Performance Analysis of Eccentrically Braced Frames (EBF) using Metallic Yielding Damper (MYD) with Hysteretic Steel Damper (HSD) Type

Eccentrically Braced Frames (EBFs) are seismic-resistant steel structures with horizontal or vertical energy-dissipating links designed to enhance ductility. To promote sustainability, future designs are moving toward easily replaceable structural systems that enable rapid post-earthquake rehabilitation. However, EBFs with horizontal links present challenges in repairing damaged links due to interference with other components, particularly beams. As an alternative, vertical links offer the potential to serve as "replaceable elements." Despite this advantage, no specific design guidelines currently address the lateral support requirements for EBFs with vertical links, unlike the horizontal ones. This study analyzes the inelastic behavior of EBFs with vertical links using numerical methods based on the finite element method. The results indicate that vertical link length classification and capacity design methods specified for horizontal links also apply to vertical links. This is evidenced by the shear force values in the three samples representing short, medium, and long links, resulting in values of 2.15Vp, 1.32Vp, and 1.13Vp, respectively, with the shortest link classified as a shear link. The degradations of the horizontal load capacities due to the application of initial deformation, simulating the first buckling mode, are less than 0.01% for all configurations. This verifies that without lateral supports, the vertical links could still effectively dissipate energy through flexural and/or shear yielding without lateral instability issues.

This study investigates the seismic performance of reinforced concrete Eccentrically Braced Frames (EBF) with vertical and horizontal link beams subjected to cyclic loading. The main objective is to compare strain histories and evaluate energy dissipation in vertical and horizontal link configurations. Experimental results indicate that vertical links, especially those with shorter lengths (15 cm), exhibit higher strain values, leading to significant plastic deformation and enhanced energy dissipation, though at the cost of increased damage and repair needs. Conversely, horizontal links remain largely within the elastic range, maintaining better structural integrity but offering less energy dissipation during seismic events. The CBF (Concentrically Braced Frame) control specimen showed minimal deformation and lower energy absorption. The findings suggest that vertical links are more suitable for energy dissipation in seismic design, while horizontal links offer greater durability and lower post-event maintenance. The balance between energy absorption and repairability is crucial for optimizing EBF systems in earthquake-prone areas. (explain the findings related to the purpose of this paper: to determine the effects of link orientation on strain distribution, energy dissipation, and structural integrity during seismic events).

Given the fact that some reinforced-concrete (RC) buildings have not met resistance against seismic loads, it is mandatory to adopt a suitable and economically cost-efficient method to retrofit them. One appropriate method is application of steel Eccentrically Braced Frames (EBFs). This article is aimed at evaluation of seismic performance of retrofitted reinforce-concrete buildings by EBFs with single and knee links. For evaluation of modeled buildings, different editions of the Iranian Seismic Code (Standard No. 2800) were reviewed. To this end, three Moment-Resisting Frames (MRF) of four-, eight-, and twelve-story buildings with medium ductility were modeled where they were designed for seismic loads based on Standard 2800, 2nd edition. In order to evaluate buildings under modified seismic loads, models were seismically reloaded based on the Standard 2800, 3rd edition. Reanalysis showed that the stress ratios exceeded 1 in most columns. Therefore, buildings were retrofitted using EBFs with knee and single vertical links and their seismic performance were evaluated using nonlinear static analysis. Results indicate that knee bracing systems are more efficient than bracing systems with vertical link in increasing rigidity and controlling displacements, while they significantly reduce ductility. For example, application of knee bracing system in the twelve-story building can cause an 11% reduction in displacement in comparison to bracing systems with vertical links.

Topology optimization of vertical shear links in eccentrically braced frames

Background: Different bracing systems of steel Eccentric Braces (EBs) and steel-concrete Buckling-Restrained Braces (BRBs) can be used in steel frames in order to make the frames stronger in resisting lateral loads. These steel frames with EBs or BRBs are generally called Eccentrically Braced Frames (EBFs) or Buckling-Restrained Braced Frames (BRBFs), respectively. Objective: This study aims to investigate steel frames with bracing systems of steel EBs and steel-concrete BRBs having moment link. Methods: The EBFs and BRBFs are nonlinearly analysed employing the finite element software ABAQUS. Experimental tests of the EBF and BRB are utilised for the validation of their modelling. The modelling is validated by comparing the modelling results with experimental tests results. Then, an EBF and a BRBF are designed having moment link. The extreme earthquake records of Tabas, Chi-Chi, and Northridge are selected for the dynamic analyses of the EBF and BRBF. The validated modelling method is applied to analyse the designed EBF and BRBF under the selected earthquake records. Results: The achieved results from the analyses are lateral displacements, base shears, and energy dissipations of the EBF and BRBF and moment link rotations. These results are compared and discussed. Conclusion: It is concluded that the hierarchy of the lateral displacements of the analysed EBF and BRBF, having moment link, is related to the Tabas, Chi-Chi, and Northridge records because the lateral displacements of the frames are directly proportional to the peak ground accelerations of the records, and there is the same hierarchy for the records in terms of their peak ground accelerations. Lower lateral displacements are witnessed for the BRBF than the EBF subjected to the Tabas and Chi-Chi records. However, larger lateral displacement is observed for the BRBF than the EBF under the Northridge record. The same procedure as the lateral displacements is also revealed for the effectiveness of the BRBF with regard to its link rotations compared with the EBF. Moreover, the BRBF improves the base shear capacities and energy dissipations of the frame compared with the EBF. Consequently, the BRBF is generally demonstrated to be superior to the EBF from the structural performance point of view. Thus, the BRBF can be used more efficiently in structures subjected to large lateral loads compared with the EBF.

EBF-V bracing is highly attractive due to its good seismic performance in high seismic zones. Vertical link beams as a component are capable of high elastic displacement and ductility to absorb lateral forces through shear-bending collapse mechanisms. However, the lateral load capacity of the bracing has to be sacrificed as it tends to decrease. The present study focuses on the capacity and lateral behavior of reinforced concrete eccentrically braced frame (EBF) with vertical link beam and tighter reinforcement spacing in the link beam in combination with GGBFS. GGBFS at 20% can improve the mechanical properties by reducing the pore number of the concrete due to the smaller particle size of OPC.This study uses CBF-V as a control to investigate the seismic behavior of tightly spaced transverse reinforcement (75 mm) in EBFs’s vertical link beam with eccentricities of 15 cm and 25 cm. In addition, the role of GGBFS was also observed through the displacement and ductility of the frame. As a result, the CBF has the highest plasticity. However, the tight reinforcement spacing of the vertical link beam in the EBF-V-15 results in the highest restraint, resulting in excellent stiffness and ductility through earthquake absorption with a shear collapse mechanism. In addition, GGBFS also plays a role in improving the collapse mechanism, which is characterized by large elastic displacement and high ductility.

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.

This study investigates the lateral displacement and lateral load capacity of two types of structural systems: Moment Resisting Frames (MRF) and Eccentrically Braced Frames (EBF), in relation to varying numbers of stories. The analysis was performed using a pushover method, evaluating displacement and shear capacity across structures with 3, 6, 9, and 12 story. The results indicate that as the number of story increases, the lateral displacement in both systems increase, but EBF structures exhibit significantly reduced displacement compared to MRF structures. Specifically, EBF reduces displacement by 84.46% for 3 story and by 86.12% for 12 story. Conversely, the Lateral Load capacity of EBF decreases as the number of story increases, but remains higher than that of MRF structures. EBF increase lateral load Capacity by 76.54% for 3 story and by 68.61% for 12 story. Performance evaluations, conducted according to FEMA 356 standards, reveal that MRF structures maintain a Life Safety (LS) level of performance, with some buckling in beams and failure at moment connections, while EBF structures perform at an Immediate Occupancy (IO) level, showing minimal damage. These findings underscore the advantages of EBF in terms of displacement reduction and overall performance in multi-story buildings.

Given their unique characteristics, Shape Memory Alloys (SMAs) have significant potential for use in different areas of engineering. The phase shift characteristics of these alloys allow them to memorize a certain shape, and if deformed, revert back to that shape through a thermal process. Given the vast potentials of SMAs, they can be utilized to address the limitation of conventional eccentrically braced frames (EBFs) with vertical links in order to achieve better residual and maximum interstory drifts. This paper presents a vibration control system equipped with SMAs to achieve improved operational domain. The Compared to conventional EBFs, the proposed system named recentering damping device (RDD) is easy to fabricate and implement and allows for the redesign of fuse members. A numerical analysis is performed for a 9-story steel frame building using nonlinear analysis program OpenSees to evaluate the system performance. Results of time history analysis demonstrate better self-centering behavior and lower residual interstory drifts of the proposed system as compared to EBF.

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.

An analytical model for inelastic cyclic response of eccentrically braced frame with vertical shear link (V-EBF)

Using vertical links in eccentric braced frames is one of the best passive structural control approaches due to its effectiveness and practicality advantages. However, in spite of the subject importance there are limited studies which evaluate the seismic reliability and response reduction factor (R-factor) in this system. Therefore, the present study has been conducted to improve the current understanding about failure mechanism in the structural systems equipped with vertical links. For this purpose, following definition of demand and capacity response reduction factors, these parameters are computed for three different buildings (4, 8 and 12 stories) equipped with this system. In this regards, pushover and incremental dynamic analysis have been employed, and seismic reliability as well as multi-level response reduction factor according to the seismic demand and capacity of the frames have been derived. Based on the results, this system demonstrates high ductility and seismic energy dissipation capacity, and using the response reduction factor as high as 8 also provides acceptable reliability for the frame in the moderate and high earthquake intensities. This system can be used in original buildings as lateral load resisting system in addition to seismic rehabilitation of the existing buildings.

Eccentrically Braced Frames (EBFs) have been widely used in the last decades and proved their efficiency to resist strong earthquake intensities by providing suitable ductility and lateral stiffness. Using the PBPD method for the design, EBFs can fulfill the target performance objectives under major earthquakes. The most commonly used configurations are the K-shaped and the recent Y-shaped EBFs, which have the advantage that the links are independent of the beam and can be easily replaced after an earthquake without serious damage to the beam and slab. This study focused on the lateral reliability of both systems under seismic loading. Nonlinear static pushover and Incremental Dynamic Analysis (IDA) were performed on 5-story and 10-story K- and Y-shaped EBFs. A series of 14 near- and 7 far-field seismic records were considered to analyze and compare the inter-story drifts of both systems using the Seismostruct software. Moreover, Peak Ground Accelerations (PGA) and the different performance levels were also examined.

The Theory of Plastic Mechanism Control (TPMC) has been recently extended to the case of Eccentrically Braced Frames (EBFs) with inverted Y-scheme, i.e., EBFs with vertical links. In this paper a further validation of the design procedure, based on TPMC, is provided by means of Incremental Dynamic Analyses (IDA) pointing out the fulfilment of the design goal, i.e., the development of a pattern of yielding consistent with the collapse mechanism of global type where all the links are yielded and all the beams are yielded at their ends while all the columns and the diagonal braces remain in elastic range with the only exception of the base sections of first storey columns. In particular, a study case is designed according to both TPMC and Eurocode 8 provisions and the corresponding seismic performances are investigated by both push-over and IDA analyses. The results show the different performances obtained in terms of pattern of yielding, maximum interstorey drift, link plastic rotation demand and sharing of the seismic base shear between the moment-resisting part and the bracing part of the structural system. The seismic performance improvement obtained by means of TPMC, compared to Eurocode 8 provisions, is pointed out.

Eccentrically Braced Frame (EBF) is an excellent steel frame system for resisting earthquake forces. This frame shows good performance in terms of stiffness and has excellent ductility. When it is subject to a severe seismic event, the links undergo inelastic deformations and become the primary source of energy dissipation. However, the performance of EBF is strongly influenced by the length of the links that are an essential part of the EBF system. Links should be limited not be too short or too long because it relates to the stiffness and ductility of the frame. The study of EBF on the 80-90s also limits the ratio both of e/L not exceed 0.5 and the diagonal brace angle between 40°- 60°. This research will review the influence of the length of the links varied from the e/L ratio of 0.005 to 0.38. This variation will divide the links into three types of yielding, i.e., the short link, intermediate link with shear dominance, and intermediate link with bending dominance. In this study, the behavior of various link lengths on Eccentrically Braced Frame will be evaluated using finite element analysis using MSC Patran and Nastran. The structure is modeled as a one-dimensional D-Braced EBF type that is given static monotonic load with displacement control. The results obtained in the form of load-displacement curves which will be analyzed in strength and ductility. In addition, an ultimate load normalization curve will be generated to obtain the load pattern for the various link length. The curve shows that the ultimate load on the EBF will decrease if there is an increase in link length. The significant decrease occurs when e/L > 0.2.