The Rigidity of RIB-Reinforced Cover Plates

Abstract

An experimental approach to the problem of rib-reinforced cover plate design is outlined. Exact tractable methods for calculating the deflections of radially ribbed plates are not available. Outlines of formal mathematical treatment which use several approximations are presented to highlight the theoretical difficulties. The technique of Fizeau interferometry was employed to study the deflections of a series of laterally loaded ribbed plates of varying proportions. From the results, values of the rigidity of the plates were found together with the best combination of parameters to ensure optimum stiffening with a minimum of localized curvature for plates of fixed total weight. The nature and character of the localized curvatures developed in an over-stiffened ribbed plate was revealed by photographic records obtained by means of the Salet-Ikeda slope-contouring technique. It was concluded that, for optimum design on a basis of rigidity of plates of given total weight, 40 per cent of the total weight of a ribbed plate should be in the ribs or webs and 60 per cent in the basic plate or flange. Localized curvature with attendant stress concentrations were found not to be serious under such a degree of stiffening. Frozen stress photoelastic studies have been initiated to elucidate stress distributions in the vicinity of the ribs.