1,721,098 research outputs found
Scienza delle Costruzioni
No full textNunziante L., Gambarotta L. and Tralli A. (2003). Scienza delle costruzioni. McGraw-Hill-Italy-ISBN-88-386-6100-6
A Reissner–Mindlin limit analysis model for out-of-plane loaded running bond masonry walls
No full textEarthquake surveys have demonstrated that the lack of out-of-plane strength is a primary cause of failure in many traditional forms of masonry. Moreover, bearing walls are relatively thick and, as a matter of fact, many codes of practice impose a minimal slenderness for them, as for instance the recent Italian O.P.C.M. 3431 [2005. Ulteriori modifiche ed integrazioni all’OPCM 3274/03 (in Italian) and O.P.C.M. 3274, 20/03/2003, Primi elementi in materia di criteri generali per la classificazione sismica del territorio nazionale e di normative tecniche per le costruzioni in zona sismica (in Italian)], in which the upper bound slenderness is fixed respectively equal to 12 for artificial bricks and 10 for natural blocks masonry. In this context, a formulation at failure for regular assemblages of bricks based both on homogenization and Reissner–Mindlin theory seems particularly attractive. In this paper a kinematic limit analysis approach under the hypotheses of the thick plate theory is developed for the derivation of the macroscopic failure surfaces of masonry out-of-plane loaded. The behavior of a 3D system of blocks connected by interfaces is identified with a 2D Reissner–Mindlin plate. Infinitely resistant blocks connected by interfaces (joints) with a Mohr–Coulomb failure criterion with tension cut-off and compressive cap are considered. Finally, an associated flow rule for joints is adopted. In this way, the macroscopic masonry failure surface is obtained as a function of the macroscopic bending moments, torsional moments and shear forces by means of a linear programming problem in which the internal power dissipated is minimized, once that a subclass of possible deformation modes is a priori chosen. Several examples of technical relevance are presented and comparisons with previously developed Kirchhoff–Love static [Milani, G., Lourenc ̧o, P.B., Tralli, A., 2006b. A homogenization approach for the limit analysis of out-of-plane loaded masonry walls. J. Struct. Eng. ASCE (in press)] and kinematic [Sab, K., 2003.Yield design of thin periodic plates by a homogenisation technique and an application to masonry walls. C.R. Mech. 331, 641–646] failure surfaces are provided. Finally, two meaningful structural examples are reported, the first concerning a masonry wall under cylindrical flexion, the second consisting of a rectangular plate with a central opening out-of-plane loaded. For both cases, the influence of the shear strength on the collapse load is estimated
A simple hybrid model for torsion and flexure of thin-walled beams
No full textThe paper presents a hybrid finite-element model for calculation of stresses and deformations of thin-walled beams of any cross section (open, closed or mixed).
The present model takes into account shear deformations and allows one to deal with beams with sharp variations of the cross section. The numerical performance of the proposed element in dealing with warping torsion is assessed by a number of meaningful examples
A Regularized XFEM framework for continuous discontinuous displacement
No full textA numerical strategy for modelling both diffuse and localized cracking in elastodamaging continua is proposed. The approach is based on the REgularized eXtended Finite Element Method (REXFEM), which has been presented in [1] [2] for assigned interfaces of elastic and cohesive type. Here, the crack development and propagation and the determination of the discontinuity path within the strain localization band are considered. The potential of the approach is that a regularization length is introduced, which can be both larger and smaller than the representative size of the finite element, while all variables remain local. © CIMNE
Sensitivity analysis for unilateral contact problems: "Boundary" variational formulations and B.E.M. discretisations
No full textA great interest has been recently devoted to the sensitivity analysis of structures in the presence of unilateral constraints and to its mathematical foundations. The problem has been usually tackled by using classical domain variational formulations, such as the ones based on the total potential energy, and its discretisation has been always performed with Finite Element models. On the contrary, this paper aims at proposing a sensitivity analysis based on boundary variational formulations and such as to retain most of the mathematical results obtained until now. It allows to take advantage of a discretisation carried out with Boundary Element Methods which appear to be more suitable than Finite Element models for this class of problems
A FAST FEM ALGORITHM FOR NON-LOCAL INTEGRAL MODELS
No full textThe Fast Gauss Transform (FGT) is applied to non-local finite element models of integral type (FEFGT) for problems requiring fine geometry discretization, as in the case of solutions that exhibit high gradients or boundary layers
FEM simulation of unsteady viscous incompressible fluid flows
No full textA fractional-step method to solve unsteady viscous incompressible flows is described. A semi-implicit time-advancement scheme is used to solve the dynamics equations, and the space discretization is performed by Finite Elements. The 2-D flow in a driven cavity at Re=1000 and around a cylinder at Re=100 are presented, with good correspondence with the benchmark solutions
A finite element model for active fluid structure interaction
No full textA numerical procedure for the simulation of multi-physics phenomena is described. The focus is on fluid-structure interaction problems in which part of the structural sub-domain exhibits an active behaviour. A brief description of the algorithm is provided: the whole domain is discretized in space by the finite element method, and a semi-implicit time integration scheme is used. The solution of the coupled system is performed by partitioned treatment, and the explicit form of the coupling terms, as well as the non-linear ones allows the independent solution of each sub-domain, and avoids the equilibrium iterations, at the expense of conditional stability. The resulting scheme exhibits good accuracy and stability, and requires comparatively small computation. A number of active FSI cases are reported
On virtual element solutions of unilateral contact problems
No full textThis contribution investigates the capabilities of an arbitrary order virtual element approach to solve a special class of contact problems, i.e. the unilateral contact between a two-dimensional elastic body and a rigid frictionless foundation of arbitrary shape, which is known as the Signorini problem. In order to account for the presence of the rigid obstacle, the virtual element formulation has been coupled to a Projected Successive Over-Relaxation (PSOR) algorithm. Due to its unique features, the Virtual Element Method (VEM) proves to be very versatile when dealing with the need of inserting new nodes on the contact surface and when a higher order interpolation field along element edges is required. The salient features of the method have been illustrated through a simple but insightful numerical example
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