In recent years, several similar bridge overturning and collapse accidents have occurred in China. All of them occurred on bridges with continuous monolithic box girders and single-column piers that were eccentrically overloaded by heavy vehicles. In this study, an explicit nonlinear dynamic finite element method is used to analyze an accident occurred on an expressway exit ramp bridge. The entire overturning and collapse process is simulated. The results show a girder revolving around the overturning axis, which is a straight line between two supports for a bridge eccentrically loaded by heavy vehicles. When the rotation of the main girder is larger than the friction limit rotation, the sliding force is greater than the friction force between the girder and the support. This causes the main girder to slide obliquely, which can induce a horizontal reaction force, pushing the piers down and collapsing the whole bridge. This underestimates the anti-overturning ability of a bridge, based on the criterion that no support disengagement occurs under overloading conditions. Second-order effects due to girder rotation (including the increase of the overturning moment arm) must be taken into account when calculating an anti-overturning stability factor based on the overturning axis between two supports.

In recent years, several accidental collapses of girder bridges have occurred under the influence of eccentric heavy vehicles in China. To explore the causes and mechanisms of the collapses, a collapsed six-span, RC, continuous box-girder bridge was introduced and analyzed. By gathering onsite information about the accident, different failure forms were determined. Simplified mechanical calculations and finite-element simulations were used to determine the characteristics of the structural response caused by the load on the bridge during the accident. Finally, the sequence of the accident was reproduced, and the controlling factors leading to the structure failure were clarified. This study suggests that bridge accidents are caused not only by instability issues of integral overturning but also by strength failures of the components. Under the circumstances caused by an extreme eccentric vehicle load, the large deformation resulted in an apparent second-order effect. Noticeable lateral horizontal ...

Without interrupting the traffic on the old bridge, the connection of the widening bridge will cause disturbance to the concrete in the splicing position. In order to study the anti-disturbance performance of concrete material, the Normal Concrete (NC) material and the Ultra-High-Performance Concrete (UHPC) material were experimentally investigated by the vertical shaking table and X-ray computed tomography scanning. It can be learnt from tests that the compressive strength of NC and UHPC can be increased by about 10% to 20% after disturbance, while the flexural tensile strength and splitting tensile strength of both NC and UHPC can be reduced by about 20% to 25% and 10% to 20%, respectively. The elastic modulus of UHPC is not significantly affected by the vibration disturbance, and that of NC can be increased by about 20%. The setting time difference of the proposed NC material can be controlled within 100 min, and it can improve its anti-disturbance performance. Excessive vibration disturbance affects the internal structure of NC, while it has little effect on the distribution of steel fiber in UHPC. Due to the high cost of UHPC materials, it is recommended to analyze the joint performance requirements before the selection of splicing materials. If the stress requirement is not particularly high, it is still recommended to apply the proposed NC material for the splicing of widening bridge.

In practice, bridge foundations and pier columns are usually constructed with cast-in-place concrete. Precast columns are currently widely used in highway bridges in China, which can save construction time and improve concrete quality. The connection between precast bridge columns and the foundation can affect how forces transfer from one to the other. This paper investigates using external sockets to form a connection between the bridge column and foundation. This method can accelerate the bridge construction time with the additional advantages of improving the orientation and creating a large erection tolerance. Two types of connections are presented and tested to investigate the behavior of the column-foundation connections and find a more suitable way to use external socket connections. The experimental results show that the column-foundation connection design satisfies the design requirements. The results also show that roughening the column surface within the external socket is more effective at connecting the column to the foundation when using an external socket compared to attaching a steel plate on the column. The experimental results are validated with a finite element analysis, resulting in a proposal regarding the column-foundation connection behavior as well as design recommendations for the external socket connection.

Twin-I girder bridge systems composite with precast concrete deck have advantages including construction simplification and improved concrete strength compared with traditional multi-I girder bridge systems with cast-in-place concrete deck. But the cracking is still a big issue at interior support for continuous span bridges using twin-I girders. To reduce cracks occurrence in the hogging regions subject to negative moments and to guarantee the durability of bridges, the most essential way is to reduce the tensile stress of concrete deck within the hogging regions. In this paper, the prestressed tendons are arranged to prestress the precast concrete deck before it is connected with the steel girders. In this way, the initial compressive stress induced by the prestressed tendons in the concrete deck within the hogging region is much higher than that in regular concrete deck without prestressed tendons. A finite element analysis is developed to study the long-term behaviour of prestressed concrete deck for a twin-I girder bridge. The results show that the prestressed tendons induce large compressive stresses in the concrete deck but the compressive stresses are reduced due to concrete creep. The final compressive stresses in the concrete deck are about half of the initial compressive stresses. Additionally, parametric study is conducted to find the effect to the long-term behaviour of concrete deck including girder depth, deck size, prestressing stress and additional imposed load. The results show that the prestressing compressive stress in precast concrete deck is transferred to steel girders due to concrete creep. The prestressed forces transfer between the concrete deck and steel girder cause the loss of compressive stresses in precast concrete deck. The prestressed tendons can introduce some compressive stress in the concrete deck to overcome the tensile stress induced by the live load but the force transfer due to concrete creep needs be considered. The concrete creep makes the compressive stress loss and the force redistribution in the hogging regions, which should be considered in the design the twin-I girder bridge composite with prestressed precast concrete deck.