1,721,032 research outputs found
Beamlike models for the analyses of curved, twisted and tapered horizontal-axis wind turbine (HAWT) blades undergoing large displacements
No full textContinuous ongoing efforts to better predict the mechanical behaviour of complex beamlike structures, such as wind turbine blades, are motivated by the need to improve their performance and reduce the costs. However, new design approaches and the increasing flexibility of such structures make their aeroelastic modelling ever more challenging. For the structural part of this modelling, the best compromise between computational efficiency and accuracy can be obtained via schematizations based on suitable beamlike elements. This paper addresses the modelling of the mechanical behaviour of beamlike structures which are curved, twisted and tapered in their unstressed state and undergo large displacements, in- and out-of-plane cross-sectional warping, and small strains. A suitable model for the problem at hand is proposed. Analytical and numerical results obtained by its application are presented and compared with results from 3D FEM analyses
Arch-piers systems subjected to vertical loads: a comprehensive review of rotational, sliding and mixed collapse modes
No full textThis paper presents a study of the stability and collapse modes of a system made up of a masonry arch resting on two piers subject to its own weight. It examines both semicircular arches and three different types of pointed arches commonly found in architecture, namely low-pointed, equilateral, and lancet-pointed arches. The collapse modes characterizing each type of arch-piers systems are then compared by extending the results obtained by the authors in previous work on stand-alone masonry arches of different shapes. The mechanical behavior of these systems is examined via Durand-Claye’s method in order to follow the evolution of the stability area and determine the collapse modes of these masonry structures. The method takes into account both the bounded bending capacity of the arch cross section and the limited friction along the joints. Furthermore, the system’s safe domain is determined in terms of the limit conditions for arch thickness, pier height and friction coefficient. As expected, arch-piers systems of different shapes exhibit different behaviors at collapse in terms of minimum thickness and collapse modes
Load-bearing capacity of circular, pointed and elliptical masonry arches
No full textThe paper illustrates some results on a comparative evaluation of the load bearing capacity of three different types of masonry arches subjected to their own weight and the weight of an overlying vertical wall masonry. The arch types considered are those most commonly found in historical masonry buildings and bridges: circular, pointed and elliptical. The analyses have been conducted using two different complementary methods: the first a simple extension of the Durand-Claye stability area method; the second based on application of a non-linear elastic one-dimensional model, already used by the authors in prior studies. In all cases, it is assumed that the arch’s constituent materials has limited compressive strength and is unable to transmit tensions. In addition, the load transferred to the arch by the overlying wall is determined under the assumption that each vertical strip of wall bears directly down on the underlying arch element. Preliminary results reveal the clearly greater bearing capacity of the pointed arch with respect to the other types, thereby confirming a widely held conviction
Non-Linear dynamics of simple elastic systems undergoing friction-ruled stick-slip motions
Full text linkOn the stability of the helicoidal configuration in ribbons subjected to combined traction and twist
No full textA one-dimensional model endowed with an energy that generalizes Sadowsky's is used to study ribbons subjected to a combination of traction and twist and to fully characterize the set of equilibrium configurations having constant curvatures. A stability analysis for the helicoidal configuration identifies a critical point at which spiral configurations branch out. A stability analysis then shows that the part of the helicoidal branch corresponding to tractions larger than the value identifying the critical point is stable
Studying the equilibrium of oval-base pointed masonry domes: the case of Pisa Cathedral
No full textThis paper addresses the equilibrium problem of an oval-base, pointed masonry dome, that of famous Pisa Cathedral. Set within the framework of the safe theorem of limit analysis, the analysis involves searching for compressive-only statically admissible internal actions for the dome under vertical loads by using the concept of 'thrust surface'. According to Heyman's hypotheses, it is assumed that no in-plane tensile stresses can be transmitted within the thrust surface. The equilibrium problem is tackled by finding an explicit solution for the stresses within a suitable collection of thrust surfaces having the shape of ellipsoids, all contained within the dome thickness. The dome intrados and extrados surfaces have been carefully reconstructed by laser scanner survey and approximated by regular surfaces. The analytical expressions used for both the stress field and the intrados and extrados surfaces have enabled determining estimates of the safety level by means of an expressly developed optimisation procedure
Searching for admissible thrust surfaces in axial-symmetric masonry domes: Some first explicit solutions
No full textDetermining the internal forces acting within a masonry dome or vault loaded by an assigned distribution of external actions is a problem that is still open, as evidenced by even recent contributions to the scientific literature on the topic. The present work intends to address this issue by proposing a method for determining admissible distributions of stresses in vaults and masonry domes. The problem is solved analytically with the aim of obtaining, when possible, explicit expressions for the internal forces. Although applicable in principle to arbitrarily distributed loads, the procedure adopted herein for searching for statically admissible internal forces is described in detail for the case of distributed and concentrated vertical loads. The analysis is performed by building suitable analytical solutions to the so-called “direct” and “inverse” problems of a thin shell in which bending forces are nil and only membrane forces are present. The solutions thusly obtained are applied to vaults and domes by making use of the so-called “thrust surface” concept, which represents a natural generalization of the thrust line for masonry arches. According to Heyman's hypothesis for masonry, when the thrust surface is entirely contained within the vault thickness, a corresponding statically admissible stress field can be found. Thrust surfaces corresponding to admissible stress fields are determined by means of an expressly developed iterative procedure that begins by assigning an initial shape to the thrust surface. Then, by suitably using the solutions of the inverse problem, the shape of the thrust surface is modified so that the corresponding stresses become, when possible, statically admissible. By using the well-known theorems of limit analysis, both the mechanical and geometric safety coefficients are assessed for vaults and existing domes. As an example, the proposed procedure is applied to three practical case studies: a hemispherical dome of constant thickness, the dome of the Rome Pantheon, and the dome of Bernini's Santa Maria Assunta Church in Ariccia (Rome)
Admissible shell internal forces and safety assessment of masonry domes
No full textThe present paper illustrates a methodology for the safety assessment of masonry domes. The dome is modelled as a thin shell made of a material satisfying Heyman's hypotheses. Based on the static theorem of limit analysis, the method searches for statically admissible distributions of internal forces within the shell, suitably combining membrane forces and bending moments, by solving a convex optimisation problem. The solution is pursued numerically by means of an expressly developed collocation method that enables obtaining the analytical expressions for each internal force component. In its present formulation the method can be applied to domes of any shape, as well as to arbitrary load distributions. After validation against the benchmark case of the spherical dome under its self-weight, the paper illustrates application of the method to the dome of Pisa Cathedral under vertical loads as a first real case study
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