Advantaages of skeletal ( framed ) structures over solid ( load bearing ) structures :

1. Saving in floor space . 
2. Flexibility in plan , building operation & future renovations because of the absence of loadbearing walls at any level . 
3. Reduction in dead weight . 

• Building frames may be classified according to the stiffness or rigidity of the joints between the members , especially between columns & beams . 
• non rigid frame can be described with presumption of a beam with simply supported & the non-rigid joints . 
• Rigidity in the framed structure as a whole is ensured by the inclusion of some stiffening elements in the structure , often in the form of trianguilating members . 
• Steel & timber frames are commonly jointed in this manner & sometimes precasr concrete frames . 
• ( triangulating steel & timber frames )  - timber roof truss - steel roof truss 
• Semi-rigid frames is one where some rigity is obtained with technique usually limited to steel frames . Whereas fully - rigid frame means all joints are rigid . 
• The joints of the structure may provide the stiffness necessary to prevent the frame as a whole from deforming under lateral wind pressure but normally additional stiffening elements are often required . 
• This types of the buuilding frame can be constructed in steel and concrete . 
• An adequate degree of fire resistance in the frame is essential in order that its structural integrity may be maintained in the event of fire .