Search Results (66)

This research experimentally and numerically evaluates the effectiveness of viscoelastic (VE) and rotational friction (RF) dampers in enhancing the seismic performance of coupled shear wall (CSW) systems. This study consists of two phases: (1) element testing to characterize the hysteretic behavior and energy dissipation capacity of VE and RF dampers, and (2) shake table testing of a large-scale CSW structure equipped with these dampers under the white noise, sinusoidal and Kokuji waves. The experimental results are validated through numerical analysis using STERA 3D (version 11.5), a nonlinear finite element software, to simulate the dynamic response of the damped CSW system. Key performance indicators, including inter-story drift, base shear, and energy dissipation, are compared between experimental and numerical results, demonstrating strong correlation. The findings reveal that VE dampers effectively control high-frequency vibrations, while RF dampers provide stable energy dissipation across varying displacement amplitudes. The validated numerical model facilitates the optimization of damper configurations for performance-based seismic design. This study provides valuable insights into the selection and implementation of supplemental damping systems for CSW structures, contributing to improved seismic resilience in buildings. Full article

Loading and clamping schemes significantly influence the behavior of shape memory alloys, specifically, the course of their solid-state transformations. This paper presents experimental and numerical findings regarding the nonlinear response of samples of the above-mentioned type of smart materials observed during tensile tests. Hysteretic properties were studied to elucidate the superelastic behavior of the tested and modeled samples. The conducted tensile tests considered two configurations of grips, i.e., the standard one, where the jaws transversely clamp a specimen, and the customized bollard grip solution, which the authors developed to reduce local stress concentration in a specimen. The characteristic impact of the boundary conditions on the solid phase transformation in shape memory alloys, present due to the specific clamping scheme, was studied using a thermal camera and extensometer. Martensitic transformation and the plateau region in the nonlinear stress–strain characteristics were observed. The results of the numerical simulation converged to the experimental outcomes. This study explains the complex nature of the phase changes in shape memory alloys under specific boundary conditions induced by a given clamping scheme. In particular, variation in the martensitic transformation course is identified as resulting from the stress distribution observed in the specimen’s clamping area. Full article

This paper presents an advanced seismic performance evaluation of reinforced concrete (RC) seismically isolated frame structures under the conditions of rare earthquakes. By employing an elastic–plastic analysis in conjunction with a nonlinear multi-degree-of-freedom model, this study innovatively assesses the incremental dynamic vulnerability of isolated structures. A novel equivalent linearization method is introduced for both single- and two-degree-of-freedom isolation structures, providing a simplified yet accurate means of predicting seismic responses. The reliability of the modified Takeda hysteretic model is verified through comparative analysis with experimental data, providing a solid foundation for the research. Furthermore, a multi-degree-of-freedom shear model is employed for rapid elastic–plastic analysis, validated against finite element software, resulting in an impressive 85% reduction in computation time while maintaining high accuracy. The fragility analysis reveals the staggered upward trend in the vulnerability of the upper structure and isolation layer, highlighting the importance of comprehensive damage control to enhance overall seismic performance. Full article

This paper presents a modeling framework for hysteretically nonlinear piezoelectric composite beams using functional differential equations (FDEs). While linear piezoelectric models are well established, they fail to capture the complex nonlinear behaviors that emerge at higher electric field strengths, particularly history-dependent hysteresis effects. This paper develops a cascade model that integrates a high-dimensional linear piezoelectric composite beam representation with a nonlinear Krasnosel’skii–Pokrovskii (KP) hysteresis operator. The resulting system is formulated using a state-space model where the input voltage undergoes a history-dependent transformation. Through modal expansion and discretization of the Preisach plane, we derive a tractable numerical implementation that preserves essential nonlinear phenomena. Numerical investigations demonstrate how system parameters, including the input voltage amplitude, and hysteresis parameters significantly influence the dynamic response, particularly the shape and amplitude of limit cycles. The results reveal that while the model accurately captures memory-dependent nonlinearities, it depends on numerous real and distributed parameters, highlighting the need for efficient reduced-order modeling approaches. This work provides a foundation for understanding and predicting the complex behavior of piezoelectric systems with hysteresis, with potential applications in vibration control, energy harvesting, and precision actuation. Full article

To address the seismic vulnerability of high-speed railway bridges (HSRBs) in seismically active regions, this study proposes a hierarchical curved steel damper (CSD) designed to mitigate excessive girder displacements induced by conventional isolation devices. The CSD integrates U-shaped and hollow diamond-shaped steel plates to achieve stable energy dissipation through coupled bending deformation. A finite element model is developed, and its hysteretic behavior is confirmed, with an energy dissipation coefficient of 1.82 and an equivalent damping ratio of 12.7%. An integrated high-speed railway track–bridge-CSD spatial coupling model is developed in OpenSees, which incorporates nonlinear springs for interlayer track interactions. Nonlinear time–history analyses under 40 spectrum-matched ground motions reveal that the CSD reduces transverse girder displacements by 73.7–79.2% and attenuates track slab acceleration peaks by 52.4% compared with uncontrolled cases. However, it increases the maximum bending moment at pier bases by up to 18.3%, necessitating supplemental energy-dissipating components for balanced force redistribution. This work provides a theoretical foundation and practical methodology for seismic response control and retrofitting of the HSRB in high-intensity seismic regions. Full article

During a seismic movement, each wave field incoming to a foundation by reflecting from the surroundings causes amplification. Therefore, the seismic response of any building is affected by both the topography and the adjacent building. In this study, the effect of the adjacent building on the seismic performance of a building located near a shallow slope is numerically assessed. In the adopted three-dimensional finite element simulation, nonlinear variation of soil stiffness and hysteretic damping, elastoplastic behaviour of the superstructure frame system showing significant deviations from linear behaviour beyond the limits of elastic behaviour and varying distances between the foundation edge and the adjacent building were employed. Two identical 10-storey moment-resisting buildings, 40 m thick dense clayey sand, and a 5 m high shallow slope were considered as a reference model and simulated using the direct method in the time domain. The seismic performance of the building was studied at a distance equal to the height of the slope from the crest. The results of the analyses represent an interaction in which both shallow slope and adjacent building effects are observed together. Incremental structure–soil–structure interaction effect, on the one hand, created additional shear stresses on the shallow slope and enhanced the foundation rocking of the building. On the other hand, as a natural result of dynamic cross-interaction, it resulted in a reduction in the maximum acceleration value captured at the foundation, a drop in the base shear demand, and a large change in the maximum storey displacements at the lower floors. As a result of these cases, storey drifts increased. The results highlighted that the structure–soil–structure interaction cannot be neglected in the presence of a slope. Full article

Two large earthquakes with a series of aftershocks struck southeastern Türkiye within 9 h and had catastrophic consequences. Following the earthquake doublet, 11 provinces corresponding to approximately 1/7 of Türkiye were declared disaster zones. Even though the epicenters of the first event and second mainshocks were in Pazarcik and Elbistan with a magnitude ($M_w$) of 7.7 and 7.6 with over 500 km of multiple-fault ruptures, Hatay province was the most heavily damaged province and had the highest number of casualties and collapsed buildings. A densely deployed strong ground motion array of the Disaster and Emergency Management Presidency of Turkey (AFAD) recorded the earthquake doublet of the two consequent mainshocks, including ground motions exhibiting near-fault features. A suite of recorded ground motions in Hatay province is incorporated to examine the destructiveness of ground motions on reinforced concrete Moment-Resisting Frame buildings and the effectiveness of seismic isolation technology to reduce the observed damage. Moreover, Turkish Seismic Design Code-2018 code provisions are elaborated to determine the characteristics of the investigated structures. Nonlinear response history analyses were conducted for 24 types of structures by following the design provisions. The inelastic hysteretic response features in the fixed-base and isolation systems are represented through an inelastic Single-Degree-of-Freedom Bouc–Wen hysteretic model. Extreme characteristics of near-fault ground motions on RC structures and seismically isolated systems resulted in excessive drift and displacement demands. Roof drifts of reinforced concrete Moment-Resisting-Frame buildings exceeded 4% roof drift in mid-rise buildings, compatible with the field observations in Antakya city center, where the displacement demand and ultimate base shear coefficient of seismically isolated structures considered in this study exceeded the elastic spectral coefficient values of the design spectrum in the proximity of fault ruptures. Full article

This paper is focused on the numerical evaluation of the equivalent damping ratio (EDR) given by a dissipative wood-based roof diaphragm in the seismic retrofitting of single-nave historical churches. In the design phase, the EDR could be a key parameter to select the optimal roof structure configuration, thereby obtaining the maximum energy dissipation. In this way, the roof structure works as a damper to facilitate a box behavior of the structure during the seismic response. The EDR measures the energy dissipated by the nonlinear behavior of the roof’s steel connections and masonry walls during seismic events. In a preliminary retrofitting design phase, an initial implementation of the geometries of the walls and the chosen geometry for the roof is carried out by adopting an equivalent frame model (FEM) with inelastic rotational hinges for the nonlinear properties of the masonry walls and inelastic shear hinges for the nonlinear behavior of the roof’s steel connections. Since, for historical churches, the transversal response under seismic events is the worst situation for the single-nave configuration, the earthquake is applied as transversal accelerograms. In this way, the damped rocking of the perimeter walls due to the dissipative roof diaphragm can be described in terms of a hysteretic variable. By varying the value of the hysteretic variable, possible configurations of the roof diaphragm are tested in the design phase, considering the different shear deformation values of the inelastic hinges of the roof. Under these hypotheses, the EDR is evaluated by performing nonlinear Time History analyses based on the cyclic behavior of the inelastic hinges of the roof, the strain energy contribution due to the walls, and the lateral displacements of the structure. The EDR values obtained with the Time History method are compared with those obtained by applying the Capacity Spectrum Method by performing nonlinear static analyses, either for the coefficient method of FEMA 356 or the equivalent linearization technique of ATC-40. The EDR evaluations are performed by considering the following different hysteretic behaviors of the roof’s steel connections: the skeleton curves with stiffness degradation and the trilinear model with strength and stiffness degradation. Finally, the variation in the EDR values as a function of the hysteretic variable is presented as well so to evaluate if the maximum EDR value corresponds to the optimal value of the hysteretic variable able to reduce the lateral displacements and to contain the shear forces acting on the roof and the façade under a safety limit. Full article

Modeling seismic isolators, one of the most effective installations in the design of earthquake-resistant buildings, is a very important challenge. In this study, we propose a new energy-based approach for the optimization of seismic isolation parameters. The hysteretic energy represents the dissipation of isolated structures in the isolation system. The minimization of input energy ensures that structural components are exposed to reduced seismic energy. For these reasons, this study aims to minimize the input energy and maximize the hysteretic energy. Additionally, an objective function is also generated with the energy ratio obtained from the input and hysteretic energy. The gray wolf optimizer (GWO) was applied to the optimization process. A four-story, 3D, and reinforced concrete superstructure was prepared and lead rubber bearings were placed under the base story. The isolation system is modeled nonlinearly, which requires two parameters: isolation period and characteristic strength. The inter-story drift ratio was selected as the structure constraint, while the isolator displacement and effective damping ratio were selected as the isolator constraints in the optimization process. The prepared base-isolated structure was optimized using 11 scaled ground motions. Nonlinear time history analyses were run in ETABS finite element software. Firstly, the optimum isolation parameters were obtained using peak roof story acceleration (PRA), in accordance with the methodology in previous studies. The outcomes generated by the PRA and energy components are compared considering the isolation parameters and structural responses. The energy ratio produced better results in terms of inter-story drift ratio than the other energy components. Secondly, the energy ratio was re-optimized with different constraints and its effectiveness was examined. Full article

Flexure-based Stirling cryocooler compressors are a critical technology in providing cryogenic temperatures in various advanced engineering fields, such as aerospace, defense, and medical imaging. The most challenging problem in the design of this type of compressor is achieving a precise alignment that preserves small gaps between the components moving relative to each other and avoids severe friction and wear. This paper introduces a novel experimental procedure for designing Stirling cryocooler compressors, leveraging a recently developed nonlinear experimental modal analysis method known as response-controlled stepped-sine testing (RCT). The alignment in a compressor prototype was significantly improved in light of a series of RCT with base excitation. The enhanced compressor design was subsequently validated though a series of constant-current tests, which confirmed the elimination of the sticking/locking phenomenon observed in the initial design. Furthermore, an indirect harmonic force surface (HFS)-based approach proposed for weakly nonlinear systems was extended to identify the high and nonlinear damping (up to a 65% hysteretic modal damping ratio) observed in the enhanced compressor design due to excessive friction. As another contribution, it was shown that the extrapolation of the HFS gives accurate results in the prediction of the nonlinear modal parameters at response levels where no experimental data are available. In light of these findings, it was concluded that the enhanced design needs further design modifications to further decrease the friction and wear between the moving parts. Overall, this study provides valuable insights for designing cryocooler compressors, with implications for aerospace and medical applications. Full article

Prefabricated insulation grid shear walls are a new type of wall which integrates structure, insulation and formwork. A grid-like reinforced concrete shear wall with vertical and transverse limbs is formed by casting concrete into the reserved vertical and transverse hollow cavities in the prefabrication of cement polystyrene granular concrete wall formworks. In this paper, based on an earthquake engineering simulation open system (OpenSees), a new modeling approach for grid shear walls is proposed, and nonlinear analysis of two grid walls with different grid sizes under cyclic load is carried out. The accuracy and effectiveness of the grid shear wall model are verified by comparison of the predicted hysteretic response and experimental results. On this basis, the seismic performance of grid shear walls with different parameters (axial load ratio, vertical reinforcement ratio, transverse reinforcement ratio and transverse limb height) is analyzed. The results show that both axial load ratio and vertical reinforcement ratio can significantly improve the load capacity of grid shear walls. However, with an increase in the axial load ratio, the ductility of the grid shear walls decreases. The influence of transverse reinforcement ratio and transverse limb height on the load capacity of shear wall with large shear span ratio is relatively small, mainly because the failure mode of shear wall with large shear span ratio is bending failure. Based on parameter influence analysis, design suggestions for reinforcement ratio in vertical and horizontal limbs and the height of the transverse limb of grid shear walls are put forward. The research in this paper provides a reference for the application of grid shear walls in engineering. Full article

This paper examines the performance of Bayesian filtering system identification in the context of nonlinear structural and mechanical systems. The objective is to assess the accuracy and limitations of the four most well-established filtering-based parameter estimation methods: the extended Kalman filter, the unscented Kalman filter, the ensemble Kalman filter, and the particle filter. The four methods are applied to estimate the parameters and the response of benchmark dynamical systems used in structural mechanics, including a Duffing oscillator, a hysteretic Bouc–Wen oscillator, and a hysteretic Bouc–Wen chain system. Based on the performance, accuracy, and computational efficiency of the methods under different operating conditions, it is concluded that the unscented Kalman filter is the most effective filtering system identification method for the systems considered, with the other filters showing large estimation errors or divergence, high computational cost, and/or curse of dimensionality as the dimension of the system and the number of uncertain parameters increased. Full article

This paper aims to examine the seismic response of prestressed self-centering moment-resisting frames (PSC-MRFs) based on concrete-filled double steel tubular (CFDST) columns and RC beams. The beam of this novel connection is divided into two parts, connected by bolts and tendons, and the beam includes a gap opening feature, which could be regarded as a normal single beam in the field. Cyclic loading analysis was performed on one-story frames with different initial parameters arranged in adjacent bays. Nonlinear dynamic analysis was conducted on a six-story frame under two seismic hazard levels. The cyclic loading analysis showed favorable self-centering performance of the frame even when the hysteretic energy dissipation ratio reached 0.808. Seismic analysis results showed that compared with the in situ reinforced concrete frame, PSC-MRFs generally had similar maximum inter-story drifts under fortification earthquakes, but the residual inter-story drifts were reduced by 33%; under rare earthquakes, the maximum inter-story drifts and residual inter-story drifts of PSC-MRFs were reduced by 22% and more than 90%, respectively. In the adjacent bays on the same story of PSC-MRFs, connections with smaller imminent moments of gap opening opened earlier under earthquake, and the maximum opening angle was larger. The general seismic performance and self-centering of PSC-MRFs was significantly more advantageous than that of in situ reinforced concrete frames. Full article

The motivation for using artificial neural networks in this study stems from their computational efficiency and ability to model complex, high-level abstractions. Deep learning models were utilized to predict the structural responses of reinforced concrete (RC) buildings subjected to earthquakes. For this aim, the dataset for training and evaluation was derived from complex computational dynamic analyses, which involved scaling real ground motion records at different intensity levels (spectral acceleration Sa(T₁) and the recently proposed I_Np). The results, specifically the maximum interstory drifts, were characterized for the output neurons in terms of their corresponding statistical parameters: mean, median, and standard deviation; while two input variables (fundamental period and earthquake intensity) were used in the neural networks to represent buildings and seismic risk. To validate deep learning as a robust tool for seismic predesign and rapid estimation, a prediction model was developed to assess the seismic performance of a complex RC building with buckling restrained braces (RC-BRBs). Additionally, other deep learning models were explored to predict ductility and hysteretic energy in nonlinear single degree of freedom (SDOF) systems. The findings demonstrated that increasing the number of hidden layers generally reduces prediction error, although an excessive number can lead to overfitting. Full article

Concrete-filled fiber-reinforced polymer (FRP) tubes (CFFTs) offer an alternative to traditional reinforced concrete columns for new construction applications due to their high strength, ductility, and corrosion resistance properties. Despite their popularity, there is a lack of accurate analytical models for the cyclic/seismic performance of CFFT columns. This is due to the absence of precise stress–strain models for FRP tubes and confined concrete under cyclic loading. Previous experiments on CFFT columns suggest that even minimal reinforcement (≤1%) provides essential energy dissipation for extreme events. However, existing stress–strain models for FRP-confined concrete often neglect the contribution of longitudinal and transverse steel reinforcement. While some researchers have proposed material models to address this issue, the analytical modeling of confinement effects from both steel reinforcement and FRP tubes, especially under lateral cyclic loading, continues to pose a significant challenge. This study aims to use previously collected experimental data to evaluate current analytical modeling approaches in OpenSeesPy3.5.1.12 to simulate the lateral cyclic behavior of CFFT columns with ±55° glass fiber-reinforced polymer (GFRP) fiber orientation. Both the lumped inelasticity and the distributed inelasticity modeling approaches are applied. The performance of various FRP confinement models is compared. The effect of plastic hinge length is also considered in the lumped plasticity approach. The findings suggest that integrating a fiber element section into the plastic hinge zone enhances the efficiency of the distributed inelasticity approach. This method accurately captures the non-linear behavior in the critical region and precisely predicts the shape of the hysteretic curve, all while reducing computational costs. Conversely, the lumped inelasticity modeling approach effectively forecasts energy dissipation and peak load values across the entire cyclic hysteresis curve, offering significant computational savings. Finally, a generalized modeling methodology for predicting the response of CFFTs under cyclic lateral load is proposed and subsequently validated using experimental results found in the existing literature. Full article