SIMPLE TRUSSES 



11 



distance from N, will be sensibly parallel to ACB. It 

 appears that the vertical shear influence diagram is con- 

 structed in precisely the manner outlined for the moment 

 influence diagram when CD is made equal to unity. 



For a load on the left of the vertical through E, the 

 vertical shear between E and F is 



(27) 



-ai) tan O s -Wi(l) =Wi(+pe-pf)-, 



= Wi(+ef). . . . (28) 



or 



therefore 



In a similar manner it is shown that the ordinates 

 directly below W 2 , W 2 f and W 3 , represent the vertical 

 shears produced by unit loads at these points. 



A negative ordinate in the influence diagram indicates 

 that the resultant shear acts upward; therefore the 

 vertical component of the stress in the web member, for 

 which the influence diagram is drawn, acts downward. In 

 Fig. 4, the member U'L' is in compression for loads on 

 the left of G. The vertical UL has the same influence 

 diagram but it is in tension for the same loads. 



The criterion for maximum shear is determined in the 

 manner given above for maximum moment. Without 

 writing all of the equations and referring to equation (13) 

 and Fig. 4, 



..rr 



-tan 05 -Ban 4 )- 



-W 3 tan $2=0. 



-tan 4 +tan 



(29) 



RETURN TO 



of APPLIED MEGHAN^ 



