Viscous Damping Ratio Research Articles

Residual displacement demand for non-degrading bilinear SDOF oscillators with self-centering viscous-hysteretic devices

The self-centering viscous-hysteretic device (SC-VHD) is a high-performance self-centering system that was recently developed to reduce structural residual displacement and damage during severe earthquakes. This study focuses on developing a residual displacement ratio C r spectrum and a residual displacement estimation method for non‐degrading bilinear SDOF oscillators with SC-VHDs. Statistical analysis is conducted to investigate the effect of design parameters on the constant-ductility residual displacement ratio C r spectrum under near-fault pulse-like earthquake ground motions (NFPE) and far-fault earthquake ground motions (FFE). Based on statistical data, a formula for the mean C r spectrum is proposed. Subsequently, an iterative calculation method for residual displacement is presented according to the equivalent linearization method and the proposed mean C r spectrum formula. Finally, using the iterative calculation method, the residual displacement of a two-story steel moment-resisting frame (MRF) with SC-VHDs is predicted, demonstrating its application. The results indicate that the mean C r spectrum under the NFPE is significantly larger than that under the FFE. Besides, the mean constant-ductility C r spectrum decreases with increasing post-yield strength ratio, ratio of preload to yield strength, ratio of loading stiffness to elastic stiffness increases, or ratio of unloading stiffness to loading stiffness, but increases with increasing viscous damping ratio. When estimating the C r spectrum, increasing the ductility ratio and decreasing the ratio of preload to yield strength can both reduce record-to-record variability. Both the formula for the mean C r spectrum and the iterative calculation method for residual displacement are validated by comparing with statistical data. • The influence of design parameters on the residual displacement C r spectrum is investigated. • A formula for the normalized mean C r spectrum is developed. • An iterative calculation method for residual displacement is proposed. • An example application is used to validate the calculation method.

A partially restrained energy dissipater: Parametric analysis and application in rocking wall

To solve the limitations of the large-scale buckling-restrained brace and expand its application in rocking structures, a partially restrained energy dissipater (PRED) was developed recently. The partially restrained mechanism and the hysteretic behavior of PREDs have been verified by tests, whereas systematic studies of the PRED considering various design parameters have not yet been formed. In this study, parametric analyses of the PRED based on five series of numerical cases were conducted, which aimed at comprehensively studying the effect of the out-of-plane gap, length and number of the yielding segments, edge chamfering and thicknesses of the restraining tube on the seismic performance of the PRED and providing design recommendations. It is determined that the equivalent viscous damping ratio and compression-strength adjustment factor of the PRED decreased with the increasing out-of-plane gap. The overall hysteretic behavior and energy dissipation capacity were almost not affected by the number of yielding segments and their length. The thickness of the restraining tube should be equal to 4 mm or larger to avoid local plasticity. A detailed design procedure for PREDs was established based on the numerical analyses. Finally, PREDs were applied in a previously tested cross-laminated bamboo (CLB) rocking wall numerically to investigate the effectiveness of the PRED in rocking structures. The results showed that the energy dissipation and stiffness of the CLB rocking wall can be significantly improved by PREDs. This study lays a foundation for the application of the PRED in actual rocking structures and promotes the development of high-rise bamboo structures.

Effects of ambient temperature on cyclic response and functional fatigue of shape memory alloy cables

In this paper, the effects of ambient temperature on the tensile response and superelastic fatigue behavior of the shape memory alloy (SMA) cable are investigated. The tested SMA cable is made of Nickel–Titanium and has an outer diameter of 8 mm with a 7 × 7 configuration. The SMA cables are subjected to an incrementally increasing loading protocol up to 14% strain amplitude under ambient temperatures varying from −20 °C to 60 °C. The effects of deformation amplitude and test temperature on stress-induced martensitic phase transformations are assessed. SMA cable specimens are also subjected to cyclic loading at a constant strain amplitude of 6% up to 1000 loading cycles at different test temperatures. The evolution of superelastic response with loading cycles is revealed by analyzing the maximum stress, residual deformation, hysteretic energy, and equivalent viscous damping ratio extracted from hysteretic curves. The results indicate that the ambient temperature considerably alters the superelastic behavior of SMA cables by shifting the stress-strain loops upward and narrowing them. When the ambient temperature is close to the reverse phase transformation temperature, the superelastic response degrades more progressively with both increasing loading amplitude and number of loading cycles. The least degradation in functional properties of SMAs takes place when the cable is tested at a temperature close to its austenitic transformation finish temperature, while increasing temperature decreases low cycle fatigue life of SMA cables when it is deformed up to the end of phase transformation. Overall, it is important to consider this temperature dependent response of SMA cables in applications where the cables will be subjected to varying outdoor temperatures.

Lateral Performance of Glulam Timber Frames with CFRP Confined Timber-Steel Buckling-Restrained Bracings

Heavy glulam timber framed structures are facing a growing inadequacy in resisting lateral actions from earthquakes and winds due to the increasing building heights. This paper presents the experimental and numerical analysis results on the hysteretic behavior of newly developed carbon fiber reinforced polymer (CFRP) confined timber-steel buckling-restrained bracings and the lateral performance of bolted glulam timber frames with such bracings. Ten timber-steel bracings and four frames with different bracing provisions were tested via reversed cyclic lateral loading. A finite-element method based model was developed, verified, and used for parametric studies. The bracing test results indicated that the design requirements for ordinary buckling restrained bracings on the confinement ratio and the transverse bulging force are adequate for the proposed timber-steel bracings. A confinement ratio no less than 4.6 is suggested. Compared to an otherwise similar bare frame, two frames with the proposed bracings were found to be 132% and 176% higher in the peak loads, more than 10 times higher in the elastic stiffness, 40% and 43% higher in ductility ratio, and on average 106% higher in the equivalent viscous damping ratio. The two frames also exhibited higher stiffness and energy dissipation than a frame braced by timber bracings, which are prone to buckling failure. Parametric studies indicated that the secant stiffness and the damping ratio of the frames at small drift can be substantially affected by the bolt slippage of the bracing-frame connections. The increased lateral stiffness ratio will lead to increase in the peak load and stiffness, but the equivalent viscous damping ratio remains nearly constant for lateral stiffness ratios larger than 2.5. The frame stiffness and peak load increase with increased rotational stiffness of the beam-column connections while the equivalent viscous damping ratio decreases.

Sensitivity analysis of self-centering column base connections with shape memory alloy bolts

This paper performs a statistical sensitivity analysis of the cyclic response of self-centering column base connections equipped with shape memory alloy (SMA) bolts. Experimentally validated finite element models are first developed for self-centering column base connections with SMA bolts. The effect of fifteen potentially influential design factors on the cyclic response of self-centering column base connections is statistically assessed using a two-level fractional factorial design. Moreover, the limit state behavior of column base connection models is evaluated and discussed by considering four limit states, including decompression, yield-like point, self-centering, and ultimate limit state. The sensitivity analysis results show that the column axial compressive force, SMA bolt diameter, and column web slenderness are the most influential factors affecting at least four response parameters with percentage contributions greater than 80%. The results from this study confirm the self-centering capability of column base connections with SMA bolts. The self-centering limit state is reached in 44% of the designed connection models; however, it is shown that reaching this limit state does not impact the self-centering capability of the connections. All the connection models can recover their undeformed shape with minimal residual rotations. The results also indicate that only 30% of the column base connections provide a minimum equivalent viscous damping ratio of 8%. Therefore, the results highlight the need for improving the energy dissipation capability of column base connections for seismic applications.

Experimental study of corroded RC beams: dissipation and equivalent viscous damping ratio identification

Corrosion of steel reinforcement is one of the most common durability issues for reinforced concrete (RC) structures, especially when located in marine areas. The study of the mechanical consequences of this pathology is of great importance to assess their performance. Experimental campaigns have been carried out on corroded structures. So far, assessing quasi-static behavior or predicting the dynamic response of structures have been based exclusively on quasi-static loadings. In particular, the dissipated energy and the damping capacity, which are important features to study when assessing the seismic performance of corroded RC members, are evaluated based on quasi-static loadings. The objective of this study is to characterize these two significant engineering demand parameters (EDP) using both quasi-static and dynamic tests. To reach this goal, an experimental campaign is conducted on large-scale RC beams. The corroded and non-corroded RC beams are subjected to a four-point bending loading and to dynamic loading keeping the same loadings and boundary conditions. The dynamic loading is applied on the specimen by means of the AZALEE shaking table. In this paper, a brief description of the experimental campaign is made. Then, results showing the influence of the corrosion rate on the dissipation capacity of RC structures are exposed. Especially, the consistency between quasi-static and dynamic results is assessed and discussed.

Experimental study and numerical simulation of all‐steel buckling‐restrained brace with distributed inspection windows

SummaryThis paper presents a novel all‐steel seismic‐resistant, buckling‐restrained brace (BRB) which can be easily detached from its steel core for post‐seismic inspections. This allows inspectors to quickly determine if the BRB needs to be replaced to reduce the impact of seismic aftershocks. The weld toes of brace stiffeners were specially smoothed to reduce the residual stress and stress concentration, thereby improving the low‐cycle fatigue performance of the brace. Two identical restraining units were connected by high‐strength bolts. A small air gap was provided by annular gaskets between the core and the restraining system to allow for lateral expansion of the core plate under compression. Five specimens were tested under different cyclic loading protocols to investigate the performance. The hysteretic behavior, compression strength adjustment factor, equivalent viscous damping ratio, failure modes, and deformation of the restraining system were analyzed. The multi‐wave buckling deformation of the core was studied in detail to provide a basis for the accurate calculation of the number of contact points. Finite element analyses were performed to compare the response with test results, which proved the structure of the novel BRB to be reasonable except for the compression strength adjustment factor of some specimens, which was greater than 1.3. A damage assessment method was proposed to evaluate the working status of the newly designed BRB after an earthquake.

Rotational behavior of glulam moment-resisting connections with long self-tapping screws

The rotational behavior of beam-column connections plays an important role on the mechanical performance of timber frames. Recently, long self-tapping screws and threaded rods applied as fasteners by virtue of their advantageous withdrawal capacity and stiffness, provide promising technical solutions to achieve beam-column connections with high moment resistance and rotation stiffness. To investigate the rotational behavior of the glulam beam-column moment-resisting connections using self-tapping screws as fasteners, a series of monotonic and low-frequency cyclic loading tests are conducted on a total of ten full-scale specimens with screw inclination as the geometric configuration parameter in this paper. Based on the experimental campaign and results, the moment resistance, rotation stiffness, deformability and energy dissipation capacity of the connections are evaluated. The results indicate that this type of connection is characterized by a high moment resistance and rotation stiffness, but not very considerable deformability and energy dissipation capacity. When the connection fails in the tensile fracture of self-tapping screws, the screw inclination at the range of 15°∼30° has negligible influence on the moment resistance but significant influence on the rotation stiffness. Besides, the connections with 15° screw inclination show larger stiffness, lower ductility, faster degradation of secant stiffness and more rapid growth of equivalent viscous damping ratio compared with the connections with 30° screw inclination.

Biaxial cyclic behavior of bolted end-plate connection to I-column reformed by box-plates

In the research study, different 3D joint concepts of a frame formed by an I-column subjected to the biaxial cyclic load were simulated. Non-linear finite element models using the Ansys software were developed to evaluate the biaxial cyclic behaviors of the joints. After verification via five existing experimental tested beam-to-column connections, six different representative finite element models of the joints, including a 3D corner joint, two 3D edge joints, and two 3D interior joints with the biaxial cyclic load as well as a 2D corner joint as a base specimen with uniaxial cyclic load, were established with and without under axial compression force on the column. A newly developed weak-axis connection detail was implemented to connect the beam to the weak-axis of the column. Two box-plates parallel to the web of the column connected between the flange tips of the I-shaped column were used to reform the region of the I-column corresponding to the beam connection. The four-bolted unstiffened end-plate connection specified in AISC 358-16 was used as the beam-to-column connection in both the strong-axis and the weak-axis directions of the I-shaped column. The results indicate that biaxial loading causes a loss of strength in the early loading cycles compared to uniaxial loading. The strong-axis connection of the 3D corner joint has less ultimate connection rotation and a greater value of rotational stiffness than that of the 2D corner. Moreover, all the connections of the joints possessed good hysteretic curves satisfying the limits given in the ANSI/AISC 341-16. Axial compression force on the column reduced performance parameters of the connections such as plastic rotation capacity, energy dissipation ability, and hysteretic equivalent viscous damping ratio. By the way, the weak-axis connections of the joints are acceptable to consider as partially restrained connections, while the strong-axis connections are fully-restrained.

Energy dissipation in reinforced concrete members before or after yielding

AbstractModels for the pre‐ and post‐yield energy dissipation in reinforced concrete (RC) members are developed using a database of about 1200 tests with over 18,000 load cycles. Before yielding, the equivalent viscous damping ratio exceeds 5%, especially if the member is initially uncracked. It can be considered by using either a dedicated pre‐yield hysteretic model with parameters established in the paper or global viscous damping and special provisions against double counting of energy dissipation. The post‐yield model can be combined with various post‐yield hysteretic laws. It accounts for the member's type, shear‐span‐to‐depth ratio and likely failure mode, the continuity, ratio, and surface characteristics of longitudinal bars, and for FRP wrapping, if any. Alternatively, it recognizes only four member types but accounts also for the transverse steel ratio and the normal stress due to the axial load.

Design of Tuned Mass Damper Used to Enhance the Response of Structure under Seismic Action

Today there is a real desire to build skyscrapers in ‎economical cities. Where they are considered the ‎weakest if they are exposed to an earthquake ‎due to their height, lightweight, flexibility, and low damping ‎resistance. Therefore, many studies and techniques ‎presented to control vibration dangers. The newer technique to enhance ‎vibration responses of ‎structures is the Tuned Mass Damper (TMD). ‎In this study, a two-story building was designed and analyzed, with Tuned Mass placed on the upper floor and friction damping between movable hose clamp ball bearings and a fixed shaft. The Friction Tuned Mass Damper is formed by combining this bearing and bearing shaft system with the Tuned Mass Damper (FTMD). The coefficient of friction and equivalent viscous damping ratio of the proposed FTMD coil were experimentally obtained based on different states of the tuned mass. To explore the potential of the proposed FTMD to suppress vibrations on a two-degree-of-freedom structure exposed to the step input, numerical modeling and simulation were done using matlbe. In addition, to verify the simulation results, a parallel experimental validation of FTMD was performed. The proposed FTMD device was able to significantly enhance the damping ratio of the core structure, according to the results of both experiments and simulations. The selected steel slide shaft had a near-perfect damping coefficient, the proposed FTMD may significantly reduce the amplitude of the structural resonant peak over the studied excitation frequency domain.

Identification of the viscoelastic properties of soft materials using a convenient dynamic indentation system and procedure

The responses of soft structures such as tissue depend on their viscoelastic properties. Therefore, the knowledge of the elastic and damping properties of soft materials is of great interest. This paper presents the identification of the viscoelastic properties of soft materials using a convenient dynamic indentation system and procedure. Using an electromagnet, a force is applied to a rigid sphere located at the soft-material interface and the dynamic response of the sphere is recorded using a high-speed camera. The recorded video is processed to identify the displacement of the sphere as a function of time. The dynamic response of the sphere located at the soft-material interface is predicted using an analytical model that considers the shear modulus and density of the soft sample, the radiation damping due to shear waves, and the radius and density of the sphere. By matching the measured and predicted steady-state displacements of the sphere, the shear modulus of the soft sample is determined. The viscous damping ratio of the soft sample is identified by using an equivalent viscous damping ratio for the soft sample in the analytical model and matching the measured and predicted oscillation amplitudes of the sphere. Experiments and analyzes are performed using gelation phantoms with different mechanical properties, spheres of different materials and sizes, and different force levels to verify the system and procedure. Three experiments are performed for each gelation phantom, sphere, and external force, and the repeatability of the results is presented. The results show that the dynamic indentation system and procedure presented in this study can be conveniently used to determine the viscoelastic properties of soft materials in practical applications.

Study on Interaction of RC Pile-Soil with High Reinforcement Ratio of Integral Abutment Bridges under Quasi-Static Test

In order to improve the ability of the reinforcement concrete (RC) pile foundation of integral abutment to absorb the horizontal reciprocating deformation under the action of temperature or earthquake, a pseudo-static low cycle test on interaction of pile-soil with high reinforcement ratio was carried out. The failure location, hysteresis curve, skeleton curve and horizontal deformation of three piles with different reinforcement ratios were compared. The test results show that, with the increase of the reinforcement ratio, the crack of the RC pile develops along the pile body to the depth, and the pile body failure area and the position where the maximum bending moment moves down, the crack resistance of the pile body is improved, and the effective interaction pile length increases; The test results also show that the hysteresis curve of the model pile becomes fuller with the increase of the reinforcement ratio, compared with the RCP-1 specimen with the lowest reinforcement ratio, the equivalent viscous damping ratio of the RCP-3 specimen is increased by 31.6%, and the energy dissipation capacity is improved. In addition, with the increase of the reinforcement ratio, the bearing capacity and deformation capacity of model piles are greatly improved. Compared with RCP-1 specimen, the ultimate bearing capacity of RCP-3 specimen increased by 150%, and the corresponding ultimate displacement increased by 153%. Increasing reinforcement ratio can significantly improve the mechanical properties and deformation capacity of RC pile.

Hysteresis and damping properties of steel and polypropylene fiber reinforced recycled aggregate concrete under uniaxial low-cycle loadings

To investigate the hysteresis and damping properties of fiber-reinforced recycled aggregate concrete (FRAC), a series of cyclic compressive tests of SF-reinforced natural aggregate concrete (SF-R-NAC), SF-reinforced RAC (SF-R-RAC), and PPF-reinforced RAC (PPF-R-RAC) with different fiber contents were carried out. The development law of residual strain was explored, and the relationship between residual strain and unloading strain was suggested. Also, a modified constitutive model of the stress–strain relationship was proposed. Variation of the hysteretic characteristics of FRAC including hysteretic strain energy and residual strain energy under cyclic compressive loadings was analyzed. An equivalent hysteretic viscous damping ratio was suggested and analyzed by using based on Jacobsen’s approach. Furthermore, a new hysteretic viscous damping model represented by residual strain was proposed accounting for the fiber content. Based on the modified constitutive model, the hysteretic viscous damping model is predicted and analyzed to verify the effectiveness and accuracy of the model.

Cyclic Responses of Two-Side-Connected Precast-Reinforced Concrete Infill Panels with Different Slit Types

This study aimed to study the cyclic behavior of two-side-connected precast-reinforced concrete infill panel (RCIP). A total of four RCIP specimens with different slit types and height-to-span ratios modeled at a one-third scale were tested subjected to cyclic lateral loads. The failure mode, hysteretic behavior, lateral strength, stiffness degradation, ductility, and energy dissipation capacity of each RCIP specimen were determined and analyzed. The specimens experienced a similar damage process, which involved concrete cracking, steel rebar yielding, concrete crushing, and plastic hinge formation. All the specimens showed pinched hysteretic curves, resulting in a small energy dissipation capacity and a maximum equivalent viscous damping ratio lower than 0.2. The specimens with penetrated slits experienced ductile failure, in which flexural hinges developed at both slit wall ends. The application of penetrated slits decreased the initial stiffness and lateral load-bearing capacity of the RC panel but increased the deformation capacity, the average ultimate drift ratios ranged from 1.41% to 1.99%, and the lowest average ductility ratio reached 2.48. The specimens with high-strength concrete resulted in a small slip no more than 1 mm between the RC panel and steel beam, and the channel shear connectors ensured that the RC infill panel developed a reliable assembly with the surrounding steel components. However, specimens with concealed vertical slits (CVSs) and concealed hollow slits (CHSs) achieved significantly higher lateral stiffness and lateral strength values. Generally, the specimens exhibited two-stage mechanical features. The concrete in the CVSs and CHSs was crushed, and flexural plastic hinges developed at both ends of the slit walls during the second stage. With increasing concrete strength, the initial lateral stiffness and lateral strength values of the RCIP specimens increased. With an increasing height-to-span ratio, the lateral stiffness and strength of the RC panels with slits decreased, but the failure mode remained unchanged.

Experimental investigations into the mechanical performance of glulam dowel-type connections with either bolts or screws as fasteners

Dowel-type connections are the most common connections in glulam structures. Bolts are often used as fasteners for dowel-type connections. However, the clearance between the bolts and the pre-drilled bolt holes leads to low rotational stiffness and insufficient moment-resisting capacity. To achieve better mechanical performance, screws can be used as alternative fasteners for dowel-type connections. In this paper, monotonic and cyclic loading tests were conducted on glulam dowel-type connections with either bolts or screws as fasteners. The failure modes, moment-resisting capacity, ductility ratio, stiffness degradation, and equivalent viscous damping ratio of the specimens were analyzed and reported. Results showed that compared with traditional bolted connections, the screwed connections had larger moment-resisting capacity and better ductility. The hysteretic loops of the screwed connections were plumper, and the pinching effect was gentler compared to those of traditional bolted connections.

Cyclic behaviour of a novel torsional steel-tube damper

A novel metallic damper with torsional-yielding on the circular steel tube, called torsional steel-tube damper (TSTD), is proposed in this paper. Four specimens are designed for testing under cyclic loading to investigate their cyclic behaviour. The torsional-yielding mechanism contributes to the uniform yielding at the tube wall, results in an outstanding hysteretic performance and a high equivalent viscous damping ratio of about 0.5. Then the finite element analysis method is used for simulating the tested specimens, and the stress, strain, and parametric influence of the damper model are analyzed. Furthermore, a modified Bouc-Wen model is proposed to describe the cyclic behaviour of the tested specimens. The particle swarm optimization algorithm is used for identifying the model parameters. The identification results indicate that the modified Bouc-Wen model can accurately predict the hysteretic behaviour of the proposed damper. Finally, the proposed damper is implemented in a reinforced concrete frame model, and the nonlinear dynamic analysis method is adopted to assess the feasibility of the damper.

Experimental study of traditional Chuan-dou frames infilled with wood panels under in-plane cyclic load

The Chuan-dou type of structure is a traditional architecture style that widely exists in rural China, with a large amount of its partition using wood as a raw material. To study the seismic behavior of Chuan-dou frames infilled with wood panels, four full-scaled single-story specimens have been designed and put through the quasi-static test. The failure modes, the hysteretic and envelop curves, the stiffness and strength degradation, the energy dissipation , and the equivalent viscous damping ratio(EDVR) have been investigated. The experimental results show that the wood panel infills greatly improved the load-bearing capacity and lateral stiffness of the wood frames. The energy dissipated in each cycle and accumulated in the whole process suggested that the compression and friction of the wood panel played an important role. All specimens presented good energy dissipation efficiency. • The quasi-static test of four traditional Chinese Chuan-dou frames with wood panel infills have been presented. • The failures, the stiffness and strength degradation and the equivalent viscous damping ratio have been investigated. • The influence of the wood panel on the performance of the Chuan-dou frames have been analyzed.

Mechanical properties of a novel buckling restrained shear panel damper with octagon restraining plates

AbstractSteel shear panel dampers (SPDs) have been widely used for the seismic protection of structures. The seismic performance of SPD is limited by the buckling deformation and low cycle fatigue tearing of the web. This study proposes a new‐type buckling restrained shear panel damper (BRSPD), in which two octagon restrainers are utilized instead of rectangular ones. The novel BRSPD is developed to prevent its web plate from stress concentration and tearing at the early stage. A basic mechanism for the novel BRSPD was proposed. Quasi‐static tests were conducted to examine the behavior of the BRSPDs. The influence of the factors, such as the configurations of the restrainers and the gap size between the restrainer and the web plate, were investigated. The experimental results indicated that the proposed octagon restrainers can effectively restrain the out‐of‐plane deformation of the web plate. The BRSPDs with the proposed restrainers presented better energy dissipation performance than both the conventional SPD and those with rectangular restraining plates. The shape and the thickness of the restrainers had significant influence on the performance of the damper, while adding grease or rubber between the restrainer and web plate had little effect. The BRSPD with no gap between the plates had the highest equivalent viscous damping ratio.

Calibrated Equivalent Viscous Damping for Direct Displacement-Based Seismic Design of Suspended Piping Trapeze Restraint Installations

ABSTRACT Direct displacement-based seismic design has been recently proposed for the seismic design of non-structural building elements. This paper deals with the development of damping models, relating equivalent viscous damping ratio to drift amplitude, for suspended piping trapeze restraint installations for direct displacement-based seismic design. The damping models are developed using reversed cyclic test data available in the literature. First, damping models are proposed using Jacobsen’s equal area approach. The damping models developed using Jacobsen’s approach are then assessed and calibrated using nonlinear time history analyses of single degree-of-freedom archetypes representing suspended piping trapeze restraint installations in buildings.