Vertical Shear Link Research Articles

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.

Enhancing the cyclic performance of shear links using longitudinal stiffeners

Shear links constitute the most crucial part of eccentrically braced frames. Their main responsibility is to dissipate the earthquake input energy away from the main structural members; therefore, keeping them responding within the elastic stage. However, the rotation capacity of vertical shear links directly influences the allowable interstorey drift of the eccentrically braced frame and the energy dissipation capacity. To enhance their rotation capacity and performance, transverse stiffeners in vertical shear links are proposed to be replaced with longitudinal stiffeners in this research. A numerical study is conducted, using Ansys Workbench, on fourteen shear links with different parameters to investigate their cyclic behaviour. The considered parameters are the stiffener configuration (transverse or longitudinal), web thickness, stiffeners number, stiffeners thickness, flanges width, and web aspect ratio. The influence of these parameters on the failure mode, hysteretic response, mechanical parameters (strength, rotation capacity, etc.), ductility, cyclic web shear buckling, and energy dissipation is analysed and discussed. The results demonstrate that longitudinally stiffened shear links surpass conventional transversely stiffened ones in terms of strength, overstrength, rotation capacity, ductility, web shear buckling resistance, and energy dissipation. Additionally, it is found that the current design provisions of EN 1998–1 cannot accurately predict the yield shear strength of longitudinally stiffened shear links. Moreover, numerous remarks involved with the influence of different parameters on the cyclic performance of longitudinally stiffened shear links are presented and discussed.

Seismic performance assessment of eccentrically braced steel frame using demountable-metallic-corrugated-shear-panel dampers

In this study, the demountable-metallic-corrugated-shear-panel damper (DCSPD) were investigated experimentally and numerically. Based on the quasi-static cyclic loading experiment of the DCSPD, the influences of different corrugation directions, shear panel thickness, and flange plate thickness on the seismic performance of the damper were discussed in detail. It is found that the variation of the shear panel thickness has a significant effect on the performance of the damper, the high stiffness of the corrugated shear panel causes the oblique buckling deformation to deflect along the direction of the principal stress and to develop at an acute angle to the crest line, which makes the failure modes of the horizontal corrugated shear panel damper (DCSPD-H) and the vertical corrugated shear panel damper (DCSPD-V) significantly different. Then, the multilinear hysteretic model of the DCSPD was established based on the peak-oriented modified Ibarra-Medina-Krawinkler model. In addition, a five story eccentrically braced steel frame with a vertical shear link was used to verify the application effect of the DCSPD on structural vibration control. The dynamic analysis results show that the DCSPD could significantly improve the seismic resilience performance of the structure, compared to the reference steel frame, the performance levels of the improved steel frame with damper showed significant improvements.

Retrofit of RC buildings using vertical shear links and hybrid connections

This study employs a retrofit system with a vertical shear link inside a steel frame to improve the structural behavior of an existing reinforced concrete (RC) frame. The steel frame is connected to the RC frame through a hybrid connection system. The hybrid connection not only provides a rigid, strong connection between the steel and RC frames but also increases the shear strength of RC columns and beams. It is referred to as a hybrid connection in light of such combined measures. The connection is composed of thin steel plates, bolts, and infilling grout. This study tested four one-bay one-story RC frames. One of the RC frames was the benchmark, while the three remaining RC frames were retrofitted under different schemes. The scale factor of the frames was set to 1/3 ∼ 1/4 to model a low-rise RC building. The experimental results of the retrofitted RC frames by vertical shear links demonstrated that the boundary steel frame played a key role in obtaining a stable hysteretic response. Moreover, the hybrid connection strongly withstood the shear force between the RC frame and the steel frame. A series of calculation approaches were proposed to find the lateral strength of retrofitted frames under different failure mechanisms. The calculated lateral strengths were observed to agree with the experimental results.

FEM Analysis of Steel Eccentric Braces for Seismic Retrofitting

The paper discusses issues about the finite element modelling of steel eccentric braces with vertical shear links used as hysteretic dampers to improve the seismic performance of existing reinforced concrete (RC) buildings. To this end, eccentric bracing systems have been designed for seismic upgrading of a case-study existing RC school building in Italy. Multiple finite element modelling approaches are described, using both frame and shell finite elements, various steel stress strain relationships, as well as including both geometrical imperfections and residual stresses. Numerical models were built using two commercial structural analysis programs, SAP2000 and Ansys, and one open-source software, Code_Aster. The numerical study allowed to (i) quantify values of the plastic overstrength factor of the considered shear links; (ii) evaluate the overall system stability and general inelastic response; (iii) compare various modelling approaches.

Seismic Performance of Eccentrical Braced Frame Retrofitted by Box Damper in Vertical Links

Passive control methods reduced the vulnerability of structures to earthquakes by decreasing the seismic demand and improving structural plasticity. One of the passive control systems is the eccentrically braced frame with a vertical shear link (V-EBF). The present study aims to direct the damage to the absorbing plates of the vertical link beam to allow the structure’s appropriate seismic performance and reparability. Yielding dampers are one of the most widely used types in systems and can provide perfect vibration control if used optimally. Different types of dampers were introduced and used; how to use them depends on the shape and the way they connect to the structure. This research investigates a new type of damper called box damper, an improved type of shear panel damper. The improvement in the way of connecting to the braced frame and the ease of using this damper in different situations are the features of this new damper. This research investigated the mechanism of these yielding dampers in structures and their strengths and weaknesses. In the next step in this study, a V-EBF with plates of thickness 4, 6, and 8 mm was analysed in the finite element software ABAQUS using the nonlinear static analysis and cyclic loading conditions. Some examples of this damper were attached to the braced frames to investigate the effect of using this damper on the seismic behaviour of the braced structures. The results show that the shear link performs like an electrical fuse absorbing all damage and plastic hinges so that other elements of the braced frame remain in their nonlinear elastic region. By increasing the thickness of the damper from 2 to 8 mm, the resistance increased by two times, and the flexibility of the structure had a noticeable change with the rise in thickness from 2 mm to 8 mm. Ductility increased from 38 to 75 mm.

Numerical Study on the Seismic Behavior of Eccentrically Braced Composite Frames with a Vertical Low-Yield-Point Steel Shear Link

An eccentrically braced composite frame with a low-yield-point (LYP) steel shear link is an efficient energy dissipation system that exhibits good mechanical properties. However, existing experimental studies have not fully demonstrated the superiority and applicability of the structural system. We present a structural mechanics and finite element model analysis of an eccentrically braced composite frame with a vertical shear link. The effect of the design parameters on the seismic performance of the structure is analyzed. First, a theoretical model of the mechanics of the structural system is established to provide a comprehensive description of the key parameters. Then, a finite element model is developed using the computer program ABAQUS to analyze the mechanical and energy dissipation mechanisms. Finally, the beam-to-column stiffness ratio, shear link web thickness, shear link web width and length, and diagonal brace stiffness are analyzed to determine their effects on the mechanical properties of the structural system. Furthermore, some design parameter values are suggested.

Seismic Response of 2-D Plane Framed Buildings Eccentrically Braced with Vertical Shear Links

Seismic Response of 2-D Plane Framed Buildings Eccentrically Braced with Vertical Shear Links

Experimental study on seismic behaviour of eccentrically braced composite frame with vertical LYP steel shear link

An experimental investigation is conducted to study the seismic behaviour of eccentrically braced composite frame (EBCF) with vertical shear links, which has a better repairability and replaceability compared with traditional EBCFs with horizontal shear links. Particularly, the low-yield-point (LYP) steel is applied in the shear links to verified its influence on the seismic performance of the EBCFs. Cyclic loads are applied to two composite frames respectively with a bare moment resisting frame system and with a dual system composed of the moment resisting frame and the eccentric bracing system, the comparison of results indicates that the eccentric bracing system can effectively increase the stiffness, strength and energy dissipation capacity of the composite frame, but has few effects on the force conditions on the ends of the primary beams and columns, both two specimens failed by the fracture and buckling of the bottom flanges of the primary beams at a story drift ratio of 1/38. Due to the low-yield-point property and high ductility of the LYP steel, the shear link starts to efficiently dissipate energy when the story drift ratio is only 1/300, and the shear link has reached an inelastic rotation capacity of 0.16 before failure. However, due to the strain hardening of the LYP steel, the shear link achieved an over-strength factor up to 2.78, and the over-strength property of the shear link has resulted an unignorable bending moment of the middle segment of the primary beam, the concrete slab in this area is severely damaged with a maximum crack width of 0.16 mm. Finally, the analysis of working mechanism and test data indicates that, the added stiffness, added strength, and added energy dissipation capacity by the eccentric bracing system are directly in proportional to the contribution of the vertical shear link, and formulas to evaluate the added damage of concrete slab are also given.

Development of a double-stage yielding damper with vertical shear links

This study proposes a novel hybrid damper called vertical links system with double-stage yielding (VLDY). The VLDY damper consists of two replaceable vertical shear links connected in series, located within a moment-resisting frame (MRF). When the MRF sustains lateral deformation, the minor link yields in shear. The inelastic shear rotation of the minor link increases till the engagement of the lockout mechanism. Thereafter, the inelastic deformation occurs in the major shear link, and the entire system enters the second yielding stage. The minor link can be adjusted to dissipate the input energy in relatively small inter-story drift levels during moderate earthquakes, and the major link maintains the structural integrity under severe earthquake ground motions. A validated nonlinear finite element modeling protocol in ABAQUS/standard was utilized to examine the applicability and cyclic response of the proposed system. The results showed that the VLDY device could provide stable energy dissipation capacity in a wide range of inter-story drift levels ranging from 0.3% to 4%. In addition, the cyclic secant stiffness, energy dissipation capacity, and equivalent viscous damping ratio of the VLDY-equipped frames significantly increased compared with those of the bare frames. Based on the results, a minimum free span-to-depth ratio of 7 has been suggested to ensure the prevention of the steep moment gradient on the story beams.

Response modification factors for dual moment-resisting frames with vertical links: Multilevel approach

Despite the growing applications of the performance-based design concepts for seismic design of structures, the response modification factors for structural systems proposed by the current design codes and standards do not generally consider different hazard and performance levels. Therefore, these factors are not directly applicable for performance-based design purposes. As a step to address this shortcoming, the present study aims to propose multilevel response modification factors for multistory dual moment-resisting frames equipped with eccentric braces and vertical links corresponding to different seismicity levels and performance targets. The concept of demand and capacity response modification factors is introduced, and these parameters are calculated for moment-resisting frame structures with 3-, 5-, and 7-stories before and after the addition of vertical steel shear links. It is shown that the calculated capacity response modification factors for the dual frames equipped with vertical links are generally higher than the demand response modification factors proposed by the design code for such systems under the design basis earthquake hazard level. This indicates the efficiency of the eccentric braces with the vertical links in improving the seismic reliability and performance of the moment-resisting steel frames. Based on the results of this study, the demand response modification factor for the studied dual lateral load-resisting system is calculated to be in the range of 7–10.

Seismic behavior of a two-level control system with double vertical shear links in series

To improve seismic behavior of structures, a two-level control system is proposed in this paper where by combining two vertical shear panels in series in a chevron bracing configuration, Double-Vertical Shear Panel, D-VSP is introduced. Utilizing two-levels of energy absorption for two different earthquake intensity levels, D-VSP is expected to beneficially change dynamic behavior parameters like strength, stiffness and damping ratio through increasing ductility. To validate research, a VSP is modeled in ABAQUS and related numerical results are compared to those of a previous experimental work. Pushover, quasistatic cyclic and seismic analyses are conducted on two models. The hysteresis curves show symmetric two-level behavior with stable strength and stiffness leading to increase ductility ratio up to 29.4%. Maximum displacement and maximum base shear under seismic loading decrease 5.91 and 11.18% respectively under moderate earthquakes when D-VSP system uses only first fuse, saving second fuse for severe earthquakes. However, in a strong earthquake, both of the shear panels absorb seismic energy and can control vibration better than conventional systems with one level control mechanism. The proposed system using a weaker panel can better control an extensive range of earthquakes as well as the earthquake with foreshocks.

Experimental investigation of smart shear dampers with re-centering and friction devices

Eccentrically braced frames (EBFs) with vertical shear links are lateral load resisting systems having considerable strength and ductility. In this study, an innovative hybrid damper, consisting of four shape memory alloy (SMA) plates, two friction devices, and six polyurethane springs, is proposed and evaluated as a replacement for the vertical shear link. The proposed smart shear dampers are designed to lessen the frequency and severity of deformation and damage to the main structure by earthquakes. Because the proposed smart shear damper is independent of the main structure, it can be repaired rapidly, which lowers the cost of maintenance. Other advantages include ease of assembly and installation. In this study, the seismic performance of the proposed damper is experimentally investigated and evaluated. Quasi-static cyclic loading with displacement control is applied to the side of the damper, and the components of the damper are considered individually. Eight shear dampers, including four SMA plates and four steel plates, are tested under identical loading protocols, and then the effect of each component is measured. The results show that the proposed SMA damper decreases residual displacement by 50%–95% depending on the type of damper system and that the polyurethane springs of the proposed shear damper provide considerable re-centering capability.

Reliability assessment of RC frames rehabilitated by eccentrically braces having vertical shear link

A considerable number of existing reinforced concrete (RC) structures need to seismic rehabilitation due to several reasons such as being designed just based on gravity loading and/or having an unsatisfactory level of ductility. One of the types of steel bracing can be referred to eccentrically braced frames with a vertical link. This system has some advantages such as an increase in ductility, stiffness and lateral strength, the ability to adapt to the architecture, and also the minimum weight added to the structure. In this study, reliability analysis assessment of two existing 3-, and 9-story RC frames in two cases including original and rehabilitated with an eccentrically braced frame having a vertical link is presented. Two limit states are defined as: maximum roof displacement and maximum inter-story displacement. The seismic behavior of frames was assessed by nonlinear static pushover analysis with finite element program OpenSees in two performance levels, including collapse prevention and life safety. Five random variables represented the variability in resistance of concrete material, bars and steel profiles yield stress, beams height, columns dimension, and also bars cross-section. Sensitivity analysis was carried out to recognize the effect of random variables on the reliability index. The reliability analysis was performed by two different methods: Hasofer–Lind and Monte Carlo with 25, 100, 1000, 10,000 and 100,000 simulated samples by considering two distributions including Normal and Log-Normal. Finally, a comparison between two common reliability methods was carried out in order to select the most appropriate method for performing the best seismic performance reliability analysis of RC frames rehabilitated by the proposed system.

Seismic performance of chevron braced frames with shape memory alloy vertical shear link

SummaryChevron braced steel frames with vertical shear link have reliable displacement dependent dampers with sufficient strength and ductility to dissipate energy of strong earthquakes through inelastic mechanisms. In this study, shape memory alloy with its superelastic behavior is utilized as material of vertical shear link to improve the ductility characteristics of the system and decrease residual displacements in the structures due to its self‐centering capability. Nonlinear time‐history, incremental dynamic analysis, and dynamic pushover analysis techniques are used to investigate the behavior of two different four‐ and eight‐story frames with steel vertical shear link (STVL) and shape memory alloy vertical shear link (SMVL) under various earthquake records. The results show that there is a negligible residual displacement in the structures with SMVL, although considerable residual displacements can be observed in the structures with STVL. For instance, when the eight‐story frame is subjected to the Northridge earthquake, a 12‐cm residual displacement is observed in the structures with STVL, whereas the structures with SMVL might experience just 3‐cm residual displacement.

Re-centering Capability of Inverted-Y Dual Eccentrically Braced Frame

Repair process of structures after a strong earthquake is often governed by the level of permanent deformation experienced by these structures during the shaking event. These phenomena drastically affect the repair cost in addition to the prolonged time needed to accomplish this complex process. In this research the feasibility of utilizing the Re-centering capability of a dual system consisting of steel special moment resisting frame ‘SMRF’ and Inverted-Y geometric configuration eccentric braced frame ‘EBF’ to create an easy-repairable structure after a severe earthquake was examined. In this structural system a removable vertical shear link (i.e. using bolted connection) which is part of the EBF will act as a fuse to dissipate the earthquake input energy while the SMRF will act as a Re-centering system that will force the structure to return to its original position after removing the shear links by intentionally keeping it in the region of elastic behavior. The proposed system’s seismic performance was evaluated through performing series of pushover analyses under different loading patterns, and time history analyses under the action of seven earthquakes. Furthermore, the design provisions provided in the American Code “Seismic Provisions for Structural Steel Buildings” ANSI/AISC 341-10 were verified against the required response and extra recommendations for designing and detailing such structural system were introduced in order to achieve the required behavior. The performed study showed that during severe earthquakes the majority of the inelastic actions were localized within the shear links only while the SMRF behaved almost elastically with few exceptions. In addition, the study provided design and detailing recommendations to create an easy repairable structure after severe earthquakes.

Effect of combined vertical and horizontal shear links on nonlinear behavior of eccentrically braced frames

In this paper, the nonlinear behavior of a proposed eccentrically braced frame (EBF) system with combined vertical and horizontal shear links (CVH-EBF) is investigated. Pushover analysis is first performed on the two types of the shear links, using 3D nonlinear shell elements model, to derive their shear-deformation behavior laws. Then, 2D spring-link elements are defined, by multilinear idealization of the behavior laws, and inserted in 2D frame model representing the CVH-EBF. Finally, a parametric study is conducted to examine the effect of the vertical link (inverted Y-scheme) stiffness on the whole frame system nonlinear behavior, on the out-link elements internal forces, and on the appearance of plastic hinges and their locations. All the results are compared to those of the conventional EBF system. It is shown that the vertical shear link significantly improves the seismic capacity of the system and induces reduction in other frame elements internal forces, particularly in shear horizontal link. Adding a vertical link to an EBF system may be an efficient solution to improve its global capacity. This link is especially interesting since it can be easily replaced after damage.

Experimentally and analytically study on eccentrically braced frame with vertical shear links

SummaryThe excellent hysteretic behavior of eccentrically braced frames (EBFs) using shear links have made these systems an effective alternative for both moment resisting frame as well as concentrically braced structures. Generally, horizontal shear links are located either at the middle or at the ends of the beam. However, large deformation of the shear links in those beam must be accepted under severe earthquakes. In those instance in which the beam have to remain elastic, vertical shear links should be designed underneath the beam thereby transferring the region of plastic deformation to location where they are tolerable and post‐earthquake repair or replacement of damaged parts is easier. In this paper, seismic behavior of vertical‐EBF (V‐EBF) have been considered experimentally and analytically. The required relation to design of the system have been proposed. In addition, to predict nonlinear behavior of V‐EBF systems, an analytical model including kinematic–isotropic strain hardening for shear, only kinematic strain hardening for moment, has been presented. Results showed a good convergence of the presented analytical model (with an upper bound for yielding surface to the V‐EBF) with experimental results.

PUSHOVER ANALYSIS OF REINFORCED CONCRETE BUILDING WITH VERTICAL SHEAR LINK STEEL BRACES

In recent decades, steel cross bracing has been used as a conventional method to retrofit concrete buildings. Most of the cases utilized concentric steel braces system. However, studies concerning the behavior of RC frames with eccentricity steel bracing are quite limited. In this research, three types of structures incorporating special moment frames, RC structure with invert V braces and RC structures with vertical link beams with different stories were modeled through SAP 2000 and analyzed by considering nonlinear static analysis (pushover). Results revealed that invert Y steel braces (vertical shear links) system is an alternative way to construct a ductile structure with great lateral stiffness. It was also found that the axial force in braces is controlled by the behavior of the vertical link beam.

Seismic performance of high-strength steel fabricated eccentrically braced frame with vertical shear link

In high-strength steel fabricated eccentrically braced frame with vertical shear link (HSSEBF-VSL), the vertical shear links use conventional steel while beam and column use high-strength steel (HSS). Using HSS for beams and columns in HSSEBF-VSL can reduce steel weight and increased economic efficiency. In this paper, static tests for two 1:2 length scaled HSSEBF-VSL specimens with one-bay and one-story were carried out, including one static pushover test and one cyclic loading test. The failure mode, load-bearing, ductility and energy dissipation capacities of the specimens were studied through the two static tests. Shake table test of a 1:2 length scaled three-story HSSEBF-VSL specimen was used to study its dynamic responses and dynamic strain responses of the vertical shear links. In addition, the finite element models of several HSSEBF-VSL and conventional EBF with vertical shear link (EBF-VSL) buildings were established for seismic effects. Nonlinear pushover and dynamic analyses were conducted to compare their seismic performance and economy. The test results indicated that the specimen with one-bay and one story had reliable lateral stiffness, ductility and energy dissipation capacity. The three-story specimen had good lateral stiffness and there was no dangerous of collapse for the specimen during the severe earthquakes. Under the same design conditions, the seismic performance of HSSEBF-VSL was slightly lower than that of EBF-VSL if it was designed to match the member section strength of EBF-VSL, but it used less steel than that of EBF-VSL, which could reduce the usage amount of steel in HSSEBF-VSL.