Research On The Flexure-Shear-Torsion Aseismic Strengthening Mechanism And Measures Of RC Piers

Under the action of strong earthquakes,the RC pier of irregular bridges,such as curved bridge,skew bridge and ramp bridge,usually results in its more serious seismic damage and even collapse,as suffered from the coupling interaction of shear force,flexural moment and torsional moment.At present,the research on the flexural-shear-torsion aseismic strengthening measures for the irregular bridge’s RC piers is very rare.Therefore,based on the existing aseismic strengthening methods and the pseudo static test,in which piers are enclosed by precast segments of steel fiber concrete on its plastic hinge region,a new aseismic strengthening measure considering the coupling interaction of shear force,flexural moment and torsional moment for irregular bridge’s RC piers is proposed in this study.Concave convex precast segments made of steel fiber concrete are adopted to reinforce the RC piers along the height,and the unbonded reinforcement is arranged in the hole reserved for the segments.And the design technique for flexure-shear-torsion aseismic strengthening measure has been presented.Meanwhile,through a nonlinear seismic response analysis of a ramp bridge,the effectiveness and the reinforcement result of the flexure-shear-torsion aseismic strengthening measure are discussed.The main contents of this paper are as follows:(1)Aimed at the flexure-shear-torsion aseismic strengthening measure,the the formulas for yield bending moment,ultimate moment,yield torque and yield torsion angle of strengthening piers is put forward,and the flexure-shear-torsion aseismic strengthening design method is proposed.(2)Three model piers(1 original model pier,1 reinforcement model pier Ⅰand 1 reinforcement model pier Ⅱ)are designed and manufactured,and then a pseudo static test for the piers is performed.By comparing the aseismic capacity of 3 piers,the effectiveness of the strengthening measure that piers are enclosed by precast segments of steel fiber concrete on its plastic hinge region is discussed,such as flexural capacity and torsion resistance,displacement ductility and torsion angle ductility,bending energy dissipation and torsion,etc.And then a new strengthening measure of RC piers that are enclosed by concave convex SFCprecast segments along the height is presented.(3)A ramp bridge finite element model 1 is established for the piers with the consideration of the coupling interaction of shear force,flexural moment and torsional moment.According to the design method,the finite element model 2with flexure-shear-torsion aseismic strengthening fixed piers and the model 3with flexure-shear-torsion aseismic strengthening fixed piers and with flexure-shear aseismic strengthening cantilever piers are established.Three grounds motion(Mianzhu Qingping ground motion,Wenchuan Wolong ground motion and Shifang Bajiao ground motion)are selected as input,and the nonlinear seismic time history response analysis is carried out for the 3 ramp bridge models.By comparing the displacement response and the failure condition of fixed piers,hinge piers and bearings in the 3 models,the effectiveness and reinforcement effect of the flexure-shear-torsion aseismic strengthening measures can be verified.