Shear Links Research Articles

Experiment and analysis on seismic performance of a self-centering Y-eccentrically braced frames structure

Conventional eccentrically braced frames (EBFs) exhibit significant residual deformations following major earthquakes, necessitating costly repairs for the damaged structures. This study proposed a novel self-centering Y-eccentrically braced frames (SC-YEBFs) system to enhance the seismic resilience. A theoretical mechanical model which takes into account its components is formulated to predict the lateral load behavior of SC-YEBFs. The pseudo-static experiments were conducted on four specimens, and the resulting observations and analyses demonstrate that the shear links effectively function as ductile fuses, dissipating a significant portion of the input energy to safeguard the main frame from damage. Furthermore, the self-centering joint exhibits a hinge-like behavior with remarkable self-centering characteristics. The structural reparability of all specimens was found to be exceptional during major seismic events. By increasing the initial prestress and sectional area of steel strands, the self-centering performance can be further enhanced. The damaged shear links could be easily detached by loosening bolts, and the consideration of prestress loss is nonnegligible to ensure an exceptional self-centering performance. The proposed theoretical model predicted the mechanical properties of SC-YEBFs, including lateral stiffness, energy dissipation, and self-centering mechanism, through a comparison with experimental results. Moreover, the theoretical model was utilized to propose an equivalent simulation method for simulating self-centering joint and shear link using Connector function in ABAQUS software, while establishing a simplified frame finite element model for further analysis.

Improved PBPD method for dual steel system considering the global effect of space frames

Performance-based plastic design (PBPD) method has been proposed to design single bay planar frames for twenty years. For a dual steel system, such as an eccentrically braced frame (EBF) structure, there will be both EBF bays and moment resisting frame (MRF) bays. So, the global effect between different frame bays cannot be considered when designing the global structure using the traditional PBPD method. In this paper, a ten-story high-strength steel composite K-shaped eccentrically braced frame (HSS-K-EBF) structure was firstly used for performance design and analysis based on a single bay EBF. The results show that the global structural model obtained by direct performance design of the single bay model cannot achieve the desired performance objectives. To this end, an improved PBPD method for the dual steel system was proposed considering the global effects of space frames. The elastic and elastic–plastic shear distribution relations were calculated for different bays of the frames including EBFs and MRFs. The performance objectives of the global structure were designed and evaluated more accurately by considering the over-strength contribution of shear links and the plastic development rate index ξ of energy dissipation members. The improved PBPD method was used to design the ten-story global HSS-K-EBF structure. The results of nonlinear dynamic time history analysis show that the improved PBPD method can ensure that the plastic damage distribution of energy dissipation members of different bays is more uniform and the plastic damage degree is more consistent with expectations.

Experimental study on seismic performance of replaceable shear links with low-yield-point steel

Based on the design concept of controllable seismic damage during earthquakes and rapid functional recovery after earthquakes, a replaceable shear link with low-yield-point steel was proposed. Quasi-static cyclic loading tests and numerical analysis were conducted on six specimens. The failure mode, seismic performance, energy dissipation behavior, and shear distribution of each specimen were carefully considered to investigate the effects of web steel, web stiffening configuration and stiffener-plate stiffness ratio. The results showed that the stiffened specimens showed full-sectional shear yielding behavior, while the non-stiffened specimens exhibited coupling behavior of web yielding and buckling. Specimens with reasonable design parameters had excellent ductility and energy dissipation capacity, with the plastic shear angle exceeding 0.157 rad and the maximum equivalent viscous damping coefficients greater than 0.51 (80% of the theoretical maximum value). Owing to the cyclic strengthening of the low-yield-point steel web and the contributions of stiffeners and flanges, the specimens showed obvious overstrength behavior, with the overstrength factor ranging from 1.99 to 2.39. The cross-stiffening configuration was conducive to enhancing the seismic performance of shear links. Smaller web width-to-thickness ratios were recommended to match with smaller stiffener-plate stiffness ratios. Extended cross stiffeners and diagonal stiffeners resulted in earlier cracking of the web welds, which adversely affected the ductility of the specimens.

Lateral-torsional buckling investigation of multi-tiers eccentrically braced frames with shear link beam

Multi-tiered braced frames (MTBF) are a type of braced frames with two or more tiers of bracing or bracing panels between horizontal diaphragm levels or locations of out-of-plane support, along with a beam at every tier level. They are commonly used in tall single-story building structures when it is not practical to use single bracing members spanning from roof to foundation levels. Additionally, they find application in multistory buildings with tall story heights. In this paper, lateral-torsional buckling of beams in a new type of MTBF called multi-tiered eccentrically braced frames (MT-EBF) is evaluated. This structural system is not mentioned in any of the current code and seismic criteria have not been provided. The main different of this system with eccentrically brace frame is the lack of laterally supported in the intermediate beam. Also, in industrial buildings that need architectural openings, this system is more useful than concentrically braced frame. For this purpose, the seismic behavior of four different MT-EBF with one and two tiers, along with two different configurations for the connection of braces to the beams, is studied. In the first configuration, the braces are connected to the beam using a gusset plate, and in the second configuration, the braces are directly connected to the beam using full penetration groove weld. The results of the numerical study indicate that in the first configuration, lateral-torsional buckling occurs in the intermediate beams, and the connection of the gusset plate to the beams lacks the necessary stiffness to prevent lateral-torsional buckling. However, in the second configuration, lateral-torsional buckling of the intermediate beams is prevented, and the connection of the braces to the beams has the adequate stiffness to prevent lateral-torsional buckling.

Topology optimization of vertical shear links in eccentrically braced frames

The inclusion of additive manufacturing (AM) in the construction industry has opened new perspectives on the production of structural members. By coupling AM technologies with topology optimization (TO), significant reductions in material usage and weight can be achieved. Although TO has been applied to optimize simply supported beams, additional factors such as stress concentrations, buckling, and low-cycle fatigue from seismic loads require further investigation. This study presents a numerical approach for optimizing shear links subjected to monotonic and cyclic loading. The numerical models for conventional shear links were validated against experimental work, including cyclic loading tests on individual shear links and scaled eccentrically braced frames (EBF). The implementation of TO led to a 12 % volume reduction in the first optimized link. The optimized link demonstrated superior performance, exhibiting higher shear strength and energy dissipation capacity under both monotonic and cyclic loading. Another study examined EBFs with vertical links, achieving 12 % and 30 % reduction in material volume. The optimized links showed improvements that reached 25 % compared to the conventional link in terms of strength and energy dissipation with 12 % volume reduction, while 30 % volume reduction showed slightly less improvement over EBFs with conventional shear links.

Composite floor slab effect on seismic performance of steel-framed-tube structures with shear links

High-strength steel-framed-tube structures with low-yield-point shear links (SFT-RLYPSL) exhibit exceptional lateral and torsional stiffness, coupled with significant energy dissipation capacities. This study aims to investigate teh influence of composite floor slabs on the seismic performance of these structures. Expanding on previous research concerning SFT-RLYPSL, this paper presents a simplified numerical model for the SFT-RLYPSL, incorporating the influence of the composite floor slab. The developed model employs the steel4 constitutive relation to accurately depict the behavior of low-yield-point steel. Furthermore, the simplified numerical model utilizes two-node link elements to simulate shear links and integrates composite beams to represent the influence of the composite floor slab. Using this simplified model, elastic-plastic pushover analysis is performed on five distinct SFT-RLYPSL structural cases, and nonlinear time-history analysis is conducted on three structural configurations. The investigation explores various aspects of the seismic performance of SFT-RLYPSL, including modal behavior, pushover curves, progression of overturning failure, time-history roof displacements, inter-story drift angles, base reactions, inter-story shear, failure modes, residual inter-story drift angles, and the manifestation of shear lag phenomena. The findings suggest that incorporating the composite floor slab effect enhances initial stiffness and peak load capacity in pushover analysis, leading to distinct three-stage pushover curves. During nonlinear time-history analysis, the composite floor slab effect increases structural stiffness, decreases roof displacements and inter-story drift angles, while simultaneously increasing base reactions, worsening component damage, and raising collapse risk. Nevertheless, its influence on residual inter-story drift angles remains relatively minor, with a mitigating effect on the shear lag phenomenon. Importantly, the degree of this impact varies with alterations in floor slab thickness and seismic intensity, highlighting the critical importance of considering the composite floor slab effect in structural design deliberations.

Lateral Load Behavior Analysis of a Novel Self-Centering Y-Eccentrically Braced Frames with Slip Connection Shear Link

Lateral Load Behavior Analysis of a Novel Self-Centering Y-Eccentrically Braced Frames with Slip Connection Shear Link

Seismic collapse performance assessment of high‐strength steel framed‐tube structures with shear links fabricated using low‐yield‐point steel

SummaryA high‐strength steel framed‐tube structure with shear links fabricated using low‐yield‐point steel (HSSFTS‐LYPSL) was developed in this study to improve the seismic performance and resilience of the conventional steel framed‐tube structure. When this HSSFTS‐LYPSL is subjected to strong earthquake excitation, its shear links undergo significant plastic deformation to dissipate seismic energy while critical components such as the spandrel beams and columns maintain their elasticity. Furthermore, the replacement of damaged links was facilitated by the use of bolted end‐plate connections. This study designed three typical HSSFTS‐LYPSL examples with 20, 30, and 40 stories to investigate the seismic collapse performances of HSSFTS‐LYPSLs at different seismic intensity levels. Three‐dimensional nonlinear finite element analysis models of these example structures were developed using the OpenSEES software, and the accuracy and effectiveness of the modeling approach was validated by comparing its results with those of quasi‐static tests on sub‐structure assemblies. Next, 40 records each of far‐field and pulse‐type near‐field ground motions were selected and applied with an incremental dynamic analysis (IDA) to obtain response curves for the example structures and calculate their collapse fragility curves and collapse margin ratios (CMRs) utilizing a modified collapse fragility model. Finally, based on the collapse fragility and seismic hazard curves, the seismic collapse risk probability curves of the HSSFTS‐LYPSLs were obtained under far‐ and near‐field earthquakes, revealing that at the maximum considered earthquake level, the CMR values ranged from 5.74 to 7.25 and from 4.85 to 6.67, respectively; at the very rare earthquake (VRE) level, the CMR values ranged from 3.83 to 4.85 and from 3.24 to 4.46, respectively. These results demonstrate that HSSFTS‐LYPSLs exhibit sufficient potential for seismic collapse resistance. As pulse‐type near‐field earthquakes had more significant and adverse impacts on the seismic collapse performances of the HSSFTS‐LYPSLs than far‐field earthquakes, the seismic collapse design of an HSSFTS‐LYPSL should particularly consider the influence of near‐field effects. In addition, the seismic hazard function had a greater effect on the structural seismic collapse risk curves than the collapse fragility function, suggesting that seismic collapse risk curves could provide a comprehensive assessment of HSSFTS‐LYPSL seismic collapse performance. Under far‐ and near‐field earthquakes, the annual collapse risk probabilities of the HSSFTS‐LYPSL examples at the VRE level were within 1.18 × 10−5–4.53 × 10−5, which is below the seismic collapse risk threshold recommended by others, indicating that HSSFTS‐LYPSLs can meet the fourth‐level performance objective of “no collapse failure at the VRE level.” However, this study only conducted seismic collapse and risk assessments using example HSSFTS‐LYPSLs; future research will focus on determining the seismic recovery capacities of and developing post‐earthquake repairability methodologies for HSSFTS‐LYPSLs.

Design procedure of a shear fuse system for steel moment-resisting frames

In steel moment-resisting frames (MRFs), seismic energy is generally dissipated through the formation of flexural plastic hinges at beam ends. In ensuring such a mechanism, current code provisions limit the utilization of beams with small span-to-length ratios in MRFs. This study presents the design procedure of a novel shear fuse system that integrates replaceable shear links with non-prismatic beams to enhance the performance and repairability of MRFs with small beam span-to-length ratios. The proposed design strategically weakens the beam at its midspan by incorporating a replaceable link, prioritizing shear yielding in the link over flexural yielding in the beam outside the link, thus ensuring adequate frame ductility and protecting the critical beam-to-column connections. It can function as an efficient replaceable shear fuse system, as the damaged fuse can be substituted with a new one following a severe earthquake. In fulfilling the study’s purpose, first, several formulas are developed to provide a comprehensive design procedure. Next, example design calculations are presented for an MRF with a small beam span-to-depth ratio. Ultimately, a numerical investigation is provided to examine the proposed system’s performance compared to conventional MRFs. The results indicate that the proposed shear fuse system provides a more consistent cyclic behavior than the conventional prismatic beam design, exhibiting stable strain-hardening behavior up to the 5 % story drift ratio without noticeable strength degradation. It appropriately shifts the plastic hinges away from the beam-to-column connections while increasing the frame’s overall ductility with 1.14 times greater energy dissipation in the final loading cycles.

Experimental investigation of band-beam slabs subjected to close-range blast loading

Portable explosions in the form of backpacks and suitcases have been at the forefront of various terrorist activities due to their ability to create unrest in crucial infrastructure such as railway stations. At close range, these portable explosives, with charge sizes ranging from 2 kg to 10 kg, can reasonably damage vital structural elements of a building. For example, the debris produced by breaching one slab can overload and damage the slabs below in a multi-storey structure or pile up to block the access and continuous functioning of a building during rescue operations. A "band-beam slab" or "slab with a shallow beam" is one of the most used slab types in modern multi-storey buildings, especially on basements and lower floors. The band-beam slabs are commonly used to save headspace and floor-to-floor heights of multi-storeyed buildings. Therefore, investigation of the performance of band-beam slabs under close-in detonation is an interest of crucial infrastructure projects. To this end, the work presented in this paper investigates the performance of band-beam slabs subjected to close-in detonations. Thirteen band-beam slabs were subjected to close-in detonations against Composition-4 (C4) charges of sizes varying from 2.5 kg to 4.5 kg. The panels were designed to withstand the overall blast load following the typical design guidelines. However, some variations were introduced in the design to observe the effect of (i) slab reinforcement ratio, (ii) primary longitudinal reinforcement ratio of the beam, (iii) shear link size and spacing in band-beams, and (iv) scaled stand-off distance. In general, all test specimens experienced minor to moderate damage. At the same time, it is observed that the effect of the shear reinforcement ratio and detailing of the reinforcement play a significant role in reducing the spalling and crater formation. The observations have been compared with the UFC-3–340-02 guidelines for spalling and breach and found that experimental results reasonably agree with UFC predictions. Finally, based on the observations, design recommendations in terms of additional reinforcement to control and mitigate spalling, cracking and scabbing were proposed.

Seismic Retrofitting of Existing Reinforced Concrete Buildings Using Aluminium Shear Links and Eccentric Steel Chevron Braces

Many existing reinforced concrete buildings have been designed based on earlier codes of practice that underestimated seismic forces, making them vulnerable to damage during seismic action. Equipping existing buildings with shear links and eccentric braces is one of the available seismic retrofitting methods to dissipate seismic energy away from the main structural members. In this paper, a proposal for the seismic retrofitting of two existing reinforced concrete buildings using aluminium shear links and steel braces is presented. First, a capacity-based design approach is followed to determine the required sizes of the shear links and eccentric braces. Second, numerical analyses are used to compare how the original and retrofitted buildings responded. These tests include pushover analysis, nonlinear time-history analysis, damage analysis, incremental dynamic analysis, fragility and reliability analysis, and damage analysis. The results reveal that the proposed retrofitting method can sufficiently upgrade the performance level of the buildings and reduce their storey displacements and interstorey drifts, as shear links are found to absorb almost all seismic energy, therefore keeping other structural members responding elastically. Yet, using shear links alters the local behaviour of the surrounding structural members, which should be considered in the design process. Furthermore, compared to the original buildings, retrofitted buildings are expected to undergo less structural damage as they have lower damage indices. Meanwhile, the fragility of retrofitted buildings is significantly reduced compared to the original ones, which indicates the efficiency of the proposed retrofitting methods in upgrading the performance of seismically deficient reinforced concrete buildings.

Experimental Investigations of Eccentrically Braced Frame(EBFs) with Replaceable Shear Links Subject to Cyclic Lateral Load

Experimental Investigations of Eccentrically Braced Frame(EBFs) with Replaceable Shear Links Subject to Cyclic Lateral Load

Seismic performance of very short links in eccentrically braced substructures

Research on the seismic performance of eccentrically braced hybrid frames indicates that utilizing very short links can enhance structural stiffness and load capacity. However, there is limited investigation into their effectiveness within eccentrically braced substructures featuring flush end plate bolted connections. This study involves an experimental and numerical investigation to understand the behavior of very short shear links with flush endplates bolted connections in the substructure. An experimental study of 8 specimens was carried out, and the variables studied included loading protocol, links length ratio, flange thickness, and end plate thickness. The experimental results showed that the co-design methodology for flush endplates and bolts of very short links exhibited acceptable performance. Very short shear links bolted with flush endplates demonstrated an average overstrength coefficient of about 1.8 and an ultimate plastic rotation angle above 0.12 rad. Numerical analysis explored the effects of length ratio, web height-to-thickness ratio, and flange width-to-thickness ratio on overstrength behaviors and yield capacity of very short links. The analysis indicated that the length ratio was crucial in determining overstrength coefficients and the yield capacity of very short links. The study established modified formulas that consider the impact of different variables to more accurately determine overstrength behaviors and yield capacity based on formulas in the Chinese code.

Multi-objective optimization of energy-dissipating steel plate fuse links using response surface method

Steel plates with openings are used to provide energy dissipation in earthquake-resistant structures. Shear-acting steel plates with butterfly-shaped or straight links are particularly used as easily replaceable fuses in low-damage design of structures. Sensitivity analyses have shown that the cyclic response of steel plate fuses varies depending on the shape of the fuse link. However, simultaneous response optimization approaches have not been applied in the past research on steel plate fuses. A multiple-response optimization study is needed to find optimal link shapes with improved cyclic response characteristics while simultaneously considering different optimization objectives. In this study, experimentally validated finite element simulations and response surface methodology are used to predict the cyclic load-displacement response of steel plate fuses. The behavior of steel plate shear links is evaluated in terms of initial stiffness, yield strength, ultimate stiffness, effective damping, peak strength, and ductility. Predictive equations are derived and verified for each response characteristic in terms of three influential factors, including the length to end-width ratio (L/b), end-width to thickness ratio (b/t), and mid-width to end-width ratio (a/b) of shear links. The predictive equations are then employed to perform multi-objective optimization studies using a desirability approach. Four different optimization objectives are considered, such as the maximization of effective damping and ductility. Optimal ranges are determined for each factor. The results show that the energy dissipation, strength, and ductility of the fuse can be simultaneously maximized if using relatively thick and moderately long links (with b/t smaller than 6.6, L/b between 2.7 and 6, and a/b between 0.33 and 0.96). Optimal fuses links are those with an intermediate a/b between 0.37 and 0.89 and a small to moderate b/t between 3.0 and 6.6.

Development and Application of an Analytical Model for LYP Steel Shear Links in Eccentrically Braced Frames

Development and Application of an Analytical Model for LYP Steel Shear Links in Eccentrically Braced Frames

An efficient nonlinear hybrid model of energy dissipation piers utilizing fiber beam and self-developed hysteretic spring elements

Energy dissipation piers comprised of concrete filled steel tubular (CFST) columns and steel shear links can exhibit good seismic performance by reasonable collaborative optimization design of columns and links. Considering the time and economic costs of experiments and fine element analysis (FEA), an efficient and accurate numerical model is critical to investigate the hysteretic behavior of energy dissipation piers under earthquake action. Therefore, a hysteretic constitutive law for steel shear links is first proposed including the theoretical shear force-deformation skeleton curve and the unloading and reloading rules during hysteretic loading. Next, a hysteretic spring model is developed for efficiently simulating the hysteretic mechanical behavior of steel shear links, which is validated to have good accuracy with comparison to fine FEA and experimental results. Then, a simplified hybrid model consisting of the self-developed spring model and fiber beam model and two multi-scale FEA models with different levels of refinement are established for nonlinear analysis of energy dissipation piers, respectively. The comparison of numerical and test results confirms that the innovative fiber beam-spring hybrid model can accurately describe the hysteretic performance of energy dissipation piers, especially the detailed mechanical behavior of steel shear links and column feet, which provides an efficient numerical tool for analysing the collaborative working mechanism of energy dissipation piers and similar energy dissipation structures.

A novel hybrid strong-back system to improve the seismic performance of steel braced frames

Soft-storey behavior is prevalent in steel braced frames designed and built following either current or pre-modern seismic standards. Based on past research, various rehabilitation or construction techniques have been proposed to detect underlying behavior patterns, increase ductility, reduce inter-storey drift, and achieve higher levels of performance in these frames. This paper investigates and presents numerical results for a newly introduced hybrid seismic resisting configuration using nonlinear cyclic and nonlinear time history analysis. This hybrid mechanism utilized a strong-back truss with shear links instead of the usual buckling braces in order to act as structural fuses. The strong-back part of this system utilizes a truss with strong braces that span the structure's height vertically to delay or eliminate soft-storey behavior and mobilizes all the shear links throughout the building's height. For this research, three different steel braced frames that use diverse bracing configurations were scrutinized, along with a typical strong-back system. Additionally, a new hybrid system that merges a strong-back with shear links at all levels was examined and compared to other systems. Results showed that this hybrid system can be a successful technique for preventing the soft-storey behavior. Moreover, the utilization of shear links as structural fuses in combination with strong-back frames has the potential to improve the seismic performance of conventional strong-back frames by engaging all of the links and utilizing the entire fuses' energy dissipation capacity.

Mechanical Properties and Influence Factors of Ordinary Shear Links

The current specification requires the same limiting values of inelastic rotation and the overstrength factor for shear links with a length ratio less than 1.6. However, recent studies have shown that the mechanical properties of ordinary shear links with a length ratio ranging from 1.0 to 1.6 are obviously different from those of very short shear links with a length ratio less than 1.0. Additionally, shear links made of different steel materials have differences in mechanical properties. Based on Q345 steel, three ordinary shear links with a length ratio of 1.36 were designed to intensively explore the influence of stiffener configurations and spacing on mechanical properties. Under cyclic loading tests, the failure modes, hysteresis curves, skeleton curves, secant stiffness curves and energy dissipation capacities of shear link specimens were recorded. The results show that the overstrength factor and inelastic rotation of specimens SL-1 and SL-2, which had different stiffener configurations, reached 1.59 and 0.10, while those of specimen SL-3, which had wider stiffener spacing, reached 1.48 and 0.07, which showed that varying the stiffener configuration has no obvious effect, while relaxing stiffener spacing can result in severe buckling of the web. Additionally, its bearing capacity, inelastic rotation, secant stiffness and energy dissipation capacity reduced. Hence, the stiffener spacing should satisfy the requirements of the specification and not be too wide. Based on ABAQUS software, finite element models of ordinary shear links proved to be accurately consistent with test specimens in terms of mechanical properties. On this basis, 114 numerical models of ordinary shear links with different length ratios, stiffener spacings, flange-to-web area ratios, flange strengths, web depth-to-thickness ratios and stiffener thicknesses were designed to study the influence on the overstrength factor.

Enhancing the seismic performance of a concentrically braced reinforced concrete frame using an I-shaped shear link made of low yield point steel

Enhancing the seismic performance of a concentrically braced reinforced concrete frame using an I-shaped shear link made of low yield point steel

Lateral Load Behavior of Self-centering Frame with Y-Eccentrically Braced Substructure: An Experiment and Numerical Analysis

A novel self-centering frame with Y-eccentrically braced structure (SC-YEBFs) has been proposed in this paper to solve the problem that the storey drift of structure may exceed the specified limit in standards when self-centering beam-column joints are applied in high-rise and larger spans buildings, and the SC-YEBFs not only has the self-centering performance of self-centering frame system, but also has the high lateral stiffness and energy dissipating capacity of Y-Eccentrically braced frame. To study the lateral load behavior and influencing factors of SC-YEBFs, cyclic loading tests of two scaled specimens of SC-YEBFs substructure (SCS) were conducted, and seven finite element models corrected by the experiment were established to perform parametric analysis. The experiment and finite element analysis results indicated that the shear link has greatly increased the lateral stiffness and energy dissipating capacity of the self-centering structure, at the same time, it has maintained a good self-centering performance and replace ability. With an increase in the cross-sectional area and initial prestress of post-tensioned steel strands, the lateral load capacity and self-centering performance can be improved. The self-centering performance can be effectively improved by reducing the friction coefficient at the rotation connections. SC-YEBFs further extending the application field of self-centering structural systems, and making it possible to be applied to high-rise and larger spans structures.