RURAL ENGINEERING. 



487 



the road on the subgrade by a wheel load of 4 tons, with a 5i-in. tire, gave the 

 following results: 



Transmission of pressure through macadam to subgrade. 



The pressure on the subsoil through a 12-in. bed of simple macadam is ap- 

 parently the same as the pressure through a 6-in. bed of macadam laid over a 

 10-in. stone foundation. It Is considered that poor soil requires at least a 12-in. 

 macadam layer or its equivalent. 



Test of a bridge slab, E. B. McCobmick (Cement Era, 13 {1915), No. 3, pp. 

 54, 55, figs. 8). — The author briefly describes experiments being conducted by 

 the OflSce of Public Roads and Rural Engineering of this Department to de- 

 termine the effective width of reinforced concrete bridge and culvert slabs 

 under various conditions of loading. The effective width is considered to be 

 " the width of a slab, which, if subjected to a load of a certain magnitude, uni- 

 formly distributed along the top fiber of the center section, will have the same 

 maximum outside fiber stress, and the same total fiber stress as the tested slab 

 showed under the concentrated load of that magnitude." 



Diagrams are given showing lines of equal stress and fiber stresses along 

 sections for a slab under one, two, and four point loadings. The diagrams 

 for center loads show that the effective width is the same for loads of different 

 magnitude, that is, " the effective width of a slab is apparently Independent 

 of the magnitude of the load," 



No conclusions are drawn, as further investigations are in progress. 



Estimating curves for standard bridges of the Illinois Highway Depai't- 

 ment, G. F. Buech (Engin. and Contract., 43 {1915), No. 6, pp. 123-126, figs. 

 13). — This article gives data and a set of curves for estimating the quantities 

 of materials in the various types of highway bridges designed by the Illinois 

 Highway Department. 



Structural engineering, J. B. Kibkham {Chicago: The Myron C. Clark Pub- 

 lishing Co., 1914, pp. V-{-669, pis. 3, figs. 452). — This bool?, while dealing pri- 

 marily with general structural engineering, contains a section covering the 

 design of simple steel highway bridges, including the beam, pony truss, and 

 high truss types. 



Tests and uses of hydrated lime, R, C. Haff {Cement Era, 13 {1915), No. 2, 

 p. 69). — The author found in his tests that the addition of from 10 to 15 per 

 cent of hydrated lime to 1 : 3 cement and sand mortar increased the strength. 

 He states that his experience has proved hydrated lime to be the best water- 

 proofing material available, and recommends the addition of 15 per cent for 

 this purpose. 



6318°— No. 5—15 7 



