the PCCBGCSW with bottom steel plate are better than those of the conventional PCCBGCSW.Finally,the effects of different design parameters on the ultimate torque of the PCCBGCSW with bottom steel plate are investigated.