Keywords: reticulated domes, non-linear analysis, ring beam stiffness.

Domes are very efficient structural systems for long clear span buildings. The introduction of laminated timber highlighted the economic advantages of this material and led to the use of timber domes even for very large spans. In this paper, reticulated timber domes of triangular network shape with decking and bottom tension ring are considered [1]. These types of domes have high stiffness in all directions along the surface and are kinematically stable. The dome is subjected to evenly distributed load over entire dome. The dome model is generated by a preprocessor program DOME-IN [2] and analysed by ABAQUS.

The focus of this paper is to evaluate the behaviour of reticulated timber domes with respect to different stiffnesses of the bottom ring beam. A non-dimensional ring area parameter is introduced to represent this stiffness of the ring beam. It is evident that this parameter is a very suitable design parameter for the ring beam. The relative values of the critical buckling pressure and maximum deflection of the dome, and maximum normal forces and bending moments in the network members versus this ring area parameter are presented. The reference values are the values obtained for an infinitely stiff bottom ring beam.

In a companion paper, the effect of different geometrical parameters on the behaviour of the reticulated dome is evaluated [3].

As far as global buckling is concerned, the critical pressure is sensitive to the bottom ring beam stiffness only if the latter is within a certain range. From a design point of view, the stiffness of the ring beam should exceed in order to utilize the full buckling load capacity of the dome system itself.

The maximum deflection, normal forces and bending moments versus the ring beam area parameter are also evalutated. The maximum deflection is also strongly dependent on the ring beam stiffness, but only for small ring area parameters . For ring area parameters larger than that value, the deflection approaches that of an infinitely stiff ring beam.

The normal forces near the bottom ring beam and bending moments near the bottom ring beam and in the middle of the dome are found to be strongly dependent on the ring beam stiffness. As ring beam stiffness decreases , the normal forces decrease rapidly, while the bending moments increase rapidly. The normal forces near the apex ring and in the middle of the dome and bending moments near the apex ring are almost unaffected by the ring beam stiffness.

A recommended value for the design of the bottom ring beam is .

1

Girhammar, U.A. et al., "Design of a Glulam Dome in Borlänge of 123 m Span Length", Martinson AB, Teknisk rapport 88:2, Bygdsiljum, Sweden, 1988 (in Swedish) (internal report).

2

Pan, D.H., "Dome-In - A Preprocessor Program for Reticulated Dome Calculations", Report 2001:1, Civil Engineering, Department of Applied Physics and Electronics, Umeå University, Umeå, Sweden 2001.

3

Pan, D. and Girhammar, U.A., "Geometrical Parameter Influence on Behaviour of Reticulated Timber Domes", Proceedings of The Sixth International Conference on Computational Structures Technology, Topping, B.H.V and Bittnar, Z, (Editors), Paper 124, Civil-Comp Press, Stirling, UK, 2002. doi:10.4203/ccp.75.124

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