ElvISHA MITCHELL SCIENTIFIC .SOCIETY. 52 



tends to cause tension in the upper fibre. Its influence 

 being- benelicicil, was not further reg-arded. 



The method has now been g-iven in full for ascertain- 

 ing' the stresses in the various members for a non-uni- 

 form loadino". 



In this particular case, the dead load per panel per 

 truss, was assumed at 4500 lbs., which is found to be 

 nearly exact on making- out weig-hts, etc. 



The live load was assumed to be that due to a crowd 

 of people vveig-hing- nearly 80 lbs. per sq. foot, for a 

 clear width between trusses of 16 feet: the portion held 

 at one apex of one truss being- 9500 pounds. As such a 

 partial load can only be obtained by supposing- the live 

 load to extend from an abutment two panels and then 

 neglecting- the part held up at the farthest apex, it is in 

 excess of any eccentric load that can be placed only at 

 one apex und thus is on the side of safety. 



The influence of temperature chang-es is seen to be very 

 marked for this combination bridge and would be still 

 more pronounced for more northern latitudes, where 

 g-reater rang*es of temperature are experienced than in 

 the Southern states. B\^ g'i^'ing* any desired value to t in 

 equation (10) above, the resulting- value of p is readily 

 found and the chord examined as before for proper width. 



It would materially tend to obviate the bad effects of 

 temperature if the truss was assembled in the heat of 

 summer without any camber in the chord. As it became 

 colder, the chord w(juld receive a slig-ht camber upwards, 

 which would increase with the fall of temperature, and 

 thus tend to diminish the large bending- stress in the chord 

 at the most heavily loaded apex. For this case, we should 

 put, say, t = — 50 in eq. (10) and thus find/= 4.65 and 

 finally the resulting- maxijuum moment in the chord act- 

 ing- as a beam which turns out to be at the rig-ht post 

 where no live load is supposed to rest. It is 1683x15 ft. 

 lbs., and thus less than for the temperature at which the 



