Abstract
It is of practical importance to estimate the effect of ribs on the bending strength of cast iron beams. However, such computation will not be as easy for cast iron as for the usual elastic materials because the stress-strain relation is not linear and the concept of section modulus is not applicable.
The authors have calculated the theoretical rupture strength of T-beam using an electronic computer with a particular attention on the non-elastic behavior of cast iron. The effect of ribs were represented by a function of the rib-web dimension ratio and the calculated values were checked experimentally.
Although the effect of ribs in cast iron may be computed much like the elastic materials within a certain range of the rib-web ratio, non-elastic behavior must be considered in estimating the effect of ribs in the other ranges. In the case of ribs in tension, when the rib was small compared to the web, the effect of the rib was greater than the elastically calculated value. Thus, the actual rupture strength of T-beam was greater than the value calculated with the section modulus. In cast iron the rib-web range that decreased the beam strength was narrower than for the elastic materials. In the case of webs in tension, the strength of T-beam calculated with the section modulus was greater than the actual strength. The narrower and the deeper the ribs, the greater was the discrepancy.
The effect of ribs varied according to the grade of cast iron. It was found that when the rib-web ratio was small, cast iron of lower strength behaved as an elastic material.
The theoretical values agreed well with the observed values for FC35 grey iron. The deviation between the experimental and the calculated values in deep ribs was explained as a size effect due to the stress gradient in bending.
