MULTICRITERIA OPTIMAL DESIGN OF CONTINUOUS CIRCULAR PLATES

The paper is devoted to a quite general version of the multicriteria optimal (minimum volume) design of axisymmetric circular plates. The constitutive material is considered as elastic perfectly plastic without any ductility limit and the actions are assumed as quasi-statically variable within a given load domain. In the design problem formulation different resistance criteria are considered, in order to investigate all the possible structural limit responses, and for each one a suitably chosen safety factor is chosen. The optimal design problem is formulated as the search for the minimum structure volume according with a statical approach. The features of the optimal structures will be studied through the relevant Euler-Lagrange equations. A numerical application is presented utilizing an appropriate discretization of the minimum volume problem

Innovative devices for the protection of welded sections in steel structures

The 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

Experimental characterization of dacron 360 woven constitutive behavior

In the present paper some experimental analyses of Dacron© 360 woven aimed to characterize its constitutive behavior are presented. This woven, widely adopted in sail manufacturing, is obtained by weaving polyethylene terephthalate (PET) yarn and it shows some peculiar features due to the manufacturing process. The experimental tests, in terms of tensile tests and cyclic tests, clearly show the orthotropy features of the material, its high strength and deformability. Finally, the examination with optical microscope of the tested specimens allows to evidence how the warp and weft yarns interact

Iterative Optimal Design of Special Moment Resisting Devices for Steel Frames

The present paper proposes an iterative procedure devoted to reaching the optimal design of an innovative, recently proposed, moment resisting device. This special device, called Limited Resistance Plastic Device (LRPD), can be utilized, as an example, to equip a steel frame when it is required that the frame must be designed to substitute a masonry panel, i.e., it must be characterized by a structural behaviour as close as possible to the one of the replaced masonry wall. This purpose can be reached by designing the relevant frame imposing appropriate constraints on the elastic stiffness and on the limit resistance. The result can be obtained just by ensuring that the elastic stiffness and the limit resistance be independent of each other. To this aim it is necessary to suitably equip the steel frame by the previously cited LRPD. In particular, these moment resisting connections ensure that in a prefixed portion of the given beam element, the limit bending moment reduces without any variation of the global elastic stiffness. In order to reach this goal, the LRPD is substantially constituted by an inner portion, devoted to exhibit the desired reduced limit bending strength and to receive the plastic deformations, and two outer portions, devoted to guarantee the invariance of the elastic bending stiffness. The proposed iterative procedure allows to design a device respecting all the required features avoiding the presence of any dangerous local instability phenomenon. To this aim, the design will contain appropriate constraints ensuring that the device cross sections appertain to class 1 or class 2 I-cross section, as prescribed in the more recent standard codes. Some examples, validated by 3D solid tetrahedral elements analysis in ABAQUS environment, prove the good reliability of the proposed procedure and show the easy applicability of the computational approach

On the optimal design of base isolation devices

The paper deals with the optimal design of a base isolation system for a given structure subjected to seismic loads. In particular, an appropriate minimum displacement seismic protection device optimal design formulation is proposed for an assigned elastic perfectly plastic steel frame constrained to behave in conditions of elastic shakedown. The chosen base isolation device is constituted by elastomeric isolators. Suitable combinations of fixed and seismic loads are considered. According to the unrestricted shakedown theory, the seismic input is given as any load history appertaining to a suitably defined seismic load admissibility domain. The relevant dynamic structural response is obtained by means of a modal analysis making reference to the non-classically damped structural model. Some numerical applications conclude the paper

Welded section defence by LRPD devices

The present paper concerns a special application of some recently proposed structural devices, called LRPD, able to protect the welded sections of frame steel structures from undesired brittle collapse ensuring the good expected ductile behaviour. Standard I-shaped cross-sections are treated, and the proposed devices are suitably considered as moment resisting connections between beams and columns. At first the domain representing the brittle safe conditions is defined in the N,V,M space; then a sample plane frame subjected to seismic load conditions is studied and it is proved that, equipping the structure with the proposed devices suitably designed, the generalized stresses at the welded sections remain within the relevant brittle safe domain and the structure is able to dissipate a significant amount of plastic dissipation energy

EFFECT OF SURFACE FINISH ON THE TENSILE BEHAVIOR OF DACRON© 360 WOVEN

Nel presente lavoro vengono presentate alcune indagini sperimentali mirate alla caratterizzazione dell’effetto del trattamento superficiale sul comportamento costitutivo di un tessuto in Dacron© 360. Tale tessuto, largamente utilizzato nella realizzazione di vele, è ottenuto dalla tessitura di fili di polietilene tereftalato (PET) e presenta alcune peculiarità dovute al processo manifatturiero. Le prove di trazione realizzate evidenziano le caratteristiche di ortotropia del materiale e l’effetto del trattamento superficiale che si manifesta principalmente in un comportamento più rigido nella direzione dell’ordito ed in quella inclinata e in un aumento della resistenza ultima in tutte le direzioni.In the present paper some experimental analyses effected on Dacron© 360 woven with and without surface treatment, aimed to characterize the effect of this treatment on the constitutive behavior, are presented. This woven, widely adopted in sail manufacturing, is obtained by weaving polyethylene terephthalate (PET) yarn and it shows some peculiar features due to the manufacturing process. The experimental tests, in terms of tensile tests, clearly show the orthotropy features of the material and the effect of the treatment which results in a stiffer behavior especially along the warp and bias direction and in an increment of ultimate strength in all directions

Probabilistic Evaluation of the Adaptation Time for Structures under Seismic Loads

In this paper, a probabilistic approach for the evaluation of the adaptation time for elastic perfectly plastic frames is proposed. The considered load history acting on the structure is defined as a suitable combination of quasi-statical loads and seismic actions. The proposed approach utilizes the Monte Carlo method in order to generate a suitable large number of seismic acceleration histories and for each one the related load combination is defined. Furthermore, for each load combination the related adaptation time is determined, if any, as the optimal one for which the structure is able to shakedown under the unamplified applied actions. A known generalized Ceradini's theorem is utilized. The adaptation time values obtained with reference to all the generated seismic acceleration histories for which the shakedown occurs allows us to define the related cumulative conditioned probability function and, therefore, to identify the optimal adaptation time as the one with a probability not lower than a suitably assigned value

Multicriterion design of frames with constraints on buckling

The present paper is devoted to the optimal design of frame structures subjected to static and dynamic loading assuming the material behaviour as elastic perfectly plastic. The relevant optimal design problem is formulated as a minimum volume search problem. The minimum volume structure is determined under suitable constraints on the design variables as well as accounting for different resistance limits: the elastic shakedown limit and the instantaneous collapse limit, considering for each limit condition suitably chosen amplified load combinations. The effects of the dynamic actions are studied on the grounds of the dynamic features of the structure taking into account the structural periods referring to the actual Italian Codes related to the structural analysis and design. The minimum volume design is developed at first as the search for the optimal structure with simultaneous constraints on the elastic shakedown behaviour and on the instantaneous collapse. Moreover, in order to avoid undesired further collapse modes, the structure will be constrained to prevent element buckling. The numerical applications are related to steel frames