Dissipative Braces Research Articles

Theoretical analysis and experimental investigation of hysteretic performance of self-centering variable friction damper braces

Traditional buildings, even with normal self-centering energy dissipation (SCED) braces, might suffer from large deformations and high mode effects under an extremely strong earthquake, leading to a concentration of inter-story drift in upper floors. To satisfy the requirements of resilience, larger post-yield stiffness and higher energy dissipation, a novel brace with pretensioned basalt fiber-reinforced polymer (BFRP) tendons and variable friction dampers (VFDs) was developed, and this brace was termed the self-centering variable friction damper (SC-VFD) brace. The variable stiffness and sliding force of the VFD system were theoretically analyzed. This was followed by quasi-static experiments on two VFD and two SC-VFD braces with different parameters. The theoretical analysis and experimental results revealed the same tendencies, demonstrating the reliability and feasibility of SC-VFD braces. The hysteretic curve of the SC-VFD braces exhibited stable and normal flag-shape behavior before the second activation, while the hysteresis curve indicated a variable flag-shape behavior with second activation, variable friction force, and larger post-yield stiffness when the brace slid at slope section. Compared with the VFD brace, the SC-VFD brace had the same energy dissipation ability but less residual displacement and lower equivalent viscous damping ratio. More combinations of disc springs in series resulted in smaller axial forces and lowers post-yielding stiffness, thereby decreasing the energy dissipation capability.

Modified flag-shaped model for self-centering system and its equivalent linearization and structural optimization for stochastic excitation

The analysis and design of self-centering structural systems have attracted substantial attention from researchers for the seismic design of structures. The flag-shaped hysteretic model has been widely used in the design and structural response analysis of self-centering devices. In this research, a modified flag-shaped (MFS) model is proposed to describe the hysteretic characteristics of self-centering energy dissipation (SCED) braces, which are commonly used in self-centering structures. The MFS model comprises three parts: a linear elastic part, a bilinear elastic part, and an elasto-plastic part with a slip zone. The effectiveness of the MFS model is validated based on the results of the quasi-static and hybrid simulation tests available in the literature. Equivalent linearization is carried out on the MFS model for stochastic earthquakes, and closed-form solutions are obtained for the linearized parameters. A one-degree-of-freedom braced system is used to verify the equivalent linearization of the MFS model in comparison with Monte Carlo simulation results. Finally, an SCED-braced five-story frame structure is optimized by minimizing the maximum ductility demand for the SCED braces using the equivalent linearization of the MFS model. The optimized design by the MFS model is observed to exhibit uniform ductility demands along the height. This can be considered as the ideal optimal solution. The responses of the multi-degree-of-freedom structure also demonstrate the effectiveness of the proposed MFS model and its equivalent linearization.

Activation control extension of a design method of fluid viscous dissipative bracing systems

Remarkable damage to non-structural elements and sometimes to structural members was surveyed in buildings retrofitted with dissipative bracing (DB) technologies recently hit by moderate-to-medium amplitude earthquakes. Damage is a consequence of the delayed contribution of protective systems to the seismic response of the buildings, caused by too high activation forces of dissipaters. In view of this, a sizing procedure for DB systems incorporating fluid viscous (FV) spring-dampers is implemented in this study. The procedure provides a simplified version of a recently proposed energy-based design criterion, and an extension of it by including a pre-evaluation of the activation force of the FV devices with respect to the normative Serviceability Design Earthquake (SDE)-related seismic demand. The sizing procedure is applied to the retrofit design of a demonstrative case study, represented by a school built in Italy in the early 1980s. Noticeable seismic vulnerabilities of the above-ground steel structure of the building are assessed in current conditions, highlighting local unsafety conditions of the profiles constituting the reticular steel columns starting from the SDE. A retrofit intervention consisting in the installation of a DB system equipped with FV spring-dampers is presented for the steel structure, designed by applying the proposed sizing method. The final verification time-history analyses confirm the activation of the FV devices at the SDE, and the attainment of the targeted elastic structural response up to the Maximum Considered Earthquake normative level.

Experimental investigation on behavior of re-centering energy dissipative brace

In this study, an innovative re-centering energy dissipation (RCED) brace was developed, and its behavior was experimentally studied. The RCED brace contained two groups of cables with zero initial cable force. This configuration helped to eliminate the difficult process of applying pretension and the problem of pretension loss that appears in traditional re-centering braces. The re-centering force was alternately provided using the two groups of cables, and energy dissipation was supplied using a frictional energy dissipative device. A restoring force model for the RCED brace was proposed. Three full-scaled RCED braces with various magnitudes of bolt pretension and cable diameters were designed and experimentally tested. The results indicated that the RCED braces exhibited stable quadrilateral hysteretic responses with effective energy dissipation, excellent re-centering capabilities, adjustable ultimate bearing capacity and appreciable ductility.

Enhanced dissipation of a jacket platform provided by a steel brace containing a multistable bilayered column

Wave-induced impacts on jacket platforms generate strong vibrations in a low-damping metal structure, which causes severe damage. To resist impact and suppress vibration, a type of steel brace containing a multistable bilayered (MSB) soft material/steel column that provides a flexible combination of high stiffness and enhanced damping is designed according to the structural composite and stability mechanism. Finite element modeling (FEM) simulations show that the dissipated power of the MSB column is several times of magnitude higher than that of an existing multistable steel column (Wang et al., 2019) under cyclic loading, whereas the initial stiffness is similar to that of the steel column. Through a combination of hybrid lamination and mixed boundary theoretical methods, the multistable transformation of the MSB column is analyzed, which indicates that the soft layer manipulates the neutral axis of bending deformation and highly enhances the damping efficiency. Parametric studies conducted on the lamination properties illustrate the stiffness and damping configurations of the MSB module. In FEM simulations under impact loading, a representative jacket platform embedded with dissipative braces containing MSB columns exhibits a substantial increase (eightfold increase in magnitude) in the decay coefficients of the system compared to those of the platform embedded with braces containing existing steel columns. The simulation results demonstrate the potential of the multistable composite member to obtain high stiffness and enhanced damping in marine structures.

Numerical Studies on the Seismic Performances of RC Two-Column Bent Bridges with Self-Centering Energy Dissipation Braces

AbstractBridges may suffer large residual displacements after strong earthquakes. These large residual displacements may increase the reinforcement cost and even lead to the collapse of the bridge....

Numerical study on seismic performance of prefabricated steel frames with recentering energy dissipative braces

The application and research of prefabricated steel structures (PPSs) have developed rapidly in China. To improve the seismic resistance of PPSs, alternative bracing systems have been developed. The seismic performance of steel frames with recentering energy dissipative (RCED) braces is investigated numerically through quasistatic and nonlinear time history analyses. A one-bay braced frame model was first created in ABAQUS and calibrated by previous experimental tests. Subsequently, a comparative study on the dynamic performances of the multistory steel frames with RCED braces and self-centering energy dissipative braces was conducted. Six far-field earthquake records were adopted, i.e., Northridge, Imperial Valley, Kobe, San Fernando, Loma Prieta, and Kocaeli, Turkey. Finally, a parametric study was performed to investigate the effects of tendon diameter and pretension magnitude of high-strength bolts on the seismic performances of the RCED model under the Kocaeli earthquake.

Seismic design and behavior of self-centering energy dissipation braced steel frame

A self-centering energy dissipation (SCED) brace that utilized disc springs to provide self-centering capability and friction pads to dissipate energy was developed. Based on Bouc–Wen model and the working principle of SCED brace, a restoring force model is developed to describe the mechanical behavior of the brace. Comparisons between the cyclic loading tests and predicted results are conducted. Results show that the restoring force model can accurately predict both the energy dissipation and self-centering capabilities of SCED brace. A performance-based design method for frame structures with SCED braces is developed corresponding to the four-level seismic fortification objective, that is, no damage under minor and moderate earthquakes, replaceable or repairable under major earthquakes, and no collapse under mega earthquakes. A typical SCED braced steel frame was designed, and nonlinear time-history analysis was conducted to analyze the seismic performance and resilience of the braced frame. It is demonstrated that the SCED braced frame has superior resilience with small residual deformation under the moderate and major earthquakes due to the self-centering capability provided by the SCED brace. The collapse of the structure is also effectively avoided due to the stable energy dissipation and lateral stiffness provided by the SCED brace.

Development and experimental validation of a steel plate shear wall with self-centering energy dissipation braces

Abstract A new type of steel plate shear wall with self-centering energy dissipation braces (SPSW-SCEDB) was developed. Validation tests of the wall plate and the pre-pressed spring self-centering energy dissipation (PS-SCED) braces were conducted and a single-bay, single-story, 1:3-scale SPSW-SCEDB specimen was designed, fabricated, and tested under cyclic loadings. The results demonstrated that the SPSW-SCEDB exhibited a stable flag-shaped hysteretic response with high initial stiffness, appreciable ductility, and excellent self-centering and energy dissipation capabilities due to the synergistic effects of the wall plate and the PS-SCED braces. The proposed theoretical equations of the compressive force of the wall plate, the ultimate lateral load capacity, and the remaining restoring force of the SPSW-SCEDB were verified. The PS-SCED braces reduced the stiffness degradation of the wall plate and improved the lateral force resistance and the stability of the SPSW-SCEDB system. The wall plate provided more energy dissipation than the PS-SCED braces. The remaining restoring force of the PS-SCED braces should be as small as possible to maximize the energy dissipation of the PS-SCED braces while ensuring that it overcomes the compressive force of the wall plate.

Experimental study on component performance in steel plate shear wall with self-centering braces

Steel plate shear wall with self-centering energy dissipation braces (SPSW-SCEDB) is a lateral force-resisting system that exhibits flag-shaped hysteretic responses, which consists of two pre-pressed spring self-centering energy dissipation (PS-SCED) braces and a wall plate connected to horizontal boundary elements only. The present study conducted a series of cyclic tests to study the hysteretic performances of braces in SPSW-SCEDB and the effects of braces on the overall hysteretic characteristics of this system. The SPSW-SCEDB with PS-SCED braces only exhibits excellent self-centering capability and the energy loss caused by the large inclination angle of PS-SCED braces can be compensated by appropriately increasing the friction force. Under the combined effect of the two components, the SPSW-SCEDB exhibits a flag-shaped hysteretic response with large lateral resistance, good energy dissipation and self-centering capabilities. In addition, the wall plate is the primary energy dissipation component and the PS-SCED braces provide supplementary energy dissipation for system. The PS-SCED braces can provide up to 90% self-centering capability for the SPSW-SCEDB system. The compressive bearing capacity of the wall plate should be smaller than the horizontal remaining restoring force of the braces to achieve better self-centering effect of the system.

Advanced Seismic Retrofit of a Mixed R/C-Steel Structure

A study concerning the performance assessment and enhanced retrofit of public buildings originally designed without any anti-seismic provisions is presented herein. A representative structure belonging to this class was demonstratively examined, i.e., a school built in Italy in the early 1970s, before a coordinate national Seismic Standard was issued. The building is characterized by a mixed reinforced concrete (ground storey)–steel (first and second storey) frame skeleton. An extensive on-site experimental investigation was developed in the first step of the study, which helped identify the mechanical characteristics of the constituting materials, and re-draw the main structural details. Based on these data, and relevant updates of the finite element model of the structure, the seismic assessment analyses carried out in current conditions highlighted several performance deficiencies, in both the reinforced concrete and steel members. An advanced seismic retrofit hypothesis of the building was then designed, consisting of the installation of a set of dissipative braces incorporating fluid viscous dampers as protective devices. This solution makes it possible to attain an elastic structural response up to the maximum considered normative earthquake level, while at the same time causing more limited architectural intrusion and lower costs as compared to conventional rehabilitation strategies.

Seismic Assessment of Buildings with Prepressed Spring Self-Centering Energy Dissipation Braces

AbstractThe seismic performance of four- and eight-story steel buildings with prepressed spring self-centering energy dissipation (PS-SCED) braces was evaluated using a proposed nonlinear mechanica...

Seismic performance of multistory CBFs with novel recentering energy dissipative braces

For concentrically braced frames (CBFs) with conventional braces, although they can prevent collapse during earthquakes, people have to confront the costly repair work and long downtime induced business interruption, which is often attributed to excessive residual deformations. Shape memory alloys (SMAs) provide promising solutions to this problem. SMAs are gaining increasing favor by the community, owing to their excellent superelasticity which endows them with capabilities of recovering large deformation and dissipating input energy. Currently, the authors analyzed the seismic performance of CBFs with a novel brace termed recentering energy dissipative brace (REDB). The REDB is essentially a parallel combination of SMA bars and steel bending plates, the former primarily provides self-centering capability and the later is to enhance damping. This paper is to understand the seismic behavior of CBFs braced with REDBs, with an additional motivation to examine whether the REDBs can outperform the corresponding buckling-restrained braces (BRBs). Nonlinear static and time-history analyses are conducted for a prototype 6-story frame building. The corresponding results are compared against similar BRB frame. The basic comparison is made under the seismic scenarios associated with the design-basis earthquake hazard level. Through the comparative analysis, it is found that the properly designed REDBs are superior to the BRBs from the perspectives of generating identical demands in terms of maximum interstory drift ratios and maximum floor accelerations, and meanwhile eliminating residual interstory drift ratios. The confidence of the results is further gained by varying the seismic intensity and the assumed damping level.

Design and testing of prefabricated steel frame with an innovative re-centering energy dissipative brace

Traditional steel frames will experience large residual drifts under strong earthquakes. An innovative re-centering energy dissipative (RCED) brace was developed, which was able to pull steel frames back to their initial positions after an earthquake and dissipate energy by a friction damper device. In order to study the re-centering and energy dissipation capacities of RCED braced frame (RCED-BF), a prefabricated steel frame (PSF) and three RCED-BFs were designed and tested. The results show that the RCED-BF almost dissipated all the energy by the RCED brace. The diameter of high-strength bolts affected the energy dissipation capacity of RCED-BF significantly, while that of tendons did not. The maximum theoretical value of the energy dissipation coefficient of RCED-BF was 4, which decreased continuously with the increase of the maximum lateral deformation of RCED-BF. The stiffness of the PSF was fairly small and therefore the stiffness of RCED-BF was dominated by RCED brace. A value of 1.2 could be taken as the re-centering resistance coefficient of the RCED-BF.

Seismic performance evaluation of steel frames with pre-pressed spring self-centering braces

Pre-pressed spring self-centering energy dissipation (PS-SCED) braces with flag-shaped hysteretic responses are expected to undergo large deformation while re-centering to their origin, providing a self-centering capability for the structures. Three 4-, 8-, and 16-story braced frames with PS-SCED braces were analyzed to assess their seismic performances in comparison to conventional steel braced frames (CSBFs) and buckling restrained braced frames (BRBFs). Detailed analytical models of the PS-SCED braces were implemented and seven suites of ground motions with three different hazard levels were used to assess the structural performances with respect to interstory drifts, residual deformations, and peak floor accelerations during earthquakes. It was shown that the CSBFs underwent larger average responses than the BRBFs and the PS-SCED braced frames. The interstory drifts and peak floor acceleration responses of the frames with the BRBs were comparable and often better than those of the frames with the PS-SCED braces due to their high energy dissipation and simpler hysteretic cycles; the difference in the performance of these two braces tended to decrease with the increase in the seismic hazard level and the building height. The PS-SCED braces reduced the residual deformations more effectively than the BRBs and CSBs.

Seismic Design and Testing of Post-tensioned Timber Buildings With Dissipative Bracing Systems

This paper describes a seismic design procedure for low-damage buildings composed by post-tensioned timber framed structures coupled with hysteretic dissipative bracing systems. The main goal of the design procedure is preventing or limiting earthquake induced damage to the structural and no-structural elements. For this aim, a target design displacement is defined according to the desired performance level. Then, the corresponding design force, strength and stiffness of the post-tensioning and of the dissipative braces are evaluated in order to size post-tensioned connections and dissipating devices. The results of shaking table testing performed at the University of Basilicata are also reported. A prototype model, 2/3 scaled, 3-dimensional, 3-storey with post-tensioned timber structure without and with V-inverted braces and U-shaped flexural steel dampers has been extensively tested. During testing, the specimen was subjected to a set of seven earthquakes at different intensity levels of the peak ground acceleration. The effectiveness of the bracing system and the reliability of the proposed procedure are experimentally demonstrated. Nonlinear dynamic analyses have been performed in order to simulate the experimental seismic response. The numerical model is based on lumped plasticity approach, which combines the use of elastic elements with linear and rotational springs representing energy dissipating devices and plastic rotations of the connections. The numerical results accurately predict the nonlinear behavior of the prototype model, obtaining a satisfactory matching with the target drift considered for design.

Seismic Assessment and Retrofit Design of a School Building in Florence

The recent earthquakes occurred in Italy highlighted again the high vulnerability of structures built before the release of national Seismic Standards. This induced several local authorities to undertake extensive performance assessment campaigns of public buildings, among which mainly schools. A study carried out within one of these campaigns, concerning the evaluation of seismic vulnerability and the design of retrofit interventions in a school building in Florence, is presented herein. The structure was built at the beginning of 1970s, and is characterized by a ground storey with reinforced concrete frame skeleton, and a first and second storey with steel structure. An extensive on-site experimental investigation was developed at a first step of the study, which allowed identifying the mechanical characteristics of the constituting materials, and re-drawing the main structural details. Based on these data, a check of the seismic performance in current conditions was carried out, which highlighted several drawbacks, especially concerning the steel members. This prompted to propose a seismic retrofit hypothesis of the building, consisting in the installation of a set of dissipative braces incorporating fluid viscous dampers as protective devices. A synthesis of the assessment analyses in current conditions and the retrofit design, which allows attaining an elastic structural response up to the maximum considered earthquake level, is reported in the paper.

Seismic Retrofit of Hospitals by Means of Hysteretic Braces: Influence on Acceleration-Sensitive Non-structural Components

The paper illustrates an investigation on the effectiveness of dissipative bracing (DB) systems for seismic retrofit of buildings with sensitive non-structural components (NSCs) and technological content (TC), such as medical centres. The “Giovanni Paolo II” hospital, located in a high seismic prone area in Southern Italy , is chosen as case-study. The retrofit intervention with hysteretic braces is designed according to the Italian Building Code. The seismic response of the hospital building is investigated by means of nonlinear history analyses carried out in OpenSees FE code and, in order to verify the full-operation after the earthquake, the integrity of NSCs and TC is checked. The retrofit design, thanks to the stiffening and damping effects introduced by DB system, proves suitable to protect both the structural frame and “drift-sensitive” non-structural components and content even under severe earthquakes (PGA=0.45g). Nevertheless, some concerns arise about the suitability of hysteretic braces for the protection of the “acceleration-sensitive” elements of the medical complex. Indeed, during weak earthquakes (PGA=0.17g), failures of several of these components are detected which can substantially impair the operation of the hospital in the aftermath of the seismic event.

Innovative Structural Solutions for Prefab Reinforced Concrete Hall-Type Buildings

Background:The anti-seismic design of prefab reinforced concrete buildings is usually carried out with a conventional ductility-based approach. This implies a remarkable plastic demand on columns, as well as damages to the connections of structural and non-structural members, for seismic events with comparable intensity to the basic design earthquake normative level.Objective:In view of this, a study was developed and aimed at extending to the field of new prefab reinforced concrete structures the application of advanced seismic protection strategies, capable of guaranteeing undamaged response up to the maximum considered earthquake normative level.Method:A benchmark building was designed as demonstrative case study for this purpose, in the three following hypotheses: (a) according to a traditional ductility-based approach; (b) by incorporating dissipative bracings, equipped with fluid viscous dampers; (c) by placing a seismic isolation system at the base, composed of a set of double curved surface sliders.Results:The results of the verification analyses show that the targeted performance for the design solutions b) and c) is obtained with sizes of columns and plinths notably smaller than those for the conventional design. This allows compensating the additional cost related to the incorporation of the protective devices, for the dissipative bracing system, and limiting additional costs below 25%, for the base isolation solution. At the same time, a supplemental benefit of the latter is represented by greater protection of contents and plants, as they are fully supported by the seismically isolated ground floor.Conclusion:The study highlights the advantages offered by the two advanced seismic protection technologies in an unusual field of application, guaranteeing an enhanced performance of structural and non-structural elements, as well as reduced member sizes, as compared to the traditional ductility-based design.

Numerical analysis of self-centering energy dissipation brace with arc steel plate for seismic resistance

A self-centering energy dissipation brace (SEDB) with an arc steel plate was designed to improve the seismic performance of a structure and reduce the residual structural deformation after an earthquake. Seven groups of self-centering energy dissipation brace models of arc steel plates with different configurations were established based on ABAQUS software. A method for calculating the internal forces, stiffness, yield displacement and yield load of a brace was derived and shows agreement with theoretical values. This brace shows a favorable hysteretic performance that corresponds to its full, flag-shaped hysteretic curve. The stiffness transition of various stages is smooth and stable. The maximum residual deformation of the component is 3.75 mm and decreases as prepressing of the disc springs is increased. The component's reset performance can be fully utilized to satisfy specific needs. The advised values for designing the energy dissipation components of an arc steel plate are described as follows: 1/250 of a radian, width of 50–80 mm and thickness of 20 mm. The damping force, damping displacement and brace stiffness of the SEDB can be adjusted by the structural parameters of the arc steel plate to satisfy the engineering requirements.