Additional Stiffness Research Articles

Experimental investigation into the lateral performance of post-tensioned steel-timber hybrid frame with tension-only braces

Low-damage timber structures provide a promising solution to build mass timber structures with both seismic safety and post-earthquake . The main objective of this research was to explore a technical solution of enhancing the lateral stiffness of post-tensioned steel-timber hybrid (PTSTH) frames without significantly compromising their self-centering capabilities. In the PTSTH frames studied, steel fixtures were installed at the beam-to-column joint zones. Each joint consisted of a steel fixture, a steel-timber column connection, and a steel-timber beam connection. The steel fixtures were connected to the timber column via the steel-timber column connection, providing a practical method for installing different types of braces. Post-tensioned steel tendons were used to connect the steel fixture to the timber beam, forming the steel-timber beam connection. Three 2/3 scaled PTSTH frame specimens underwent cyclic loading tests. The impact of tension-only braces on various system properties was studied and compared to an alternative solution involving additional damping and stiffness (ADAS) braces. The results showed that tension-only braces contributed to more than 70 % of the stiffness enhancement in the PTSTH frame compared to a post-tensioned timber frame with the same geometry. However, their contribution to energy dissipation was less than 50 %. Tension-only braces did not significantly hinder the self-centering performance of PTSTH frames, while ADAS braces did. Replacing glued-in rod (GIR) connections with screw connections affected the gap opening process in the steel-timber beam connection. Consequently, this change led to an increase of at least 25 % in residual deformation.

MS‐IS Hypoplastic Model Considering Stiffness Degradation Under Cyclic Loading Conditions

ABSTRACTModelling the cyclic response of granular materials is key in the design of several geostructures. Over the years, numerous constitutive models have been proposed to predict the cyclic behaviour of granular materials. However, pertaining to the hypoplastic constitutive models, one of the significant limitations is their inability to accurately predict the geomechanical response during the unloading and reloading phases. This study introduces an extension of the MS‐IS hypoplastic model designed to enhance the predictions during non‐monotonic loading conditions. Addressing the limitations observed in the hypoplastic models during the unloading and reloading phases, the proposed model incorporates an additional stiffness feature. This new stiffness function is integrated into the foundational framework to enhance the model's overall stiffness response. For the unloading phase, the introduction of a stiffness degradation factor aims to modify the volumetric response and account for the realistic stiffness degradation. Additionally, for the reloading phase, stiffness is now a function of the mean effective stress. The novel model's performance is validated against experimental data, encompassing diverse loading and boundary conditions.

Soft Artificial Muscle of Poly(vinyl chloride) Gel with an Imperceptible Liquid Metal Electrode.

Electrodes with high electrical conductivity, yet good flexibility and mechanical compliance, are critical for electroactive artificial muscles. Herein, a promising liquid metal (LM) electrode is proposed by transforming eutectic gallium-indium (EGaIn) LM with high surface tension into paste-like LM with solid Ga2O3 shells. The developed compliant LM electrode not only shows high conductivity and negligible additional stiffness but also displays excellent electrical stability during cyclic actuation. Based on the LM electrode, the poly(vinyl chloride) gel (PVCG) artificial muscle developed exhibits the maximum actuation strain of 18.7% at a low electric field strength of 9 V μm-1 and maintains excellent durability without obvious performance attenuation after 10,000 s. A comparison shows that the as-developed PVCG artificial muscle is superior over that based on widely used carbon electrodes. Moreover, an artificial upper limb and crawling worm were manufactured to explore the great potential of PVCG artificial muscle in the robotic field. In addition, the practical application demonstration of the PVCG artificial muscle in the biomimetics field is also successfully fulfilled through the design of reasonable structures. Due to its easy fabrication, excellent electrical conductivity, and high mechanical compliance, the newly developed LM electrode is promising for high-performance PVCG artificial muscles in bionic robots.

Adaptive seismic isolation system combining gap dampers for pounding mitigation in base-isolated structures

Seismic base isolation systems have been widely used in structures located in highly earthquake-prone regions to mitigate the earthquake responses of superstructures. An effective isolation function is achieved at the expense of deformations that are mostly concentrated at the isolation layer due to the lower lateral stiffness of the isolation system. Hence, a sufficient clearance is required to accommodate this large deformation demand. However, isolation clearance may be limited because of practical and architectural constraints. Therefore, moat wall (MW) pounding potentially occurs in base-isolated structures under extreme earthquakes, inducing increased story drifts and floor accelerations of the superstructures. Considering this reason, this study presents an adaptive seismic isolation system that combines gap dampers (GDs) for mitigating pounding in base-isolated structures. The GD isolation system incorporates steel U-shaped GDs into a lead rubber bearing system where steel U-shaped dampers (UDs) provide additional stiffness and energy dissipation when bearing deformation exceeds a certain threshold. Quasi-static cyclic tests were conducted to explore the hysteretic responses and fatigue behavior of UDs under cyclic loading. Experimental results confirm that the UDs exhibit stable energy dissipation and high fatigue capacity under different loading conditions. Subsequently, seismic performances of two base-isolated buildings designed with GDs and MWs were investigated computationally under far- and near-field earthquakes. The results reveal that compared with the conventional MW pounding in the isolation layer, the GD isolation system can effectively mitigate the responses of the isolation layer and the superstructure. Finally, parametric analyses were performed to investigate the sensitivity of various mechanical properties of GDs to isolation effectiveness.

DEVELOPMENT OF COMPUTATIONAL SCHEMES OF GROUP TARGET CONSTRAINTS FOR SOME ELASTIC SYSTEMS

For some elastic systems with a finite number of degrees of freedom of masses, in which the directions of mass movement are parallel, methods have been developed for creating additional constraints, the intro-duction of each of which purposefully increases the value of only one natural frequency to a given value, while not changing any of the other natural frequencies and not one of the natural modes (forms of natural oscillations). If it is necessary to increase the values of several natural frequencies in a targeted manner, then this requirement can be implemented by creating an appropriate number of separate targeted constraints. The computational scheme of each of the individual targeted constraints should include racks installed at the nodes of mass application and directed along the trajectory of their movement. In some cases, individual targeted constraints can be independently installed on the original (initial) system. In most cases, on the basis of individual targeted constraints, a computational scheme of a united group targeted constraint is developed, which increases all the intended frequencies to the set values, without changing any of the other natural frequencies and not one of the natural modes. The distinctive paper is devoted to a method for forming a matrix of additional stiffness, which corresponds to a group targeted constraint. The requirements for those targeted constraints, on the basis of which a group targeted constraint is formed, are formulated. An algorithm for the development of group targeted constraint is proposed with allowance for the formulated requirements.

Cyclic stretch enhances neutrophil extracellular trap formation

BackgroundNeutrophils, the most abundant leukocytes circulating in blood, contribute to host defense and play a significant role in chronic inflammatory disorders. They can release their DNA in the form of extracellular traps (NETs), which serve as scaffolds for capturing bacteria and various blood cells. However, uncontrolled formation of NETs (NETosis) can lead to excessive activation of coagulation pathways and thrombosis. Once neutrophils are migrated to infected or injured tissues, they become exposed to mechanical forces from their surrounding environment. However, the impact of transient changes in tissue mechanics due to the natural process of aging, infection, tissue injury, and cancer on neutrophils remains unknown. To address this gap, we explored the interactive effects of changes in substrate stiffness and cyclic stretch on NETosis. Primary neutrophils were cultured on a silicon-based substrate with stiffness levels of 30 and 300 kPa for at least 3 h under static conditions or cyclic stretch levels of 5% and 10%, mirroring the biomechanics of aged and young arteries.ResultsUsing this approach, we found that neutrophils are sensitive to cyclic stretch and that increases in stretch intensity and substrate stiffness enhance nuclei decondensation and histone H3 citrullination (CitH3). In addition, stretch intensity and substrate stiffness promote the response of neutrophils to the NET-inducing agents phorbol 12-myristate 13-acetate (PMA), adenosine triphosphate (ATP), and lipopolysaccharides (LPS). Stretch-induced activation of neutrophils was dependent on calpain activity, the phosphatidylinositol 3-kinase (PI3K)/focal adhesion kinase (FAK) signalling and actin polymerization.ConclusionsIn summary, these results demonstrate that the mechanical forces originating from the surrounding tissue influence NETosis, an important neutrophil function, and thus identify a potential novel therapeutic target.

Manufacturing of Stretchable Wavy-Patterned Fiber-Reinforced Elastomer Composites and Its Behaviors Under Tensile Loading Conditions

The wavy-patterned carbon fiber reinforced elastomer composites that offered both the elongation characteristic of the elastomer and the stiffness of the fiber reinforcement before the elastomer reached its elongation at failure was introduced in this study. The goal of this study was to develop and demonstrate the manufacturing process of the wavy-patterned fiber-reinforced elastomer composites and investigate its behaviors under tensile loading conditions. A carbon fiber tow was impregnated with a silicone elastomer and placed in the test specimen manufacturing mold with a specific pattern using a wavy-patterned fiber placing jig. The silicone elastomer was then poured into the mold to cast test specimens. Various wavy-patterned fiber-reinforced elastomer composites, each with different allowed elongation levels and different amount of fiber, were designed and fabricated. Due to fiber slippage during the tensile test with the traditional test grip fixture, a roller grip fixture was used for the tensile test. The test results showed a unique behavior of the wavy-patterned fiber reinforced elastomer composites that elongated until the patterned fiber became straightened, providing additional stiffness to the test specimen under tensile loading. It was observed that the maximum strength and elongation at failure varied with different patterns and amounts of fiber. The unique failure mechanisms of the fiber-reinforced elastomer composite during the tensile test were analyzed and discussed. Despite the fiber being fully impregnated with the elastomer, weak adhesion between the fiber and elastomer led to disbonding between them.

Understanding the biopsychosocial knee osteoarthritis pain experience: an ecological momentary assessment.

Psychological, social, and lifestyle factors contribute to the knee osteoarthritis (OA) pain experience. These factors could be measured more accurately using smartphone ecological momentary assessment (EMA). The objective of this study was to characterise the pain experiences of those with knee OA by a smartphone EMA survey and explain how momentary psychological and social states influence knee OA pain experiences. A smartphone EMA survey was designed and piloted. Eligible participants completed smartphone EMA assessing the knee OA pain experience 3 times daily for 2 weeks. Descriptive statistics were used to characterise factors involved in knee OA pain followed by the development of mixed-effects location scale models to explore heterogeneity and relationships between symptoms involved in the knee OA pain experience. Eighty-six community-dwelling volunteers with knee OA were recruited. Pain, psychosocial, and lifestyle factors involved in knee OA pain experience were heterogeneous and variable. Those with greater variability in pain, fatigue, negative affect, and stress had worse levels of these symptoms overall. In addition, fatigue, negative affect, stress, anxiety, loneliness, and joint stiffness demonstrated within-person relationships with knee OA pain outcomes. Knee OA pain is a heterogeneous biopsychosocial condition. Momentary experiences of psychological, social, fatigue, and joint stiffness explain individual and between-individual differences in momentary knee OA pain experiences. Addressing these momentary factors could improve pain and functional outcomes in those with knee OA. Validation studies, including individuals with more severe knee OA presentations, are required to support findings and guide clinical interventions to improve outcomes for those with knee OA.

Dynamic Response of Steel Structure with Bracings and Translational Tuned Mass Dampers

In this work the dynamic response of steel structure with Bracings and Translational Tuned Mass Damper (TTMD) are studied. TTMD is a device that consists of a mass which is connected to the structure by means of a spring and a damper. The mass is tuned to vibrate at the different frequency as the structure, which allows it to cancel out the vibrations of the structure. Bracings are added to the structure to provide additional stiffness and strength. G+5, G+15 and G+25 Storeyed steel structure models with the different combinations of bracings and TTMD are considered in this study. Following which the FE Analysis involving the modal, equivalent static and response spectrum analysis are performed and results are obtained in terms of Time period, Base Shear, storey displacement and Storey drift all are discussed.

Reinforcing the aneurysmal aorta by additional layering: old and new strategies to prevent rupture

Adventitial crosslinking is a method in current investigational stage for preventing the rupture of aortic aneurysms. It is based on the photochemical crosslinking of adventitial collagen by exposure to ultraviolet A radiation. Essentially, an adventitial top layer is generated that displays enhanced mechanical properties and imparts additional strength and stiffness to the aneurysmal wall. Looking back upon the history of aortic surgery during 1940s, the aortic film wrapping, then dubbed “cellophane wrapping”, also was a procedure employed for delaying the aneurysmal rupture. In principle, the two procedures are similar in that both result in laminar composites, although the top layers differ fundamentally from each other. This review discussed in some detail the use and clinical outcomes of the aortic wrapping with artificial films, also mentioning the contemporary procedures still grouped under this umbrella term. The focus of the review was a comparative view on two procedures, the aortic film wrapping and adventitial crosslinking. It was concluded that the methods are different in many aspects, including the mechanisms of action. In fact, the promoters of adventitial crosslinking were not aware of the prior existence of aortic film wrapping. However, the achievements of the classical wrapping, by now regarded as merely historical episodes, did not discard prior knowledge, but repurposed it in a process that led to innovative strategies.

Bolt-bearing behavior of hybrid CFRP-steel laminates at low temperature

Hybrdization of CFRP with steel sheets enhances bolt-bearing performance. At room temperature, bearing strength is reported to increase while minimum edge and width distances decrease. To assess if this advantage persists under low temperature conditions, bolt-bearing tests following AITM 1-0009 are conducted at 23°C and −55°C. Various monolithic and hybrid configurations with different metal content and joint geometries are examined. Furthermore, ultrasound scanning and optical microscopy of the fracture plane is conducted. Hybridizing composites notably improves bearing capacity. However, the reinforcement effect is less pronounced at low temperatures compared to room temperature. The reduction in minimum edge and width distances with metal hybridization largely depends on the composite ply stacking, challenging general literature recommendations. Regarding damage mechanisms in the joints, fractography indicates that introduction of steel sheets relieves composite plies, isolates damage, and enhances load-bearing capacity through additional bending stiffness and significant plastic deformation of the metal.

Study on Vibration Reduction Effect of the Building Structure Equipped with Intermediate Column–Lever Viscous Damper

Generally speaking, the traditional lever amplification damping system is installed between adjacent columns in a building, which occupies a significant amount of space in the building. In contrast to amplification devices in different forms, the damper displacement of the intermediate column damper system is smaller, and the vibration reduction efficiency is lower. In light of these drawbacks, this study proposes a new amplification device for energy dissipation and vibration reduction, which is based on an intermediate column–lever mechanism with a viscous damper (CLVD). Initially, a specific simplified mechanical model of CLVD is derived. Subsequently, an equivalent Kelvin mechanical model of CLVD is derived to intuitively reflect CLVD’s damping and stiffness effect. The damping ratio added by CLVDs to the structure is calculated according to that model; the additional damping ratio and additional stiffness are utilized to calculate the displacement ratio Rd and shear force ratio Rv of the structure with CLVDs to the structure without CLVDs. Rd and Rv are introduced to evaluate the vibration reduction effect of the structure with CLVDs, and the effects of various parameters (such as intermediate column position, beam’s bending line stiffness, lever amplification factor, damping coefficient, and earthquake intensity) on Rd and Rv are analyzed. The results indicate that when the ratio of the distance from the intermediate column to the edge column to the span of the beam is 0.5, CLVD owns the optimal vibration reduction effect. Increasing the beam’s bending line stiffness is beneficial for CLVD to control structural displacement and shear force; when the leverage amplification factor is too large, the CLVD provides the structure with stiffness as the main factor, followed by damping. Additionally, when the ratio of the displacement amplification factor to the geometric amplification factor satisfies fd/γ = 1/21−0.5α, the CLVD has the optimal displacement control effect on the structure. After that, measures are provided to optimize the CLVD in different situations in order to effectively control the inter-story displacement and the story shear force of the structure. Consequently, a nine-story frame is taken as an example to elaborate the application of CLVDs in the design for energy dissipation and vibration reduction. The results reveal that the CLVD scheme adopting the proposed optimization method can effectively enhance the displacement amplification ability of CLVDs, resulting in an additional damping ratio of up to 12%. At the same time, the inter-story displacement was reduced by almost 40% under fortification earthquakes. Through the research in this study, designers can obtain a new choice in structural vibration reduction design.

Effects of passive ankle exoskeletons on neuromuscular function during exaggerated standing sway

Wearable robotic exoskeletons designed to assist human movement should integrate with the neuromusculoskeletal system. This means assisting movement while not perturbing motor control. We sought to test if passive ankle exoskeletons, which have been shown to successfully assist human gait, affect neuromuscular control of an exaggerated anterior–posterior standing sway task. Participants actively swayed while wearing an ankle exoskeleton that provided 0, 42 or 85 Nm rad −1 of additional stiffness to the ankle joint in resistance to dorsiflexion. Sway amplitude was controlled via biofeedback to elicit similar ankle angle displacements across conditions. With greater exoskeleton stiffness, participants swayed at lower sway-cycle frequencies and slower centre of pressure speeds. Furthermore, increasing exoskeleton stiffness resulted in longer operating lengths of the medial gastrocnemius and overall reduced plantar flexor muscle activation. For the soleus, there was also a temporal shift in the cross-correlation of its electromyogram with the centre of pressure displacement, meaning that muscle activation peaked later than anterior sway displacement. Together, these data suggest that assistive ankle exoskeletons influence neuromuscular control of ankle-based sway tasks. Changes in fascicle lengths could influence afferent feedback signals and the short-range stiffness of ankle muscles, while shifts in muscle activation timing suggest changes in neural control. The observed neuromuscular adaptations to exoskeleton assistance demonstrate the potential implications for standing balance and overall movement control, prompting future investigations.

Investigations on the modal vibration caused by bolted joint interface contact in the rotor-AMBs systems: Modelling and experimentation

Rotor-active magnetic bearings (rotor-AMBs) systems nowadays have been widely used in fluid machinery and the impeller and the shaft are commonly connected by bolted joint. However, when a certain pre-tightening force is applied to the bolted joint and the interface contact between the shaft and the impeller is formed, causing flexible modal vibrations when rotor is levitated. The mechanism of this modal vibration needs to be revealed to ensure stable operation of the machine. In traditional modelling, the effect of the interface contact is equated to an additional stiffness matrix by massless spring units, whose certain contact stiffness is uniformly distributed over the interface. Particularly, the calculation of contact stiffness and the effect of AMBs are neglected, resulting in the inaccurate response compared to experiments. Based on traditional modelling, we consider that there is partial separation in the contact interface due to the AMBs supporting and a novel additional stiffness matrix related to contact status is proposed by calculating the real-time contact area. The contact stiffness is calculated by microscopic contact model based on fractal theory and surface topography measurement. Finally, numerical simulation shows that the interface contact influences the system robustness and the unstable mode is excited. The increase of pre-tightening torque and contact radius both will increase the steady vibration amplitude, with the former being the major contributor. Moreover, the influence and order of the vibration are quantitatively validated by the experiments.

Phase field modeling of hyperelastic material interfaces –Theory, implementation and application to phase transformations

Interface mechanics can significantly govern the evolution of multiple phases on smaller scales, e.g., determining the properties of TWIP- and TRIP-steels, geopolymers or Li-ion batteries. The present contribution is specifically centered around the influence of interface elasticity on mechanically induced phase transformations. A geometrically exact finite element framework is developed for this purpose based on incremental energy minimization. It is set up in three-dimensional space and comprises an Allen-Cahn type phase field formulation based on a Modica-Mortola double-well functional, as well as a Ginzburg-Landau type viscosity formulation. The phase field approximation of the interface deformation gradient is derived by means of homogenization theory. A monolithic solver is employed for the resulting set of non-linear coupled equations. The example of coalescing spheres shows that larger interface energies can amplify and accelerate coalescence. Lower interface energies, in contrast, allow for distinct spreading of the energetically favorable bulk phase. Deformation-dependent interface energies particularly add stress peaks to this process that are localized at the phase transition zone. The relaxation of a stepped interface shape showed that deformation-dependent interface energies favor a plane partition of the bulk phases. Yet, they also delay breakup events compared to simple constant interface energies. This peculiarity can be beneficial for calibration purposes. Strain dependence moreover causes an additional elastic stiffness in the direction of the interface tangent plane and constitutes thus another origin for anisotropy of the overall structure.

Subsonic aeroelastic behaviors of a composite plate with embedded MFC actuators under hygrothermal environment

Subsonic aeroelastic effects of train-body skin structures have been intensely attractive among researchers due to the improvement of high-speed train speed. In this article, the aeroelastic behaviors of a laminated composite plate with embedded Macro Fiber Composite (MFC) actuators in hygrothermal environment under the subsonic airflow has been investigated. The Von Karman large deflection theory and the subsonic aerodynamic model based on the Bernoulli's equation are applied in the formulation. The principle of virtual work is adopted to obtain the nonlinear aeroelastic equations of the laminated composite panel with embedded MFC actuators. Subsequently, the Newmark method and Newton-Raphson method are combined to solve the framework in order to capture the nonlinear aeroelastic response of the subsonic laminated panel in time domain. Since the presence of moisture concentrations, temperature rises and applied voltages of the embedded MFC actuators will result in additional stiffness effects on composite panels by inducing prestress, thus change the aeroelastic behaviors of the composite panel, the influences of these main parameters on aeroelastic performance are analyzed. The results show that the aeroelastic flutter velocity of the composite panel gets remarkably deteriorated due to the adverse hygrothermal environment and can be strengthened through the applied voltages and appropriate lamination angles of embedded MFC actuators. Besides, the main findings of this study are the anti-symmetric laminate buckles then changes to an periodic oscillation like the limit-cycle-oscillation while there is no such phenomenon for the symmetric ones.

STUDY OF THE WALL RIGIDITY OF A VERTICAL CYLINDRICAL STEEL TANK DURING ITS INSTALLATION BY THE SPIRAL-WOUND METHOD

The paper presents the results of a study of the influence of the wall diameter of a vertical cylindrical steel tank designed for storing petroleum products on its stiffness characteristics and the applicability (for the manu-facture of this wall) of the spiral-winding metod, according to which the tank wall is made of rolled sheet metal, during the unwinding of which a wall is formed in the form of a spiral, ad-jacent turns of which are continuously connected by a welded seam, forming a sealed shell.To solve the problem, a finite element analysis of the tank wall was performed, within which the wind load was taken as the calculated one, due to which the greatest lateral deformations of the tank wall during its construction are possible, which can cause disruption of the technological process of its construction using spiral-winding method.The paper considers tank wall solutions of different diameters (in the range from 10 to 65 m), which have the smallest wall thicknesses adopted in accordance with the recommendations from the Russian standard.Modeling of the tank wall included the preparation of geometric and calculation models. The geometric model is presented in the form of an axisymmetric cylindrical shell, on the outside of which flat ribs are placed at a constant pitch along the shell axis, giving it additional stiffness. The calculation model includes a geometric model of the wall, to which a wind load is applied from the outside, the pressure from which on the tank wall is constant along its height; it is maximum under normal action and decreases to zero under tangential action. Using the calculation model, firstly, a dependence was obtained that reflects the effect of a change in the height of the tank wall on the maximum radial displacements in its base near the supports, and, secondly, the dependence of the maximum radial displacements of the tank wall in its base near the supports, depending on its diameter.The results of the analysis, in particular, showed that the stiffness of the wall obtained on the basis of the spiral-winding method practically does not change with an increase in its diameter (and a corresponding increase in thickness).

Effect of impregnated organophilic (hydrophobic) nano clay on asphalt binder properties and performance

This research paper presents the effects of electrophilic modification on raw nano clay (which is hydrophilic in nature) through wet impregnation method to transform it into hydrophobic nature. The reactivity, adsorption capability, and compatibility of nano clay with hydrocarbon and organic materials are improved by entailing functional group (QAS) on raw nano clay surface. Impact of impregnated organophilic nano clay (hydrophobic) on asphalt binder properties and mixture’s performance are studied. Organophilic(hydrophobic) nano clay with 3–5% content to the weight of the binder were selected after extensive trials for modification of asphalt binder. To analyze the electrophilic changes in organophilic nano clay (ONC) and its bonding chemistry with asphalt binder, FTIR analysis, and X-ray diffraction techniques were utilized. In addition, viscosity, low & high-temperature stiffness, bitumen bond strength, and phase separation were studied in the lab. The effect of organophilic nano clay modified binder on asphalt mixture was also measured by deploying rut resistance, moisture susceptibility& fatigue resistance tests. The study revealed that raw nano clay showed chemical compatibility with asphalt binder after electrophilic modification through wet impregnation method. ONC modified binder had better rheological properties, homogenized composition, and storage stability than hydrophilic nature. Mixtures prepared with ONC showed better resistance to rutting, fatigue, and moisture susceptibility.

Evaluation of vibration properties of an 18-story mass timber–concrete hybrid building by on-site vibration tests

Timber–concrete hybrid structural systems are a practical option to provide tall mass timber buildings with a lateral load-resisting system. This paper discusses the dynamic behavior of an 18-story timber–concrete hybrid building based on the vibration properties evaluated by on-site vibration tests. First, microtremor measurements and human-powered excitation tests were carried out and the obtained vibration data were analyzed using a stochastic subspace identification method to derive natural frequencies, damping ratios, and mode shapes. Then, a finite-element (FE) model was developed based on detailed structural design information, and its eigenvalues and eigenvectors were compared with the test results. The vibration test results showed various mode shapes, including in-plane deformation of the floor diaphragm composed of cross-laminated timber (CLT) panels. The damping ratios in all the modes were scattered between 1 and 3%, and no frequency dependency was observed. The modal properties of the FE model agreed well with the test results by considering the additional stiffness of non-structural components. In order to simulate the in-plane deformation of the CLT floor diaphragm, detailed modeling of the connection between each CLT floor panel and the connection between CLT floor panels and concrete cores is recommended. The findings provide practitioners with an insight into dynamic properties and FE modeling methods of tall timber–concrete hybrid buildings.

Study on dynamic performance of 140 km/h metro vehicles with rubber stack traction structure: rolling vibration test and simulation

This paper analyzes whether the rubber stack traction structure can be applied to 140 km/h metro vehicles from the perspective of vehicle dynamics. The rolling vibration test results indicate that the vehicle Ride Index exceeds the standard limit, the low-frequency vibration of the car body is significantly greater than that of the frame and axle box, and the lateral motion mode of the car body reaches 2.0 Hz. Through the stiffness test, it is found that when the displacement is less than 5.93 mm, the additional stiffness of the rubber stack traction structure exceeds 0.55 MN/m, which is far greater than the stiffness exhibited by the Z-shaped traction rod at the same displacement. The simulation results demonstrate that the excessive additional stiffness of the traction rubber stack is the primary factor for the car body abnormal vibration and does not effectively improve the vehicle stability. It is recommended that this type of metro shall use a rubber stack traction structure with small additional stiffness or Z-shaped traction rod to improve the car body vibration characteristics at 140 km/h. Furthermore, the recommended maximum operating speed for the bogie with the studied rubber stack traction structure is 80 km/h.