Search Results (8)

The relative displacements between the girders and piers of isolated bridges during intense earthquakes are usually so large that traditional restrainers cannot accommodate the resulting deformation. A novel superelastic shape memory alloy (SMA) honeycomb damper (SHD) is proposed as a means to combine the large strain capacity of SMA and the geometrical nonlinear deformation of honeycomb structures. As a result, the large deformation capacity of the novel damper satisfies the requirements for bridge restrainers. The proposed device consists of a superelastic shape memory alloy (SMA) honeycomb structure, which enables a self-centering capability, along with steel plates that serve to prevent the buckling of the SMA honeycomb. An examination of the SHD was undertaken initially from theoretical perspectives. A multi-cell SHD specimen was subsequently manufactured and evaluated. Following this, numerical simulation analyses of the SHDs using a three-dimensional high-fidelity finite element model were employed to examine the experimental results. In the end, a technique for improving the SHD was suggested. The results indicate that the SHD is able to demonstrate superior self-centering capabilities and stable hysteretic responses when subjected to earthquakes. Full article

To investigate the hysteretic behavior of an X-shaped metal damper (XMD) with an oblique angle, cyclic loading tests were carried out on nine specimens, including two XMDs without buckling-restrained devices, four XMDs with stiffening ribs, and three XMDs with cover plates as references. The test results showed that the oblique angle could effectively increase the stiffness, strength, and energy dissipation of the XMD. When the oblique angle of an XMD with stiffening ribs increased from 0° to 30° at the applied displacement of 8.4 mm, the mean strengths and cumulative energy dissipation of specimens increased by about 80.77% and 80.57%, respectively. Although asymmetric hysteretic loops were also observed in specimens with an oblique angle and buckling-restrained devices, stable hysteretic curves were obtained. This indicated that the stiffening ribs and cover plates can effectively constrain the buckling behavior of XMDs. Additionally, the mean strengths of specimens with stiffening ribs were a little higher than those of specimens with cover plates. Subsequently, the finite element analysis models of the XMDs were proposed, in which the metal plasticity model considering isotropic and kinematical hardening was used to model the material properties of steel, and the simulation results matched well with the test results. Finally, the theoretical calculation method was proposed to predict the elastic stiffness of specimens, and the theoretical elastic stiffness matched well with the test results. Full article

Buckling-restrained brace (BRB) is a dual-function device that improves the seismic resistance and energy-dissipation capacity of structures in earthquake engineering. To achieve the expected performance under severe ground motions, BRB is usually designed to remain elastic under mild earthquakes, leading to the increased seismic forces and insignificant vibration-reduction effect on the structures at this stage. This study extends the concept of adaptive passive-control of structures by proposing a novel frictional-yielding compounded BRB (FBRB). FBRB is fabricated by connecting the BRB steel casing and end plates with the friction dampers (FDs) in such a way that the BRB steel core and FDs undergo compatible deformation. In this way, FD dissipates seismic energy under mild earthquakes, while FD together with the BRB core dissipates energy under severe ground motions, resulting in an efficient self-adaptive vibration-reduction mechanism. The proposed FBRB construction was experimentally validated by carrying out the reversed-cyclic test, and the result indicated reliable connection with stable hysteretic behavior. Subsequently, the FBRB-equipped frame was proposed and studied which adopted FBRB as the energy-dissipative devices. A parametric design method was developed to determine the FBRB parameters with which the maximum elastic drift of the system could be reduced to the code-allowable value. The approach was implemented on a 48-story mega FBRB-equipped steel frame as the case study. The seismic behavior of the FBRB-equipped case structure was compared with that of the BRB-equipped system, and critically evaluated by carrying out the nonlinear time-history analyses. Results revealed that FBRB compensated for the conventional BRB in terms of inadequate energy dissipation under mild earthquakes and, meanwhile, was more efficient than the conventional BRB in reducing the lateral drifts under severe ground motions. The analysis indicated potential application prospect of FBRB in practical engineering. Full article

A buckling-restrained brace (BRB) serves as a typical load-bearing and energy-dissipative device for the passive control of structures under seismic loading. A BRB is generally designed to not yield under frequently occurring earthquake (FOE) and wind loads, resulting in it having less effectiveness in vibration reduction compared with post-yielding performance. To address this dilemma, this study proposed the concept and technique details of the viscoelastic-yielding compounded BRB (VBRB). Different from a conventional BRB, a VBRB is fabricated by attaching the viscoelastic damper (VED) to the surface of a BRB’s steel casing, ensuring a compatible deformation pattern between the VED and the BRB’s steel core. A dynamic loading test of VBRB specimens was carried out in which 0.2 Hz~0.6 Hz in loading rate and a maximum of 550 kN in load-bearing capacity had been applied, verifying the feasibility and performance of the VBRB. Subsequently, a parametric design procedure was developed to determine the required VBRB parameters so that the maximum elastic drift response of the structure could be reduced to the code-prescriptive value. The wind-resistance and seismic performances of the VBRB were critically evaluated through dynamic time-history analyses on a 48-story mega VBRB-equipped frame designed according to the Chinese seismic design code (GB50011-2010), and the effectiveness of the approach was also verified. Results indicate that the VBRB has advantages over a conventional BRB by providing a multi-stage passive energy dissipation capacity, resulting in a better vibration-control effect than conventional BRBs for structures subjected to wind load and seismic excitations. Full article

This study addresses an alternative use of viscous dampers (VDs) associated with buckling restrained braces (BRBs) as innovative seismic protection devices. For this purpose, 4-, 8- and 12-story steel bare frames were designed with 6.5 m equal span length and 4 m story height. Thereafter, they were seismically improved by mounting the VDs and BRBs in three patterns, namely outer bays, inner bays, and all bays over the frame heights. The structures were modeled using SAP 2000 software and evaluated by the nonlinear time history analyses subjected to the six natural ground motions. The seismic responses of the structures were investigated for the lateral displacement, interstory drift, absolute acceleration, maximum base shear, and time history of roof displacement. The results clearly indicated that the VDs and BRBs reduced seismic demands significantly compared to the bare frame. Moreover, the all-bay pattern performed better than the others. Full article

Conservation of heritage buildings has become a very important issue in many countries, as it is in Italy, where a great number of existing buildings of historical–artistic importance are seismically vulnerable. To improve existing building behavior, researchers focus on the design of retrofit interventions. This paper presents the application of energy dissipation devices in the retrofit of two existing Reinforced Concrete (RC) buildings, both irregular in plan and along their heights, designed for gravitational loads only. These buildings are representative of Italian public housing built in the 1960s and early 1970s. Technical information and mechanical properties of materials are presented, and non-linear analyses are carried out to evaluate the buildings’ behavior under earthquake loads. Many of their structural members do not satisfy the verifications required by the Italian Building Code. Retrofit interventions with buckling-restrained axial dampers in one building and viscous fluid dampers in the other are proposed. The verifications of the retrofitted buildings and the amount of the energy absorbed by the devices with respect to that absorbed by the unretrofitted buildings show the effectiveness of the proposed interventions. Moreover, it is demonstrated that adequate dispositions of the dissipative devices in plan and along the height increase the torsional stiffness of the buildings, improving their structural response under seismic action. Full article

In the present paper a new and innovative way to approach the regeneration of public buildings and public housing is proposed. It consists in a dissipative steel frame to reduce the displacement demand and to improve the energy efficiency of a real existing structure, inserting buckling-restrained axial dampers (BRAD) type dissipative braces. This system is adaptable to any construction made of reinforced concrete frames and improves energy efficiency and earthquake-resistant performance; moreover, it upgrades the aesthetics of buildings and the quality of life for the users. In fact, the system is capable of assuming different and pleasant architectural shapes offering benefits in terms of earthquake-resistant performance, energy saving, and energy production from renewable sources. The attention to the aesthetic results renders the intervention a redevelopment strategy not only on an architectural scale, but also in the urban contexts for degraded and marginalized suburbs. The performances of the proposed kit were evaluated on a case study consisting in a social house located in the south of Italy. Numerical analyses have been carried out and the results have been reported both from the seismic protection and energy efficiency points of view. As a result, the produced renewable energy from the retrofitting system and the building seismic capacity increased. A rapid and precise control process, able to return a suitable structural dimensioning of the frame, according to the different application contexts, is finally proposed. Full article

Buckling Restrained Bracings (BRBs) are widely used to improve the seismic behavior of buildings. They are employed for bridges as well, but their application in this respect is limited. BRBs can also be used as a function of the individual damper rather than the structural component or the bracing, in which case the device may be called a Buckling Restrained Damper (BRD). Yet, such application has not been explored much. There are quite a few bridges designed according to the old design codes in Japan. Their seismic resistance may not be satisfactory for the current seismic design codes. Against this background, the behavior of a steel truss bridge under a large seismic load was investigated by nonlinear dynamic finite element analysis. Some members were indeed found to be damaged in the earthquake. Retrofitting is needed. To this end, the application of BRD was tried in the present study: a parametric study on the seismic behavior of the truss bridge with BRD was conducted by changing the length, the cross-sectional area, the location and the inclination of BRD. The effectiveness of BRD was then discussed based on the numerical results thus obtained. In all the analyses, ABAQUS was used. Full article