INVESTIGATION OF THE LATERAL RESPONSE OF FRICTION-BASED ISOLATORS UNDER MULTI-CYCLIC EXCITATIONS

The frictional response of Concave Surface Slider (CSS) devices has been more and more investigated both experimentally and numerically. These isolators have shown many advantages in comparison to the commonly used typologies of devices, such as lead rubber bearings or low and high damping rubber bearings: when implemented in structural systems, the eccentricity of the resultant base shear with respect to the center of mass is significantly reduced, since the lateral response of the devices is a direct function of the applied vertical force, i.e. the weight of the structure; furthermore new innovative sliding materials have been studied and implemented in real applications, in order to achieve high levels of energy dissipation, together with a high recentering capability, due to the geometry of the steel sliding surfaces. On the other hand, a number of issues about the behavior of friction-based isolators still have to be accurately analyzed. Among the others the distribution of the vertical load applied to the device is usually assumed constantly smeared on the sliding pad: however, recent research works have shown rather than constant distributions of contact pressure and this aspect is expected to cause variations in the commonly known dependency of the friction coefficient on the vertical load. Moreover, when a CSS device is subjected to long lasting dynamic excitations, the so called “cyclic effect” leads to a decay of the friction coefficient during time. Such a decay trend can be analyzed in terms of friction coefficient as a function of the cumulative dissipated energy, and can be fully described by an exponential equation, properly calibrated; the decay behavior is also supposed to be characterized by dependencies on both sliding velocity and contact pressure, i.e. vertical load. Then, a direct comparison between flat and concave sliding motions needs to be carried out, aiming at highlighting the differences in the frictional response of these typologies of movements. In the present work the dynamic behavior of a friction based device has been deeply examined, thanks to the outcomes of a wide experimental campaign carried out at the EUCENTRE TREES Lab in Pavia on full scale flat and curved sliders, equipped with innovative sliding materials. Precisely, the cyclic effect caused on the friction coefficient by long lasting bi-directional dynamic motions has been characterized, by assuming several combination of sliding velocity and vertical load values. Moreover, the comparison among different diameters for the sliding pads in flat motions has been studied, in order to underline any “size effect” on the frictional response. Then, the comparison between flat and curved sliding motions has been carried out. Finally, such results have also been considered analytically, aiming at evaluating the consequences of the aforementioned features on the response of structural system base-isolated with CSS devices

An overview of seismic testing needs in Europe: towards a new advanced experimental facility

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Experimental Investigation and Analytical Modeling of Prefabricated Reinforced Concrete Sandwich Panels

The behavior of prefabricated reinforced concrete sandwich panels (RCSPs) was investigated experimentally and analytically in this study. Initially, tests were carried out on single full-scale RCSPs with or without openings, reproducing the behavior of lateral resisting cantilever and fixed-end walls. The performance and failure mode of all panels tested revealed coupling between the flexure and shear response. However due to their well-detailed reinforcement, all panels exhibited a relatively gradual strength and stiffness degradation and did not suffer from sudden shear failure. Then, an analytical column model was developed for the analysis of the walls’ nonlinear response under cyclic loading. The model consists of an elastic bar with nonlinear flexural and shear springs concentrated at the column ends. It was concluded that this simple model represents very satisfactory effects of flexural and shear forces in the global response of the walls. The agreement of the proposed model with experimental response characteristics was quite good when the proper constitutive law were used.JRC.G.5-European laboratory for structural assessmen

Influence of classroom acoustics on the vocal behavior of teacers

Erroneous vocal behavior of teachers and their changes in the voice production due to poor acoustics in classrooms can be investigated through recently developed voice-monitoring devices. These devices are portable analyzers that use a miniature contact-microphone glued to the jugular notch in order to sense the skin acceleration level due to the vibration of the vocal folds. They estimate the Sound Pressure Level (SPL) at a certain distance from the speaker's mouth provided that a preliminary calibration procedure is performed, the fundamental frequency and the time dose. Two different devices are compared in this work: the former is a commercial device, whose phonation sensor is a small accelerometer; the latter, recently developed by the authors, uses an electret condenser microphone to sense the skin acceleration level. SPL and fundamental frequency are estimated over fixed-length frames and the results that refer to a sample of 25 primary school teachers and a university professor are analyzed. The duration of the voice and pause periods is investigated in order to detect the peaks of occurrence and accumulation in different conditions of reverberation. A method for the detection and analysis of the emphatic speech is also propose

Experimental Assessment of the Seismic Response of a Base-Isolated Building Through a Hybrid Simulation Technique

Base-isolated structural systems have been more and more investigated through both numerical and experimental campaigns, in order to evaluate their effective advantages, in terms of vulnerability reduction. Thanks to the lateral response of proper isolation devices, large displacement demands can be accommodated, and the overall energy of the seismic event can be dissipated, by means of hysteretic behaviors. Among the common typologies of isolators, curved surface slider devices represent a special technologic solution, with potentially high dissipative capacities, provided by innovative sliding materials. On the other hand, the overall behavior is highly non-linear, and a number of research works have been developed, aiming at the definition of the most comprehensive analytical model of such devices. The most realistic response of a base-isolated structure could be returned by a shake table test of a full-scale building. However, dimensions of the available shake tables do not allow consideration of the common load conditions, to which the isolation devices are subjected, and consequently, scaled specimens are needed, and unrealistic responses could be found. Hybrid simulations seem to solve such an issue, by accounting for an experimental substructuring, represented by a physical device tested in a testing equipment, and a numerical substructuring, consisting of a numerical model of the superstructure. Thus, a much more realistic response of the full-scale structure can be computed. In this work, the outcomes of a number of hybrid simulations have been deeply analyzed and compared to a similar numerical model. Proper non-linear constitutive laws for isolation devices have been adopted, in order to evaluate the effectiveness of design and assessment procedures, commonly adopted in real-practice applications

Investigation of the Response Variability of Base-A Isolated Building Equipped With Lead Rubber Bearings

Nowadays analytical models of seismic isolators can fairly reproduce the force response of such devices, when implemented in a large variety of structural systems, such as buildings and bridges. Consequently, realistic hysteretic rules are available for the definition of the dynamic system for Non-Linear Time History Analyses, and earthquake simulations of the considered isolated structural systems can be computed. Such models are generally defined, according to mean values of mechanical properties of isolation devices, even though a certain variability has been experimentally assessed: precisely, statistical analyses of the outcomes of test database have outlined that the main response parameters of isolators should be considered as random variables, rather than as deterministic values. On the other hand, in the common practice both design and assessment procedures are mainly based on deterministic approaches, and bound analyses are ruled in just few standard codes. The present endeavor presents a wide parametric study on a case study structure, in order to assess the variability of the main response parameters, by accounting for random mechanical properties of isolation devices. Precisely, a combination of Lead Rubber Bearings and Flat Slider devices have been considered, and the spatial layout of isolators has been defined, according to a given performance point. The structural response of the case study building has been computed through Non-Linear Time History Analyses, by extracting 10'000 individual values of mechanical properties of devices. Presented results are related to the mean response of a spectrum-compatible set of natural records, in terms of displacement and force of both superstructure and isolation system

A computational framework for fast‐time hybrid simulation based on partitioned time integration and state‐space modeling

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A framework for hybrid simulation with online model updating suitable for hard real-time computing

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A First Assessment of Carbon Nanotubes Grown on Oil-Well Cement via Chemical Vapor Deposition

In this study, carbon nanotubes (CNTs) were synthesized on an oil-well cement substrate using the chemical vapor deposition (CVD) method. The effect of synthesis process on cement was investigated in depth. In this regard, FE-SEM, RAMAN and X-Ray spectroscopy were used to characterize the cement before and after the synthesis process to reveal the modifications to the cementitious matrix and some unique morphological features of CNTs

EUCENTRE and seismic emergency: technical preparedness activities and response after the central Italy earthquake

Modul za napredne seizmičke procjene je služba za tehničku intervenciju nakon potresa koju je EUCENTRE tijekom godina razvijao kroz niz nacionalnih i europskih pilot-projekata, terenskih vježbi i izravnih iskustava nakon posljednjih velikih potresnih događaja koji su pogodili Italiju od 2009. Sustav se sastoji od službe čije se središte za izradu scenarija štete i mobilne jedinice za procjenu oštećenja na terenu nalazi u Paviji. Nakon potresa u središnjoj Italiji, EUCENTRE je oko osam mjeseci bio uključen u niz aktivnosti, uključujući tehničku podršku talijanskom Odjelu civilne zaštite, zajedničku izviđačku misiju s međunarodno prepoznatim istraživačkim institutima.The ASA (Advanced Seismic Assessment) module is a post-earthquake technical intervention service, developed over the years by the EUCENTRE Foundation through a series of national and European pilot projects, field exercises, and direct experience, after the latest major seismic events that struck Italy since 2009. The system consists of a service managed at the headquarters in Pavia for the development of damage scenarios, and of a mobile unit for the on-site damage assessments. After the Central Italy earthquake, the Foundation has been involved for about eight months in several activities, including provision of technical support to the Italian Department of Civil Protection, joint reconnaissance with internationally acknowledged research institutes