LII. J. I. HAYCROFT. 



between centres of gravity of the flanges is 3 metres, and from 

 what has already been proved the vertical stress on the end 

 diagonals = 2*5 W = 29 tons say and on the intermediate 



W 



verticals = -— =5*7 tons. 

 Z 



The mean values of the moments of Inertia and areas of cross 

 section are taken to apply in the above equations, as they vary 

 but little, but still, if great exactness is required, the actual 

 values can be taken : the mean values in function of a metre are- 

 as follows : 



\ x = 0-00158 

 I a = 0-00134 

 Sj = 0-02350 

 S 2 = 0-01890 



Note : The sections are nett. 



Substituting these values in the equations we get 



P x = 28,563 kgs 



P, = 42,525 „ 



P 3 = 36,827 „ 



P 4 = 15,186 „ 



P B - 6,074 „ 



To complete the calculation of stress on this Bridge it i* 

 necessary to find the stresses in the flanges : these are got from a 

 diagram of bending moments, Fig. 6. The full line gives the 

 B.M., due to the external loads and internal vertical stresses at 

 each vertical, the moments being taken round the point of 

 inflexion of each vertical. 



The dotted stepped line gives the moments of the horizontal 

 reactions at the inflexion point of each vertical. These moments 

 are calculated round either end of each vertical. 



The effective Bending moment on each bay of the flanges is 

 equal to the vertical ordinate included between the fuil line and 

 dotted line : their values, at a distance of one metre on each side 

 of the centre point of each bay of the flange, are written on the- 

 diagram. 



