STRENGTH EEQUIREMEXTS FOR ROUND CONDUIT 



745 



bedding, the moment at the l^ottom may vary up to 235 per cent, and 

 the moments at the side points maj^ change a maximum of 12 per cent.^ 

 The field data indicate that l)edding is of particular importance with 

 moist clay backfill, and to a lesser degree for moist fine sand. However, 

 bedding did not appear to affect the moment distribution of the tube for 

 a dry sand or gravel backfill. 



TRENCH WIDTH 



The effect of the trench width on the magnitude of the bending mo- 

 ments in a conduit has been investigated. The presently available test 

 results indicate the following: 



a. Xo significant difference in the magnitude of the bending moments 

 of the tube (4.5-inch diameter) could be observed for a trench width 



MMM 



,, p =2.22 PSI 



LOAD DISTRIBUTION 



M = pr2 

 M = pr2 



■icosae + 3^00594-1-] 

 _3^cose-siNe + | + i] 



o^e<90 



90£e<l80 



Fig. 6 — Theoretical moment distribution in a thin-walled tube subjected to 

 uniformly distributed vertical pressure at the top and point load at the bottom. 



