450 research outputs found
Life-cycle cost assessment of inelastic buildings with tuned mass dampers in seismic areas
No full textLifecycle cost optimization of tuned mass dampers for the seismic improvement of inelastic structures
No full textThe seismic performance of tuned mass dampers (TMDs) on structures undergoing
inelastic deformations may largely depend on the ground motion intensity.
By estimating the impact of each seismic intensity on the overall cost of
future seismic damages, lifecycle cost (LCC) proves a rational metric for evaluating
the benefits of TMDs on inelastic structures. However, no incorporation
of this metric into an optimization framework is reported yet. This paper presents
a methodology for the LCC‐optimal design of TMDs on inelastic structures,
which minimizes the total seismic LCC of the combined building‐TMD
system. Its distinctive features are the assumption of a mass‐proportional
TMD cost model, the adoption of an iterative suboptimization procedure, and
the initialization of the TMD frequency and damping ratios according to a conventional
linear TMD design technique. The methodology is applied to the seismic
improvement of the SAC‐LA benchmark buildings, taken as representative
of standard steel moment‐resisting frame office buildings in LA, California.
Results show that, despite their limited performance at the highest intensity
levels, LCC‐optimal TMDs considerably reduce the total LCC, to an extent that
depends on both the building vulnerability and the TMD unit cost. They systematically
present large mass ratios (around 10%) and frequency and damping
ratios close to their respective linearly designed optima. Simulations reveal the
effectiveness of the proposed design methodology and the importance of
adopting a nonlinear model to correctly evaluate the cost‐effectiveness of TMDs
on ordinary structures in highly seismic areas
A novel bidirectional pendulum tuned mass damper using variable homogeneous friction to achieve amplitude‐independent control
No full textPassive tuned mass dampers (TMDs) are widely used in controlling structural vibrations. Although their principle is well established, the search for improved arrangements is still under way. This effort has recently produced an innovative paradigm of bidirectional pendulum TMD (BTMD) that, moving along a specially designed three‐dimensional (3D) surface, can simultaneously control two in‐plane orthogonal structural modes. In existing versions of BTMDs, energy dissipation is provided either by ordinary horizontal viscous dampers or by an original arrangement of vertical friction dampers. In this paper, a new paradigm is proposed, in which energy dissipation comes from the tangential friction arising along the pendulum surface out of an optimal spatially variable friction coefficient pattern. Within this paradigm, if the friction coefficient is taken proportional to the modulus of the pendulum surface gradient, the dissipation model results nonlinear homogeneous in the smalldisplacement domain, and the performance of the absorber, herein called the homogeneous tangential friction BTMD (HT‐BTMD), results independent from the excitation level. The present work introduces this concept, derives the analytical model of the HT‐BTMD, establishes a method for its optimal design, and numerically verifies its seismic effectiveness in comparison with viscously damped devices. The validity and feasibility of the concept are demonstrated through experimental tests on a small‐scale lab prototype, which also show the efficacy of a stepwise approximation of the homogeneous friction pattern. The new device proves a competing alternative to existing BTMDs, and homogeneous tangential friction proves a promising new paradigm to provide pendular systems with amplitude‐independent structural damping
Ball vibration absorbers with radially-increasing rolling friction
No full textBall vibration absorbers (BAs) are a simple, low-cost and compact way to realize the principle of tuned mass damping. The basic arrangement of a BA consists of a spherical mass rolling without sliding in a rubber-coated spherical cavity, and dissipating through rolling friction. In a conventional BA, the rubber coating is uniform along the cavity, and so is rolling friction. This makes the BA equivalent damping inversely proportional to the excitation amplitude, and its performance amplitude dependent. In this study, two new BA types are proposed. The first type, called the homogeneous BA (HBA), has a rolling friction radially increasing in proportion to the ball angular displacement. Hardly realizable in practice, this ideal friction model is homogeneous in the first order, ensuring an amplitude-independent optimal performance. The second type, called the discrete-homogeneous BA (DBA), is the stepwise approximation of the HBA. Not exactly homogeneous, its variable friction model can be easily realized through the juxtaposition of multiple coating regions, having different thickness or material quality. After establishing a unifying, fully nonlinear, nonholonomic analytical model, valid for various types of friction and viscous BAs, this paper first derives an optimal design procedure applicable to each type, then experimentally and numerically demonstrates (1) the validity of the homogeneous and discrete-homogeneous concepts, (2) their practical feasibility, (3) the accuracy of the proposed model, (4) the effectiveness of the design procedure, and (5) the superior performance of the HBA and the DBA over conventional friction absorbers
Modeling and design of bidirectional pendulum tuned mass dampers using axial or tangential homogeneous friction damping
No full textAs a development of the classical pendulum vibration absorber, bidirectional pendulum TMDs (BTMDs) have been recently proposed, capable to resonate with the main structure along both its horizontal directions by virtue of their optimally designed three-dimensional (3D) pendulum surface. To provide BTMDs with the required energy dissipation capability, two damping mechanisms based on respectively axial and tangential friction were invented as an alternative to ordinary viscous dashpots. The first one consists of a vertical axial-friction damper connecting the BTMD to the main structure. The second one consists of a tangential friction spatially variable along the pendulumsurface in proportion to the modulus of the surface gradient vector. Both mechanisms are fundamentally characterized by a nonlinear but homogeneous first-order model which makes their effectiveness independent from the excitation level. This paper compares the two friction paradigms with the classical viscous one. To this purpose, first a unifying fully nonlinear 3D model is established through Lagrangian mechanics, then an optimal design method is proposed, based on either H1 or H2 norm minimization criteria. Extensive numerical simulations are performed to show the pros and cons of the three damping options and of the two optimization approaches. Results demonstrate that the three types exhibit a similar performance against unidirectional excitation but that the axial-friction type loses most of its effectiveness under bidirectional excitation whenever the pendulum surface is axial- or nearly axial-symmetrical, because of the insurgence of a peculiar rotational motion which virtually deactivates the friction damper. Results also show that theH1 design criterion is more robust than theH2 design criterion, and that both criteria outperform previous simplified approaches proposed in the literature. It is concluded that, once properly designed and until stroke demand does not exceed their intrinsic stroke limitations, BTMDsare an effective vibration control strategy, which can be implemented through a variety of damping options, and that the two homogeneous friction mechanisms, and particularly the tangential one, are promising paradigms to provide amplitude-independent damping to engineering pendular systems
An innovative bidirectional rolling-pendulum vibration absorber for the seismic protection of building structures
No full textPendulum vibration absorbers with spatially-varying tangential friction: modelling and design
No full textPassive vibration absorbers are widely used in structural control. They usually consist in a single-degree-of-freedom appendage of the main structure, tuned to a selected structural target mode by means of frequency and damping optimization. A classical configuration is the pendulum type, whose mass is bilaterally constrained along a curved trajectory and is typically connected to the structure through viscous dashpots. Although the principle is well known, the search for improved arrangements is still under way. In recent years this investigation has inspired a new type of bidirectional pendulum absorber (BPA), consisting of a mass moving along an optimal three-dimensional (3D) concave-up surface. For the BPA, the surface principal curvatures are conceived to ensure a bidirectional tuning to both principal modes of the structure, while damping is provided either by horizontal viscous dashpots or by vertical friction dampers between the BPA and the structure. In this paper, a BPA variant is proposed, in which damping is produced by the variable tangential friction force developing between the pendulum mass and the 3D surface, because of a spatially-varying friction coefficient. In fact, a friction coefficient pattern is proposed that varies along the pendulum surface proportionally to the modulus of the surface gradient. With this assumption, the absorber dissipative model proves nonlinear homogeneous at low response amplitudes. The resulting homogeneous BPA (HBPA) has a fundamental advantage over conventional friction-type absorbers, in that its equivalent damping ratio is independent of the amplitude of oscillations, i.e. its optimal performance is independent of the excitation level. At the same time, the HBPA is more compact and simpler than viscously damped BPAs, not requiring the installation of dampers. This paper presents the analytical modelling framework of the HBPA and a method for its optimal design. Numerical simulations under wind and earthquake loads are reported to compare the HBPA with classical viscously damped BPAs. Finally, the HBPA proves a promising alternative to existing pendulum absorbers, and the homogeneous tangential friction proves an effective way to realize amplitude-independent damping in structural systems
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