Innovation Connection for Precast Frames Using Debonded Tendons

预制混凝土框架采用梁单元与后张法预应力筋连接的多层柱单元，已被认为是一种经济可行的高层建筑施工方法。最近的研究表明，使用完全灌浆的筋的梁柱节点组件具有与按现行规范设计的整体式钢筋混凝土组件相当的延性。但在达到中等延性水平后，筋在低位移时经常遭受过度的刚度退化。这是由于通过柱的有效预应力夹紧力减小，这是由于关键截面处的预应力筋的非弹性应变造成的。该项目进行了一项试验性研究，以试验验证使用无粘结预应力筋连接预制抗震框架的新概念。筋将连接预制梁和柱的截面，从而实现非线性弹性响应，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，因此可以提高节点的剪切能力，而不需要广泛的节点剪切配筋。利用加州大学圣地亚哥分校现有的拟动力测试设施，将建造两个分别代表外部连接和内部连接的大型测试单元，并在循环侧向变形下进行测试。将选择保守的横向配筋细节，并进行严格的应变测量。预计将提出减少配筋的建议，并将通过实验研究对这一概念进行验证。该项目由探索性研究小额资助计划(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.