FORCES ACTING ON STRUCTURES 



Art. 3 



one or many pieces. 

 Fig. 1. 



Several forms of girders are shown 



Flange 

 Flange ~TH"*~ 



II 

 .JL 



F/ange 



F/ange 



F/ange 

 PLATE 



F/ange 



Fig. 1- 



A plate girder is a girder having one web a single plate. 



A box girder is a girder having two or more webs. 



The flanges are usually made of angles or of angles and 

 plates. 



A TRi'SS 1 is a beam composed of a number of members con- 

 nected together, by pins or rivets, so as to form a stable struc- 

 ture, the stresses in the members being tensile and compressive, 

 and the loads being applied at the joints. 2 See Fig. 2 for the 

 names of the different members of a truss and Chapter XI for 

 different kinds of trusses. 



TOP 



L- 



BOTTOM CHO&D 

 6pane/s ofp - span L 



Fig. 2. 



3. Forces Acting on Structures. When structures are in 

 service there are external and internal forces acting. The ex- 

 ternal forces are the loads and the reactions. The reactions are 

 caused by the loads and are the forces acting at the supports 

 to hold the structure in equilibrium. 



term girder is sometimes used in place of truss, especially for con- 

 tinuous or lattice trusses. 



Occasionally, ;i truss carries loads which are not applied at the joints 

 and some of the members must also act as beams. 





