Eccentrically Braced Frames Research Articles

Evaluation of Link Overstrength Factor for the Seismic Design of Eccentrically Braced Frames

In eccentrically braced frames (EBFs), inelastic behavior is only permitted in the links. All members, except for the links, are designed according to the capacity design concept by using the link overstrength factor, Ω, so that they remain elastic even when the links develop their ultimate strength (including the strain-hardening effect). AISC 341 specifies that the Ω factor of link members must be 1.25 for beam and brace design and 1.1 for column design. In this study, the relevance of the current Ω factor was investigated. A total of 471 K-braced EBF systems with various conditions were designed using a multi-objective optimization technique, and nonlinear dynamic analyses were performed to evaluate the Ω factor. The results indicate that it is reasonable to use the current Ω factor for the design of beam outside link and brace; however, it leads to an overestimation of axial force in columns, especially in the lower stories of tall buildings. From the analysis results, a new Ω factor equation for column design was proposed. It was demonstrated that the structural quantities of 15-story frames designed using the proposed equation decreased by an average of 19% compared to those designed using the current Ω factor.

Analytical and experimental study of fuses with simple replaceability in eccentrically-braced frames

Analytical and experimental study of fuses with simple replaceability in eccentrically-braced frames

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.

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.

Triple network hydrogel-based structure triboelectric nanogenerator for human motion detection and structural health monitoring

In this study, we developed a high-performance triple network (TN) PVA/PAAM/PEDOT/Zn2+ (PMPZ) hydrogel with exceptional mechanical properties and stable output performance. The robust and highly tough TN structure, fabricated via a Zn2+ pinned hydrogel and multi-network interpenetrating polymerization process, demonstrates high mechanical strength alongside exceptional mechanical properties. The PMPZ hydrogels exhibit notable mechanical sensing capabilities (gauge factor: 48.6) while maintaining excellent tensile (83.79 KPa) and compressive (96 MPa) strengths. As a triboelectric nanogenerator (TENG), the PMPZ-TENG shows outstanding flexibility and integrability, achieving a maximum open-circuit voltage (Voc) of 326.89 V and a peak power density of 368.3 μW/cm² with a load resistance of 10E8 Ω. Furthermore, the PMPZ-TENG demonstrates enduring practicality and responsiveness as a self-powered sensor. These properties make the PMPZ-TENG highly suitable for applications in human health monitoring. Additionally, we conducted computational simulations on the hydrogel and seismic-resistant civil models. 48 prototype structures simulated different seismic hazard levels to effectively capture plastic hinge deformation within high-strength steel composite K-shaped eccentric braced steel frames. The plastic hinge deformations informed the establishment of physical seismic models for structural health monitoring (SHM). This study not only introduces a high-performance PMPZ-TENG meeting practical requirements but also establishes a novel pathway for integrating TENGs in SHM.

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.

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.

Numerical investigation on stress concentrations of circular steel X joints

The most important reasons for the usage of steel as a building material are its high strength and ductile behavior, which can be defined as inelastic deformation or displacement capacity under a certain load. Steel frames are required to sustain the horizontal loads during an earthquake. The steel frames are classified as moment-resisting steel frames, concentric steel braced frames, eccentric braced steel frames, and buckling restrained braced frames. These steel frames can be designed with a high ductility level frame, limited ductility level frames, and ductility level mixed frames. In this study, stress concentrations due to the maximum compression force that may occur during an earthquake have been examined by the finite element method at the connection point of the circular cross-sectional braces of the central X-type braced steel frame with a high ductility level. Stress concentrations in the X-type brace were investigated depending on the variation of the cut surface required for the connection plate due to the change in the angle between the braces and the differences in the weld thickness applied in this region. In the models, the angle between the braces is designed as 60°, 75°, and 90° and the weld thicknesses are defined as 3.5 mm, 5 mm, and 7 mm. The results are obtained by applying the same compressive and tensile forces to the braces under the same boundary conditions and compared for these different models. It is obtained that the highest stress values occur along the direction of the tensile force in the tension profile and nearly at a distance of 5 mm after the cut. The maximum stress values decrease when the intersection angle between the braces increases from 60° to 90°.

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

Mitigation of residual deformations in eccentrically braced frames through a low‐cost re‐centering mechanism

AbstractPrevious studies have demonstrated that the response of stable yielding systems to random excitations such as earthquakes is inherently accompanied by residual deformations. Stable yielding systems with highly enhanced ductility capacity are more prone to residual deformations. Steel eccentrically braced frames (EBFs) are designed to sustain significant localized inelastic deformations in the segment of the beam referred to as the yielding link, which results in much larger link rotations when compared to inter‐story drift ratios (SDR). Recent experimental and numerical studies on the response of EBFs have demonstrated that even with moderate residual inter‐SDR (less than 0.5%), severe link residual rotations could be expected, which could render the structure difficult to repair. For replaceable yielding links, which were developed to expedite the repair and recovery process in EBFs after major seismic events, large residual link rotations will hinder the link replacement process or at times make it impossible. Therefore, mitigation of residual deformations is of greater importance in EBFs with replaceable yielding links than in conventional EBFs with a continuous beam. This paper provides a brief review of past research on residual deformations and methods for their mitigation. A low‐cost re‐centering system for use in EBFs is proposed to work in parallel with the yielding link, in order to mitigate residual deformations. The proposed system is adopted for two prototype structures designed with EBFs equipped with cast steel replaceable modular yielding links. The effectiveness of the re‐centering strategy is evaluated by means of pseudo‐dynamic hybrid simulations, as well as numerical simulations. The hybrid simulations and numerical studies both demonstrate that not only the proposed system is highly effective at mitigating the residual deformations, but also it is effective in reducing the peak deformations in EBFs.

Seismic Performance of Steel Buildings with Eccentrically Braced Frame Systems with Different Configurations

Although eccentrically braced frames (EBFs) can be used with different configurations according to architectural requirements, it has not yet been indicated which configuration has a better seismic performance; therefore, this paper presents an analytical study focused on evaluating the seismic behavior of various steel buildings with EBF systems, factoring in different configurations. Furthermore, the objective is to compare the performances of EBF systems with one another, to learn more about their structural efficiency. The results obtained indicate that seismic response, in terms of peak interstory drifts, depends on the structural period and hysteretic behavior of the links, because high levels of plastic rotation increase lateral displacement. In addition, it was observed that maximum drift demands are concentrated in the lower floors where the links exhibit inelastic behavior, while the level of interstory drift decreases as height increases.

Seismic Performance of IWF Flexural Link in Inverted-V Eccentrically Braced Frames With Different Stiffener Spaces

Resistant structures, such as Eccentrically Braced Frames (EBFs), are required to be established in earthquake-hazard areas. In EBFs, an essential beam component, known as link, plays a crucial role in determining the performance of these structures. As the seismic energy dissipator, link experiences failure to prevent heavy damage to other EBFs members, such as beams and columns. Although several studies have been carried out to enhance the seismic performance of link, there is still limited regarding these elements. Therefore, this study aimed to investigate several IWF flexural links constructed in FE models of Inverted-V EBFs. A total of three flexural links with different stiffener spaces were considered namely non-spacing, 250 mm, and 100 mm stiffener spacing links. To assess their performance, cyclic loading with yield displacement control was used in EBFs models. Observations were mainly conducted on EBFs performances consisting of strength, stiffness, and dissipation energy. The results showed that the best seismic performance was specified on a 100 mm-stiffener spacing link by presenting the largest and most stable hysteresis curve. Based on these results, the configuration of the narrow space stiffener in the link element was recommended to improve the seismic performance of EBFs.

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.

Capacity design of a steel building with eccentric braced frames and its influence on seismic behavior

The study focused on the design of a steel structure with eccentric braced frames by capacity and its influence on the behavior under different levels of earthquakes.This work contributes significantly to structural engineering by creating comparative tables and graphs detailing loads and stresses in strength design versus capacity design across all elements and levels of the structure. Plans and visual representations from DM Structural Engineering were used to process data through Etabs, modeling the structure, and verifying the revisions to the E-030 regulations. The spectra were calculated with spreadsheets and the design was carried out according to AISC 341-16 and AISC 360-16 regulations. The seismic performance evaluation followed the guidelines of ASCE 41-13 and Vision 2000 of SEOAC 2000.The results showed that the design complies with the distortion limits of the E.030 regulation; as well as adequate capacity for design demands according to AISC 341-16 and AISC 360-16, and satisfactory seismic performance according to Vision 2000. This work validates the effectiveness of capacity design in steel structures and provides a solid comparative basis for future work in earthquake resistant design.

Column Link Behavior in Eccentrically Braced Composite 3-Dimensional Frames

Eccentrically braced frames are renowned for their capacity to absorb seismic forces while offering greater adaptability. These frames incorporate bracings that are joined to the beams with an intentional offset, forming a connection within the beams. Nevertheless, there are drawbacks associated with implementing these beam connections when renovating frames. This paper seeks to enhance the design approach by introducing an eccentric link within the column of a composite structure. Eccentric braced frames (EBFs) are hybrid systems that offer both ductility in moment resisting frames (MRFs) and lateral stiffening in the concentrically braced system. The study examines composite frames with 5, 10, and 15 stories using eccentric X- and V-type bracings with an eccentricity of 0.5 m and 1 m. Three different earthquake zones are considered, based on Indian seismic code provisions: zone 3, zone 4, and zone 5. The structures are analyzed computationally by nonlinear time history analyses. The lateral load-resisting behavior of the structure with the same eccentricity in beam links and column links is compared. Then, the structure is subjected to a pushover analysis to study the performance characteristics such as capacity curve, lateral displacement, inter-storey drift, and plastification of the structure. As anticipated, compared to conventional moment resisting frames (MRFs) and concentrically braced frames (CBFs), eccentrically braced frames have better energy dissipation. Furthermore, the behavior of X-braced column links is found to be similar to the performance of beam links, but V-braced frames showed better performance in column link frames than in beam link frames. Also, the increase of the link length played a major role in the ductility of the frames.

Investigation on the behaviour and performance of replaceable inverted-Y dissipation device in eccentric braced frame steel structures

Investigation on the behaviour and performance of replaceable inverted-Y dissipation device in eccentric braced frame steel structures

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.

Nonmodel rapid seismic assessment of eccentrically braced frames incorporating masonry infills using machine learning techniques

This study investigates the seismic behavior of eccentrically braced frames (EBFs) taking into account the influence of masonry infill walls using a nonmodel scenario-based machine learning framework. Predicting engineering demand parameters (EDPs) by exploiting data-driven approaches and developing the associated fragility curves of infilled EBFs are the main objectives of this research. To this end, a set of 4- and 8-story archetype EBF structures considering 12 distinct infill properties, a total number of 4 bare and 48 infilled EBF models, are created in OpenSees software. A nonlinear pushover analysis is then conducted to assess the overall impact of infills on 4- and 8-story EBFs. Incremental dynamic analysis under 44 far-field ground motions is performed to collect an extensive raw database consisting of 37,164 and 461,480 data points for each variable of bare and infilled EBFs, respectively. It encompasses seismic intensity measure (Saavg), wavelet-based robust damage sensitive feature (rDSF), derived from roof absolute acceleration, frame geometric information, and infill parameter as input features and also EDPs containing peak and residual story drift ratios and peak floor accelerations (PFA) as response variables. After data preprocessing, both regression analysis and machine learning (ML) techniques are utilized to estimate EDPs under two scenarios of Input-Output and Output-Only based on the availability of Saavg. Comparing error measures, particularly in the Extreme Gradient Boosted Tree (ExGBT) algorithm, reveals strong observed-predicted EDP compatibility. Linear equations from bare frame data predict infilled frame EDPs without modification coefficients. Data preprocessing demonstrates that infills decrease drift-based EDPs due to stiffness improvement, while their impact on PFA remains inconclusive. Saavg and rDSF-based fragility curves at three damage states show accurate predictions and effectively reduce vulnerability in infilled 4-story EBFs. However, infills undesirably affect non-ductile behavior in 8-story EBFs, leading to increased global damage as supported by pushover analysis.

Experimental and numerical study of a damage‐free self‐centring link for seismic resilient EBFs

AbstractSignificant progress has been made in recent years for the definition of seismic‐resilient structures, chasing the urgent need for structures able to return to undamaged, fully functional conditions in a short time after an extreme event. Seismic‐resilient steel structures have been widely investigated, mainly considering solutions based on moment‐resisting and concentrically braced frames. However, while the first category may be characterised by low stiffness, the second is often characterised by low ductility. Eccentrically Braced Frames (EBFs) allow overcoming these drawbacks and well‐balance stiffness, strength and ductility. This paper presents the numerical and experimental study of a damage‐free self‐centring link for EBFs. The proposed device uses post‐tensioned bars to control the self‐centring behaviour and friction devices to provide dissipation capacity. Experimental cyclic tests have been carried out to evaluate the response of the device. A 3D ABAQUS model has been developed to investigate the local response. Finally, a six‐storey EBF has been numerically investigated in OpenSees to evaluate the global response. Incremental Dynamic Analyses were performed demonstrating the increased seismic performance of the proposed solution.

Experimental qualification of replaceable bolted links in dual eccentrically braced frames

AbstractThe performance of structures under severe seismic action is ensured by properly calibrated ductility, stiffness, and strength. The “plastic” members of ductile mild carbon steel (S235 to S355) dissipate the seismic energy, acting as “structural fuses”, while the “elastic” members must be provided with adequate overstrength, to have the capacity to carry the stresses corresponding to yielded and strain hardened plastic hinges. High strength steels, such as S460 to S690, might be used for these elastic members, providing them with the necessary overstrength, without enhancing the stiffness, as that could unbalance the structural system. Dual structural systems, as moment resisting frames (MRFs) combined with eccentrically braced frames (EBFs), can be equipped with replaceable mild carbon steel dissipative links acting as seismic fuses. The MRFs, possibly fabricated from high strength steel, remain elastic, being able to recover the initial position. The key problem in such systems is the design and calibration of the fuses, i.e. the replaceable bolted links, which should be carefully qualified by tests. The present paper reviews past research on bolted replaceable links and discusses the experimental qualification requirements.