Computational methods for optimal shakedown design of FE structures

The paper concerns the optimal shakedown design of structures discretized by elastic perfectly plastic finite elements. The design problem is formulated in four alternative versions, i.e. as the search for the minimum volume design whose shakedown limit load multiplier is assigned or as the search for the maximum shakedown limit load multiplier design whose volume is assigned; both problems are approached on the grounds of the shakedown lower bound and upper bound theorems. Correspondingly four computational methods, one for each original problem, are presented. These methods consist in solving iteratively new problems which are simpler than the original ones, but expressed in such a way th…

Comparison among different dynamic shakedown approaches

The 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 th…

A proposal for improving the elastic behaviour of dogbone

The Reduced Beam Section (RBS) connections are one of the prequalified connections approved by international standards and adopted to improve the seismic behaviour of steel Moment Resisting Frames (MRF) also protecting the joint between beams and columns. This goal is reached by locally reducing the resistance of a selected portion of the beam element by suitably trimming the flanges, to promote in that portion the onset of plastic deformations. In the framework of RBS, the most important typology proposed is the so-called dogbone (DB) connections that are widely diffused in seismic engineering. The essential advantages of DB are related to the protection of the welded cross section between…

INFLUENZA DEL TRATTAMENTO SUPERFICIALE SUL COMPORTAMENTO MECCANICO DEL DACRON TNF 360

Fixed strength and stiffness hinges for steel frames

A new type of device able to connect steel beam elements is proposed. Specifically, the device is designed in such a way that the required bending stiffness and limit resistance can be independently imposed. To this goal, the device is realized as a "sandwich" section whose wings possess a particular geometry able to guarantee the required characteristics. Further technological requirement is that the device has to engage plan dimensions equal to those of the elements to which it is connected. The procedure to design the device is presented in the paper with reference to a simple plane steel portal constituted by appropriate profiles in such a way it behaves following an assigned force/disp…

Optimal shakedown design of beam structures

The optimal design of plane beam structures made of elastic perfectly plastic material is studied according to the shakedown criterion. 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 problems are formulated: one searches for the minimum volume design whose shakedown limit load is assigned; the other searches for the design of the assigned volume whose shakedown limit load is maximum. The optimality conditions of the four problems above are found by the use of a variational approach; such…

Structural Design of Frames Able to Prevent Element Buckling

Two formulations of a special multicriterion optimal design problem devoted to elastic perfectly plastic steel frame structures subjected to different combinations of static and dynamic loads are presented. In particular, two minimum volume design problem formulations are proposed: in the first one the structure is designed so as to be able to elastically behave for the assigned fixed loads, to elastically shakedown for serviceability seismic load conditions and to prevent the instantaneous collapse for suitably chosen combinations of fixed and ultimate seismic loadings; in the second one the structure must also satisfy further appropriate constraints related to element buckling. The action…

Dynamic shakedown design of structures under repeated seismic loads

The paper is devoted to the formulation of an optimal design (minimum volume) problem of elastic perfectly plastic structures subjected to suitable combinations of static (fixed) and dynamic (seismic) loads. The structure is constrained to simultaneously respect two different safety criteria; actually, it must exhibit an elastic shakedown behaviour for the combination of loads characterizing the serviceability conditions and it must prevent the instantaneous collapse for the highest expected load condition (combination of loads characterized by the presence of fixed loads and maximum expected intensity of seismic action). The shakedown limit behaviour for the optimal structure will be impos…

Ludus absentiae et praesentiae

Volendo descrivere la soluzione di progetto come narrazione di scelte già realizzate sul corpo del Tempio-Duomo di Pozzuoli, come si guardasse a volo d'uccello, questa potrebbe essere descritta sinteticamente, come una architettura inclusa in un prisma di cristallo. Tale immagine riesce a rendere il senso complessivo di molti degli atti progettuali ipotizzati sul volume della chiesa ma, accanto a questi, vanno posti quelli che riconnettono in più punti il Tempio-Duomo al tessuto del rione Terra.

On the modern use of the bòvedas tabicadas

The paper concerns the study of the so-called “bòvedas tabicadas” (i.e. thin vaults constituted by layers of “rasillas” suitably superimposed) based on the results obtained by specific experimental investigations effected on the material of which they are constituted as well as on a vault that is still working. In particular, aim of the present research is the implementation of a first analysis of the structure in its present configuration (often unusable), with the purpose to evaluate the real structure serviceability related to the prescribed intensity of the acting loads, and moreover the execution of a new second analysis of the same structure but suitably reinforced by placing further …