U-shaped Damper Research Articles

Theoretical and experimental study on seismic performance of T-section metallic damper

The poor stiffness and strength of traditional U-shaped dampers is an issue that is addressed in the present work by the development of a new form of T-section metallic damper, termed as the TSMD. Theoretical and experimental studies are carried out to evaluate the seismic performances of TSMD. Based on the principle of virtual work and Castigliano's second theorem, theoretical formulas of yield strength and initial stiffness of TSMD are derived and verified. Stiffness, strength and energy dissipation capacity of TSMD are significantly higher than those of the U-shaped damper with the same size of flange. A finite element model which can capture the cyclic responses and fracture failures of TSMD is established. Based on the numerical simulation and parametric study, the effects of geometrical dimensions and material properties on the seismic performances of TSMD are quantified. The mechanical characteristics of the damper are significantly affected by the web width, height, flange width, and thickness of the T-section of TSMD. Shape memory alloy-made TSMD shows stronger strength hardening and fracture resistance capacities than traditional steel-made TSMD and decreases damper residual displacement after cyclic loading. This study aims to provide valuable insights into the behavior and potential applications of the TSMD.

Analytical and numerical investigation of natural rubber bearings incorporating U-shaped dampers behaviour for seismic isolation

Although Natural Rubber Bearings (NRBs) constitute a reliable and cost-effective conventional bearing system, they are rarely used for seismic isolation because of their low damping. There are various seismic isolation systems based on NRB, but they mostly have multiple drawbacks (cost, capacity, environmental, etc.). The U-shaped damper (UD) is an efficient energy dissipating device used in seismic-resistant design. However, no guidelines or procedures are available to understand its behaviour nor for design purposes. This paper presents an analytical and numerical investigation of the cyclic behaviour of the NRB system combined with UDs that allow to increase the systems’ damping capacity and seismic performance. An analytical study of the UD is performed to predict its initial elastic parameters and numerical models are developed to study the nonlinear behaviour of the NRB-UDs, under large cyclic loadings. A set of UDs and NRBs subjected to cyclic loadings are then studied to investigate their behaviour and the effect of different geometric, loading and design parameters. Results show that the UD significantly dissipates vibration energy based on its large plastic deformations and achieves comparable and predictable performances corresponding to the in-plane and out-of-plane loading directions. Its cyclic behaviour depends on geometrical parameters and material yield stress. The developed analytical formulas provide a reliable estimation of initial elastic parameters of UD, which is essential for the selection and sizing of preliminary designs of the devices. The NRB-UDs systems show a high energy dissipation capacity with stable hysteresis behaviours in any direction. Further, the performance of these devices can be easily adjusted by varying the geometry, number and cross-section of UDs, making them an effective solution that meets a wide range of seismic isolation design requirements in high and moderate seismic areas.

Evaluation of Structural Behavior of Hysteretic Steel Dampers under Cyclic Loading

This study proposes a relatively simple steel damper with high energy dissipation capacity. Three types of steel dampers were evaluated for structural performance. The first damper with U-shape had two vertical members and a semicircular connecting member for energy dissipation. The second damper with an angled U-shape replaced the connecting member with a horizontal steel member. The last damper with D-shape had a horizontal member added to the U-shaped damper. All the dampers were designed with steel plates on both sides that transmitted external shear force to the energy-dissipating members. To evaluate the structural performance of the dampers, an in-plane cyclic shear force was applied to the specimens. The D-shaped damper showed ductile behavior with excellent energy dissipation capacity after yielding without decreasing in strength during cyclic load. In other words, the D-shaped specimen showed excellent performance, with about 3.5 times the strength of the U-shaped specimen and about 3.8 times the energy dissipation capacity due to the additional horizontal member. Furthermore, the efficient energy dissipation of the proposed D-shaped steel damper was confirmed from the finite element (FE) analytical and experimental results.

Improving Seismic Behavior of MRFs by U-shaped Hysteretic Damper Along Diagonal Brace

This paper presents seismic assessment of a U-shaped hysteretic damper as an enhancement system, in moment resisting frames. The proposed system is consisted of a damping box at the middle of a diagonal brace. The box includes U-shaped steel plates welded to the side plates. When a transverse load, like earthquake, is exerted to the building, relative displacement between the stories forms and will be transmitted to the braces where energy dissipation will be achieved by adding a displacement-dependent U-shaped damper. For this purpose, the system is applied to a 2D 2-span 3-story frame to which by applying eight different earthquake records, far-field, near-field and mid-field, seismic response are evaluated. The responses are the roof displacement, inter-story drifts, root mean squared of roof displacement and base shear. Result verification is carried out via calibrating characteristics of this damper with an experimental work on a somewhat similar device conducted at the University of Toronto. The results showed that by using this system, the roof maximum displacement decreased 38.9, 40.0 and 37.1% and the maximum base shear decreased 36.5, 28.5 and 39.5% respectively under near-field, mid-field and far-field records, averagely. Similar results were observed in inter-story drifts and roof displacement RMS.

Superelastic SMA U-shaped dampers with self-centering functions

As high-performance metallic materials, shape memory alloys (SMAs) have been investigated increasingly by the earthquake engineering community in recent years, because of their remarkable self-centering (SC) and energy-dissipating capabilities. This paper systematically presents an experimental study on a novel superelastic SMA U-shaped damper (SMA-UD) with SC function under cyclic loading. The mechanical properties, including strength, SC ability, and energy-dissipating capability with varying loading amplitudes and strain rates are evaluated. Test results show that excellent and stable flag-shaped hysteresis loops are exhibited in multiple loading cycles. Strain rate has a negligible effect on the cyclic behavior of the SMA-UD within the dynamic frequency range of typical interest in earthquake engineering. Furthermore, a numerical investigation is performed to understand the mechanical behavior of the SMA-UD. The numerical model is calibrated against the experimental results with reasonable accuracy. Then, the stress–strain states with different phase transformations are also discussed.

U-shaped metallic-yielding damper in building structures: Seismic behavior and comparison with a friction damper

This paper presents the performance of U-shaped metallic-yielding dampers in steel building frames as well as a comparison with rotational friction dampers, known as Friction Damper Devices (FDD). For this purpose, an installation detail to use a U-shaped damper in steel building frames was suggested. Next, each type of dampers was added to the 3, 5 and 10-story building frame models together with inverted V-braces. Nonlinear time history analyses were applied to models under four different earthquake ground motions. The results show that by adding dampers in both systems to moment resisting frames, nonlinear behavior is transferred from frame members to the damper system; therefore, structural damages are reduced or removed. According to the numerical results, adding the dampers decreases maximum base shear of the structure and the roof lateral displacements by cutting down about 6% to 40% and 13% to 57% using the U-shaped damper and about 15% to 41% and 9% to 53% using the FDD, respectively. Therefore, it can be said that the performance of the FDD in reducing maximum base shear of frames is slightly better than the U-shaped damper while the results are vice versa for frames lateral displacements.

Shape optimization of U-shaped damper for improving its bi-directional performance under cyclic loading

A U-shaped damper typically has a stable and saturated hysteretic performance along the in-plane direction and is usually installed in the isolation layer. However experimental study shows that the conventional U-shaped damper presents an unstable hysteretic performance when it sustains bi-directional deformations. Therefore, shape optimization is needed to improve the hysteretic performance of the U-shaped damper. To obtain an optimal shape for the U-shaped damper, a finite element (FE) model was built using a general FE analysis software called ABAQUS. Comparisons of results obtained from FE models with those obtained from experimental studies demonstrated the effectiveness of the FE models. Optimization of a U-shaped damper was carried out using the FE model. The length and shape of the straight part of the U-shaped damper were treated as optimization parameters and the enlarging the end of the straight part was adopted as the improved approach. The formula for the ratio of the energy dissipated by rate-independent and rate-dependent plastic deformation (ALLPD) to the maximum cumulative equivalent plastic strain (PEEQ) was derived though regression analysis. After four levels of optimization processes the optimal shape of the improved U-shaped damper was obtained, and the bi-directional performance was significantly improved compared to that of a conventional U-shaped damper.

A New Energy-Absorbing Device for Motion Suppression in Deep-Sea Floating Platforms

Deep-sea floating platforms are one of the most important large structures for ocean energy exploitation. A new energy-absorbing device named S-shaped Tuned Liquid Column Damper (TLCD) has been invented for the suppression of the horizontal motion and vertical in-plane rotation of a deep-sea floating platform. A conventional tuned liquid column damper has a U-shaped water tunnel to absorb the excessive energy of the main structure. The application of U-shaped dampers in deep-sea floating platforms is difficult due to the restriction of a large horizontal length. A novel S-shaped damper is proposed to retain the same amount of liquid using a shorter S-shaped tunnel. Theoretical and experimental works are conducted and prove that an S-shaped damper needs less than half the horizontal length to provide the same suppression as a U-shaped damper. A coupling calculation model is proposed and followed by the sensitivity analysis. The study demonstrates the applicability of the novel S-shaped damper for the motion suppression in deep-sea floating platforms.