GRAPHIC STATICS 



225 



truss into one having vertical reactions. This rod will also change 

 the diagram and render it possible to start from either end of the 



load line and project the 

 members. This the student 

 is advised to do as an exer- 

 cise. If the reactions from 

 roof trusses are not vertical, 

 walls will be forced out and 

 the trusses will sag. 



A step forward from the 

 scissors truss gives the truss 

 with curved tie, shown in 

 Fig. 149. This is very often 

 seen in churches. Some- 

 times the framing is exposed and at 

 other times a ceiling is attached to the 

 Fig. 148. Scissors Truss. 



curved tie. 



The curved tie is usually 

 a T iron which is bolted to 

 the rafters at the ends. The 

 upright leg of the T is set 

 into the horizontal brace 

 and into the rafters as well. 

 Though the tie is curved the 

 pull is straight from joint 4 

 to joint 3 and joint 7 and is 

 straight from 3 to 1 and 

 from 7 to 8. At (6) is shown 

 the truss diagram and at (c) 

 is shown the force diagram. 

 Between the joints the T 

 must have enough stiffness to 

 retain the curved form into 

 which it is rolled, or bent. 



The hammer-beam truss, 

 shown in Fig. 150, is a hand- 

 some truss much used for 

 churches and stately halls, 

 with exposed rafters. The 



Fig. 149. Truss with Curved Tie. 



