Combination of mechanical and informational modeling to predict hysteresis behavior of I beam‐to‐CFT column connection

The behavior of beam‐to‐column connections is significantly complicated because it depends on the material, nonlinear relationship between different members, and contact of connecting elements. Their hysteretic response exhibits highly inelastic characteristics and continuous variation in stiffness, strength, and ductility. Therefore, accurate hysteretic models of bolted connections are essential to accurate seismic assessment and design. Composed (Hybrid) modeling approach is presented to represent the complex hysteretic behavior of I beam‐to‐concrete‐filled‐tube (CFT) column bolted connection. For the purpose in this study, experimental evaluation of I beam‐to‐CFT column connection with bolted end‐plate under cyclic loading is done. It must be mentioned to make the connection easily applicable practically and also prepare the column flanges continuity, a connection with the bolts penetrated into the CFT column are used since using the stiffeners in hollow sections is not easily applicable. In the composed mechanical–informational modeling framework, the conventional mechanical model is complemented by information‐based model components. Finally, moment–rotation curves of composed model have been compared with experimental results. Comparison showed that the composed model has a good agreement with experimental results. A newly designed specimen for validation purpose of the composed modeling was made and experimented. Composed model was well applied to predict the behavior of new connections. The presented results show that the composed model has a good ability to predict of hysteretic behavior.     

复式钢管混凝土柱与H形钢梁连接节点抗震性能试验研究

借鉴方钢管混凝土柱-钢梁外肋环板节点形式,将非梁柱连接面的柱两侧外肋环板改为竖贴于柱侧的竖向肋板并伸出与梁翼缘焊接,同时设置锚固腹板,形成复式钢管混凝土柱与H形钢梁连接节点。通过7个梁柱组合体试件的低周反复荷载试验,分析各试件的破坏过程及特征,并对试件的滞回性能、承载力、延性、耗能能力和承载力及刚度退化等抗震性能进行研究。研究结果表明：节点的破坏形态基本相同,梁端先屈曲,形成塑性铰;锚固腹板可有效提高节点的承载力和变形能力;竖向肋板外伸长度可提高试件的初始刚度,使梁端塑性铰外移,有效保护节点核心区;试件的滞回曲线呈明显的梭形,具有良好的承载力、延性及耗能能力;试件在整个加载过程中刚度退化现象明显,承载力退化很小,可应用于抗震设防地区。     

Foundation connections for circular concrete-filled tubes

Concrete filled steel tubes (CFTs) promote economical and rapid construction. They offer increased strength and stiffness relative to structural steel and reinforced concrete. The steel tube serves as formwork and reinforcement to the concrete fill, thereby reducing the labor requirements. CFT components encourage the optimal behavior of each material (concrete and steel) while providing a symbiotic relationship between the two to mitigate undesirable failure modes. The fill increases the compressive strength and stiffness, delays and restrains local buckling of the tube, and enhances ductility and resistance if composite action is achieved.Both rectangular and circular CFT have been employed, but circular CFT provide better performance, because they provide increased confinement of the concrete and composite action. A missing component for circular CFT construction is reliable and ductile connections. The research described herein that investigated and develops design procedures for simple and economical connections of circular CFT piers or columns to reinforced concrete foundations, pile caps and wide cap beams (bridge construction) is presented and evaluated. The connection requires no dowels or internal reinforcement connecting the tube to the footing or cap beam. Experiments and analytical studies evaluate the inelastic seismic performance and establish design criteria for the connection. The seismic performance of a CFT column and connection assembly is compared to a conventional reinforced concrete column. The research shows that the proposed connection develops the full capacity of the composite column. The assembly provides excellent ductility and inelastic deformation capacity under seismic loading while mitigating damage even at larger drift demands.     

圆形钢管混凝土柱的基础连接件

钢管混凝土柱促进了经济且快速的建设方式。两者的组合增大了结构钢和混凝土的强度和刚度,使用钢管作为模板和核心混凝土的约束减少了工作量。钢管混凝土柱为混凝土和钢材提供了一个共生关系来缓和其不良的失效模式,激发了各种材料的最优性能(混凝土和钢材)。综合作用下,混凝土抗压强度和刚度增大,延缓和抑制了钢管的局部屈曲,并提升其延展性和抗力。矩形钢管混凝土柱与圆形钢管混凝土柱都被应用于实际建设生产中,但由于圆形钢管混凝土柱可以提供更强的混凝土约束和综合作用而拥有更好的性能。对于圆形钢管混凝土柱来说,其缺少可靠的、有延展性的连接件。对这方面的研究调查进行介绍,包括关于圆形钢管混凝土柱柱脚或钢筋混凝土地基柱的简便经济的连接件的开发设计过程,并介绍和评价了桥梁结构中的桩帽与宽桩梁。这种连接件不需要销子和内在的加固就能将钢管与基脚或桩梁相连接。试验分析研究和评估了这种连接件的非弹性抗震性能,并确立了设计标准。将1个装配这种连接件的钢管混凝土柱的抗震性能与传统的钢筋混凝土柱相比较。结果显示,此种连接件进一步增强了组合柱的承载力。这种形式在地震荷载下能提供极佳的延展性和非弹性变形能力,甚至在大侧移情况下也能减轻损害。     

Seismic behavior of exterior connections with steel beams bolted to CFT columns

In order to improve the constructability and meanwhile ensure satisfactory seismic behavior, an innovative type of connection for concrete filled circular steel tube (CFT) column-to-steel beam composite structures was conceived and studied. The proposed connection details are characterized by an extended endplate that is welded to a steel beam in factory and then bolted to a CFT column using high-strength steel rods in the field. An experimental investigation on seismic behavior of the proposed bolted endplate connection and evaluation of the effect of concrete floor slabs and reduced beam sections was conducted by testing three full scale joint models. The experimental results indicated that the presence of floor slabs contributed to the strength of joints significantly and reduced beam sections were effective in moving the buckling zone away from the welds. Analytical models for the bolted endplate connections were also constructed using OPENSEES1.7.3 to simulate the experimental results.     

Compressive behavior of central gusset plate connections for a buckling-restrained braced frame

Buckling-restrained braced frames (BRBFs) are used as lateral-load resisting systems in seismic design. The braces in BRBFs are connected to beams and columns by gusset plate connections, and can yield in both tension and compression instead of buckling. Although tests of buckling-restrained braces (BRBs) have demonstrated their ability to withstand significant inelastic axial deformation, large-scale BRBF tests have exhibited central gusset plate buckling before BRBs develop the ultimate compressive strength. To extend and better understand the experimental work, this paper presents an analytical study of the compressive behavior for BRBF central gusset plate connections using the finite element computer program ABAQUS. A model of a previously tested BRBF is conducted to predict experimental buckling load of the central gusset plate and verify the accuracy of a simple model of a central gusset plate connection including a beam and part of the BRB. The out-of-plane deformation of the central gusset plate resembles the buckled shape of a gusset plate with low bending rigidity provided by the BRB end. The experimental buckling load of the central gusset plate cannot be predicted based on the AISC-LRFD approach with an effective column length factor of 1.2. Therefore, a parametric study on the compressive strength of BRBF central gusset plate connections is conducted with various gusset plate dimensions and free-edge stiffeners. An inelastic plate buckling equation together with coefficient charts is proposed to predict ultimate load. For gusset plates with sufficient free-edge stiffener rigidity, the yield load can be developed and increased to the post-yield strength level. A required free-edge stiffener size is also recommended for BRBF central gusset plates to develop compressive yield load.     

Punching shear strength and post-punching behavior of CFT column to RC flat plate connections

This paper summarizes full-scale test results on CFT (concrete filled tube) column to RC (reinforced concrete) flat plate connections subjected to gravity loading. CFT construction is gaining wide acceptance due to its various structural and constructional advantages. However, efficient details for CFT column to RC flat plate connections have not been proposed yet. Based on the strategies that maximize economical field construction, several connecting schemes were proposed and tested in this study. Test results showed that the proposed connections can exhibit punching shear strength and connection stiffness exceeding those of RC flat plate counterparts. A semi-analytical procedure is presented to model the behavior of CFT column to RC flat plate connections. The parameters needed to model the behavior from elastic to post-punching range are calibrated based on the test data of this study. The application of the proposed model to progressive collapse analysis is also illustrated.     

Evaluation of Three Support Shapes on Behavior of New Bolted Connection BBCC in Modularized Prefabricated Steel Structures

Bolted connections are suitable due to high quality prefabrication in the factory and erection in the workplace. Prefabrication and modularization cause high speed of erection and fabrication, high quality and quick return of investment. Their technical hitches transportation can be removed by prefabrication of joints and small fabrication of components. Box-columns are suitable members for bolted structures such as welded steel structures with moment frames in two directions etc., but their continual fabrication in multi-story buildings and performing the internal continuity plate in them will cause some practical dilemmas. The details of the proposal technique introduced here, is to remove such problems from the box columns. Besides, some other advantages include new prefabricated bolted beam-to-column connections referred to BBCC. This connection is a set of plates joined to columns, beams, support, and bolts. For a better understanding of its fabrication and erection techniques, two connection and one structural maquettes are made. The present work aims to study the cyclic behavior of connection numerically. To verify the accuracy of model, a similar tested connection was modelled. Its verification was then made through comparison with test results. The behavior of connection was evaluated for an exterior connection using three different support shapes. The effects of support shapes on rigidity, ductility, rotation capacity, maximum strength, four rad rotation strength were compared to those of the AISC seismic provision requirements. It was found that single beams support has all the AISC seismic provision requirements for special moment frames with and without a continuity plate, and box with continuity plate is the best support in the BBCC connection.     

中空夹层钢管混凝土柱与钢-混凝土组合梁节点抗震性能试验研究

以中空夹层钢管混凝土柱与带钢筋混凝土楼板的钢-混凝土组合梁采用高强螺栓及T形钢连接件构成的组合节点的抗震性能为研究对象,对6个十字形组合节点以梁端反对称加载的形式进行拟静力试验。试验中以柱轴压比、加劲肋、T形钢连接件尺寸、楼板厚度和楼板配筋率等为变化参数,研究该组合节点的破坏特征、滞回性能、抗剪性能、承载力衰减、刚度退化规律、耗能特性以及应变变化等力学性能。研究结果表明：柱内置钢管在增加柱受压承载力的同时可以有效增加节点核心区受剪能力,改善了节点整体受力性能;增大楼板配筋率(当1%≤ρ≤ρmax时)和减小柱轴压比(当n≤0.3时)能增强节点总耗能能力,但会降低节点延性且对节点承载力无明显提高作用;T形钢翼缘厚度和设置加劲肋对节点抗震性能影响较大。     

方钢管钢骨混凝土柱与钢梁端板螺栓连接节点抗震性能试验研究

为研究方钢管钢骨混凝土柱与钢梁端板螺栓连接节点的抗震性能,进行了5个节点拟静力试验研究,分析了端板厚度、螺栓直径、混凝土强度和轴压比等因素对承载力、弯矩-转角曲线、耗能能力、承载力衰退、刚度退化、延性以及破坏模式的影响。研究结果表明：方钢管钢骨混凝土柱与钢梁端板螺栓连接节点均属于半刚性节点,初始转动刚度随着端板厚度和螺栓直径增大而提高,但节点的极限转动能力随着端板厚度的增大而减小;当承载力由端板或钢梁控制时,其具有良好的转动和耗能能力;试件承载力退化系数在0.8～1.0之间,变化幅度不大,刚度退化相比荷载退化严重;设计中应避免高强螺栓发生脆性破坏。     

Design and construction of UHPC-filled duct connections for precast bridge columns in high seismic zones

One of the column connection types that has been recently emphasised for accelerated bridge construction (ABC) in high seismic zones is grout-filled duct connections. Experimental results have shown that the seismic behaviour of reinforced concrete columns connected to precast cap beams using this connection type is emulative of conventional columns. However, an alternative ABC connection is required to connect precast columns to shallow cap beams and footings due to insufficient anchorage length in those elements. Ultra-high-performance concrete (UHPC) was proposed in this study to be used instead of conventional grout in the connection to reduce the anchorage length. First, fourteen large-scale pullout tests were performed to investigate the bond strength of UHPC-filled duct connections. The test results showed that the incorporation of UHPC instead of normal grout as duct filler can reduce the bar embedment length by 50% or more. Second, design equations were developed based on the pullout test data to compute the bar development length in these connections. Subsequently, two half-scale precast bridge columns utilising this connection type at the column base were tested to verify the design equations. Full column plastic moment was developed in both specimens under cyclic loading with no UHPC-filled duct connection failure such as bar pullout even under 12% drift ratio cycles. Finally, a guideline was proposed based on the pullout and column test data for the design and construction of the UHPC-filled duct connections to facilitate field deployment.     

Evaluation of the moment-rotation curve of I beam-to-CFT column connection with endplate,using mechanical modeling

Through this study, a method is presented to estimate moment-rotation (M-) curve of I beam-to-the concrete filled tube (CFT) connections. This method is based on the components method in which components are analyzed and modeled as different mechanical models. These components are considered as springs with specific mechanical properties of stiffness, strength, and rigid bars. Their force-displacement relationship is assumed bi-linear and 3-linear. The connection behavior is assumed through assembling the stiffness of different components. In this study, connection of I beam-to-CFT column with bolted endplate connection under monotonic loading, which has been tested in the laboratory, is evaluated. It must be mentioned that those bolts which penetrated into the column depth have been used in order to create continuity between flanges of the column. The suggested method has been compared with the experimental test and the advanced finite element model in terms of stiffness, strength, and rotational capacity; moreover, its operation was satisfactory.     

反复荷载作用下PBPS竖缝抗震性能试验及理论研究

本文对装配式大板结构(PBPS)竖缝在反复荷载作用下的抗震性能进行研究,以便使装配式结构最终成为一种完善的抗震体系。共设计、试验了18榀试件,描述了试件在反复荷载作用下的受力破坏过程,分析了竖缝的抗震性能及受力机理。认为接缝最大受剪承载力随接合筋直径的增大而增大,与接缝宽度成非线性关系,且通过接缝混凝土的斜压杆机制和接合筋的压力摩擦机制表现出来;反复荷载作用下,接缝强度及刚度退化,脆裂后的接缝受剪承载力通过削弱的斜压杆机制和接合筋的销栓作用表现出来,其大小随接缝宽度的增大而增大,随接合筋直径的增大而增大。提出了竖缝受剪承载力计算公式,并对计算值与试验值进行比较,二者吻合较好。     

约束钢管混凝土柱的开发研究(英文)

本文提出了一种更适合抗震设计的新型钢管混凝土体系———约束钢管混凝土柱体系。它建立在清楚的力学概念基础上,其设计着眼于在可能出现塑性铰的部位附加横向约束以控制钢管的局部屈曲和更有效地约束混凝土。这一新型钢管混凝土柱体系兼具了钢管混凝土及套管混凝土柱两者的优点,克服了传统钢管混凝土柱的抗震缺陷,为抗震地区的高层结构和桥梁设计提供了理想的选择。在本研究的第一阶段,作者们对FRP约束的圆钢管柱和钢板约束的方钢管柱进行了模拟地震力的加载试验。其结果验证了约束钢管混凝土柱的良好抗震性能。     

Investigation of Proposed Concrete Filled Steel Tube Connections under Reversed Cyclic Loading

Concrete-filled steel tube (CFT) columns are used in the primary lateral resistance systems. The objective of this research is to analyse the behavior of the steel beam to CFT column connections. A three-dimensional numerical model for simulating the behavior of CFT connections was developed with the aid of the general purpose nonlinear finite element analysis package ABAQUS. In this paper, 90 CFT connection specimens include simple and moment connections that were tested under reversed cyclic loading. Shear capacity of joint, moment-drift response, energy absorption, and displacement ductility were studied in those models. The results have indicated that, the hysteresis curve of CFT columns was plump; no pinch phenomenon can be found; the damage and degradation degree of the strength and stiffness of specimens is lower; and high energy dissipation capacity can be achieved. Improvement in the behavior of CFT connection depends on the beam characteristics and column features.     

WUF-W connection performance to box column subjected to uniaxial and biaxial loading

The prequalified connections presented in AISC are limited to the connections of the I beam to wide flange columns. It is necessary to investigate the seismic performance of the prequalified connections to the box column, which has a very low strength and stiffness panel zone in contrast with the wide flange column. In this study, the seismic behavior of the WUF-W (welded unreinforced flange) connection to the box column was investigated through full-scale cyclic loading tests. The experimental results revealed that this type of connection to the box column can satisfy the prequalified criteria of the special moment frame. Moreover, the main advantage of using box column is its high biaxial bending strength. Therefore, as part of the analytical study, the connection subjected to biaxial loading for a series of parameters was investigated. The analytical investigation showed that in order to achieve the desired performance under biaxial loading, the panel zone must provide the strong column/weak beam ratio of more than what is suggested by AISC. Furthermore, the analytical study revealed that for the box column under biaxial loading, the inner diaphragm may not be suitable because of the potential for the weld to fracture.     

节点构造对不同梁高的特殊抗弯框架抗震性能的影响研究

对不同梁高的特殊抗弯框架抗震性能的差异进行研究,主要考虑节点构造的影响。对由连续板组成的节点进行研究,如直板、斜板、盖板、法兰及扁梁一侧加腋节点,这种节点能替代扁梁或深梁与柱的连接节点。在实际工程中,这种节点构造经常出现,但规范没有考虑这种情况。为了研究采用这种节点构造的框架的抗震性能,进行6个足尺试验。分析节点构造对结构破坏的影响,并进行对比分析。试验及分析结果表明:结构在强度退化20%之前,层间侧移比至少达到4%～6%。通过混和使用法兰和加腋节点,可消除大多数节点构造中都可能发生的深梁下翼缘的裂缝开展。     

多层钢框架半刚性端板连接的循环荷载试验研究

为研究多层钢框架半刚性梁柱端板连接的抗震性能,对8个不同构造端板连接足尺试件进行了循环荷载试验研究, 分析了端板厚度、螺栓直径、端板外伸加劲肋、柱腹板加劲肋、平齐式和外伸式等因素对节点承载力、转动刚度、极限转动 能力、耗能能力、延性和极限破坏状态的影响。试验结果表明,半刚性梁柱端板连接具有良好的延性和耗能能力,可以应用 于多层抗震钢框架中。根据试验结果及相关分析,提出了多层抗震钢框架中端板连接的标准构造为:两端外伸,设置柱腹 板加劲肋和三角形端板加劲肋,柱翼缘在端板外伸边缘上下各100mm范围内局部加厚,厚度与端板厚度相同。对提高端 板连接节点的抗震性能提出了宜采用大直径螺栓、中等厚度端板的设计建议。本文还在"强节点,弱构件"抗震设计一般原 则的基础上提出了"强连接,弱板件"的端板连接抗震设计概念。     

法兰连接L形钢管混凝土柱-H型钢梁全螺栓节点抗震性能研究

为降低多高层钢结构的梁柱间的装配难度,提出了法兰连接L形钢管混凝土柱-H型钢梁全螺栓装配节点,包括梁与柱连接和柱与柱连接,梁与柱现场全螺栓连接,柱与柱现场法兰连接。为研究连接件形式及加劲肋对该种节点抗震性能的影响,以改变连接件形式、加劲构造为主要变化参数,设计了4个该类型节点,通过低周反复加载试验和有限元分析获得了节点的破坏模式、滞回曲线、耗能能力和性能指标。研究结果表明：4个节点的滞回曲线均呈梭形,具有良好的耗能能力;节点正负方向的塑性转角超过0.05 rad,满足抗震规范要求;L形连接件与T形连接件均有足够的刚度传递荷载,4个节点的破坏模式、耗能能力与滞回曲线形状较为接近;连接件与梁翼缘之间的滑移提高了节点的延性、耗能能力与转动能力。     

CCTV新台址主楼外筒“米”形节点滞回性能的试验研究

中央电视台(CCTV)新台址主楼外筒由SRC组合斜柱、箱形截面钢支撑及工形截面钢梁组成,其外筒节点呈"米"形。本文对外筒中两种有代表性的"米"形节点进行了模型试验研究,考察了两个关键节点和两个典型节点在反复荷载作用下的延性性能和滞回性能,检验强节点弱构件的设计思想是否满足。试验采用对与节点相连的柱子施加恒定轴力,对两对交叉斜撑施加反复交叉拉压轴力,逐步循环加载直至节点破坏。试验现象及结果表明,所有试件在节点板区域破坏前,其所连接的杆件(斜撑)已失去承载力,节点板在杆件达到极限承载能力时部分进入塑性,但仍具有较高的安全储备。作者建议节点板与斜撑、柱连接处形成光滑过渡并在深化设计中改进,避免应力集中现象造成节点延性降低。