Eccentrically Braced Frames Research Articles

Study of inelastic behaviour steel structure of special moment frame (SMF) and eccentrically braced frame (EBF) with pushover analysis

High rise buildings should be made as sufficient seismic performance, so it won’t immediately collapse when an earthquake occurs. Therefore, lateral strengthened stories are required in high rise buildings to enhance the lateral rigidity of structure. The use of lateral strengthening has a great effect on the entire seismic performance. A 20-stories high rise steel structure building was evaluated on this research comparing the structures’ inelastic behaviour using two seismic force-resisting system, i.e., special moment frame and eccentrically braced frame. The analysis of inelastic behaviour in this research using static non-linear analysis, i.e., pushover analysis. By using pushover analysis, the inelastic behaviour of structures, including story drift, shear story, displacement, plastic joint formation, and ductility, were obtained. In the elastic condition, the shear story of the eccentrically braced frame system is smaller than the special moment frame system. While in plastic condition, the shear story of the eccentrically braced frame system is larger than the special moment frame system. The story drift and the displacement of the special moment frame system are indicated to be larger than the eccentrically braced frame system. These results show that the eccentrically braced frame system has better rigidity than the special moment frame system.

Optimized stiffener detailing for shear links in eccentrically braced frames

Eccentrically braced frames (EBFs) are utilized as a lateral resisting system in high seismic zones. Links are the primary source of energy dissipation and they are exposed to high deformation, which may lead to buckling. Web stiffeners were introduced to prevent buckling of shear link. AISC 341 provides the required vertical stiffeners for a shear link. In this study, different stiffener configurations were examined. The main objective is to improve the behavior of short links using different stiffener configurations. Pursuant to this goal, a comprehensive numerical study is conducted using ABAQUS. Shear links with different stiffener configurations were subjected to cyclic loading using loading protocol mandated by AISC 341. The results are compared in terms of energy dissipation and shear capacities and rupture index. The proposed stiffener configurations were further verified with different link length ratios, I-shapes and thickness of stiffener. Based on the results, the stiffener configuration with two vertical and two diagonal stiffeners perpendicular to each other is recommended. The proposed stiffener configuration can increase the shear capacity, energy dissipation capacity and the ratio of energy/weight up to 27%, 38% and 30%, respectively. Detailing of the proposed stiffener configuration is presented.

Seismic performance of eccentrically braced frames designed to AISC341 and EC8 specifications

In the United States, steel eccentrically braced frames (EBFs) are designed according to AISC341 Specification while in Europe EC8 provisions are used. The European provisions were developed mostly based on the research works conducted in the US. While EBF design recommendations in AISC341 and EC8 have similarities, marked differences exist in the amount of lateral force reduction and distribution of member over-strength among the stories. In addition, the effect of link over-strength on non-dissipative members is treated differently in the two specifications. A study has been undertaken to evaluate the performance of EBFs designed according to AISC341 and EC8. Pursuant to this goal, EBF archetype buildings with 3, 6, and 9 stories were designed using US and European provisions taking into account different force reduction factors. The archetype buildings were subjected to 44 far-field ground motions at the maximum considered earthquake level as recommended by FEMA P695. Nonlinear time history analyses were conducted by OpenSees analysis platform to obtain the link rotation angle, residual frame drift and column axial forces. The results showed that using larger force reduction factors and disregarding the distribution of member over-strength among stories result in large residual frame drifts and non-uniform link rotation angles along the height of the building. Considering a force reduction factor of 5 and imposing a limit on link over-strength among the stories were found to improve the performance considerably. Design recommendations were developed to enhance the performance of EBFs by unifying the rules given in AISC341 and EC8. The study was complemented by investigating the behavior of EBFs subjected to near-field ground motions with pulse. The results showed that near-field ground motions with pulse produce much higher link rotation angles when compared with the demands produced by far-field ground motions.

Effectiveness of Seismically Resistant Braced Frames to Blast Loading

The increment in the tally of terrorist radicalisation from the past time has exhibited that the consequence of blast loads on structures is a crucial matter that should be taken into cogitation. This paper considers the effect of blast load on seismically designed framing systems namely Moment Resisting Frame (MRF), Concentric Braced Frame (CBF), Eccentric Braced Frame (EBF) and Buckling Restraint Braced Frame (BRBF). The bracings are one of the efficient lateral load resisting systems and their behaviour is observed under the blast loading. The burst load is estimated to be an unconfined surface burst explosion on front face of the structure. Comparative analysis of storey displacement among different framing systems is performed. Failure of members is studied through the analysis of plastic hinge formation. The results indicate that braced frames perform better when exposed to such kind of impact load. Buckling Restraint brace (BRB) exhibited higher level of resistance to blast loading due to its ability to yield in both compression and tension.

ANALISA PERBANDINGAN STRUKTUR BAJA 3 LANTAI MENGGUNAKAN SYSTEM CBF DAN EBF DENGAN METODE PUSH OVER ANALYSIS

Indonesia merupakan termasuk negara yang berada di ring of fire dan di beberapa batas lempeng tektonik, sehingga tingkat risiko terjadinya gempa bumi sangatlah tinggi.Analisa struktur yang digunakan yaitu perbandingan sistem concentrically braced frames (CBF) dan eccentrically braced frames (EBF) berdasarkan pada peraturan struktur tahan gempa. Hasil analisis menunjukkan Daktilitas struktur dengan sistem CBF lebih kecil daripada sistem EBF. Struktur dengan sistem CBF lebih kaku dan kokoh dibandingkan dengan sistem EBF. Daktilitas yang bagus adalah yang bernilai lebih dari 1, sehingga struktur tidak mudah runtuh. Pada kondisi linier, sistem CBF memiliki perilaku atau kinerja yang lebih baik ditunjukkan dengan penggunaan material, displacement maksimum dan drift ratio yang lebih kecil. Pada kondisi nonlinier, sistem ini (EBF) memiliki perilaku maupun kinerja yang lebih baik terbukti dengan penyerapan energi dan daktilitas yang lebih baik.

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.

Optimal Design Parameters of Stiffeners for Improving Seismic Performance of Links in EBFs

In eccentrically braced frames (EBFs), the link beam is the main factor determining the behavior of this type of system. In order to enhance the ductility and delaying the web and flange buckling, the link beam is reinforced using intermediate web stiffeners to improve its performance and energy dissipation capacity. The web stiffeners spacing criteria is based on short links under pure shear, which have been applied without considering the bending effect on intermediate links. In this paper, first the effects of stiffener details and section geometry on the link behavior are investigated using finite element modeling, and then by proposing an optimization model, new spacing is proposed for stiffeners of intermediate links that is also consistent with bending distribution, and enhances the performance of intermediate links significantly. To further investigate the results of the optimization model and sensitivity analyses results, the behavior of a total of 52 short, intermediate and long links with different lengths and sections is simulated and investigated under cyclic loading based on ANSI/AISC 341-10 (Seismic provisions for structural steel buildings, Chicago, American Institute of Steel Construction, 2010) using ABAQUS. The results show that the section geometry in W-beams affects the stiffeners spacing and thereby, the behavior of intermediate and long links. According to the obtained results in short links, stiffeners spacing are very conservative and can be increased, and for intermediate links, adjusting the stiffeners spacing based on the proposed optimization model can significantly enhance the performance of the link beam.

Evaluasi Perbandingan Kinerja Bangunan Momen Frame dengan Eccentrycally Brace Frame

Generally, earthquake resistant design is based on elastic structural analysis with load factor to simulate ultimate condition. Actually, behavior of collapse structures during earthquake is in-elastic. Evaluation to predict in-elastic condition of structures during earthquake is needed in order to guarantee that it can perform well during earthquake. Analysis and performance evaluation can be done with pushover analysis given in SAP2000, while evaluation of performance point must be determined manually with various methods (except for capacity spectrum method). Pushover analysis is a non linear static analysis as a behavior of structural failure due to earthquake, while performance point is structural maximum displacement during design earthquake.
 Study on steel frame 3D concludes that performance evaluation for pushover in longitudinal direction according to ATC-40 gives displacement target for moment frame building of 0.054 m, building with eccentrically braced frame (EBF): 0.022 m. Pushover in transverse direction according to ATC-40 gives displacement target for moment frame building of 0.022 m, building with EBF: 0.015 m. According to FEMA 356, displacement target in longitudinal direction for moment frame building: 0.0803 m, building with (EBF): 0.0728 m. For building with moment frame in transverse direction: 0.1183 m, building with (EBF): 0.0614 m.

Seismic performance of eccentrically braced frames designed by the conventional and equivalent energy procedures

Eccentrically braced frame (EBF) is a robust structural system designed for seismic application. The design philosophy for EBF is to utilize the link beams to dissipate the earthquake energy. While such system has been proven to provide sufficient stiffness and strength to prevent the structure from collapse, the structural performance in terms of damage and resilience after strong earthquakes is not explicitly considered. In this paper, a novel design method, named the Equivalent Energy Design Procedure (EEDP), is adopted to design the EBF. EEDP is an alternative design procedure for fused structural systems, where engineers can design the structure to achieve the intended performance objectives at different earthquake hazard levels. To evaluate the performance of the EBF, a 5 storey EBF located in Vancouver, British Columbia, Canada is designed using both the EEDP and the Equivalent Static Force Procedure (ESFP) outlined in the 2015 National Building Code of Canada. Detailed nonlinear dynamic analyses were conducted. The results show that the EEDP designed EBF has better performance with lower initial and repair costs at different levels of earthquake shaking intensities.

Experimental and numerical studies on Seismic Performance of The SCFST Column Eccentrically Braced Frames

The quasi-static experiments and finite element analysis of three groups of special-shaped concrete-filled steel tube (SCFST) column chevron braced frames (two groups of eccentrically braced frames and one group of concentrically braced frame) were carried out. The differences of quasi-static mechanical properties between the three groups frame were compared. The damage mechanism of the concentrically and eccentrically braced frames was significantly different, and the eccentrically braced frame could significantly improve the energy-dissipation ability and ductility. When the single limb of columns was connected by double-steel-plate, the stiffness of eccentrically braced structure could be improved around 10.4% and showed better energy-dissipation capacity. The finite element simulation was built on the basis of experiments, and parametric analysis was examined. The analysis results showed that section forms of the SCFST column and the thickness of brace have significant impacts on the quasi-static properties of such type of structure.

The Pushout Test of Seismic Reinforcement System (SRM) Connection that Respond to Earthquake Extensive Level

This paper introduces a state-of-the art seismic retrofit method (SRM) that has the resistance mechanism of eccentrically braced frames (EBF). In EBF, local failure is induced to the link beam such that other members remain in the elastic state when an earthquake load is applied. SRM works by attaching to an existing building in the form of an external frame to enhance its seismic performance. The seismic reinforcement of medium- and low-rise reinforced concrete buildings has a small inter-story drift; hence, the adhesion between the two materials has a great influence on the seismic reinforcement effect. In this study, a push-out test was performed to show the adhesion performance under various conditions. The performance of various attachment methods was also explored to improve adhesion with the RC structure for securing the performance of the SRM system. Additionally, this study proposes a shear strength equation that considers the influence of the contact direction of steel, increase in plate thickness, and anchor yield strength. The test results indicated that it can be used as a new shear strength equation as the error rate is within 10% compared to the experimental results. Although the web direct bonding method using end plates is disadvantageous in terms of processability, it showed the highest strength improvement results. Furthermore, the chemical anchor (Hilti) connection exhibited stable performance results regardless of the bonding method.

High‐strength steel and dissipative fuse solutions for seismic‐resistant building structures

AbstractExtended keynote paper of Eurosteel 2021The robustness of steel structures during severe earthquakes is largely based on the calibration of stiffness, strength and ductility. Such a robust system dissipates the energy by plastic deformations in the plastic members (fuses) made from mild carbon steel (MCS), while the other members remain elastic. In the case of concentrically braced frames (CBF), the fuses can be in the form of buckling‐restrained braces (BRB), while for eccentrically braced frames (EBF), the short links could take on this role. In the case of shear walls (SW), slender steel plates can be used. To avoid oversized elastic members, they can be made of high‐strength steel (HSS). Structures made from HSS and MCS are called dual steel (DS) structures. In order to ease the post‐earthquake intervention, the fuses can be detachable. Furthermore, their replacement is less costly if the structure is re‐centred using moment‐resisting frames (MRF) connected to the main dissipative system, i.e. a dual frame (DF) structure. This paper presents the concept of DS DF structures and some examples.

English

The seismic performance of non ductile reinforced concrete (RC) buildings with eccentric steel bracing of inverted Y type is investigated. 10, 15 and 20 storey buildings are analyzed by using pushover analysis. The analysis is carried out by using software SAP2000v17. The effect of distribution of steel bracing over the height of RC frame was studied. The study also concentrates on effect of link length of eccentric bracing on seismic performance of RC frame. The performance of RC frame with inverted eccentric bracing is evaluated in terms of energy absorption capacity, stiffness of frame and ductility. The behavior of eccentric braced frame (EBF) is compared with conventional RC frame and inverted V bracing.

Seismic performance assessment of eccentrically braced steel frames with energy-absorbing links under sequential earthquakes

Recent studies have indicated the need of considering aftershocks in the seismic design/assessment of structures. This article investigates the effect of sequential mainshock and aftershock earthquakes on eccentrically braced steel frames with vertical energy-absorbing links. To achieve this, 4, 8 and 12-storey frame buildings are modelled in Perform3D® software considering non-linear behaviour of materials and components. The frames are subjected to a set of 12 main earthquake records corresponding to the required hazard level, and then subsequent aftershocks are applied using incremental dynamic analysis (IDA). To reduce the computational cost, an alternative approach is also adopted by applying the main earthquakes to the system followed by pushover analyses on the damaged building assuming a lateral load distribution proportional to the shape of the first vibration mode. Subsequently, the fragility curves are obtained for different damage levels, before and after the main earthquake. The results show that the eccentric braced frames with vertical links subjected to sequential earthquakes comply well with the performance levels of the Iranian Seismic Code. This study contributes toward the assessment and seismic validation of structures with eccentrically braced steel frames with vertical energy-absorbing links to sequential earthquakes.

A simplified multi-performance approach to life-cycle assessment of steel structures

This paper presents an application of a simplified assessment approach to steel structures which takes into account sustainability requirements. The proposed approach is based on a time-dependent, multi-performance-based design methodology. The simplified procedure is organized in three main steps concerning the environmental conceptual design, the ordinary structural design and the life-cycle analysis devoted to defining service life scenarios in order to assess the structural, economic and environmental performances of structures during their entire life-cycle. Three different seismic-resistant steel structural typologies are designed for a multi-storey residential building and compared in terms of sustainability. Those comprise Moment Resisting Frames (MRF), Concentrically Braced Frames (CBF) with removable Chevron braces and Eccentrically Braced Frames (EBF) with removable shear links. The structural, environmental and economic performances of the three examined design options are assessed and compared in order to evaluate their sustainable potentialities and criticalities for two design scenarios, namely an ordinary condition characterized by an expected deterioration and an exceptional case in which a seismic event hits the structures during their service life.

Seismic Analysis and Evaluation of Y-shaped EBF with an Innovative SSL-SSBC

During severe earthquakes, the ductility and energy dissipation capacity of shear links in Y-shaped eccentrically braced frames (EBFs) are crucial to achieve desirable seismic performance and structural safety. In this study, an innovative SSL-SSBC combining the advantages of a shear slotted bolted connection (SSBC) and a very short shear link is developed to improve the seismic performance of Y-shaped EBFs. Finite element (FE) analysis methods are first validated through comparison with existing experimental results for slotted bolted connection and very short shear links. Further, FE simulations of the SSBC, very short shear link with shear slotted bolted connection (SSL-SSBC), and Y-shaped EBF are conducted to determine their mechanical behavior systematically. The FE results demonstrate that a reasonable SSBC can effectively increase the ductility and energy dissipation capacity through friction slipping, allowing the SSBC to maintain elastic behavior throughout the entire range of seismic loading, while the very short shear link in the SSL-SSBC could undergo severe damage to dissipate seismic energy. As expected, the SSL-SSBC is capable of working as both a shear dissipation damper and a metallic ductile damper in the Y-shaped EBF. This study also clearly identifies that no yielding or damage of the very short shear links occurs during small and medium earthquakes, and the deformation and damage of the very short shear link can be minimized during severe earthquakes, allowing the seismic resilience capacity of the Y-shaped EBF to be dramatically enhanced.

Effect of Hinge Properties on Nonlinear Analysis of Eccentrically Steel Braced Frames

Eccentrically Braced Frame (EBF) is one of seismic resistance of steel structures. Dissipation of seismic energies is designed by allowing plastic hinges to form in link element. Design of link elements allow plastic hinge to form due to shear or flexural failure. Structural analysis using finite element software require shear plastic hinges to be modelled. It is found that hinge properties proposed by two references, FEMA 356 and Richards & Uang are different. Study of effect of hinge properties on non-linier analysis of EBF was performed. The research is limited to hinge properties of shear link of EBFs. Numerical study was conducted on one and three storey of EBFs in two and three dimensional geometric of EBFs. Two different hinge properties from FEMA 356 and Richard-Uang were compared each other. Results show that hinge properties affect the structural response. It is found that EBFs modelled by hinge properties according to Richards-Uang has close result to experimental result than modelled built by FEMA 356. The difference between FEMA 356 and Richard-Uang to experiment are 34,54% and 15,55%, respectively.

Influence of link length on re-centring capability of dual eccentrically braced frames

Repair costs and downtime of a structure hit by an earthquake can be reduced, by implementing the concepts of removable dissipative members (bolted links which are intended to provide the energy dissipation capacity and to be easily replaceable) and re-centring capability (which is provided by the more flexible moment resisting frames) in a dual structure, obtained by combining steel eccentrically braced frames (EBFs) with removable bolted links, with moment resisting frames (MRFs). The seismic performance, re-centring capability and link replacement feasibility of a dual re-centring EBF with removable flush end-plate bolted links were already studied and experimentally validated. In this case, very short shear links were used in order to achieve the flush end-plate connection over-strength, so the connection can be kept elastic in order to make the link removal possible. Re-centring capability of EBFs with other types of removable links has not been yet approached. One of the main objectives of an ongoing research project is to extend the validation of re-centring capability and link replacement feasibility on extended end-plate bolted links. This type of connection geometry provides a larger connection capacity, thus shear links can be designed longer. The present paper numerically investigates the influence of using different link lengths (and connection detailing) on the recentring capability of two height levels structures.

Studi Numerik Performa Rangka Bresing Eksentrik Link Vertikal Profil Tubular

Eccentrically Braced Frames (EBF) have been used as earthquake suppression systems, especially in buildings. This system relies on yielding at link on the main beam which is located between the eccentric bracing (EBH). EBH has important weaknesses to review. In the event of an earthquake that causes the link beam to rotate vertically, causing the structure above the beam damaged. Also it is not easy to repair the beam link at EBH after a severe earthquake. To overcome the problems in the EBH system, a new system was proposed, called Vertical-EBF (EBV). Links with WF and tubular profiles are two profiles commonly used in structures. In this research, EBF specimen modeling with tubular profile vertical links was compared with EBF horizontal links. The results showed a structure with EBV had a lighter weight.Yielding only occur at link so its better for earthquake rehabilitation.

Numerical Study: Effect of Various Link Length to Lateral Force in Eccentrically Braced Frame

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.