1844.] 



of a Pier at Madras. 



79 



braces 3sq. i. 24sq. I. for each and for the four \2sq. i. dGsq. I. consequently 

 the whole area of the wrought iron braces is 53sq. i. 9'6sq. I. The resistance 

 to the traction of wrought iron being 90 cwt. for a square inch* the whole 

 resistance will be 4830 cwt and relatively to the power as 21 to 1. 



But it is not only the wrought iron braces which resist the force exerted 

 upon the rows of the Pier. The supports of the rails and the planking 

 resist in the same manner, for the first cannot give way without the last 

 being torn off at the same time. Now the area of support is 60sq. i. 

 which gives for the four 240sq. i. the area of the planking being altoge- 

 ther 600s<7. i. the whole area of the timber work will be 840s<?. i. esti- 

 mating the resistance to the traction of teak wood to be only 10 cwt 

 for each square inchf the whole resistance will be 8400 which 

 added to 4830 cwt, resistance of the wrought iron braces will give 

 a total of 13,230 cwt. The force exerted being 229 cwt. the proportion as 

 to the resistance will be as 1 is to 58, but the resistance is still increased 

 on that account that the braces which bind two rows, cannot be torn off, 

 without the neighbouring ones are bent and crushed. Besides the struc- 

 ture having a certain degree of elasticity the shock exerted upon one 

 row will extend itself to the following ones, constantly decreasing in 

 intenseness so that the force, exerted at the point which receives the shock 

 will be less than has been estimated ; it is therefore perfectly established 

 that the stability and solidity are much greater, than is required to stand 

 the force exerted upon the Pier, it remains now to examine if it ensures 

 equally the requisite of durability, on the subject, let us say, at first, that 

 the fears entertained of a rapid corrosion of iron are generally exaggerated. 



This is what we read, in the Civil Engineer and Architect's Journal vol. 

 v. page 255, in an article upon iron ship building. 



The corrosion of iron plates by the action of the sea water proves a 

 groundless alarm, no case of destruction from this cause, in many years 

 experience has yet occurred. In the same vol. page 54 in speaking of a 

 bridge of iron wire built at Brest, it is said. 



" It appears from the proces-verbal 1st that the continuous ligature, 

 which covered the cables, was slightly attacked, but that, by the first 

 scratch of the file, the oxidized portion was removed, 2d that the exterior 

 wires of the cables showed slight traces of oxidation, but that the slightest 



* 1. The maximum of resistance to the traction of wrought iron is more than double 

 than what has been estimated in the calculations. 



t 2. The maximum of resistance to the traction of teakwood, supposing it is the 

 same as that of oak, is ten times as much as has been estimated, in the above calcu- 

 lations, 



