Eccentric Bracing Research Articles

Seismic Capacity of Reinforced Concrete Eccentric Braced Frame (EBF) With Vertical Link Using 20% GGBFS

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.

Seismic Performance Evaluation of Steel Braces in Enhancing the Lateral Load Resistance of RCC Flat Slab Structures

This research paper conducts a comprehensive investigation into the seismic performance of reinforced concrete flat slab structures, employing different configurations of steel bracing systems. The seismic behavior of flat slab buildings with 5, 7, and 9 stories is scrutinized through Equivalent Lateral Force (ELF) analysis and Response Spectrum Analysis (RSA). The study delves into the efficacy of various bracing configurations, encompassing X-bracing, eccentric bracing, and knee bracing, in augmenting the lateral load resistance of these structures. Additionally, the research evaluates the influence of bracing systems on crucial structural response parameters such as displacement, drift ratio, base shear, and fundamental natural period. Keywords: steel bracing, seismic performance, flat slab structures, comparative study

Shaking table test and numerical analyses of a multi‐story traditional tower‐style building

AbstractThe traditional tower‐style building (TTSB) is an innovative structural form constructed in modern cities imitating the overall appearance of ancient timber pagodas, and it is an extraordinarily cultured high‐rise construction. The limited stipulations for high‐rise TTSBs in the seismic design code pose challenges in assessing the reliable performance of the unique structure subjected to severe earthquakes. This paper presents the shaking table test and numerical analyses of a 1/15‐scale 13‐story TTSB specimen with an integral tower height of 5.36 m, which is a steel frame‐braced core‐tube structure consisting of seven bright floors (built‐out stories evident from the outside, BF) and six dim floors (built‐in stories not apparent from the outside, DF), with transition columns and stiffening trusses around the exterior perimeter. The experimental results showed that the tested tower‐style building had excellent seismic performance and reliable structural integrity. It only experienced minor damage when subjected to extremely high‐intensity motions. The interstory drift, dynamic strain, and floor acceleration response of the core‐tube region with eccentric steel braces were more significant under severe excitation than those with cross‐centered symmetric steel braces. The vertical reaction increased at the upper floor of the tower under vertical acceleration, and differences in the dynamic response of the middle and upper floors were much more apparent after the test. Moreover, 3D numerical simulation models of the tested tower were established and validated against the test responses. Successively, the validated numerical model was used to investigate the influence of the transition column at different floors on the peak interstory drift response and the relevant strain distribution, and the proposal for a proper position of the transition column was recommended at the end.

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.

Analysis and optimization of brace system in scaffold

Scaffold consists of horizontal components, vertical components and lateral braces, while the lateral stiffness of structure is mainly provided by brace system. Brace system can be classified into three groups: concentric brace, eccentric brace and knee brace. Concentric brace enables to offer greater stiffness, for providing direct load transfer. Eccentric brace and knee brace belong to ductile system, maintaining stability by energy consumption braces. Eccentric brace dissipates energy by deforming and buckling, while knee brace disposes energy by form a plastic hinges. Concentric brace is a common way for enhancing lateral stiffness in scaffold. Current studies aimed to investigate detail parameter effects in one brace pattern, while few comparative studies were carried on multiple brace pattern. In this paper, a simplified simulation method was proposed. Throughout simulation analysis, some regulations of brace arrangement were summarized, which provides a guidance during the scaffolding design and optimization process.

Seismic Performance of Iwf Flexural Link in Chevron Eccentrically Brace Frames (V-EBFs) with Different Stiffener Space

Eccentrically Braced Frames (EBFs) are the structural systems that are recommended to be constructed in Earthquake Hazard Areas. This system combines good characteristics in withstanding the seismic load, i.e., stiffness, ductility, and dissipation energy. Link is a component in EBFs that play the role of the seismic energy dissipator. As far, several studies have been conducted to enhance the link performance, but the information is still limited. This study observed the structural performance of the IWF flexural link, where this link will experience failure at the flange due to seismic energy dissipation. The investigation was conducted by establishing three Finite Element (FE) models of flexural link. Each link was designed with the same length, i.e. 1000 mm. Three-link models were distinguished by the differences in web stiffener configuration, i.e., non-stiffener link, 250 mmstiffener spacing link, and 100 mm-stiffener spacing link, respectively. All models were examined under cyclic loading with yield displacement controlled. The research discovered that adding the web stiffener on the IWF flexural link significantly escalated the EBFs’ seismic performance, i.e., strength, stiffness, ductility, and dissipation energy. The best seismic performance was presented by a 100 mm-stiffener spacing link. Accordingly, it is indicated that arranging the web stiffeners at the narrow space in the IWF link can be suggested to improve the seismic performance of EBFs.

Seismic effect of steel bracing systems in RC frame models

A bracing system is a common type of construction used in multi-storyed buildings for strengthening the structure. This type of technique may be used for retrofitting of existing building. Steel braced frame is used to resist earthquake loads in multistoried buildings. Steel bracing systems are affordable, simple to install, take up less space and may be designed in a variety of ways to achieve the desired strength and stiffness. In this study, three different heights of building model were considered to analyze the effect of bracing systems. For the study, each model is considered to be different bracing system viz. X-bracing, diagonal bracing, inverted V-bracing, eccentric bracing. The bracing is provided for peripheral columns of each model. Using STAAD Pro software, the building models were analyzed for seismic zone IV according to IS 1893: 2002. According to the results, the X type of steel bracing significantly increases structural rigidity and reduces the maximum interstorey drift of the frames. Global and story drifts are used to analyze the building's performance.

Numerical and analytical studies for a novel steel brace retrofit system

To upgrade the existing RC frame structure with insufficient seismic design, a novel and advanced gapped eccentric steel brace (GESB) system was proposed. The finite element modeling methods based on fiber cross-section and macroscopic models were established and calibrated through the test results. The impact of three key design parameters, including axial load ratio (ALR) isolation thickness (IT) and Clamping Joint Spacing (CJS), was investigated. Based on the results of the numerical analysis, it is recommended that the drift demand controlled by IT should be between 0.6% and 1%, while the CJS should be 1/4 to 1/3 in response to the ductility and strength requirements. And the effect of ALR on the retrofitted frame can be ignored. An analytical method was also presented, which proved to be accurate for estimating the mechanical response of the retrofitted frame by comparison with the experimental and numerical response.

Behavior of a Multi-Story Steel Structure with Eccentric X-Brace

Eccentrically Braced Frames (EBFs) outperform moment-resisting frames in seismically active regions because of their strength, stiffness, energy dissipation, and ductility. Conventional bracing systems, such as X, Y, V, or K types, are utilized to enhance structural integrity. This study employs computational modelling to analyze multi-story steel buildings featuring an eccentric X-brace system. In this investigation, 120 multi-story steel frame buildings were selected. These multi-story structures comprise six-, nine-, and twelve-story geometries. ETABS built a full-scale FE model of multi-story structures. The study's parametric variables are the X-brace eccentricity, steel X-brace section size, and X-braced placement. Steel X-braces may have an eccentricity of 500, 1000, or 1500 millimeters. The ETABS model was validated when its findings matched experimental data. According to the data, the eccentric X-brace increases top-story displacement more for 6-story multi-story structures than for 9- and 12-story ones. Eccentric X-braces reduced lateral stiffness, allowing more significant floor movement. Eccentric and diagonal braces offer less lateral rigidity than concentrically braced frames due to their flexibility. Eccentricity reduces stiffness, even if the X-braced component has a larger cross-section. EBFs may migrate horizontally. Since the EBF absorbs more energy, changing the X-brace section size and eccentricity affects its ductility.

Seismic performance and damage evolution of RC frames retrofitted by the novel GESB system: A numerical study

A novel gapped eccentric steel brace (GESB) system was developed to enhance the seismic performance of existing reinforced concrete (RC) frame structures. To thoroughly investigate the mechanism and damage mode of the novel retrofitting system, numerical analysis was conducted on retrofitted frames with various brace eccentricity configurations, using a comprehensive multi-scale finite element model. Six suitable damage indices were defined to carry out the structural damage evolution study during the whole loading process. On this basis, a simplified damage model was developed. The results demonstrated that GESB effectively modified the mechanical mechanism and failure modes of the frames. The brace eccentricity configuration exerted a significant influence on the structural strength, stiffness, and ductility. With regards to both of strength and ductility requirements, an eccentricity range of 0.3 to 0.4 was recommended. The proposed simplified damage model was used to indicate the allowable drift ratios associated to performance levels, which were found to be very variable with various eccentricity configurations. The outcomes are essential and timely for design decision of RC frames retrofitted by GESB.

Sustainable Seismic Design of Triple Steel Structures

Dual systems composed of steel Moment Frames (MFs) and Eccentric Braced Frames (EBFs) are some of the most popular earthquake-resisting structures (ERSs) worldwide. Triple systems are similar to ERSs but with added hybrid rigid rocking cores (HRRCs) that render the trio sustainable against seismic events. Economy-based Sustainable Seismic Design (SSD) is a new concept with a view to achieving financial benefits and environmental protection. Earthquakes impose the utmost load conditions accompanied by large inelastic distortions of almost all structures. The challenge is always the same: to prevent collapse and attempt repairs. Hence, the aim is to design ERSs with an emphasis on the economy and Post-Earthquake Realignment and Repair (PERR), rather than complying with antiquated guidelines. In conventional ERSs, the aim is to satisfy code requirements, whereas in SSD, the economics and post-earthquake attributes of the system are as important as those during the event. The physical effort involved in PERR is directly affected by the design objectives. SSD is part of neither college curricula nor design guidelines. This article promotes the notion that seismic sustainability (SS) in a structure can be highly economical and environmentally friendly if it can prevent collapse, overcome residual effects, and lend itself to PERR. To gain insight into the inner workings of SSD, this report discusses the principles of performance control (PC), design-led analysis (DLA), and the use of replaceable energy-dissipating devices (REDDs). In conclusion, the main contribution of this paper is that it shows that the conventional design can be upgraded to economy-based SSD without resorting to untenable costs and technologies. All the results have been verified via independent computer analysis.

Seismic Behaviour of Multistorey Steel Framed Tall Buildings Using Intentionally Eccentric Braces

Braces with intentional eccentricity (BIE) are recently proposed to improve the seismic behaviour of conventional buckling braces (CBBs) by inserting intentional eccentricity along the brace length. Due to this eccentricity and the resultant bending moment, the BIE bends uniformly from small storey drifts and moves smoothly into the postbuckling behaviour under compression and sustains trilinear behaviour under tension. This behaviour delays the appearance of midlength local buckling which causes unstable energy dissipation. BIEs have a desirable postyielding stiffness which results in stable energy dissipation during cyclic loading and are capable of dissipating energy during low-intensity earthquakes. The seismic behaviour of structures with BIEs for use in buildings has not yet been investigated, specifically in tall buildings. Therefore, this study concentrates on investigating the seismic behaviour of tall buildings equipped with BIEs that uses a 3-dimensional (3D) finite element model in ETABS. In the first step, a 20-storey structure is designed using both eccentric brace frame (EBF) and BIE system and their seismic performance under the TABAS earthquake record is compared. In the second step, the seismic performance of a 25-storey irregular structure is assessed to evaluate the efficiency of the BIE system in irregular structures. Results show the desirable performance and energy dissipation capacity of the BIE system but it also shows large out-of-plane deformation in some cases.

Experimental study on PSPC beam – Concrete encased CFST column frame installed with novel steel panel dampers

A concrete-filled steel tubular (CFST) column has a bearing capacity with a relatively small cross section. From the perspective of the assembly, a partially steel-reinforced precast concrete (PSPC) beam can combine the merits of both the reinforced concrete beam and steel beam. However, strong earthquake action puts forwards a dramatic seismic requirement for the high-rise frame. In this study, to improve the seismic performance of the structure in an economical way, the duplex assembled I-shaped steel panel damper (DAISPD) was introduced to the PSPC beam-concrete encased CFST column frame through the eccentric brace. A half-scaled two-storey two-bay substructure specimen was tested under cyclic loading. A series of seismic properties was then analysed, including the failure modes, hysteretic performance, and energy dissipation capacity. To further investigate the contribution of the damper, groups of numerical analyses were conducted on the key design parameters of the DAISPD. The introduction of the damper provides an adequate lateral stiffness and energy absorption to the frame, especially when the interstorey drift is within the elastic and plastic drift limits. The damage of the damper and the beam hinge mechanism occurs sequentially, which results in a two-stage failure mode. Considering the predamage contribution and the postdamage influence of the damper, it is recommended to design with a moderate yield force and a small height.

Seismic fragility functions for RC As-built and eccentric steel brace frames

Quasi-static cyclic loading tests were performed on single-story reduced-scale reinforced concrete as-built (un-retrofitted) and eccentrically steel braced (retrofitted) frames. The frames damage mechanism, force–displacement hysteretic response and capacity backbone envelopes were studied and a damage scale was developed. A simplified numerical modeling technique was proposed in the finite element-based package SeismoStruct and the model was evaluated, calibrated and validated with the test data. The proposed modeling technique was employed further to perform incremental dynamic time history analysis on two-story as-built and eccentric steel braced frames. Fragility functions for the frames in terms of immediate occupancy, life safety and collapse prevention were developed using a probabilistic-based methodology. The as-built frame was more fragile in terms of immediate occupancy, life safety and collapse prevention damage states as opposed to the retrofitted frame.

Seismic performance evaluation of RC frames strengthened with eccentric steel braces and column jackets

Seismic performance evaluation of RC frames strengthened with eccentric steel braces and column jackets

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 Analysis for Zone III, IV, V of (G+14) Multistorey Building with Bracings System Using Staad Pro Software

Abstract: This present study focuses G +14 Simple Building model In STAAD PRO software. With beam size 300 X 400 mm and column size 400 X 500 mm this reinforced concrete building having M30 grade of Concrete and Fe415 high density steel. To study the response of building with and without bracing system. The performance of the building is analyzed in Zone III, Zone IV, Zone V. Metallic braces is the easiest of simplest way of reducing response of building which gave rise to nine models for the analysis.Model1 in -BFB- Bare frame RCC Building.Model2 in -BX1-Framed building with Bracing at the exterior side along X-direction.Model3 in -BY2- Framed building with Bracing at the exterior side along Y-direction.Model4 in -BXY3- Framed building with Bracing at the exterior side along X and Y-direction.Model5 in-BEC4- Framed building with Bracing at the exterior side around the corners. This system of bracing is used because eccentric bracing systems consist of a link element that undergoes inelastic deformation for energy dissipation. This link is possibly beam element of frame structure which is more suitable for steel structures and not for reinforced concrete structures and a shear wall is a structural panel that can withstand the impact of lateral forces on it. Lateral forces are those parallel to the wall plane and are usually wind loads and seismic loads. This building has been modeled as 3D Space frame model with six degree of freedom at each node using STAAD PRO. software for stimulation of behavior under gravity and seismic loading.

Analytical and numerical study of an eccentric continuous cable bracing system with friction slip mechanism

This study proposes a very simple and low-cost friction mechanism using a pre-stressed cable passing over two fixed pulleys without rotation along with an eccentric continuous cable bracing as a lateral-resistant system for structures subjected to lateral loading such as earthquake. The performance of this mechanism is investigated using analytical solution method and finite element modeling. The purpose of this system is to provide a structure with sufficient stiffness and lateral resistance as well as energy dissipation through frictional slip between the cable and pulleys. The system exhibits two-phase behavior. In case of a small lateral displacement, the system exhibits high stiffness in the linear elastic phase (first phase) and behaves well under normal winds and small earthquakes. In case of large lateral displacement such as a strong earthquake, the system experiences a nonlinear slip phase (second phase) and, accordingly, exhibits a nonlinear behavior with an increase in stiffness and input energy dissipation which protects the structure from displacement. The seismic performance of the proposed system is investigated in terms of three parameters: friction coefficient, initial pre-stressing force, and span length. As the friction coefficient value increases, the lateral resistance of the system rises. In the event of extra rotation of the cable around the pulleys, the coefficient values at static and dynamic friction phases are 5.6 and 5.1 times those in the frictional state, respectively. The rise of the span length and reduction of initial pre-stressing force decrease the system lateral resistance and the initial stiffness of the system, respectively. Upon increasing the initial pre-stressing force up to twice that of the base state, the slip threshold of the system lateral resistance force increases by 33% and as a result, the system remains more at the static friction phase. Also, by reducing the initial pre-stressing to half of its value in the base state, the lateral resistance force corresponding to the slip threshold of system is decreased by 52%; therefore, the slip of the cable on pulleys is initiated earlier. Finally, the cyclic behavior of the steel moment frame with the proposed system is investigated with ATC24 protocol, which increases the stiffness and energy dissipation by 19% compared to the moment frame without the proposed system.

Effect of Using Eccentric Braces with Different Link Lengths on the Seismic Demand of CFST Column-Composite Beam Frames Subjected to Near-Field and Far-Field Earthquakes

Effect of Using Eccentric Braces with Different Link Lengths on the Seismic Demand of CFST Column-Composite Beam Frames Subjected to Near-Field and Far-Field Earthquakes

Seismic performance evaluation of Y-shaped eccentric brace–high-strength steel frame structure based on remote collaborative hybrid test

A remote collaborative hybrid test (RCHT) system based on the OpenFresco platform was established. The seismic performance of the Y-shaped eccentric brace–high-strength steel frame (YEB–HSSF) structure was evaluated via the RCHT loading of a multistory and multi span YEB–HSSF model with two test substructures at different locations. The test phenomena and results showed that the maximum inter-story drift angles of the RCHT model were 0.0018 and 0.0077 rad under frequent-intensity and rare-intensity earthquakes, respectively, which satisfies the requirements of GB 50011-2010. Under the action of a rare intensity earthquake, the webs of the test substructure links preferentially entered the yield state with shear deformation, whereas the other members remained in the elastic state; this conforms with the design concept of damage-controllable structures. Finally, a finite-element pure numerical model corresponding to the RCHT model was established to further evaluate the seismic performance of YEB-HSSF structure. The results showed that the base shear distribution ratio resisted by the HSSF part in the global model tended to increase with increasing peak ground acceleration. Under the action of a rare 9 intensity earthquake, the shear links were close to the ultimate bearing capacity, and the shear distribution ratio resisted by the HSSF part exceeded 40%. This indicates that the YEB-HSSF structure satisfies the design requirements for dual systems based on GB 50011-2010.