1,721,153 research outputs found
Collapse analysis of masonry bridges taking into account arch-fill interaction
No full textExperimental collapse tests on full and model scale masonry bridges have shown that fill and spandrels can strongly affect the collapse behaviour and increase the load carrying capacity. To provide a structural description of the arch–fill interaction effects, a two-dimensional model of multi-span masonry bridges is developed in which arches and piers are described as beams made up of elastic, non-tensile resistant (NTR), ductile in compression material, and the fill as a Mohr–Coulomb material modified by a tension cut-off under plane strain conditions.
The load carrying capacity is evaluated by a finite element limit analysis procedure based on the kinematic theorem. The fill domain is discretized by triangular elements connected by interface elements in order to allow possible velocity discontinuities at common sides of adjacent triangular elements; arches and piers are discretized by two-noded straight beam elements. By linearization of the limit domains in the generalized stress space, a linear programming problem is formulated and upper bounds of the collapse loads are obtained. Two examples are discussed, concerning a real single-span bridge, tested up to collapse, and a multi-span bridge. The ideal ductility assumption implicit in limit analysis is discussed by comparing the upper bound evaluations to the results obtained by incremental analysis in order to obtain the validity limits of the upper bound limit analysis for the proposed model
Delamination fracture and core crushing in composite sandwich beams
No full textThe paper deals with the nonlinear response of composite sandwich beams subject to static and dynamic out-of-plane loading. The internal structure of such composite systems gives rise to complex damage and failure mechanisms, which include multiple delamination of the skin, interfacial fracture at the skin-core interface and core crushing. The objective of the study is to analyse how different damage mechanisms interact and how these interactions affect the mechanical behavior of the system. The study refers to the model system of a sandwich beam, continuously supported by a rigid plane and subject to out-of-plane loading; the problem is studied using the schematic of a multiply delaminated beam on a nonlinear Winkler foundation. Static and dynamic analyses are performed and the influence on damage propagation of the initial position and size of delaminations in the skin and the constitutive parameters of skin and core are analysed.
The skin-core interaction strongly affects the fracture parameters of the delaminations. When the foundation is elastic, a shielding phenomenon is observed on increasing the ratio between the stiffness of the core and the flexural stiffness of the skin. The same ratio controls phenomena of localized amplification, which occur when the delamination tips come close to each other, as well as phenomena of localized shielding. These local effects can induce accelerated growth of the delaminations or crack arrests due to the presence of energy barriers. Under dynamic loading conditions, inertial effects enrich the response with new regimes of behavior leading for instance to oscillations in the arms of the delaminated beam which are characterized by different frequencies and amplitudes that favour damage propagation
Two-dimensional Finite Element Upper Bound Limit Analysis of Masonry Bridges
No full textA two-dimensional model for the evaluation of the load carrying capacity of masonry bridges is proposed that takes into account the strengthening effects due to arch–fill interaction observed in experimental tests. Upper bounds on the collapse load and the corresponding mechanism are obtained by means of a finite element application of the Kinematic Theorem of Limit Analysis. Arches and piers are modelled as beams made up of non-tensile resistant (NTR) and ductile in compression masonry, while the fill is represented as a cohesivefrictional material with tension cut-off. Kinematically admissible mechanisms are obtained by discretizing the fill domain with triangular elements and including velocity discontinuities in order to increase the degrees of freedom of the model and thus reduce locking; arches and piers are discretized by two-node straight beam elements. A piecewise linearization of the limit domains allows the upper bound on the collapse load and the corresponding mechanism to be obtained as a solution of a Linear Programming problem. The capabilities and the validity limits of the proposed numerical model are shown in two examples. The collapse test on a real single span bridge is simulated and discussed in the first example; a multi-span bridge is analysed in the second, where complex interactions between arches, piers and fill are obtained
Lower bound limit analysis of masonry bridges including arch-fill interaction
No full textCollapse tests on full and model scale masonry bridges have shown the structural role of fill and spandrels, which has to be taken into account to obtain realistic evaluations of the load carrying capacity of existing bridges. A plane model of multi-span masonry bridge is proposed in which the vault–fill interaction effects are considered, whose lower bounds on collapse load are obtained by a finite element application of the lower bound theorem of limit analysis. Arches and piers are modelled as beams made up of no tension, ductile in compression material and the fill as a cohesive-frictional material with a tension cut-off. The fill domain is discretized by triangular elements connected by interface elements in order to increase the ratio of the unknowns to the conditions of static admissibility; arches and piers are discretized by two-node straight beam elements.
By linearisation of the conditions of plastic admissibility, a Linear Programming problem is formulated and lower bounds on the collapse load are obtained. The procedure is successfully applied to two example bridge models, where a comparison with the results obtained from the kinematic approach is made. The first example is a simulation of a collapse test on a single span bridge; the second concerns a multi-span bridge and highlights the capability of the procedure to describe complex interactions between the arch–pier structural system and the fill at collapse
Il valore economico del cibo per lo sviluppo del territorio: un legame indissolubile tra qualità alimentare, patrimonio archeologico e comunità locali
No full textQuesto contributo cerca di individuare una definizione di prodotto tipico che comprenda le diverse sfaccettature del fenomeno; successivamente, il lavoro si sofferma su due di queste dimensioni, ovvero sul valore della storia e dell'archeologia come discipline essenziali per la qualificazione e la valorizzazione dei prodotti, anche alla luce di una ricognizione effettuata sui disciplinari delle Indicazioni Geografiche Marchigiane. Infine, dopo aver illustrato il ruolo delle Università nel processo di candidatura di una nuova indicazione geografica, i Vincisgrassi alla Maceratese STG, si delineano alcuni spunti per ulteriori ricerche e per un'azione coordinata che possa coinvolgere gli attori di diversi territori in un percorso virtuoso di costruzione e comunicazione collettiva del valore presente in ogni prodotto tipico
Book Review: "The New Cultures of Food: Marketing Opportunities from Ethnic, Religious and Cultural Diversity"
No full textBook Revie
Book Review: "Shopper Marketing. How to Increase Purchase Decisions at the Point of Sale"
No full textInteraction effects of multiple damage mechanisms in composite sandwich beams subject to time dependent loading
No full textAbstractTheoretical models are formulated to explain evolution and interaction of the damage mechanisms for multiple delamination of the face-sheet and core crushing in composite sandwich beams subjected to dynamically applied out-of-plane loading and continuously supported by rigid planes. The models are based on simplified one-dimensional formulations and describe the impacted face of the sandwich as a set of Timoshenko beams joined by cohesive interfaces and resting on a nonlinear Winkler foundation, which approximates the response of the core; the dimensionless formulation highlights the material/structure groups that control the mechanical response. The characteristic features of the problem and transitions in damage progression are explored on varying geometrical parameters and material properties and magnitude and duration of the applied load. For quasi-static loading and low velocity impact, core/face-sheet interactions generate energy barriers to the propagation of delaminations; the efficacy of the barriers in controlling damage in the face-sheets depends on the relative stiffnesses of face-sheet and core and on the foundation yielding strength. For dynamic loading conditions, significant dynamic effects arise in certain regimes and cause substantial changes in behavior: shielding of the crack tip stress fields provided by the foundation is reduced, especially after the load is removed when important delamination openings occur; core plasticity generally opposes this behavior and limits damage in the face-sheet
Computational modeling of reconstructive surgery: the effects of the natural tension on skin wrinkling
No full textA computational model is presented for the simulation of procedures of reconstructive surgery charac- terized by the excision of a cutaneous defect and the closure and suture of the wound edges. The skin is modeled as a plane membrane with zero flexural stiffness. The membrane undergoes large deformations and is characterized by a Fung type constitutive response in biaxial tension. Skin wrinkling, which is a typical outcome of the surgery in the form of extrusion of the wound edges and dog-ears, is considered through a modification of the elastic potential as originally proposed by Pipkin's Relaxed Energy Density theory [A.C. Pipkin, The relaxed energy density for isotropic elastic membranes, IMA J. Appl. Math. 36 (1986) 85–99; A.C. Pipkin, Relaxed energy density for large deformations of membranes, IMA J. Appl. Math. 52 (1994) 197–308]. The post-buckling analysis of a stretched annular membrane performed by Geminard et al. [Wrinkle formations in axi-symmetrically stretched membranes, Eur. Phys. J. E 15 (2004) 117–126] is used to validate the model under conditions similar to those of the surgery and to discuss the influence of a pre-existing tension in the membrane on the extension of the wrinkled regions. The model is applied to simulate different surgical procedures and investigate the effects of the natural state of the skin and the shape and size of the excisions. The results explain and validate current practice
- …
