Art. 124. 



SPECIAL TYPES OF BRIDGE TRUSSES. 



231 



The three-hinged arch is so built that the crown is free to 

 move up and down with changes in temperature. In the other 

 kinds, changes of temperature induce stresses in the arch. 



The trusses used in suspension bridges are simply stiffening 

 trusses, suspended from the cables, and prevent excessive deflec- 

 tions of them. The cables themselves are sometimes trussed to 

 stiffen them. 



