142 STRESSES IN TWO-HINGED ARCH 



sidering the arch a simple truss with allowable stresses, say, twice 

 those to be finally allowed. In the latter case the first approximation is 

 usually worthless on account of the reversal of stresses in the members 

 which have been designed as tension members. If the value of H in the 

 first method is taken large enough to make members in compression 

 that the designer's judgment or experience says should be in compres- 

 sion, the second approximation is usually final. 



