1,720,986 research outputs found
Computational enhancement of a mixed 3D beam finite element with warping and damage
Full text linkThis paper describes the computational aspects of the beam Finite Element formulation recently developed by the authors to simulate the nonlinear response of structural members subjected to shear and torsion, accounting for cross-section warping. The paper focuses on an efficient consistent solution algorithm that by-passes the iterative procedure required in forcebased and mixed Finite Elements and makes the model easy to be implemented in a standard code. Moreover, it proposes a new non-iterative technique to condense out the stress components derived by the three-dimensional constitutive response and not directly included in the fiber section formulation. The efficiency and accuracy of the proposed numerical model are validated by simulating the response of steel and reinforced concrete structural member
Corotational beam-interface model for stability analysis of reinforced masonry walls
No full textUnder horizontal loadings, such as seismic actions, buckling phenomena can strongly affect the bearing capacity of masonry walls to gravity loads. Indeed, due to the low tensile strength of the mortar, when vertically loaded masonry members are subjected to bending moments induced by load eccentricity, out-of-plane collapse mechanisms often prevail on compressive vertical crushing. This work presents a two-dimensional micromechanical approach relying on force-based beams and nonlinear interface elements for the out-of-plane stability analysis of regular brick/block masonry walls under eccentric vertical compressive loads. The elastic beams model the horizontal brick courses, while interfaces describe the bed mortar joints and reinforcing layer nonlinear behavior. A damage-plastic constitutive relationship is adopted for the mortar and a piece-wise linear damage-based law is proposed for the reinforcing layer. A corotational formulation is considered for both the beams and interface elements to account for large nodal displacements and P-Delta effects occurring during instability phenomena. Hence, the response of eccentrically loaded masonry walls, both reinforced and unreinforced, is reproduced, comparing the numerical results with experimental data
Mixed beam formulation with cross-section warping for dynamic analysis of thin-walled structures
No full textThis paper presents the formulation of a three-dimensional beam finite element (FE) that accounts for cross-section warping and dynamic inertia effects. The model is the extension of an existing mixed formulation, originally developed for the static analysis of thin-walled beams, to the case of dynamic loading conditions. Four independent fields are considered to derive the element governing equations, i.e. material rigid displacements, strains and stresses and an additional displacement field, describing the out-of-plane warping displacement of the beam cross-sections. The latter is independently interpolated in the element volume by including additional degrees of freedom (DOF) to the nodal translations and rotations classically considered in beam formulations. To obtain a consistent form of the element mass matrix, the cross-section displacement shape functions are computed, relating the generalized cross-section displacement fields to the element nodal variables. In mixed FE formulations, these are not assigned a priori, as in displacement-based approaches, but are derived on the basis of material stiffness and element geometry, together with compatibility conditions. Thus, the Unit Load method is applied to deduce the expressions of the shape functions consistent with the force-based approach, assuming the simply-supported beam as reference element configuration. As opposed to the original FE model, the additional warping DOFs are not condensed-out with the definition of the element quantities but are treated as additional global unknowns. This permits a correct description of the inertia effects and ensures continuity of the warping displacement fields between adjacent FEs. Correlation studies are presented to validate the proposed model and investigate the effects of cross-section warping on the dynamic behavior of thin-walled structures. For selected specimens, the studies compare solutions obtained adopting the proposed beam element with those resulting from shell or brick FE models. Modal decompositions and time-history analyses are conducted, assuming both linear elastic and nonlinear constitutive behavior for the latter
Vulnerability assessment of historical masonry buildings to excavation-induced settlements: palazzo assicurazioni generali
Full text linkHistorical masonry structures represent a conspicuous part of the European architectural heritage. However, these often are more vulnerable to damage risk than other constructions due to their peculiar mechanical properties. This justifies the lively interest in the development of efficient and reliable approaches for their structural capacity assessment. This work presents the vulnerability assessment of the historical masonry building, “Palazzo Assicurazioni Generali”, for the effects induced by the underlying tunnel excavation required for line C of the Rome underground. The structure is a 12-floor building, built in 1902-1906 in Piazza Venezia, one of the most prestigious areas of the city. A detailed macromechanical three-dimensional numerical model of the entire structure is developed and two kinds of static analyses are conducted, assuming linear elastic and nonlinear constitutive response for masonry. © 2023, Association of American Publishers. All rights reserved
Nonlinear dynamic analysis of thin-walled structures adopting a mixed beam finite element model with out-of-plane cross-section warping
No full textThis paper focuses on the dynamic response of thin-walled structural elements. A mixed three-dimensional (3D) beam formulation is adopted, that includes the effect of inertia forces under dynamic loading conditions and accounts for out-of-plane cross-section warping. This is introduced by adding a specific displacement field to those due to rigid body motions, and is interpolated in the element volume with the definition of specific shape functions. The element governing equations are derived by expressing the Lagrangian functional in terms of four independent fields, i.e. the material rigid displacements, the strains and stresses and the additional warping displacement field. Four Lagrange’s equations of motion result, corresponding to the element compatibility condition enforced in weak form, the material constitutive law, and two sets of element equilibrium conditions associated to the rigid and warping displacements, respectively. The FE model has been implemented in a standard numerical code and used to investigate the effect of cross-section warping on the dynamic response of thin-walled structures. A T-shape beam is analyzed by performing modal decomposition and time-history analyses under linear elastic and nonlinear constitutive behavior
Influence of the objective function in the dynamic model updating of girder bridge structures
No full textIn the context of model updating of bridge structures, dynamic approaches are currently dominant. This is mainly due to the opportunity of performing dynamic tests under environmental and traffic loadings, without putting the bridges out of service. Several techniques have been proposed in the literature to control and address the relevant model updating workflow. These methods typically consider the structural frequencies, or a combination of frequencies with vibration modes. Dissipative properties are, on the contrary, more rarely considered in updating procedures, given their strong dependence on the amplitude of the vibrations and on the type of forcing load. In this work, six ruling objective functions are considered for the dynamic model updating of girder bridge structures. The first one, taken from the literature, is a widely used function based on discrepancies among numerical and experimental frequencies. Two additional functions, also derived from the existing literature, are subsequently considered: one focuses on vibration modes, utilizing the Modal Assurance Criterion (MAC), and the other incorporates both structural frequencies and mode shapes, deploying the Modal Flexibility Matrix (MFM). Three novel objective functions are introduced, which are adaptations of the previously mentioned ones, with alternative applications of MAC and MFM. These six functions are analyzed and discussed through two comprehensive experimental case studies, in which the relative weights of the specific function terms are also investigated. A quantitative selection criterion is proposed and examined in order to choose the most suitable objective function based on identifiability. The method implementation, leveraging second-order derivatives, is executed via a finite difference scheme
Multi-scale analysis of masonry structures
No full textMasonry is one of the most famous and widely used heterogeneous composite material, largely employed in historic and architectural buildings. Among the different approaches proposed to study masonry structural behavior, multi-scale procedures are modern and promising tools, representing a fair compromise between detailed description of masonry microstructure and computational burden. This work presents a multi-scale beam-to-beam model for the analysis of unreinforced and strengthened periodic masonry panels under out-of-plane loadings. A two-dimensional Timoshenko force-based beam Finite Element (FE) is used to model the panel at the macroscale. At the microscale, a Unit Cell (UC) made of a brick, a mortar joint and eventually a reinforcing layer is adopted as representative volume element. The UC mechanical behavior is described by a Timoshenko beam model and is linked to the macroscale FE through a semi-analytical homogenization technique. Nonlinear constitutive relationships are considered for mortar and bricks, accounting for the evolution of damage, friction, and unilateral effect. A damage-based bi-linear relationship is assumed for the reinforcing layer, to reproduce the behavior of fabric-reinforced cementitious matrix (FRCM) composite materials. Applications on masonry structural elements of engineering interest are presented, showing also comparisons with experimental evidences
Enriched beam finite element models with torsion and shear warping for the analysis of thin-walled structures
Full text linkThis paper presents three beam Finite Element (FE) formulations developed for the analysis of thin-walled structures. These account for out-of-plane cross-section warping by removing the classical rigid body cross-section hypothesis and capture the interaction of axial/bending stress components with shear and torsion.
The beam FE models rely on different kinematic assumptions to describe out-of-plane cross-section deformations. Indeed, warping displacement field is interpolated in the element volume according to different approaches, with increasing level of accuracy and detail. First two models adopt a coarse warping description, where warping displacement field is defined as the linear combination of assumed warping profiles and unknown kinematic parameters. In the first model, these are considered as equal to the generalized cross-section torsional curvature and shear strains and a classical displacement-based formulation is adopted to derive the element governing equations. In the second model, warping parameters are assumed as independent kinematic quantities and a mixed approach is considered to derive the FE formulation. Third model, also relying on a mixed formulation, independently interpolates warping by introducing additional degrees of freedom on the cross-section plane, thus, resulting in a richer description of the out-of-plane deformations. This latter is also adopted to propose a numerical procedure for the warping profile evaluation of thin-walled beams subjected to torsional and shear forces, for general cross-section geometry.
The efficiency and accuracy of the proposed FE formulations are validated by simulating the response of thin-walled structures under torsion and coupled torsion/shear actions and the influence of the kinematic assumptions characterizing each formulation is discussed
Micromechanical and multiscale computational modeling for stability analysis of masonry elements
No full textThis paper presents two micromechanical and a multiscale finite element models for the analysis of masonry walls under out-of-plane instability effects. A two-dimensional modeling of the wall is considered in all approaches, assuming a cylindrical bending. The micromechanical analyses are performed considering elastic beams to model the bricks and either nonlinear beams or interfaces to model the mortar layers. The beam finite elements rely on the force-based formulation and account for large displacements by making use of the corotational approach. This latter is properly formulated and extended to interface elements to include nonlinear geometry effects. The multiscale model is defined by applying a two-scale beam-to-beam homogenization procedure, developed for masonry elements with periodic brick arrangements. Hence, a Unit Cell made of a single linear elastic brick and a single nonlinear mortar layer is introduced at the microscopic level, which is linked to the macroscale level through a semi-analytic homogenization technique. In all models, a damage formulation with friction plasticity governs the mortar constitutive relationship. Computational details on model implementation and solution procedures are given for all approaches. Correlation studies are performed to assess the proposed numerical micromechanical and multiscale procedures. In particular, the behavior of an unreinforced wall tested under a compressive eccentric load is reproduced and advantages and disadvantages of the proposed approaches are discussed
A mixed 3D corotational beam with cross-section warping for the analysis of damaging structures under large displacements
No full textThis paper presents the formulation of a tri-dimensional (3D) beam-column finite element (FE) with cross-section warping, based on a corotational approach for the analysis of damaging structures including material and geometric nonlinear effects. The model derives from an extended Hu–Washizu formulation and is an enhancement of a previously proposed beam FE formulation originally adopted for steel and reinforced concreted structures under linear geometry. The warping of the cross-sections is described by introducing additional degrees of freedom to those standard for a classic 3D beam FE and interpolating the corresponding displacement field with polynomial shape functions. The effects of large displacements are modeled through a corotational approach also including the axial-torsion interaction due to the Wagner effect. A 3D plastic-damage model is introduced to reproduce the degrading phenomena typical of many structural elements. This is used to simulate both damage occurring in ductile materials under large deformations and the non-symmetric tensile-compressive damage of brittle-like materials. The paper concludes with some numerical studies to validate the proposed FE and investigate the performances of the adopted corotational approach
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