Restoring Force Characteristics Research Articles

Quasi-Static Loading Tests and Numerical Simulations of Restoring Force Characteristics of T-Joints Between PCCC Columns and RC Ring Beams

Quasi-Static Loading Tests and Numerical Simulations of Restoring Force Characteristics of T-Joints Between PCCC Columns and RC Ring Beams

Numerical and experimental study of a suspension bridge with combined viscous-steel damping system under train and seismic loads

The longitudinal dynamic performance of long-span bridges with passive vibration control devices when subjected to vehicle and seismic loads has raised extensive attention of the civil engineering community. This study aims to provide numerical and experimental assessments of the dynamic performance of a railway suspension bridge with the Combined Viscous-Steel Damping System (CVSDS) under various excitations. The deck is simplified to a single-degree-of-freedom (SDOF) system according to the longitudinal vibration characteristics of the suspension bridge. The Dynamic Equation Method (DEM) and Fourier Expansion Method (FEM) are suggested for the equivalence of the spatiotemporal variable train loads to horizontal excitations. A simplified two-stage analytical model is proposed to simulate the restoring force characteristics and fuse-lock function of the CVSDS. Shake table tests are conducted to further illustrate the feasibility of the simplified model and evaluate the effectiveness of the CVSDS. The results indicate that the SDOF system is reasonable and satisfactory in simulating the deck displacement. The two-stage working mechanism of the CVSDS is verified by both the simulation and experiment, i.e. the viscous fluid damper works under train loads and the steel yielding damper operates under earthquakes. The vibration mitigation effectiveness of the CVSDS is remarkable.

Friction-based connectors with wooden dowels for timber shear walls: Shake table and time-dependent test

Prestressing in wood connection, due to frictional forces, improves mechanical properties of the connection. This paper presents novel friction-based connectors, and corresponding tests at the connection and system levels. The friction-base connector is composed of a softwood or hardwood dowels inserted into the wood-based material and tightened to generate frictional force. Long-term performance was evaluated by stress relaxation tests and time-dependent connection tests. To evaluate dynamic performance of shear walls with friction-based connectors, shake table tests were conducted. The shake table tests showed that the restoring force characteristics of the wood friction shear walls were bilinear reflecting the behaviors of the friction-based connectors. The strength degradation of the wood friction shear walls due to cyclic input was small that more seismic inputs could be applied before any significant damage to the wood friction shear wall. Results of stress relaxation tests, for periods of 1 to 3 years, showed that the stresses were maintained at 70–90% under uncontrolled environment. On the other hand, the results of time-dependent connection tests, for 1 to 6 years, showed high initial clamping stresses caused large performance loss, but high performance could be maintained when tightened below the allowable stress for sustained loading.

Mechanical properties of glulam moment-resisting joints reinforced by inclined self-tapping screws

Self-tapping screws (STS) are an effective fastener to enhance wooden moment-resisting joints. However, the effects of the arrangement and insertion angle of STS on the mechanical properties of wooden joints are less studied. Therefore, this study investigated the influence of these two factors on the mechanical properties of wooden joints by conducting cyclic loading tests using glulam moment-resisting joints reinforced by STS with different arrangements (round and square) and insertion angles (45° and 90°). The failure modes, bearing performances, and energy dissipation capacities were considered. The results showed that the insertion angle affected the bearing and energy dissipation capacity of the joints significantly, while the effect of arrangement was slight. The anti-rotation bending moments of the joints reinforced by inclined STS were higher by 31.7% and 13.5% when the arrangement of STS was circular and rectangular respectively compared with the joints reinforced by vertical STS under compression state, and were lower by 17.5 % and 22.9 % under tensile state. The restoring force characteristics of the joints were similar when the insertion angle of STS was the same. Furthermore, the joints had optimal ductility and stiffness when the arrangement was rectangular, and the insertion angle was 45°.

Seismic Capacity of R/C Buildings Retrofitted with a V-Bracing System Equipped with a Novel Laterally Layered Friction Damper

This study proposed a novel V-bracing system equipped with a laterally layered friction damper (LLFD), which can supplement the shortcomings of conventional vibration control systems and is applicable to existing reinforced concrete (R/C) buildings. A material test was used to evaluate the material performance and energy dissipation capacity of this LLFD. Pseudo-dynamic testing was conducted on two-story frame specimens based on an existing R/C building with non-seismic details to verify the seismic retrofitting effects of applying the LLFD V-bracing system to existing R/C frames, i.e., the restoring force characteristics, energy dissipation capacity, and seismic response control capacity. Based on the results of the material and pseudo-dynamic tests, restoring characteristics were proposed for the non-linear dynamic analysis of a building (frame specimen) retrofitted with the LLFD V-bracing system. A non-linear dynamic analysis was conducted based on the proposed restoring force characteristics, and the results obtained were compared with the pseudo-dynamic test results. Finally, for evaluating the commercialization potential of the LLFD V-bracing system, a non-linear dynamic analysis was conducted on an existing R/C building with non-seismic details retrofitted with the system. The seismic retrofitting effect was verified by examining the seismic response load and displacement characteristics, energy dissipation capacity, and damper load and displacement response before and after seismic retrofitting. The study results showed that the R/C frame (building) with non-seismic details exhibited shear failure at a design basis earthquake scale of 200 cm/s2; however, light seismic damage could be expected for a frame (building) retrofitted with the LLFD V-bracing system. At a maximum considered earthquake scale of 300 cm/s2, insignificant seismic damage was also anticipated, thereby verifying the validity of the newly developed LLFD V-bracing system.

A nonlinear quasi-zero stiffness vibration isolator with quintic restoring force characteristic: A fundamental analytical insight

The nonlinear mechanical oscillator with X-shaped-spring suspension has attracted relevant attention in the past couple of years due to its ability to tailor the corresponding stiffness characteristic on purpose and fit diverse engineering needs. This paper deeply investigates the conditions for such a configuration to exhibit a quasi-zero stiffness behaviour with both the linear and cubic elastic term of the force-displacement curve equal to zero. The resulting quintic characteristic leads to a vibration isolator with a much larger isolation frequency band respect to the classical isolator with non-zero cubic elastic term only. A systematic comparison between the quintic and cubic characteristics is performed, emphasizing the asymptotic trends, and thus showing the fundamental behaviours. It is found that the critical damping for an unbounded response of the quintic isolator is proportional to the square of the normalized excitation amplitude, while that of the cubic isolator is directly proportional to the normalized displacement amplitude. This makes the critical damping of the quintic isolator much lower, and thus more favourable in practical engineering applications, where the values of the normalized excitation amplitude are less than one.

Tailored nonlinear stiffness and geometric damping: Applied to a bistable vibration absorber

A novel device is proposed to obtain arbitrary restoring force characteristics and nonlinear geometric damping. It consists of linear springs and dampers that are compressed along a track. The obtained nonlinear damping and stiffness law depend on the track’s shape. The device is then applied to obtain a nonlinear energy sink (NES) to damp the vibrations of a host system. Both the case of transient vibrations, induced by shock loads, and sustained vibrations, induced by harmonic loads, are studied. For arbitrary stiffness and damping, slow flow dynamics and slow invariant manifolds (SIMs) are derived by applying harmonic balancing and multiple timescales techniques. Under transient vibrations, two performance measures are derived from the SIM, the relative residual energy and the pumping time, and are found for generic nonlinear spring force and nonlinear geometric damping. For sustained vibrations, a load-dependent frequency response (FR) is derived from the SIMs. This FR predicts the occurrence of the efficient strongly modulated responses but also the occurrence of the unfavorable detached responses called isolas, where the NES fails to mitigate and even amplifies vibrations.This research investigates the performance of a conventional cubic NES and a bistable NES (BNES) with nonlinear damping obtained from the proposed device. Especially the BNES with nonlinear damping shows attractive properties, with a high degree of robustness over a wide energy range and a low vibration threshold under transient loading. Under harmonic loads, the nonlinear damping helps reduce the effect of isolas. A novel tuning methodology is proposed to avoid isolas for a range of load magnitudes. The new device opens up a whole range of possibilities regarding energy dissipation through nonlinear damping.

Reinforcement learning and approximate Bayesian computation (RL-ABC) for model selection and parameter calibration of time-varying systems

This paper extends the recently developed methodology for model selection and parameter identification called RL-ABC (Ritto et al., 2022) (reinforced learning and approximate Bayesian computation) to time-varying systems. To tackle slowly-varying systems and detect abrupt changes, new features are proposed. (1) The probability of sampling the worst model has now a lower bound; because it cannot disappear, once it might be useful in the future as the system evolves. (2) A memory term (sliding window) is introduced such that past data can be forgotten whilst updating the reward; which might be useful depending on how fast the system changes. (3) The algorithm detects a change in the system by monitoring the models’ acceptance; a significant drop in acceptance indicates a change. If the system changes the algorithm is reset: new parameter ranges are computed and the rewards are restarted. To test the proposed strategy, new experimental data is obtained from a test rig with non-linear restoring force characteristics. The amplitude of the dynamical experiment is obtained with the control-based continuation strategy varying the excitation amplitude, and three Duffing-like models are used to represent the system. The results are consistent, and the strategy is able to detect changes and update parameter estimation and model predictions.

Tensile damage development and constitutive relationship establishment of recycled coarse aggregate concrete based on a double–interface numerical model

The tensile constitutive relationship is essential for determining the ductility and restoring force characteristics of seismic-resistant concrete structures and studying the mechanisms causing damage and fracture to concrete structures. This study investigates the axial tensile stress–strain curves of mortar, the interface between new and old mortar, and recycled aggregate concrete (RAC) with different water-binder ratios and ages. First, the tensile constitutive relationships of mortar and new-old mortar interface were established. Then, based on the experimental results and the random aggregate model, a double-interface numerical model of RAC was established to investigate the development of tensile damage in RAC and the influence law and mechanism of the old mortar strength, thickness and curing age on the curve of the tensile stress–strain of RAC. The results are a comparison of the peak tensile strengths at the same age and water-binder ratio for the above three mortar types, where new mortar > RAC > new-old mortar interface. Under the same thickness of old mortar, the peak stress, elastic modulus and peak cutline modulus of RAC increased with the increase of old mortar strength, and the amplitude of change increased with the increase of mortar thickness. Based on the tensile constitutive relationship of ordinary concrete, the tensile constitutive relationship of recycled coarse aggregate concrete is proposed by combining the experimental results and numerical analysis results.

高減衰ゴム系積層ゴム支承を有する免震建物のバイリニアモデルへの置換

High damping laminated rubber bearings are highly popular in seismic isolation application. However, due to the nonlinear dependency of the force restoring characteristics on shear strain, energy balance methods cannot be applied to evaluate the response of the isolation layer. Therefore, by replacing the complex restoring force characteristics of high damping rubber bearings with a simple bi-linear model, energy balance methods can be applied. In this paper, several replacement methods are compared in reproducing the accuracy of the response of the isolation layer using time history analysis and considering different earthquake motion phase characteristics and shear strain conditions.

Hysteresis Performance and Restoring-Force Model of Precast Concrete Ring-Lap Beam-Column Joints

In order to study the restoring-force characteristics of precast concrete ring-lap beam-column joints, three precast concrete ring-lap beam-column joint specimens and one cast-in-place concrete beam-column joint specimen were designed and fabricated, and low-circumferential repeated loading tests were conducted. The results show that the bearing capacity of the ring-lap beam-column joint is higher than that of the cast-in-place beam-column joint, and with the increase in the lap length, the bearing capacity, ductility, and energy dissipation capacity of the ring-lap beam-column joint increase significantly, and the local damage is also mitigated. Based on the test results and the existing restoring-force model theory, a trifold restoring-force model is proposed for precast concrete ring-lap beam-column joints considering the effect of lap length. The proposed restoring-force model is consistent with the hysteresis curve of the assembled column, which indicates that the proposed restoring-force model can better reflect the influence of the lap length on the hysteresis characteristics, and can provide a reference for the structural elastic–plastic analysis and engineering application of the precast concrete ring-lap beam-column joint. The proposed restoring-force model can better reflect the influence of lap length on the hysteretic properties, which can provide a reference for the structural elastoplastic analysis and engineering application of this precast concrete ring-lap beam-column joint.

A STUDY ON THE EFFECT OF ADDITIONAL STIFFNESS IN THE PLASTIC REGION OF WOODEN FRAMEWORKS

In this paper, the property of energy conservation and the dynamic responses are analytically examined for the bilinear restoring force characteristics. Next, the restoring force characteristics of wooden frameworks are clarified experimentally. The frameworks have bearing wall elements and steel bar braces that are placed in parallel. The steel bar braces are placed to add the secondary stiffness after yielding of the bearing wall elements of the frameworks. There is a loose hole on the prate at the end of the steel bar brace.

THE EFFECT OF STIFFNESS AND STRENGTH OF COLUMN BASES IN FIRST STORY ON DAMAGE DISTRIBUTION OF WEAK-BEAM TYPE RIGID STEEL FRAMES

Exposed-type column bases are classified by two yield types, i.e., anchor-bolt type, and base-plate type. Restoring force characteristics are slip-type and maximum point orientation type respectively. The characteristics of damage distribution in steel frames with exposed-type column bases have been clarified by many past studies. However, the literature concerning quantitative evaluation and prediction formulas is limited. The prediction formulas are needed to design such structures avoiding damage concentration as much as possible. In this paper, the damage to column bases, the upper beam of the first story, and inside the first story in steel frames with column bases that have elastic perfectly plastic restoring force characteristics are evaluated quantitatively based on the comparison with "Basic Frame". After that, the proposed prediction formula is contrasted with the time-history response analyses.

A STUDY ON STATIC MECHANICAL PROPERTIES OF VERTICAL SEISMIC ISOLATION SYSTEM WITH PARALLEL LINK MECHANISM

This paper discusses the basic mechanical properties of a newly proposed parallel link mechanism as a three-dimensional seismic isolation system capable of supporting large loads. Specifically, the static restoring force characteristics of the entire mechanism, the moment caused by the spring force, and the inclination of the top surface due to 3-dimensional displacement were analyzed. The results show that stable static restoring force can be obtained by setting the initial angle within a certain range and using multiple units with a separation distance of 4 m or more between mechanisms.

ANALYSIS OF ROCKING COLUMN BEHAVIOR CONSIDERING STRESS DISTRIBUTION OF COLUMN USING FIBER ELEMENTS

In this paper, a numerical model considering the embedment reaction of column foot by the beam-column finite element method was proposed for evaluating the restoring force characteristics of the rocking column in traditional timber structures. Wood compression tests in contact with stones were conducted to investigate the characteristics of the embedment reaction and initial deformation generated at the end of the wood, and these characteristics were considered in the column foot numerical model. The validity and applicability of the numerical model were verified by analyzing several static loading tests of the rocking column.

RESTORING FORCE CHARACTERISTICS OF PRECAST CONCRETE BEAMS POST-TENSIONED BY UNBONDED TENDONS AT WIDENED BEAM END

Modeling on restoring force characteristics of unbonded precast prestressed concrete beams with widened beam end was proposed in this paper. One model has rotational springs at both the outer end of the general and widened beam end, and another model has one spring with a rigid zone at the end. Ten unbonded precast prestressed concrete beams whose parameters are beam longitudinal rebar amount, widened beam end size, prestressing force, etc., were constructed and tested. The proposed method captured the restoring force characteristics of the test results in good accuracy.

Restoring Force Model for Composite-Shear Wall with Concealed Bracings in Steel-Tube Frame

Establishing a restoring force model is a fundamental yet critical task for the analysis of structural responses to earthquakes. Such a model has a substantial impact on the structural analysis results. Composite-shear walls with concealed bracings in steel-tube frames (composite-shear walls) offer several advantages, including convenient construction processes, high-bearing capacity, and excellent ductility. In this study, the mechanical properties of virtual test pieces were simulated when subjected to low-cyclic-reversed loading in ABAQUS. The simulation results agreed well with the experimental results. Subsequently, 24 additional virtual test pieces were obtained by adjusting the parameters of the original four test pieces, including the strength of the recycled concrete, thickness of the wallboard, and axial compression ratio. Finally, the restoring force model was validated using the experimental test results from our previous study. The results demonstrate the excellent performance of the proposed restoring force model in simulating the mechanical response of a composite shear wall. In particular, this model can accurately reflect the restoring force characteristics of the composite shear wall explored in this study. The restoring force model provides an effective theoretical support for the analysis of the elastoplastic seismic response of similar types of structures.

Disintegration of low and normal strength concrete in shear localized bands and its constitutive modeling

The shear resistant mechanism along cracks of concrete changes as localized shear deformation progresses. The aggregate interlock mechanism shifts to the Coulomb friction mechanism. A disintegration model considering the transient shear transfer has been proposed. In this study, the applicability of this constitutive model to low and normal strength concrete was verified through experiments and post-peak analysis. As a conclusion, it is clarified that when this graveling formation progresses along the localized shear bands in structures, it is necessary to consider the transition of shear disintegration and the proposed model has fair consistency with the experimental results. Moreover, the average frictional coefficient of disintegrated cementitious composite is inversely idealized about 1.0 for concrete and about 0.4 for mortar. It is expected that the proposed model will increase the accuracy of analyzing the structural restoring force characteristics of reinforced concrete and its post-peak behaviors.

Seismic Strengthening of R/C Buildings Retrofitted by New Window-Type System Using Non-Buckling Slit Dampers Examined via Pseudo-Dynamic Testing and Nonlinear Dynamic Analysis

In the present study, a window-type seismic control system (WSCS) using non-buckling slit dampers (NBSDs) was proposed and developed to address the disadvantages of conventional seismic control systems so that it can be effectively applied to existing reinforced concrete (RC) buildings. Materials testing was also conducted to examine the material performance and energy dissipation capacity of NBSD. A full-scale two-story test frame modeled from existing RC buildings with non-seismic details was subjected to pseudo-dynamic testing. As a result, the effect of NBSD-WSCS, when applied to existing RC frames, was examined and verified, especially as to its seismic retrofitting performance. In addition, based on material testing and pseudo-dynamic test results, a restoring force characteristics model was proposed to implement the nonlinear dynamic analysis of a test building retrofitted with NBSD-WSCS. Based on the proposed restoring force characteristics, nonlinear dynamic analysis was conducted, and the results were compared with those obtained by the pseudo-dynamic tests. Finally, in an attempt to commercialize this NBSD-based WSCS, nonlinear dynamic analysis was conducted on the entire RC building with non-seismic details retrofitted with NBSD-WSCS. The results showed that the RC frame (building) with no reinforcement applied underwent shear failure at seismic intensity of 200 cm/s2, a typical threshold applied in seismic design in Korea. In contrast, in the frame (building) retrofitted with NBSD-WSCS, only minor earthquake damage was expected, and even when the seismic intensity was set to 300 cm/s2, the maximum intensity that had been observed in Korea, only small or moderate seismic damage was expected. These results confirmed the effectiveness of the seismic retrofitting method using NBSD-WSCS developed in the present study.

Seismic performance evaluation of recycled aggregate concrete-filled steel tubular columns with field strain detected via a novel mark-free vision method

In this study, low cycle reciprocating load tests were conducted on nine recycled aggregate concrete-filled steel tube columns (RACSTCs) and a solitary ordinary concrete-filled steel tube contrast column (OCSTC). The axial compression ratio and steel-tube wall thickness were considered as the parameters of interest. Accordingly, the failure mechanism, hysteresis performance, skeleton curve, ductility coefficient, energy consumption performance, and stiffness degradation of the two types of columns were compared. A vision measurement system was developed to track the full field deformations of specimens, and a quadocular vision system was constructed to determine the concrete column deformations. The deformations were compared with those obtained from laser measurements using an image and point cloud stitching algorithm. The results show that the hysteresis curves of RACSTCs are non-pinched with large ductility coefficients for all the specimens and the equivalent viscous damping coefficients are in the range of 0.462–0.975. RACSTC specimens exhibit good seismic and deformation performance. A three-fold restoring force model was established for RACSTC specimens based on skeleton curve test data. The theoretical hysteresis curve obtained using the skeleton curve model and hysteresis rule shows good agreement with the hysteresis curve obtained from experiment. This can be used as a reference for research on the restoring force characteristics of RACSTCs. The results obtained using the vision measurement system show that the measured mean relative error values are less than 0.504%. This confirms that the multiple vision measurement method can be used to accurately measure curved surface deformations as well as the full field strain values of RACSTCs. Therefore, the proposed method can be used to evaluate the asymmetric deformation of structures subjected to vibrations, impact, and other load types, thereby providing early warning decision data.