July 4, 1902.] 



SCIENCE. 



15 



security is obtained in every detail of the 

 connections as in the principal members 

 which compose the structure. 



Experiments on a large scale are very 

 much needed to determine the proper per- 

 centage of tlie live load to be allowed for 

 the effect of impact, so as to secure the 

 necessary strength with the least sacrifice 

 of true economy. While the extreme 

 economy of material that was fonnerly 

 practised is not now desirable, since stiff- 

 ness receives due consideration, some idea 

 of the importance of such an investigation 

 may be gained by considering the magni- 

 tude of the industries involved. 



In March, the Railroad Gazette published 

 a supplement containing a list of bridge 

 projects under consideration. This list 

 was intended to include only the larger 

 steel and stone structures, whether for 

 railroads or highways, the aim being to 

 exclude those that are obviously unimpor- 

 tant. Besides this, the bridges needed on 

 1,500 new railroad projects recorded in 

 the same supplement are likewise excluded. 

 After excluding both of these classes the 

 list still contains about l,-300 new projects 

 for bridges. 



An investigation might also be advan- 

 tageously made to determine the proper 

 ratio of the thickness of cover plates in 

 chord members which are subject to com- 

 pression, to the transverse distance between 

 the connecting lines of rivets. The same 

 need exists in regard to the stiffening of 

 the webs of plate girders, concerning which 

 there is a wide variation in the require- 

 ments of different specifications. 



A movement which has done much good 

 during the past decade and promises more 

 for the future is that of the organization 

 of bridge departments by the railroad com- 

 panies. The great economy of making 

 one design rather than to ask a number of 

 bridge companies to make an equal num- 

 ber of designs, of which all but one are 



wasted, is the first advantage ; but another 

 of even greater significance in the develop- 

 ment of bridge construction is that which 

 arises from the designs being made by 

 those who observe the bridges in the con- 

 ditions of service and who will naturally 

 devote closer study to every detail than is 

 possible under the former usual conditions. 

 •The larger number of responsible designers 

 also leads to the introduction of more new 

 details to be submitted to the test of ser- 

 vice, which will indicate those worthy of 

 adoption in later designs. In order to 

 save time and labor and secure, greater 

 uniformity in the design of the smaller 

 bridges, some of the railroads prepare 

 standard plans for spans varying by small 

 distances. For the most important struc- 

 tures consulting bridge engineers are more 

 frequently employed than formerly, when 

 so much dependence was placed upon 

 competitive designs made by the bridge 

 companies. 



An investigation was recently made by 

 a committee of the Railway Engineering 

 and Maintenance of "Way Association in 

 regard to the present practice respecting 

 the degree of completeness of the plans 

 and specifications furnished by the rail- 

 roads. It was found that of the 72 rail- 

 roads replying definitely to the inquiry, 

 33 per cent, prepare 'plans of more or less 

 detail, but sufficiently full and precise to 

 allow the bidder to figure the weight cor- 

 rectly and if awarded the contract to at 

 once list the mill orders for material'; 18 

 per cent, prepare 'general outline drawings 

 showing the composition of members, but 

 no details of joints and connections ' ; while 

 49 per cent, prepare 'full specifications 

 with survey plan only, leaving the bidder 

 to submit a design -^^dth his bid.' If, how- 

 ever, the comparison be made on the basis 

 of mileage represented by these 72 rail- 

 roads, the corresponding percentages are 

 48, 24 and 28 respectively. The total mile- 



