Art. 118. 



TYPES OF ROOF TRUSSES. 



209 



sheds of the New England mills, but ha; come to be used ex- 

 tensively for shops of all kinds. The steep sides of the trusses 

 are placed to face the north, and this side of the roof is made 

 of glass. The slope of the steep side is such that the direct rays 

 of the sun will not strike the glass. This gives a very light 

 interior for the building without the objection of direct sun- 

 light. If there is objection to having columns in the building 

 at points m and n, a top chord member opq (shown dotted) 



Three Hinged Arch 



Scissors Truss 



r 



Cantilever Truss 



Saw Tooth Roof 



Fig. 150. 



may be put in. This top chord member will be exposed above 

 the roof. 



119. Stresses in Roof Trusses. Great refinement is 

 not necessary in calculating the stresses in roof trusses, as the 

 loads which they have to carry cannot be accurately determined. 

 The stresses should usually be calculated for the following con- 

 ditions of loading : 



I. Dead Load. 



II. Snow Load on the Whole Roof. 



III. Snow Load on Half the Roof. 



IV. Live Load (if any). 

 V. Wind from the Right. 



VI. Wind from the Left. 



The dead load includes the weight of the structure itself 

 with the roof covering and all fixed loads. live load would 



be the weight of a traveling crane inside the building and sup- 



