Test on full‐scale three‐storey steel moment frame and assessment of ability of numerical simulation to trace cyclic inelastic behaviour

A test on a full‐scale model of a three‐storey steel moment frame was conducted, with the objectives of acquiring real information about the damage and serious strength deterioration of a steel moment frame under cyclic loading, studying the interaction between the structural frame and non‐structural elements, and examining the capacity of numerical analyses commonly used in seismic design to trace the real cyclic behaviour. The outline of the test structure and test program is presented, results on the overall behaviour are given, and correlation between the experimental results and the results of pre‐test and post‐test numerical analyses is discussed. Pushover analyses conducted prior to the test predicted the elastic stiffness and yield strength very reasonably. With proper adjustment of strain hardening after yielding and composite action, numerical analyses were able to accurately duplicate the cyclic behaviour of the test structure up to a drift angle of 1/25. The analyses could not trace the cyclic behaviour involving larger drifts in which serious strength deterioration occurred due to fracture of beams and anchor bolts and progress of column local buckling. Copyright © 2005 John Wiley & Sons, Ltd.     

Replaceable links with direct brace attachments for eccentrically braced frames

This paper reports findings of an experimental study conducted on replaceable links for steel eccentrically braced frames (EBFs). A replaceable link detail which is based on splicing the directly connected braces and the beam outside the link is proposed. This detail eliminates the need to use hydraulic jacks and flame cutting operations for replacement purposes. Performance of this proposed replaceable link was studied by conducting eight nearly full‐scale EBF tests under quasi‐static cyclic loading. The link length ratio, stiffening of the link, loading protocol, connection type, bolt pretension, gap size of splice connections, and demand‐to‐capacity ratios of members were considered as the prime variables. The specimens primarily showed two types of failure modes: link web fracture and fracture of the flange at the link‐to‐brace connection. No failures were observed at the splice connections indicating that the proposed replaceable link detail provides an excellent response. The inelastic rotation capacity provided by the replaceable links satisfied the requirements of the AISC Seismic Provisions for Structural Steel Buildings (AISC341–10). The overstrength factor of the links exceeded 2.0, which is larger than the value assumed for EBF links by design provisions. The high level of overstrength resulted in brace buckling in one of the specimens demonstrating the importance of overstrength factor used for EBF links. Copyright © 2017 John Wiley & Sons, Ltd.     

Seismic performance assessment of a hybrid coupled wall system with replaceable steel coupling beams versus traditional RC coupling beams

This study assesses the seismic performance of a hybrid coupled wall (HCW) system with replaceable steel coupling beams (RSCBs) at four intensities of ground motion shaking. The performance of the HCW system is benchmarked against the traditional reinforced concrete coupled wall (RCW). Nonlinear numerical models are developed in OpenSees for a representative wall elevation in a prototype 11‐story building designed per modern Chinese codes. Performance is assessed via nonlinear dynamic analysis. The results indicate that both systems can adequately meet code defined objectives in terms of global and component behavior. Behavior of the two systems is consistent under service level earthquakes, whereas under more extreme events, the HCW system illustrates enhanced performance over the RCW system resulting in peak interstory drifts up to 31% lower in the HCW than the RCW. Larger drifts in the RCW are because of reduced coupling action induced by stiffness degradation of RC coupling beams, whereas the stable hysteretic responses and overstrength of RSCBs benefit post‐yield behavior of the HCW. Under extreme events, the maximum beam rotations of the RSCBs are up to 42% smaller than those of the RC coupling beams. Moderate to severe damage is expected in the RC coupling beams, whereas the RSCBs sustain damage to the slab above the beam and possible web buckling of shear links. The assessment illustrates the benefits of the HCW with RSCBs over the RCW system, because of easy replacement of the shear links as opposed to costly and time‐consuming repairs of RC coupling beams. Copyright © 2016 John Wiley & Sons, Ltd.     

Parametric study of ductile moment‐resisting steel frames: A first step towards Eurocode 8 calibration

A parametric study of 13 608 ductile moment‐resisting steel frames designed according to Eurocodes 3 and 8 is performed. A flowchart for the evaluation of the seismic‐resistant capacity of the designed frames is developed based on the N2 method. The design structural overstrength, ductility supply, plastic redistribution parameter, supply reduction factor and performance ratio of the frames are analysed. We determine that the frames have performance ratios higher than 1, mostly due to high values of design structural overstrength, showing that the seismic supply produced by the restraints of Eurocodes 3 and 8 is always higher than the seismic demand. Copyright © 2008 John Wiley & Sons, Ltd.     

Evaluating performance of post‐tensioned steel connections with strands and reduced flange plates

The seismic performance of post‐tensioned steel connections for moment‐resisting frames was examined experimentally and analytically. Cyclic tests were conducted on three full‐scale subassemblies, which had two steel beams post‐tensioned to a concrete‐filled tube (CFT) column with high‐strength strands to provide recentring response. Reduced flange plates (RFPs) welded to the column and bolted to the beam flange were used to increase the dissipation of energy. Test results indicated that (1) the proposed buckling‐restrained RFP could dissipate energy in axial tension and compression, (2) the subassemblies could reach an interstorey drift of 4% without strength degradation, and (3) buckling of the beam occurred towards an interstorey drift of 5%, causing a loss of the strand force, the recentring response, and the moment capacity. A general‐purpose non‐linear finite element analysis program (ABAQUS) was used to perform a correlation study. The behaviour of the steel beam under both post‐tensioning and flexural loadings was compared to the test results and predictions. Copyright © 2006 John Wiley & Sons, Ltd.     

Experimental and analytical investigations of steel panel dampers for seismic applications in steel moment frames

A ductile Vierendeel frame can be constructed by incorporating steel panel dampers (SPDs) into a moment‐resisting frame (MRF). Thus, the stiffness, strength, and ductility of the lateral force–resisting system can be enhanced. The proposed 3‐segment SPD possesses a center inelastic core (IC) and top and bottom elastic joints. This paper discusses the mechanical properties, capacity design method, and buckling‐delaying stiffeners for the SPDs through the use of cyclic loading tests on 2 specimens. Tests confirm that SPDs' cyclic force vs deformation relationships can be accurately predicted using either the Abaqus or PISA3D model analyses. The paper also presents the capacity design method for boundary beams connected to the SPDs of a typical SPD‐MRF. The seismic performance of an example 6‐story SPD‐MRF is evaluated using nonlinear response history analysis procedures and 240 ground accelerations at 3 hazard levels. Results indicate that under 80 maximum considered earthquake ground accelerations, the mean‐plus‐one standard deviation of the shear deformation of the ICs in the SPDs is 0.055 rad, substantially less than the 0.11 rad deformational capacity observed from the SPD specimens. The experimental cumulative plastic deformation of the proposed SPD is 242 times the yield deformation and is capable of sustaining a maximum considered earthquake at least 8 times before failure. This paper introduces the method of using one equivalent beam‐column element for effective modeling of the 3‐segment SPD. The effects of the IC's relative height and stiffness on the overall SPD's elastic and postelastic stiffness, elastic deformation limits, and inelastic deformational demands are discussed.     

Biaxial testing of unbonded post‐tensioned rocking bridge piers with external replacable dissipaters

The biaxial response of two bridge piers is experimentally investigated. A post‐tensioned precast bridge pier with external replaceable mild‐steel dissipaters is tested under biaxial loading. The performance of the post‐tensioned bridge pier is compared with a conventionally reinforced monolithic bridge pier. The experimental biaxial response is then compared with previous uniaxial experimental testing of identical bridge piers to understand the influence of biaxial loading, specifically concerning post‐tensioned rocking sections. A 3‐dimensional moment–curvature and moment–rotation analysis program is created to generate the monotonic section response of a conventional and post‐tensioned bridge pier. After comparing the accuracy of the section analysis program to the experimental testing of the monolithic pier, the program is validated against the experimental testing of the post‐tensioned bridge pier. This section analysis program is then used in the calibration of a macro‐model to capture the entire cyclic response of the post‐tensioned bridge pier. The macro‐model adopts multiple linear‐elastic compression‐only springs at the rocking interface, combined with non‐linear inelastic springs for each of the mild‐steel dissipaters and returns encouraging results at both local and global levels. The paper concludes with a number of biaxial moment‐interaction design charts for monolithic and post‐tensioned bridge piers as a function of mechanical and geometric section properties. The design charts define the biaxial yield surface at nominal yield and at the design section capacity defined by one of three material limit states. Copyright © 2011 John Wiley & Sons, Ltd.     

Shaking table tests of a reinforced concrete waffle–flat plate structure designed following modern codes: seismic performance and damage evaluation

Shaking table tests were conducted on a scaled reinforced concrete waffle–flat plate structure. It represented a conventional construction design under current building codes in the Mediterranean area. The test structure was subjected to a sequence of four seismic simulations of increasing magnitude. Each simulation was associated with a seismic hazard level characterized by the mean return period P_R. The test structure performed well for the simulations associated with P_R = 95, 475 and 975 years but collapsed under the maximum considered earthquake of P_R = 2475 years. Damage concentrated at column bases, where the maximum chord rotation reached 93% of the ultimate capacity, and at the transverse beams of the exterior plate‐to‐column connection that failed in torsion. It is shown that most (from 85% to 90%) of the energy input by the earthquake that contributes to damage is dissipated by the plate. The capacity curve of the tested structure estimated from the experimental base shear vs. top displacement relationship allowed us to compute the overstrength (1.4). It is close to the maximum established by European code EN 1998‐1 (1.5). Based on a detailed study of the test results, potential updates to current codes and design recommendations are suggested. Copyright © 2015 John Wiley & Sons, Ltd.     

Analysis of tubular steel bridge piers

A one‐dimensional model is proposed for the static and dynamic analysis of tubular steel bridge piers subjected to strong ground motions. The present formulation does not require experimental results nor shell analysis to obtain the constitutive equation of the model, which shows strength deterioration. The material properties and dimensions of bridge piers are required for static and dynamic analysis of the present model. The present analysis consists of two steps. The first step is to obtain the stress and strain relationship of the base plastic‐hinge region, where local inelastic buckling is observed. The modified Shanley's model and fiber elements are used to establish the compressive skeleton curve. The strength deterioration is taken into account in the resulting constitutive model. The second step is to analyze static and dynamic responses of tubular steel bridge piers. For overall analysis, the base plastic‐hinge region is discretized in the circumferential direction by using fiber elements whose constitutive equation was obtained in the first step. The validity of the present model has been confirmed through comparisons with existing experimental results. Copyright © 2005 John Wiley & Sons, Ltd.     

反复荷载作用下锈蚀钢筋混凝土柱力学性能研究

采用有限元软件ABAQUS,以锈蚀率（0%、5%、10%、15%和20%）为变量,对5根钢筋混凝土柱的力学性能进行了数值模拟,研究各试件的滞回性能、骨架曲线、延性及耗能能力,分析钢筋锈蚀率对承载力、延性、耗能和塑性铰转动能力的影响。研究结果表明:模拟分析得到的锈蚀钢筋混凝土柱的强度和变形与试验结果吻合较好,建立的有限元模型可用于锈蚀钢筋混凝土柱的力学性能分析;混凝土开裂前,锈蚀构件的力学性能基本与未锈蚀构件相同,混凝土开裂后,构件的承载力、屈服荷载、极限位移、延性等均随钢筋锈蚀率的增大而降低;轻度锈蚀构件的滞回性能和破坏形式与未锈蚀构件类似,随着钢筋锈蚀率逐渐增大,滞回环的饱满程度降低,“捏拢”现象严重,滞回曲线由“弓形”逐渐发展成“反S形”,耗能能力降低,破坏形式趋于脆性破坏,位移延性系数、平均耗能系数等指标逐渐下降。     

A numerical study on response modification,overstrength, and displacement amplification factors for steel plate shear wall systems

Design recommendations for steel plate shear wall (SPSW) systems have recently been introduced into seismic provisions for steel buildings. Response modification (R), overstrength (Ω_o), and displacement amplification (C_d) factors for SPSW systems presented in design codes were based on professional experience and judgment. A numerical study has been undertaken to evaluate these factors for SPSW systems. Forty‐four unstiffened SPSW possessing different geometrical characteristics were designed based on the recommendations given in the AISC Seismic Provisions. Bay width, number of stories, story mass, and steel plate thickness were considered as the prime variables that influence the response. Twenty records were selected to include the variability in ground motion characteristics. In order to provide a detailed analysis of the post‐buckling response, three‐dimensional finite element analyses were conducted for the 44 structures subjected to the selected suite of earthquake records. For each structure and earthquake record, two analyses were conducted in which the first includes geometrical nonlinearities and the other includes both geometrical and material nonlinearities, resulting in a total of 1760 time history analyses. In this paper, the details of the design and analysis methodology are given. Based on the analysis results, response modification (R), overstrength (Ω_o), and displacement amplification (C_d) factors for SPSW systems are evaluated. Copyright © 2008 John Wiley & Sons, Ltd.     

Probabilistic evaluation of seismic performance of 3‐story 3D one‐ and two‐way steel moment‐frame structures

This paper presents the results of a probabilistic evaluation of the seismic performance of 3D steel moment‐frame structures. Two types of framing system are considered: one‐way frames typical of construction in the United States and two‐way frames typical of construction in Japan. For each framing system, four types of beam–column connections are considered: pre‐Northridge welded‐flange bolted‐web, post‐Northridge welded‐flange welded‐web, reduced‐beam‐section, and bolted‐flange‐plate connections. A suite of earthquake ground motions is used to compute the annual probability of exceedence (APE) for a series of drift demand levels and for member plastic‐rotation capacity. Results are compared for the different framing systems and connection details. It is found that the two‐way frames, which have a larger initial stiffness and strength than the one‐way frames for the same beam and column volumes, have a smaller APE for small drift demands for which members exhibit no or minimal yielding, but have a larger APE for large drift demands for which members exhibit large plastic rotations. However, the one‐way frames, which typically comprise a few seismic frames with large‐sized members that have relatively small rotation capacities, may have a larger APE for member failure. The probabilistic approach presented in this study may be used to determine the most appropriate frame configuration to meet an owner's performance objectives. Copyright © 2008 John Wiley & Sons, Ltd.     

Incremental dynamic analysis for estimating seismic performance sensitivity and uncertainty

Incremental dynamic analysis (IDA) is presented as a powerful tool to evaluate the variability in the seismic demand and capacity of non‐deterministic structural models, building upon existing methodologies of Monte Carlo simulation and approximate moment‐estimation. A nine‐story steel moment‐resisting frame is used as a testbed, employing parameterized moment‐rotation relationships with non‐deterministic quadrilinear backbones for the beam plastic‐hinges. The uncertain properties of the backbones include the yield moment, the post‐yield hardening ratio, the end‐of‐hardening rotation, the slope of the descending branch, the residual moment capacity and the ultimate rotation reached. IDA is employed to accurately assess the seismic performance of the model for any combination of the parameters by performing multiple nonlinear timehistory analyses for a suite of ground motion records. Sensitivity analyses on both the IDA and the static pushover level reveal the yield moment and the two rotational‐ductility parameters to be the most influential for the frame behavior. To propagate the parametric uncertainty to the actual seismic performance we employ (a) Monte Carlo simulation with latin hypercube sampling, (b) point‐estimate and (c) first‐order second‐moment techniques, thus offering competing methods that represent different compromises between speed and accuracy. The final results provide firm ground for challenging current assumptions in seismic guidelines on using a median‐parameter model to estimate the median seismic performance and employing the well‐known square‐root‐sum‐of‐squares rule to combine aleatory randomness and epistemic uncertainty. Copyright © 2009 John Wiley & Sons, Ltd.     

Seismic performance of a 3D full‐scale high‐ductile steel–concrete composite moment‐resisting frame—Part II: Test results and analytical validation

This paper presents the results of a multi‐level pseudo‐dynamic seismic test program that was performed to assess the performance of a full‐scale three‐bay, two‐storey steel–concrete composite moment‐resisting frame built with partially encased composite columns and partial‐strength beam‐to‐column joints. The system was designed to develop a ductile response in the joint components of beam‐to‐column joints including flexural yielding of beam end plates and shear yielding of the column web panel zone. The ground motion producing the damageability limit state interstorey drift caused minor damage while the ultimate limit state ground motion level entailed column web panel yielding, connection yielding and plastic hinging at the column base connections. The earthquake level chosen to approach the collapse limit state induced more damage and was accompanied by further column web panel yielding, connection yielding and inelastic phenomena at column base connections without local buckling. During the final quasi‐static cyclic test with stepwise increasing displacement–amplitudes up to an interstorey drift angle of 4.6%, the behaviour was ductile although cracking of beam‐to‐end‐plate welds was observed. Correlations with numerical simulations taking into account the inelastic cyclic response of beam‐to‐column and column base joints are also presented in the paper together. Inelastic static pushover and time history analysis procedures are used to estimate the structural behaviour and overstrength factors of the structural system under study. Copyright © 2008 John Wiley & Sons, Ltd.     

Dynamic buckling and seismic fragility of anchored steel tanks by the added mass method

Buckling plays a fundamental role in the design of steel tanks because of the small thicknesses of the walls of this class of structures. The first part of the paper presents a review of this phenomenon for liquid‐containing circular cylindrical steel tanks that are fully anchored at the base, considering the different buckling modes and especially the secondary buckling occurring in the top part of the tank. A case study based on a cylindrical tank is then introduced in order to investigate various aspects of dynamic buckling. The finite element model of the case study tank is set‐up using the added mass method for fluid modelling. The influence of pre‐stress states caused by hydrostatic pressure and self‐weight on the natural periods of the structure is first studied and it is found that this influence is very small as far as the global behaviour of the tanks is considered, while it is important for local, shell‐type, vibration modes. In the following, the efficiency and sufficiency of different ground motion intensity measures is analysed by means of cloud analysis with a set of 40 recorded accelerograms. In particular, the peak ground displacement has been found being the most efficient and sufficient intensity measure so far as the maximum relative displacement of the tank walls is concerned. Finally, incremental nonlinear time‐history analyses are performed considering the case study structure under recorded earthquake ground motions in order to identify the critical buckling loads and to derive fragility curves for the buckling limit state. Copyright © 2013 John Wiley & Sons, Ltd.     

A novel type of angle steel buckling‐restrained brace: Cyclic behavior and failure mechanism

A novel type of angle steel buckling‐restrained brace (ABRB) has been developed for easier control on initial geometric imperfection in the core, more design flexibility in the buckling restraining mechanism and easier assembly work. The steel core is composed of four angle steels to form a non‐welded cruciform shape restrained by two external angle steels, which are welded longitudinally to form an external tube. Component test was conducted on seven ABRB specimens under uniaxial quasi‐static cyclic loading. The test results reveal that the consistency between the actual and design behavior of ABRB can be well achieved without the effect of weld in the core. The ABRBs with proper details exhibited stable cyclic behavior and satisfactory cumulative plastic ductility capacity, so that they can serve as effective hysteretic dampers. However, compression–flexure failure at the steel core projection was found to be the primary failure mode for the ABRBs with hinge connections even though the cross‐section of the core projection was reinforced two times that of the yielding segment. The failure mechanism is further discussed by investigating the N_u– M_u correlation curve. It is found that the bending moment response developed in the core projection induced by end rotation was the main cause for such a failure mode, and it is suggested that core projection should be kept within elastic stage under the possible maximum axial load and bending moment response. Copyright © 2010 John Wiley & Sons, Ltd.     

Experimental research on the seismic behavior of CSPSWs connected to frame beams

The seismic performance of composite steel plate shear walls (CSPSWs) that consist of a steel plate shear wall (SPSW) with reinforced concrete (RC) panels attached to one or both sides by means of bolts or connectors is experimentally studied. The shear wall is connected to the frame beams but not to the columns. This arrangement restrains the possible out-of-plane buckling of the thin-walled steel plate, thus significantly increasing the bearing capacity and ductility of the overall wall, and prevents the premature overall or local buckling failure of the frame columns. From a practical viewpoint, these solutions can provide open space in a floor as this type of composite shear walls with a relatively small aspect ratio can be placed parallel along a bay. In this study, four CSPSWs and one SPSW were tested and the results showed that both CSPSWs and SPSW possessed good ductility. For SPSW alone, the buckling appeared and resulted in a decrease of bearing capacity and energy dissipation capacity. In addition, welding stiffeners at corners were shown to be an effective way to increase the energy dissipation capacity of CSPSWs.     

Test and simulation of full-scale self-centering beam-to-column connection

A new type of beam-to-column connection for steel moment flames, designated as a ＂self-centering connection,＂ is studied. In this connection, bolted top-and-seat angles, and post-tensioned （PT） high-strength steel strands running along the beam are used. The PT strands tie the beam flanges on the column flange to resist moment and provide self-centering force. After an earthquake, the connections have zero deformation, and can be restored to their original status by simply replacing the angles. Four full-scale connections were tested under cyclic loading. The strength, energy-dissipation capacity, hysteresis curve, as well as angles and PT strands behavior of the connections are investigated. A general FEM analysis program called ABAQUS 6.9 is adopted to model the four test specimens. The numerical and test results match very well. Both the test and analysis results suggest that： （1） the columns and beams remain elastic while the angles sustain plastic deformations for energy dissipation when the rotation of the beam related to the column equals 0.05 tad, （2） the energy dissipation capacity is enhanced when the thickness of the angle is increased, and （3） the number of PT strands has a significant influence on the behavior of the connections, whereas the distance between the strands is not as important to the performance of the connection.     

Effect of gravity framing on the overstrength and collapse capacity of steel frame buildings with perimeter special moment frames

This paper investigates the effect of the gravity framing system on the overstrength and collapse risk of steel frame buildings with perimeter special moment frames (SMFs) designed in North America. A nonlinear analytical model that simulates the pinched hysteretic response of typical shear tab connections is calibrated with past experimental data. The proposed modeling approach is implemented into nonlinear analytical models of archetype steel buildings with different heights. It is found that when the gravity framing is considered as part of the analytical model, the overall base shear strength of steel frame buildings with perimeter SMFs could be 50% larger than that of the bare SMFs. This is attributed to the gravity framing as well as the composite action provided by the concrete slab. The same analytical models (i) achieve a static overstrength factor, Ω_s larger than 3.0 and (ii) pass the collapse risk evaluation criteria by FEMA P695 regardless of the assigned total system uncertainty. However, when more precise collapse metrics are considered for collapse risk assessment of steel frame buildings with perimeter SMFs, a tolerable probability of collapse is only achieved in a return period of 50 years when the perimeter SMFs of mid‐rise steel buildings are designed with a strong‐column/weak‐beam ratio larger than 1.5. The concept of the dynamic overstrength, Ω_d is introduced that captures the inelastic force redistribution due to dynamic loading. Steel frame buildings with perimeter SMFs achieve a Ω_d > 3 regardless if the gravity framing is considered as part of the nonlinear analytical model representation. Copyright © 2014 John Wiley & Sons, Ltd.     

Buckling‐restrained brace using steel mortar planks; performance evaluation as a hysteretic damper

The authors developed a buckling‐restrained brace that enables increased design freedom at both ends of the core plate and strict quality control while providing stable hysteresis characteristics even under high strains. The buckling‐restrained brace can be formed by welding a core plate covered with unbonded material to a pair of mortar‐filled channel steels (steel mortar planks) as a restraining part. The use of this approach enables visual confirmation of the status of the mortar filling and also facilitates standardizing structural members and member‐by‐member quality control. Specimens of a buckling‐restrained brace with different steel mortar plank heights are fabricated to adjust the restraining force, along with specimens with different core plate width‐to‐thickness ratios. The tests were conducted to reveal the hysteretic characteristics of the braces, as well as their cumulative plastic strain energy, elastoplastic properties, and stiffening properties. A performance evaluation formula as well as a buckling‐restrained brace design method using the test results is proposed. Copyright © 2006 John Wiley & Sons, Ltd.