158 THE IMPROVEMENT OF RIVERS. 



P^ H ^Wseca H ^//seca vx 



M- -X 7=seca-tt>X 7= X 7=^X ^^X62^1bs. 



3 V 3 V 3 2 N/3 3 v/3 



*sec*aX62i Ibs. 



The total section required is then found by the formula 



inch-pounds. 



where A - total area required; 5= total allowed strain per square inch; d = amount 

 of direct compression or tension in the member; Af maximum bending moment in 

 inch-pounds; c = distance in inches of extreme fiber from neutral axis; and r radius 

 gyration of the section. 



The angles a and ft can only be determined by trial, as there is usually only one 

 position for each height of trestle which will give the greatest clearance when the dam 

 is lying down. 



AB and AC should be strongly connected at the top with deep gusset-plates, as, 

 if the legs are wide apart there, secondary bending stresses will be introduced, causing 

 a tendency to buckle. 





