Concentric Braces Research Articles

Seismic behavior of steel fiber reinforced high strength concrete shear walls with different embedded steel configurations

Four steel fiber reinforced high strength concrete shear walls with different embedded steel configurations were conducted under quasi-static tests, to investigate the influences of the diagonal steel bar bracings in the wall web, the embedded steel tubes in the boundary zone, and the concealed steel truss on the seismic behavior of the proposed shear walls. Furthermore, the finite element modelling and the parametric analysis were conducted and verified against the test results. Research shows that both the reinforcement bracings and the channel steel bracings restrained the development of cracks and decreased the crack widths, especially the channel steel bracings, which showed a more remarkable effect on alleviating the damage of the wall. The two types of the concealed bracings could slow down the stiffness degradation rate, and enhance the plastic deformation capacity of the shear walls. The finite element analysis indicated that a reasonable axial load ratio was conductive to exert the cyclic behavior of the concealed bracings. For the steel truss reinforced concrete walls, the increase of the cross sectional ratio of steel tubes within a reasonable range could improve the co-working performance for the wall panel and the boundary columns.

Seismic performance of superimposed RC shear walls with concealed bracings using different horizontal connections

To enrich the horizontal connection method and to further study the seismic performance of superimposed RC shear walls with concealed bracings (SRCBSWs) using different horizontal connections, three specimens including SRCBSW with horizontal connection by steel plate bolt kit (SPBK), SRCBSW with horizontal connection by U-ring buckle insert (URBI) and cast-in-place shear wall with concealed bracings were tested under quasi-static loading test. Test results indicated that SRCBSWs exhibited the seismic performance close to that of cast-in-place specimen. The horizontal connection of URBI not only enabled achieve the goal of equivalent cast-in-place connection, but had a beneficial effect on the energy consumption. Due to the fact that the steel plates of SPBKs slipped relative to the contact concrete, the horizontal connection by SPBK was not conducive to energy dissipation and stiffness degradation of the wall, while the load-bearing capacity and deformation characteristic could be enhanced due to the cooperative work of steel plates and concrete in later loading. Finite element analysis of SRCBSWs by Abaqus was conducted based on the proposed modelling techniques, and the reasonable accuracy of the numerical method was verified. The parametric analysis results showed that the axial load ratio, volumetric ratio of the X-shaped steel plate bracings and longitudinal reinforcement ratio in hidden column had obvious effect on the load-bearing capacity and elastic stiffness of SRCBSWs. Taking displacement ductility into account, the axial load ratio of SRCBSWs should be reasonably restricted in practice. Moreover, appropriate thickness of steel plates in SPBKs should be determined according to actual demand, but at least one set of SPBK needed to be arranged in the middle of the wall along the height direction when conducting the layout of SPBK. Besides, the inserted reinforcement ratio in URBI could be reinforced in accordance with the constructional requirements.

Behavior of Reinforced Concrete Frames Retrofitted by Different Configurations of Concentric Steel Braces

Behavior of Reinforced Concrete Frames Retrofitted by Different Configurations of Concentric Steel Braces

Performance-based rules for the simplified assessment of steel CBFs

In this work, a simplified method for the evaluation of the seismic performance of steel Concentrically Braced Frames (CBFs) in everyday practice is presented. This method, applicable in the immediacy of a seismic event and for quick mapping of the seismic vulnerability of a built area is fully analytical, allowing the representation of the capacity curve of a structure through a trilinear approximation and considering the second order-effects. To set the methodology, extensive parametric analysis is performed on 420 simple CBFs designed according to 3 different approaches namely the Theory of Plastic Mechanism Control ensuring the design of structures characterized by global collapse mechanism (Global Concentrically Braced Frames (GCBFs), the Eurocode 8 provisions (Special Concentrically Braced Frames (SCBFs)) and the design for seismic forces only (Ordinary Concentrically Braced Frames (OCBFs)) without any hierarchy criterion. The capacity-demand checking procedure according to the code-compliant approach and Nassar & Krawinkler is also reported.

Performance evaluation and strengthening of reinforced concrete buildings

In view of the past earthquakes, it is stated that several structures are located in active seismic zones around the world. So, improvement of the earthquake performance levels of the existing buildings by using various strengthening methods has been the major interest in structural engineering. Non-linear analysis procedures that are defined in several seismic codes exhibit reliable results in the evaluation of seismic performances of existing buildings. In this study, seismic performances of three, five and eight storey existing and strengthened reinforced concrete buildings having the common floor plan, material and section properties of the structural members are investigated according to Turkish Building Earthquake Code-2018 and American Standard, ASCE. To obtain the earthquake performance results of reinforced concrete buildings, displacement demands of the buildings have been obtained and utilized in nonlinear analyses. SAP2000 structural analysis software is used in the solutions. The determined strengthening techniques are provided by adding concentric steel bracing members to existing reinforced concrete buildings and jacketing of the determined columns. As a result of non-linear analyses applied to the existing and strengthened buildings, damage situations of the structural members are determined, seismic performances of the buildings are evaluated according to both codes and the results are interpreted in the end.

Investigation of the Occurrence of Progressive Collapse in High-Rise Steel Buildings with Different Braced Configurations

Abstract The progressive collapse phenomenon refers to a chain of damages in a structure where all or a large part of the structure is destroyed by an initial local collapse in it, which can lead to very disastrous results. Therefore, the prevention of progressive collapse has become a necessary action in the design and analysis of buildings and it is vital to investigate this topic more accurately. This study aims to present a proposed pattern in the configuration of braces at the height of a high-rise steel building for reducing the probability of progressive collapse. In this regard, the vertical displacement of 18-story structure with four scenarios of column removal and five concentric bracing patterns including V, Inverted V, X, discontinuous X-bracing at height, and a combination of Xbracing in the side spans and discontinuous X-bracing at height in the middle spans are investigated and compared. In this study, the Alternative Path Method (APM) is used based on the GSA guideline for the analysis of progressive collapse. The results of this research showed that the use of X-bracing in the side spans and discontinuous X-bracing in the middle spans in nonlinear static and dynamic analyses performed better in reducing the probability of progressive collapse than other bracing configurations. Finally, it is recommended to use discontinuous X-bracing at the height that would place the bracings in one direction and providing alternative paths for force transferring in the structure.

Hysteretic behavior of high-performance frame-shear wall composite structure with high-strength steel bars

Three 2-story frame-shear wall structures that integrated the advantages of composite structure and high-performance materials were designed and tested under cyclic lateral loading to develop a high-performance structure with satisfactory seismic behavior and reparability. HRB 600 MPa steel bars (i.e., hot rolled ribbed rebar with nominal yield strength of 600 MPa) and 1400 MPa ultra-high strength (UHS) steel bars were used for vertical component reinforcement, and different reinforcement configurations were taken as the design parameters. The results showed that the proposed structure can be repaired at a large drift of 2% and ensure sufficient collapse resistance capacity as well. The structure only reinforced with HRB 600 MPa longitudinal bars in vertical components showed better energy consumption capacity but serious concrete damage. Replacing all HRB 600 MPa longitudinal bars with an equal strength of UHS longitudinal bars have a more pronounced role in avoiding the deformation and damage concentration in the lower floor and controlling the growth rate of residual drift than partially replaced hybrid reinforced structures. The UHS reinforcement concealed bracing can effectively decrease the shear strength degradation, control the damage of shear wall, and improve the reparability of the structure. According to the failure mechanism, an ideal load-deformation response to reflect the damage state was proposed.

Dual system design for a low-ductility concentrically braced frame with a reserve moment frame

To address shortcomings of the moderate-seismic design philosophy currently implemented in the United States, this paper proposes design criteria for a Concentrically Braced Dual Frame (CBDF). In contrast to existing low-ductility Concentrically Braced Frame (CBF) systems, such as R=3 CBF (R3CBF) and Ordinary Concentrically Braced Frame (OCBF) systems, the proposed CBDF design approach explicitly considers the strength and integrity of the post-elastic, degraded (reserve) system. Specifically, the CBDF is defined to consist of a stiff low-ductility primary concentrically braced frame (PCBF) supplemented by a flexible, distributed reserve moment-resisting frame (RMRF). Relative to the R3CBF and OCBF systems, the proposed CBDF system achieves superior collapse performance without the need for costly ductility detailing requirements or substantial changes to traditional seismic design provisions. Consequently, the CBDF system is proposed as a practical, reliable, and cost-effective design alternative to R3CBF and OCBF systems.

Modelling issues and pushover response of singlestory older steel buildings

AbstractThe paper describes a study concerning the seismic response of some typical non‐residential single‐story older steel buildings. To this end, the design of two archetype buildings was simulated according to structural codes and standards of practice used in Italy in the 1980s‐1990s. The basic structural layout was assumed to be made of trussed portals in the transverse direction and concentric braces in the longitudinal direction. In the direction of the trussed portals, two alternative structural options were considered: (a) a pinned column base with moment action provided by the truss, and (b) a semi‐continuous column base with a pinned connection between the truss and the column top cross section. 3D finite element non‐linear models of the two case study structures were built. The model included the main frame members, some critical connections and explicit representation of fracture propagation for braces. Results from non‐linear static analysis are then presented and discussed. The paper highlights differences in the structural response due to differences in the selected design options, comparing both global and local response results.

Numerical‐experimental analysis of a braced steel frame subjected to fire following earthquake

AbstractMany historical events have shown that, after an earthquake, fire may be triggered by seismic‐induced rupture of gas piping, failure of electrical systems, etc. The current engineering design methods still ignores many aspects of multi‐hazard and in particular fire following earthquake (FFE) analysis. In this respect, the aim of this paper is to study the behaviour of a braced steel frame subjected to seismic‐induced fire. In particular, FFE numerical analyses were conducted on a four‐storey three‐bay braced steel frame with concentric bracings. The results of the numerical analyses served to design the FFE tests performed on unprotected and protected columns belonging to the bracing system. The fire tests after the seismic event were carried out by considering the effects of the surrounding seismically damaged structure. Results of the FFE tests on unprotected columns are reported along with the numerical model calibration.

Quasi‐static test and strut‐and‐tie modeling of precast concrete shear walls with unconnected vertically distributed reinforcements

AbstractTo solve the fabrication problems of traditional precast shear walls caused by too many connections joints, a new type of precast shear wall with unconnected vertically distributed reinforcements and concealed bracings is developed in this paper. Four full‐scale shear walls, including one cast‐in‐place specimen and three precast specimens, were tested under low‐cycle lateral loading conditions to evaluate the seismic performance of the new type of precast shear wall. The test results showed that the loading capacity and energy dissipation of the new type of precast shear wall were comparable to those of the cast‐in‐place specimen; however, the failure mode was similar to the damage mechanism of an infilled wall frame, not the traditional bending‐shear mode of shear walls. Then, a new strut‐and‐tie model considering dowel action was proposed for this new type of precast shear wall. Finally, a parametric study was conducted by finite element analysis to determine a reasonable value of the effective strength coefficient for the strut‐and‐tie model. Good agreement was achieved between the test and model results.

Comparative Analysis and Study the Behavior of Transmission Line Tower with using Eccentric and Concentric Bracing System with using STAAD Pro Software

The principle objective of this project is to “Model, Analysis and Study the behavior of transmission line tower with Concentric and Eccentric type of bracing system by using STAAD Pro software”. The Model methods used in STAAD Pro analysis are limit state Design conforming to Indian Standard Code of Practice. STAAD Pro features a state-of-the-art user interface, visualization tools, powerful analysis and design engines with advanced finite element and dynamic analysis capabilities from model generation, analysis and design to visualization and result verification, STAAD Pro is the professional’s choice. Our Final work was the “Comparative Analysis and study the behavior of transmission line tower with Concentric and Eccentric type of bracing system” under various load combinations. Using Indian equal angle section, wind zone II and seismic zone III. And considering the plane terrain

Proposal and validation of a design procedure for concentrically braced frames in the chevron configuration

AbstractIn the recent past, several research studies have highlighted that the prescriptions reported in codes for the design of structures with concentric braces in the chevron configuration are often not effective in preventing yielding or buckling of non‐dissipative members and in ensuring collapse mechanisms characterised by uniform damage of braces. To investigate the reasons of these deficiencies, in this paper the seismic response of concentrically braced structures designed according to procedures reported in the literature and in the European seismic code is first examined. Then, a new design procedure is proposed, in which the innovative aspects are mainly related to the estimation of the bending moments in columns and to the formulation of requirements on the stiffness of braced beams and columns. The impact of the proposed procedure on the structural costs is computed on a large number of buildings characterised by different occupancy types and geometric properties. The seismic performance of these structures is evaluated by incremental nonlinear dynamic analysis and discussed at the achievement of the significant damage and near‐collapse limit states.

Effects of Bracing System on Multistoryed Steel Building

In recent years, in regions of the highly seismic prone area, steel construction has changed from moment resistant frames to concentrically braced frames. To withstand earthquake forces, bracing part of the structural pattern by providing extra stiffness plays a crucial role in structural action. Concentric bracing in building frames is one of the most common horizontal load resistance patterns. For this reason, seven distinct models were created by changing the bracing pattern in the steel frame and analyzed for wind and seismic forces A 20-story steel frame structure is explored in this presented work. From this research, it can be inferred that the bracing factor will have a very significant impact on structural behavior under seismic loading. The most desirable bracing framework is the Backward bracing pattern. Horizontal displacement at the top floor is decreased by approximately 50 percent for Backward braced in frame structure compared to without bracing pattern.

Performance of a New Model of Rectangular Damper in Diagonal Concentric Brace

In this study, the performance of rectangular added damping and stiffness (RADAS) dampers has been introduced in the diagonal element site to avoid brace buckling and energy dissipation by dampers. The innovation of this research is in the type of site of steel plates and the way of connection in the vicinity of gusset plates which can be easily replaced. To investigate the cyclic performance of the ADAS damper, 15 numerical examples have been simulated by ABAQUS software. The study of cyclic behavior on the single-bay and single-floor steel frame has been done, and the sensitivity of cyclic behavior based on the thickness, length and ratio of dimension to the thickness has been studied. The studied thicknesses of the damper were 12, 21 and 30 mm, the studied lengths of the damper were 400, 500 and 600 mm, the studied geometry of the damper was rectangular, and the studied thicknesses of the brace were 12, 21 and 30 mm. The results of this study showed that this type of damper has good behavior in the energy dissipation of the frame and the total stiffness of the steel plates forming ADAS dampers must be less than the stiffness of the brace to show acceptable frame performance. By changing the damper length parameter from 600 to 500 and 400 mm, each of the indicators of stiffness, ultimate strength and energy has increased by a maximum of 144, 46 and 149%, by changing the damper thickness parameter from 12 to 21 and 30 mm, each of the mentioned indices has increased by a maximum of 147, 52 and 160%, and by changing the brace thickness parameter from 12 to 21 and 30 mm, each of the mentioned indices has increased by a maximum of 5, 7 and 9 percent. The values ​​of the damper thickness and length, when they are less stiff than the stiffness of the brace, cause the plastic hinge formation to be made on the damper, and the damper performance is optimized.

Effect of the Bracing System on the Probability of Collapse of Steel Structures under Maximum Credible Earthquake

Simple bracing frames can be divided into two types in terms of concentric or eccentric. Concentric bracing frames are frames that intersect with other structural members at one point in the structure along the bracing members. Otherwise, the braced frame will be eccentric. It is said empirically that due to this type of shaping, eccentric bracing frames exhibit more ductile behavior and concentric bracing frames exhibit more stiff behavior. This behavioral difference caused this study to be numerically computing for five frames, including unique concentric and eccentric bracing frames of 5 and 10 stories and an ordinary 5‐story concentric bracing frame. Their tensions and drift ratios should be acceptable for the use of residential buildings. Using the primary two steps of the new PEER probabilistic framework, namely, probabilistic seismic hazard analysis and structural analysis, which leads to the drawing of fragility curves, the probability of collapse is obtained to compare the safety capability of these frames according to their different characteristics against earthquakes. The results show that increasing the ductility or increasing the number of floors or the height of these systems can reduce collapse. Also, according to the results of the probability of collapse obtained in frames with 5‐story concentric bracing frames, it can be said that some of the current regulations, which work based on previous approaches of analysis, can lead to unsafe structures with a high probability of collapse.

Creating and designing repairable regular steel buildings with seesaw motion to achieve seismic resilience

Using seesaw structural system in buildings is a way for creating earthquake-resilient buildings, namely buildings which can be easily and quickly repaired with little cost, even after major earthquakes. To create such a system, all internal columns at the lowest story are removed and instead, a central mega support is used, combined with a grid of orthogonal strong girders as the first floor, and all circumferential columns at the lowest story are equipped with energy dissipaters at their bottoms. In this article, after presenting a simplified dynamical model for seesaw buildings, to create the analytical base for proposing the preliminary design rules for this type of buildings, the proposed rules have been developed and supported by conducting several non-linear time history analyses (NLTHA) cases on a set of regular steel buildings with concentric bracings, having 3, 5, 7 and 9 stories with different number of bays, and various bay sizes. NLTHA results indicate that the immediate occupancy performance level is mostly achieved in the designed seesaw buildings. The efficiency of this system in low-rise buildings is more than mid-rise ones. Although seesaw buildings respond relatively well to both near- and far-field events, they behave less effectively in near-field pulse-like earthquakes.

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.

Evolution of EC8 Seismic Design Rules for X Concentric Bracings

Eurocodes are currently under revision within a six-year program by CEN/TC 250. In this framework, concentric bracings, particularly in cross configuration, have been largely debated; indeed, several criticisms affect the seismic design procedure currently codified within Eurocode 8, entailing significant design efforts and leading to massive and non-economical structural systems, even characterized by poor seismic behavior. The efforts of SC8 have been aimed at improving the codified seismic design criteria for concentrically braced frames, by providing requirements and detailing rules conceived to simplify the design process and to improve the seismic performance. The current paper provides recent advances in the field of computational and structural engineering focusing on symmetric X concentrically bracings in seismic area, outlining the evolution of Eurocode 8 (EC8) seismic design rules, by examining the following aspects: (i) ductility class and behavior factor, (ii) analysis and modelling aspects, (iii) design of dissipative members; (iv) design of non-dissipative zones; (v) brace-to-frame connections.

Simulation Analysis on Maximum Height of Semi-Rigid Concentrically Braced Steel Frame

The prefabricated semi-rigid concentrically braced steel frame is a highly-assembled seismic structure. The structure is subject to definite stress and has two seismic precautionary lines. It can be utilized in multi-story and high-rise steel structures. Finite element software is used in this study for response spectrum analysis of a 12-storey semi-rigid concentrically braced steel structure under the conditions of frequent earthquakes to assess the seismic performance of the structure. Dynamic elastic-plastic time history analysis of this structure is also performed under the conditions of rare earthquakes in the case of various seismic precautionary intensities. Critical performance indicators of the structure including plastic hinge development, maximum inter-storey drift angle, and storey shear distribution are also investigated. The results indicate that under earthquakes of various seismic precautionary intensities, the maximum inter-storey drift angles of the prefabricated semi-rigid concentrically braced steel frame structure do satisfy the seismic demands. The brace and the semi-rigid joint steel frame show excellent cooperative work performance. The structure can only be applied in regions with low seismic precautionary intensity.