1,721,033 research outputs found
Optimality conditions for shakedown design of trusses
No full textThis paper deals with optimal shakedown design of truss structures constituted by elastic perfectly plastic material. The design problem is formulated by means of a statical approach on the grounds of the shakedown lower bound theorem, and by means of a kinematical approach on the grounds of the shakedown upper bound theorem. In both cases two different types of design problem are formulated: one searches for the minimum volume design whose shakedown limit load is assigned; the other searches for the maximum shakedown limit load design whose volume is assigned. The Kuhn-Tucker equations of the four problems here above mentioned are found by utilizing a variational approach; these equations prove the equivalence of the two types of design problem and provide useful information on the structure behaviour in optimality conditions. A suitable computational procedure of iterative type devoted to the reaching of the minimum volume design is presented. It is shown that the design obtained by this technique is the optimal one, since it satisfies the optimality conditions of the relevant search problem. In the typical step of this technique the dependency of the elastic response on the design variables is approximately taken into account. In the application stage a numerical example, aimed at utilizing this special technique, is presented. © 1995 Springer-Verlag
Optimal Bounds on Plastic Deformations for Bodies Constituted of Temperature-Dependent Elastic Hardening Material
No full textBounds are investigated on the plastic deformations in a continuous solid body produced during the transient phase by cyclic loading not exceeding the shakedown limit. The constitutive model employs internal variables to describe temperaturedependent elastic-plastic material response with hardening. A deformation bounding theorem is proved. Bounds turn out to depend on some fictitious self-stresses and mechanical internal variables evaluated in the whole structure. An optimization problem, aimed to make the bound most stringent, is formulated. The Euler-Lagrange equations related to this last problem are deduced and they show that the relevant optimal bound has a local character, i.e., it depends just on some fictitious plastic deformations produced in the same region of the body where the bounded real plastic deformations are considered. The bounding technique is also generalized to the case of loads arbitrarily varying in a given domain. An application is worked out. © 1997 ASME
Experimental analysis of new moment resisting steel connections
Full text linkIn the recent past, the authors proposed a new steel device devoted to representing an innovative moment resisting connection for steel frame elements called LRPD (Limited Resistance Plastic Device). It is a steel element characterized by symmetry with respect to three orthogonal barycentric planes and constituted by a sequence of three portions with abrupt cross section changes, each of one identifies a steel element of suitably designed geometry. LRPD possesses the following characterizing features: any elastic flexural stiffness variation with respect to the original selected member must be avoided; the bending moment resistance must be an appropriate reduced percentage of the original beam bending resistance; any local instability phenomenon must be avoided ensuring a full plastic deformation field. In previous papers the deep description of the geometrical and mechanical features of the device and the optimal design formulation are reported.
In the present paper a first stage of experimental campaign on the mechanical behaviour of LRPD is presented. Specifically, the pure bending behaviour of LRPD is investigated by performing the four-point bending test. The test is performed monotonically until the selected ultimate plastic bending moment acts on the specimen. The mechanical response of LRPD, both in terms of deflections as well as of axial strains is evaluated by means of suitably positioned displacement and strain gauges. The experimental test is performed on LRPD designed for HEB240 cross section beams. The obtained results confirm the expected performance of LRPD constituting a
fundamental step for the subsequent experimental steps mainly constituted by cyclic tests
Comparison among different dynamic shakedown approaches
No full textThe paper concerns the search for the limit load multiplier of structures subjected to seismic actions under shakedown conditions. The search problem is treated referring to two fundamental different approaches: The unrestricted dynamic shakedown approach and a new stochastic one recently proposed. The comparison between the above cited approaches is effected with the aim of evaluate the goodness of the obtainable results and the related computational effort. The structure sensitivity with respect to shakedown is evaluated through the analysis of the shakedown limit load multiplier cumulative distribution function. This function is determined by means of the stochastic approach, adopting the Monte Carlo method and on the grounds of a suitably defined generalized Ceradini theorem. For the sake of simplicity and without loss of generality, the search problems are formulated referring to elastic perfectly plastic steel frames. The effected numerical applications allow obtaining very interesting information on the structure shakedown behaviour, they confirm the great reliability of the stochastic approach and they provide useful suggestions for the improvement of the method
A bounding technique for plastic deformations
No full textOn the grounds of the known proportionality between the kinematical part of the solution of the Euler-Lagrange equations relative to the shakedown load factor problem for an elastic perfectly plastic solid subjected to cyclic loads and the gradient of the kinematical part of the elastic-plastic steady-state response of the solid to cyclic loads at the shakedown limit, a special bounding technique is developed. Such technique consists of computing a bound on the proportionality factor between the two kinematical solutions and, consequently, bounds on any measure of real plastic deformation produced by cyclic loads slightly above the shakedown limit. The technique is then generalized to the case of loads arbitraily varying within a given load domain. Some computational aspects are also discussed. Two examples solved in analytic form and one numerical application conclude the paper. © 1992 Springer-Verlag
Elastic plastic analysis iterative solution
No full textThe step-by-step analysis of finite element elastic plastic structures subjected to an assigned (quasistatic) loading history, is considered; it identifies with the well-known sequence of linear complementarity problems. An iterative technique devoted to solve the relevant linear complementarity problem is presented. It is based on the recursive solution of a suitable linear complementarity problem, deduced from the relevant one and easier than it The procedure convergency is proved. Some noticing particular cases are examined. The physical meaning of the procedure is shown to be a plastic relaxation. The suitable numerical ranges for some check parameter values, to be utilized in the application stage, is provided
A new design problem in the formulation of a special moment resisting connection device for preventing local buckling
Full text linkIn the present paper an improved formulation devoted to the optimal design problem of a special moment resisting connection device for steel frames is proposed. This innovative device is called a Limited Resistance Plastic Device (LRPD) and it has been recently proposed and patented by some of the authors. It is thought to be preferably located at the extremes of the beam, connecting the beam end cross section with the relevant column. The typical device is a steel element characterized by symmetry with respect to three orthogonal barycentric planes and constituted by a sequence of three portions with abrupt cross section changes. The main novelty of the present proposal is related to the design of special geometry for the optimal device ensuring that it possesses a reduced resistance with respect to the relevant connected beam element, is characterized by an equivalent bending stiffness equal to the one of the connected beam elements and exhibits full plastic deformations avoiding any local instability phenomenon. The optimal design is formulated as a minimum volume one and is subjected to suitable constraints on the geometry of the device and on its elastic and plastic behavior. The optimization problem is a strongly non-linear programming one and it is solved by adopting an interior-point algorithm that is available in the MATLAB Optimization Toolbox. The numerical simulations are devoted to the most used standard steel profiles (IPE, HE) and the results prove the great reliability of the proposed device. In addition, the relevant elastic and plastic domains of the designed devices are defined, and the expected behavior of the device is verified by appropriate 3D finite element models in the ABAQUS environment
Innovative devices for the protection of welded sections in steel structures
Full text linkThe paper proposes the use of innovative devices devoted to the brittle collapse
protection of welded steel sections, typically represented by the end beam cross-sections in framed
structures. Reference is made to I-shaped cross-sections. At first, limiting to the case of plane
stress, the relevant elastic domain is defined in the NN, TT, MM space; then a plane frame equipped
with the proposed devices and subjected to seismic load condition is studied, ensuring that the
generalized stresses at the welded sections be within the relevant elastic domain
Optimal design of new steel connections
No full textThe Limited Resistance Rigid Perfectly Plastic Hinge (LRPH) are special steel connections mainly usable to join beam elements of plane or spa-tial steel frames. The fundamental characteristics of these devices are the mutu-al independence of their own resistance and stiffness features as well as the re-spect of assigned constraints related to the elastic and limit behaviour of the joined elements. Within the frame structural scheme, the device plays the role of a rigid perfectly plastic hinge, constituted by a suitably sized sandwich sec-tion. The efficient use of the LRPH in the relevant frame depends on the appro-priate design of the device geometry. In the present paper, a new approach de-voted to the optimal flexural design of the LRPH is presented, according with the imposed mechanical constraints as well as with further suggested technolog-ical ones. The optimization procedure is based on a genetic algorithm approach and different applications are reported confirming the good applicability of the computational method as well as the reliability of the relevant device
Optimal Shakedown Design of Circular Plates
No full textThe optimal design of circular plates of elastic-perfectly plastic material and subjected to variable repeated loads is studied according to the shakedown criterion. Two different types of design problem are formulated: one searches for the minimum volume design whose shakedown limit load is assigned; the other searches for the maximum shakedown limit load design whose volume is assigned. In both cases the design problem is formulated by means of a statical approach on the grounds of the shakedown lower-bound theorem, and by means of a kinematical approach on the grounds of the shakedown upper-bound theorem. The Euler- Lagrange equations of these problems are found by a variational approach. The equivalence of the two types of design problem is proved and the design optimality condition is shown to constitute an extension to the shakedown context of the well- known Drucker-Prager-Shield-Rozvany theorem of optimal plastic design; namely, a modified unit cost is envisaged, the sum of the plate unit cost with some energy density, whose gradient with respect to the thickness equals, at the optimum, the analogous gradient of the plate plastic dissipation density. A few numerical applications are presented. © ASCE
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