Damped Braces Research Articles

Displacement-based seismic design of hysteretic damped braces for retrofitting in-plan irregular r.c. framed structures

A displacement-based design procedure is proposed for proportioning hysteretic damped braces in order to attain, for the in-plan least seismic capacity direction and a specific level of seismic intensity, a designated performance level of a reinforced concrete (r.c.) irregular framed building to be retrofitted. To this end, a computer code for the nonlinear static analysis of spatial frames is developed to obtain the pushover curve for an assigned in-plan direction of the seismic loads. The town hall of Spilinga (Italy), a two-storey r.c. framed structure with an L-shaped plan built at the beginning of the 1960s, has been considered as case study. Four alternative structural solutions are examined, derived from the first one by the insertion of hysteretic damped braces, considering: the extended N2 and the extended pushover methods combined with a proportional and an inversely proportional in-plan stiffness distributions of hysteretic damped braces. To check the effectiveness and reliability of the design procedure, the nonlinear static response of the unbraced and damped braced frames is compared for different in-plan directions of the seismic loads. Frame members are simulated with a lumped plasticity model, including a flat surface modeling of the axial load-biaxial bending moment elastic domain, while the behavior of a hysteretic damped brace is idealized through the use of a bilinear law. Vulnerability index domains are adopted to estimate the directions of least seismic capacity at the ultimate (i.e. life-safety and collapse prevention) limit states prescribed by Italian and European seismic codes.

Equivalent viscous damping for displacement-based seismic design of hysteretic damped braces for retrofitting framed buildings

A displacement-based design (DBD) procedure aiming to proportion hysteretic damped braces (HYDBs) in order to attain, for a specific level of seismic intensity, a designated performance level of a structure is proposed for the retrofitting of framed buildings. A key step for the reliability of the DBD procedure is the selection of the equivalent viscous damping in order to account for the energy dissipated by the damped braced frame. In this paper, expressions of the equivalent damping are obtained considering the energy dissipated by the HYDBs and the framed structure. To this end, dynamic analyses of an equivalent single degree of freedom system, whose response is idealized by a trilinear model, are carried out considering real accelerograms matching, on the average, Eurocode 8 (EC8) response spectrum for a medium subsoil class. Then, a three-storey reinforced concrete (r.c.) framed structure of a school building, designed in a medium-risk seismic region according to the Italian code in force in 1975, is supposed as retrofitted as if in a high-risk seismic region of the current seismic code (NTC08) by the insertion of HYDBs. Nonlinear static analyses are carried out to evaluate the vulnerability of the primary structure, characterized by the lack of interior girders along the floor slab direction, and to select optimal properties of the HYDBs. The effectiveness of the retrofitting solutions is checked referring to nonlinear dynamic analyses, considering artificially generated accelerograms whose response spectra match those adopted by NTC08 for the earthquake design levels corresponding to the serviceability and ultimate limit states.

Nonlinear seismic analysis of RC framed structures equipped with hysteretic damped braces

The insertion of damped braces proves to be very effective for the seismic retrofitting of framed buildings. In the last few decades several applications have been used in many countries, adopting damping systems with different characteristics, depending on both the arrangement of the damped braces and kind of damping device. However, for a widespread application of this technique, practical design procedures and simple numerical models are needed. In this paper, attention is focused on the modelling and nonlinear seismic analysis of framed structures equipped with friction, metallic yielding, viscoelastic and viscous dampers. A design procedure is proposed for proportioning damped braces in order to attain, for a specific level of seismic intensity, a designated performance level of the structure. A six-storey reinforced concrete (RC) framed building, designed in a medium-risk seismic region, is supposed to be retrofitted as in a high-risk seismic region. Two different criteria are followed for distributing the stiffness and strength properties of dissipative braces, over the whole of each storey and among the single braces. A numerical investigation is carried to study the nonlinear dynamic behaviour of the designed structures under real and artificially generated ground motions. The results show that the proposed design procedure is effective and reliable.

Study on the Strengthening Effect of a Typical RC Frame in Wenchuan Earthquake with Attached Substructures

This work is based on a typical RC frame that was closed to the epicenter and collapsed during the Wenchuan Earthquake. The seismic collapse resistance of the frame was strengthened by attached substructures, including conventional brace, buckling restrained brace (BRB) and viscous damper. Collapse fragility analysis based on incremental dynamic analysis is implemented for each strengthening scheme to compare their effects and to analyze the influence of critical parameters. The results show that the viscous damper performs better than the BRB, and the BRB performs better than the conventional brace. With the same strengthening parameters, the A-shaped bracing scheme is better than the X-shaped scheme.

A noniterative design procedure for supplemental brace–damper systems in single‐degree‐of‐freedom systems

SUMMARYIn this paper, a method for designing supplemental brace–damper systems in single‐degree‐of‐freedom (SDOF) structures is presented. We include the effects of the supporting brace stiffness in the dynamic response by using a viscoelastic Maxwell model. On the basis of the study of an SDOF under ground excitation, we propose a noniterative design procedure for simultaneously specifying both the damper and the brace while assuring a desired structural performance. It is shown that to increase the damper size beyond the value delivered by the proposed criteria will not provide any improvement but actually worsen the structural response. The design method presented here shows excellent agreement with the FEMA 273 design approach but offers solutions closer to optimality. Copyright © 2013 John Wiley & Sons, Ltd.

The Empirical Analysis on the Reinforcement Application of the Energy Dissipation to the Framework Structure

With the development of passive energy dissipation technology, using friction damped braces to retrofitted structural are suggested in this paper. Described the basic principles and mechanism of seismic controlled by energy dissipation. The comparative analysis of structure with or without friction damped braces is conducted, and the results show that energy dissipation system is very effective and the working behavior of structure is stable.

Risk‐based optimal retrofit of a tall steel building by using friction dampers

SUMMARYFriction dampers, whose configuration is optimized on the basis of the probabilistic seismic loss associated with a building's damage due to ground motion, were utilized in this study to optimally retrofit a 15‐story steel structure. In line with the concept of performance‐based earthquake engineering (PBEE), a decision‐making procedure based on the monetary seismic loss was incorporated for optimizing the dampers' configuration. A nonlinear numerical model was initially established for representing the structure. In this regard, a brace–damper system was modeled with the buckling of brace elements being addressed accurately and by representing the friction damper's load–displacement relationship on the basis of laboratory evidences. By monitoring the structural deformations in two different response levels, two patterns were established for the distribution of the dampers' strengths throughout the structure, and a number of retrofit alternatives were proposed subsequently. By using incremental dynamic analysis and following the PBEE methodology, the annualized loss (AL), which accounts for all potential damage states in the building and a broad range of seismic intensities, was calculated for each alternative frame. The AL is regarded as a decision variable upon which the best damper configuration is selected. Revealing conclusions were finally made regarding optimal configuration of the damper–brace system. Copyright © 2011 John Wiley & Sons, Ltd.

E-DEFENSE SHAKING TABLE TESTS ON A STEEL HIGH-RISE BUILDING RETROFITTED BY STEEL DAMPERS AGAINST LONG-PERIOD GROUND MOTIONS

A series of shaking table tests on a high-rise building are conducted in order to assess effects of retrofit using steel dampers. The specimen consists of a four-story steel frame and an upper substitute layers made of concrete slabs and rubber bearings. Steel brace dampers are attached to the steel frame, and modeled steel dampers are utilized for the substitute layers. Long-period ground motions and a design ground motion are used for the tests. Total input energies of the specimen reasonably correspond to the estimations of energy spectra. The deformations of specimen are reduced especially in the portion having dampers. In the steel frame, the energy is mostly dissipated in the steel brace dampers. The capacities of the steel brace dampers are estimated about ten times larger than the seismic demand in a strong long-period ground motion.

DYNAMIC BEHAVIOR AND SIMPLIFIED MODELING METHOD FOR A TIMBER FRAME WITH KNEE BRACE DAMPERS

In this paper, wooden frames with knee brace dampers are designed, and their performance is demonstrated. Lateral dynamic loading tests are conducted in order to examine their dynamic properties. Knee brace system can add stiffness and damping to wooden house without closing its opening, which is a great advantage to reduce torsional response of structure. Simplified modeling method for passively controlled frame is also proposed, and it is based on the characteristics of the frame in two states ; without damper and with rigid damper. Dynamic property, maximum response and member's force and deformation can be predicted.

Effects of brace stiffness on performance of structures with supplemental Maxwell model‐based brace–damper systems

AbstractShear‐type buildings with Maxwell model‐based brace–damper systems are studied in this paper with a primary emphasis on the effects of brace stiffness. A single‐story building with a viscous damper installed on top of a Chevron‐brace is first investigated. Closed‐form solutions are derived for the simple structure, relating the brace stiffness and damper coefficient to the targeted reduction in response displacement or acceleration. For a given brace stiffness, the solution is minimized to give a set of formulae that will allow the optimal damper coefficient to be determined, assuring the desired performance. The model is subsequently extended to multistory buildings with viscous dampers installed on top of Chevron‐braces. For a targeted reduction in the mean square of the interstory drift, floor acceleration or base shear force, the minimum brace stiffness and optimal damper coefficients are obtained through an iterative procedure. The response reduction, which signifies the improved performance, is achieved by a combination of brace stiffness and viscous damper coefficients, unlike conventional approaches where damper coefficients are typically optimized independent of brace stiffnesses. Characteristics of multi‐degree‐of‐freedom systems are studied using a 2‐story and a 10‐story buildings where the effects of brace stiffness on the overall performance of the building can be quantified. Copyright © 2010 John Wiley & Sons, Ltd.

Experimental Study of Buckling-Restrained Brace System with Pall-Typed Frictional Damper

In view of general braces of Pall-typed frictional damper will produce additional axial forces on side column in frame, considering the buckling-restrained braces(BRB) to replace the general braces to make the braces action fully, it would not generate the growth of additional axial forces on side columns, to settle basis for BRBs’ application in Pall friction damping brace system. Because hysteresis behaviors of the Pall-typed friction damper are not affected by brace buckling forces, this paper puts forward that the braces use the ordinary steel plate replacing BRB core plate to do Pall-typed frictional damping brace experimental research, meanwhile considering the geometric nonlinearity the finite element simulation analyses are done for this brace system in ANSYS software. The experimental results and simulation results show that the Pall friction force and brace forces’ variation rule is almost the same, and the brace force is almost the same.

Demand of Seismic Brace Dampers Installed in Steel Arch Bridges

Demand of Seismic Brace Dampers Installed in Steel Arch Bridges

Seismic Design and Dynamic Analysis of Steel Frames with Bolted Beam-to-Column Connection using Buckling-Restrained Knee Brace Dampers

Seismic Design and Dynamic Analysis of Steel Frames with Bolted Beam-to-Column Connection using Buckling-Restrained Knee Brace Dampers

A brace-type seismic damper based on yielding the walls of hollow structural sections

Abstract This paper proposes a new brace-type seismic damper designed for earthquake protection of structures. It consists of a tube-in-tube assemblage of two commonly available hollow structural sections. The outer hollow section of the Tube-in-Tube Damper (TTD) has a series of strips created by cutting a series of slits though the wall, and it is welded to the inner hollow section in such a way that when the brace damper is subjected to forced displacements in the direction of its axis, the strips dissipate energy through flexural/shear yielding. In comparison with other existing brace-type dampers such as the popular buckling restrained brace, the TTD has the advantages of being much simpler–thus entailing a lower cost–and the yielding part of the damper can be easily inspected after an earthquake. The performance of the proposed damper was assessed experimentally by an initial series of four cyclic tests, and compared with that of conventional steel plates with slits in another series of five tests. The experimental results show that the damper possesses very stable hysteric characteristics and excellent energy dissipation capacity, both similar to the conventional steel plates with slits already in use for seismic applications. Based on the test results, a hysteric model and a procedure for predicting the ultimate energy dissipation capacity and failure of the new damper are proposed.

Efficiency of the motion amplification device with viscous dampers and its application in high-rise buildings

After nearly a decade of application and investigation, a motion amplification device with viscous dampers for energy dissipation has been recognized as an effective solution to mitigate wind or seismic excitation, especially for stiff structural systems. As a result of compensation of amplified motion, it has been proved that the efficiency of viscous damper largely depends on the motion amplification device configuration, particularly for device stiffness. In this paper, a “scissor-jack” type of motion amplification device, called a “toggle brace damper” system, is studied. It is demonstrated that the efficiency of such a device reflected by its amplification factor is not merely a function of its geometric configuration, but is highly dependent on the support elements’ stiffness as well, similar to the mechanism of a leverage arm. Accordingly, a mathematical model in terms of complex modulus of the viscous damper with consideration of the support brace’s stiffness is established. The results indicate that the efficiency of the motion amplification device with viscous dampers significantly depends on the stiffness of the support elements. Other parameters, such as toggle brace configuration and damping values of the viscous damper, are studied and compared. As an application example, numerical analyses are conducted to study the dynamic performance of a 39-story office tower installed with toggle brace dampers constructed on soft soil in a reclaimed area, under a combined effect of the vortex shedding of an adjacent existing 52-story building and earthquakes. The results show that viscous dampers with a motion amplification system using a properly designed toggle brace device proved to be an effective solution to alleviate the external excitations.

DEVELOPMENT OF WELD-FREE BEAM-TO-COLUMN CONNECTION OF H-SA700A HIGH STRENGTH STEEL FOR BUILDING STRUCTURES

The objective of this study is to develop weld-free beam-to-column connection for H-SA700A high strength steel members, and verify the structural behavior of the proposed connections. Knee brace damper and friction damper were used to connect beam and column by high strength bolts; the trigger level of these dampers were designed to remain beam and column as elastic. Full-scale testing of knee-brace connection showed that damper yielded at the target level and all part of the connections performed as expected. Friction damper, which aluminum is sprayed at the surface, obtained 0.7 as the slip coefficient and a stable elasto-plastic structural behavior were observed after the slippage.

Seismic Protection of Frame Structures by Fluid Viscous Damped Braces

A research study on a damped bracing system incorporating pressurized silicone fluid viscous devices for seismic protection of frame structures is presented in this paper. This technology features an inverse-chevron brace configuration, where a pair of interfaced devices are placed, parallel with the floor-beam axis, at the tip end of each couple of supporting steel braces. The experimental section of this study consisted of a pseudodynamic testing campaign on a 2:3-scale three-story steel frame and a full-scale three-story reinforced concrete frame seismically retrofitted by the technology considered. Test results were elaborated to evaluate: the improvement of seismic response of both structures after retrofit, also assessed through a formal performance-based evaluation analysis; the capabilities of the assumed analytical and numerical models in reproducing the observed structural response; and the feasibility of a methodology previously formulated to select the damping coefficient of fluid viscous devices, herein implemented with further details for practical use. This methodology was applied to the design of the protection systems of the two test structures, and checked by comparing the target and experimentally obtained values of the governing energy-ratio coefficients.

Seismic Analysis of Concentrically Braced Frame Systems with Self-Centering Friction Damping Braces

This paper presents a special type of bracing element termed self-centering friction damping brace (SFDB) for use in seismic-resistant concentrically braced frame (CBF) systems. The SFDB is a passive energy dissipation device with its core recentering component made of stranded superelastic Nitinol wires while enhanced energy dissipation mechanism of the SFDB is achieved through friction. Compared with conventional braces for steel frame buildings, SFDB has a few desirable performance characteristics such as minimized residual drifts of the CBF system and its ability to withstand several design level earthquakes without the need for replacement. The mechanical configuration of the SFDB is first described. A comparative study of SFDB frame and buckling restrained braced (BRB) frame was carried out, which is based on nonlinear dynamic analysis of two prototype CBF buildings—a three- and a six-story steel frame. Two suites of earthquake ground motions, which represent the frequent and design basis earthquakes for Los Angeles, were considered in the nonlinear time-history analysis. The results of the nonlinear time-history and pushover analysis show that the SFDB frame can achieve a seismic response level comparable to that of the BRB frame while having significantly reduced residual drifts. The SFDB thus has a potential to establish a new type of CBF system with self-centering capability.

Special Issue on Design and Analysis of Structures with Seismic Damping Systems

The papers in this special issue focus on the theme of design and analysis of structures with seismic damping systems, the intent being to provide a summary of current research activities within the general field of seismic energy dissipation systems. The special issue originated within the ASCE-SEI Task Committee on Supplemental Damping Systems for Seismic Applications, a committee serving under the ASCE-SEI Committee on Seismic Effects. Two members of the task committee, Finley A. Charney and Andrew S. Whittaker, were particularly helpful in developing the special issue, assisting with its early development, and the soliciting manuscript reviews. Their efforts are gratefully acknowledged. In addition, the general membership of the Seismic Effects Committee supported the efforts of the task committee by serving as reviewers for many of the manuscripts. Their collective efforts are sincerely appreciated. The special issue begins with a lead paper, “Energy Dissipation Systems for Seismic Applications: Current Practice and Recent Developments,” which is coauthored by a mix of academicians and practitioners Symans, Charney, Whittaker, Constantinou, Kircher, Johnson, and McNamara. The lead paper provides an overview of current practice and recent developments in the application of passive energy dissipation systems for seismic protection of structures, with particular attention given to the application of such systems within the framing of building structures. Furthermore, emphasis is given to descriptions of viscous, viscoelastic, metallic, and friction damping systems, including recent applications of such systems. In the paper “Design Formulations for Supplemental Viscous Dampers to Building Structures,” Hwang, Huang, Yi, and Ho examine the accuracy of existing design formulas for determining the damping coefficients corresponding to a specified added damping ratio. They conclude that the effect of flexural deformations of a building is as significant as the shear deformations and that neglecting flexural deformations leads to inaccurate damping ratios. New design formulas are presented that account for both flexural and shear deformations, providing more accurate predictions of the damping ratio contributed by linear viscous dampers and ensuring a more conservative design for buildings that employ nonlinear viscous dampers. In “Comparison of Methods for Computing Equivalent Viscous Damping Ratios of Structures with Added Viscous Damping,” Charney and McNamara demonstrate that the approach used to compute modal damping ratios can have a significant influence on the computed values and that the axial flexibility of toggle-brace linkages can result in reduced system damping as the damping constant of the damper increases, a phenomenon that is readily observed through examining complex-valued mode shapes. In their paper “Seismic Protection of Frame Structures by Fluid Viscous Damped Braces,” Sorace and Terenzi present results from experimental testing of two three-story building frames, one constructed of steel and the other of reinforced concrete, each containing a bracing system employing fluid viscous dampers. The method by which the damping coefficient of the dampers was selected is discussed and evaluated by comparing the target response with the experimentally measured response. An analytical study entitled “Fluid Dynamics and Behavior of Nonlinear Viscous Fluid Dampers” is presented in the paper by Hou. In this study, the dynamics of the fluid flow are evaluated through solving the Navier-Stokes equations, and the shear-thinning effect and viscoelasticity of the fluid are considered. Comparisons with experimental data show that both the nonlinear viscous and restoring force behavior can be captured. The seismic response of a three-story reinforced concrete frame with viscous wall dampers is investigated by Lu, Zhou, and Yan in their paper “Shaking Table Test and Numerical Analysis of RC Frames with Viscous Wall Dampers.” In addition, the effect of the wall dampers on the seismic performance of a partially damaged reinforced concrete frame is examined. The test results demonstrate that the viscous wall dampers add significant damping while also providing some increase in stiffness, reducing the test structure displacements, and in some cases, increasing accelerations.

Earthquake Response of High-rise Steel Frames with Bolted Beam-to-Column Connection using Buckling-Restrained Knee Brace Dampers

Earthquake Response of High-rise Steel Frames with Bolted Beam-to-Column Connection using Buckling-Restrained Knee Brace Dampers