Response analysis of hybrid damping device with self-centring

Lead extrusion dampers have been used to dissipate seismic energy in structures and can contribute to damage avoidance design (DAD) rocking connections. In rocking connections that utilises unbound post-tensioned tendons, re-centering of the overall structure is typical. However, the lead extrusion dampers alone are strictly dissipative, have no inherent self-centering and without careful integration into a structural system can lead to residual story drifts. In this study a modified version of High Force-To Volume (HF2V) extrusion damper is introduced to overcome the lack of inherent re-centring, while maintaining the energy absorption capability. The new device is a combination of HF2V and ring spring dampers to provide an overall device with large energy dissipation and inherent self-centering. Response spectral analysis for multiple, probabilistically scaled earthquake suites are used to delineate the displacement reduction factors due to the added damping. Hysteresis analysis of the device under a variety of seismic loadings are also performed and design plots are provided for different sized dampers. Overall, the results indicate an important trade-off between force contributions from the HF2V and ring spring components. Moreover, increasing the ring spring participation force level leads to less residual displacement in exchange for less reduction in peak displacement. This approach of larger ring spring contributions shows less dependence on the structural period, indicating a robustness of the design to a broad spectrum of ground motion inputs

Analytical Modelling of Jointed Precast Concrete Beam-to-Column Connections with Different Damping Systems

Jointed precast concrete systems typically have low inherent damping and are thus particularly suitable for applying supplemental damping systems. Analytical modelling is utilised to characterise jointed beam-to-column rocking connections, using a rate-dependent tri-linear compound version of the well-known Menegotto-Pinto rule. The analytical model is verified against near full-scale experimental results. The beam-column connections are constructed utilising Damage Avoidance Design (DAD) principles with unbonded post-tensioned tendons. High force-to-volume extrusion-based energy dissipaters are externally fitted to provide supplemental energy dissipation and modify joint hysteretic performance. Multiple joint configurations are analysed, with supplemental damping systems modified to investigate the effect of damping forces on joint hysteresis. Particular attention is given to the re-centring limit. Good agreement between the analytical models and experimental results is demonstrated, with discussion of possible improvements. Overall, system damping behaviour is significantly improved by adding the extrusion based damping system

Influence Of HF2V Damping Devices On The Performance Of The SAC3 Building Subjected To The SAC Ground Motion Suites

Recent advances in energy dissipation for structural systems can create structural connections that undergo zero sacrificial energy absorbing damage, even at extreme story drifts. However, questions exist around the ability of such structures to re-center after a major event. In this paper, the seismic performance of the as-designed SAC LA3 seismic frame with rigid moment connections at the beam ends is compared with the same frame using semi-rigid connections with high force-to-volume (HF2V) lead dissipators. Non-linear dynamic analysis is preformed using Abaqus™. With respect to re-centering, the presence of the gravity frames in the model is also considered. It was found that the placement of dissipators, ignoring the effect of gravity frames, caused a 12% increase in period due to the decreased stiffness of the connections. During design level ground shaking the semi-rigid connections with HF2V dissipators have slightly lower accelerations, up to an 80% increase in peak drift, and a 200% increase in the permanent displacement compared to the as-designed case, but no structural damage is expected. When gravity frames are considered, the floor accelerations decrease further, the peak displacements do not significantly change, but the residual storey drift ratios reduce to approximately 0.17%. This result is less than one half that of the as-designed frame, where typically gravity frame effects are not considered. The addition of braces with a stiffness 20% of the pushover stiffness ensures that the structures can re-center after any given event to within construction error. The realistic non-linear dynamic analyses combining HF2V lead dissipators with gravity frames and well-designed non-structural elements creates a system with almost no structural damage and low residual displacements

Spectral Evaluation of High Force-Volume Lead Dampers for Structural Response Reduction

Response spectra analysis across multiple earthquake suites is used to investigate the reductions in structural response from the addition of lead extrusion damping, based on ongoing research with high force/volume devices suitable for packaging in beam-column connections. Reduction factor statistics are used to characterise the response using suites of ground motions from the SAC project. Regression analysis is used to characterise reduction factors in the constant acceleration, velocity, and displacement regions of the response spectra. Peak damping reduction factors achieved with the addition of extrusion damping equal to 10% of structural weight are approximately 6.5x, 4.0x, and 2.8x for the low, medium and high ground motion suites respectively, based on a validated full-scale prototype device. The results provide initial proof-of-concept in a performance based design context, at experimentally verified forces, for using these devices to increase the seismic resilience of critical infrastructure

Is the Asymmetrical Friction Connection (AFC) a low damage dissipater?

Asymmetrical Friction Connections (AFC) are used in structures in earthquake zones to dissipate energy without causing major damage to the structural members. This means that the structure itself does not require replacement after a major seismic event. Testing of these connections has been undertaken and degradation in strength has been observed. However, (i) reasons for this degradation have not been clear, (ii) a means of assessing the strength degradation has not been available, (iii) the importance of the strength degradation (which is related to the amount of strength degradation) has not been described, (iv) the ability to reinstate the joint using new bolts is not known, and (v) effective friction factors for the connection after connection reinstatement are not known. This paper describes the testing of AFC specimens with high hardness shims (i.e. Bisalloy 500) under increasing cyclic displacements to address the issues stated above. Tests were conducted twice with the same setup. In the second test, the change in performance as a result of the first test was able to be observed. Then the bolts were replaced and tests were conducted twice more

Off-diagonal 2-4 damping technology using semi-active resetable devices

Semi-active resetable devices are an emerging and effective method of minimising structural degradation due to environmental loads. Of particular importance in implementing supplemental damping, such as resetable devices, is the ability to retrofit existing structures. However, supplemental damping also tends to increase base shear demand, limiting practical gains. The use of a two-chamber resetable device enables a control law to be used that adds damping only into quadrants 2 and 4 of the force-deflection plot, adding damping forces on the opposing diagonals to the structural force. Thus, base shear can be reduced, creating significant potential for retrofit applications. The impact of off-diagonal 2-4 damping on the displacement structural response, structural force and total base shear is investigated through spectral analysis. The 2-4 control law is shown to be the only law that can reduce the structural force as well as the total base shear for a structure; a unique result. Off-diagonal damping equal to 100% additional stiffness reduced both the structural force and total base-shear by 20-35%. Therefore, semi-active enabled off-diagonal damping could be incorporated into large scale retrofit applications where present passive approaches have significant limitation

Seismic Behaviour of the Christchurch Women's Hospital

1-pageThe objective of this project is to collect perishable seismic response data from the baseisolated Christchurch Women's Hospital. The strong and continuing sequence of aftershocks presents a unique opportunity to capture high-fidelity data from a modern base-isolated facility. These measurements will provide quantitative information required to assess the mechanisms at play in this and in many other seismically-isolated structures

No hair for spherical black holes: charged and nonminimally coupled scalar field with self--interaction

We prove three theorems in general relativity which rule out classical scalar hair of static, spherically symmetric, possibly electrically charged black holes. We first generalize Bekenstein's no--hair theorem for a multiplet of minimally coupled real scalar fields with not necessarily quadratic action to the case of a charged black hole. We then use a conformal map of the geometry to convert the problem of a charged (or neutral) black hole with hair in the form of a neutral self--interacting scalar field nonminimally coupled to gravity to the preceding problem, thus establishing a no--hair theorem for the cases with nonminimal coupling parameter $\xi<0$ or $\xi\geq {1\over 2}$. The proof also makes use of a causality requirement on the field configuration. Finally, from the required behavior of the fields at the horizon and infinity we exclude hair of a charged black hole in the form of a charged self--interacting scalar field nonminimally coupled to gravity for any $\xi$.Comment: 30 pages, RevTeX. Sec.IV corrected, simplified and shortened. Corrections to Sec.IIA between Eqs. 2.7 and Eq.2.1. First two paragraphs of Sec. VC new. To appear Phys. Rev. D, Oct. 15, 199

The Theory of Brown Dwarfs and Extrasolar Giant Planets

Straddling the traditional realms of the planets and the stars, objects below the edge of the main sequence have such unique properties, and are being discovered in such quantities, that one can rightly claim that a new field at the interface of planetary science and and astronomy is being born. In this review, we explore the essential elements of the theory of brown dwarfs and giant planets, as well as of the new spectroscopic classes L and T. To this end, we describe their evolution, spectra, atmospheric compositions, chemistry, physics, and nuclear phases and explain the basic systematics of substellar-mass objects across three orders of magnitude in both mass and age and a factor of 30 in effective temperature. Moreover, we discuss the distinctive features of those extrasolar giant planets that are irradiated by a central primary, in particular their reflection spectra, albedos, and transits. Aspects of the latest theory of Jupiter and Saturn are also presented. Throughout, we highlight the effects of condensates, clouds, molecular abundances, and molecular/atomic opacities in brown dwarf and giant planet atmospheres and summarize the resulting spectral diagnostics. Where possible, the theory is put in its current observational context.Comment: 67 pages (including 36 figures), RMP RevTeX LaTeX, accepted for publication in the Reviews of Modern Physics. 30 figures are color. Most of the figures are in GIF format to reduce the overall size. The full version with figures can also be found at: http://jupiter.as.arizona.edu/~burrows/papers/rm