Study On Bi-directional Pseudo-dynamic Test Of Prestressed Precast Concrete Box Piers

Prestressed precast concrete box piers are one of the most commonly used pier types in cross-sea bridges and urban viaducts.At present,domestic scholars have not systematically studied the seismic performance of prestressed precast concrete box piers,especially the seismic performance under the action of two-way seismic loads.In view of this,this paper attempts to find out the characteristics of seismic response,the law of damage evolution and the failure mode of prestressed precast concrete box piers by combining bi-directional pseudo-dynamic test and finite element analysis.Moreover,the paper will study the effect of different design parameters on the seismic performance of the structure,and discuss the applicability of the prestressed prefabricated assembly technology in the field of high piers,and discuss the failure mode and performance indicators.The main research will be done as follows:(1)Three concrete box pier specimens are designed and manufactured,and bi-directional pseudo-dynamic tests will be carried out.The response characteristics of acceleration,displacement and base shear,the law of strength and stiffness degradation and the mechanism of earthquake damage are compared and analyzed.(2)On the basis of the OpenSees program,three finite element models were numerically simulated using fiber element.The effects of segment form,segment number,axial compression ratio,reinforcement ratio of longitudinal reinforcement and reinforcement ratio of prestressed reinforcement on the seismic performance of prestressed precast concrete box piers are analyzed.(3)Based on OpenSees,a prestressed prefabricated concrete box type high pier model was established,and the IDA analysis method was used to study the structural performance of this prefabricated box-shaped high pier.By comparing the action of the manifestation and destruction mode of integrated high piers and prefabricated high piers on the effect of the earthquake,we can verify the suitability of this type of prefabricated box-shaped high piers,and study the earthquake damage mechanism and reasonable seismic performance indicators.The main conclusions are as follows:(1)The integral cast-in-place box-shaped piers are mainly subjected to bending damage,and the damages are mainly concentrated in the plastic hinge area.The prestress prefabricated box piers have an obvious increase in the prestress of the corner under the action of two-way load,and finally lead to the cracks and splits of the pier wall concrete in one side of the structure,and the breakage of the prestressed tendons in the other side caused structural damage,which damages are mainly concentrated in the joint area.The skeleton curve of the integral box-shaped pier is roughly a tri-fold line.The skeleton curve of the prefabricated box-type pier is bi-folded.It is necessary to consider the influence of two-way load on seismic analysis of prestressed prefabricated box-type piers.(2)Parallel springs can be used to simulate the actual mechanical behavior of the joint of the prefabricated box piers.On this basis,a series of parameter sensitivity analysis are carried out.The results show that the parameters such as segment form,number of segments and position of prestressed reinforcement have little influence on the seismic performance of the structure.The reinforcement ratio of prestressed tendons has little effect on the seismic performance of the structure under the condition of satisfying the earthquake resistance and imposing the prestress.Increasing the dead load axial ratio and the initial prestress will be detrimental to the structural anti-seismic effect when the peak ground acceleration is larger.The increase of the reinforcement ratio will be beneficial to the structure earthquake resistance when the peak ground acceleration is larger.The use of bonded tendons for prestressed tendons has a significant increase in energy dissipation compared to non-bonding.(3)The prestressed precast assembly technology has good applicability in the field of high piers.The applicability of the three basic performance indicators of pier bottom section curvature,pier top displacement,and prestress in the field of prestressed prefabricated box-type high piers was discussed.It was found that the use of pier bottom section curvature with the prestress is suitable for prestressed precast concrete box pier.