4-28 Mr. Seaward on Suspension Chain Bridges. 



gether, were equal to the strain on the catenary curve at B 

 (fig. 1.), yet as the rods ZB. ?B, &c. (supporting equal portions 

 of the load) are' much shorter than the others, there would 

 from that circumstance alone arise a very considerable saving. 

 But taking into account the diminution of the sti'ain on the 

 shorter rods, as also the dispensing with the vertical rods al- 

 together, it must be quite clear to every one, on a little re- 

 flection, that the advantages in point of strength must be 

 decidedly in favour of a bridge built on the new plan. 



But as it will be much more satisfactory to illustrate what 

 has been stated above by a practical example, I will proceed 

 to describe, as far as is essential, a suspension bridge which 

 has been proposed to be erected in a distant part of England 

 on the common principle of the catenary curve : and com- 

 paring it with one recommended to be built on the new plan, 

 with the same quantity of materials, the superiority of the 

 latter will readily appear. 



The bridge in question is proposed to be 400 feet between 

 the points of suspension A and B (see fig. 1.); the height of 

 the points of suspension from B to F 33 feet; the versed sine 

 or deflexure of the curve H to C 27 feet ; and from the ver- 

 tex of the curve to the top of the platform C to D 6 feet ; the 

 length of the platform or roadway from E to F about 392 

 feet. The weight of the timber platform, the tram plates, 

 fencing, vertical rods, the chains between the points of sus- 

 pension, &c., is estimated to amount to about 150 tons ; and 

 on an extraordinary occasion, — the passing of a regiment of 

 soldiers, or of a large drove of cattle, — it is presumed might 

 throw an additional load of 150 tons weight on the bridge, 

 making in the whole an aggregate weight of 300 tons to be cal- 

 culated for in the strength of the supporting chains. 



The chains are proposed to be formed of sixteen If in, 

 round rods connected together in 9 feet lengths by pins and 

 shackles, and the roadway supported by 1 in. round vertical 

 rods. 



Now a flexible chain of uniform weight suspended at two 

 points 400 feet distant from each other, and hanging freely 

 with a deflexure of 27 feet, will, according to writers on the 

 catenary curve, make the angle CBH equal 15° 12' nearly: 

 and the length of the chain will be 404-816 feet. And sup- 

 posing the whole weight to be 300 tons as above stated, the 

 strain at each point of suspension will be equal to 572*105 

 tons. 



The strain upon every square inch of sectional area in the 

 sixteen chains will be equal to 14"865 tons, or 15 tons nearly. 



And 



