646 WM. HERBERT HOBBS 



Examination of the photograph of the Manshai bridge reproduced 

 in Fig. 5, D, will show in the lateral kink of the rails and the dropping 

 of the span conformity with the general rule that there is a shortening 

 of the distance between piers. 



CALIFORNIA EARTHQUAKE OF APRIL 18, I906 



The report upon this earthquake^ purporting to discuss the effect 

 on structures particularly is a disappointment in that a single bridge 

 only is mentioned, and this in such ambiguous language that the 

 nature of the damage sustained can only be guessed.^ The bridge 

 referred to is that of the Southern Pacific Railway where it crosses the 

 Pajaro River near Chittenden Station. Abundant material for a 

 study of the damage to bridges existed, and we are fortunate in 

 having been able to collect the data concerning some interesting 

 examples. One of these is illustrated by a photograph of the county 

 bridge over the Pajaro River at Chittenden, which, as well as any 

 we have seen, illustrates a typical effect of earthquakes upon such 

 structures (see Fig. 5, C).^ 



The damage sustained by the SaHnas Highway Bridge in the same 

 province has been described and photographed by Derleth^ (see 

 Fig. 5, -S), and is shown to conform to the rule which elsewhere 

 obtains. The bridge rests on pile-bent abutments. The north 

 abutment was not disturbed, but the south abutment was bent back 

 from the river at the top and it is stated that the ground moved out 

 toward the river beneath it a distance of six feet. A three -inch oil 

 pipe-line crossing the bridge was bent into an S and ruptured. 



In the same article Derleth has given us a clear account of the 

 damage to the Southern Pacific Railway bridge over the Pajaro 

 River, from which it appears that this case is an unique exception to 



I Grove Carl Gilbert, Richard Lewis Humphrey, John Stephen Sewell, and 

 Frank Soule, The San Francisco Earthquake and Fire of A pril l8, iQo6,and Their 

 Effect on Structures and Structural Material, Bull. 324, U. S. Geol. Surv., 1907, pp. 

 170, pis. 56. 



a Loc. cit., p. 20, PL XI ^. 



3 Reproduced in Salisbury's Physiography CNew York, Holt & Co., 1907), p. 424. 



4 Charles Derleth, Jr., C. E., "The Destructive Effect of the San Francisco Earth- 

 quake of 1906," Engineering News, Vol. LV, No. 26 (June 28, 1906), p. 712, Figs. 

 15 and 16. 



