大轴力桩基托换梁-柱接头模型试验

MODEL TESTS OF BEAM-COLUMN JOINTS FOR LARGE-AXIAL-LOAD-PILE UNDERPINNING

深圳地铁百货广场桩基托换工程 ,采用“梁抱柱”托换方案 ,由于托换柱轴力大、梁 -柱结合周长小、接合处承受剪力大、接头处于斜交状态 ,接头受力复杂 ,因此接头强度是托换成败的关键。本文对接头选型进行了一系列试验研究。对一般凿毛、锚筋、企口、预应力、企口 +锚筋 +预应力五种不同接头形式进行的 1∶4模型试验表明 :一般凿毛涂刷截面剂接头不能满足接头抗剪承载力的要求 ;加锚筋可以提高承载力约 5 0 % ;企口接头可以提高承载力 80 %以上 ;施加预应力可以有效地防止梁体裂缝 ,但如果单纯施加预应力 ,会导致柱 -梁斜交面产生剪切破坏 ,反而降低接头抗剪承载力 ;采用企口 +锚筋再施加预应力的接头 ,各项承载力可以迭加 ,初始滑移荷载和极限承载力均最大 ,分别达 2 84倍和 3 3 8倍托换荷载。进一步的 1∶2接头模型试验结果表明 ,企口 +锚筋 +预应力接头初始滑移安全系数大于 1 8,与 1∶4试验结果吻合。为检验实际托换过程接头性状 ,仍采用企口 +锚筋 +预应力形式进行了 1∶4整体模型试验 ,其结果表明 :在实际托换过程中接头不会出现初始滑移 ,故采用企口 +锚筋 +预应力的斜交构造是可行的 ,可以保证托换过程和使用过程中梁 -柱接头强度的安全性。

The Beihuo Guangchang pile underpinning project,with la rg e underpinning axial load and complex construction environment,is one of the imp ortant parts of the Shenzhen Metro project.The project adopts a beam clasp column scheme.Because of large axial load,small circumference and large shear fo rce,oblique junction of the beam-column joints,the mechanical condition at the j oints is complex,and the shear strength of the joints is the key factor for the und erpinning scheme.Five types of model tests demonstrate that simple mortising wit h bonding agent joints (S1 joint) cannot provide sufficient shear resistance,jo int with anchor bar(S4 joint)can improve shear resistance by 50%,tongue-and-gro ove joint(S3 joint) can improve shear resistance by more than 80%.Joints pre-str essing can prevent the beam from cracking,however,such joints(S2 joint)can reduc e the joint's shearing capacity and cause the shear failure of the inter face.Joints with tongue and groove,anchor bar and pre-stressing can greatly impr ove the shear resistance.The S5 joints' initial slide capacity equals 2 .84 times the underpinning load,and the ultimate capacity equals 3.38 times th e underpinning load.The S5 joint possesses the largest capacity among the five t ypes of joints,and can be practically employed.To test the size effect, 1∶2 model tests are conducted for the S5 joint.The tests demonstrate that the joint's shear resistance is consistent with the 1∶4 model tests.The initial shear resistance factors of the joint's are great than 1.8.To check th e characteristics of the S5 joint in practical underpinning,1∶4 model test are perfor med,and the results indicate that the S5 joint is safe without initial sliding a nd can be used for the Beihuo Guangchang pile underpinning project.