Paolo Martinelli

Pressure--impulse diagrams for RC and FRC circular plates under blast loads

In this work, simplified models for the dynamic analysis of traditional reinforced concrete (RC) and fibre-reinforced concrete (FRC) circular plates under blast loads are proposed. The cases of plates simply supported or resting on Winkler-type soil are studied. The two cases under study intend to provide a simplified tool for predicting the response respectively for specimens subjected to blast pressure wave inside shock-tube facilities and for slabs on ground under blast loads. The second case also represents the loading conditions inside a new shock-tube facility specifically intended for the investigation of underground tunnel lining subjected to blast loads. The aim of this work is the pressure--impulse diagrams derivations for circular plates with several material characteristics, radius/thickness ratio and Winkler’s constant. Des modèles simplifiés sont proposés dans cet article pour étudier le comportement dynamique de plaques circulaires en béton armé renforcées, soit de façon traditionnelle soit par des fibres, lorsqu’elles sont soumises à des ondes de choc. Deux types de supports sont considérés pour les plaques: un support simple et un support qui reproduit la réaction d’un sol avec un modèle du type Winkler. Ces modèles sont des outils simplifiés pour prédire les réponses de maquettes soumises à une onde de pression à l’intérieur d’un tube à choc ou de plaques posées à même le sol et soumises à une onde de choc. Ce dernier cas représente les conditions de chargement obtenues dans un nouveau tube à choc spécialement conçu pour étudier le comportement du revêtement des tunnels souterrains soumis à des ondes de choc. L’objectif de ce papier est de présenter les diagrammes pression--impulsion de plaques circulaires, pour différents rapports rayon/épaisseur et constantes de Winkler.

Layered high-performance concrete plates interacting with granular soil under blast loads: an experimental investigation

A new-layered precast tunnel segment made of different fibre-reinforced cementitious composites is here proposed. The article aims to study the effect of impulsive distributed pressure over tunnel rings under blast loads for the development of this new design solution. Shock tube experiments have been carried out to investigate a small portion of tunnel segment interacting with soil subjected to a plane shock wave. A set of accelerometers mounted on the specimen and placed inside the soil, as well as strain gauges mounted on the ad hoc chamber containing the specimen and the soil, have provided valuable information on the soil–structure interaction response. A careful investigation on the possible delamination between concrete layers is also carried out by UPV measurements. The experimental results have pointed out the great potential of this new design solution for precast tunnel segments subjected to internal explosions.

Bearing capacity assessment of a 14th century arch bridge in Lecco (Italy)

ABSTRACT The article presents the results of an experimental and numerical investigation on Azzone Visconti bridge, a 14th century arch bridge in Lecco (northern Italy). Starting from the historical data and from an extensive mechanical characterization of both the soil constituting the riverbed and of the masonry constituting the piers, the aim of the study is to investigate the bearing capacity of the bridge. A testing loading scheme defined according to the current Italian Code is adopted to check the structural behavior. A simplified finite element structural model was conceived and calibrated as a control tool to safely perform the experimental tests. Post-test nonlinear finite element analyses have allowed the prediction of the bridge bearing capacity and the definition of the bridge class according to the Italian regulations.

Quantification of Modeling Uncertainties Based on the Blind Prediction Contest Submissions

Modeling uncertainty can have a significant impact on the assessed risk of earthquake-induced damage and collapse in a building obtained through the performance-based earthquake engineering framework. This paper quantifies the effect of modeling uncertainty on performance-based risk assessments, accounting for differences in software platforms, solution algorithm, element-types, and model parameter calculation or selection, using results of the 7-story reinforced concrete (RC) building blind prediction contest (2006) at University of California at San Diego (UCSD). The blind prediction test data provide a unique opportunity to quantify the influence of modeling uncertainty on structural response predictions. In this study, the bias and variability of predicted drift in the contest submissions are taken to represent modeling uncertainty. The modeling uncertainty quantified from the UCSD test submissions is combined with uncertainty due to record-to-record variability and a set of fragility curves are computed for different drift levels. The final fragility curves account for modeling and ground motion uncertainty. Results are compared with the results with no modeling uncertainty. The key contribution of this study is to investigate the uncertainty embedded in the response due to combination of ground motion and modeling uncertainty.

SDOF Models for RC and FRC Circular Plates under Blast Loads

This work presents simplified models, in the form of single degree of freedom (SDOF)elasto-plastic systems, for the dynamic analysis of traditional reinforced concrete (RC) and fibre-reinforced concrete (FRC) circular plates under blast loads. Two cases have been examined inthis study: simply supported and resting on Winkler-type soil plates. Both cases intend toprovide a simplified tool for predicting the response respectively for specimens subjected toblast pressure wave inside shock-tube facilities and for slabs on ground under blast loads. Thesecond case also represents the loading conditions inside a new shock tube facility specificallyintended for the investigation of underground tunnel lining subjected to blast loads.

On the Design Response of a FRC Statically Undetermined Structure

Fibre reinforced concrete is a concrete with a diffused reinforcement based on fibre pull-out resistance and its toughness in tension is strongly affected by fibre distribution. The material response of a representative volume is significantly affected by the uncertainties related to fibre location and number: only a homogeneous distribution of fibres can guarantee an isotropic behaviour, but in any case its mechanical behaviour dominated by mode I failure, identified by means of a bent notched beam, shows a large standard deviation. By the way, a structure characterized by a significant capability to redistribute stresses and large fracture volume at the onset of collapse can reduce the sensitivity to the high standard deviation and exhibits a bearing capacity aligned to the average mechanical properties of the composite. In the paper several approaches to compute the coefficient that quantifies this structure ability, K Rd , are proposed, taking as a reference cases a slab on ground and an elevated slab.

Numerical Simulation of the Partial Seismic Collapse of a 1960s RC Building

AbstractThis study focuses on the partial seismic collapse of a building during the earthquake of L’Aquila (Italy) on April 6, 2009. Designed in the early 1960s, the seven-story building has a rein...

Underground Tunnels Exposed to Internal Blast: Effect of the Explosive Source Position

The design procedure recently proposed by the same authors and based on a simplified FE model for underground tunnels subjected to internal explosion is extended in this work taking into account different possible positions of the explosive source inside the tunnel. The situation in which the internal explosion is preceded by fire accidents is also analyzed. The reference situation is represented by the explosive source located at the center of the tunnel cross–section. The tunnel geometry considered is that of the metro line in Brescia, Italy. It has an internal diameter of about 8.15 m and is located about 23.1 m below the surface. Six segments and a smaller key segment (6+1) make up the tunnel. The ring has an average width of about 1.5 m. Dynamic analyses were carried out in order to reproduce the blast scenario. The aim of this work is to evaluate the influence of the position of the explosive source on the tunnel dynamic response. An ultimate limit state criterion based on the eccentric ultimate flexural capacity and capable of including fire–blast interaction is adopted. An innovative layered precast tunnel segment solution made of different fiber–reinforced cementitious composites is considered.