Keywords: steel cooling tower, tubular structure, thin-walled section, bolted endplate connection, gusset plate, model development, non-linear FEM, virtual experiment.

A new type of steel cooling tower is under development by a Hungarian "Steel Cooling Tower Consortium" in the framework of a governmental R&D project. Beside the investigation of the available structural design methods, the project involves real and virtual experiments of the connections [1]. This paper focuses on these numerical analyses and virtual experiments completed on the first prototype of the joint.

Members of the structure are prefabricated tubular elements characterized by a high radius-to-thickness ratio. The 3D shape of the tower and the possible in-situ connection types result in extremely complex joints: thin-walled horizontal and vertical bars connected to the joint transfer element by bolted endplates; the joint made of gusset plates welded to tubular elements; and diagonal bars jointed by pinned connections. In this way, over the global and local failure modes of the tubular bars (such as overall yielding, global and local buckling), further failure modes are present due to the structural and geometrical forming. Moreover, complicated interactions of them may occur.

The paper proceeds to preliminary studies on problematic structural details, i.e. the bolted endplate connection that owns semi-rigid feature. Different numerical modelling ways are investigated. Applying the experiences, the numerical model of the whole joint is built up.

All of the analyses in this research have been done by the system ANSYS [2] using finite element method. To build the numerical models up, a MATLAB [3] platform is prepared, including extended graphical input interface and functions to compose the script-file being used by ANSYS.

Stability analysis to find out whether elastic instability phenomena occur is discussed.

One of the major aims of the research was to find out how the joint transfers the forces in different loadcases, whether there is any part of the gusset plates that are significantly bended. For this, linear finite element analysis has been used. The convergence of the results with different mesh density is also checked in this way. These analyses draw general idea about the possible critical points that should be examined in further studies.

Other subject of the paper is to investigate the actual failure modes and the complex behaviour by virtual experiments, separate their influence on the ultimate behaviour, support the planning and preparing the real experiments. For this purpose, geometrical and material non-linear finite element analysis has been used. The required level of detail modelling is scanned, resulting in accurate and efficient models. Based on these experiences and by the application of the MATLAB platform, several virtual experiments have been done, which are being calibrated to real ones. The possible failure modes are defined and separated.

Based on these investigations, the required joint improvement is determined. These analyses owned absolute necessity in preparing the real experiments, and now, based on the results, the calibrated models are sufficient for further use in theoretical analyses as well as in the development of advanced design method of the cooling tower joint.

1

Dunai, L., Horváth, L., Kaltenbach, L., Tóth, J., Vigh, L.G., "Analysis of steel cooling tower joint" (in Hungarian), Research report #1, Budapest University of Technology and Economics, Department of Structural Engineering, Budapest, 2001.

2

"ANSYS Structural Analysis Guide", Online Documentation, ANSYS Inc., 2001.

3

"The MathWorks Home", Online Documentation, MathWorks Inc., 2001

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