39. Comparison of the behaviour of three types of braced domes

Abstract

Domes provide an easy and economic method of covering large areas. The three types of braced domes, i.e. geodesic, Schwedler and three-way grid domes, composed of steel tubular members are investigated with a. view to understand their behaviour. The behaviour of these domes is studied under four load cases with two boundary conditions and two height to span ratios. Furthermore, a comparison is made of the behaviour of these domes. For this purpose, a well known computer package - LUSAS (based on finite element method of analysis) is used assuming pin-connected conditions. The data for the analysis are prepared with the help of an automatic data generation system using formex algebra. Computer program using the FORTRAN77 incorporating Gino routines were developed to present the results graphically. These results include member forces, nodal deflections and support reactions. Each dome is optimized by choosing the required member sizes according to the magnitude of forces considering all four load cases. For convenience in construction , the number of different cross-sections for a dome is kept to four. The study shows that member axial forces in the domes are almost uniform. This is true with the exception of members in the two outer rings of the domes, where both vertically and fully translational restraints are used as boundary conditions. Particularly, force concentrations are found in the members near the fully constrained supports. The majority of members in the domes are carrying compressive forces and the extent of tensile forces is limited to the members near the supports. Nevertheless, the maximum tensile force is not larger than 67% of the maximum compressive force in any dome for any load case. Particularly, the tensile forces are practically non-existent where all the boundary nodes of the domes are fully restrained.