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Prestressed concrete (PC) box girder is an innovative structure that is widely used in large-span bridges. Under eccentric loads such as vehicles, PC girders are inevitably under combined bending and torsion. To study its bending-torsional behavior, a refined full-range analysis model based on the combined action softening truss model (CA-STM) was proposed, where a simple and effective solution procedure and failure criteria were provided. The equilibrium equation, initial estimation equation for torque, and material constitutive model were modified by considering the prestressing effect to improve the CA-STM. An optimized algorithm was also employed to simplify the solution procedure instead of the traditional trial-and-error method, thus increasing the solution rate and stability. The theoretical curves predicted from the improved CA-STM exhibited great agreement with the available experimental results, and the predicted cracking and ultimate loads were also close to the experimental values. Hence, the improved CA-STM can reasonably predict the full-range mechanical response and failure modes of PC box girders subjected to combined bending and torsion, which provides great support to the design evaluation of such bridges. [ABSTRACT FROM AUTHOR]

A new type of composite structure, the composite box girder with corrugated steel webs (CSWs) and trusses, is proposed recently. In order to investigate the structural behavior under positive and negative bending moments, flexural tests of the continuous girder were carried out, and the failure modes, deformation patterns, strain distribution, and development of the concrete cracks were investigated. Finite element analysis was conducted to investigate the effect of the range of concrete in the steel tube and the thickness of CSWs on the flexural behavior. The experimental and numerical results show that the test beam has a good ductility and integrity under flexural load. The contribution of CSWs to the flexural bearing capacity is very small and can be neglected. Besides, the plane section assumption is still valid when only top concrete slab and bottom steel tubes are concerned. The concrete filled in bottom steel tubes increases the stiffness and the bearing capacity of the girder. Equations to calculate the flexural bearing capacity under positive and negative bending moments were put forward and then verified with experimental results. [ABSTRACT FROM AUTHOR]

The composite rigid-frame bridge presented in this study is a new type of structural solution that combines the steel–concrete composite box girder and the concrete-filled double-skin steel tube (CFDST) piers with rigid connecting joints. Compared with the conventional prestressed concrete rigid-frame bridge, it shows superior static and dynamic performances. This study performs shake table tests of a 1:10-scaled three-span steel–concrete composite rigid-frame bridge (SCCRFB) to explore its seismic characteristics and damage modes. The details of the bridge model design, construction, measurements, and testing process are presented. The seismic responses of the bridge under one typical near-fault and one far-field ground motions were experimentally investigated. Testing results revealed that the damage to the bridge is mainly located at the upper and lower ends of the CFDST piers, with yielding of the outer steel box and separation between the steel skins and infilled concrete. The testing results also indicated that the near-fault ground motions containing strong velocity pulse could significantly amplify the structural responses compared with the far-field ground motions. Furthermore, a detailed finite element (FE) model of the SCCRFB with CFDST piers is developed and validated by the experimental results, and numerical studies are then carried out to compare the seismic performances of this bridge type and the one supported by the conventional reinforced concrete (RC) piers. The numerical results show that the SCCRFB with CFDST piers exhibits superior seismic performances compared with the traditional bridge, especially when subjected to the near-fault ground motions. This study can provide useful references for the engineering solution and seismic design of long-span, high-pier composite rigid-frame bridges. [ABSTRACT FROM AUTHOR]

• Two 1:5 scale models of composite beams with CSWs and trusses are tested. • The effects of bottom trusses and concrete in steel tubes are examined. • Finite element simulation is used to simulate the full behavior of tested specimens. • Theoretical model is developed to predict the nonlinear behavior. The composite box girder with corrugated steel webs (CSWs) and trusses is a bridge structure developed on the basis of traditional box girders with CSWs. In this research, experimental, numerical and analytical studies were carried out to investigate the flexural performance of simply supported composite box girders with CSWs. Two 1:5 scale models of a real bridge were fabricated and tested, including one with concrete filled steel tubes and another with hollow steel tubes. The test results show that the two specimens have good ductility and failed in a ductile manner. The concrete filled inside steel tubes reduces the deflection and increases the yield load. The cross sections of the two specimens basically satisfy the "plane section assumption". Finite element models were also developed for the two specimens and validated based on the experimental results. Afterwards, a parametric study was carried out with the validated finite element models, which shows that the steel ratios and the structure of bottom trusses strongly influences the flexural behavior. At last, a theoretical model is developed to calculate the bending moment of composite beams at the ultimate load. [ABSTRACT FROM AUTHOR]

This paper aimed at developing a theoretical model for prestressed composite box girders with corrugated steel webs (CSW) under pure torsion, based on the combined action softened truss model (CA-STM). The equilibrium equations and materials' constitutive laws were modified, considering the relationship between the initial stress and strain generated by prestressing. According to the yield state of the CSW, proper shear flow conditions were also introduced to describe the deformation coordination relationship between the CSW and concrete slabs. The effect of the width of cantilever slabs on the torsional performance of composite box girders was investigated. An optimized algorithm was employed to solve the CA-STM, resulting in a more efficient and stable solution procedure. The validity of the model was confirmed through the available experimental data. Results showed that the prediction accuracy of the improved CA-STM for depicting entire torsional behavior is great, when considering the reasonable shear strain relationship and modified initial torque calculation formula. • Developing a theoretical model for PC composite box girders with CSW under pure torsion. • Modifying the load distribution equation to account for the mechanical behavior of CSW. • Employing an optimization algorithm to solve the full-range force behavior. • Building the initial torque equation to consider the mechanical behavior of prestressing bars. [ABSTRACT FROM AUTHOR]