Concentrically Braced Frames Research Articles

Seismic Collapse Performance of Multitiered Ordinary Concentrically Braced Frames

Seismic Collapse Performance of Multitiered Ordinary Concentrically Braced Frames

Effect of Link Length Variation on the Performance of Cold Formed Steel EBF Structures

Abstract Building damage due to earthquake shocks causes affected victims to potentially lose their homes so that temporary housing is needed. Therefore, strengthening of buildings using bracing is needed to support building resistance to lateral loads in earthquake areas. Bracing can be divided into two types, namely concentric and eccentric. Eccentric braces have links that will form inelastic rotation when yielding occurs due to deformation that occurs in the structure so that they are considered effective in absorbing lateral loads. EBF (eccentric braced frames) have better stiffness when compared to MRF (moment resisting frames) but are able to provide better ductility behavior compared to CBF (concentric braced frames). The purpose of this experimental study was to determine the performance of variations in EBF split-k cold-formed steel wall panel links against lateral loads. The aspects reviewed are maximum load, maximum deviation, and stiffness. The flow of this research is the manufacture, testing of test objects, and data processing. In this study, the following results were obtained: the short link variation obtained the largest maximum load result with 134.62 kg, the smallest maximum deviation of 30.472 mm, and the largest stiffness with 18.363 kg/mm.

A Numerical and Parametric Study on Metallic Double Corrugated Damper Directly Connected to CBF Braces

ABSTRACTAlthough concentrically braced frames (CBFs) pertain to high elastic stiffness and strength, they suffer from low energy dissipation capacity. This dilemma is due to the susceptibility of the diagonal member of the CBF to buckling. On the contrary, adding passive metallic energy dampers, although improving the behavior of the system, imposes more cost to structure and more constructional complexity. To overcome the problem, in this study, an innovative shear damper is made of a double corrugated plate for the web and two flange plates, called double corrugated damper (DCD). The numerical results using the Finite Element Method (FEM) indicated that the proposed damper pertains to a suitable performance with stable hysteresis curves under cyclic loading without degradation in stiffness, strength, and energy dissipation. This is true just to a certain lateral deformation. Also, numerical results under the monotonic loading indicated that the proposed damper shows an overstrength, Ω, of more than 1.5 (as recommended by AISC), and thus, Ω = 2.5 was proposed for it. Although links are categorized according to the factor in AISC 341‐16, the results indicated that dampers with the same revealed different response curves. Also, using the proposed damper with a corrugation angle instead of leads to an increase in the ultimate strength and stiffness, respectively, between 12% and 19% and 6% and 13% related to the flange thickness . The effect of on this damper's performance is greater on dampers with thin flange plates than on dampers with thick flange plates.

Validation and Application of a Simplified Approach for Seismic Performance Evaluation of Steel CBFs

This paper validates a simplified approach for evaluating the seismic performance of concentrically braced frames (CBFs). The method, based on a performance-based design, defines a structure’s capacity curve through elastic and rigid plastic analyses. It is validated by comparing the results with those from 420 pushover analyses. Additionally, the method is applied to two case studies designed according to older code provisions, and its accuracy is verified through Incremental dynamic analyses (IDA). The results demonstrate that the simplified method is reliable and provides an accurate evaluation of the structure’s capacity compared to code-based tools.

Improving the Behavior of Reinforced Concrete Frame Using an Innovative Metallic Shear Damper

ABSTRACTDespite the advantages of reinforced concrete (RC) frame, they are susceptible to damages under seismic loading. This is due to the fact that the main elements of the RC frame carry the gravity load in addition to the lateral loading. So imposed seismic energy is dissipated through the two ends of the beam, making the repair of the element complicated due to the gravity load. Although adding concentrically braced frames (CBFs) improves the lateral strength and stiffness, the ductility of the system is reduced. This shortcoming is due to the susceptibility of the diagonal elements to buckling. To do so, in this paper, an innovative metallic damper was investigated numerically and parametrically. The damper compound of the shear plate is surrounded by two HSS sections at two ends. The damper pertains to simplicity of construction and implementation. Also, the required equation to design and prediction of the system is presented. To investigate the behavior of the system, dynamic (to consider its suitable performance against seismic expiation) and static analyses (to determine the structural parameters) were carried out. Results revealed that the HSS section used as flanges for the shear plate not only improves the behavior of the plate but also contributes to resisting the applied load. Also, the reduction of the length to the height ratio of the damper enhances the stiffness and strength and stiffness. Subsequently, the variable Ф was defined as the ratio of the strength of the flanges to the web plate that affects the response of the damper. Although raising the Ф reduced the stiffness and ultimate strength, it is suggested to design dampers with Ф > 2 to achieve suitable overstrength in accordance with economical aspects. Also, time‐history analysis indicated that the proposed damper prevents the buckling of the CBF elements and improves the energy‐dissipating capacity of the system.

Seismic performance of steel braced frames equipped with dissipative replaceable components

Seismic performance of steel braced frames equipped with dissipative replaceable components

The extended consecutive modal pushover (ECMP) procedure for the seismic assessment of tall dual steel concentrically braced-moment resisting systems and concentrically braced frame (CBF) buildings

The extended consecutive modal pushover (ECMP) procedure for the seismic assessment of tall dual steel concentrically braced-moment resisting systems and concentrically braced frame (CBF) buildings

Validation of a Numerical Model for Novel Self-Centring Concentrically Braced Steel Frames

Significant inelastic deformations induced in structural systems lead to structures possibly possessing some degree of permanent lateral deformation following major seismic events. These permanent deformations have led to considerable research being conducted over the past 20 years into developing structural systems that exhibit self-centring behaviour. For a structural system such as the concentrically braced frame (CBF), for which the dissipating mechanism is the tensile yielding and compressive buckling of the diagonal steel tubular members, these residual deformations present a problem when considering the structure’s overall resilience to the seismic loading both during and after an event. This paper describes the numerical modelling of a novel self-centring, concentrically braced frame (SC-CBF) system that combines a conventional CBF with a self-centring arrangement to produce a structure that possesses the desirable lateral load-resisting capacity of the CBF but which also re-centres when subjected to many cycles of large inelastic brace deformation. First, an experimental test programme for the SC-CBF is briefly described, followed by a numerical model to capture the SC-CBF’s characteristics during cyclic loading. This numerical model is validated using the experimental test data, showing that the experimental and numerical simulation data match rather well. This development presents a platform upon which further research through experimental testing and numerical simulation can be conducted. The proposed SC-CBF system can then be developed into a viable lateral load-resisting system that will provide a more resilient system than the current conventional CBF.

Performance-based seismic design of sliding gusset plate braced frames incorporating thermodynamic models

Performance-based seismic design of sliding gusset plate braced frames incorporating thermodynamic models

Seismic Design and Evaluation of Elevated Steel Tanks Supported by Concentric Braced Frames

The current investigation delved into the seismic analysis, design intricacies, and assessment of the response of elevated steel containment tanks when supported by concentrically braced frames. The primary focus was placed on comprehending the behavior of the supporting structure, recognizing its heightened vulnerability to damage under horizontal excitation—insights gleaned from reconnaissance teams studying earthquake aftermaths worldwide. A specific case study unfolded featuring a steel concentrically braced frame as the supporting structure, aligning with prevalent industry norms. Throughout the entire process, spanning design phases, seismic vulnerability assessments, and response evaluations, special emphasis was placed on the internal fluid sloshing phenomena. This nuanced consideration plays a pivotal role in shaping the dynamic response of the system. The study introduces two distinct design methods: the first method aligns with relevant international codes, while the second method innovatively incorporates the compressive strength of the braces into its approach. To evaluate the dynamic response of the elevated tank, both linear and nonlinear advanced analyses were employed. The comparative analysis of various strategies underscores the impact of the chosen design methodology on the overall system response. This multifaceted exploration aims to contribute valuable insights to the seismic resilience and design optimization of elevated steel containment tanks, furthering the understanding of their performance under seismic forces.

Comparative Analysis of Concentrically Braced Frames with FeSMA and Steel BRBs Under Long-Duration Earthquakes

ABSTRACT Owing to high fatigue life, the iron-based shape memory alloy (FeSMA) buckling-restrained braces (BRBs) are emerging as a promising candidate against long-duration earthquakes. However, the corresponding analysis cannot be found. Current emphasis is paid on unveiling the seismic response differences between concentrically braced frames (CBFs) with FeSMA and steel BRBs when they are attacked by long-duration earthquakes. To directly assess the effect of earthquake duration, this paper selects a total of 90 pairs of short- and long-duration earthquake records, which are record-to-record spectrally equivalent over a wide range of fundamental periods, for nonlinear time history analysis. A benchmark six-story CBF is selected for demonstration purposes. In the numerical simulation process, the fatigue-induced damage is particularly considered. A preliminary examination is first conducted in the case study, in which a representative pair of short- and long-duration records is selected. In what followed, the statistical results from the ground motion suites are analyzed. This work not only highlights the higher failure risk of steel BRBs than FeSMA BRBs under long-duration earthquakes associated with maximum considered earthquake hazard level, but also confirms the advantages of FeSMA BRBs over steel BRBs in controlling residual deformations.

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°.

Improving the behavior of the CBF system using an innovative box section damper: Experimental and numerical study

Improving the behavior of the CBF system using an innovative box section damper: Experimental and numerical study

Seismic performance of rocking braced frames with double base plate connections

Seismic performance of rocking braced frames with double base plate connections

Unveiling the Seismic Performance of Concentrically Braced Steel Frames: A Comprehensive Review

Steel braced frames resist earthquake ground motion by undergoing several cycles of inelastic deformation. These deformations include elongation under tension and buckling in compression. To facilitate an understanding of the inelastic response of concentrically braced steel members under cyclic loading, several experimental, numerical, and analytical studies have been carried out by various researchers around the world. To overcome buckling, one of the primary failure mechanisms in Concentrically Braced Frames (CBFs), different bracing systems with recently developed mechanisms were implemented to tackle this phenomenon. The main features of these systems are to dissipate the earthquake-induced energy effectively, with minimum damage to buildings and infrastructure. Such systems still have some drawbacks, such as weight, price and specific performance issues. This work comprehensively studies CBFs, including concept, design, seismic behavior and performance for conventional, modern, and self-centering bracing systems. It summarizes 27 test programs for conventional CBFs, highlighting the different alternatives and approaches used by various researchers. Several additional studies incorporating self-centering bracing systems are also emphasized. The work finally highlights the advancements and challenges in achieving more sustainable solutions for the built environment.

Structural Performance of Single and Double-Section CBF Braces with Different Lengths Under Cyclic Loading

Concentrically Braced Frames (CBFs) are structural systems that are recommended to be constructed in earthquake-hazard areas. The brace is a CBF component that plays a role as an energy dissipator due to the seismic action. To result in a good performance, the brace is required to be strengthened. Adding a sectional area to the brace is one method for strengthening. Accordingly, the axial load is able to be distributed over a larger area, which may reduce the axial stress in the brace. So far, many kinds of research have been conducted to study brace behavior. However, the influence of adding a sectional area and increasing brace length to enhance brace performance has not yet been clarified. This paper experimentally investigated several braces under cyclic loading. Those braces were distinguished by their sectional area and length. The cyclic loading was managed by yield displacement control. The observation was mainly conducted on the performance parameter, which comprises strength, stiffness, and dissipation energy. The study discovered that enlarging the area section significantly increases the structural performance. Contrarily, the brace's performance tends to decrease when the brace is lengthened. Eventually, it can be recommended that enlarging the sectional area be taken as a solution to improve long-brace seismic performance in the CBFs system.

Inelastic Deformation and Local Slenderness Requirements for Rectangular HSS Braces

Rectangular hollow structural sections (HSS) are commonly used as bracing in concentrically braced frames (CBFs) designed and detailed for seismic design requirements. As the primary yielding component in CBFs, braces are expected to sustain large inelastic axial deformation during earthquake loading. It is well known that their deformation capacity depends on the width-to-thickness ratio (local slenderness). Until 2013, HSS sections were produced to meet ASTM standard A500/A500M; after 2013, the ASTM 1085 specification was implemented, and since that time, HSS sections have also been produced to meet ASTM A1085/A1085M standards. Where the ASTM A500/A500M specification requires minimum yield and tensile stress values as well as a minimum elongation and tolerances on the wall thickness, the ASTM A1085/A1085M specification also requires a minimum Charpy V-notch (CVN) toughness, a maximum yield stress of the steel, and tighter tolerances on the wall thickness and radius of curvature of the corner. These requirements offer a more reliable brace for CBFs in seismic regions. Yet there has been limited research investigating the cyclic axial response of these members. A research study was undertaken to investigate the response of ASTM A1085/A1085M tubes using the response of ASTM A500C tubes as their reference. Forty-one brace specimens were tested under cyclic inelastic axial deformation. Comparison of the data shows that most of the ASTM A500/A500 M Grade C and ASTM A1085/1085M braces meet the respective requirements of their respective ASTM standard and that the differences between the performance of ASTM A500/A500M and ASTM A1085/1085M braces are not dramatic. In addition, the study investigated the impact of width-to-thickness ratio, global slenderness, and displacement history on the response of the braces. The data show that the current AISC 341-22 high-ductility slenderness limit for special concentrically braced frame (SCBF) braces is slightly conservative. However, the data suggest that the moderate ductility slenderness limit used for ordinary concentrically braced frame (OCBF) braces is significantly more conservative than required for consistent seismic safety. Further research is required to determine appropriate limits; this paper provides some initial recommendations based on this dataset.

Seismic retrofit strategy for existing steel buildings with CBFs

Seismic retrofit strategy for existing steel buildings with CBFs

Performance evaluation of concentrically braced frames equipped with pure bending yielding damper

Performance evaluation of concentrically braced frames equipped with pure bending yielding damper

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.