CONCRETE DESIGN 283 



MODULI OF RUPTURE OF VARIOUS MINERALS 



safe load instead of the ultimate breaking load are being 

 solved. The weight of the stone itself must almost always 

 be taken into account. 



EXAMPLE. Design a Quincy granite lintel 6 in. wide on 

 a 5-ft. span to carry a uniform load, which includes its 

 own weight, of 300 Ib. per ft., with a factor of safety of 10. 



SOLUTION. In this example, W = 300X5 = 1.500 Ib. and 

 / = 5X12 =60 in. Therefore, 



ll,250m.-lb. 

 8 8 



According to the table, the modulus of rupture for Quincy 

 granite is 1,800, and if a factor of safety of 10 is used, the 

 value of s is 1,800 -MO = 180 Ib. per sq. in. Therefore, 



