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PROCEEDINGS OF THE ELEVENTH INTERNATIONAL CONFERENCE ON CIVIL, STRUCTURAL AND ENVIRONMENTAL ENGINEERING COMPUTING
Edited by: B.H.V. Topping
Dynamic Response of Pre-Stressed Steel Columns
R.R. de Araujo1, P.C.G. da S. Vellasco2, J.G.S. da Silva3 and S.A.L. de Andrade1
1Civil Engineering Department, Pontifical Catholic University of Rio de Janeiro, Brazil
R.R. de Araujo, P.C.G. da S. Vellasco, J.G.S. da Silva, S.A.L. de Andrade, "Dynamic Response of Pre-Stressed Steel Columns", in B.H.V. Topping, (Editor), "Proceedings of the Eleventh International Conference on Civil, Structural and Environmental Engineering Computing", Civil-Comp Press, Stirlingshire, UK, Paper 150, 2007. doi:10.4203/ccp.86.150
Keywords: pre-stressed steel columns, experimental analysis, steel structures, computational modelling, non-linear analysis.
Although this structural solution dates back from the 1960s its structural behaviour, especially when subjected to dynamic actions, is not fully understood. This motivated a detailed study of the system structural behaviour, by means of ANSYS  dynamic finite element simulations, aiming to determine the natural frequencies and associated mode shapes.
The current dynamic finite element analysis was performed on twelve metre length pre-stressed steel columns. The load bearing capacity of these structural elements was substantially increased by the additional restriction provided by the tie forces that are transferred to the main columns by means of horizontal tubes, perpendicularly welded to the column midpoint.
In the parametric study, the main variables represented the pre-stressed element shape and area (cable or reinforced bar), and the adopted element pre-stress force. These two variables substantially altered the dynamic response and proved to be key elements for a better understanding of the structural system dynamic response.
The stayed column without pre-stress forces indicated that the structural system fundamental frequency significantly increases with an increase of the column stay diameter. This conclusion is independent from the column stay modelling (cable or beam elements). As expected, when the column stays are simulated by beam finite elements the column fundamental frequency value is higher than with the cable element modelling strategy. Evidently the fundamental frequency of a column without stays is substantially lower than an equivalent stayed column.
For a column with 6.3mm diameter stays, the influence of varying the pre-stress stay force over the system fundamental frequency is illustrated in the paper. The column stay modelling with cable elements adopted two pre-stress force levels, i.e. the optimum pre-stress level (inducing the system to achieve its maximum load carrying capacity) and the maximum pre-stress force supported by the column investigated.
The column fundamental frequency is higher when the stays, simulated by cable elements, are not pre-stressed. A distinct situation occurs when the stays are modelled with beam elements. In this case the fundamental frequency is higher when the stays are subjected to compressive pre-stress forces. On the other hand, when the column stays are subjected to tension pre-stress forces the fundamental frequency is slightly reduced.
In the present investigation it was observed that the computational modelling strategy, in terms of the adopted stay finite element (cable or beam), plays a significant role in the predicted stayed column dynamical response. The natural frequency values presented a substantial variation but the vibration mode configurations were not significantly altered according to the stay modelling.