Viscous Damping Coefficients Research Articles

Experimental study on seismic performance of assembled buckling-restrained brace with low yield point steel

Based on the design concept of seismic resilience, which aims to achieve controllable damage during earthquakes and rapid post-earthquake functional recovery within the structure, an assembled buckling-restrained brace with low yield point steel (ALYBRB) was proposed. To evaluate its seismic performance, quasi-static cyclic loading tests were conducted on five ALYBRB specimens. The influence of core steel material, bolt spacing of the external restraint system, and the gap between the core and the external restraint system on the seismic performance of ALYBRBs were investigated. The results indicated that the ALYBRBs exhibited superior plastic deformation capacity, stable energy dissipation capacity, and exceptional fatigue performance, as well as significant cyclic hardening characteristics and hysteretic properties with good symmetry. The cumulative plastic deformation coefficient (CPD) of ALYBRBs with LYP100 and LYP160 steel were 2.33 times and 1.51 times greater than that with Q235 steel, respectively. The maximum equivalent viscous damping coefficients of all specimens can achieve a range of 73.0 % to 86.2 % of the theoretically maximum value. The strain hardening adjustment factors of all specimens ranged between 1.34 and 1.90. The average compression strength adjustment factor for the properly designed ALYBRB specimens was 1.12. Reducing the bolt spacing can effectively inhibit the multi-wave buckling of the core, which is conducive to the improvement of energy dissipation efficiency in ALYBRBs. ALYBRB specimen with excessive gap exhibited decreased ductility, energy dissipation efficiency, and fatigue performance, and its out-of-plane deformation mode was a combination of bending deformation in the constrained yield segment and the transition segment deformation.

Experimental study on seismic performance of replaceable shear links with low-yield-point steel

Based on the design concept of controllable seismic damage during earthquakes and rapid functional recovery after earthquakes, a replaceable shear link with low-yield-point steel was proposed. Quasi-static cyclic loading tests and numerical analysis were conducted on six specimens. The failure mode, seismic performance, energy dissipation behavior, and shear distribution of each specimen were carefully considered to investigate the effects of web steel, web stiffening configuration and stiffener-plate stiffness ratio. The results showed that the stiffened specimens showed full-sectional shear yielding behavior, while the non-stiffened specimens exhibited coupling behavior of web yielding and buckling. Specimens with reasonable design parameters had excellent ductility and energy dissipation capacity, with the plastic shear angle exceeding 0.157 rad and the maximum equivalent viscous damping coefficients greater than 0.51 (80% of the theoretical maximum value). Owing to the cyclic strengthening of the low-yield-point steel web and the contributions of stiffeners and flanges, the specimens showed obvious overstrength behavior, with the overstrength factor ranging from 1.99 to 2.39. The cross-stiffening configuration was conducive to enhancing the seismic performance of shear links. Smaller web width-to-thickness ratios were recommended to match with smaller stiffener-plate stiffness ratios. Extended cross stiffeners and diagonal stiffeners resulted in earlier cracking of the web welds, which adversely affected the ductility of the specimens.

Seismic performance of an assembled monolithic concrete column

A prefabricated concrete column-to-column structure connected by high-strength bolts is proposed. To explore the seismic performance and failure form of the structure, the finite element analysis software is used to simulate the low-cycle repeated load test. The hysteretic curve and skeleton curve of the structure are obtained, and the stiffness degradation law, ductility and energy dissipation capacity of the structure are quantitatively analyzed to evaluate the seismic performance of the structure. The results show that the ductility coefficient of the structure is basically between 2.19 and 4.97, and the ductility coefficient of most specimens is greater than 3.0, indicating that the structure has good ductility and deformation capacity. The equivalent viscous damping coefficients of the specimens are in the range of 0.21–0.29, indicating that the structure has good energy dissipation capacity. In a certain range, increasing the thickness of the end plate has no significant impact on the energy consumption capacity of the structure. The compressive strength of the concrete in the core area is greatly improved under the constraint of the end plate bolts, and end plate bolt connection can well realize the transmission of force and give full play to the performance of materials.

Seismic performance of self-centering steel column base with buckling-restrained bars

Self-centering structures, emerging as a vital innovation in earthquake-resilient design, offer notable advantages in structural integrity, rapid functional recovery post-earthquake, and economic efficiency over the building's life cycle. This paper introduces a self-centering steel column base, employing buckling-restrained bars for energy dissipation. Through an analysis of its force mechanism, it conducts low-cycle reciprocating load test on four set of specimens with varying buckling-restrained bars and axial compression ratios. The results demonstrate the column base's superior seismic performance, characterized by its ability to rapidly restore seismic functionality after unloading and replacing the buckling-restrained bars. The force-displacement hysteresis curves exhibit a distinctive double-flag shape, with a minimal residual story drift of 0.001 rad, underscoring the structure's exceptional self-centering capability. The displacement ductility coefficients and equivalent viscous damping coefficients confirm the column base's excellent deformation and energy dissipation capabilities. Furthermore, a refined ABAQUS finite element model is developed and validated against the load test results, further analyzing the seismic performance relative to key structural parameters.

Lateral behavior of low-rise aluminum alloy frames infilled with composite wallboards

In this paper, cyclic tests were conducted on three specimens to investigate the lateral performance of low-rise aluminum alloy frames infilled with composite wallboards. The test variables were set based on the opening on the composite wallboard and the rise-span ratio. The test phenomena indicated that the failure modes of the three specimens were the fracture of the core material of the composite wallboard and the shearing off of the blind-rivets between the composite wallboards and the aluminum alloy frame. Through the analysis of the data obtained from the strain gauges and the displacement transducers, the high rise-span ratio would lead to a noticeable pinching phenomenon in the hysteresis curves. It is also found that the opening on the wallboard resulted in a significant asymmetric shape in skeleton curves. Furthermore, the increase in the rise-span ratio had more significant impacts on the initial stiffness of the structure, leading to a reduction of 44%. Utilizing the relevant formula, the equivalent viscous damping coefficients for the specimens were calculated, which scaled to 0.2–0.3, 0.15–0.25, and 0.1–0.225, respectively. The lateral load-resisting capacities for the three specimens were evaluated using the characteristic values of load and displacement. And the desirable ductility of the three specimens was concluded for their ductility coefficients exceeding 3. This research aims to provide technical reference for low-rise structures with aluminum alloy frames infilled with composite wallboards.

Seismic behavior of an improved drilled flange connection for I-beam to CFST column

The use of cold-formed steel tubes in the concrete-filled steel tubular (CFST) columns makes the design of the moment connections between beams and CFST columns much more challenging. This is because setting the internal diaphragms in the CFST column to transfer the bending moment of the beam end becomes impossible, and thus new joints are needed. A novel joint was proposed in a previous study by the authors, where two end plates were used for the force transmission between CFST columns and beam flanges. Moreover, to satisfy the “weak member strong joint” requirement, the I-beams were reduced by drilling a series of circular holes in their flanges. However, most of the tested specimens failed by the unexpected rupture of the complete joint penetration (CJP) groove welds between the beam flanges and end plates. In this paper, three specimens are redesigned and tested, where modifications are made to improve their behaviors under the seismic load. In this test, the local buckling of beam flanges at the drilled sections was observed in all specimens, and two specimens failed due to the fracture at the drilled sections, while CJP weld fracture and significant bending of beam flanges both occurred at the failure of the rest specimen. The hysteresis curves of all specimens are fusiform, indicating their good energy dissipations (the maximum equivalent viscous damping coefficients between 0.35 and 0.40). The failure rotation angles are about 2.44–3.01, and the ductility coefficients are between 2.26 and 2.66. According to EC3, all specimens can be classified into the rigid and full-strength joints. Subsequently, the parametric analyses using the validated finite element model are carried out, where the effects of main parameters are investigated on the seismic behavior of the presented joint. This study brings insights into the moment connections between the steel beam and CFST column with the outer cold-formed section.

Enhanced Trajectory Tracking of 3D Overhead Crane Using Adaptive Sliding-Mode Control and Particle Swarm Optimization

Cranes hold a prominent position as one of the most extensively employed systems across global industries. Given their critical role in various sectors, a comprehensive examination was necessary to enhance their operational efficiency, performance, and facilitate the control of transporting loads. Furthermore, due to the complexities involved in disassembling and reinstalling cranes, as well as the challenges associated with precisely determining system parameters, it became essential to implement adaptive control methods capable of efficiently managing the system with minimal resource requirements. This work proposes a trajectory tracking control using adaptive sliding-mode control (SMC) with particle swarm optimization (PSO) to control the position and rope length of a 3D overhead crane system with unknown parameters. The PSO is mainly used to identify the model and estimate the uncertain parameters. Then, sliding-mode control is adapted using the PSO algorithm to minimize the tracking error and ensure robustness against model uncertainties. A model of the systems is derived assuming changing rope length. The model is nonlinear of second order with five states, three actuated states: position x and y, and rope length l, and two unactuated states, which are the rope angles θx and θy. The system has uncertain parameters, which are the system’s masses Mx, My and Mz, and viscous damping coefficients Dx, Dy and Dy. A simulation study is established to illustrate the influence and robustness of the developed controller and it can enhance the tracking trajectory under different scenarios to test the scheme.

Cyclic behavior of self-centering RCFST column to beam joints with prefabricated connectors

This paper presents the cyclic behavior of reinforced concrete-filled steel tube (RCFST) column to beam joint with prefabricated connectors. The cyclic performance of four specimens was investigated to focus on the hysteretic behavior, reinforcement tension, residual deformation, and strain distribution of joints. The equivalent viscous damping coefficients (ξeq) corresponding to the four specimens range from 0.049 to 0.087 at the yield point. And the final residual drift ratio of the specimens ranged from 3.6% to 12.9%. The tested column-beam joint specimens had good hysteretic behavior, energy dissipation, and self-centering ability. The PT steel bars without hollow channel or weakened treatment enhanced the self-centering ability and workability of joints. The finite element models were developed to verify the main mechanical properties of the self-centering RCFST column to beam joint. The average of KE/ KFEA, Mc,y/ My,FEA and Mc,p/ Mp,FEA were 0.89, 0.98, and 1.03, respectively. The FEA models could predict mechanical properties of the joints with high accuracy.

Seismic design and experimental testing of precast tolerance concrete shear wall subject to cyclic load

A precast tolerance concrete shear wall (PTCW) characterized by proper-length steel connectors is proposed to adjust the tolerance and improve the joint failure model of the precast wall. The design method for this wall is also presented in this study and verified by test results. Four full-scale walls, including two cast-in-situ walls (RCWs) and two precast walls (PCWs) with axial compression ratios of 0.2 and 0.3, respectively, were tested under lateral loading. The seismic behavior of the panels, including the failure modes, hysteretic behavior, strength envelope curves, stiffness degradation, energy dissipation, and steel strains, was analyzed and discussed herein. The test results showed that all four walls were in a flexural-shear failure mode, and the PCWs showed better performance in terms of hysteretic behavior, strength envelope, stiffness, and energy dissipation, particularly under an axial compression ratio of 0.3. Furthermore, the peak load of PCW1 (axial compression ratio is 0.2) and PCW2 (axial compression ratio is 0.3) increased by 5.93% and 15.51%, and the yield load increased by 12.1% and 11.39% compared with those of RCW1 (axial compression ratio of 0.2) and RCW2 (axial compression ratio of 0.3), respectively. The equivalent viscous damping coefficients of all four panels were higher than 0.05. The lateral bearing capacity of the walls increased with an increase in the axial compression ratio. Moreover, no visible damage or slippage was observed when the PCWs were demolished after testing. The main nonlinear strain was concentrated on the vertical bar and not on the connectors, indicating that the plastic hinge position was transferred from the joint interface to the wall panel. The results indicated that the use of steel connectors to strengthen the joints can achieve the seismic design concept of strong joints and weak members.

Sensing and control the static deflection of a cantilever beam by using piezoelectric patches

Abstract Different mechanical structures when comes under static and dynamic loadings then they respond. It is very important to sense it so that the dynamic behavior of the structure in terms of natural frequencies, its mode shapes, and viscous damping coefficients can be successfully predicted or measured. The accurate prediction of the dynamic response of the oscillating structure always plays an important role to design its physical parameters. However, in this paper, the simulated and experimental study is conducted to accurately sense the static deflection of the cantilever beam by using piezoelectric patches. The accurate prediction of the static deflection of the beam and its control through piezoelectric patches is the novelty of the present work. Mostly, the finite element model of the beam is developed to predict its dynamic behavior. The finite element modeling provides an approximate solution. In this regard, the finite element model updating technique such as the direct updating algorithm is used in this study to correct the simulated finite element model of the beam. The updated simulated finite element model is then used to predict the accurate value of the static deflection. It is observed that the maximum percentage error between the predicted and measured static deflection is 29.1%. The updated simulated finite element model is also used to design the controller. The direct output feedback controller is developed and it is found that the static deflection of the beam has been reduced by 46.65%.

Experimental Investigation on the Seismic Behavior of Ultra-High Performance Concrete Filled Steel Tubular Columns

ABSTRACT In this work, a total of nine ultra-high performance concrete (UHPC) filled steel tubular columns (UHPCFSTs) were fabricated and tested under cyclic loading. The results indicated that UHPCFSTs mainly exhibited flexural failure mode, compression-flexure failure mode and welding line fracture, and it changed from flexural failure mode to compression-flexure failure mode when the axial compression ratios exceeded 0.3. The elastic and ultimate drift ratios of UHPCFSTs were within the ranges of 1.37–2.05% and 2.38–4.32%, respectively, and the equivalent viscous damping coefficients were within the range of 0.197–0.358 when they failed, UHPCFSTs could sever as good choices in high seismic intensity areas.

The damped vibrating string equation on the positive half-line

In this paper, the existence of a solution to the problem describing the small vertical vibration of an elastic string on the positive half-line is investigated in the case when both viscous and material damping coefficients are present. The result is obtained by transforming the original partial differential equation into an appropriate abstract second-order ordinary differential equation in a suitable infinite dimensional space. The abstract problem is then studied using the combination of the Kakutani fixed point theorem together with the approximation solvability method and the weak topology. The applied procedure enables obtaining the existence result also for problems depending on the first derivative, without any strict compactness assumptions put on the right-hand side and on the fundamental system generated by the linear term. The paper ends by applying the obtained result to the studied mathematical model describing the small vertical vibration of an elastic string with a nonlinear Balakrishnan–Taylor-type damping term.

A consistent dynamic stiffness matrix for flutter analysis of bridge decks

A consistent dynamic stiffness matrix is formulated for the flutter analysis of bridge decks. The equations of motion corresponding to the vertical, lateral, and torsional degrees of freedom are considered, and the associated self-excited lift, drag, and torsional moment are based on the unsteady linear model involving eighteen flutter derivatives. The velocity-dependent and the strain rate-dependent viscous damping coefficients, obtained in terms of the corresponding modal damping ratios, are also incorporated throughout the formulation. The flutter speed and the corresponding flutter frequency are determined through an iterative search of the determinant of the assembled dynamic stiffness matrix for flutter. Using the present formulation flutter analysis can be accurately performed with very few number of elements, as compared to the analyses with the conventional finite element approach. The flutter derivatives-based self-excited force model is especially suitable for the flutter analysis of a bluff-body bridge deck with experimentally available flutter derivatives. Numerical results for three examples verify the accuracy and efficacy of the present formulation.

Dynamical analysis and numerical verification of a non-smooth nonlinear energy sink

The performance of the vibration reduction of a lightweight non-smooth nonlinear energy sink (NES) attached to a two-story linear damped primary structure (PS) is studied through dynamical analysis and numerical verification. First, a three-degree-of-freedom non-smooth nonlinear system is formulated to describe the coupled dynamics involving the PS and non-smooth NES, in which nonlinearity is induced by the piecewise linear restoring force of the NES and described by a non-smooth function. Second, when a 1:1:1 internal resonance case of the coupled system is considered, a modified complex-average technique and the method of multiple scales are employed to obtain a set of algebraic equations between the vibration amplitudes of the PS and attached non-smooth NES. The stability conditions and initial critical energy for activating targeted energy transfer (TET) can be analytically obtained. Finally, the linear stiffness, equivalent viscous damping coefficients and impact clearance of the non-smooth NES are numerically optimized by the peak estimates. The initial critical energy for the TET of NES is numerically verified to show the excellent performance of vibration reduction for the non-smooth NES by comparing with other attached dissipation devices under a wide range of impulsive loads.

An Analytical Solution for the Dynamics of a Functionally Graded Plate resting on Viscoelastic Foundation

This paper deals with the dynamic response of Functionally Graded Material (FGM) plates resting on a viscoelastic foundation under dynamic loads. The governing equations are derived by using Hamilton’s principle using the classical plate theory and the higher-order shear deformation plate theory. Using state-space methods to find the closed-form solution of the dynamic response of functionally graded rectangular plates resting on a viscoelastic foundation. Numerical examples are given for displacement and stresses in the plates with various structural parameters and the effects of these parameters are discussed. The result of the numerical example shows a marked decrease in displacement and stresses as the coefficient of viscous damping is increased.

Influence of staggered floor and unequal height of left and right beam on seismic behavior of CFSST column-to-HSS beam composite frames

One-third scale models of three concrete-filled square steel tubular (CFSST) column-to-H-shaped steel (HSS) beam composite frames with two bays and three stories were designed and manufactured. A failure test of the specimens under lateral cyclic loading was conducted. The experimental parameters included a staggered floor ratio and unequal depth ratio, staggered floor ratios of 0 and 0.5, and unequal height ratios of 0 and 0.75. The skeleton curves, hysteresis curves, and the stiffness and strength degradation of the CFSST column-to-HSS beam composite frame were analyzed. The results showed that the test frames exhibited excellent seismic performance, and the order is KJ-1, KJ-2 and KJ-3. The drift ratio ranges of δy, δm, δu were 1/123-1/191, 1/37-1/38, and 1/27-1/29, respectively, indicating that the three test frames possessed sufficient ductility and met the seismic objective of not collapsing in large earthquakes. The equivalent viscous damping coefficients of the specimens in the failure stage were in the range of 0.24–0.18, meeting the earthquake protection requirements. A simulation model have developed to predict the P-Δ response envelope. The model results were consistent with the test results.

Experimental Study on Tenon and Mortise Joints of Wood-Structure Houses Reinforced by Innovative Metal Dampers

To improve the seismic performance of Chinese traditional wood-structure houses, this paper proposes to strengthen their mortise and tenon joints by applying an innovative metal damper. According to the dimensions of the “Yikeyin” wood-structure houses in the Tonghai area of Yunnan Province, two groups of six samples of three types of mortise and tenon joints were manufactured, in which one group was mounted with dampers made of Q235 steels. Subsequently, a low-cycle repeated loading test was conducted to examine the overall behavior of these joints. Various characteristics of seismic performance indexes, such as the moment–rotation hysteresis curve, skeleton curve, stiffness degradation, energy dissipation capacity, residual amount of tenon and the removal before and after reinforcements of straight, penetrated and dovetail tenon joints were analyzed. The test results show that these tenons exhibit good deformation capacity, their hysteresis curves became fuller and their “pinch” effects were significantly reduced, all after their joints became strengthened, indicating that their joint slips were reduced during the loading processes and their residual amounts of tenon removals were under effective control. Compared with the blank group, the joint stiffness was substantially improved, and the increase in the reverse stiffness turned greater than that of the positive stiffness at each stage of loading, while the degradation curve of the whole joint stiffness became steeper. After mounting the dampers, the bearing capacity and energy dissipation of the joints were significantly improved, the equivalent viscous damping coefficients of the straight and penetrated tenon joints were increased, but that of the dovetail joint was slightly reduced. These study results can provide a reference for the reinforcement and protection of traditional wood-structure houses.

INVESTIGATION OF DYNAMICS OF A SYSTEM WITH TWO SIDED IMPACTS

In the elements of manipulators and robots, various types of impact interactions take place. Among them two sided impacts are often observed. For their investigation a special numerical procedure is proposed. Numerical results for typical parameters of the investigated system having one degree of freedom are presented. Results without application of this procedure and with it are presented and mutually compared.
 Results for various values of coefficient of viscous damping and of coefficient of restitution were obtained. They are presented for three typical sets of those parameters. The first set of typical values of parameters describe the motion of the investigated system with two sided impacts corresponding to the case of conservative impacts. The second set of typical values of parameters describe the motion of the investigated system with two sided impacts corresponding to the case of conservative inter impact motions. The third set of typical values of parameters describe the motion of the investigated system with two sided impacts corresponding to the case of fully dissipative dynamics.
 Time history of displacement, time history of velocity and dynamics of the system with two sided impacts in the phase plane are represented. The obtained graphical representations show the advantages of the improved calculation of impact interactions.
 The results are applied in the design of elements of manipulators and robots with two sided impacts.
 Keywords: nonlinearity of impact type, harmonic excitation, two sided impacts, nonlinear transient processes, graphical representations.

Synchronization characteristics of two vibrators in a novel hydraulic coupling system

The machines that utilize the synchronization of vibrators, such as pile sinkers, breaking hammers and sonic drilling rigs, play an important role in municipal construction and resource exploration. In this paper, a novel hydraulic coupling system with large specific power, handy control and robust stability for vibrator synchronization is presented. To investigate the feasibility and precision of the synchronization of the vibrators in the system, a mathematical model is established. According to the model, the synchronization characteristics of two vibrators are discussed when the errors of their masses, eccentricities and viscous damping coefficients are considered. Furthermore, simulation analyses are performed to verify the numerical results. The results demonstrate that two vibrators can be synchronized by coupling the components. The precision of synchronization is attractive, although the precision at high speed is inferior to that at low speed. The precision of the synchronization is more dominated by eccentricity than the other two parameters.

Experimental study of the hysteretic behavior of prefabricated frame-shear wall structures with grouting sleeve connections

In this study, a cast-in-place frame-shear wall specimen (CWS) and two prefabricated frame-shear wall specimens (PCWS1 and PCWS2) connected by grouting sleeves with different assembly schemes were tested under horizontal low-cycle reciprocating loading. The hysteretic curves, skeleton curves, ductilities, stiffness degradation, equivalent viscous damping coefficients, story drifts, crack development trends, and failure modes of the specimens were analyzed. The effects of different assembly schemes on the hysteretic behavior of prefabricated frame-shear wall structures connected by grouting sleeves were also studied. By analyzing the law of variation of reinforcement strain in the components, the interactions between the components and the overall stress mechanisms of the specimens were investigated. The results showed that the energy dissipation capacities of the prefabricated specimens PCWS1 and PCWS2 were 29.8% and 23.9% higher than that of the cast-in-place specimen, respectively; the peak bearing capacities of the prefabricated specimens were reduced by 3.1% and 5.3%, respectively, and the ultimate story drifts of the first floors were increased by 76.6% and 28.1%, respectively. The redistribution of internal forces between components caused by the separations of the interfaces between the cast-in-place regions and the prefabricated regions effectively prevented the brittle failure of the connecting beams. The introduction of additional prefabricated components in the assembly scheme facilitated local failure of the components. The stress process of a prefabricated specimen was divided into four stages. The method for calculating the lateral displacement of prefabricated specimens in the elastic range was described and suggest that the limit value of the story drift based on the elastic design method be set to the maximum value that the prefabricated frame-shear wall structures achieves in stage II.