Influence of seismicity level and height of the building on progressive collapse resistance of steel frames

Influences of building height and seismicity level on progressive collapse resistance of buildings are investigated in this paper. For the height, 4‐story, 8‐story and 12‐story steel special moment resisting frames are focused. The obtained results indicate that taller buildings are safer against progressive collapse. To study the influence of seismicity level, different four‐story structures having special moment resisting frame systems are designed for different levels of seismicity, namely, very high, high, moderate and low. The structures are evaluated, using nonlinear dynamic method and two main scenarios of the codes, including sudden removal of a corner and a middle column in the first floor. Some graphs are presented for progressive collapse resistance of the structures, depending on their seismic base shears. It is shown that the structures designed for greater seismic base shears are more resistant against progressive collapse. Copyright © 2016 John Wiley & Sons, Ltd.     

Experimental Study of Composite Steel Plate Shear Wall with Flush End-Plate Connection

This paper presents an investigation on the structural performance of steel plate shear wall (SPSW) with flush end-plate beam–column connections and infill precast reinforced concrete (precast RC) panels. Two single-span two-story SPSW specimens, including unstiffened SPSW (NBRP) and precast RC panel restrained SPSW (Con-BRP), are first tested, followed with a parametric study by finite element method. Precast RC cover panels are installed on both sides of the infill steel plate and are disconnected from steel frame. Test results indicate that the use of precast RC cover panels increases the load carrying and energy dissipation capacities of the SPSW structure, but decreases its ductility. It is also effective in reducing the inward flexural deformation of columns. Moreover, the stiffening effect of the infill steel plate on the beam–column connections remains, which is a result of the precast RC cover panel’s resistance to the local buckling and the tears of the infill steel plates. The influence of the gap size between the precast RC cover plate and frame members on the failure mode of the specimen Con-BRP is also investigated, based on which a maximum gap size is recommended. Conclusions are drawn that SPSW structure with flush end-plate beam–column connections and precast RC cover panels fully exploits the strength of infill steel plates and exhibits excellent structural performance.     

Collapse analysis of steel moment frames with various seismic connections

Seismic connections with high ductile capacity are generally considered to be effective for resisting seismic loads. However, additional studies are still needed to evaluate the performance of seismic connections during progressive collapse. In this study the progressive collapse resisting capacity of the Reduced Beam Section (RBS), Welded Cover Plated Flange (WCPF), and Welded Unreinforced Flange-Welded Web (WUF-W) connections, which are seismic connections recommended by the FEMA/SAC project, was investigated. For progressive collapse analysis, two types of steel moment frame buildings were considered; one designed for high-seismic load and the other designed for moderate-seismic load. The vertical displacement at the point of column removal and the plastic hinge rotation at beam ends were checked by using an alternative load path method proposed in the guidelines. The analysis results showed that the performance of the Cover Plate connection turned out to be the most effective in resisting progressive collapse, especially in structures located in moderate-seismic regions.     

Performance of bolted angle connections in progressive collapse of steel frames

This paper is mainly focused on the behaviour of bolted top‐seat angle connections with double web angles, categorized as partially restrained connections, in progressive collapse of semi‐rigid steel frames due to sudden column loss. The main characteristics of this type of loading are declared and the effect of the imposed boundary conditions on the motivated elements is depicted. To study the performance of frame connections under these conditions, refined nonlinear finite element modelling technique is used. The models are created based on the previous experimental studies and their accuracy is examined through a comparison to the results of these tests. New models are created under conditions of the progressive collapse and the behaviour of the connections is studied. The study showed that due to the applied boundary conditions, the connections behave stiffer and show a higher moment capacity. Based on the results of the numerical models, equations are presented to estimate the moment‐rotation response of the studied connections under progressive collapse conditions based on the beam and connection mechanical and geometrical properties and the connection rotation. Copyright © 2009 John Wiley & Sons, Ltd.     

The design and seismic performance of low-rise long-span frames with semi-rigid connections

Moment-resisting steel frames are used frequently in low-rise and mid-rise buildings located in high seismic areas due to their high ductility and economic solutions. In these type of structures, strong-column weak-beam design requirements result in larger column sections and overdesign in low-rise long-span buildings. To mitigate this problem, moment-resisting steel frames with energy-dissipative semi-rigid/partial strength connections can be used as an alternative to perimeter frames. By using energy-dissipative semi-rigid connections, the strong-column weak-beam requirement is eliminated and more economical column sections are used. In this study, a three-span three-bay frame with 7 and 9 m span lengths is designed with semi-rigid connections having four different capacities in high seismic zones. Their seismic performance is evaluated analytically under three different earthquake levels by modeling connections with two different moment-hardening ratios and two different hysteretic behavior models. The design with reduced connection capacity resulted in an increase in the beam weights, a decrease in the column weights and an overall decrease in the structural weight. The seismic performances of 26 sample frames are evaluated with pushover and dynamic analyses under 25 real strong ground motion records. All of the sample frames satisfied the acceptance criteria and showed reliable performance under earthquake loading. The overdesign problem in low-rise long span-buildings is eliminated to some extent without using the perimeter frame approach. Furthermore, under some specific ground motion records, the top displacements in semi-rigid frames become lower than those of their rigid counterparts.     

基于增量动力分析的梁贯通式支撑钢框架地震易损性研究

为了得到梁贯通式支撑钢框架节点刚度及承载力设计方法,基于增量动力分析(IDA)方法,研究了节点性能对多层梁贯通式支撑钢框架地震易损性的影响,得到了不同节点刚度和承载力设置下四种模型(刚接、全强度半刚接、半强度半刚接和铰接模型)的易损性曲线,定量评价了各模型超越各极限状态的概率和倒塌储备系数.研究结果表明:无论节点刚度和...     

矩形钢管混凝土柱与钢梁半刚性节点的抗震性能试验研究

本文进行了两种矩形钢管混凝土柱与钢梁半刚性连接节点———加劲端板(SEP)连接节点与双T板(DST)连接节点在柱端低周反复荷载作用下的拟静力试验,目的在于了解这两类节点在不同轴压比下的滞回性能、强度与刚度退化、延性与破坏机制。并与常规焊接翼缘板(WFP)连接节点作了比较。结果表明:不同轴压比对节点转动有一定的影响,加劲端板(SEP)连接节点与双T板(DST)连接节点具有良好的转动延性与耗能能力。     

钢柱外包式柱脚抗震设计问题

柱脚是钢结构中上部主体结构与基础连接的重要节点,外包式柱脚常用于重钢结构厂房,其计算假定为柱脚刚接,在地震作用效应时传递弯矩至基础。GB50011-2010《建筑抗震设计规范》明确规定了这种柱脚设计时的极限承载力计算方法。构造要求的柱截面面积条件在节点弹塑性承载力设计中起控制作用的情况,在实际设计过程中常出现。从钢结构框架柱的截面确定方法入手,对不同规范规定的长细比限值进行比较,用极限弹塑性设计抗弯承载力要求和多遇地震抗弯承载力要求来分析比较外包式柱脚的设计,满足柱脚配筋设计的经济性和合理的计算要求。     

Q690高强钢端板连接梁柱节点抗震性能试验研究

对3个齐平式端板螺栓连接节点试件进行低周反复荷载试验,其中1个为普通钢端板节点试件,另2个为Q690高强钢端板节点试件。通过改变端板和柱的尺寸与材料,得到普通钢与高强钢端板节点、刚性柱和非刚性柱节点的性能差别,并与欧洲规范EC3的计算结果进行对比。结果表明：Q690高强钢端板节点的受弯承载能力比Q345钢端板节点高30%,但因其端板弹性变形能力较强,易于导致螺栓破坏,因此,需提高螺栓的承载力以提高其延性;刚性柱节点的受弯承载能力与非刚性柱节点基本相同,但其转动能力、延性、耗能能力等抗震性能明显优于非刚性柱节点;EC3组件法普通钢节点承载能力的预测公式可直接用于高强钢端板节点,但转动刚度及破坏模式的预测方法并不适用于高强钢端板节点。     

Ductility reduction factor and collapse mechanism evaluation of a new steel knee braced frame

In this study, the suitability of a new structural system called the knee braced frames (KBFs) is investigated for seismic resistant steel structures. In these structural systems, ends of beams are connected to columns by hinges (simple connection) instead of rigid connections, and ends of knee braced elements are connected to columns and beams by hinges as well. In the present paper, in addition to a comparison between elastic behaviour and elastic fundamental natural period, the ductility reduction factor and the type of collapse mechanism in steel KBFs and steel moment resisting frames (MRFs) are compared. The study revealed that the stiffness of steel buildings can be increased considerably by applying knee braced elements and the effects of knee braced elements are highly dependent on knee braced configuration. By applying the pushover analysis, it was observed that the type of collapse mechanism of KBFs is very similar to the mechanism of MRFs. Furthermore in most cases, the ductility reduction factor, R_μ, obtained from steel KBFs is greater than the ductility reduction factor obtained for steel MRFs. Based on the similarity between type of collapse mechanism and the proximity of ductility reduction coefficients of the KBFs and MRFs systems, it can be concluded that the new steel knee braced frame systems can be categorised as steel MRFs with rigid connections.     

Progressive collapse analysis of a steel building with pre‐northridge moment connections

This study is on progressive collapse analysis of a sample steel building using various procedures suggested by the General Service Administration and the Department of Defense. The progressive collapse was accommodated by removing columns as per above guidelines. The analysis methods considered were linear static, linear dynamic, non‐linear static and nonlinear dynamic using SAP2000 structural simulation program. The analysis model was a 3D nine‐storey steel moment resisting building. For linear analysis, rigid moment connections were used, while for nonlinear analysis pre‐Northridge connections were used. The effect of an extreme event was incorporated by removing a column in the analysis model. The static analysis was performed on the model with a column removed subjected to static gravity loadings. The dynamic analysis employed a ramp function to simulate the dynamic effect of the removal of a column. For nonlinear analysis, material nonlinearity was incorporated using strength degrading nonlinear hinges of pre‐Northridge connections as per FEMA 356. The paper documents the results of this analysis with comparison among methods. The potential for collapse and performance levels of the building were determined using the demand capacity ratio and the rotational limit obtained through the analysis. Copyright © 2010 John Wiley & Sons, Ltd.     

The establishing of performance level thresholds for steel moment‐resisting frame using an energy approach

In this study, an energy design approach is proposed within the framework of the performance‐based seismic design of steel frames. Accumulated plastic rotation is selected as a parameter to establish the performance level thresholds. The test results of steel connections are investigated to quantify the performance level thresholds. The hysteretic energy input is acquired from a previous statistical study of twelve six‐storey steel moment‐resisting frames. The seismic performance of three‐storey steel moment resisting frames using the energy approach is examined. The research concluded that the structure designed by the energy method performed better than the steel frame designed by the equivalent lateral force (ELF) of UBC‐97 in view of accumulated plastic rotation. Performance levels such as functional, life safety and collapse are discussed based on the ductility level and the performance characteristics. Copyright © 2001 John Wiley & Sons, Ltd.     

套筒式钢管混凝土梁柱节点试验研究

利用ANSYS软件分析了套筒式钢管混凝土梁柱节点的承载性能,同时进行了采用力位移混合加载控制的节点承载力低周反复荷载试验。结果表明,套筒式节点和环板式节点的极限受弯承载力都能满足设计要求,但套筒式节点的转角较小,节点为刚性连接。在相同的轴压比下,两种形式节点的抗震性能相当。     

Internal flange stiffened moment connections with low-damage capability under seismic loading

This study presents the seismic performance of steel moment connections using internal flange stiffeners (IFSs) welded at the face of the wide-flange column and inner side of the beam flange. The objective is to develop a steel moment connection that can achieve good seismic performance with low-damage capability during a large earthquake loading and minimize the repair cost. Four large-scale moment connections were tested to validate the cyclic performance. One connection which represented a welded-unreinforced flange-bolted web connection failed before finishing cyclic tests at a drift of 4%. Three IFS moment connections showed excellent performance and low damage after experiencing the AISC seismic load twice up to the target drift of 4%, without strength reduction. The specimens were also modeled using the computer program ABAQUS to further verify the effectiveness of the IFS in transferring beam moment to the column and to investigate potential sources of connection failure.     

Hysteretic behaviour of flush end plate joints to concrete-filled steel tubular columns

The results of an experimental research study involving the testing of four bolted moment-resisting connections under simulated seismic loading conditions are presented. Each test specimen modeled the interior joint of a moment-resisting frame consisting of H-shaped steel beams and circular or square concrete-filled steel tube (CFST) columns using high-strength blind bolts. In order to investigate the seismic behaviour of the blind bolted flush end plate joints to CFST columns, the hysteretic performance, failure modes, stiffness degradation and energy dissipation of the connection type are evaluated in detail. The test parameters varied included the column section type and the thickness of the end plate. The experimental results indicate that both the blind bolted connections with circular and square sections exhibited excellent hysteretic behaviour in terms of their moment–rotation response, strain distributions and energy dissipation. Under cyclic loading, all tested specimens displayed large rotation ductility capacities, and the failure modes were similar to those under monotonic loads. The effects of cyclic loading on the behaviour of the composite joint were obvious, especially on load bearing and stiffness of the connections. The joint type exhibited excellent seismic performance, so that it can be effectively utilized in moment-resisting composite frame structures.     

The rigid seismic connection of continuous beams to column

This paper presents a new rigid connection with some specific features for earthquake-resistant steel structures. In common practice, beams are separately placed between two adjacent columns and connected to their flanges. In this new proposed connection, two beams pass next to the column faces without interruption and are connected to the column flanges by vertical plates. Two different details of this connection have been studied experimentally and analytically. In the first detail, two integrated vertical plates which are placed next to the column flanges and welded to the column flanges’ edges and beam flanges were used in order to connect the two channel-section beams to the column. In the second detail, four vertical trapezoidal plates which are welded to the edges of the column flanges and beam flanges were used in order to connect the two I-section beams to the column. Two experimental specimens for each of the two different details were tested under cyclic loading. Experimental results show that all experimented specimens sustained the interstory drift angle greater than 0.08 rad without any significant loss of strength, which is far in excess of the requirements for a beam-to-column connection given by the latest seismic codes. The experimental and analytical results show that moment capacity of these connections is more than bending resistance of connected beams. Therefore, the structural ductility in this structural system is controlled by the flexural behaviour of beam ends; and the total behaviour of connections and also of column might remain reasonably elastic. As a result, the structure might have high ductility and safe seismic behaviour. Parametric studies show that the design relationships of connection plates safely determine the thickness of connection plates for different sizes of beams and columns.     

Seismic design, performance, and behavior of composite-moment frames with steel beam-to-concrete filled tube column connections

Concrete filled steel tube (CFT) columns have been widely used in composite-moment frames (C-MFs) both in non-seismic and in high seismic zones. The objective of this research is to develop a design methodology of such moment resisting frame structures designed with CFT columns in achieving ductile behavior and high strength. These composite-moment frames mostly constructed around the perimeter of the building provide the enough stiffness to withstand the lateral displacement due to wind or seismic loads. In this research, three sets of prototype composite frame models were designed on the basis of the proposed design examples as 3-, 9-, and 20-story post-Northridge SAC buildings with composite-special moment frame (C-SMF) systems designed for the western US area. The exact moment-rotational behavior of steel beam-to-CFT column connections including the strength degradation was simulated using the 2D joint model with the rigid boundary element. Nonlinear pushover analyses were conducted on the numerical frame models so as to evaluate the over-strength, inelastic deformation, and P-Delta effect for the entire structure. The statistical investigation was introduced to nonlinear dynamic analyses under 40 SAC ground motions corresponding to a seismic hazard level of 2% probability of exceedence in 50 years in order to efficiently examine seismic performance and behavior of entire composite frame structures. All frame models meet the allowable limit for safe designs. In addition, the entire frame design becomes conservative as the number of stories increases. The distribution of interstory drift ratios (ISDRs) as well as the over-strength ratio also demonstrates this conservative design of low to high-rise CMF structures.     

组合效应对钢节点抗震性能的影响因素分析

钢—混凝土组合梁当前在钢框架结构中已经得到了广泛的应用,但是地震荷载作用下组合节点的设计方法却一直在完善和发展.基于组合节点的数值分析,着重研究钢框架梁柱节点的抗震性能,进行了有限元分析、模型参数分析,研究了不同变量条件下节点抗震性能与梁强度的平衡关系,并针对混凝土板中的配筋率、混凝土板板厚、钢节点类型等因素进行了分析和讨论.分析结果表明,在进行钢框架梁柱节点的抗震设计时,应该考虑混凝土板的组合效应.     

梁端柔性对装配式框架结构的内力影响

通过采用有限单元法进行分析,研究了柔性连接对框架结构内力的影响。研究表明,在竖向荷载作用下,相比较于刚性连接,梁端弯矩和柱脚弯矩均减小,而梁跨中弯矩变大。在水平荷载作用下,相比较于刚性连接,梁端弯矩减小,底层柱脚弯矩明显增大,此时梁跨中的弯矩几乎没有变化。当水平荷载和竖向荷载共同作用时,刚性连接与柔性连接之间的内力差别也是显著的。     

超高层钢管混凝土重力柱-混凝土核心筒结构振动台试验研究

提出一种新型的钢管混凝土重力柱-核心筒结构体系,通过地震模拟振动台试验验证其抗震性能。以实际超高层钢管混凝土柱框架-混凝土核心筒建筑结构为参考,将钢框架梁与柱或核心筒的刚性节点改为螺栓连接的铰接节点,简化结构并制作1/40的缩尺结构模型,采用4条地震动记录进行不同工况的振动台试验,分析结构的震损特点、动力特性、侧向位移、层间位移角、扭转角、地震惯性力、楼层剪力和倾覆弯矩等。结果表明：震损主要出现在下部楼层的混凝土楼板与柱连接、楼板与核心筒连接、楼板与钢梁连接、核心筒角部等部位;基本自振周期和阻尼比随震损增加而增大,动力放大效应减小,长周期地震动反应显著,侧向变形和层间位移显著增大;外排架柱的层间位移主要为不产生内力的刚体转动,核心筒层间位移角达1/26,超过规范JGJ 3—2010中规定的框架-核心筒结构体系不倒塌限值的3.85倍而未出现倒塌;外排架抗扭刚度小,结构扭转反应由核心筒主导;地震惯性力和楼层剪力受地震长周期分量的影响小,随结构损伤增大楼层内力增加幅度减小。