Probabilistic time variant assessment of thin-walled steel members under atmospheric corrosion attack

Atmospheric corrosion is a relevant problem for steel structures and components exposed in aggressive environment in case of poor and/or unfeasible maintenance and inspection during service life. As for thin-walled members, the corrosion hazard can be exacerbated due to the thin thickness of components and the coupled effect between corrosion and buckling can significantly reduce the structural capacity of such structures. Following these considerations, this paper presents a study on the reliability of a thin-walled steel section subjected to the damage induced by atmospheric corrosion in outdoor environments, combining predictive corrosion models for metals with structural reliability applications. A general procedure for the evaluation of the time variant capacity is proposed and discussed in detail. Finally, an application to a C-lipped cold formed section is presented and a reliability analysis of the deteriorating section is carried out to evaluate the coupled effect of corrosion and buckling, according to the proposed procedure

Experimental and Numerical Analysis of Seismic Response of Unreinforced Masonry Cross Vaults

The present paper shows an experimental and numerical analysis to understand the seismic behaviour of unreinforced masonry cross vault. The experimental tests were performed on a 1:5 scale model of a cross vault made of 3D-printed blocks with dry joints. The seismic actions was experimentally simulated as a horizontal force proportional to the vault\u2019s mass by using a quasi-static tilt testing setup. The vault 3D collapse mechanism and its strength expressed in terms of collapse multiplier was investigated, also considering the direction of the seismic action with respect to the vault\u2019s base. The tests results were compared to those obtained from a numerical analysis using a rigid-block model based on 3D limit analysis. The model formulation allows to take into account both associative and non-associative behaviour. A sensitivity analysis on friction angle variation was also investigated to evaluate the accuracy and robustness of the model

The prediction of collapse mechanisms for masonry structures affected by ground movements using Rigid Block Limit Analysis

Abstract Masonry structures belonged to the Cultural Heritage suffered severe damages in the last decays due to the action of the settlement-induced ground movements. The researchers have been developing numerical tools for the vulnerability analysis and assessment of masonry structures subjected to settlements. Continuous, discrete and rigid block models were proposed in literature. The analysis of both local or global failure modes due to settlement is a still debated topic, involving several questions related to the modelling techniques and to the investigation of the parameters which affect the masonry behaviour against foundation movements. In this framework, the paper focuses on a numerical approach for the settlement analysis based on the rigid block limit analysis. The Italian Code (NTC 2018) also suggests linear kinematic approach for the seismic-induced collapse mechanisms analysis. In such a formulation, the structure is modelled as a collection of polyhedral rigid blocks assuming frictional contact interfaces with infinite compressive strength and zero tensile strength and neglecting the mortar contribution. Originally formulated for the in-plane and out-of-plane mechanisms analysis, the numerical formulation was recently improved in order to analyze blocky-structures subjected to uniform settlement. Numerical case study of a monumental masonry church facade subjected to uniform settlement at the base was presented in this paper aiming at testing the numerical procedure. The results were discussed to evaluate the software capability and accuracy in the settlement-induced collapse mechanisms prediction

Rigid block and finite element analysis of settlement-induced failure mechanisms in historic masonry wall panels

The paper is related to the assessment of collapse mechanisms of historic masonry structures suffering settlements induced by ground movements. Two numerical strategies are adopted in order to study the influence of the settled zone on the cracking of masonry buildings: a discrete rigid block model and a continuous homogenized model. The first approach provides an estimate of the collapse load and failure pattern of masonry based on the lower bound theorem of limit analysis. The second approach is formulated in the framework of multi-surface plasticity and implemented in a FE code for the path-following non-linear analysis of masonry wall described as continuous anisotropic plate. Several settlement configurations, of masonry walls under moving ground support are investigated and the corresponding failure patterns resulting from the analysis are obtained resulting in local or global failure modes. The results of the two modeling formulations are compared and discussed in order to highlight the features of the two different approaches in the prediction of settlement-induced damage

18^{18}F-PSMA-1007 salivary gland dosimetry: Comparison between different methods for dose calculation and assessment of inter- and intra-patient variability

Dosimetry of salivary glands (SGs) is usually implemented using simplified calculation approaches and approximated geometries. Our aims were to compare different dosimetry methods to calculate SGs absorbed doses (ADs) following 18F-PSMA-1007 injection, and to assess the AD variation across patients and single SG components. Five patients with prostate cancer recurrence underwent PET/CT acquisitions of the head and neck, 0.5, 2 and 4 hours after 18F-PSMA-1007 injection. Parotid and submandibular glands were segmented on CT to derive SGs volumes and masses, while PETs were used to derive Time-Integrated Activity Coefficients. Average ADs to single SG components or total SG (tSG) were calculated with the following methods: i) direct Monte Carlo (MC) simulation with GATE/GEANT4; ii) spherical model (SM) of OLINDA/EXM 2.1, adopting either patient-specific or standard ICRP89 organ masses (SMstd); iii) ellipsoidal model (EM); iv) MIRD approach with organ S-factors from OLINDA/EXM 2.1 and OpenDose collaboration, with or without contribution from cross irradiation originating outside the SGs. The maximum percent AD difference across SG components ({\delta}max) and across patients ({\Delta}max) were calculated. Compared to MC, ADs to single SG components were significantly underestimated by all methods (average relative differences between -14.5% and -30.4%). Using MC, SM and EM, {\delta}max were never below 25% (up to 113%). {\delta}max up to 702% were obtained with SMstd. Concerning tSG, results within 10% of the MC were obtained only if cross irradiation from the remainder of the body or from the remainder of the head was accounted for. The {\Delta}max ranged between 58% and 78% across patients. Specific masses of single SG components should always be considered given their large intra- and inter- patient variability.Comment: 33 pages, 3 figures, sumbitted to "Physics in Medicine & Biology

Force-Based Seismic Evaluation of Retrofitting Interventions of Historic Masonry Castles by 3D Rigid Block Limit Analysis

This paper deals with the force-based assessment of collapse mechanisms and strengthening interventions of the historic masonry castle “Bussi sul Tirino” (Abruzzi, Italy) using rigid block limit analysis (RBLA). The structure, which is a fortified palace dating back to the 11th century, has experienced severe earthquakes over the centuries and was hit once again in 2009 by the L’Aquila earthquake. Based on the historical analysis and the results of in situ investigations, a spatial rigid block model of an entire structural unit was generated using the in-house software LiABlock_3D. The software is a MATLAB® based tool for three-dimensional RBLA, which provides as outputs collapse failure modes and collapse load multipliers. In addition, a specific routine was developed for the purpose of the study to compute the participating mass ratio and the spectral acceleration that activated the failure mechanisms. The results of the numerical analysis were used to address three different retrofitting interventions, based on the use of connection elements and ties that, according to the minimum intervention principle, progressively enhanced the seismic capacity. Comparisons in terms of seismic safety indices are finally provided in order to give a quantitative measure of the effectiveness of the adopted retrofitting strategies