Performance-based seismic risk assessment for buildings equipped with linear and nonlinear viscous dampers

Fully Flexible Electromagnetic Vibration Sensors with Annular Field Confinement Origami Magnetic Membranes

For the public welfare and safety, buildings such as hospitals, industrial facilities, and technology centers need to remain functional at all times; even during and after major earthquakes The values of these buildings themselves may be insignificant when compared to the cost of loss of operations and business continuity Seismic isolation aims to protect both the integrity and the contents of a structure Since the tolerable acceleration levels are relatively low for continued services of vibration-sensitive high-tech contents, a better understanding of acceleration response behaviors of seismically isolated buildings is necessary In an effort to shed light to this issue, following are investigated via bi-directional time history analyses of seismically isolated benchmark buildings subject to historical earthquakes: (i) the distribution of peak floor accelerations of seismically isolated buildings subject to seismic excitations in order to find out which floors are likely to sustain the largest accelerations; (ii) the influence of equivalent linear modeling of isolation systems on the floor accelerations in order to find out the range of possible errors introduced by this type of modeling; (iii) the role of superstructure damping in reducing floor accelerations of seismically isolated buildings with flexible superstructures in order to find out whether increasing the superstructure damping helps reducing floor accelerations notably Influences of isolation system characteristics and superstructure flexibility are both taken into account

Protecting vibration-sensitive contents: an investigation of floor accelerations in seismically isolated buildings

Summary
High-damping natural rubber (HDNR) bearings are extensively employed for seismic isolation of structures because of their low horizontal stiffness and high damping capacity. Filler is used in HDNR formulations to increase the dissipative capacity, and it induces also a stress softening behaviour, known as the Mullins effect. In this paper, a wide experimental campaign is carried out on a large number of virgin HDNR samples to better investigate some aspects of the stress softening behaviour, such as the direction dependence and recovery properties, and to characterize the stable and softening response under different strain histories. Test results are also used to define a model for simulating the response of HDNR bearings in shear that advances the state of the art in the description of the stress softening, which can be significant during the earthquake time history. The proposed model is used to analyse the seismic response of a simplified isolated structure modelled as an SDOF system under ground motions with different characteristics and by considering two different conditions for the bearings: one assuming the virgin (or fully recovered) rubber properties and the other assuming the stable (or fully scragged) rubber properties. The results show that, in the case of far-field records, the differences between the responses are limited although not negligible, whereas for near-fault records, modelling the bearings as being in their virgin state significantly reduces the effect of this kind of motion on isolated structures. Copyright © 2017 John Wiley & Sons, Ltd.

Stress softening behaviour of HDNR bearings: modelling and influence on the seismic response of isolated structures

A 142-m, three-span continuous footbridge over the Esino River (Italy) is considered as a case study to illustrate a number of challenging aspects in its static and dynamic design. The adoption of an optimized steel deck with a variable cross section together with the use of external prestressing tendons in the central span allows a substantial reduction of structural weights. The resulting footbridge requires a proper model for the assessment of its behavior up to the ultimate limit state as well as attention to vibration control under pedestrian loading at the service limit state. The former issue is addressed through the use of a specifically developed material and geometric nonlinear finite-element formulation. Regarding vibration control, an original combination of two different systems is used, i.e., high damping rubber (HDR) stripes and tuned mass dampers (TMDs). The HDR stripes, applied between the steel deck and the concrete floor, increase the overall damping of the footbridge, whereas t...

Andrea Dall'Asta

Papers

Dynamic system with high damping rubber: non-linear behaviour and linear approximation