Alberto Pavese

FRP SEISMIC RETROFIT OF RC SQUARE HOLLOW SECTION BRIDGE PIERS

The research work presented in this paper deals with the seismic assessment of hol-low bridge piers strengthened with fibre-reinforced polymer (FRP). The scope of the strengthening is to overcome some common deficiencies derived from the use of non-seismic design rules, which can often lead to inadequate response when operating in cyclic loading. The strengthening design was studied by means of a parametric analysis considering different fibres and geometrical parameters applied to typical case studies. Quasi-static cyclic tests were performed on five 1:4 scaled piers designed according to old non-seismic Italian codes and strengthened according to the previous analytical study. Efficiency of FRP strengthening was evaluated by comparing the experimental results with those obtained in a previous experimental research performed on similar non-strengthened specimens. Base shear versus lateral deflection curves, dissipated en-ergy and collapse mechanisms comparison shows the achievable effectiveness once the debonding risk has been overcome.

Evaluation of Response of an Isolated System Based on Double Curved Surface Sliders

Nowadays, the use of seismic isolation within the Italian and European context is gaining more and more acknowledgement, thanks to the high level of protection from the earthquake damage which can be guaranteed. However, the installation of devices within complex structural systems may influence the actual response due to the random variation of the installation and operating conditions with respect to the theoretical model. It is then of paramount importance a proper assessment of the overall isolating system response, considering the variability of the construction conditions. The main objective of the present work is to study the response of a particular installation system for Double Curved Surface Sliders (DCSS) for buildings with large plan development in case of construction defects related to the non-perfect co-planarity of the devices. A case study is presented, in which the effects of randomly simulated construction defects are analyzed. Preliminary results showed that the simulated construction defects have only limited influence on the global hysteretic behaviour of the system and that the simultaneous loss of contact may occur only for a limited number of devices. On the other hand, the effects of the vertical and horizontal force redistribution may cause important increase of the actions locally induced in the base connecting slab and create an eccentricity of the resultant horizontal force.

Computer Vision System for Monitoring in Dynamic Structural Testing

In combination with standard transducers and data acquisition systems, computer vision can be adopted in order to perform the analysis of the behaviour of structures during dynamic tests such as earthquake simulations on shake tables. The paper describes the design and implementation of a machine vision system aimed at providing bi-dimensional position measurement of reflective markers directly placed on test specimens. The developed solution is composed of a scalable set of acquisition units, each consisting of a high definition digital camera and a personal computer. A sequence of images is acquired by the cameras and the position of the markers in the scene is estimated by means of a software application running on the computers. Each unit can perform measurements in a single plane which is defined in a previous calibration phase. The method has many advantages over the most commonly used acquisition devices such as accelerometers and potentiometers: first, the absence of contact between the acquisition device and the tested structure, which allows the non-invasive deployment of an arbitrary number of measurement targets, which is even more important in destructive tests, for preventing the loss of expensive transducers; second, the direct calculation of the position of an object in length units, without the need of post processing like integration and conversion, as required when using accelerometers in shake table tests. Besides, in the selected plane, thanks to the adoption of infrared illumination and filters to reduce environmental lighting interferences, each unit can follow the movements of a large number of markers (up to 50 for each camera in the performed tests) with a precision of around 0.05 mm. On the other hand, the method is by itself unable to overcome problems deriving from the three-dimensional movement of the selected markers. The paper also explains the different approaches and the corresponding results obtained while solving this issue.

Eucentre TREES Lab: Laboratory for Training and Research in Earthquake Engineering and Seismology

Italian awareness about the seismic vulnerability of its building stock dramatically increased after two earthquakes hit the nation: Umbria-Marche earthquake (1997) and Molise earthquake (2002). These two seismic events caused important losses in terms of human life as well as to the economic and artistic wealth. From here the decision to take important actions aiming to the reduction of the national seismic risk: creation of a new seismic zonation of Italy; adoption of a new seismic code; foundation of a research center on earthquake engineering. The paper reviews the development of Eucentre Foundation (European Centre for Training and Research in Earthquake Engineering) and its experimental laboratory TREES Lab (Laboratory for Training and Research in Earthquake Engineering and Seismology). A brief description of the experimental facilities at TREES Lab is reported, describing the principal characteristics of Shaking Table, Bearing Tester System, Reaction Wall-Strong Floor Structure and Mobile Unit. Furthermore, an introduction to some past and current research projects is given to explain what can be done exploiting the capabilities of the TREES Lab facility. Finally, the experimental activities within the SERIES (Seismic Engineering Research Infrastructures for European Synergies) project are described.

Equivalent uniaxial accelerogram for CSS-based isolation systems assessment under two-components seismic events

ABSTRACT Concave surface slider (CSS) devices represent an effective solution for base-isolation design problems. In such isolators the energy dissipation capability is induced by the sliding motions which occur at one or more sliding interfaces. The spherical shape of the sliding surfaces provides a significant recentering behavior, by means of the stepwise projection of the applied vertical load with respect to both horizontal directions. For two-components earthquake excitations, the recentering force is computed as a linear spring with respect to displacements along the main directions of motion; whereas, the frictional response is returned by the stepwise projection of the total frictional force, which is aligned with respect to the trajectory of the device: thus, a bi-axial interaction of the directions of motion has to be accounted for, when a friction-based device is modelled. However, available commercial software which can capture such a behavior are limited. In this work an analytical procedure is defined, for the computation of an “equivalent uniaxial accelerogram” for the seismic assessment of a base-isolated structure, subjected to a bi-directional earthquake. Thanks to the proposed theory, it is possible to compute a single ground acceleration time-history, related to a proper direction angle, which can reproduce the same effects of a two-components seismic event on a base-isolated structural system: the analogy between the equivalent uniaxial and the bi-directional events has been studied in terms of acceleration, velocity and displacement spectra respectively. Results for the base-isolated structure have been analyzed in terms of displacement, absolute acceleration and interstorey shear responses.

Seismic Vulnerability Assessment of an Infilled Reinforced Concrete Frame Structure Designed for Gravity Loads

In the last decades, particular attention has been paid to the seismic vulnerability of existing reinforced concrete buildings designed for gravity loads only. Such buildings, designed before the introduction of capacity design in modern seismic codes, are very common, particularly in seismic prone countries of the Mediterranean area. Due to poor detailing and lacking of capacity design principles, high vulnerability has been highlighted in several past studies. In this article, inadequate seismic response and peculiar damage pattern are investigated by means of shake table tests performed on a 1:2 scaled 3-story infilled prototype. Particular attention is given to the role of beam-column joints and frame-panel interaction. The effectiveness of the EC8-based assessment approach is then evaluated; both linear and nonlinear numerical models, with different levels of sophistication, have been implemented in order to explore their behavioral aspects.

Experimental dynamic response of spherical friction-based isolation devices

ABSTRACT This article presents a summary of the experimental dynamic response of curved surface sliders as resulting from more than 1000 dynamic tests on about 60 different types of devices performed at the laboratory of the EUCENTRE foundation. Two different kinds of low-friction sliding materials have been employed in the devices, derived from polyamide (PA), or polyethylene (PE) materials. The rate of change of the dynamic friction coefficient as a function of sliding velocity and contact pressure is assessed and the transition phase between dynamic and static friction, with the consequent possible evidence of static/stick-slip phenomena, has been carefully considered.

Development of Software and Hardware Architecture for Real-Time Dynamic Hybrid Testing and Application to a Base Isolated Structure

Real-Time Dynamic Hybrid Test (RTDHT) is a promising experimental testing technique, which combines numerical simulation and experimental testing of physical specimen in a complementary and efficient way. However, taking advantage of both numerical and experimental capabilities requires facing issues related to both environments. In this article, the design and implementation of a RTDHT hardware and software architecture is presented. Issues related both to the numerical model and to the experimental setup are discussed; this is done from a general perspective, as well as referring to a base isolated structure which represents the implemented case study.

Investigation of the consequences of mounting laying defects for curved surface slider devices under general seismic input

ABSTRACT Experimental studies performed on friction-based isolators have shown widely sparse frictional response, as direct effect of intrinsic properties of the devices and the vertical load variation. Moreover, in practical applications mounting laying defects consisting of uneven inclinations of the sliding surfaces with respect to the horizontal plane have been recognized as a potential cause of deviation from the response assumed in the design phase. In this paper mono and biaxial motions of a base-isolated RC building have been investigated; the aim of the work is to identify the effects of both laying defects and friction variation on the seismic response.

Experimental vs. Numerical Simulations: Seismic Response of a Half Scale Three-Storey Infilled RC Building Strengthened Using FRP Retrofit

Received: January 12, 2017 Revised: May 15, 2017 Accepted: July 10, 2017 Abstract: Background: In the field of seismic analysis of structures, the use of appropriate Finite Elements software packages to manage more complex numerical models and to run more sophisticated analyses (such as nonlinear dynamic time-history analyses) in very short runtimes has increased significantly in the last decades. In order to have confidence in the numerical results of these complex analyses, it has become an increasingly widespread practice to verify and validate the FE computers programs against literature case studies as well as experimental results. Focusing on this latter aspect, shaking-table experiments on real buildings play an important role in understanding the actual behaviour of such structures.