1,721,223 research outputs found
Critical analysis of seismic codes’ provisions on second order effects
No full textThis paper is aimed to discuss the conceptual troubles currently appearing in the codified rules to account for second-order effects in the seismic design of structures. First of all, starting from SDOF systems, the distinction between second-order effects in the elastic range and second-order effects in the plastic range is clarified. Moreover, the attention is focused on the conceptual difference occurring between a parameter measuring the structural proneness to second-order effects and a demand parameter measuring the safety level against the phenomenon of dynamic instability. Successively, the critical issues concerning the behaviour occurring in real MDOF structures when compared to SDOF systems is pointed out underlining the uncoupling between secondorder effects in the elastic range and second-order effects in the plastic range, due to the influence of the collapse mechanism typology. The codified rules to account for second-order effects in Eurocode 8 are analysed showing why they are conceptually wrong giving rise to a lot of unjustified problems in the seismic design of steel MRFs. Recent proposals to improve Eurocode 8 are also analysed. Finally, it is shown how relevant studies already existing in the technical literature can be exploited in order to set up code provisions having a sound theoretical background. Finally, a new proposal, accounting for the influence of the collapse mechanism, for codification of P - Delta effects in seismic design is presented
The influence of strain-hardening on the ultimate behaviour of aluminium RHS-beams under moment gradient
No full textIn this paper, the influence of strain-hardening on the ultimate behaviour of aluminium beams made of rectangular hollow sections (RHS) and subjected to non-uniform bending is investigated by analysing different aluminium alloys. The strain-hardening behaviour is related to the Ramberg-Osgood exponent of the constitutive stress-strain law of the material. A wide parametric analysis has been accomplished referring to both cooled, heat-treated and naturally-aged alloys. The results of comprehensive regressions analyses fitting the results obtained from numerical FE models are presented. Therefore, the main outcome of the work is the proposal of empirical relations for the prediction of the ultimate behaviour of RHS aluminium beams, accounting for the flange slenderness, the flange-to-web slenderness ratio, the non-dimensional shear length and the Ramberg-Osgood exponent. The proposed mathematical relationships allow a quick estimation of the ultimate non-dimensional flexural resistance and both total and stable part of plastic rotation capacity
Interactive Plastic Local Buckling of Box-shaped Aluminium Members under Uniform Compression
No full textA theoretical approach for predicting the ultimate resistance of aluminium alloy members subjected to local buckling under uniform compression is presented focusing the attention on box sections. Starting from the J2 deformation theory of plasticity, the theory of plastic buckling of plates is presented including, as an original contribution, also the variability of the Poisson's ratio depending on the stress levels. The differential equation of the plates at the onset of buckling is developed and the corresponding solution is provided. Starting from the obtained closed-form solution, the interactive buckling either in the elastic or in the plastic range is analysed. The interaction between the plate elements constituting the member section is explicitly accounted for using a completely theoretical approach where the evaluation of the critical stress leading to local buckling in the plastic range is derived as the value corresponding to the existence of a non-trivial solution for which the determinant of the matrix of the equation system is equal to zero. The accuracy of the plastic buckling theory is pointed out by comparing the buckling resistance obtained by the theoretical approach with the values of the ultimate resistance provided by stub column tests. Finally, some advances concerning the use of the effective thickness approach, currently adopted by Eurocode 9, are also proposed and herein presented for the first time and compared with test results
THEORETICAL PROCEDURE TO PREDICT THE LOCAL BUCKLING RESISTANCE OF ALUMINIUM MEMBERS IN ELASTIC-PLASTIC RANGE
No full textIn the present research work, a theoretical approach to evaluate the ultimate resistance of aluminium alloy members subjected to local buckling under uniform compression is provided. In particular, starting from the J2 deformation theory of plasticity, the theory of plastic buckling of plates has been extended including the variability of the Poisson’s ratio depending on the stress levels. the differential equation of the plates at the onset of buckling is developed and the corresponding solution is determined. This derivation represents an innovative step compared to the theoretical solutions currently existing in the technical literature because the variability of the Poisson’s ratio in the elastic-plastic region is commonly not accounted. Subsequently, starting from the obtained closed-form solution, the interactive buckling either in the elastic or in the plastic range of a generic aluminium members in compression is analysed. Two types of cross-sections are analysed: Box-shaped members. To this scope, the Levy solution of the differential equation of a single plate in elastic-plastic range is applied to the assembled plates constituting the cross-sections. Obviously, the interaction between the plate elements constituting the section is explicitly accounted by means of the boundary conditions accounting for restraining action. The previous boundary conditions lead to a system of equations whose trivial solution corresponds to the member in its non-deformed configuration. The prediction of the critical stress corresponding to local buckling in the elastic-plastic region is obtained as the value corresponding to the existence of a non-trivial solution for which the determinant of the matrix of the equation system is equal to zero. Finally, in order to consider the geometric imperfections of aluminium members, the procedure has been repeated by considering different geometric properties of plates composing the analysed cross-sections
Behaviour and Design of Set-Back Steel Frames.
No full textEurop. Workshop on the Seismic Behaviour of Asymmetric and Setback Structures, Anacapri, October 4-5, 199
Plastic Design of Semirigid Frames for Failure Mode Control.
No full textIABSE Conference on "Semi-rigid Connections", Istanbul, September 199
Different uses of the Perry Robertson formula for assessing stability of aluminium columns.
No full textInternational Colloquium on Stability of Steel Structures, Budapest, Hungary, 25-27 April 199
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