Silvia Alessandri

Seismic Assessment of Petrochemical Piping Systems Using a Performance-Based Approach

The need of enhanced seismic analysis and design rules for petrochemical piping systems is widely recognized, where the allowable stress design method is still the customary practice. This paper presents an up-to-date performance-based seismic analysis (PBSA) of piping systems. The concept of performance-based analysis is introduced and a link between limit states and earthquake levels is proposed, exemplifying international code prescriptions. A brief review on seismic design criteria of piping systems is then provided by identifying the main critical issues. Finally, the actual application of the performance-based approach is illustrated through nonlinear seismic analyses of two realistic petrochemical piping systems.

Seismic vulnerability analysis of storage tanks for oil and gas industry

OIL AND GAS TRANSPORTATION LINE components are particularly vulnerable to natural hazard events. Steel tanks are recognized as the most vulnerable equipment to seismic action, whose damage may result in the release of materials and thus the increase of overall damage to nearby areas. The seismic vulnerability of tanks is commonly expressed by fragility curves, which are conditional probability statements of potential levels of damage over a range of earthquake intensities. This paper aims to present an appropriate procedure for analytically deriving fragility curves of tanks with the treatment of uncertainties. At first, the analysis of critical damage states of steel storage tanks observed during past earthquakes is presented. Possible numerical models of tanks subjected to earthquakes are then discussed. An overview of seismic fragility methodologies for tanks is next presented. Attention is paid to an analytical method, i.e. cloud method, which is conducted by using a probabilistic seismic demand model and non-linear time-history analyses. A broad tank, which is located in a refinery in Italy, is considered for the fragility evaluation. Resulting fragility curves for critical damage states of the tank, such as the plastic rotation of the shell-to-bottom plate joint, the buckling of the bottom shell course, and the material yielding of the shell plate, show a high seismic vulnerability of the tank.

Seismic design and characterization of a new isolation system for high voltage circuit breakers based on wire-rope devices

This paper briefly describes the design and the characterization of a new base isolation system for the seismic protection of HV ceramics circuit breakers, in order to be qualified according to the standard CEI 62271-207. The solution adopted is based on the use of Wire Ropes. Accurate numerical analyses and experimental tests performed on a typical HV breaker upon a shaking table demonstrated the effectiveness of the proposed solution. An on-site installation in several Italian substations of this system has permitted to verify the simplicity and rapidity of the intervention necessary for the seismic upgrading of the circuit breaker.Copyright

Assessment of the seismic vulnerability of an old RC viaduct with frame piers and study of the effectiveness of base isolation through PsD testing

The RETRO project aims at studying the seismic behaviour of existing reinforced concrete bridges (RC) and the effectiveness of innovative retrofitting systems. Emphasis has been paid on old bridges generally not properly designed for seismic action. On the basis of a previous experimental campaign consisting of cyclically imposed displacements on 1:4 reduced scale models of a frame pier, belonging to a typical old RC highway viaduct, a new experimental activity has been proposed. Two specimens (scale 1:2.5), a frame pier of 2 levels (height 5.8 m) and a frame pier of 3 levels (height 10.3 m), have been built and tested using the PsD technique with sub-structuring technique, including the modelling of the entire viaduct to which they belong. Two test configurations have been considered: 1) retrofitted viaduct using Friction Pendulm Isolators, and an 2) as-built configuration imposing a Serviceability and Ultimate limit state conditions. For each phase of the experimental campaign model identification has been performed. The aim of the campaign was twofold: 1) increasing the knowledge on the non-linear behaviour of RC frame piers in presence of plain steel bars and detailing of the late 1950s for which few studies have been carried out, and 2) study the effectiveness of seismic isolation systems for the seismic response mitigation

Procedure for the Statistical Determination of the Design FRP-Confined Concrete Strength

Worldwide research has now reached a level of integration where an effort towards the harmonization of procedures is absolutely needed. Such harmonization may regard, for example, the various steps that lead to the definition of capacity models to be included in design codes, specifically: definition of the test setup, quantities to be measured, identification of the basic variables influencing the phenomenon, distinction between average values and other fractiles, disaggregation of the model in different parts accounting for me-chanics, fine-tuning and randomnesses, and, finally, assessment of the model against the experimental results. Test results and ensuing model developed according to this procedure would naturally lend themselves to be easily shared among the scientific community and would facilitate the task of calibrating the partial coeffi-cients, with the ambitious aim of attaining a uniform reliability level among all capacity equations. This paper, based on previous author works, proposes the application of a procedure for the development of capacity design equations to the capacity model of concrete confined with FRP. The procedure has been applied, with some improving, to a new capacity model proposal and to the one included in the Italian Instructions CNR DT 200–2004. The comparison has the aim of evaluating the uncertainties of the assumed model (both of the me-chanical model and of the basic variables) to obtain a constant level of structural reliability and to outline the implication that a not very well calibrated equation could have in the definition of the characteristic value.