Marcello Ciampoli

Seismic vulnerability of monumental buildings

Abstract Monumental buildings are by definition unique buildings that cannot be reduced to any standard structural scheme: this makes it difficult to evaluate their seismic reliability, because—in addition to the many uncertainties that are common to all existing (and in particular “old”) buildings—no statistics on the behaviour of similar buildings can be available. To overcome this problem, the macroelement approach has been proposed a few years ago and since then repeatedly used to analyse and compare the seismic response of monumental buildings: the structural organism is considered as the assemblage of few components (e.g. the whole facade of a church) whose behaviour is typical of the behaviour of analogous macroelements in other buildings, and whose possible collapse mechanisms can be identified. In these studies, quasi-static loads have been used, as indeed common in many analyses of the seismic behaviour of masonry structures. This paper accepts these simplifying assumptions, and shows how—assuming appropriate probabilistic properties of the relevant quantities and a “logical diagram” describing the relation between collapse of macroelements and whole building—the probability of collapse and damage of each macroelement and of the whole building under given horizontal loads can be assessed. The procedure is formulated in detail with special reference to churches, and illustrated on two example cases. The same procedure can be used as the basis of a statistical extrapolation aimed at evaluating the probability distributions of collapse and damage among monumental buildings that are similar with regard to both the macroelement typologies and the logical diagram.

Optimal planning of retrofitting interventions on bridges in a highway network

The aim of the co-ordinated research effort initiated by the Authors consists in developing life-cycle reliability-based methodologies for the management and retrofitting of deteriorating structures and lifelines. As a first step, network systems with vulnerable nodes are considered. The object of this paper is the optimal planning of retrofitting interventions on bridges included in a highway network, taking into account their deterioration and the limitation of available economic resources. The procedure is illustrated with reference to a 10-node network. It is assumed that the resources available for retrofitting are not sufficient to guarantee the required structural reliability for all bridges throughout the design service life: thence the set of retrofitting interventions is sought that maximizes the network reliability (defined as the probability of maintaining connectivity) under a constraint on the total expenditure. The allocation is performed by means of a dynamic programming procedure.

Performance-based wind design of tall buildings

A probabilistic procedure for the performance-based design of tall buildings subject to wind actions is illustrated. The central objective of the procedure is the assessment of the adequacy of the structure through the probabilistic description of a set of decision variables (DVs). Each DV is a measurable attribute that represents a specific structural performance (no collapse, occupant safety, accessibility, full functionality, admissible displacements or accelerations, etc.). The structural risk is conventionally measured by the probability of exceeding a relevant value of the corresponding DV; the probability is evaluated by taking into account the Aeolian hazard at the site, the calculated structural response and damage and the correlation between the attained damage and the relevant DV. The procedure is applied to an example case: the assessment of the comfort requirement for a 74-storey building. Probabilistic calculations are carried out in frequency domain, but the parameters of the wind velocity field are calibrated on the basis of the time histories of the forces that have been obtained by experimental tests on a 1:500 scale rigid model of the building. The occupant comfort is related to motion perception and measured by the probability of not exceeding threshold values of the across-wind acceleration at the top of the building.

Optimal allocation of resources in reduction of the seismic risk of highway networks

Abstract The optimization of preventive upgrading interventions on the bridges of a highway network in an earthquake prone area is tackled. The bridges are assumed to be the vulnerable elements of the network, whose main purpose is to connect two sites. If the probability of collapse of each bridge under an earthquake of given intensity is known, the topology of the network allows us to calculate its reliability, i.e., the probability of maintaining the connection between the source node and the destination node. To increase the reliability, preventive upgrading interventions must be designed: the main purpose of this study is to present a procedure, based on dynamic programming, which is able to distribute the interventions among the bridges so that, for a given total amount of employed resources, the increase in reliability is maximized. The applicability of the procedure is demonstrated by some complete numerical examples. Alternative choices of the objective function and other further developments are also discussed.

Heritage buildings and seismic reliability

Within ‘heritage buildings’, a distinction can be made between ‘historical buildings’, i.e. those that can be defined as buildings of artistic an/or cultural value and which are found in significant numbers, and ‘monumental buildings’ that are truly unique. This paper summarizes existing procedures for the seismic reliability assessment of both heritage building categories: statistics can be applied to ‘historical buildings’ while it appears possible to evaluate the reliability of ‘monumental buildings’ only by subjective probabilities. Specific procedures are described for both cases.

A probabilistic methodology to assess the reliability of deteriorating structural elements

Abstract A probabilistic procedure for the analysis of current and future reliability of existing structural systems is proposed: they are assumed subject to deterioration over time, due to the exposure to an aggressive environment as well as to the effects of wear during ordinary service, of improper use and maintenance and of extreme accidental events. The assumption is made that the structural elements deteriorate because of the effects of two different sets of phenomena: the first, denoted by ageing, manifest their effects on a substantially continuous basis during the structural lifetime; the others, denoted by shocks, have effects that superimpose only occasionally to the first ones. The evolution of the structural damage due to deterioration through ageing and shocks is derived as the solution of an Ito stochastic differential equation, and then used to assess the time-dependent reliability of the deteriorating structural element. In this paper the probabilistic procedure is presented and illustrated with reference to a realistic example: a reinforced concrete shear wall located in a nuclear power plant and subject to deterioration due to expansive aggregate reactions and to exposure to earthquake loading.

Bounds to the probability of collapse of monumental buildings

Abstract In recent years, the seismic reliability of monumental buildings has been the object of several studies. In particular, it has been shown in previous papers that the probabilities of collapse and damage and their distributions can be obtained by looking at a monumental building as an assemblage of macroelements of known static and collapse behaviour, and considering the relevant mechanisms: in this way, the kinematic approach to limit analysis is followed, and in rigour only lower bounds to the probability of collapse are obtained. In this paper the static theorem of probabilistic limit analysis is also introduced in order to obtain upper (i.e. “safe”) bounds to the probability of collapse under a given load. The procedure of seismic reliability assessment is exemplified on a specific church in Friuli (North-East Italy), well studied after it was damaged in the 1976 earthquake: upper and lower bounds to the probability of collapse of each macroelement and of the whole church are obtained as a function of the applied horizontal load, i.e. of the earthquake intensity.

Multi-objective optimal allocation of resources to increase the seismic reliability of highways

To reduce the risk of disruption of lifeline systems during the emergency following an earthquake (or any other disaster) preventive interventions on the existing concerned facilities are necessary, but often hindered by the limitation of the available economic resources. In this paper, procedures for the optimal allocation of these resources are presented, with special reference to the case of road networks. It is assumed that the bridges are the only vulnerable elements, and an example of application on a specific network is developed in detail. In the first part of the paper, optimization with respect to several alternative objective functions is dealt with, while in the second part multi-objective optimization is tackled. The results obtained are compared and discussed.

Seismic protection of constructed facilities: optimal use of resources

Abstract The problem is tackled of the allocation of the resources assigned for upgrading an ensemble of buildings or other constructed facilities, whose seismic reliability is not considered sufficient. The resources are allocated in order to minimize the predicted value of either the economic losses, the number of endangered persons or the risk of severance of a network. The optimization procedure, although formulated in general terms, is illustrated with reference to simple examples, in which realistic values are attributed to the relevant parameters. These examples refer to masonry buildings, whose damages can be summed with each other to obtain the total damage of the ensemble, and to a highway network, whose critical elements are reinforced concrete bridges. The presence of several discrete quantities and discontinuous relationships requires the use of specific algorithms, and in particular of dynamic programming.

A Preliminary Proposal for a Probabilistic Performance-Based Hurricane Engineering Framework

This paper proposes an innovative fully probabilistic Performance-Based Hurricane Engineering (PBHE) approach for risk assessment and design of structural systems located in hurricane-prone regions. The methodology is based on the Total Probability Theorem and disaggregates the risk assessment analysis into independent elementary components, namely hazard analysis, structural characterization, interaction analysis, structural analysis, damage analysis, and loss analysis. The proposed PBHE methodology accounts for the multi-hazard nature of hurricane events by including the separate effects of, and the interaction among, hurricane wind, flood, windborne debris, and rainfall hazard. A review of existing models with the ability to describe the different sources of hazard is performed, and a consistent vector of intensity measures for hurricane hazard analysis is proposed. The PBHE approach illustrated in this paper represents a first step toward a rational methodology for risk assessment and design of structures subjected to multi-hazard scenarios. INTRODUCTION Performance-Based Engineering (PBE) is a general methodology that (1) defines the performance objectives for structural systems during their design life, (2) provides criteria and methods for verifying the achievement of these performance objectives, and (3) offers appropriate methodologies to improve the design of structural systems. In the last two decades, significant research efforts have been devoted to the development of PBE in earthquake engineering (Ellingwood 2001, Porter 2003), and have led, e.g., to the Pacific Earthquake Engineering Research center (PEER) Performance-Based Earthquake Engineering (PBEE) framework (Porter 2003). Several motivations have generated significant interest in the possible development and extension of PBE to other subfields of civil engineering (Augusti and Ciampoli 2008). In particular, Performance-Based Blast Engineering has received considerable attention in the US after the terrorist attacks of September 11, 2001 (Hamburger and Whittaker 2003). Other PBE 1618 Structures Congress 2011