Seismic assessment and strengthening of 3D beam-column joints

本项目的主要目标是：（i）开发实用可靠的模型，用于NSD结构三维梁柱节点的真实性能评估，同时考虑板和横梁的影响;（ii）开发低侵入性、高效的三维梁柱节点加固解决方案及其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子组件上，没有考虑横向梁或板的影响。现有的有限的研究清楚地表明，板和横梁以及双向加载的显着影响的梁柱节点的抗震性能，特别是NSD结构。为了加强不充分的平面梁柱接头，申请人和其他研究人员已经研究了完全紧固的加腋改造解决方案（FFHRS），并且显示出如果用于将加腋元件连接到结构构件的紧固件表现良好，则完全紧固的加腋改造解决方案（FFHRS）是实际可行且有效的加强方法。加固方案的有效性在很大程度上取决于连接构件的相对刚度、加腋元件和后安装锚固件的刚度。板在梁柱节点中的参与可以显着修改这些相对刚度值，因此，现有的2D节点数据不足以开发可靠的加固解决方案。基于上述主要目的，本项目将对全尺寸梁柱节点进行试验研究，以明确和逐步地揭示（i）横梁、（ii）整体板和（iii）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研究和参数研究来量化各种参数的影响。将对采用FFHRS加固后的足尺梁柱节点进行进一步的试验研究。然而，首先将在循环荷载下对锚具进行试验，以：（i）确定将加腋元件连接到框架构件的最合适的锚类型，以及（ii）提供有关锚的荷载-位移和滞后性能的信息。这些测试将使用新的基于位移的方案。基于在该项目框架内进行的试验和数值研究，将开发多弹簧模型，该模型可用于竣工节点以及用FFHRS改造的节点的性能评估，同时考虑板、横梁、双向加载和锚固行为的影响。

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.