1,720,991 research outputs found
Recent Developments in the Dynamic Stability of Elastic Structures
No full textDynamic instability in the mechanics of elastic structures is a fascinating topic, with many issues still unsettled. Accordingly, there is a wealth of literature examining the problems from different perspectives (analytical, numerical, experimental etc.), and coverings a wide variety of topics (bifurcations, chaos, strange attractors, imperfection sensitivity, tailor-ability, parametric resonance, conservative or non-conservative systems, linear or non-linear systems, fluid-solid interaction, follower forces, etc.). This paper provides a survey of selected topics of current research interest. It aims to collate the key recent developments and international trends, as well as describe any possible future challenges. A paradigmatic example of Ziegler paradox on the destabilizing effect of small damping is also included
Revisitation of elastic buckling of circular rings: Some analytical and numerical issues
No full textElastic buckling of circular rings under external pressure is one of the oldest and most ubiquitous problems in structural engineering and the first meaningful solution to it was proposed by Levy (1884). This basic solution, based on the Euler–Bernoulli beam model, can be found in the vast majority of textbooks on stability. However, there are a number of subtleties in the formulation of the problem which need to be taken into account so and one should always be well aware of the underlying analytical fundamentals, especially in the current world which strongly relies on numerical analyses. Therefore, starting from the general nonlinear kinematics of the problem, the buckling load is revisited by means of a direct energy approach and on the basis of an in-depth discussion of the classic kinematic hypotheses. Possibly different outcomes are pointed out and remarked. Finally, some inconsistencies which unexpectedly arise in pursuing the solution by means of commercial FE packages are presented and commented
Optimisation of suspended-deck bridge design: a case study
No full textThe study deals with the optimum suspended-deck bridge (i.e. suspension, cable-stayed and tied-arch bridges) design through cable adjustment. An easy linear analysis procedure is proposed based on the Force Equilibrium Method. It includes a preliminary identification of the objective function through a mathematical Sensitivity Analysis (SA) and an optimisation procedure based on the Influence Matrix Method (IMM). It neglects time-dependent effects and geometric nonlinearities. In spite of its simplicity, the proposed approach has proven to be good and functional and, on account of its straightforward physical meaning, also suitable to practising engineers. It aims to obtain an optimal moment distribution on the deck with a reasonable increment in the cable forces. An optimal distribution of stress in the cables can also be pursued. The proposed procedure is rather general and can be applied to both the design and the construction stages. The Gravina Bridge in Matera, Italy, is used as a model to illustrate the method and its applicability to practical engineering problems
Settlement-induced damage assessment in unilateral masonry-like structures: A piecewiserigid displacement approach
No full textSettlements severely affect historic masonry structures, and in fact, settlement-induced structural failures are common worldwide. This paper describes a rigid block detection and identification procedure of the crack pattern in masonry-like structures subjected to dead loads and finite displacements (e.g., settlements). The procedure is based on the Piecewise Rigid Displacements (PRD) approach. The equilibrium problem is formulated in the framework of Limit Analysis by means of a suitable variational formulation for the Boundary Value Problem (BVP) of Normal Linear Elastic No-Tension material (NENT). The equilibrium states of masonry-like structures are obtained as an optimization of Total Potential Energy (TPE). The application of the proposed method to real case studies highlights its potential in the field of mechanics and the mechanisms of fracture
On the design, elastic modeling and experimental characterization of novel tensegrity units
No full textPurpose: This study aims to focus on a short review on recent results dealing with the mechanical modelling and experimental characterization of a novel class of tensegrity structures, named class θ = 1 tensegrity prisms. The examined structures exhibit six bars connected by two disjoint sets of strings. Design/methodology/approach: First, the self-equilibrium problem of tensegrity θ = 1 prisms is numerically investigated for varying values of two aspect parameters and, next, their prestress stability is studied. The mechanical behavior of the examined structures in the large displacements regime under uniform compression loading is also numerically computed through a path-following procedure. Finally, the predicted constitutive response is validated through experimental tests. Findings: The presented results highlight that the examined structures exhibit a large number of infinitesimal mechanisms from the freestanding configuration, and reveal that they exhibit tunable elastic response switching from stiffening to softening. Originality/value: This multi-faceted elastic response is in agreement with previous literature results on the elastic response of minimal tensegrity prism, and suggests that such units can be usefully used as non-linear springs in next-generation tensegrity metamaterials
Lateral torsional buckling of compressed open thin walled beams: Experimental confirmations
No full textThis paper provides an approximate solution for the differential equations that govern the buckling of beams with a gradually changing of the thin-walled C cross section. This is a coupled problem of flexural and torsional buckling, whose exact solution is hard to get. We have therefore chosen to use an energy approach through the Dirichlet's principle. It allows, using the Ritz-Rayleigh algorithm, the quick implementation of a solution close to the real value of the critical load. Because of the complexity of the problem, it was considered appropriate to provide an experimental validation of the theoretical results with proper laboratory tests
From static buckling to nonlinear dynamics of circular rings
No full textThe dynamic buckling of circular rings is a pervasive instability problem with a major impact in various fields, such as structural, nuclear and offshore engineering, robotics, electromechanics, and biomechanics. This phenomenon may be simply seen as the complex motion that occurs deviating from the original circular shape under, for instance, any kind of time-dependent forcing load. Despite the fact that this topic has progressively gained importance since the mid-20th century, it seems that the same points have not been made completely clear. In fact, even some subtleties in the derivation of classical static buckling load may still give rise to misinterpretations and lead to misleading results. A fortiori, research concerning the nonlinear dynamics of rings still suffers the inherent difficulties associated with different possible analytical formulations of post-buckling dynamics. Advancement in this respect would be relevant, both from a theoretical and a practical point of view, since the applications are endless, with countless possibilities, especially in the biomedical and biotechnological fields: buckling-driven transformations of thin-film materials for applications in electronic microsystems, self-excited oscillations in collapsible tubes and pliable fluid-carrying shells, vocal-fold oscillations during phonation and snoring, pulse wave propagation in arteries, closure and reopening of pulmonary airways, stability of cardiac and venous valves during vascular surgery, stability of annuloplasty devices, flow-induced deformation and ultimate rupture of a cerebral aneurysm, and much more. The present article, in the framework of a critical review of the classic formulation of elastic ring buckling, proposes a straightforward approach for the nonlinear dynamics of an elastic ring that leads to a Mathieu–Duffing equation. In such a manner, some possible evolutions of the system under pulsing loads are analyzed and discussed, showing the inherent complexity of its dynamic behavior
On the solitary wave dynamics of tensegrity lattices with stiffening response: A numerical study
No full textWe present some peculiar results about the solitary-wave dynamics of novel tensegrity-based metamaterials. It has been previously shown that one-dimensional chains of triangular tensegrity prisms with stiffening behavior support the propagation of compressive solitary waves. We show that such result can be generalized to two-dimensional and three-dimensional modular tensegrity lattices composed of polygonal and polyhedral units. Differently from the one-dimensional case, the stiffening response of these lattices originates at the interface between adjacent units, not from the unit themselves. We present numerical results on the response to impulsive loads of slender assemblies composed by square units in two-dimensions, and cubic units in three-dimensions. We observed compact compressive waves forming at impact locations, together with localized thermalization effects. Such compact waves propagate with nearly constant speed and energy, while maintaining their shape, and emerge from collision with other compact waves almost unaltered, losing a small fraction of their energy. These results suggest the investigation of the dynamics of regular and quasi-regular tessellations formed by other types of polygonal and polyhedral units
NONLINEAR FE ANALYSIS OF A MASONRY SPIRAL STAIRCASE IN NISIDA: A REFINED NUMERICAL CASE STUDY
No full textFollowing previous work by some of the present authors based on the linear arch static analysis (LASA), which models the masonry material as a no-tension material according to Heyman (Heyman, J., The Stone Skeleton, Int. J. Solids Struct., vol. 2, no. 2, pp. 249–279, 1966) and on the safe theorem of the limit analysis (LA), an in-depth numerical study of a case study based on a masonry spiral staircase in Nisida, near Naples, is here presented by means of an accurate finite element (FE) model. The nonlinear FE model has been obtained by the use of the ANSYS Parametric Design Language (APDL), and a precise representation of all the material involved and of the boundary conditions, has been obtained. The results confirm that LASA can be an alternative to much more complex numerical analyses, such as FE, but it cannot account for the main cause of collapse or stress redistribution in these type of structures, that is sagging and subsidences. The results are presented and discussed in some detail
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