部分充填钢管混凝土桥墩振动台试验

为了完善部分充填圆形钢管混凝土桥墩的抗震设计理论及其工程应用,对2座采用此类桥墩的两跨高架桥缩尺模型(相似比为1∶6.7)进行了强地震动输入下的破坏性振动台试验,研究无偏心部分充填圆形钢管混凝土桥墩和有偏心部分充填圆形钢管混凝土桥墩的破坏机理和地震响应。研究发现无偏心桥墩在墩底附近产生了均匀的钢管局部屈曲变形和明显的水平裂缝,而有偏心桥墩并没有产生水平裂缝,所以无偏心桥墩的纵桥向墩顶位移远大于有偏心桥墩。同时,受横桥向恒载偏心的影响,有偏心桥墩的墩顶横桥向位移和墩底局部屈曲变形主要集中在靠近中轴线的一侧,塑性发展区域也大于无偏心桥墩,这使得其墩顶横桥向最大位移大于无偏心桥墩。不过,由于有偏心桥墩并未发生开裂,所以其横桥向残余位移与无偏心桥墩相差不大,均在3 cm左右,验证了有偏心部分充填圆形钢管混凝土桥墩若经过合理的截面设计,其抗震性能也能满足既定的要求。此外,恒载偏心使得有偏心桥墩在横桥向两侧所耗散的能量不相等,可能会导致其横桥向两侧的累积塑性变形存在差异,不利于其优越的抗震性能和耗能能力的充分发挥。因此在设计有偏心部分充填圆形钢管混凝土桥墩时,需要合理选取混凝土充填高度和径厚比等结构参数,减少恒载偏心对其抗震性能的不利影响。

Plastic Buckling of Cylindrical Shells Under Transverse Loading

Thick cylindrical shells under transverse loading exhibit an elephant foot buckling mode, whereas moderately thick cylindrical shells show a diamond buckling mode. There exists some intermediate geometry at which the transition between buckling modes can take place, This behavior is significantly influenced by the radius-to-thickness ratio and the material yield strength, rather than the length-to-radius ratio and the axial force. This paper presents a critical value at which the transition of buckling modes occurs as a function of the radius-to-thickness ratio and the material yield strength. The result shows that the circumferential wave number of the diamond buckling mode increases with decreasing wall thickness. The strain concentration is also intensified for the diamond buckling modes compared with the elephant foot buckling modes.