Abstract
Compared with the solid pier with the same external size,the hollow pier has the advantages of saving masonry and reducing the dead weight of the structure,and can ef fectively reduce the seismic inertia force to a certain extent,and achieve the purpose of protecting the overall safety of the bridge[1].Although some achievements have been made in the study of seismic performance of hollow piers[2-5],these results are more derived from the research of rectangular hollow section piers,whether the research results can be widely used in other types of hollow piers is not clear[5].
In order to reveal the difference of seismic performance of reinforced concrete hollow piers with different crosssections under repeated loads,low-cycle reciprocating loading tests were carried out on 6 hollow piers with three different cross-sections(Scheme of the hollow piers are seen in Table 1 and shown in Figure 1).The evolution mechanism of pier body crack of hollow pier was analyzed,and the differences of pier crack evolution mechanism,hysteretic energy dissipation capacity,plastic rotation capacity,damping and stiffness characteristics of bridge piers with different cross sections were discussed.The test and analysis results showed that the seismic performance of square hollow pier was consistent with that of rectangular hollow pier,but it was different from that of thin-walled hollow pier at circular end,which mainly performanced as the following aspects:(1)Compared with square hollow piers and rectangular hollow piers,the distribution of cracks in the pier body of thin-walled hollow pier with variable cross-section was denser and wider,grid oblique cracks appeared on the side of pier body,the distribution range of bending cracks in pier body was about 0.61～0.75 times of pier height,and the through cracks in pier body were scattered.There were certain vertical cracks at the top of the pier.(2)In the limit state,the tension/buckling and concrete collapse of the steel bar of the square hollow pier and the rectangular hollow pier were mainly concentrated in the chamfer position at the bottom of the pier,while the thin-walled hollow pier at the circular end was mainly concentrated near the variable cross-section chamfer at the bottom of the pier(Damage description of specimens are shown in Figure 2).(3)For the square hollow piers and the rectangular hollow piers,the plastic hinge position of the thin-walled hollow pier at the circular end moved up and the plastic area was enlarged,which showed a better ductile capacity(Hysteresis curves of specimens are shown in Figure 3).(4)Compared with square hollow piers and rectangular hollow piers,the stiffness of thin-walled hollow pier at circular end degraded faster,but the effective stiffness corresponding to the equivalent yield point of the three kinds of cross-section was consistent with the compression ratio,shear span ratio and material characteristic parameters.(5)The equivalent damping ratio of thin-walled hollow pier with circular end before equivalent yield was slightly higher than that o f hollow pier with square section and hollow pier with rectangular section.After equivalent yield,the equivalent damping ratio of hollow pier with square section and hollow pier with rectangular section changed faster than that of thinwalled hollow pier with circular end.
Table 1 Design parameters of quasi-static test model for piers
Note:L is the height of the members,h is the height of the component section,b is the width of the component section,tw is the thickness of wall of the hollow piers,f'c is the compressive strength of concrete,ρl is the stirrup ratio,ρs is the stirrup volumetric ratio,λis the aspect ratio.
Figure 1 Scheme of the hollo w pier(unit:cm)
Figure 2 Damage description of specimens
Figure 3 Hysteresis curves of specimens