Seismic assessment and strengthening of 3D beam-column joints

本项目的主要目标是：(1)在考虑楼板和横梁影响的情况下，为NSD结构三维梁柱节点的实际性能评估开发实用可靠的模型；(2)为三维梁柱节点开发低侵入、高效的加固方案和相应的性能评估模型。现有的研究工作主要集中在平面二维梁柱节点组件上，没有考虑横向梁或板的影响。现有有限的文献研究清楚地表明，板和横梁以及双向荷载对梁柱节点抗震性能的显著影响，特别是NSD结构。对于不足平面梁柱节点的加固，申请人和其他研究人员已经研究了完全紧固后腿加固方案（FFHRS），并证明了在连接后腿单元与结构构件的紧固件性能良好的情况下，这是一种切实可行和有效的加固方法。改造方案的有效性在很大程度上取决于连接构件的相对刚度、支腿元件和后安装锚的刚度。楼板在梁柱节点中的参与可以显著地改变这些相对刚度值，因此，现有的二维节点数据不足以制定可靠的加固方案。基于上述主要目标，本项目将对全尺寸梁柱节点进行试验研究，逐步清晰地揭示(1)横向梁、(2)整体板、(3)双向荷载对NSD结构梁柱节点抗震性能的影响。实验将通过详细的数值调查和参数研究来量化各种参数的影响。采用FFHRS加固后的全尺寸梁柱节点将进行进一步的试验研究。然而，将首先对循环荷载下的锚固进行试验，以：(i)确定将后端构件连接到框架构件的最合适的锚固类型，以及（ii）提供有关锚固的载荷-位移和滞后行为的信息。这些测试将采用一种新的基于位移的方案。在项目框架内进行的试验和数值研究的基础上，将开发多弹簧模型，用于在考虑板、横梁、双向荷载和锚固行为影响的情况下，对已建成节点以及经FFHRS改造的节点进行性能评估。

The primary goals of this project are (i) to develop practical and reliable models for realistic performance assessment of 3D beam-column joints of NSD structures while taking into account the influence of slabs and transverse beams, and (ii) to develop a low-invasive, high-effective strengthening solution for 3D beam-column joints and the corresponding models for their performance assessment. The existing research work has primarily been focused on the planar 2-dimensional beam-column joint sub-assemblies without considering the influence of transverse beams or slabs. Limited studies existing in literature clearly brought out the significant influence of slabs and transverse beam as well as bi-directional loading on the seismic performance of beam-column joints especially of NSD structures. For the strengthening of insufficient planar beam-column joints, fully fastened haunch retrofit solution (FFHRS) has been investigated by the applicant and other researchers and is shown to be a practically viable and effective strengthening method provided the fasteners used to connect the haunch element to the structural members perform well. The effectiveness of the retrofit solution is largely dependent on the relative stiffness of the connecting members, the haunch element and the stiffness of post-installed anchors. The participation of slab in a beam-column joint can significantly modify these relative stiffness values and therefore, the existing data on 2D joints is insufficient to develop a reliable strengthening solution. With the above-mentioned primary goals in sight, in this project, experimental investigations will be performed on full-scale beam-column joints to clearly and step-by-step bring out the influence of (i) transverse beam, (ii) monolithic slab, and (iii) bi-directional loading on the seismic performance of beam-column joints of NSD structures. Experiments will be augmented by a detailed numerical investigation and parametric study to quantify the influence of various parameters. Further experimental investigations on full-scale beam-column joints after strengthening using FFHRS will be carried out. However, tests will first be performed on anchorages under cyclic loading to: (i) identify the most suitable anchor type for connecting the haunch elements to frame members, and (ii) provide information on the load-displacement and hysteretic behavior of the anchors. A new displacement based protocol will be used for these tests. Based on the experimental and numerical investigations carried out within the framework of the project, multi-spring models will be developed that can be used for the performance assessment of as-built joints as well as the joints retrofitted with FFHRS while taking into account the influence of the slabs, transverse beam, bi-directional loading and anchorage behavior.