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一九七六年发生的唐山地震波及到塘沽新港地区的码头构筑物,造成了不同程度的震害,其中叉桩和叉桩桩帽的损坏最普遍、严重。为减轻这种震害,建议将叉桩顶部节点改为摩擦或摩擦——阻尼节点。具体方法是,在叉桩帽上表面与上部横梁接触部分预埋一块比接触面稍大的钢板,在浇捣上部横梁时,须在桩帽上铺设水泥袋纸或塑料薄膜,使二者隔开,形成摩擦面。摩擦面应制做得平整,不得有明显的凸凹不平。此时上部桩台只是单纯地搁置在叉桩帽上,而没有其它的连接。地震时,当上部桩台承受的地震力未超过桩台与桩帽间的摩擦力时,桩帽与上部横梁间相当于铰接;当超过摩擦力后,叉桩帽与上部桩台将产生相对滑动,地震力不再增加。通俗地说,相当于在受力最大的叉桩帽上表面设置了一个“限力阀”,以保护主体结构不受破坏。结构示意图见图1。
The Tangshan earthquake that occurred in 1976 and the pier structures in the Tanggu Newport area caused various degrees of earthquake damage. Among them, fork piles and fork pile caps were the most common and serious. To mitigate this damage, it is recommended that the top node of the fork pile be changed to a friction or friction-damping node. The specific method is to embed a steel plate slightly larger than the contact surface on the contact surface of the fork pile cap with the upper cross beam. When pouring the upper beam, a cement bag paper or a plastic film shall be laid on the pile cap to separate the two. Open, forming a friction surface. The friction surface should be made flat and must not have obvious unevenness. At this point the upper piling simply rests on the fork pile cap without any other connection. In an earthquake, when the seismic force sustained by the upper pile platform does not exceed the friction between the pile platform and the pile cap, the pile cap and the upper beam correspond to articulation; when the friction force is exceeded, the pile cap and the upper pile platform will generate relative forces. Slide, the seismic force no longer increases. In layman’s terms, it is equivalent to placing a “force limit valve” on the upper surface of the most fork pile cap to protect the main structure from damage. The structure diagram is shown in Figure 1.