ON THE DESIGN OF GIRDER BRIDGES. 475 



limited, more often than elsewhere prohibitory of the adoption of the 

 most economical form for the main girders ; and although the question of 

 design requires careful study, there is no evidence of the existence of 

 inherent national errors or prejudices in design which would be likely to 

 place English engineers at a disadvantage in dealing with colonial work, 

 or to account for the fact that they have lost it in Canada, and recently 

 in one case in Australia. 



It has been suggested that the position of the designer in America is 

 more favourable to economy of construction. 



In America when a bridge is required the railroad company invite 

 tenders for its construction and erection in accordance with their speci- 

 fication, which generally states the class of bridge preferred, the load 

 which it is to carry, and the quality of the material, and defines in con- 

 siderable detail the stress to which its parts may be subjected. The 

 design is left to the bridge company tendering for its construction, but it 

 is required that sufficient information shall be supplied with each tender 

 to enable the railroad engineer to examine the proposal and determine 

 whether it fulfils the required conditions. 



The designer, who is consequently employed by the bridge company, 

 has in the first place to produce the most economical structure, while the 

 primary responsibility for its safety lies with the railroad engineer who 

 has prepared the specification, and will be enabled to check the corre- 

 spondence of the design with his requirements before the tender is ac- 

 cepted, and to make the necessary modifications — a work of considerable 

 difficulty unless the design is a good one to begin with. 



The English designer, on the other hand, has in the first place 

 to design a safe structure, since he is seldom immediately subject to 

 competition in respect to its economy, and is entirely responsible for its 

 security. 



The English system has advantages with respect to security ; while 

 its economic disadvantages are that the engineer is seldom able to 

 ascertain either the exact cost of his designs, or the relative economy of 

 their details, nor has he any personal interest to serve, or any other in- 

 ducement to reduce the cost to the lowest point. The system moreover 

 entails a want of correspondence between the design and the appliances 

 of the manufactory, where it is afterwards executed, especially if the work 

 is let by open tender. These disadvantages are accidental rather than 

 essential in their nature, and this should suggest their remedy in detail 

 rather than the condemnation of the system under which they arise. 



Much could be effected by manufacturers to promote economy in 

 design by the pubUcation of particulars of the relative cost of different 

 details of construction, in such a way as not to injxu'e their commercial 

 interests. 



It is also an open question whether standard sections could not be 

 adopted for the usual sizes of angle, tee, and other rolled bars, so that no 

 difficulty need arise — in this respect at least — in making the design in 

 accordance with the scantling of the materials readily available for its 

 manufacture. 



Both the design of bridges generally, and the personal position which 

 the designer should occupy, are matters which may be left entirely to the 

 discretion of those concerned ; but engineers are in England very properly 

 subject to a certain degree of Government supervision in regard to struc- 

 tures which directly affect the safety of the travelling public. 



