An efficient numerical method for shakedown analysis

The algorithm proposed in [9] for incremental elastoplasticity is extended and applied to shakedown analysis. Using the three field mixed finite element proposed in [22] a series of mathematical programming problems or steps, obtained from the application of the proximal point algorithm to the static shakedown theorem, are obtained. Each step is solved by an Equality Constrained Sequential Quadratic Programming (EC-SQP) tech- nique that allows a consistent linearization of the equations improving the computational efficiency

An efficient mixed variational reduced order model formulation for non-linear analyses of elastic shells

The Koiter-Newton method had recently demonstrated a superior performance for non-linear analyses of structures, compared to traditional path-following strategies. The method follows a predictor-corrector scheme to trace the entire equilibrium path. During a predictor step a reduced order model is constructed based on Koiter's asymptotic post-buckling theory which is followed by a Newton iteration in the corrector phase to regain the equilibrium of forces. In this manuscript, we introduce a robust mixed solid-shell formulation to further enhance the efficiency of stability analyses in various aspects. We show that a Hellinger-Reissner variational formulation facilitates the reduced order model construction omitting an expensive evaluation of the inherent fourth order derivatives of the strain energy. We demonstrate that extremely large step sizes with a reasonable out-of-balance residual can be obtained with substantial impact on the total number of steps needed to trace the complete equilibrium path. More importantly, the numerical effort of the corrector phase involving a Newton iteration of the full order model is drastically reduced thus revealing the true strength of the proposed formulation. We study a number of problems from engineering and compare the results to the conventional approach in order to highlight the gain in numerical efficiency for stability problems

A quasi-static nonlinear analysis for assessing the fire resistance of 3d frames exploiting time-dependent yield surface

In this work an automatic procedure for evaluating the axial force-biaxial bending yield surface of reinforced concrete sections in fire is proposed. It provides an accurate time-dependent expression of the yield condition by a section analysis carried out once and for all, accounting for the strength reduction of the materials, which is a function of the fire duration. The equilibrium state of 3D frames with such yield conditions, once discretized using beam finite elements, is formulated as a nonlinear vectorial equation defining a curve in the hyperspace of the discrete variables and the fire duration. A generalized path-following strategy is proposed for tracing this curve and evaluating, if it exists, the limit fire duration, that is the time of exposure which leads to structural collapse. Compared to the previous proposals on the topic, which are limited to local sectional checks, this work is the first to present a global analysis for assessing the fire resistance of 3D frames, providing a time history of the fire event and taking account of the stress redistribution. Numerical examples are given to illustrate and validate the proposal

A mixed algorithm for incremental elastoplastic analysis

A new method for the incremental analysis of elastoplastic associated materials is presented. The method fully retains all the equations and variables of the problems at the same level and uses a sequential quadratic programming with equality constraints to solve in an efficient and robust fashion the elastoplastic step equations derived by means of a suitable mathematical programming formulation of the problem. The new proposal is compared with standard strain driven formulations which use a return mapping by closest point projection schemes. The numerical tests performed show a good performance and a great robustness of the proposed formulation also in the case of multi–surface elastoplasticity

Sclerosing Haemangiomas of the Liver: Two Cases of Mistaken Identity

We describe two cases where patients undergoing hepatic resection for metastatic disease of colorectal origin were found to have concomitant sclerosing haemangiomas. The typical radiological and histological appearances of these lesions are discussed

The chronostratigraphy of the Haua Fteah cave (Cyrenaica, northeast Libya)

The 1950s excavations by Charles McBurney in the Haua Fteah, a large karstic cave on the coast of northeast Libya, revealed a deep sequence of human occupation. Most subsequent research on North African prehistory refers to his discoveries and interpretations, but the chronology of its archaeological and geological sequences has been based on very early age determinations. This paper reports on the initial results of a comprehensive multi-method dating program undertaken as part of new work at the site, involving radiocarbon dating of charcoal, land snails and marine shell, cryptotephra investigations, optically stimulated luminescence (OSL) dating of sediments, and electron spin resonance (ESR) dating of tooth enamel. The dating samples were collected from the newly exposed and cleaned faces of the upper 7.5 m of the w14.0 m-deep McBurney trench, which contain six of the seven major cultural phases that he identified. Despite problems of sediment transport and reworking, using a Bayesian statistical model the new dating program establishes a robust framework for the five major lithostratigraphic units identified in the stratigraphic succession, and for the major cultural units. The age of two anatomically modern human mandibles found by McBurney in Layer XXXIII near the base of his Levalloiso-Mousterian phase can now be estimated to between 73 and 65 ka (thousands of years ago) at the 95.4% confidence level, within Marine Isotope Stage (MIS) 4. McBurney’s Layer XXV, associated with Upper Palaeolithic Dabban blade industries, has a clear stratigraphic relationship with Campanian Ignimbrite tephra. Microlithic Oranian technologies developed following the climax of the Last Glacial Maximum and the more microlithic Capsian in the Younger Dryas. Neolithic pottery and perhaps domestic livestock were used in the cave from the mid Holocene but there is no certain evidence for plant cultivation until the Graeco-Roman period

O cultivo da macieira na Itália: porta-enxertos, cultivares, adubação e irrigação

A Itália é um dos principais países produtores de maçãs na Europa, destinada principalmente ao consumo in natura no mercado nacional e internacional. A produção e a qualidade dos frutos é dependente da cultivar, do porta-enxerto e das práticas de manejo, como a adubação e a irrigação adotado no pomar. Esta revisão tem por objetivo reportar as principais cultivares e porta-enxertos de macieira e o manejo da adubação e irrigação e suas atualizações em pomares de macieira da Itália. Os programas de melhoramento genético nesse país envolveram a seleção de cultivares e porta-enxertos de macieira que permitem a obtenção de altas produtividades e frutos de qualidade exigida pelo mercado consumidor. No manejo da adubação e irrigação, os nutrientes e a água têm sido fornecidos em quantidades próximas a real necessidade das plantas, proporcionando nutrição adequada, produção satisfatória e frutos de boa qualidade, além de evitar, sempre que possível, as perdas de nutrientes e água no ambiente