284 Lateral Stability of the Victoria-street Bridge. 



the bridge is seen to have most abundant stability against 

 wind pressure, far beyond the practical requirements of the 

 case. 



As comparative examples confirming this view, it may be 

 noted that ordinary chimneys have a resistance to wind 

 pressure of from 20 to 50 lbs. per square foot, and that 

 hundreds whose resistance is less than 30 have been stand- 

 ing for many years in positions far more exposed than the 

 Victoria-street bridge. Further, that ordinary railway 

 carriages have a resistance of in no case more than 55, and 

 in many cases of less than 30 lbs., and yet have for many 

 years traversed high embankments and viaducts in positions 

 far more exposed than the structure ^ in question, and that 

 without accident. 



In view of what has been above stated, it might appear un- 

 necessary to refer to the proposed alteration. It is, how- 

 ever, a very singular fact that the recommendation greatly 

 exceeds the requirements of the calculation upon which it is 

 supposed to be based. Granting for the time being the 35 

 lbs. wind pressure as observed, and the desirability of pro- 

 viding a resistance of threefold the greatest force that can 

 be brought to bear, all requirements may be complied with 

 in a far simpler and cheaper way than that proposed. In- 

 stead of placing additional cylinders on both sides of the 

 pier, as shown in Fig. 1, suppose we place them on the down- 

 stream, or south side, only, as in Fig. 2. We shall find that 

 the overturning wind pressures become 192 lbs. per square 

 foot on the north side and 115 lbs. on the south ; and as the 

 greatest observed pressures are 35 and 23 lbs. respectively, it 

 will be seen that in this way much greater stability might 

 be obtained than the calculation requires. 



A strong protest having been entered against the preced- 

 ing proposals, a second engineer was called in, and he en- 

 dorsed the recommendation to place additional cylinders on 

 both up and down stream sides, but refrained from submit- 

 ting any calculation, contenting himself with briefly express- 

 ing an opinion that it was desirable in view of floods. 



This aspect of the question we must next proceed to 

 examine, for it is manifestly conceivable that, though amply 

 safe against wind, the structure might be dangerous when 

 exposed to high floods. Particulars as to flood velocities and 

 pressures are difficult to obtain, and consequently the only 

 way to proceed is to institute comparisons with existing 

 successful structures whose moment of stability does not ex- 



