Concentric Braces Research Articles

Experimental study of a new pure bending yielding dissipater

In this paper, a new yielding dissipater device is introduced for seismic protection of concentrically braced structures. The device is fabricated by a set of transverse plates inserted in the middle of a diagonal brace. The special configuration of the new device transforms the axial force of a concentric brace to pure bending in the dissipater plates. The dissipater plates are designed to bend inelastically over their whole surface to dissipate energy. Welding is avoided in the dissipater plates and consequently the ductile behavior of steel results in a good hysteric behavior of the new device. Experimental results of sixteen specimens of the proposed dissipater device show a stable hysteretic behavior of the brace and similar behavior in tension and compression. An analytical model is developed and verified to predict the behavior of the proposed dissipater.

Achieving a more effective concentric braced frame by the double-stage yield BRB

The steel Concentric Braced Frame (CBF) is a popular structural type for buildings in seismic areas. In fact, it can conveniently provide the building with large strength and stiffness. Furthermore, the simplicity of fabrication that derives from the use of shear connections between beams and columns appeals to structural designers. Unfortunately, the dissipation capacity of steel braces is limited and the structural type is low redundant and thus prone to storey collapse mechanisms. To improve the seismic performance of the CBF double-stage BRBs (DYBs) could be used instead of conventional steel braces. The DYB exhibits high dissipative and stable cyclic response and, if inserted into a steel frame, promote the spread of damage owing to the shape of its hysteresis loop. Despite its qualities, in literature there are no design methods that allow its use. Hence, in this paper, a design method for steel frames with DYBs is formulated in compliance with the principles of the European seismic code. The behaviour factor q is calibrated to meet the performance objectives of Eurocode 8. The calibration is performed by nonlinear dynamic analysis conducted with OpenSees on 75 frames with different features. The numerical model is calibrated on the results of the experimental tests performed by Pan and his co-workers at Tsinghua University in Beijing (China). The deduced results confirm the effectiveness of the frame with DYBs, which can be designed with q values greater than those used for traditional steel braced frames.

Seismic Evaluation of Reinforced Concrete Moment Frames Retrofitted with Steel Braces Using IDA and Pushover Methods in the Near-Fault Field

One of the methods for seismic retrofitting in reinforced concrete structures is the application of steel braces. In this paper, the effect of concentric and eccentric bracing systems on the seismic performance of dual reinforced concrete building systems was inspected through seven near-fault earthquake records. Pursuant to that, two reinforced concrete frames with 10-story and 5 spans were designed and analyzed by means of the incremental dynamical analysis (IDA) method where the braces were placed in the 1st and 5th spans. The results revealed that the bearing capacity of the reinforced concrete frame by applying CBF and EBF braces increases up to 2.3 and 2 times, respectively. The use of EBF brace in a reinforced concrete frame reduces the amount of the base shear applied to the structure up to 7 times compared with the CBF frame. Approximately, the displacement of the roof in the EBF frame is less than the CBF frame. Moreover, the ductility of the EBF frame against earthquake records causes an increase in the performance level of structure to the immediate occupancy (IO).

Evaluating inelastic performance of mega-scale bracing systems in low- and medium-rise structures

In this paper, the various aspects of the seismic performance of different concentric bracing arrangements have been inelastically analyzed in a comprehensive manner. The results suggested that mega-scale bracing systems rendered more controlled performances during severe seismic events. These systems distributed the plastic hinges in much superior manners, allowing for the inelastic capacity to come into use. They reduced the target displacements due to the reduction in the natural periods of the structures. The mega-scale bracing systems also led to 25% reduction in the weight of the structures, 54% less drift ratios and 45% smaller uplift forces. The stiffness of the stories in these systems increased up to 100% and lateral displacements reduced by up to 32%.

Experimental investigation of strengthening reinforced concrete moment resisting frames using partially attached steel infill plate

Numerous methods such as adding different eccentric and concentric braces, steel or concrete shear walls, etc. are used to strengthen reinforced concrete (RC) frames. If the seismic characteristics of the hybrid seismic resistant system are not known, choosing the suitable system for strengthening would be difficult. In this paper, the behavior of a moment resisting reinforced concrete frame strengthened with partially attached steel infill plate subjected to cyclic lateral loads has been investigated. The assessment has been carried out through an experimental approach with conventional and perforated steel infill plates. Five moment resisting reinforced concrete frames with identical dimensions, steel content, and concrete strength were built with the scale of 1:3. Among the four samples, two incorporated perforated, partially attached infill plates and the other two were strengthened with conventional partially attached steel infill plates. Finally, the cracking pattern, effective stiffness, strength reduction factors, ductilities, ultimate strengths, and energy absorption capacities of all the samples were calculated and compared. The results show that using partially attached steel infill plate causes the cracking pattern of the strengthened frame to be almost similar to that of the initial frame. In addition, the perforated steel infill plate not only increases the stiffness and lateral strength of the frame, it also increases the strength reduction factor by 35%.

Experimental study on seismic behavior of shear wall with fiber reinforced polymer concrete

In order to improve the seismic performance of common concrete shear wall with concealed bracings, fiber reinforced polymer modified concrete instead of ordinary concrete was applied to the shear wall as described in this paper. In this paper, the experimental study on the seismic performance of two different types of shear walls under cyclic loading was carried out, and also the failure characteristics, bearing capacity, ductility, hysteretic curve, stiffness attenuation and energy dissipation performance of the proposed shear wall were analyzed systematically. The test results show that the seismic performance of fiber-reinforced polymer modified concrete shear wall is significantly improved because its the damping ratio, deformation capacity and energy dissipation capacity are greatly improved compared with ordinary concrete shear wall with concealed bracings, which ensures its better stiffness stability in the later stage.

Seismic Performance and Retrofitting of Steel Building

Some special Engineering firms are taken for rehabilitation by Performance based seismic design (PBSD). The existing building that has high value of facilities is important to make functional after immediate post-earthquake. Current codes and provisions cannot cover all structures located in active seismic zone and these structures are not capable of withstanding seismic action. Furthermore, heavy active earthquakes in urban areas have obviously established an urgency to measure performance of the existing building, upgrade and strengthen these seismic undersupplied structures. Many researchers worked in recent years to measure the performance of the building structures and develop various strengthening and rehabilitation techniques to improve the seismic performance of structures. The main objectives of this research are to evaluate the seismic performance of the steel frame building is designed as a multi-storey office building under seismic action located in Timisoara, Romania and using pushover analysis for the Life Safety performance level under an earthquake hazard level with 10% probability of exceedance in 30, 50, 100, 225, 475 and 975 years. The seismic performance of the building is measured by the push-over analysis by FEM software SAP2000. For this push over analysis, the target displacement of the top of the building is measured for life safety performance. The demand curve for the life safety, emergency occupancy, Local damaged, structural damaged, collapse of the building is conducted for different seismic actions. Capacity curve of the building is compared to the demand curve for checking the performance mentioned above. The capacity curve is less than the demand curve for all seismic actions. The building must be retrofitted for increasing the performance during seismic actions. The steel building is retrofitted by providing the steel bracing. The bracing size used is TUB-168.3x4 mm in the direction of tension and the performance of the building is tested by using pushover analysis for the same conditions that are done for unbraced structure. The performance of the building again determined for the same seismic actions. The lateral displacement of the building has significantly improved. The capacity curve coincides the first four accelerations for unbraced structure. The capacity curve is more than the demand curve and coincide all demand curves for all return periods and all accelerations for braced frame. The size of concentric tension brace is bigger; that is why no plastic hinges formed for all peak ground accelerations.

Modeling and Seismic Response Analysis of Italian Code-Conforming Single-Storey Steel Buildings

ABSTRACTThis article describes the structural design, nonlinear modeling, and seismic analysis of prototype single-storey non-residential steel buildings made of moment-resisting portal frames in the transverse direction and concentric braces in the longitudinal direction. Various design parameters (building geometry, seismic hazard, foundation soil category) and different modeling assumptions (bare frame model, model including cladding elements, ground motions including vertical accelerations, and modeling uncertainties) were considered to investigate their effects on the simulated seismic performance.

Low reversed cyclic loading tests for integrated precast structure of lightweight wall with single-row reinforcement under a lightweight steel frame.

Given the development of precast structures for low-rise residential buildings, this study explores a new structure—namely, an integrated precast structure of lightweight recycled concrete wall with single-row reinforcement—under a lightweight steel frame filled with recycled concrete (integrated precast structure for short). The lightweight steel frame and lightweight wall cooperate to bear the forces. The applied concealed bracing, either a rebar bracing or a steel plate bracing, increases the shear resistance of the wall. The lightweight steel frame is designed to bear the vertical loading, whereas the seismic load in the horizontal direction is jointly borne by the frame and wall. This study presents the results of low reversed cyclic loading tests on nine specimens of integrated precast structures. An analysis is then carried out to investigate the mechanical properties of the specimens; based on these results, a formula for the force-bearing performance of the inclined section is developed. The results show satisfactory performance as an integrated piece; the proposed structure has two seismic lines of defence, with the lightweight wall restraint by the side frame being the first line and the steel frame being the second line. Because the failure of the wall can be categorized as shear failure, the restraint of the lightweight steel frame significantly reduces the potential damage of the wall. As the beams and columns of the steel frame tend to bend against failure, the wall filling helps resist sliding. Therefore, the reinforced joints of the connecting beams and columns show no visible signs of damage, indicating that the connection between the beams and columns is reliable. The narrow spacing of rebars and the setting of concealed bracing contribute to the increase in ductility and energy efficiency of the integrated structure and the evident reduction in the failure process. Furthermore, the recycled concrete increases the seismic resistance of the structure.

The Seismic Investigation of Off-Diagonal Steel Braced RC Frames

Abstract Steel bracing may be used to enhance the seismic strength of RC frames. Concentric steel bracing generally reduces ductility, which is a key component of seismic design. To overcome the problem, ductile steel brace-RC frame systems are therefore usually introduced in the form of eccentric braces. In the present study, the Off-Diagonal Bracing System (ODBS), which works as a concentric type of bracing, is investigated. In this paper the response of ODBS elements to cyclic loading is first explored and compared with those of other types of bracing such as X-bracing and inverted-V bracing systems. The time history analysis responses and cyclic hysteresis responses of a number of lowrise to mid-rise RC frames retrofitted with different types of bracing systems are then evaluated and compared. It is shown that under seismic excitation, a much reduced base shear is experienced by frames retrofitted with ODBS compared to other bracing systems. The results of time history and cyclic hysteresis response analyses also indicate a far greater energy dissipation capacity and ductility for the ODBS compared to other bracing systems. It is also concluded that ODBS performs best in lowrise frames. The out-of-plane buckling response of the ODBS is also investigated, and it is shown that a double-plated central connection can control such an adverse response.

PUSHOVER ANALYSIS OF REINFORCED CONCRETE BUILDING WITH VERTICAL SHEAR LINK STEEL BRACES

In recent decades, steel cross bracing has been used as a conventional method to retrofit concrete buildings. Most of the cases utilized concentric steel braces system. However, studies concerning the behavior of RC frames with eccentricity steel bracing are quite limited. In this research, three types of structures incorporating special moment frames, RC structure with invert V braces and RC structures with vertical link beams with different stories were modeled through SAP 2000 and analyzed by considering nonlinear static analysis (pushover). Results revealed that invert Y steel braces (vertical shear links) system is an alternative way to construct a ductile structure with great lateral stiffness. It was also found that the axial force in braces is controlled by the behavior of the vertical link beam.

Numerical evaluation of ductility and energy absorption of steel rings constructed from plates

Several studies have been performed to increase the ductility of concentric braces in the past decades. Incorporating an energy-dissipator member in the braces is one of the novel approaches to increase the ductility of the braces. Experimental and numerical studies have shown that steel rings made of steel pipes can be an effective energy-dissipator in the braces. However, due to the limitations on the size of the steel pipes, it is not always possible to find an appropriate pipe to be used in the braces. In the current study, performance of the steel ring made of two half-steel rings is investigated. In addition, effect of the welding or utilizing bolts, thickness of the ring, and material properties on the ductility and energy absorption of the braces is evaluated. Results indicated to the appropriate ductility and energy absorption of made-up steel rings.

Seismic Behavior of Chevron Concentrically Braced Frames with Weak Beam

Concentrically braced frames provide ductility and imparted seismic energy dissipation through yielding of tension braces and buckling of compression braces. In braced frames with chevron configuration, difference of actions in tension and buckled brace results in considerable unbalanced force at brace-beam intersection, which is addressed in modern seismic design provisions. In this paper, effect of flexural capacity of beam to carry this unbalanced force and consequently seismic behavior of braced frame is investigated by finite element analysis. Two-story and four-story chevron braced frames were modeled in ABAQUS software and studied by means of nonlinear cyclic pushover and nonlinear response history analysis methods. Results showed that inadequate flexural strength of the beams reduce lateral stiffness and strength of braced frame significantly as lateral drift increases; therefore, concentration of lateral deformation in one story may cause formation of soft and weak story. Furthermore, seismic behavior of chevron braced frame and two-story X braced frames were compared.

A Suggested Method for Improving Post Buckling Behavior of Concentric Braces Based on Experimental and Numerical Studies

Concentrically braced structures are one of the most common resistant systems in steel buildings due to their high stiffness and lateral strength. These systems have a good performance under mild earthquakes that behave in the elastic range. However, when these structures are subjected to moderate and severe earthquakes, their main weakness is being revealed. Under these earthquakes, the structure enters the inelastic zone and thus the braces that are pressurized begin to buckle. This makes it impossible to use the full capacity of braces in the energy dissipation exerted on the structure. In the past decades, researchers have conducted a variety of studies to improve the behavior of concentric bracing systems. This paper introduces a method for improving the post-buckling behavior of concentric braces. In this method, a side-mounted fuse is used in the middle of the brace to modify the post-buckling behavior of concentric braces. The results of experimental and numerical researches of this study indicate the better performance of this structural system in terms of ductility and energy dissipation capacity compared to the common concentric braces. The suggested system can be utilized to reduce the capacity of bracing connection which results in reduced costs of the project.

Experimental and Numerical Evaluation of Older Chevron Concentrically Braced Frames with Hollow and Concrete-Filled Braces

AbstractDetailed seismic provisions for concentrically braced frames have evolved continuously since 1988. Thus, vintage-era braced frames, especially those designed prior to 1988, may be prone to ...

Steel Plate Cold‐Rolled Section Steel Embedded High‐Strength Concrete Low‐Rise Shear Wall Seismic Performance

Four test pieces with different steel plate center‐to‐center distances and reinforcement ratios are subjected to low‐cycle repeat quasistatic loading to optimize properties as failure mode, hysteretic curve, skeleton curve, energy dissipation parameters, strength parameters, and seismic performance of high‐strength concrete low‐rise shear walls. The embedded steel plates are shown to effectively restrict wall crack propagation, enhance the overall steel ratio, and improve the failure mode of the wall while reducing the degree of brittle failure. Under the same conditions, increasing the spacing between the steel plates in the steel plate concrete shear wall can effectively preserve the horizontal bearing capacity of the shear wall under an ultimate load. The embedded steel plates perform better than concealed bracing in delaying stiffness degeneration in the low‐rise shear walls, thus safeguarding their long‐term bearing capacity. The results presented here may provide a workable basis for shear wall design optimization.

Local fuse for improving concentric braces behavior

Local fuse for improving concentric braces behavior

A survey of hysteresis energy distribution and lateral displacement in steel buildings with CCB brace at internal and external frames

PurposeThe purpose of this paper is to study the method of hysteresis energy distribution and maximum relative lateral displacement in buildings’ stories, under the influence of scaled records for near-fault and far-fault earthquakes. The bracings in the considered buildings’ plan are distributed in two different ways: in the first case, the braces are added in external frames of the building, and in the second case, in the internal ones.Design/methodology/approachThis research first selects some steel buildings with concentric braces and studies the seismic vulnerability of buildings under different earthquakes in accordance with the concepts of input and Hysteresis energy. In order to study the impact of braces’ distribution in the building’s plan, the buildings were modeled in this study in two ways. In the first way the braces were added to the building’s external frames and in the second way in its internal ones.FindingsResults show that the need for far-fault scaled records’ displacement is more than the near ones and that the resultant relative lateral displacements in buildings with external braces are more than those with internal ones.Originality/valueAfter these studies on the way of hysteresis energy distribution, it was shown that in case of buildings with internal braces, as the building’s height increases, the share of higher stories of the hysteresis energy rises. Also, it was illustrated that hysteresis energy distribution in buildings with internal braces is more uniform than those with external ones.

Earthquake Control of Highrise Buildings Using Combination of Shear wall and Concentric Steel Bracing

Earthquake Control of Highrise Buildings Using Combination of Shear wall and Concentric Steel Bracing

Seismic collapse margin of steel frame structures with symmetrically placed concentric braces

This paper focuses on the seismic collapse assessment conducted on the steel frame structures with symmetrically placed concentric braces using collapse margin ratio (CMR). The main issue with concentrically braced frames (CBFs) is the existence of a vast number of possible combinations in their topology. Therefore, selecting the most efficient group of retrofit schemes (RS), regarding the overall performance index (PI) of the structure requires a simple and quick method of brace manipulation, specifically, removal and/or addition, and a series of basic symmetrical principles in the retrofitting process. However, identifying the optimal RS for new or existent structures requires an evaluation of the optimal CMR value and the retrofitting cost as well. The influence of both cross-section and configuration type of the bracing system provides new insights into the collapse margin. Finally, this paper points out new parameters that should not be neglected in the retrofit design of bracing systems for steel frame structures.