Month: December 2017

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In the present paper, the nonlinear seismic behavior of a concrete gravity dam- reservoir-massed foundation system is studied focusing on the foundation material nonlinearity. For this purpose, a finite element program utilizing the elasto-plastic formulation for the foundation medium is provided considering the tensile and shear failure modes. Hoek-Brown and Mohr Coulomb criteria are used as the yield and plastic potential function of the shear failure mode, respectively; and in the tensile failure mode, various levels of the tensile strength are applied to the foundation. Bearing capacity is studied considering the localized plastic elements and forming the sliding path by plastic elements is studied for investigating the sliding stability of the foundation. It is found that the foundation nonlinear model and the magnitude of tensile strength of the foundation can have significant effects on the failure mechanisms happened within the foundation rock.

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A growing attention is developing on the analysis of seismic reliability of structures. Usually the assessment is performed via non-linear dynamic analyses carried out on computer models and aimed at assessing failure rates associated with a set of possible performance levels. The present work aims to highlight how the process of record selection can significantly influence the final results, being a source of relevant uncertainty. A case study application is presented and results are critically discussed.

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In this work, the prediction of the seismic performance of moment-resisting (MR) steel frames with full-strength beam-to-column connections was investigated with respect to the variability in the response due to dissipative zone modelling. 4 numerical models with different degrees of sophistication (Smooth Hysteretic Model, Bouc-Wen, Hysteretic and simple Elastic-Plastic models) were utilized, and each one was calibrated against data coming from monotonic and cyclic experimental tests according to a multi- objective approach recently developed by the authors. Subsequently, Incremental Dynamic Analyses (IDA) were performed by considering two different earthquakes (Spitak and Kobe). This preliminary analysis pointed out that the influence of the joint modelling on the overall frame response is negligible up to interstory drift ratio values equal to those conservatively assumed by the codes to define conventional collapse (0.03 rad). Conversely, if more realistic ultimate interstory drift values are considered for the q-factor evaluation, the influence of joint modelling can be significant, and thus the response prediction may require accurate modelling of the joint cyclic behavior.

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The research work presented is aimed at the assessment of the influence of infill walls on the seismic vulnerability of existing RC buildings. In particular, the paper presents some results obtained from the analysis of recurrent building typologies, for which the structural representative models have been defined from the observation of existing building stock at the regional scale. A sensitivity analysis was performed by assuming various hypothesis about the infills’ features, and the results allowed to point out and discuss the differences regarding the structural behavior, the seismic demand and other representative output parameters.

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The work herein presented is devoted to the comparison between two design approaches leading to the same design goal, i.e. the design of structures able to develop a collapse mechanism of global type. These selected design procedures are the Performance- Based Plastic Design approach (PBPD) and the Theory of Plastic Mechanism Control (TPMC). To this scope reference is made to several MR-Frame structures designed by means of both procedures. The seismic performances of such MR-Frames have been investigated by both push-over and dynamic non-linear analyses.

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The seismic vulnerability assessment of existing and historical masonry structures is an important priority to preserve them over time. Several mechanical models available in literature are based on the limit analysis and may require a relevant computational burden. In this paper, an adaptive numerical method to analyse the seismic response of masonry vaults is presented. The approach is developed within Heyman’s safe theorem and extends the funicular curve concept to the 3D case, by searching a ‘safe’ thrust surface within a design domain. The thrust surface is obtained by means of a Genetic Algorithm applied to a refinement adaptive finite element model. This approach can be easily implemented in existing FEM codes and gives a useful tool to assess seismic vulnerability of curved masonry structures and to design selective reinforcements. It is validated against a case study of a vault available in literature. Some numerical results dealing with a cloister vault subject to static and dynamic loads are given.

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In the framework of risk assessment at national and regional scale, the analysis of collapse mechanisms induced by seismic accelerations constitutes a useful tool to understand the behaviour of masonry structures and to plane mitigation strategies and rehabilitation interventions. In this perspective, the objective of the present study is the identification of the correlations among three factors: 1) structural-typologies which characterize Italian masonry buildings, 2) possible collapse mechanisms (in-plane and out- of-plane), 3) ground accelerations. The analyses developed concern a sample of 100,000 models representing the structural typologies of ordinary masonry buildings distributed on Italian territory. They have been derived through examination of structural characteristics (dimensions of structural elements, mechanical characteristics of material, typologies of horizontal structures and roofing, presence of vaults and/ or ties or ring beams, number of floors, etc.) collected by ‘in situ’ survey of about 250,000 buildings distributed along the Italian territory. For each model, the acceleration able to induce the first collapse mechanism has been calculated, adopting simplified limit state analyses. The results have been then elaborated to set, for different vulnerability classes (assigned combining typological- structural characteristics), the probability of occurrence of each collapse mechanism varying the peak ground acceleration (PGA) is analysed.

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