Innovation Connection for Precast Frames Using Debonded Tendons

预制混凝土框架使用梁单元连接多层柱单元与后张预应力筋已被确定为一种经济可行的高层建筑施工方法。最近的研究表明，使用全灌浆肌腱的梁柱节点子组合具有与当前规范设计的整体钢筋混凝土子组合相当的延性。但在达到中等延性水平后，在低位移下往往会出现过度的刚度退化。这是由于通过柱的有效预应力夹紧力的减少造成的，这是由于预应力筋在临界截面的非弹性应变造成的。本项目进行了一项试点研究，以实验验证使用无粘结预应力筋连接预制抗震框架的新概念。预应力筋将连接预制梁和柱截面，允许非线性弹性响应并实现相当大的位移能力。这种能力不存在与永久变形相关的问题，因此可以在不需要广泛的接缝剪切加固的情况下增强接缝的剪切能力。两个大型测试单元将分别代表外部和内部连接，并在循环横向变形下使用加州大学圣地亚哥分校现有的伪动力测试设备进行测试。将选择保守的横向加固细节，并进行大量应变测量。预计将提出减少强化的建议，并从实验研究中验证这一概念。本项目由探索性研究小额资助项目（SGER）资助。

Precast concrete frames using beam elements connected to multi-story column elements with post-tensioned prestressing tendons has been identified as an economically viable method of construction for tall buildings. Recent research has indicated that beam-column joint subassemblages using fully grouted tendons developed ductility comparable to monolithic reinforced concrete subassemblages designed to current specifications. But the tendons often suffer excessive stiffness degradation at low displacements after moderate ductility levels had been chieved. This was caused by a reduction of effective prestress clamping force through the column, resulting from inelastic strain of the prestressing tendon at the critical section. This project conducts a pilot study to experimentally verify a new concept for connecting precast seismic frames using unbonded prestressing tendons. The tendons will connect precast beam and column sections which allows a nonlinear elastic response and achieves a considerable displacement capacity. This capacity is free from problems associated with permanent deformation, thus enable the joint shear capacity to be enhanced without the need for extensive joint shear reinforcement. Two large scale test units representing an external and an internal connections respectively will be constructed and tested under cyclic lateral deformations using the existing pseudo-dynamic testing facility at University of California, San Diego. Conservative transverse reinforcement details will be chosen and heavily strain gauged. It is expected that recommendations for reduced reinforcement will be made and verification of the concept will be achieved from the experimental research. This project is supported under the provision of Small Grants for Exploratory Research (SGER) program.