Seismic Performance And Design Method Of Hybrid Reinforced Precast Segmental Bridge Columns

Three performance objectives of bridge stuctures are raised by the modern society,namely,high construction efficiency,stable seismic performance and reliable post-earthquake serversicability.The traditional reinforced concrete(RC)bridge columns are constructed by the cast-in-place method,which resultes in significantly long construction periods and has severely adverse impacts on the environment and traffic system.Moreover,the cast-in-place RC bridge columns tends to perserve large residual drifts after earthquakes,leading to the u nserversicability of the bridge structures.Differently,the precast segmental bridge column(PSBC)is errected by assembling prefabricated modular RC segments with post-tensioned tendons.Therefore,the PSBC offers many inherent advantages over conventional cast-in-place bridge columns,including higher construction speed,reduced environmental impact and increased site safety.So far,however,most of the PSBCs with various configurations proposed by the researchers can not realize good seismic performance and post-earthquake serversicability simultaneously.In addition,there is a lack of seismic design method for the PSBCs due to the inadequate understanding of their seismic performnce.Motivated by the aforesaid background,this study was conducted to make contributions to the application of the PSBC in moderate and high seismic regions.A novel bridge column system,named the hybrid reinforced PSBC(HR-PSBC),was proposed,aiming at improving the construciton efficiency,seismic performance and the post-earthquake functionality of the bridge structure.The HR-PSBC was reinforced by both energy dissipation(ED)bars and self-centering(SC)bars.The common steel bars were adopted as ED bars to dissipate the seismic energy;whereas the fiber-reinforced polymer(FRP)bars or the prestressing screw-thread bars were employed as the SC bars to improve the post-yield stiffness of the PSBC,thus to mitigate the post-earthquake residual drifts.Theoretical analyses,quasi-static tests and FE analyses were conducted to verify the design concept and to investigate the seismic performance of the HR-PSBC;finally,on the basis of the research work,a detailed seismic design method of the HR-PSBC was proposed.The major research contents,methods and conclusions are as follows:(1)Finite strip method was first used to analyze the effects of major parameters on the moment-curvature relationship of the hybrid reinforced section;after that,theoretical analyses were condected to study the evolution of the mechanical state and the rational failure mode of the column section;finally,in order to ensure the rational failure mode and targeted mechanical performance,three potentional selection strategies of the hybrid reinforcements were determined;(2)According to the above analysis results,eight large-scale PSBC specimens with the section of 0.6m×0.4m and the total height of 4.2m were designed and tested under lateral displacement reversals;tested parameterson included the ratio between ED bars and SC bars,the elastic modulus and strength of the SC bars and the axial load ratio;the effects of these parameters on the seismic performance of the HR-PSBC were analyzed;based on the experimental results,the hybrid reinforcement concept has proven to be effective in improving the post-yield stiffness and the selfcentering capacity of the PSBC,while the energy dissipation ability was maintained;(3)An efficient fiber element model of the HR-PSBC was developed,which simulated the FRP bar fracture,strain penetration effects and the joint openingclosing behavior;the validated fiber modeling method was further adopted to study the effects of major design parameters on the monotonic,hysteretic and dynamic time-history responses of the HR-PSBCs;based on the analysis results,the simplified envelop curve and the prediction method of the post-earthquake residual drift of the HR-PSBC was proposed for seismic design;(4)On the basis of the above results and the current seismic design codes,the two-level seismic performance objective was determined,and a seismic design method of the HR-PSBC was proposed to ensure the above performance objective;the proposed design method can take into consideration both the maximum drift demand and the residual drift demand,thus to ensure good seismic performance and post-earthquake servicability.