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International audience; The paper is devoted to the generation of seismic accelerograms compatible with a given response spectrum and other associated properties. The time sampling of the stochastic accelerogram yields a time series represented by a random vector in high stochastic dimension. The probability density function (pdf) of this random vector is constructed using the Maximum Entropy (MaxEnt) principle under constraints defined by the available information. In this research, a novel algorithm, adapted to the high stochastic dimension, is proposed to identify the Lagrange multipliers introduced in the MaxEnt principle to take into account the constraints. The algorithm is validated through an application for which the available information is relative to the variance of each component of the random vector representing the accelerogram, statistics on the response spectrum such as the mean value and the envelopes, statistics on the Peak Ground Acceleration (PGA) and the velocity and displacement traces (behavior of the signals at the final time) .

A straightforward methodology, named FAST , for earthquake damage assessment of infilled reinforced concrete buildings, is carried out using the consolidated framework empl oyed in Performance Based Earthquake Engineering. FAST approach carries out peak ground acceler ation (PGA) capacities calculated from mean inelastic drift capacities of inf illed reinforced concrete (RC) moment resisting frame (MRF) buildings at various damage states. The damage states ar e classified according to EMS 98 scale. FAST covers the range from slight to heavy damage states (DS1 up to DS3), not including very heavy damage and destruction (DS4 and DS5). FAST is a spectral methodology and employs IN2 cu rves. Mean PGA capacities for infilled RC MRF buildings at DS1, DS2, and DS3 can be employed for preliminary prediction of damage. A calibration of FAST is herein provided through the evaluation of root mean square deviations from a set of post-earthquake inspections collected in the area of Pettino, L’Aquila, after the 2009 earthquake.

Earthquakes are typically clustered both in space and time. Seismic h azard , expressed in terms of rate of exceedance of a ground motion intensity measure , classically refers to ma i nshock s, which means that such a rate is computed filtering the rate o f occurrence of events of largest magnitude within each cluster of earthquakes. This kind of probabilistic seismic hazard analysis (PSHA) is used for structural design or assessment in t he long - term. R ecently, a similar probabilistic approach has been adopted to perform aftershock probabilistic seismic hazard analysis ( APSHA) , c onditional to mainshock occurrence. It is to be used for short - term risk management. PSHA often refers to a h omo geneous Poisson p rocess to describe event occurrence, while APSHA models aftershock occurrence via a non - homogeneous Poisson process , whose rate depend s on the magnitude of mainshock that has triggered the considered sequence . However, the whole cluster , c omprised of mainshock and aftershocks, occurs with the same rate of the mainshock , and this paper shows how it is possible to analytically co mbine results of PSHA and APSHA to get a probabilistic seismic hazard analysis for mainshock - aftershocks seismic se quences (SPSHA) . Results of the illustrative application presented help to assess the increase in seismi c hazard considering the probability of exceeding a n acceleration threshold (e.g., that considered for design) also considering aftershocks .

In this paper the idea of the “shock-absorbing soft story concept”, originally proposed at the end of ‘60s by Fintel and Khan, is reviewed and developed within the framework of Performance Based Seismic Design. The purpose is to conceive a first-storey isolated building capable of satisfying selected seismic performance objectives. Among all the possible solutions, in this study the seismic story isolation is obtained through the insertion (only at the bottom level of the building) of special hysteretic devices, which are specifically designed in order to satisfy the prefixed seismic performance objectives. Without loss of generality, this design approach is fully detailed with reference to the specific case study of a five-storey steel frame building. The performances of the building under multiple earthquake design levels are finally verified through non-linear time-history analyses whose results confirm the effectiveness of the proposed approach.

Major earthquakes (i.e., mainshocks) typically trigger a sequence of lower-magnitude events clustered both in time and space. Recent advances of seismic hazard analysis stochastically model aftershock occurrence (given the main event) as a non-homogeneous Poisson process with rate that decays in time as a negative power law . Risk management in the post-event emergency phase has to deal with this short-term seismicity. In fact, because the structural systems of interest might have suffered some damage in the mainshock, possibly worsen by damaging aftershocks, the failure risk may be large until the intensity of the sequence reduces or the structure is repaired . At the state-of-the-art, to quantitatively assess the aftershock risk serves to as building tagging , that is to regulate occupancy. The study, on the basis of age-dependent stochastic processes, derived closed-form approximations for the aftershock reliability of simple elastic-perfectly-plastic damage-cumulating systems, conditional on different information about the structure. Results show that, in the case hypotheses apply, the developed models may represent a handy tool for risk-informed tagging by stakeholders and decision makers.

Analytical fragility curves corresponding to a prescribed limit state can be evaluated by propagating the various sources of uncertainty in the performance assessment of structures. This work proposes an efficient Bayesian parameter estimation method suitable for fragility curves based on a given probability model; in particular, the bi - parameter Log Normal probability distribution. This approach consists of Bayesian param eter estimation for the mean and the standard deviation of the L og Normal Fragility Model, given a limited (in the order of 10 to 50) number of structural analysis results for a specific structural performance variable denoted as Y. This leads to calculati on of the robust fragility and its percentiles or plus/minus standard deviation confidence interval underlying the number of simulations/realizations. The application of the robust fragility method is investigated in two cases: ( a ) vulnerability assessment to flooding for a class of non - engineered structures ; ( b ) seismic vulnerability assessment for an existing structure. . In case ( a ), the critical flooding height for collapse limit state is adopted as structural performance variable Y. In this case , the r esulting fragility curves are validated with respect to the results of Standard Monte Carlo simulation. In case ( b ), the spectral acceleration value corresponding to a critical demand to capacity ratio of unity is adopted as the structural performance para meter Y for the near collapse limit state

The Garisenda Tower represents one of the main symbols of the historical heritage of the city of Bologna. In 2011 an advanced monitoring system has been installed on the Tower with the purpose of monitoring the time evolution of: (i) Tower’s inclination; (ii) cracks at selected locations; (iii) stresses of the steel ties placed over the years to provide lateral confinement to the masonry. This paper aims at presenting the rationale of the monitoring system and analysing the data of the first two years of monitoring.

International audience; In the context of a seismic crisis where successive aftershocks threaten to bring down previously damaged structures, damage state-dependent fragility curves may constitute a useful tool to reassess the updated vulnerability of the exposed structures. This study builds on a methodology to derive state-dependent fragility curves without record-scaling and suggests some improvements. A set of natural ground-motion records is applied multiple times to a 2D model of a reinforced-concrete moment-resisting frame building with hysteretic degradation. The relationship between the aftershock intensity measure and the engineering demand parameter (here the maximum transient drift ratio) is obtained in two steps: A modified least-squares regression is first performed between the maximum additional transient drift ratio achieved during simulation and the intensity measure, and the results are then compounded with the distribution of the initial residual drift ratio. A comparison is finally made with fragility curves derived using an incremental dynamic analysis (IDA) approach.

The research activities on n onstructural components conducted in the past few years at the Department of Structural Engineering, University of Naples Federico II are described in the paper. The research is focused on the seismic qualification of plasterboard ceiling systems and plasterboard and brick internal partit ions through shake table tests. The test campaign on continuous ceiling systems highlights the low fragi lity of the tested specimen, primarily caused by: (a) the continuous nature of the ceiling, (b) the dense suspension grid, and (c) the large number of hangers being used. Different tests show an excellent seismic performance of the plasterboard partition w all, characterised by innovative anti - seismic details subjected to interstorey drifts even larger than 1%. The dynamic tests performed at different intensity levels on hollow brick partitions, instead, highlight an extensive damage for moderate interstorey drift demand. Finally, a study on the seismic demand in acceleration - sensitive nonstructural components is conducted