Lmit and shakedown analysis based on solid shell models

The paper treats the formulation of the shakedown problem and, as special case, of the limit analysis problem, using solid shell models and ES-FEM discratization technology. In this proposal the Discrete shear gap method is applied to alleviate the shear locking phenomenon

Existence of weak solutions for elliptic systems with p,q-growth

We consider a non-linear system of m equations in divergence form and a boundary condition: {Sigma(n)(i=1) partial derivative/partial derivative x(i) (A(i)(alpha)(x, Du(x))) = 0, 1 <= alpha <= m, in Omega u = (u) over tilde on partial derivative Omega. The functions A(i)(alpha)(x, z) are Holder continuous with respect to x and vertical bar z vertical bar(p) - c(1) <= Sigma(m)(alpha=1) Sigma(n)(i=1) A(i)(alpha)(x, z)z(i)(alpha) <= c(2)(1 + vertical bar z vertical bar)(q), 2 <= p <= q. We prove the existence of a weak solution u in ((u) over tilde + W-0(1,p)(Omega; R-m)) boolean AND W-loc(1,q)(Omega; R-m), provided p and q are close enough and under suitable sununability assumptions on the boundary datum (u) over tilde

Unconditionally stable dynamic analysis of multi-patch Kirchhoff-Love shells in large deformations

This work presents a numerical framework for long dynamic simulations of structures made of multiple thin shells undergoing large deformations. The C1-continuity requirement of the KirchhoffLove theory is met in the interior of patches by cubic NURBS approximation functions with membrane locking avoided by patch-wise reduced integration. A simple penalty approach for coupling adjacent patches, applicable also to non-smooth interfaces and non-matching discretization is adopted to impose translational and rotational continuity. A time-stepping scheme is proposed to achieve energy conservation and unconditional stability for general nonlinear strain measures and penalty coupling terms, like the nonlinear rotational one for thin shells. The method is a modified mid-point rule with the internal forces evaluated using the average value of the stress at the step end-points and an integral mean of the strain-displacement tangent operator over the step computed by time integration points

Trattamento chirurgico della malattia emorroidaria: quale tecnica è il gold standard?

Lo scopo dello studio è mettere a confronto le due tecniche principalmente usate (Milligan-Morgan e Longo) in relazione ad alcuni fattori (tempi operatori, durata della degenza, prolasso residuo, dolore, emorragia post-operatoria, percentuali di re-intervento e il riscontro di “incidentalomi” dopo esame istopatologico del gavocciolo emorroidario asportato [4-8]) nonché una breve descrizione della tecnica THD, che non può essere correlata statisticamente alla casistica delle altre due tecniche per l’esiguità degli interventi praticati presso il nostro Dipartimento con questa tecnica. La scelta del tipo di trattamento chirurgico da adottare per la malattia emorroidaria, quindi, deve tener conto di vari aspetti per cercare di effettuare il miglior intervento, a secondo del grado delle emorroidi, dell’eventuale presenza di flogosi e fibro-sclerosi e del prolasso emorroidario, tenendo presente anche il dolore e l’andamento della convalescenza del paziente nel post-operatorio

Is long-lasting mucosal elevation the only valid parameter when evaluating a lifting agent?

Stefano Pontone, Simone Manfredelli, Dimitri Krizzuk, Giovanni LeonettiDepartment of Surgical Sciences, “Sapienza” University of Rome, Rome, ItalyDear editorConsidering the relevance of the topic, our attention was strongly attracted by the study reported by Al-Taie et al. This study, based on our experience, begs some questions. Although the limitations of the lifting agent have been correctly identified by the authors, it would be useful to know the timing and details of the procedures used for preparation of blood, plasma, and serum

Limitatezza locale di minimi vettoriali di funzionali non convessi

We prove a local boundedness result for local minimizers of a class of non-convex functionals, under special structure assumptions on the energy density. The proof follows the lines of that in [CupLeoMas17], where a similar result is proved under slightly stronger assumptions on the energy density.Dimostriamo un risultato di limitatezza locale per minimi locali di una classe di funzionali non convessi, con particolari ipotesi di struttura sulla densità di energia. La dimostrazione procede come quella in [CupLeoMas17], dove un risultato simile è dimostrato con ipotesi leggermente più forti sulla densità di energia

Local boundedness of vectorial minimizers of non-convex functionals

We prove a local boundedness result for local minimizers of a class of non-convex functionals, under special structure assumptions on the energy density. The proof follows the lines of that in [CupLeoMas17], where a similar result is proved under slightly stronger assumptions on the energy density

Evaluation of the capacity surfaces of reinforced concrete sections: Eurocode versus a plasticity-based approach

The classical Eurocode-compliant ultimate limit state (ULS) analysis of reinforced concrete sections is investigated in the paper with the aim of verifying if and how this well-established design procedure can be related to plasticity theory. For this reason, a comparative analysis concerning capacity surfaces of reinforced concrete cross sections, computed via a ULS procedure and a limit analysis approach, is presented. To this end, a preliminary qualitative discussion outlines modeling assumptions aiming to reproduce the physical behavior of reinforced concrete cross sections with respect to ductility and confinement issues. Besides the theoretical importance of the proposed approach, numerical experiments prove that limit analysis yields not only very accurate results but also a computationally effective procedure that can be affordably used in common design practice

Shakedown analysis of 3D frames subjected to complex statical and seismic load combinations

ABSTRACT Despite its technical implications, nowadays shakedown analysis still seems confined to the research community instead of being a common tool in structural design. This is largely due to the difficulties in managing the large number of load conditions and the complex combination rules required by widely employed building codes which greatly increase the solution costs and prevent analysis. In the paper, with respect to 3D frames, a strategy for an efficient treatment of complex statical and seismic load combinations is proposed with the aim of making the shakedown analysis an affordable design tool to be used in practical applications. An algorithm capable of detecting a small number of significant elastic stresses within those corresponding to the load domain and suitable for use in the case of response spectrum analyses, is proposed. [2,3]. A series of numerical tests are presented to show both the accuracy and the effectiveness of the strategy. The yield surface of the beam sections is defined by its support function values associated to pressoflexural mechanisms and it is approximated as Minkowski sum of ellipsoids. The analysis is performed on the basis of the algorithms proposed i

Shakedown analysis of 3D frames under multiple load combinations using mixed fiber beam elements

If the stress intensity at a certain point of a structure made of ductile materials reaches the yield point, the structure does not necessarily fail or deform excessively. Instead, stress redistribution could take place and some further load increments could be supported. Thus, the actual load-carrying capacity of a structure is generally higher than the elastic limit and this overstrength can be exploited for a cost-effective design. However, during their operational life, structures are subjected to variable loads, whose law of variability in time is often unknown. Instead, it is usually possible to have a good estimate of the variability range in terms of maximum and minimum load amplitude. Within this context, shakedown analysis is able to provide a reliable safety factor against plastic collapse, loss in functionality due to excessive deformations (ratcheting) or collapse due to low cycle fatigue (plastic shakedown). This work presents an efficient fiber analysis for evaluating the shakedown safety factor of 3D frames under multiple load combinations. Mixed beam elements are employed for an accurate discretization of the structures. A continuation method, similar to an incremental elasto-plastic analysis, is used at structural level. It evaluates a fictitious equilibrium path made of a sequence of safe states with a converging non-decreasing load factor. Each point of the path is obtained by finding kinematic variables corresponding to self-equilibrated stresses satisfying Melan's condition for the current load factor to be safe. The stress admissible domain is defined at fiber level as a function of the load factor using the maximum and minimum effect due to all loads. An iterative state determination provides finite element stresses corresponding to assigned kinematic variables and load factor. The overall analysis differs from previous proposals for two novelty points. Firstly, a direct application of the Newton method is possible, without any need for constrained optimization solvers. Moreover, dimension and complexity of the load domain does not affect the computational cost of the nonlinear analysis. Numerical tests highlight an accurate estimate of the safety factor using a small number of fibers and an efficient solution also for large buildings