NEESR-CR: An Innovative Seismic Performance Enhancement Technique for Steel Building Beam-Column Connections

该奖项由2009年美国复苏和再投资法案(公法111-5)资助。该奖项是NSF 09-524项目征集“小乔治·E·布朗地震工程模拟(NEES)研究网络(NEESR)”竞赛的结果，包括北卡罗来纳州立大学(NCSU，牵头机构)和北卡罗来纳大学彭布罗克分校(UNCP，子奖)。该项目将利用明尼苏达大学的NEES设备现场来实验验证一种用于增强钢建筑梁柱连接的抗震性能的创新技术。智能优点：拟议的抗震增强技术包括对梁法兰的部分进行热处理，在缓慢的空气冷却之前将这些部分暴露在非常高的温度下一定时间。这样的热处理工艺降低了法兰热处理区域的钢的强度。因此，在地震荷载作用下，热处理梁截面(HBS)处会产生塑性铰。通过这种技术增强的连接将具有流行的减梁截面(RBS)连接的优点，但HBS将具有比RBS连接更好的能量耗散。在RBS连接中，梁翼缘的“弱化”会导致远离焊缝的塑性铰链。在HBS连接中，由于钢的强度降低，在热处理部分形成了塑料铰链。此外，在梁翼缘保持不变、钢材的弹模不变的情况下，HBS节点的抗弯、抗扭能力将高于RBS节点。因此，与RBS连接相比，HBS连接将以最小的强度或刚度损失消耗更大的能量。通过NCSU的初步研究，对抗震性能增强技术进行了分析验证。该项目将通过进行全尺寸连接实验来验证该技术。由于其抗震性能和性价比，RBS是目前最受欢迎的节点设计。HBS连接预计将比RBS连接更抗震、更经济。这项研究将通过综合实验和分析研究进行。将进行热处理和非条件试件的材料实验，并对数据进行分析，以量化热处理参数(峰值温度和保温时间)对强度降低的影响，并确定本构模型参数。将对HBS连接进行详细的结构分析，以确定HBS的最佳热处理参数和几何形状。将建立和不安装HBS的梁柱节点，并进行试验，以展示修改后的节点的抗震性能增强。将记录不同位置的应变、位移和旋转的详细测量，以调查HBS连接的局部和全局故障模式。实验和分析结果将被用来改进技术，并为技术的实际应用开发一种方法。广泛的影响：研究结果将被整合到专业发展课程中，研究将包括来自以本科生为主的美洲原住民机构的教职员工和学生参与实验活动。将制定和传播应用这一新技术的方法。热处理概念适用于钢结构或桥梁连接；拟议的热处理技术将使使用焊接接头的行业受益。该项目的实验数据将被存档，并通过NEES数据库向公众提供。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).This award is an outcome of the NSF 09-524 program solicitation "George E. Brown, Jr. Network for Earthquake Engineering Simulation (NEES) Research (NEESR)" competition and includes the North Carolina State University (NCSU, lead institution) and the University of North Carolina at Pembroke (UNCP, subaward). This project will utilize the NEES equipment site at the University of Minnesota to experimentally validate an innovative technique for enhancing the seismic performance of steel building beam-column connections.Intellectual Merit: The proposed seismic enhancement technique involves heat treating sections of beam flanges by exposing these sections to a very high temperature for certain amount of time before slow air cooling. Such a heat treatment process reduces the strength of steel in the heat treated areas of the flange. Consequently, under seismic loading, a plastic hinge develops at the heat treated beam section (HBS). A connection enhanced by this technique will have the advantages of the popular reduced beam section (RBS) connection, but the HBS will have better energy dissipation than the RBS connection. In RBS connections, "weakening" of the beam flanges induces a plastic hinge away from the welds. In HBS connections, a plastic hinge develops at the heat treated section because of the reduced strength of steel. Moreover, as the beam flange remains intact and the inelastic modulus of steel is not altered at the HBS, the lateral and torsional buckling resistances of the HBS connection will be higher than those of the RBS connection. Consequently, the HBS connection will dissipate a larger amount of energy with a minimum loss of strength or stiffness compare to the RBS connection. Through a pilot study at NCSU, the seismic performance enhancement technique is validated analytically. This project will validate the technique by conducting full-scale connection experiments. Currently, RBS is the most popular connection design because of its seismic performance and cost effectiveness. The HBS connection is anticipated to be more seismically robust and economical than the RBS connection. The research will be performed through integrated experimental and analytical studies. Material experiments of heat treated and unconditioned coupons will be conducted and data will be analyzed to quantify the influence of heat treatment parameters (peak temperature and hold time) on the reduction of strength and to determine the constitutive model parameters. Detailed structural analyses of HBS connections will be performed to determine the optimum heat treatment parameters and geometry of HBS. Beam-column connections with and without HBS will be built and tested to demonstrate seismic performance enhancement of the modified connections. Detailed measurement of strains, displacements and rotations at various locations will be recorded for investigating both the local and global failure modes of HBS connections. Experimental and analytical results will be used to refine the technique and to develop a methodology for practical application of the technique.Broader Impacts: The research results will be integrated into professional development courses, and the research will involve faculty and students from a predominantly undergraduate Native American institution in the experimental activities. A methodology for application of the novel technique will be developed and disseminated. The heat treatment concept is applicable to steel building or bridge connections; the proposed heat treatment technique will benefit industries that use welded joints. Experimental data from this project will be archived and made available to the public through the NEES data repository.