Energy Dissipation Capability Research Articles

Neural Network Parameter Identification Based Constitutive Modeling of Superelastic Shape Memory Alloys

AbstractSuperelastic shape memory alloys (SMAs) are two‐phase polycrystal materials with hysteretic energy dissipation and deformation recovery capabilities. This feature opens numerous application possibilities, particularly using SMA wires in structural vibration control. However, vibrations, such as wind and earthquake induced, may occur in high rate regimes with alternating amplitudes. Experiments show that the thermodynamically coupled SMA behavior is highly sensitive to strain rate and amplitude. Accordingly, the prediction accuracy of the constitutive models depends notably on their thermodynamic parameters, such as latent heat, heat transfer coefficient and specific heat. The identification of these parameters requires extensive experiments. To circumvent this challenge, this study proposes for SMA wires a machine learning based parameter identification procedure using artificial neural networks (ANNs). In this approach, a recently improved uniaxial macroscopic constitutive SMA model is utilized as a forward physics based model to compute all possible responses in an expected parameter space. With the generated data, a multilayer ANN is trained as a data based inverse model. The Latin hypercube sampling and the backpropagation learning algorithms are applied. After training, the data based model is able to identify suitable thermodynamic parameters from SMA stress responses. With the identified parameters, the constitutive model replicates the strain rate and amplitude dependent SMA response effects. The experimental results are matched by the model with high accuracy.

Effects of solvent osmolarity and viscosity on cartilage energy dissipation under high-frequency loading

Articular cartilage is a spatially heterogeneous, dissipative biological hydrogel with a high fluid volume fraction. Although energy dissipation is important in the context of delaying cartilage damage, the dynamic behavior of articular cartilage equilibrated in media of varied osmolarity and viscosity is not widely understood. This study investigated the mechanical behaviors of cartilage when equilibrated to media of varying osmolarity and viscosity. Dynamic moduli and phase shift were measured at both low (1 Hz) and high (75–300 Hz) frequency, with cartilage samples compressed to varied offset strain levels. Increasing solution osmolarity and viscosity both independently resulted in larger energy dissipation and decreased dynamic modulus of cartilage at both low and high frequency. Mechanical property alterations induced by varying osmolarity are likely due to the change in permeability and fluid volume fraction within the tissue. The effects of solution viscosity are likely due to frictional interactions at the solid-fluid interface, affecting energy dissipation. These findings highlight the significance of interstitial fluid on the energy dissipation capabilities of the tissue, which can influence the onset of cartilage damage.

Antiseismic Method of Prestressed Fabricated Building Structure under Intelligent Big Data

Compared with traditional buildings, prefabricated buildings have the advantages of simple construction technology, low construction requirements, and shorter construction time, which can generate more economic benefits for the construction industry. In order to study the seismic capacity of prestressed fabricated building structures under intelligent big data, this article takes fabricated frame structures as the research object and the reinforced walls at the nodes as the starting point to study the damage patterns and energy dissipation capabilities of different seismic waves on the structure. In order to observe the overall seismic performance, the fabricated frame structure was used. The results of the study found that the prestressed fabricated building structure has the best seismic effect when the axial compression is 0.3, and the prestressed degree is below 0.5, which meets the seismic requirements. Therefore, the prestressed degree of the prestressed fabricated building structure should be below 0.5. According to statistics on the results of structural residual deformation and steel bar deformation of buildings under different seismic waves, it can be found that the prestressed fabricated building structure has better self-recovery ability and can better respond to earthquakes with different seismic waves.

Seismic demands of structural and non-structural components in self-centering precast concrete wall buildings

Self-centering (SC) precast concrete wall structures have been developed as an earthquake resilient structural system characterized by low structural damage and controllable residual drift. Despite the superior structural performance, harmonizing to seismic performance between structural and non-structural components is expected to be considered for further comprehensive performance assessment. This paper extensively evaluates the seismic demands of structural and non-structural components, especially for those sensitive to accelerations in SC precast concrete wall structures. Factors considered include building heights, earthquake ground motion types and intensities, energy dissipation, as well as base rocking, and impact against the foundation. The seismic demands of SC precast concrete walls are firstly compared with conventional reinforced concrete (RC) walls by nonlinear time history analysis (NTHA) in terms of displacement and acceleration responses. Then, attention is focused on investigating the dominant factors for the seismic demands of acceleration-sensitive non-structural components in SC precast wall structures through floor response spectrum analysis and parametric analyses. The results confirm that the SC precast walls exhibit excellent lateral response, especially with limited residual drifts. However, for the floor acceleration response, which is highly related to the demands of non-structural components, the results show that higher modes have a critical influence on SC precast wall structures. It also indicates that the floor acceleration response of SC precast wall structures is strongly influenced by the location of the story levels but not strongly influenced by the base rocking impact and energy dissipation capability.

Experimental study on the seismic performance of steel–concrete beam–column connections for prefabricated concrete frames

A novel type of prefabricated steel–concrete beam–column connection with different configurations for moment-resisting frames was developed for better constructability . Five beam–column connections, four prefabricated steel–concrete specimens, and one reference monolithic joint were tested under reversed cyclic load–displacement controlled conditions. The main variables were the steel form in beams and columns, fabrication method , and use of steel fiber reinforced concrete (SFRC) in the joint and connection parts. The cracking patterns and load–displacement hysteresis curves were recorded during the test. The efficiency of the developed connection was compared based on bearing capacity, energy dissipation , ductility, and stiffness. The results revealed that the prefabricated specimens with welded reinforcement connection exhibited flexural failure at the prefabricated beam, whereas the specimens with bolted end plates or weld-bolted H-steel beam connecting method failed through joint shear failure. The proposed prefabricated H-steel concrete connection with bolted end plates and SFRC had higher strengths and stiffnesses, more stable load–displacement cycles, and better energy dissipation capabilities. Moreover, the concrete spalling in the joint was adequately controlled, and shear deformation was also reduced. The H-steel beam connector in the proposed connection could effectively transfer loads under earthquakes. • A new prefabricated concrete beam–column connection connected with variable steel configurations is developed. • Cyclic loading tests performed on four prefabricated connections and one monolithic connection. • The prefabricated connection with welded reinforcements to H–steel flange fails in flexural failure. • Connections with bolted end plates or weld-bolted H-steel connection shows shear failure. • The prefabricated connections demonstrate satisfactory strength, stiffness and energy dissipation capacity.

Impact performance of rubber reinforced concrete with waste steel fibres

This study introduces cementitious composite with rubber granulate and waste steel fibres as a new material for construction industry with an enhanced energy absorption capability and impact toughness. Detailed research on physico-mechanical properties of high-performance concrete with waste steel fibres and partial replacement of the aggregates by rubber granulate was performed, with emphasis on impact energy absorption potential. Different aggregate replacement ratios (0–30% wt.) and fibre amount (0–3% wt.) were investigated. The influence of rubber sizes, rubber content and steel fibre content on the mechanical parameters of the rubberized concrete at both quasistatic and dynamic loads was evaluated and discussed. With increasing amount of rubber granulate, the concrete suffered from reduction of its mechanical parameters – compressive and flexural strength, however the energy dissipation capability showed rising trend. This study demonstrated the potential of rubberized concrete with waste steel fibres for use in structures with higher impact resistance requirements.

Manufacturing, testing and simulation of novel SMA-based variable friction dampers with enhanced deformability

This study presents a novel type of self-centering damper employing NiTi Shape Memory Alloy (SMA) bars combined with variable friction mechanism for tunable hysteretic behavior and enhanced deformability. The new damper, which is called SMA-based variable friction damper (SMA-VFD), aims to significantly amplify the maximum deformability and energy-dissipation capability compared with the existing self-centering devices with tensioning SMA members. The cyclic response, phase transformation behavior, and in-situ observation of the microstructure of individual SMA bars receiving different heat treatments were first investigated to promote an adequate understanding of the link between the microscopic structure and the macroscopic property of the large size SMA bars. This is followed by a detailed discussion of the SMA-VFD, where theoretical equations as well as three performance parameters, i.e., self-centering factor γ, displacement amplification factor ω, and energy-dissipation factor λ, were derived to predict the mechanical behavior of the damper. Proof-of-concept SMA-VFD specimens were manufactured, where different preloads and friction coefficients were considered which could affect the cyclic performance. A three-dimensional finite-element model was then developed to simulate the nonlinear responses of the test specimens. Both the analytical prediction and numerical simulation exhibited good agreements with the experimental results. Utilizing the validated numerical model, the influence of manufacturing tolerance on the initial stiffness of the proposed damper was particularly investigated to help explain some important findings from the present experimental study.

Size effects on the dynamic indentation modulus of films

The dynamic mechanical characteristics of viscoelastic films play a significant role in the load-bearing functions of various engineering and natural composite materials systems. Identifying these film characteristics is a prime objective in both fundamental and applicative materials science fields. However, as the film thickness decreases, its analysis by dynamic nanoindentation methods becomes convoluted due to the emergence of mechanical coupling between the film and its underlying substrate. These yet unexplored size effects pose major limitations in approaching the elemental mechanical characteristics of thin films. Here, we analyze the film size effects on its dynamic indentation modulus by theoretical modeling and Finite-Element simulations. We develop compact analytical formulae that link the indentation modulus magnitude, loss coefficient, storage modulus, and loss modulus to those of the pristine film, draw functional insights into the energy-storage and energy-dissipation capabilities of the integrated film–substrate laminate, and outline an approach to back-calculate the elemental film characteristics via simple linear scaling of its dynamic indentation modulus measurements. Our analysis generally holds for synthetic and biological film materials—paving the way to identify the dynamic mechanical characteristics of various thin-film configurations, such as polymeric assemblies, functional surfaces, and biomechanical coatings.

Experimental study on seismic behavior of SCRC column base joints with replaceable dampers

Self-centering reinforced concrete (SCRC) column base joints can effectively reduce residual drift under horizontal seismic action as unbonded post-tensioning strands provide self-centering capacity. The connection also utilizes a steel tube collar, and a new type of replaceable damper to dissipate seismic energy. Six specimens of SCRC column base joints were designed, constructed and subjected to cyclic horizontal loading in conjunction with axial compression. The experiments investigated the mechanical behavior, hysteretic curve, energy dissipation capability, self-centering capacity, and replaceability of the SCRC column base joints. The experimental results showed that the SCRC column base joint performed satisfactorily in moment capacity, residual drift, and energy dissipation. The behavior of specimens with replaced dampers was almost the same as their behavior with the original dampers, indicating the efficacy of replacement. Moreover, the steel tube protected the concrete at the column base from local compression failure.

Dynamic Properties and Energy Dissipation Study of Sandwich Viscoelastic Damper Considering Temperature Influence

Viscoelastic dampers are a kind of classical passive energy dissipation and vibration control devices which are widely utilized in engineering fields. The mechanical properties and energy dissipation capacity of the viscoelastic damper are significantly affected by ambient temperature. In this work, dynamic properties tests of the sandwich type viscoelastic damper at different environmental temperatures are carried out. The equivalent fractional Kelvin model which can characterize the mechanical behavior of the viscoelastic damper with varying frequencies and temperatures is introduced to describe the dynamic properties and energy dissipation capability of the sandwich viscoelastic damper. The self-heating phenomenon of the sandwich viscoelastic damper is studied with a numerical simulation, and the dynamic properties and energy dissipation variation of the viscoelastic damper with self-heating processes are also analyzed. The results show that the dynamic properties of the viscoelastic damper are significantly affected by temperature, excitation frequency and the internal self-generated heating.

Seismic Design and Performances of Frame Structures Connected to a Strongback System and Equipped with Different Configurations of Supplemental Viscous Dampers

The paper investigates the dynamic behavior of structural systems obtained by connecting a moment-resisting frame structure with a vertical rigid truss pinned at the base, known in literature as “strongback,” and equipped with added fluid-viscous dampers. The strongback, designed in order to remain in the elastic field under strong seismic ground motion, acts as a mast by imposing to the structure a linear lateral deformed shape. By regularizing the lateral drift profile of the structure, the strongback limits undesired effects such as weak-storey mechanisms, damage concentration and residual drifts. In addition, when supplemental dampers are inserted in the structure, a considerable amount of energy can be dissipated, thus reducing the peak seismic response. The aim of the work is twofold: i) to provide analytical formulations for the preliminary design of added dampers based on the Generalized Single Degree Of Freedom (GSDOF) concept, and ii) to evaluate the increase in energy dissipation capabilities for selected dampers configurations thanks to the presence of the strongback. The formulas are developed for different configurations of added viscous dampers: dampers inserted within the frame between all or selected consecutive storeys (inter-storey placement) and dampers located at the base of the strongback to realize a rigid “dissipative tower.” The effectiveness of the dampers configurations is evaluated through dynamic time-history analyses.

An experimental study of the seismic behaviour of precast concrete shear walls with bolted-plate connections

The seismic resistance of an innovative precast reinforced concrete shear wall with vertical plates along its bottom edge to be bolted to plates protruding from the foundation was tested in reduced-scale model in the laboratory. Five precast shear walls with different wall heights and axial loads, as well as one reference cast-in-place shear wall, were tested. Horizontal cyclic loading was applied to examine the seismic performance of the specimens. The failure modes of the shear walls are discussed, along with their hysteretic behaviour, stiffness degradation, energy dissipation capacity, slip at the bolted connections, and strains in the reinforcement and in the connecting plates. The test results show that the bolted-plate connections can effectively transfer vertical and shear forces, as well as bending moments, to the foundation beam without any slip along the connection. The precast specimens exhibited approximately the same seismic behaviour as the cast-in-place one. In general, the failure mode shifts from compression-bending to shear-compression at smaller heights of the walls, with an increase in the bearing capacity, but a reduction in wall deformability and the energy-dissipation capability. At smaller values of the axial loads, the bearing capacity decreases but the deformability increases. The existing Chinese design code for normal reinforced concrete shear walls gives safe design limits also for the precast walls with bolted-plate connections.

Influence of Geocomposite Properties on the Crack Propagation and Interlayer Bonding of Asphalt Pavements.

The application of geocomposites as reinforcement in asphalt pavements is a promising solution for the maintenance/rehabilitation of existing pavements and for the construction of new pavements, whose effectiveness strongly depends on the physical and mechanical properties of the geocomposite. This study aims at assessing the influence of four different geocomposites, obtained by combining a reinforcing geosynthetic with a bituminous membrane, on the crack propagation and interlayer bonding of asphalt pavements. First, a laboratory investigation was carried out on double-layered asphalt specimens. The crack propagation resistance under static and dynamic loads was investigated through three-point bending tests (carried out on specimens with and without notch) and reflective cracking tests respectively, whereas the interlayer shear strength was evaluated through Leutner tests. Then, a trial section was constructed along an Italian motorway and a Falling Weight Deflectometer (FWD) testing campaign was carried out. The laboratory investigation highlighted that—as compared to the unreinforced system—the geocomposites increased the crack propagation energy in the layer above the reinforcement from five to ten times, indicating that they can significantly extend the service life of the pavement by delaying bottom-up and reflective cracking. However, they also worsened the interlayer bonding between the asphalt layers (de-bonding effect). The field investigation indicated that all geocomposites decreased the stiffness of the asphalt layers with respect to the unreinforced pavement as a consequence of the de-bonding effect, thus corroborating the laboratory results. Based on the results obtained, it is desirable that the geocomposite possess a high energy dissipation capability and an upper coating ensuring good adhesion between the asphalt layers. The monitoring of the existing trial section in the future will provide useful data on the long-term field performance of reinforced pavements subjected to actual motorway traffic.

Performance evaluation of built-up composite beams fabricated using thin-walled hollow sections and self-compacting concrete

The present study proposes an innovative steel–concrete composite beam fabricated using self-compacting cementitious (SCC) composite, thin-walled steel plates, and hollow sections. In order to validate the performance of the proposed composite beam, the experimental investigation was conducted in terms of flexural strength, ductility, flexural stiffness, energy dissipation capability, and failure mode. Furthermore, the hallow sections spacing, slab depth, and SCC mixtures wereconsidered as design variables in order to probe into their effects on the structural performance of the proposed composite beam. The results indicated that hollow section spacing and fiber percentage had the most influence on load capacity and energy absorption of the composite beams. Further, the interaction between slab integration significantly prevented concrete crushing of failed composite beam. Moreover, the composite beam introduced in this study showed higher stiffness, ductility, and energy dissipation compared to the conventional one. Ultimately, a design flowchart was developed to determine the ultimate bearing capacity of the proposed composite beam.

RESTORING FORCE MODEL OF DISC SPRING DEVICES AND ITS APPLICATION IN SELF-CENTERING RC SHEAR WALL

The working principle and mechanics behavior of disc spring device are analyzed to accurately simulate the mechanics performance of disc spring device and the self-centering RC shear wall. Furthermore, the restoring force model of disc spring device is proposed and developed. The accuracy of the restoring force model is verified through experiments. The hysteretic performance of the self-centering RC shear wall with disc spring device is numerically simulated and compared with the experimental results due to cyclic reversed loading. Results indicate that the numerical model using a restoring force model of disc spring device can effectively simulate the hysteretic behavior, self-centering performance and energy dissipation capability of the self-centering RC shear wall. The bearing capacity of the self-centering RC shear wall increases with the increase of the pre-pressed force of disc springs, the additional friction force and the stiffness of disc spring device. The energy dissipation capacity increases with the increase of the additional friction force. The residual displacement increases with the increase of additional friction and decreases with the increase of the pre-pressed force of disc springs and the stiffness of disc spring device.

Microbeam bending of hydrated human cortical bone lamellae from the central region of the body of femur shows viscoelastic behaviour

Bone is a biological tissue with unique mechanical properties, owing to a complex hierarchical structure ranging from the nanoscale up to the macroscale. To better understand bone mechanics, investigation of mechanical properties of all structural elements at every hierarchical level and how they interact is necessary. Testing of bone structures at the lower microscale, e.g. bone lamellae, has been least performed and remains a challenge. Focused ion beam (FIB) milling is an attractive technique for machining microscopic samples from bone material and performing mechanical testing at the microscale using atomic force microscopy (AFM) and nanoindentation setups. So far, reported studies at this length scale have been performed on bone samples of animal origin, mostly in a dehydrated state, except for one study. Here we present an AFM-based microbeam bending method for performing bending measurements in both dehydrated and rehydrated conditions at the microscale. Single lamella bone microbeams of four human donors, aged 65–94 yrs, were machined via FIB and tested both in air and fully submerged in Hank's Balanced Salt Solution (HBSS) to investigate the effect of (de)hydration and to a certain extent, of age, on bone mechanics. Bending moduli were found to reduce up to 5 times after 2 h of rehydration and no trend of change in bending moduli with respect to age could be observed. Mechanical behavior changed from almost purely elastic to viscoelastic upon rehydration and a trend of lower dissipated energy in samples from older donors could be observed in the rehydrated state. These results confirm directly the importance of water for the mechanical properties of bone tissue at the microscale. Moreover, the trend of lowered capability of energy dissipation in older donors may contribute to a decrease of fracture toughness and thus an increase in bone fragility with age.

Cyclic experimental and numerical analytical investigation of precast concrete frames with buckling-restrained braces considering various assembling connections

Buckling-restrained braces (BRBs) are able to provide good lateral stiffness and energy dissipation capability for precast concrete (PC) frames under the earthquake. However, there is little research on the reliable connection between BRBs and PC frames with different beam-column assembling joints. To investigate cyclic response and failure modes of PC frames with BRBs, cyclic loading tests of four PC frames with BRBs and one bare reinforced concrete (RC) frame were conducted in this paper. Two types of beam-column assembling joints, i.e. the integral type and the concealed corbel type, were designed to check their connection reliability. Moreover, three novel connection types between BRBs and PC frames, i.e. the end plate connection type, the column-only connection type and the splicing connection type, were developed to explore their cooperative working performance under lateral cyclic loading. The experimental phenomena and failure features were observed and recorded. The hysteretic and skeleton curves, ductility coefficients, stiffness degradation and energy dissipation capacity of the structure were compared and analyzed. It indicated that the bearing capacity and failure modes of specimens are close to each other when the two reasonable beam-column assembly joints were adopted. Meanwhile, specimens with different BRB-PC frame connection types exhibited similar seismic performance. It demonstrated that the BRBs could effectively enhance the seismic performance of PC frames in comparison with the bare counterpart. Furthermore, the finite element (FE) model was established and verified by the test results. Then the parametric analysis, including load, material, and geometric parameters, was performed systematically. The above research results could be contributed to promoting the design and application of BRBs in PC frames.

Analytical and experimental study on sloped sliding‐type bearings

Seismic isolation design has been publicly accepted as one of the most effective strategies to reduce seismic threat to (or seismic demand for) the to-be-protected targets including building structures, infrastructure, and equipment. Recently, many studies have aimed to develop nonlinear seismic isolation systems, of which the sloped sliding-type bearing can exhibit the nonlinear behavior by mechanically designing a simple slope for sliding motion. Therefore, this bearing does not have a fixed isolation frequency. In addition, it features that the seismic isolation performance is realized through the sliding mechanism, the inherent self-centering capability is provided through the slope design, and the excellent and stable energy dissipation capability is contributed by the sliding friction. In this study, the equation of motion of the bearing is deduced first. Sensitivity analysis is then performed, and the results demonstrate that the maximum horizontal acceleration transmitted to the isolated superstructure is only dependent on two important design parameters-sliding friction coefficients and sloping angles. In other words, the acceleration control performance of the bearing is irrelevant to different characteristics of external disturbance. Finally, shaking table tests were conducted to verify the effectiveness of the bearing and the accuracy of the numerical prediction.

Strengthening of RC beam-column joints using steel plate with shear connectors: Experimental investigation

This paper presents experimental analyses on beam-column joints strengthened with steel plate & steel plate with shear connectors subassemblies subjected to cyclic loading. For the investigation, a total of six reduced-scale external beam-column joints were cast. Two specimens with individual closed stirrups are used as the reference models. Among the remaining, two specimens were strengthened with steel plates and two specimens were retrofitted with steel plates and shear connectors. The reinforced beam-column subassemblies were subjected to cyclic tests to determine their crack propagation and resistance capability during seismic excitations. The primary objectives of the analyses have been to monitor the seismic performance of the joints in terms of load–displacement pattern, hysteresis behavior, failure pattern, and energy dissipation capability. In addition, some experiments were carried out to differentiate and evaluate the efficiency of conventionally closed stirrups. The results are inspiring as the steel plate with shear connectors outperformed the traditional stirrups in terms of lateral strength, stiffness, and accumulated energy dissipation. The results indicated that the proposed methodology can be used as a feasible and adequate technique to improve the seismic resilience of RC structures in regions of high seismicity.

Hysteresis behavior of bottom-story self-centering shear wall with steel brace-assembled bottom

A self-centering shear wall (SC-SW) with a steel brace-assembled bottom is proposed to avoid the residual drift of reinforced concrete shear walls (RCSWs) due to damage in corners and achieve an adequate earthquake-resilience. The residual displacement of traditional RCSW is caused by the bending and shear deformations of the plastic hinge and the deformation of the upper plate, as is confirmed by a cyclic loading test on a typical RCSW specimen. A steel brace-assembled bottom consisting of a steel V-shaped connecting beam, a bearing, and two self-centering braces is designed to control the residual deformation of the RCSW plastic hinge zone. The simplified equations governing the skeleton curve of the SC-SW are derived. An RCSW and SC-SW with the same initial stiffness and ultimate bearing capacity are simulated and compared via the experimentally validated finite element model. The results indicate that the SC-SW exhibits a flag-shaped hysteresis response with an excellent self-centering capability. The maximum residual story drift ratio is less than 0.125%. The skeleton curve equations agree well with the measured data of the analytical specimen. The overall performance of the SC-SW is primarily affected by the braces. The energy dissipation capability of the SC-SW remains insufficient due to the lesser development of plastic deformation.