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Keywords: multicriterion design, steel frames, dynamic loads, buckling.

Summary

In recent decades, structural optimization has been object of interest and several studies have been devoted to proposing new search problem formulations as well as appropriate computational methods [1,2,3,4]. Actually, the continuous progress in technology, the upgrading regarding the computational techniques and the related software encourage designers to require more and more structural efficiency.

Most of the international design codes, and in particular the Italian one, require the design of elastoplastic structures to be according to two different limit criteria: the elastic one (or elastic shakedown) under serviceability conditions and the limit one (instantaneous collapse) under exceptional earthquake loadings.

Making reference to plane frames constructed from slender elements, the fulfillment of the above criteria does not guarantee the avoidance of other undesired structural phenomena. Actually, the relative floor displacements producing an increment of bending actions on the pillars must be taken into account and the element slenderness in order to avoid buckling must be considered as well.

Therefore, the present paper is devoted to the formulation of a special multicriterion design problem of elastic perfectly plastic frames subjected to different combinations of static and dynamic loads. In particular, the structure must be designed so as to be able to elastically shakedown in the presence of serviceability conditions and to prevent the instantaneous collapse for suitably chosen combinations of fixed and seismic loadings. Moreover, in order to avoid undesired further collapse modes the design problem is improved so that the structure is constrained to prevent element buckling. The related constraints consist of appropriate limits imposed on the axial forces suffered by the pillars and the resistance vector elements are suitable rates of the appropriate critical loads of the relevant elements.

A four floor plane steel frame has been investigated and the relevant minimum volume structure has been obtained solving both the original and the improved optimization problem. The features of the obtained optimal structures have been deduced by the interpretation of the related Bree diagrams.

It has been found that the structure obtained using the improved optimal design formulation guarantees a decisively more safe behaviour with respect to all the imposed limit states even with a very modest cost increment with respect to the original optimal design.

References

1: R.H. Gallagher, O.C. Zienkiewicz, "Optimum structural design", John Wiley & Sons, London, 1973.
2: M.A. Save, W. Prager, "Structural optimization", Plenum Press, New York, 1985.
3: F. Giambanco, L. Palizzolo, C. Polizzotto, "Optimal shakedown design of beam structures", Struct. Optimization, 8, 156-167, 1994. doi:10.1007/BF01743313
4: J. Atkociunas, "Optimal shakedown design of elastic-plastic structures", VGTU Publishing House Technika, Vilnius, 2011.

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Front Page Browse CCP CSETS CTR IJRT Other Authors Search Purchase Guide FAQ Contact us	Civil-Comp Proceedings ISSN 1759-3433 CCP: 99 PROCEEDINGS OF THE ELEVENTH INTERNATIONAL CONFERENCE ON COMPUTATIONAL STRUCTURES TECHNOLOGY Edited by: B.H.V. Topping Paper 18 Structural Design of Frames Able to Prevent Element Buckling F. Giambanco, S. Benfratello, L. Palizzolo and P. Tabbuso Department of Civil, Environmental, Aerospace, Material Engineering, University of Palermo, Italy doi:10.4203/ccp.99.18 purchase the full-text of this paper Full Bibliographic Reference for this paper F. Giambanco, S. Benfratello, L. Palizzolo, P. Tabbuso, "Structural Design of Frames Able to Prevent Element Buckling", in B.H.V. Topping, (Editor), "Proceedings of the Eleventh International Conference on Computational Structures Technology", Civil-Comp Press, Stirlingshire, UK, Paper 18, 2012. doi:10.4203/ccp.99.18 Keywords: multicriterion design, steel frames, dynamic loads, buckling. Summary In recent decades, structural optimization has been object of interest and several studies have been devoted to proposing new search problem formulations as well as appropriate computational methods [1,2,3,4]. Actually, the continuous progress in technology, the upgrading regarding the computational techniques and the related software encourage designers to require more and more structural efficiency. Most of the international design codes, and in particular the Italian one, require the design of elastoplastic structures to be according to two different limit criteria: the elastic one (or elastic shakedown) under serviceability conditions and the limit one (instantaneous collapse) under exceptional earthquake loadings. Making reference to plane frames constructed from slender elements, the fulfillment of the above criteria does not guarantee the avoidance of other undesired structural phenomena. Actually, the relative floor displacements producing an increment of bending actions on the pillars must be taken into account and the element slenderness in order to avoid buckling must be considered as well. Therefore, the present paper is devoted to the formulation of a special multicriterion design problem of elastic perfectly plastic frames subjected to different combinations of static and dynamic loads. In particular, the structure must be designed so as to be able to elastically shakedown in the presence of serviceability conditions and to prevent the instantaneous collapse for suitably chosen combinations of fixed and seismic loadings. Moreover, in order to avoid undesired further collapse modes the design problem is improved so that the structure is constrained to prevent element buckling. The related constraints consist of appropriate limits imposed on the axial forces suffered by the pillars and the resistance vector elements are suitable rates of the appropriate critical loads of the relevant elements. A four floor plane steel frame has been investigated and the relevant minimum volume structure has been obtained solving both the original and the improved optimization problem. The features of the obtained optimal structures have been deduced by the interpretation of the related Bree diagrams. It has been found that the structure obtained using the improved optimal design formulation guarantees a decisively more safe behaviour with respect to all the imposed limit states even with a very modest cost increment with respect to the original optimal design. References 1 R.H. Gallagher, O.C. Zienkiewicz, "Optimum structural design", John Wiley & Sons, London, 1973. 2 M.A. Save, W. Prager, "Structural optimization", Plenum Press, New York, 1985. 3 F. Giambanco, L. Palizzolo, C. Polizzotto, "Optimal shakedown design of beam structures", Struct. Optimization, 8, 156-167, 1994. doi:10.1007/BF01743313 4 J. Atkociunas, "Optimal shakedown design of elastic-plastic structures", VGTU Publishing House Technika, Vilnius, 2011. purchase the full-text of this paper (price £20) go to the previous paper go to the next paper return to the table of contents return to the book description purchase this book (price £65 +P&P)
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