Alessio Lupoi

On the role of road networks in reducing human losses after earthquakes

A road-network reliability analysis for a scenario seismic event is performed for a region of southern Italy characterised by a large number of small to medium municipalities quite close to each other and served by a dense network of roads. Among the many functions of the road network, whose links may fail after an earthquake due to the collapse of the bridges within them, the one selected for the present study is that of allowing rescue operations to be carried out at the sites of collapsed schools. For this to be possible, connection must be maintained between schools that survived, rescue centres and hospitals. Required elements for the study are the fragility curves of the bridges, the schools, the hospitals and the rescue centres. Output of the study is the expected value of the fraction of the total population in the area that is in need of assistance and cannot be hospitalised due to either failure of the network or other vulnerable components.

A probabilistic method for the seismic assessment of existing concrete gravity dams

This work presents a probabilistic seismic assessment method able to manage the physical complexity of the dam–foundation–reservoir system and the uncertainties regarding structural data and external actions. The seismic response of the structure is estimated from a reduced number of dynamic time-history analyses, performed employing a finite element discretisation of dam body, reservoir water and foundation rock mass. The system fragility curves are then obtained via a standard Monte Carlo simulation procedure. The methodology has been applied to the case of Kasho Dam, a concrete gravity dam located in Japan, which experienced in 2000 the Western Tottori earthquake with no damage at dam body. The assessment has been carried out with respect to an operational limit state, for which several ‘critical’ failure mechanisms have been identified and numerically evaluated, both in terms of demand definition and capacity evaluation.

Seismic fragility of reinforced concrete structures using a response surface approach

A statistical approach for time-variant system-reliability problems has been developed and investigated in this study. The basic proposal is to use a response surface, characterised by a statistical model of the mixed type, to represent the capacity part in an analytical limit state function. The fragility of the system is then calculated by SORM analysis, with the constructed empirical limit state function as input. The developed method has been applied to a reinforced concrete frame: investigations have been carried out to check the stability and accuracy of the suggested procedure.

SEISMIC RISK ASSESSMENT OF RC STRUCTURES WITH THE "2000 SAC/FEMA" METHOD

The applicability of a new, fully probabilistic approach to seismic design and assessment of reinforced concrete (RC) structures is investigated. Fundamental advantages of the method are mathematical simplicity and comparatively light computational effort. The original formulation, which was developed for steel structures, is first illustrated; ah extension which allows consideration of multiple failure mechanisms, typical of RC structures, is then proposed. The applicability of the method is demonstrated through an example: the seismic risk of a four storey RC building that was not designed for seismic resistance is evaluated. Three failure mechanisms are considered: joint failure, column shear failure and drift failure.

The Role of Probabilistic Methods in Evaluating the Seismic Risk of Concrete Dams

A recent research on seismic assessment of concrete dams is illustrated in this chapter, including a brief comparison with other available approaches to the subject. The work of the authors has been focused on development and validation of a probabilistic methodology taking into account the uncertainties affecting structural data and external actions as well as the physical complexity of the dam-foundation-reservoir system. The seismic response of such a system is estimated from a reduced number of dynamic finite element analyses and the corresponding fragility curves are obtained via a Monte Carlo simulation procedure. The main results of the application of the proposed methodology to the case of an existing concrete gravity dam are finally summarized.

Methods for seismic risk analysis: State of the art versus advanced state of the practice

The core of the paper consists of the illustration of a method for seismic reliability analysis of non-linear structures. The method, which is a development over a recent previous proposal, is quite comprehensive in scope since it includes consideration of randomness in the input, in the mechanical properties of the structure and in the limit-state, or capacity, conditions. Essentially, the problem is formulated as the out-crossing of the response process out of a (scalar) safe threshold, and this problem is solved by time-invariant FORM methods. An application to an idealised five-storey building demonstrates the salient theoretical and computational features of the method. The new approach is presented in a broader framework, which involves a discussion on present trends and capabilities in the area of probabilistic seismic design. For the sake of this discussion, two approaches just appeared in the literature are outlined, which are less demanding from a theoretical standpoint, and hence closer to engineering practice, but also less general in scope. It is argued that their introduction on code-assisted design would be feasible immediately with obvious advantages, while approaches of more rigorous nature would be given some more time to mature and to become more accessible to professional use.

The response of isolated bridges accounting for spatial variability of ground motion

The effects of the spatial variability of ground motion (loss of coherence, wave passage, and local site conditions) on the response of isolated bridges are investigated. Therefore, a statistical approach is adopted to represent uncertainties in both the bridge configuration and the ground motion variability. The response of isolated bridges, designed for a standard input motion, under a spatially varying ground motion, is evaluated by nonlinear time-history analyses; the system performance is measured by the displacement demand on isolators. Results show that the phenomenon affects the structural response considerably; the demand increases for the majority of isolators, irrespective of bridge configuration.

Application to a network of hospitals at regional scale

The seismic performance of a regional Health-Care System (HCS) is investigated. The earthquake effects both on hospitals and on the Road Network (RDN), connecting towns to hospitals, are evaluated and the interaction among them accounted for. Victims move to hospitals until their request for a bed or for a surgical treatment is satisfied, if possible. A novel “dynamic” model for hospitalization is developed and implemented. The road network is modelled in connectivity terms. The vulnerability of hospitals and bridges is expressed by pre-evaluated fragility curves. Seismic hazard is described by a state-of-the-art model. The reliability problem is solved by Monte Carlo simulation. The un-hospitalized victims, the risk that hospitals are unable to provide medical care, the demand of medical care on hospitals, the hospitalization travel time, are among the useful results of the analysis. The methodology is exemplified with reference to a case-study region, with population of 877,000, 20 towns, 5 hospitals and 32 bridges.

Component Fragilities and System Performance of Health Care Facilities

Hospitals belong to the so-called “complex-social” systems since they depend on several components of different nature to function properly and they provide a societal service to citizens. The basic components of a hospital are: the staff, the organization and the facility. They jointly “contribute” to provide medical care to patients. This chapter focus on the seismic assessment of the facility. A hospital has to be capable of providing medical after the occurrence of a major earthquake; hence the facility target performance is set as operational. Such a performance depends on the response of both structural and non-structural elements. Fragility curves for “typical” non-structural elements are provided. A probabilistic-based procedure for the evaluation of the fragility curve of the facility is then derived. Finally, an index adequate to measure the performance of the hospital under emergency condition is proposed.

A Bayesian Network Model to Assess Seismic Risk of Reinforced Concrete Girder Bridges

Infrastructure owners or governmental agencies need tools for rapid screening of assets in order to prioritize resources allocation for detailed risk assessment. This paper provides one such tool based on Bayesian Networks and aimed at replacing so-called generic/typological seismic fragility functions for reinforced concrete girder bridges. Resources for detailed assessments should be allocated to bridges with highest consequence of damage, for which site hazard, bridge fragility and traffic data are needed. The presented Bayesian Network predicts the seismic fragility of a bridge at a given site based on data that can be obtained by visual inspection at low cost. Results show that the predicted fra- gilities are of sufficient accuracy for establishing relative ranking based on risk and assign priorities. While the actual data employed to train the network (establishing conditional probability tables) refer to the Italian bridge stock, the network structure and engineering judgment behind it can be easily transferred to other situations.