Hysteretic Behavior Research Articles

Intercalated water-induced hysteretic friction behavior of graphene, h-BN, and MoS[formula omitted

Two-dimensional (2D) materials have extraordinary properties that promise significant advancement of electronic, mechanical, and electrochemical devices. However, these properties are often measured in ideal, clean states, absent from contamination from their surrounding environment. Here we study the impact of water intercalation on the mechanical and lubricating properties on 2D nanofilms of graphene, h-BN, and MoS2 using atomic force microscopy (AFM) and molecular dynamics (MD) simulations. Comparing the performance of pristine 2D nanofilms and those with water intercalated between the substrate and the 2D nanofilm, we observed higher friction in intercalated samples than in pristine samples. In load dependent friction measurements, we also observed that the friction hysteresis varied from pristine samples to those with water intercalated. MD simulations suggest that this difference was a result of a decrease in the apparent out-of-plane mechanical stiffness of the 2D nanofilm and a reduction in the adhesive interaction between substrate and nanofilm that occurred when water was intercalated between the 2D material and the substrate, allowing for a change in the out-of-plane deformation behavior of the supported 2D nanomaterial. These observations suggest that 2D materials experience performance degradation when exposed to ambient conditions.

Data based constitutive modelling of rate independent inelastic effects in composite cables using Preisach hysteresis operators

AbstractThis contribution aims at introducing first steps to develop hysteresis operator type inelastic constitutive laws for Cosserat rods for the simulation of cables composed of complex interior components. Motivated by the basic elements of Cosserat rod theory, we develop a specific approach to constitutive modelling adapted for this application. Afterwards, we describe the hysteretical behaviour arising from cyclic bending experiments on cables by means of the Preisach operator. As shown in pure bending experiments, slender structures such as electric cables behave inelastically, and open hysteresis loops arise with noticeable difference between the first load cycle and the following ones. The Preisach operator plays an important role in describing the input-output relation in hysteresis behaviours, and it can be expressed as a superposition of relay operators. Hence, a mathematical formulation of the problem is introduced, and a first attempt is made to determine the hysteresis behaviour that describes the relation between curvature and bending moment. Therefore, a suitable kernel function is identified in a way that its integration over the Preisach plane results in the bending moment of the specimen, and a comparison between different kernel functions is performed.

Hysteretic Behaviour of Composite Reduced Web Section (RWS) Connections for Seismic Applications

ABSTRACT Whilst there has been research about reduced web section beams; RWS, their seismic behaviour when they are overlaid by slabs is not well understood. This study addresses this by assessing a high-definition finite element representation of non-seismically detailed RWS connections with slabs. The composite action is investigated, focusing on effects of the size and location of the web openings. These connections can reach a 4% interstorey drift, thus comprising special moment frames in accordance with AISC 341. Moreover, beam, column, and joint tearing were avoided entirely, and at the most, brittle failure of bolts in the end plate was observed.

Mechanical Characterisation of Woven Pneumatic Active Textile

Active textiles have shown promising applications in soft robotics owing to their tunable stiffness and design flexibility. Given the breadth of the design space for planar and spatial arrangements of these woven structures, a rigorous and generalizable characterisation of these systems is not yet available. In order to characterize the response of a stereotypical woven pattern to actuation, we undertake a parametric study of plain weave active fabrics and characterise their mechanical properties in accordance with the relevant ISO standards for varying muscle densities and both monotonically increasing/decreasing pressures. Tensile and flexural tests were undertaken on five plain weave samples made of a nylon 6 (polyamide) warp and EM20 McKibben S-muscle weft, for input pressures ranging from 0.00 MPa to 0.60 MPa, at three muscle densities, namely 100 m <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{-1}$</tex-math></inline-formula> , 74.26 m <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{-1}$</tex-math></inline-formula> and 47.62 m <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{-1}$</tex-math></inline-formula> . Contrary to intuition, we find that a lower muscle density has a more prominent impact on the thickness, but a significantly lesser one on length, highlighting a critical dependency on the relative orientation among the loading, the passive textile and the muscle filaments. Hysteretic behaviour as large as 10% of the longitudinal contraction is observed on individual filaments and woven textiles, and its onset is identified in the shear between the rubber tube and the outer sleeve of the artificial muscle. Hysteresis is shown to be muscle density-dependent and responsible for a strongly asymmetrical response upon different pressure inputs. These findings provide new insights into the mechanical properties of active textiles with tunable stiffness, and may contribute to future developments in wearable technologies and biomedical devices.

Experimental and numerical investigation of the seismic behaviour of corroded precast concrete piers with grouting sleeve connections

Due to several advantages, including controllable tolerance, accelerated construction and environmental friendliness, the grouting sleeve connections has been widely used in precast concrete pier structures. However, the seismic capacity of precast concrete piers would be significant impaired under the marine or deicing-salt environment. This article presents an experimental investigation on the seismic behaviour of corroded precast concrete piers with grouting sleeve connections. Five specimens with different corrosion levels were tested under cyclic loads. Seismic capacities of specimens with different corrosion levels, including hysteretic behaviour, stiffness degradation and energy-dissipation capacity, were analysed. The results showed that corrosion of reinforcements and grouting sleeve connections would significantly affect the seismic behaviour of the piers. The crack load, yield load and peak load decreased gradually with the increase of corrosion ratio, with the effect of corrosion on peak load being slightly greater than that on yield load. An approximate exponential decrease in yield displacement and peak displacement was observed as the corrosion ratio increased, and the decline rate in yield displacement and peak displacement gradually decreased. A numerical method for simulating the seismic behaviour of corroded precast concrete piers with grouting sleeve connections is proposed, and agreement between simulated and experimental results is observed.

A multi-objective calibration framework for capturing the behavioral patterns of autonomously-driven vehicles

Calibration of car-following (CF) models is considered a very important task towards reproduction of individual vehicle behaviors and collective traffic phenomena. In most works, calibration is performed on trajectories of leading and following vehicles either on speed or spacing quantities, with the combination of the two plus the acceleration quantity to be considered as the most appropriate according to the literature. With the advent of adaptive cruise control (ACC) technology, there are intrinsic behavioral differences between human- and ACC-driven vehicles that are visible in experimental observations. Some examples include constant headway for ACC-enabled vehicles, string instability, hysteretic behavior, human-like response time and others. Since calibration is performed only on basic vehicle dynamics, i.e., the spacing, speed and acceleration, even after proper parametrization we cannot be certain that CF models will be able to reproduce some or all of the above phenomena and to what extend. The aim of this work is to propose a multi-objective calibration framework validated on empirical observations of car platoons. Furthermore, it investigates if, and to what extent, the traffic dynamics and behavioral patterns of ACC-driven vehicles can be reproduced. Two state-of-the-art CF models are tested with the empirical dataset. The results indicate that the proposed framework leads to acceptable errors and comparable performance, facilitating the models to capture phenomena in a way that is not possible until now, using the calibration on basic vehicle dynamics.

Experimental Study on the Seismic Mechanism of Full-scale Specimens of Superimposed Slab Shear Walls with Innovative Construction Details

The seismic performance of precast reinforced concrete structures has long been a source of concern that impedes their use in seismic regions and high-rise buildings. To further optimize the reinforcement configuration and enhance the seismic performance of the superimposed slab shear wall structures, this research proposed a superimposed slab shear wall with innovative construction details. Five innovative superimposed slab shear walls and one cast-in-place concrete shear wall were designed and tested under low cycle lateral load. The effect of axial compression was considered during tests and analyses as well. In this paper, the seismic performance, including failure mode, hysteretic behavior, load-bearing capacity, lateral stiffness degradation, energy dissipation, and seismic ductility was investigated and analyzed. The experimental results showed that five innovative superimposed slab shear walls and one cast-in-place concrete shear wall exhibited a similar failure mode of flexural-shear failure, and a large area of concrete was damaged and crushed at the shear wall corner. However, the area of crushing concrete in the cast-in-place concrete shear wall was relatively small. And the area of crushing concrete in the superimposed slab shear walls increased with the axial compression ratio. For the superimposed slab shear walls, the development of concrete cracks decreased gradually with the enlargement in the axial compression ratio, while the length of the cracks increased in this respect. The results indicated that innovative superimposed slab shear walls had a higher strength capacity and lower lateral-resistant stiffness than the cast-in-place concrete shear wall. With the enlargement in the axial compression ratio, the peak strength capacity of the superimposed slab shear wall increased obviously, while it degraded rapidly after the peak load. It is suggested that the contribution of axial compression to the shear resist capacity of the inclined section should not be considered in practical design. Meanwhile, the ductility coefficients of the six specimens were larger than 2.2, which was in accordance with the seismic requirements. This investigation could provide effective experimental data for future structural seismic performance evaluations and applications of precast superimposed slab shear wall structures.

A novel parametric model for nonlinear hysteretic behaviours with strain-stiffening of magnetorheological gel composite

Magnetorheological (MR) gels are a new class of MR composite materials that can effectively address the issue of particle agglomeration in MR fluids, enhancing the controllability of materials in engineering applications. In this study, a novel parametric model was developed to track the nonlinear hysteretic behaviours with strain-stiffening of the MR gel. The model parameters were identified using the measurement data pertaining to five current levels (0A, 0.2A, 0.5A, 0.8A, and 1A) under a strain amplitude of 10% and a frequency of 0.1 Hz. The fruit fly optimisation algorithm (FOA) was used to determine the optimal solution for the model parameters. The model parameters were generalised with respect to the loading current, and the reliability of the generalised model was verified. The results of the study demonstrate that the proposed model outperforms two classical models, the Bouc–Wen model and viscoelastic–plastic model, in capturing the nonlinear and strain-stiffening behaviour of MR gels, particularly for higher current excitations. This study has potential applications in predicting the nonlinear hysteresis behaviour of automotive dampers, and provides a theoretical basis for the semi-active control of suspensions.

Wettability impacts residual trapping of immiscible fluids during cyclic injection

Understanding the hysteretic behaviour in fluid–fluid displacement processes in porous media is critical in many engineering applications. In this work, we study the quasi-static immiscible displacement process in two-dimensional porous media during cyclic injections in the context of carbon geosequestration. The role of wettability on the residual trapping of CO $_2$ is investigated numerically using an extended interface tracking algorithm. Despite that higher CO $_2$ saturation can be achieved in CO $_2$ -wet porous media after the first CO $_2$ injection, the majority of CO $_2$ is found to be unstable and can be mobilised during subsequent water injection processes. An improvement in the residual trapping of CO $_2$ is observed as the number of injection cycles increases, which is associated with the dispersion of continuous CO $_2$ ganglia into numerous smaller blobs. Compared with either water-wet or CO $_2$ -wet porous media, it is found that less CO $_2$ is trapped within the neutral-wet ones at equilibrium state after a sufficient number of injection cycles. The hysteretic behaviour of saturation between water/CO $_2$ injection cycles is found to follow an exponential decay, which eventually reaches a finite value. This process corresponds to the shift of the mobile region during displacement from typical capillary fingering to a less ramified regime, which ultimately converges towards main flow channels. This work highlights the hysteretic behaviour during cyclic injections, providing insights on the wettability impacts on multiphase flow in porous media, which is of great importance in applications such as carbon geosequestration and geological hydrogen storage.

Force-Displacement Hysteresis Model of Exterior PCRB Joints under Low Cyclic Loading.

The seismic behaviors of exterior polyvinyl chloride-carbon-fiber-reinforced polymer (PVC-CFRP) confined concrete (PCCC) column-ring-beam joints (hereafter referred to as exterior PCRB joints) under low cyclic loading were investigated. A total of 11 specimens were tested to analyze the effects of the structural parameters (i.e., the reinforcement ratio of the ring beam, the CFRP-strip spacing, the ring-beam width, the reinforcement ratio of the frame beam, and the axial compression ratio) on the failure modes and hysteretic behavior. Three different failure modes, including the failure of the frame beam, the failure of the junction between the frame beam and the ring beam, and the shear failure of the ring-beam joint, were observed. The experimental results showed that the pinching effects of the hysteresis curves decreased and that the slope of the descending stage of the skeleton curves gradually decreased with the enhancement of the reinforcement ratio of the ring beam, axial compression ratio, and ring-beam width. The effects of the CFRP-strip spacing and the reinforcement ratio of the frame beam on the hysteresis loops and skeleton curves were marginal, while the reinforcement ratio of the frame beam exerted significant effects on the failure modes. Therefore, a model for predicting the skeleton curves of exterior PCRB joints and hysteresis rules was proposed, based on the softening constitutive relation of the concrete and a regression analysis of the test data. Ultimately, a load-displacement hysteresis model of the exterior PCRB joints was established and validated by the test data, with good agreement.

PH-dependent water permeability switching and its memory in MoS2 membranes.

Intelligent transport of molecular species across different barriers is critical for various biological functions and is achieved through the unique properties of biological membranes1-4. Two essential features of intelligent transport are the ability to (1) adapt to different external and internal conditions and (2) memorize the previous state5. In biological systems, the most common form of such intelligence is expressed as hysteresis6. Despite numerous advances made over previous decades on smart membranes, it remains a challenge to create a synthetic membrane with stable hysteretic behaviour for molecular transport7-11. Here we demonstrate the memory effects and stimuli-regulated transport of molecules through an intelligent, phase-changing MoS2 membrane in response to external pH. We show that water and ion permeation through 1T' MoS2 membranes follows a pH-dependent hysteresis with a permeation rate that switches by a few orders of magnitude. We establish that this phenomenon is unique to the 1T' phase of MoS2, due to the presence of surface charge and exchangeable ions on the surface. We further demonstrate the potential application of this phenomenon in autonomous wound infection monitoring and pH-dependent nanofiltration. Our work deepens understanding of the mechanism of water transport at the nanoscale and opens an avenue for the development of intelligent membranes.

Influence of Profile Geometry on Frictional Energy Dissipation in a Dry, Compliant Steel-on-Steel Fretting Contact: Macroscopic Modeling and Experiment

Dry, frictional steel-on-steel contacts under small-scale oscillations are considered experimentally and theoretically. As indenting bodies, spheres, and truncated spheres are used to retrace the transition from smooth to sharp contact profile geometries. The experimental apparatus is built as a compliant setup, with the characteristic macroscopic values of stiffness being comparable to or smaller than the contact stiffness of the fretting contact. A hybrid macroscopic–contact model is formulated to predict the time development of the macroscopic contact quantities (forces and global relative surface displacements), which are measured in the experiments. The model is well able to predict the macroscopic behavior and, accordingly, the frictional hysteretic losses observed in the experiment. The change of the indenter profile from spherical to truncated spherical “pushes” the fretting contact towards the sliding regime if the nominal normal force and tangential displacement oscillation amplitude are kept constant. The transition of the hysteretic behavior, depending on the profile geometry from the perfectly spherical to the sharp flat-punch profile, occurs for the truncated spherical indenter within a small margin of the radius of its flat face. Already for a flat face radius which is roughly equal to the contact radius for the spherical case, the macroscopic hysteretic behavior cannot be distinguished from a flat punch contact with the same radius. The compliance of the apparatus (i.e., the macrosystem) can have a large influence on the energy dissipation and the fretting regime. Below a critical value for the stiffness, the fretting contact exhibits a sharp transition to the “sticking” regime. However, if the apparatus stiffness is large enough, the hysteretic behavior can be controlled by changing the profile geometry.

Theoretical model to predict the seismic drift concentration effect for self-centering-braced frame

This study is motivated to predict such drift concentration effects for SCB frames with the perfect flag-shape hysteretic behavior. Nonlinear time history analyses are conducted to compare and elucidate different deformation mechanisms between BRB and SCB frames. An elastic-plastic static model is established to predict the static drift concentration factor (DCFS) for the SCB frame under static lateral loads, where influential parameters include the column-to-frame stiffness ratios, α, and the SCB's post-yielding stiffness ratio, βk,2. To capture the dynamic loading effect, a regressive formula is further developed as the dynamic amplification factor by normalizing the dynamic drift concentration factor (DCFD) with the DCFS under static loads. The results show that unlike BRB frames with drift concentrated in the bottom story, SCB frames often feature peak story drifts in the top story. As opposed to BRB frames, the equivalent lateral loads do not feature an inverted triangle distribution but a parabolic distribution along the building height. The drift concentration effect for the SCB frame is reliably predicted by multiplying static DCFS with the corresponding closed-form formula for the dynamic amplification factor. The predicted DCFD is also utilized to identify a design range of βk,2 (i.e., 0.2–0.4) to effectively control the peak story drift and drift concentration for SCB frames.

Seismic performance of elliptical FRP-concrete-steel tubular columns under combined axial load and reversed lateral load

By combining FRP composites with both steel and concrete, double-skin tubular columns (i.e., DSTCs) with a hollow core are a novel structural member to be used as bridge piers or other columns in harsh environments. Up to now, DSTCs with circular or square sections (i.e., C-DSTCs or S-DSTCs) have been investigated extensively, while DSTCs with an elliptical section (i.e., E-DSTCs) are rarely studied. E-DSTCs are composed of two concentric elliptical tubes (i.e., the external FRP tube and the internal steel tube) and a sandwiched concrete layer. E-DSTCs can be designed with two distinct bending stiffness with respect to the two axes of symmetry. Similar to C-DSTCs, E-DSTCs have an FRP tube with a continuously curved circumference, thus effectively confining the concrete layer. To extend the existing research, this paper tested six large E-DSTCs under combined axial load and reversed lateral load to investigate the effect of elliptical aspect ratio. The testing parameters also included the direction of reversed lateral load and the FRP thickness. Experimental results showed that, E-DSTCs performed with rounded hysteresis loops and remarkable ductility even for the specimen with a large aspect ratio (i.e., for the elliptical aspect ratio from 1.0 to 2.0, the ductility index increased monotonically from 6.50 to 7.75); a thicker FRP tube led to marginally higher peak load but noticeably better ductility (i.e., the specimen with 2.10 mm FRP had an average peak load of 77.65 kN and a ductility index of 7.14, while the corresponding specimen with 1.05 mm had an average peak load of 77.35 kN and a ductility index of 6.29); as expected, the specimen bending around its strong axis had much superior ductility than the companion specimen bending around its weak axis. A numerical column model was established based on OpenSees to simulate the hysteretic behavior of E-DSTCs, and a parametric study was conducted to assess the influences of FRP thickness, concrete strength, axial load ratio, steel tube thickness, void ratio as well as elliptical aspect ratio. In practical engineering design, it was recommended that: (a) the elliptical aspect ratio as well as other key parameters (e.g., the FRP thickness, the steel tube thickness, the area void ratio) should be optimized based on specific loading conditions; (b) to make more effective usage of FRP composites, the FRP tube thickness should be optimized for different height regions of the column according to the moment gradient caused by the reversed lateral load.

Seismic performance of an assembled self-centering buckling-restrained brace with controllable initial stiffness

An innovative assembled self-centering buckling-restrained brace (ASC-BRB) with controllable initial stiffness is introduced. The brace consists of a self-centering system and an energy dissipation system. Unlike existing post-tensioned self-centering energy dissipation braces, whose initial stiffness has high uncertainty and is sensitive to machining errors, the proposed ASC-BRB can obtain highly controllable initial stiffness because of its unique working mechanism. Therefore, structural seismic response uncertainties can be reduced significantly. The configuration, working mechanism, and theoretical restoring force model of the ASC-BRB are first presented. Quasi-static tests are then conducted to examine the feasibility of the brace, and typical flag-shaped hysteretic behavior and stable energy dissipation capability are observed. The main components of the ASC-BRB keep intact after repeated loadings, except for the core plates, which are damaged; however, the core plates can be easily replaced. This observation highlights the superiority of the ASC-BRB in terms of damage concentration and high recoverability. The proposed theoretical restoring force model can accurately predict the hysteretic response of the brace, especially for the initial stiffness, with the predicted value being within 5 % of the experimental value. A simplified numerical model is developed and used in a parametric study conducted to examine the effects of two key design parameters on the brace behavior. Furthermore, the effect of machining errors on the initial stiffness of the ASC-BRB is studied. An analysis of steel frames with ASC-BRBs indicates that the ASC-BRB can effectively reduce the residual inter-story drift and help achieve a peak floor acceleration response comparable to that of the frame with BRBs. However, the peak inter-story drift is amplified owing to the lower initial stiffness of the proposed brace. On the basis of a system-level parametric analysis, recommended optimized design parameters of the ASC-BRB are presented to facilitate efficient control of structural seismic responses.

Structural fuse performance and earthquake-resilient performance of beam-column joints with replaceable T-stub

In order to ensure that steel frame systems have excellent structural fuse performance and earthquake-resilient performance on the basis of good seismic performance, a novel steel beam-column joint with replaceable T-stub connection components (SBCJ-RTCCs) was proposed. The pseudo-static cyclic tests of original and replaced specimens were carried out. As an extension of the experimental tests, numerical parametric analyses were performed to determine an optimal range of resistance capacity ratio to make a balance between the seismic performance, structural fuse performance and earthquake-resilient performance. The analysis results demonstrated that despite seismic performance of specimen with a small resistance capacity ratio is relatively weak, the structural fuse performance and earthquake-resilient performance performed well. With the increase of resistance capacity ratio, the seismic performance consisting of initial stiffness and bearing capacity gradually improved. However, the plasticity and damage would be shifted from RTCCs to non-fuse components, which adversely affected the structural fuse performance, despite the earthquake-resilient performance of specimen was still good. In terms of comprehensive consideration of seismic performance, structural fuse performance and earthquake-resilient performance, the resistance capacity ratio was suggested as 0.53–0.63. Moreover, a design procedure of SBCJ-RTCCs was proposed, and its rationality was validated by a design example RT-D. The result indicates that by adopting the proposed design procedure, the RT-D exhibited stable hysteretic behavior without experiencing strength degradation. The RTCCs can play the role of structural fuses by dissipating more than 90% of the input energy, which effectively protect the non-fuse components from damage.

Hysteretic model for corroded reinforced concrete columns retrofitted with FRP

A hysteresis model was developed for fiber reinforced polymer (FRP)-retrofitted reinforced concrete (RC) columns with corroded reinforcing bars. The test data of 49 FRP-retrofitted corroded columns and 19 intact columns (with no corrosion or FRP wraps) under repeat-cyclic loading were collected to establish a database. A polygonal model was adopted to simulate the hysteretic behavior of FRP-retrofitted corroded columns. This was determined using backbone and cyclic parameters. For the backbone parameters, a hybrid influence factor (HIF) was introduced to incorporate the coupling effects of corrosion and FRP retrofitting. A suite of empirical equations was developed using multivariate linear regression analysis to predict the HIFs of each backbone parameter in association with the corrosion rate and important column design parameters. Moreover, an empirical relationship was developed to determine the cyclic parameters of the hysteretic model using a regression analysis. The predicted hysteretic curves were compared with the experimental results, demonstrating sufficient accuracy for both intra- and extra-database tests. Finally, the developed hysteretic model was used to establish a macro-type structural model for the FRP-retrofitted corroded RC frames. This benefitted the analysis of structural collapse under earthquakes, and the effects of the corrosion rate and FRP retrofitting schemes on the seismic collapse capacity of RC frames were examined.

Finite element model evolution of perforated steel plate shear walls under cyclic loading

A linked mathematical-informational model to approximate the Force-Drift relationship of surrounding perforated steel plate shear walls under monotonic and cyclic loading is proposed. The proposed model has three physical parameters, along with two curve-fitted factors. These physical parameters are generated from dimensional details and material properties of the shear wall. In this study, two different methods are suggested to consider the intricate hysteretic behavior of perforated shear walls. To use the benefits of both mathematical and informational presentations, a novel method, a linked modeling skeleton, is created and demonstrated through representing the complex hysteretic behavior of perforated shear walls. Hysteretic models are mathematical models capable of simulating the complex nonlinear behavior characterizing mechanical systems and materials used in different fields of civil structures. The model yields acceptable results in good agreement with actual shear wall behavior. Besides, comparison between the presented model and other existing equations, in prediction of the perforated shear wall’s F–D curve, shows the reasonably accurate results of the proposed model.

Mechanical Behavior of Two-Side Bolted Steel Plate Shear Wall Considering Top-Seat Constraints with Frame Beams

A steel plate shear wall (SPSW) is a useful component for resisting lateral action. To improve the performance of frame columns, some studies focus on a two-side connected SPSW, in which the wall plate is not connected with the frame columns. However, few studies conducted on a two-side connected SPSW consider the effect of frame constraints or the connections between the infill plates and frame beams. In this study, by using finite element modeling (FEM), two unstiffened SPSW models with two-side fixed connections and six unstiffened SPSW models with two-side bolt connections were simulated. Their performance under the presence of out-of-plane frame beam flange constraints and different numbers of bolts between the infill plates and frame beams was analyzed. The mechanical performances such as hysteretic behaviors, the capacity of energy dissipation and the out-of-plane deformation of the members were investigated by applying monotonic and cyclic loading. The results revealed that non-negligible deformation would be generated at the lateral border of the bolt connections and that the out-of-plane deformation of the frame could be significantly affected by constraints. These findings can guide the engineering design of SPSWs in the future.

Hysteretic behaviors of Pingshenke Dou-Gong brackets of ancient timber buildings under different loading directions

To study the effect of loading directions on the seismic behavior of Dou-Gong bracket, numerical analysis was conducted on two Pingshenke Dou-Gong brackets under the overhanging direction (DG-1) and width direction (DG-2). The simulated hysteretic characteristic, stiffness degradation, and energy dissipation of Dou-Gong brackets were compared and validated by the test results. The horizontal displacement and relative slip of Dou-Gong components were discussed. Besides, parameter analyses considering the loading direction, wood grain direction, and material properties were performed. Results indicate that DG-2 has higher stiffness, bearing and energy dissipation capacity than DG-1, but poor deformation capacity. The positive component displacement of DG-1 is greater than DG-2, while the negative is the opposite. The relative slip between Da-Dou and Pingban-Fang is larger than other components. The overhanging and width direction are the most adverse direction for DG-1 under positive and negative load, respectively. DG-1 has the largest bearing capacity when Da-Dou is friction in the longitudinal surface under the tangential grain direction, but the grain direction has little influence on DG-2. The larger the friction coefficient and compressive strength, the greater the bearing capacity, but the initial stiffness is not improved. The elastic modulus has little effect on the initial stiffness and bearing capacity of Dou-Gong bracket.