Fabrizio Paolacci

Design of yielding or friction-based dissipative bracings for seismic protection of buildings

The problems of designing dissipative bracing systems, based on yielding or friction mechanisms, for the seismic protection of buildings, either for new structures or the retrofitting of existing buildings are considered. After introducing a one-degree-of-freedom (one-DOF) model of a building equipped with dissipative bracings, inelastic response spectra, useful for designing the bracings, are considered. The extension of the design methodology to multi-DOF systems is also considered, paying particular attention to the distribution of stiffnesses and strengths within the structure. The results of a broad parametric investigation of simple shear-type models are discussed.

Seismic vulnerability mitigation of liquefied gas tanks using concave sliding bearings

The aim of this paper is to evaluate the effectiveness of a concave sliding bearing system for the seismic protection of liquefied gas storage tanks through a seismic fragility analysis. An emblematic case study of elevated steel storage tanks, which collapsed during the 1999 İzmit earthquake at Habas Pharmaceutics plant in Turkey, is studied. Firstly, a fragility analysis is conducted for the examined tank based on a lumped-mass stick model, where the nonlinear shear behaviour of support columns is taken into account by using a phenomenological model. Fragility curves in terms of an efficient intensity measure for different failure modes of structural components demonstrate the inevitable collapse of the tank mainly due to insufficient shear strength of the support columns. A seismic isolation system based on concave sliding bearings, which has been demonstrated a superior solution to seismically protect elevated tanks, is then designed and introduced into the numerical model, accounting for its non-linear behaviour. Finally, a vulnerability analysis for the isolated tank is performed, which proves a high effectiveness of the isolation system in reducing the probability of failure within an expected range of earthquake intensity levels.

MAIN ISSUES ON THE SEISMIC DESIGN OF INDUSTRIAL PIPING SYSTEMS AND COMPONENTS

A significant number of damages in piping systems and components during recent seismic events have been reported in literature which calls for a proper seismic design of these structures. Nevertheless, there exists an inadequacy of proper seismic analysis and design rules for a piping system and its components. Current seismic design Codes are found to be over conservative and some components, e.g., bolted flange joints, do not have guidelines for their seismic design. Along this line, this paper discusses about the main issues on the seismic analysis and design of industrial piping systems and components. Initially, seismic analysis and component design of refinery piping systems are described. A review of current design approaches suggested by European (EN13480:3) and American (ASME B31.3) Codes is performed through a Case Study on a piping system. Some limits of available Codes are identified and a number of critical aspects of the problem e. g., dynamic interaction between pipes and rack, correct definition of the response factor and strain versus stress approach, are illustrated. Finally, seismic performance of bolted flange joints based on the results of experimental investigations carried out by the University of Trento, Italy, will be discussed.

Pseudo-Dynamic Testing Based on Non-linear Dynamic Substructuring of a Reinforced Concrete Bridge

The assessment of the seismic performance of an old concrete bridge was conceived within the RETRO Transnational Activity funded by the SERIES research project. The installation of isolation devices -one per column- for each pier portal frame interposed between the cap beam and the deck was proposed as seismic retrofit, fully complying with Eurocode 8 requirements. A comprehensive set of hybrid simulations was conceived to simulate the dynamic response of the existing 400 m span Rio Torto Viaduct, both in the isolated and the non-isolated cases. In order to support the pseudo-dynamic test design, a refined fiber based FE model of the bridge was implemented in the well-known OpenSEES software; time history analyses highlighted appreciable nonlinearities in the dynamic response of the system under the Serviceability Limit State (SLS). As a consequence, a Numerical Substructure (NS) capable of reproducing such nonlinear behaviour was deemed necessary. Nonetheless, implementation issues relevant to the typical solving time dictated by the controller time step, made the use of complex fiber based FE models not suitable for testing purposes. In this perspective, the paper presents the design of a suitable NS, which is based on a rational and nonlinear reduction of the aforementioned OpenSEES Reference Model (RM). Moreover, in order to impose a consistent degradation of physical and numerical piers, a testing procedure based on recursive identification and model updating sessions is proposed. The numerical tools and simulations developed in the project are presented and discussed.

Analysis of the Seismic Risk of Major-Hazard Industrial Plants and Applicability of Innovative Seismic Protection Systems

Seismic action can cause serious accidents to industrial plants as shown in several occasions. The actual worldwide situation of major-hazard plants against earthquakes should be considered as critical. For instance, in Italy about 30% of industrial plants with majoraccident hazards are located in areas with a high seismic risk. In addition, in case of a seismic event, the earthquake can induce the simultaneous damage of different apparatus, whose effects can be amplified because of the failure of safety systems or the simultaneous generation of multiple accidental chains. (a) (b)

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.

Assessment of the Seismic Behaviour of a Retrofitted Old R.C. Highway Bridge Through PsD Testing

The RETRO project aims at studying the seismic behaviour of existing reinforced concrete (RC) bridges and the effectiveness of innovative retrofitting systems. A typical as-built RC highway viaduct, designed primarily for gravity loads, has been analysed experimentally. The objective of the laboratory test program is twofold: (1) improve the knowledge of the non-linear behaviour of RC framed piers without seismic detailing and (2) assess the effectiveness of seismic isolation systems as a structural mitigation measure. Two large scale framed piers with two and three levels were re-designed and tested using the PsD method with hybrid (analytical and experimental) simulation. Two test configurations were considered: (1) the as-built bridge layout and (2) the viaduct retrofitted by means of Friction Pendulm (FP) isolators. The seismic performance evaluation was carried out at two limit states, i.e. at serviceability and ultimate limit states. The experimental tests stressed the high structural vulnerability of the viaduct, confirmed by the extensive shear damage in the transverse beams and the fix-end rotation effects generated by the bond slip of plain steel bars in the columns embedded in the foundation. The effectiveness of the isolation system with FP devices was also demonstrated. Nevertheless, the friction of the FP devices is a critical response parameter which may vary significantly because of the pressure due to vertical loads, strong motion velocity and temperature. The reliable evaluation of the friction parameter is of paramount importance to prevent the onset of damage within the framed piers.

Refined and Simplified Numerical Models of an Isolated Old Highway Bridge for PsD Testing

RETRO’ project aims at studying the seismic behaviour of existing reinforced concrete (RC) bridges and the effectiveness of retrofitting systems based on seismic isolation of the deck of the viaduct. The research program focuses on a typical non-compliant bridge system for earthquake loading, designed for gravity loads only. The prototype structure is the Rio Torto bridge system, which is located in a region of medium seismic hazard in Italy. The seismic vulnerability of the as-built framed pier bridge is first assessed. A typical seismic isolation system, employing slide spherical bearings, is then designed as a passive control retrofitting measure. The present chapter discusses the non-linear response of the Rio-Torto viaduct in the “as-built” and “isolated” configurations. The seismic performance assessment is carried out by utilizing refined non-linear structural models implemented in an advanced and reliable computer platform. The earthquake behaviour of refined models used for the sample structure accounts for non-linear phenomena of the viaduct, e.g. strain penetration of plain bars, shear deformation of transverse beams, flexural deformations in columns and beams. The finite element models are calibrated on the basis of experimental tests results. The assessment of the seismic response system is investigated in terms of local and global response parameters. In addition, the effectiveness of the isolation systems used as a retrofitting system is also investigated numerically. The outcomes of the comprehensive nonlinear analyses are used to simulate the seismic response of the viaduct in the as-built and isolated configurations during Pseudo-dynamic testing, which is illustrated in a companion chapter.

Quantitative Seismic Risk Assessment of Process Plants: State of the Art Review and Directions for Future Research

Earthquakes represent a class of Natural-Technical hazards which in the past has been responsible of major accidents and significant losses in many industrial sites. However, while codes and standards have been issued to design specific structures and equipment in the civil and industrial domain, established procedures for Quantitative Seismic Risk Assessment (QSRA) of process plants are not yet available. In this paper a critical review of seismic risk assessment methods applicable to process plants is carried out. Their limitations are highlighted and areas needing further research are identified.Copyright

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.