GIRDERS AND TRUSSES 119 



Referring to Figs. 48, 49, 50, wherein the stress is shown to 

 be equal to the moment divided by the depth, the compressive 

 stress in the long horizontal member is, 



The length of the diagonal portion of the tie is found by the 

 formula ,-7-5 , ,i\ t 



= o 



and the tensile stress in the diagonal is 



r-fl 



2d 



The compressive stress in the vertical strut depends upon the 

 construction of the horizontal member. If it is in two pieces joined 

 over the strut, one- 



half the load, P, is "f ? -""1 



carried by the strut. ^ 

 If it is in one piece, 

 or composed of 



several planks so Kg 7 6.-Single Strut Belly Rod Beam 



joined that they act 



as one piece, the strut carries f P when P is a single concentrated 

 load or |TF when W is a uniformly distributed load. This value 

 must be used for P in the above formulas. 



When the single strutted beam carries a single concentrated 

 load over the strut the latter carries the whole load, plus half the 

 weight of the uniformly distributed load of the beam. The ten- 

 sile and compressive stresses in the horizontal and diagonal members 

 are found as explained above. 



In Fig. 77 is shown a beam with struts at the third points. 



The bending moment for a beam carrying two equal loads, P, 

 at a distance - L + 3 from each end, is 



PL 



The horizontal stress C - -rr* 



M 



Pt 

 The diagonal stress, T - -3- 



The compressive stress in each strut - P. 



