161,105 research outputs found
SMA-based rocking dual-core braced-frame system for seismic retrofit of RC buildings
No full textNew seismic-resistant systems enhance structural resilience by dissipating energy, minimizing damage, and enabling self-centering for efficient post-earthquake recovery. Among them, base-rocking dual-core (BRDC) braced-frame systems have shown promise for retrofitting existing buildings. This study investigates the application of a BRDC exoskeleton equipped with shape memory alloy (SMA) dampers for the seismic retrofit of reinforced concrete (RC) buildings. The SMA dampers function as replaceable fuses, providing energy dissipation while facilitating the self-centering of the structure to its original position. A displacement-based design method is proposed to optimize the performance of the SMA dampers. Nonlinear analyses demonstrate that the proposed system effectively reduces inter-story drifts and enhances seismic resilience. The results underscore the promise of this retrofit strategy. By ensuring both structural integrity and rapid post-earthquake recovery, the approach offers a viable solution for the protection of critical infrastructure
Dissipative exoskeletons based on self-centering sma braces for seismic retrofit of rc buildings
No full textA great number of buildings in seismic-prone areas were designed without provisions for earthquake resistance. Therefore, they are not expected to possess the necessary properties to withstand earthquake excitations, which cause strong plastic deformations, performance deterioration, and damage. This has stimulated the development of a new generation of seismic codes based not only on stiffness, strength, and ductility requirements but also on structural resilience, which is the ability to rapidly resume the use of structures following an earthquake. In recent years, the resilience of structural retrofit systems for existing buildings has attracted more and more attention. Moreover, a variety of external sub-structure retrofitting methods have been proposed in the literature generally based on non-dissipative steel exoskeletons. This article presents the design and assessment of dissipative exoskeletons based on recentering shape memory alloy (SMA) dampers for the seismic retrofit of RC buildings. Although many studies have been presented in the literature on SMA bracing systems, most of them are devoted to experimental and numerical investigations on small-scale SMA devices or brace components. Only a few studies focus their attention on the application of SMA-brace devices to full-scale RC buildings. This paper focuses on evaluating the effect of using self-centering shape memory alloy dampers for buckling-restrained braces in dissipative exoskeletons applied for the seismic retrofit of a reinforced concrete (RC) school building structure. A design method has been implemented to size the SMA dampers to be placed on selected spans and stories of the exoskeletons. The effectiveness of the design procedure has been demonstrated by nonlinear time-history analyses under different sets of earthquake-strong ground motions
Seismic resilient self-centering braces for orthogonal steel exoskeleton structures
No full textExternal sub-structures, such as steel exoskeletons, have emerged as effective retrofitting solutions by incorporating controlled rocking and post-tensioning to enable self-centering. Shape memory alloys (SMAs) provide an alternative approach, offering flag-shaped hysteresis loops that combine high energy dissipation with shape recovery after large strains. This paper investigates orthogonal dissipative exoskeletons equipped with SMA dampers for retrofitting reinforced concrete buildings. A design strategy is proposed to optimize the dampers for both energy dissipation and self-centering performance. Nonlinear time-history analyses confirm the effectiveness of this approach, showing significant energy dissipation at lower stories and minimal residual drifts, which enhance seismic resilience and support rapid post-earthquake recovery.External sub-structures, such as steel exoskeletons, have emerged as effective retrofitting solutions by incorporating controlled rocking and post-tensioning to enable self-centering. Shape memory alloys (SMAs) provide an alternative approach, offering flag-shaped hysteresis loops that combine high energy dissipation with shape recovery after large strains. This paper investigates orthogonal dissipative exoskeletons equipped with SMA dampers for retrofitting reinforced concrete buildings. A design strategy is proposed to optimize the dampers for both energy dissipation and self-centering performance. Nonlinear time-history analyses confirm the effectiveness of this approach, showing significant energy dissipation at lower stories and minimal residual drifts, which enhance seismic resilience and support rapid post-earthquake recovery
Current understanding of the role of cytoskeletal cross-linkers in the onset and development of cardiomyopathies
No full textCardiomyopathies affect individuals worldwide, without regard to age, sex and ethnicity and are associated with significant morbidity and mortality. Inherited cardiomyopathies account for a relevant part of these conditions. Although progresses have been made over the years, early diagnosis and curative therapies are still challenging. Understanding the events occurring in normal and diseased cardiac cells is crucial, as they are important determinants of overall heart function. Besides chemical and molecular events, there are also structural and mechanical phenomena that require to be investigated. Cell structure and mechanics largely depend from the cytoskeleton, which is composed by filamentous proteins that can be cross-linked via accessory proteins. Alpha-actinin 2 (ACTN2), filamin C (FLNC) and dystrophin are three major actin cross-linkers that extensively contribute to the regulation of cell structure and mechanics. Hereby, we review the current understanding of the roles played by ACTN2, FLNC and dystrophin in the onset and progress of inherited cardiomyopathies. With our work, we aim to set the stage for new approaches to study the cardiomyopathies, which might reveal new therapeutic targets and broaden the panel of genes to be screened
Novel insights into cardiomyocytes provided by atomic force microscopy
No full textCardiovascular diseases (CVDs) are the number one cause of death globally, therefore interest in studying aetiology, hallmarks, progress and therapies for these disorders is constantly growing. Over the last decades, the introduction and development of atomic force microscopy (AFM) technique allowed the study of biological samples at the micro- and nanoscopic level, hence revealing noteworthy details and paving the way for investigations on physiological and pathological conditions at cellular scale.
The present work is aimed to collect and review the literature on cardiomyocytes (CMs) studied by AFM, in order to emphasise the numerous potentialities of this approach and provide a platform for researchers in the field of cardiovascular diseases. Original data are also presented to highlight the application of AFM to characterise the viscoelastic properties of CMs
Experimental lap-shear tests on friction dampers with single and double slotted holes
No full textSeveral experimental lap shear tests have been performed to assess the initial values of the slip resistance and their evolution during a cyclic loading history. Both friction dampers with parallel slotted holes and double slotted holes have been investigated. Friction devices with shims made of a previously tested material, called M4, have been tested and the tribological behaviour, the degradation of the friction coefficient, the influence of the bolts’ preload and the effect of Belleville washers have also been investigated. Moreover, a phenomenological model for the force-displacement response has been calibrated for the modelling of the cyclic response of the friction device. This is particularly important for the development of non-linear dynamic analyses of seismic resistant frames equipped with friction joints aiming at an accurate prediction of the structural response during a seismic event. Finally, a quality control of the friction properties of different batches of friction shims has been performed by means of the Fisher-Berens and Snedecor tests
Proceedings of the 18th World Conference on Earthquake Engineering - WCEE 2024
No full textA large number of highly seismically vulnerable buildings includes several relevant and strategic buildings. Relevant buildings like schools, assembly halls, public offices, cultural institutions, and, in general, buildings with significant crowding, should retain their structural integrity since their collapse could cause major human losses and significant economic impact. Moreover, it would be appropriate for such buildings to remain fully operational even during seismic retrofit work. This has supported the development of seismic retrofit solutions based on rapid, low-impact, and reversible interventions that offer many advantages. First, they can be done while the building is operational. Second, they can be removed and rapidly replaced if damaged due to earthquake shaking. Third, they can be integrated to combine seismic resilience and energy efficiency, thus reducing the time and costs of two separate interventions. This situation has stimulated the use of external additive structures, commonly called exoskeletons, as a feasible solution based on a circular and sustainable economy. Typically, the research and applications deal with non-dissipative steel exoskeletons involving the application of diagonal grids (diagrids) or external steel concentric braces from the outside of existing RC buildings. This paper presents the design and assessment of dissipative exoskeletons based on steel slit dampers for the seismic retrofit of RC buildings. To this aim, a real case-study school building has been considered. The dissipative exoskeletons have been designed using a displacement-based design procedure that takes into account the secant stiffness and damping of the existing structure at the peak response. The geometry of the dumbbell-shaped steel strip dampers has been selected to avoid stress concentration, accumulation of plastic strain, and premature buckling failures and increase their energy dissipation capacity. The effectiveness of the retrofit strategy has been finally demonstrated by nonlinear time-history analyses under different sets of earthquake-strong ground motions
A Design Method for Seismic Retrofit of RC Buildings Using Dissipative Exoskeletons
No full textAn emerging solution among rapid, low-impact, and reversible retrofit strate-gies is the implementation of external additive structures or exoskeletons. Most current research emphasizes non-dissipative steel exoskeletons, such as diagrids or steel braces, while comprehensive design procedures for dissipa-tive exoskeletons remain underdeveloped. This study introduces a design procedure for the seismic retrofitting of RC buildings using dissipative exo-skeletons. The proposed strategy is initially applied to a real-world school building and subsequently validated through nonlinear time-history analyses with various input ground motions
Dissipative steel exoskeletons for seismic retrofit of RC buildings
No full textThis paper addresses the seismic retrofitting of highly vulnerable reinforced concrete (RC) buildings, with a focus on relevant and strategic structures such as schools, public offices, and cultural institutions. It proposes innovative retrofit solutions using external additive structures, or exoskeletons, designed for rapid, low-impact, and reversible interventions. These exoskeletons can be installed while the building remains operational, removed, replaced if damaged, and integrated with energy-efficient upgrades, reducing the time and cost of separate interventions. The research investigates two retrofit strategies for a school building: parallel exoskeletons with eccentric braced frames (EBFs) and steel slit dampers (SSDs), and orthogonal exoskeletons with concentric braced frames (CBFs) and shape memory alloy dampers (SMADs). A displacement-based design methodology ensures optimal energy dissipation and prevents premature buckling. Nonlinear time-history analyses validate the effectiveness of the retrofits across various earthquake scenarios. Peak inter-story drift ratio (IDR) responses are significantly reduced, remaining below the 2% collapse prevention limit. The parallel exoskeleton achieves IDR values of 0.66% and 0.86% in the X- and Y-directions, while the orthogonal exoskeleton records 0.63% and 1.06%, respectively. Additionally, the self-centering capability of SMA braces minimizes residual inter-story drifts, with permanent drifts as low as 0.0321% in the X-direction and 0.0090% in the Y-direction, ensuring repairability even after severe seismic events. These findings highlight the efficacy of dissipative exoskeletons in enhancing structural resilience while maintaining practicality and cost-efficiency for retrofitting critical infrastructure in earthquake-prone regions
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