Research On The Seismic Deformation Capacity Of RC Bridge Columns

The vulnerabilities of reinforced concrete (RC) bridge columns toseismic actions have been repeatly demonstrated in recent events such as theLoma Prieta earthquake (1989), Northridge earthquake (1994), Kobeearthquake (1995), Chi-Chi earthquake (1999), and the Wenchuan earthquake(2008). The research on the seismic performance of RC bridge columns isimportant to ensure the seismic safety of RC bridges and crucial loads, andthe seismic ductility and energy absorption capacity of the RC bridgecolumns are key prerequisites of displacement/performance based seismicdesign of the bridges.Based on analysis of the collected seismic test results for RC bridgecolumns, quasi-static experimental research and numerical simulation, theseismic deformation capacity of solid and hollow bridge columns withnormal and high strength concrete and reinforcement was studied. Whichincluding the ductile deformability and drift based confining reinforcementof the bridge columns, the equivalent plastic hinge length for normal andhigh strength RC bridge columns, quasi-static experiment for thin-walledhollow bridge columns, the seismic deformability of hollow bridge columnsand the flexural-shear seismic analysis model for RC bridge columns. Themain work results and conclusion are summarized as follows:1. To study the seismic deformation capacity and confiningreinforcement for RC bridge columns,234quasi-static test results for solidRC bridge columns were collected, the code provisions for the amount ofconfining reinforcement in the potential plastic hinge region of the bridgecolumns were evaluated via comparing with the test results. The equation forthe deformability of the solid rectangular bridge columns was proposed basedon regression analysis of the collected test results. Then, design equations forconfining reinforcement required to achieve drift ratios of2%and3%of thebridge columns are suggested and verified.2. To assess the influence of using high strength reinforcement andconcrete on the equivalent plastic hinge length of the bridge columns,108testresults of the plastic hinge length for normal and high strength RC bridgecolumns were collected and analyzed, and the code provisions for the plastichinge length in and out of China were evaluated. The main influencing factorson the plastic hinge length of the bridge columns were discussed and a newequation for the plastic hinge length of RC bridge columns is proposed by regression analysis on the collected test results. It is concluded that theequivalent plastic hinge length mainly depending on the specimen length,section width in the loading direction and the diameter of longitudinalreinforcement.3. The application of hollow columns in large bridges in China wassummarized. Two same large-scale hollow RC pier specimens were designedand tested. One specimen was subject to displacement-controlled cyclic lateralloading with a constant axial load, and the other was subject todisplacement-controlled cyclic lateral loading with variable axial load.Behavior of the specimens were evaluated in terms of damage progress andfinal failure pattern, concrete cracking width, residual displacement and shearstrength. Test results revealed that both specimens exhibited a mixedflexure-shear damage mode firstly and exhibited stable hysteretic loops. Thedamage of the column including flexural and shear cracking, crushing of theconcrete, and buckling of the reinforcement. When the top displacementexceeding2%of the pier height, all the specimens collapsed suddenly due tolocal compression flange buckling, and the specimen under variable axial loadcollapsed more severely than the one under constant axial load.4. Based on the collected seismic test results for hollow bridge columns,the seismic deformability of the columns with flexure, flexure-shear and shearfailure modes were studied, the main influencing factors on the deformabilityof the columns were discussed and the code provisions were evaluated. It isfound that the deformation capacity of the hollow bridge piers will beincreased as the transverse reinforcement, longitudinal reinforcement, andweb width increasing, and decreased as the axial load ratio increasing. At last,design equations for confining reinforcement in the potential plastic hingeregion of hollow bridge columns are suggested based on the Caltrans seismicdesign code for bridges.5. A flexure-shear seismic analysis model for RC bridge columns wasproposed based on the fiber element model and the Modified CompressionField Theory (MCFT). In the seismic analysis model, the flexuraldeformation and the ultimate strength of the column were obtained by thefiber element model, while the shear deformation of the column was obtainedby the MCFT. The fiber model and the MCFT coupled to simulate theflexure-shear-axial interaction of the bridge piers. The accuracy of the modelis verified by comparing with quasi-static test results for6circular bridgecolumns with flexure-shear failure modes.