A STUDY OF THE DAMAGE TO BRIDGES DURING 

 EARTHQUAKES.^ 



WM. HERBERT HOBBS 



To the study of the damage sustained by buildings during earth- 

 quakes a vast amount of attention has been devoted, while other 

 structures, better suited to reveal the nature of the disturbance have 

 hardly been examined at all from the scientific standpoint. This 

 is in part to be explained because the damage has been supposed to 

 result wholly from elastic waves, but in part it has been determined 

 by the obvious necessity of safeguarding the lives of the inmates of the 

 buildings. Adopting the newer viewpoint that the vibrations felt at 

 the surface of the earth are genetically at least a secondary rather 

 than a primary cause of the disturbance, our attention must be turned 

 in a different direction. In place of high structures we must study 

 low ones, and from inspecting damage at isolated points we must note 

 the distribution of the damage along complete sections crossing the 

 affected district. Buildings thus give place in importance to rail- 

 ways, pipe lines, and to metal cables, and in fact to any continuous 

 structures of fairly uniform strength and rigidity over long distances. 

 Such structures are suited to register either tensional or compressional 

 stresses. 



Railway tracks, now the most generally available of these struc- 

 tures, preserve a record of tension in the tearing out of fish-plates and 

 separation of rail ends, and of compression in the jamming of the 

 joints and the buckling or kinking of the metals. The first and 

 most striking result of observation of the damage to such structures, is 

 the common occurrence of distinctly local maxima of deformation (see 

 Fig. I, C and D). The zones of deformation are not always, however, 

 so narrow as in these instances, but may be betrayed by a sinuous 

 course of the rails extending over a considerable fraction of a mile 

 (see Fig. i, A). 



I A paper read before the American Association for the Advancement of Science at 

 the Chicago Meeting, December, 1907. 



636 



