Performance Of Steel Moment Resisting Frames Research Articles

Effect of U-Shaped Metallic Dampers on the Seismic Performance of Steel Structures based on Endurance-Time Analysis

Seismic performance of steel moment-resisting frames is investigated through the incorporation of U-shaped metallic dampers. The primary objective is to assess the effectiveness of these dampers in mitigating seismic responses by utilizing various analysis techniques. Two representative structural configurations (5 and 10-story) are studied in both damped and undamped states to reveal the impact of dampers on seismic response reduction. The study utilizes the endurance time analysis (ETA) method, known for its efficiency in evaluating structural seismic performance. To validate the analysis results, a benchmark comparison is made through nonlinear time history analysis (NTHA). Incremental dynamic analysis (IDA) is also conducted to assess structures’ intensity measures with respect to their damage intensity index. The findings demonstrate that U-shaped metallic dampers substantially reduce inter-story drift and story shear forces. Importantly, a close alignment between the results obtained from ETA and NTHA underscores the reliability of the former in assessing seismic performance with supplemental damping devices.

Seismic response of high strength steel frames equipped with energy dissipation bays subjected to seismic sequences

Most of the seismic codes currently used are based on isolated earthquakes, whereas most earthquakes are seismic sequences acting repeatedly. In contrast to isolated earthquake scenarios, seismic sequences involve a series of seismic events, including a mainshock followed by aftershocks, suggesting that seismic sequences can reflect the structural damage accurately. This paper investigated the seismic performance of steel moment-resisting frames equipped with energy dissipation bays (EDBs) subjected to seismic sequences. It was demonstrated that the EDBs perform well in protecting main frames from isolated earthquakes of a certain magnitude, and the seismic sequences did not worsen the main frames' plastic damage. However, when the magnitude exceeded a certain threshold, the EDBs began to lose some of their protective capabilities, and the main frames' plastic damage from seismic sequences significantly increased. For the high strength steel frames equipped with EDBs, an approach that is more appropriate for estimating the residual damage of main frames in finite elements was suggested. The comparison results demonstrated the method's improved accuracy.

Hybrid-self-centring steel frames: Insights and probabilistic seismic assessment

This paper comprehensively discusses the seismic performance of steel moment-resisting frames with hybrid-self-centring connections (SMRF-HSCC) employing energy dissipation sequences by probabilistic seismic assessment. The hysteretic model of the HSCC was first developed based on experimental results, and a simplified nonlinear-spring-based model to simulate the behaviour of the connection was proposed and verified by physical test data. A series of codified prototype structures were developed, considering the fracture behaviour of post-tensioned (PT) steel strands in the connections. The seismic performance of prototype structures was assessed in terms of nonlinear static analyses and nonlinear dynamic analyses. The results indicated that the hysteretic response of SMRF-HSCC exhibited trilinear hysteretic features with the expected energy dissipation sequences. The influence of the high-mode effects on SMRF-HSCC was mitigated with the increase in energy dissipation and post-yield stiffness of the structure. Finally, the fragility analyses of the prototype structures were further performed, and the risk assessment was also made considering a 50-year service period. The collapse probability and the exceedance probability of target residual drift over a 50-year service period of SMRF with conventional self-centring connections showing flag-shaped hysteresis were higher than that of SMRF-HSCCs. The results also confirmed that the collapse probability and exceedance probability of target residual drift over a 50-year service period of SMRF-HSCC can be adjusted by reasonably modulating the arrangement of the HSCCs.

Mitigating ground motion duration impact on steel moment-resisting frames using viscous dampers

This paper explores the significant influence of ground motion duration on the seismic performance of steel moment resisting frames. It demonstrates that during long-duration strong earthquakes, the structural response of such frames can be substantially larger than under short-duration ground motions. To address this challenge, viscous dampers, known for their stable hysteretic behavior and resistance to degradation under cyclic loading, are introduced as a retrofitting solution. To evaluate the effectiveness of viscous dampers, incremental dynamic analysis was conducted on three prototype steel moment-resisting frames of varying heights, both before and after retrofitting with viscous dampers. A total of 44 pairs of short-duration and long-duration spectrum-matched ground motions were employed as seismic inputs to isolate the effects of seismic motion duration from those arising from seismic amplitude and acceleration spectral shape. The findings underscore the potential of viscous dampers to significantly enhance the seismic performance of steel moment-resisting frames. Furthermore, these dampers effectively mitigate the impact of ground motion duration, reducing the uncertainty in structural response and facilitating more accurate evaluations of seismic performance.

Machine learning-aided peak and residual displacement-based design method for enhancing seismic performance of steel moment-resisting frames by installing self-centering braces

Conventional steel moment-resisting frames (SMRFs) absorb seismic energy through steel yielding behavior, leading to significant residual displacement. Although steel yielding behavior can ensure the seismic safety of SMRFs under strong earthquakes, excessive residual displacement may lead to post-earthquake demolition decisions, causing a large amount of economic loss. This paper aims to develop a peak and residual displacement-based design (PRDBD) method for controlling the peak and residual inter-story drift responses of SMRFs by installing self-centering braces. The peak and residual displacements are both set as the design targets in the proposed PRDBD method. To this end, the machine learning prediction models of inelastic and residual displacement ratios were first developed based on the median responses of single-degree-of-freedom systems under earthquakes. The detailed design steps of the proposed PRDBD method were subsequently introduced. The three- and nine-story demonstration buildings were retrofitted by using the PRDBD method with two different design targets. Static and dynamic analyses were conducted to validate the effectiveness of the proposed PRDBD method. The static analysis results indicated that the self-centering braces could efficiently enhance the SMRF’s stiffness and strength. The retrofitted SMRFs showed no strength deterioration, whereas the original SMRFs showed obvious strength deterioration at the roof drifts of 3.2% and 2.5% in the three- and nine-story buildings, respectively. The dynamic analysis results confirm that the self-centering braces can efficiently reduce the peak and residual inter-story drift responses of the existing SMRFs and the retrofitted SMRFs can achieve the peak and residual inter-story performance objectives under the considered seismic intensity. Moreover, the retrofitted SMRFs can be fully recoverable after maximum considered earthquakes by controlling the maximum residual inter-story drift lower than 0.2%.

Eurocode 8 revision – Implications on the design and performance of steel moment-resisting frames: Case study

Since the 2004 release of the European seismic code – Eurocode 8, various improvements have been proposed to its rules. The standard is being revised and, in its current revised state, it has been restructured and expanded in content. The revisions related to steel structures and especially to the design of steel moment-resisting frames (SMRFs) are notable. Modifications in the definition of the ductility classes, grade-dependent material randomness factors, behaviour factors, inter-storey drift sensitivity index (θ), the local hierarchy criteria, and the design rules for the dissipative ductility classes (DC2 & DC3) are a few of the notable proposed changes. This paper aims to study and compare seismic designs and performances of SMRFs using the revised specific rules for steel design. To this end, a parametric case study, consisting of 96 frames, is devised by varying the key parameters such that the effects of the recent changes can be highlighted. The parameters varied are the design code, ductility classes, number of storeys, span length, and material strength. The case study frames are analysed and designed to both versions of the EC8. Later, the seismic performance of the case study SMRFs designed to the current and revised EC8 provisions are investigated through non-linear static and dynamic analyses using OpenSees. Additionally, the significance of two distinct joint modelling techniques is explored.The results show that stability is not the governing requirement with the revised code. Lighter solutions in terms of steel mass were possible for the regularly spaced frames using the revised code. It was noted, however, that contrary to the design intent and despite the higher behaviour factor used in DC3 & DCH frames, their solutions were not found to be lighter than those designed to DC2 & DCM in both code versions. The actual behaviour factors estimated from non-linear analyses were also found to be different from those used in design by a considerable margin. The over-strength component of the behaviour factor varied significantly between frames of different steel grades and ductility classes. It was observed that the component plays such a significant role in the overall behaviour factor that assigning a constant value may result in misleading estimates. The dynamic analyses results showed that the frames designed to both versions of EC8 demonstrated acceptable performance even at the near collapse limit state.

Soil-structure interaction effects on the seismic performance of steel moment-resisting frames equipped with optimal rotational friction dampers

This study investigate the soil-structure interaction (SSI) effects on the seismic performance of steel moment-resisting frames (SMRF) equipped with optimal rotational friction dampers (RFDs). Firstly, a simultaneous optimal design based on the energy concepts is expanded to find the optimal placement and the corresponding optimal parameters of the RFDs for the seismic protection of a nonlinear six-story SMRF. Then, the direct method is adopted to simulate the nonlinear SSI effects on the optimal RFDs-equipped SMRF. The input, hysteretic, dissipated energies and the drift of stories of the controlled SMRF subjected to four real earthquake excitations indicate that SSI can considerably influence the seismic performance of the controlled SMRF. Nevertheless, the significant amount of the seismic input energy is dissipated by optimal RFDs and therefore its limited amount is dissipated by the structural. Moreover, the optimal RFDs can maintain the story drift ratios within the acceptable drift limits.

Development and Experimental Validation of Dissipative Embedded Column Base Connections for Enhanced Seismic Performance of Steel Moment-Resisting Frames

This paper proposes a novel embedded column base (ECB) connection that defies the current paradigm in capacity-designed steel moment-resisting frames (MRFs) where column bases have been traditionally considered as nondissipative. In the proposed concept, a dissipative zone is introduced as part of the embedded portion of the steel column. This zone features a reduced cross section and is decoupled from the concrete footing with a debonding material layer. The surrounding concrete effectively restrains the embedded section against nonlinear geometric instabilities, thereby retaining simplicity in the design process. Large-scale experiments suggest that, contrary to its conventional counterpart, the proposed dissipative ECB connection exhibits a stable hysteretic response until large lateral drift demands (i.e., 7% rad). It is also demonstrated that the dissipative ECB connection is resilient to local buckling-induced axial shortening, such that it lowers the repairability needs of slender wide-flange steel columns after earthquakes. Column twisting is also minimized throughout the loading history. The results indicate that both the elastic stiffness and flexural yield strength of the proposed ECB connection can be analytically derived for potential use in engineering design. It is found that a simple nondegrading bilinear model suffices to describe the hysteretic response of the proposed ECBs for performance-based assessment of steel MRFs.

Effect of column strength deterioration on the performance of steel moment-resisting frames subjected to multiple strong ground motions

This study evaluates the effect of column strength deterioration caused by local buckling on the seismic performance of steel moment-resisting frames (SMRFs) considering multiple strong ground motions. Various SMRF models considering two main design parameters, i.e., the column width-to-thickness ratio and the column-to-beam moment capacity ratio, are analyzed by conducting an inelastic earthquake response analysis that simulates the occurrence of multiple strong ground motions. A column hysteretic model that takes into account the strength deterioration caused by local bucking is employed in this analysis. The numerical analysis results show that column strength deterioration may cause the shift to a weak story mechanism and weak story collapse under the excitation of multiple strong ground motions. The number of excitations that can be withstood by the structure (before collapse) varies among the models. The collapse fragility under multiple excitations is investigated to find the combination of design parameters that can achieve a certain acceptable performance.

Modeling flexural overstrength factor for steel beams using heuristic soft-computing methods

When evaluating the structural performance of steel moment-resisting frames, significant consideration is given to the flexural behavior of steel beams. This analysis focuses on the primary response parameters, such as the ultimate flexural resistance and rotation capacity that dictate the behavior of the steel beam. In practice, the flexural behavior of steel beams determines the ductile design of steel structures, and a sufficient ductility of steel permits plastic hinge rotations until a full-collapse mechanism is attained. However, it is relatively impossible to guarantee the occurrence of a full-collapse mechanism if the beam’s flexural overstrength is not appropriately quantified by the application of capacity design procedures. Therefore, this study developed analytical formulations to predict the steel beam’s flexural overstrength factor (s) using the multilayer perceptron (MLP)11AMFF: adaptive multilayer feed forward; ANFIS-PSO: adaptive neuro fuzzy system with particle swarm optimization; ANOVA: analysis of variance; GA: genetic algorithm; KKT: Karush–Kuhn–Tucker; LSSVR: least-square support vector regression; M5 Tree: M5 model tree; MAE: mean-absolute errors; MARS: multivariate adaptive regression splines; MLP: multi-layer perceptron; MLR: multiple linear regression; PSO: particle swarm optimization; RBNN: radial basis-function-based neural network; RHS: rectangular hollow section; RMSE: root-mean-square errors; SHS: square hollow sections; SIS: swarm intelligence systems., radial-basis-function-based neural network (RBNN), least-squares support vector regression (LSSVR), adaptive neuro fuzzy system with particle swarm optimization (ANFIS-PSO), multivariate adaptive regression splines (MARS), M5 model tree (M5 Tree), and multiple linear regression (MLR). Numerous cross-sectional geometries were tested with square and rectangular hollow sections, and with I and H sections. The data used for the analysis were sourced from completed experimental studies available in the open literature. The data were categorized as training and testing datasets to develop the models based on the aforementioned methods. For the models, the mechanical properties of the materials, shear length of steel beams, and the geometric properties of the sections constituted the independent variables. Overall, the RBNN demonstrated the best prediction of the steel beam overstrength with a root-mean-square error of 0.099 mm, mean absolute error of 0.066 mm, and a correlation coefficient of 0.825. It was observed that all six machine learning methods provided better estimates than the MLR. The machine learning models developed in this study are expected to serve as a hand tool for engineers and steel structure constructors.

Blast Performance Evaluation of Steel Moment-Resisting Frame Equipped with Smart Bolted Connection

This paper deterministically evaluates the blast performance of steel moment-resisting frame (MRF) smart structures equipped with nickel titanium shape-memory alloy (NiTi SMA) bolted connections. The recentering capacity of the NiTi SMA bolts is exploited to limit the structural damage and reduce the residual drift after a near-field explosion event. A simplified blast over-pressure calculation approach is used to draw the blast overpressure profile. Numerically, the NiTi SMA–based connection is designed conforming to current European standards and is modeled with a solid finite element. The effect of high-strain-rate actions is considered. The response of the NiTi SMA–based connection is obtained by the nonlinear transient analysis and compared with the steel bolted connection. The NiTi SMA–based connection provided excellent recentering capacity. Later, the moment-rotation response of the NiTi SMA–based connection is utilized in the MRF structure. A simplified self-centering connection is proposed to produce smart behavior in the MRF structures. The results reveal that using NiTi SMA connections keep interstory drift relatively low and substantially provide reasonable structural lateral resistance under near-field blast loading.

Performance of steel moment-resisting frames in post-earthquake horizontally traveling fire

PurposeThe study investigates the performance of a three-story unprotected steel moment-resisting frame (SMRF) designed for high seismic demand in the fire-only (FO) and post-earthquake uniform and traveling fires (PEF). The primary objective is to investigate the effects of seismic residual deformation on the structure's performance in horizontally traveling fires. The traveling fire methodology, unlike conventional fire models, considers a spatially varying temperature environment.Design/methodology/approachMulti-step finite element simulations were carried out on undamaged and damaged frames to provide insight into the effects of the earthquake-initiated fires on the local and global behavior of SMRF. The earthquake simulations were conducted using nonlinear time history analysis, whereas the structure in the fire was investigated by sequential thermal-structural analysis procedure in ABAQUS. The frame was subjected to a suite of seven ground motions. In total, four horizontal traveling fire sizes were considered along with the Eurocode (EC) parametric fire for a comparison. The deformation history, axial force and moment variation in the critical beams and columns of affected compartments in the fire heating and cooling regimes were examined. The global structural performance in terms of inter-story drifts in FO and PEF scenarios was investigated.FindingsIt was observed that the larger traveling fires (25 and 48%) are more detrimental to the case study frame than the uniform EC parametric fire. Besides, no appreciable difference was observed in time and modes of failure of the structure in FO and PEF scenarios within the study's parameters.Originality/valueThe present study considers improved traveling fire methodology as an alternate design fire for the first time for the PEF performance of SMRF. The analysis results add to the much needed database on structures' performance in a wide range of fire scenarios.

Study of the seismic behavior of rigid and semi-rigid steel moment-resisting frames

Steel moment resisting frames are prevalent seismic force resisting systems that are used extensively in high seismic regions worldwide. New design procedures suggested by codes have resulted in extensive use of semi-rigid connections in moment resisting frames. These connections have some degree of flexibility. This study focuses on seismic performance of steel moment-resisting frames with different degrees of moment connection rigidities. Three moment frames (5, 10 and 15 stories), each with different levels of connection rigidities (full, 80%, 70% and 60% rigidities) are analyzed under the 22 far-field ground motions presented in FEMA P695. Detailed modal analysis, non-linear static (pushover) analysis and incremental dynamic analysis (IDA) were conducted. Results reveal that semi-rigid frames have lower base shears and higher structural deformations, but higher energy absorption capability. Lastly, detailed performance analysis was conducted. The results show that probability of exceeding the fully operational performance level is higher in semi-rigid frames as compared to rigid connections. The inclusion for the rigidity in the beam-column can have an impact on the performance of steel moment frames which cannot be ignored during the design and retrofit of steel moment-resisting frames.

Probabilistic seismic performance of steel structures with FVDs designed by DDBD procedure

In this paper, the probabilistic seismic performance of steel moment-resisting frames (MRFs) equipped with fluid viscous dampers (FVDs) designed based on the deterministic direct displacement-based design (DDBD) method is investigated by taking into account the effect of the aleatory and epistemic uncertainties . For probabilistic analysis, two intensity measure (IM)-based approaches, including the determination of the mean annual frequency (MAF) of exceeding design target and the ratio of factored demand to factored capacity (F.D/F.C) in fragility/hazard design format, have been used. The maximum drift ratio has been selected as the demand parameter, and for controlled structures, the geometric mean of spectral acceleration, Sa avg , has been selected as the suitable IM. For numerical analysis, three 4, 8 and 12-story steel MRFs fitted with linear and nonlinear FVDs and designed based on the deterministic DDBD method have been considered. By performing the incremental dynamic analysis (IDA), the exceeding probability and F.D/F.C ratios have been determined for different nonlinearity levels of FVDs. The results show that the seismic performance of the structure designed using DDBD method has been significantly affected by the uncertainties. Moreover, the structures with nonlinear FVDs have a higher exceeding probability and F.D/F.C ratio than linear dampers due to their low damping coefficient in the deterministic DDBD method as well as minor capability of controlling displacements in higher velocities. In addition, considering the epistemic uncertainty has led to an increase in the F.D/F.C ratio up to 20%, while the probabilistic evaluation results altered slightly by the type of input record. • Uncertainties in performance of the structures with FVDs designed by DDBD. • Linear FVDs caused a higher capacity intensity for an IMC, compared to nonlinear FVDs. • In structures with nonlinear FVDs, F.D/F.C has increased up to 1.74. • Epistemic uncertainty affected the F.D/F.C ratio which is not negligible. • UD method for distributing FVDs improved the probabilistic performance of controlled structures.

An improvement of direct displacement-based design approach for steel moment-resisting frames controlled by fluid viscous dampers

Direct displacement-based design (DDBD) method is one of the most effective methods for performance-base design of structures that has been also employed to design structures controlled by fluid viscous damper (FVD). In previous studies, a modified DDBD has been developed to apply the higher mode effects as well as difference between spectral velocity and pseudo-spectral velocity on the design velocity of FVD. To this end, two constants were defined to correct the damping coefficient of FVD that these correction constants had been determined in a non-classical and iterative manner. In this study, a new classical method is proposed for determining these constant such that no iteration is required in DDBD. In order to be able to introduce this design approach as a reliable framework, its performance is validated under different sets of earthquake records and this design approach is also developed for structures controlled by nonlinear FVD. Steel moment-resisting frames with different numbers of stories have been designed using this method. For comparison, structures have been also designed based on DDBD proposed in previous researches. The results show that DDBD approach improved in this study is capable to achieve the design performance level under different sets of earthquake records and this design approach has more effective performance than previous design methods. Performance of steel moment-resisting frames equipped with nonlinear FVD also shows excellent performance of this design approach in achievement of desirable performance level. Therefore, DDBD approach proposed in this study can be introduced as a new classical and reliable framework because of its simplicity and excellent performance under different sets of earthquakes.

Improving the nonlinear seismic performance of steel moment-resisting frames with minimizing the ductility damage index

In this paper, the parameters optimization of a tuned mass damper (TMD) is presented to enhance the seismic performance of a six-story steel structure based on the ductility damage index. Herein, the six-story frame is modeled nonlinearly in the OpenSees software by a concentrated plasticity model. Finally, the most suitable algorithm is selected among several optimization algorithms based on the convergence rate and the objective function's values. In this process, the water cycle algorithm has shown the best results. Therefore, the optimal parameters of the TMD are calculated by this algorithm in such a way that the ductility damage index is minimized in the six-story structure under earthquake loads. For this purpose, the nonlinear dynamic analysis of the structure is performed under earthquakes loads using the OpenSees software. Also, the optimum parameters of the TMD are computed to minimize the ductility damage index under the earthquake loads by linking the OpenSees and Matlab software. The results show that the optimum parameters of the TMD system obtained by the water cycle algorithm could appropriately decrease the ductility damage index. It can simultaneously increase the structure's seismic performance to reduce the displacement, stories damage, and drift ratio.

Effect of Base-Connection Strength and Ductility on the Seismic Performance of Steel Moment-Resisting Frames

AbstractColumn-base connections in steel moment-resisting frames (SMFs) in seismic regions are commonly designed to develop the capacity of adjoining column with an intent to develop a plastic hing...

Seismic Performance of Ductile Steel Moment-Resisting Frames Subjected to Multiple Strong Ground Motions

This study evaluates the seismic performance of steel moment-resisting frames (SMRFs) under multiple strong ground motions. The cumulative damage of beam members is used as the main damage index. A cumulative damage formula is generated based on the experimental results of the steel beam-to-column connection test considering the ductile fracture. Local buckling of members is not considered in this study. Six SMRF models with two parameters (the number of stories and the strength of the column base) are analyzed by conducting an inelastic response analysis. Three different ground motion intensities (peak ground velocity = 0.5 m/s (design level), 0.75 m/s, and 1.0 m/s), each with five repeated excitations are used in the inelastic response analysis to simulate the occurrence of multiple strong ground motions. Stable behavior with a linear increment in cumulative damage is found in most cases, especially when the ground motion intensity is equal to the design level. However, when the intensity is greater than the design level, both ductile fracture and weak story collapse are observed in several cases.

Effect of semi-rigid connections in improvement of seismic performance of steel moment-resisting frames

Seismic performances of dual steel moment-resisting frames with mixed use of rigid and semi-rigid connections were investigated to control of the base shear, story drifts and the ductility demand of the elements. To this end, nonlinear seismic responses of three groups of frames with three, eight and fifteen story were evaluated. These frames with rigid, semi-rigid and combined configuration of rigid and semi-rigid connections were analyzed under five earthquake records and their responses were compared in ultimate limit state of rigid frame. This study showed that in all frames, it could be found a state of semi-rigidity and connections configuration which behaved better than rigid frame, with consideration of the base shear and story drifts criterion. Finally, some criteria were suggested to locate the best place of the semi-rigid connections for improvement of the seismic performance of steel moment-resisting frames.

Numerical study of seismic performance of steel moment-resisting frame with buckling-restrained brace and viscous fluid damper

The seismic performance assessment of modified steel moment-resisting frame (SMRF) was carried out by nonlinear time-history analysis. The basic bare SMRF was reduced in strength first and then enhanced by installing passive energy dissipating devices (EDDs) to develop modified frame. Passive EDDs comprise both rate-dependent and rate-independent devices. Viscous fluid damper (VFD) is a rate-dependent device whereas buckling-restrained brace is a rate-independent device. The lateral strength of structure was improved by using these devices either alone or in combination. Seven-scaled time-history records were used for incremental dynamic analysis. The stiffness effect on the stories is demonstrated through the lateral displacement profile of the building. The VFD is found to be a good EDD as it significantly improved the performance of the frame at all levels of seismic analysis.