Improvement and evaluation on the seismic performance of RO composite bridge piers by OFT reinforcements

钢筋混凝土桥墩缺乏抵抗地震荷载的变形能力。即钢筋混凝土受压断裂引起受压钢筋屈曲，从而使钢筋混凝土结构的抗弯强度急剧下降。因此，为了提高钢筋混凝土结构的变形能力，有效地防止压杆因屈曲而丧失强度。对钢管混凝土柱和钢筋混凝土柱进行了轴向恒定荷载和横向低周反复荷载作用下的试验研究。研究了钢管的配筋形式、钢管的径厚比以及钢管与混凝土的粘结方式对柱的承载力和变形能力的影响。（1）循环荷载严重降低了柱的变形能力，即延性指标，尤其是配筋混凝土柱。（2）在其他条件相同的情况下，轴压比为N/f_c_0 =0.1时，混凝土柱的屈服荷载和最大荷载均高于轴压比为N/f_c_0 =0.05时。轴压比N/fc =0.05时，延性指数δ U/δ y较高。（3）与配筋混凝土柱相比，CFT混凝土柱的承载能力、变形能力和能量吸收能力优异。（4）钢管的径厚比不影响钢管的承载能力和变形能力。钢管的表面处理对这些性能有很好的影响。因此，改进粘结法对CFT的应用具有重要意义。

The bridge piers of reinforced concrete lack the deformation capacity against an earthquake load. Namely, the compression rupture of reinforced concrete causes the buckling of a compression reinforcing-bar and consequently weakens the bending strength of RC structures sharply. Therefore, in order to improve the deformation capacity of RC structures it is effective to prevent reinforcing-bars from losing strength due to buckling. The concrete columns reinforced with CFTs or with reinforcing bars have been tested under an axially constant load and a transversely cyclic load. The reinforcement types, the diameter-thickness ratio of steel-tubes and the bond method of a tubular steel to concrete have been investigated in relation to the load carrying capacity and deformation capacity of the columns.The following have been found.(1)The cyclic load seriously reduces the deformation capacity, i.e. the ductility index, especially that of the concrete column with reinforcing bars.(2)Both yield load and maximum load are high in the concrete columns under the axial load ratio of N/f_c0=0.1 as compared with N/f_c=0.05, when the other conditions are same. Conversely, the ductility index, δ_U/δ_y, is high in the specimens under the axial load ratio of N/f_c=0.05.(3)The concrete column with CFT is excellent in load-carrying capacity, deformation capacity, and energy absorption capacity as compared with the concrete column with reinforcing bars.(4)The diameter-thickness ratio of tubular steel does not influence the load-carrying capacity, and deformation capacity. The surface treatment on a steel-tube has a good effect on those capacities. It is important for us to improve the bond method in order to employ CFT.