Stiffness Method

Structural Analysis by Stiffness Method
The stiffness or displacement method of structural analysis is analogous to the flexibility method; whereas in the latter the forces were unknowns, here the displacements are unknowns. Some of the basic principles and equations applying to the stiffness method have already been developed by the generalisation of existing methods and well known principles. In the matrix formulation of the stiffness method there is no need to distinguish between a statically determinate structure and an indeterminate one, since the steps are identical in both cases.
Of the two methods, the matrix displacement method of analysis is commonly preferred particularly when the degree of static indeterminacy is high. The stiffness

are roof trusses and are used up to 30 m span. The other types of trusses are commonly used in bridges.

Space Truss
The analysis of space trusses can be regarded as an extension of plane truss analysis. However, special consideration is necessary in view of the third dimension involved. Stresses are interrelated between members not lying in one plane. Space trusses include towers. Antennas, guyed masts, derricks, framing for domes, aircraft framing etc. to name a few.
To simplify computations, the connections of the members in a three dimensional trusses are considered to be ball and socket joints. It is assumed that the joints transmit no moments and the external loads son the truss are applied only at the joints. Therefore, members are subjected only to axial forces as in planar trusses.
An idealized truss is termed just rigid if the removal of any of its members destroys its rigidity. If the removal of a member does not destroy its rigidity, the truss is said to be over rigid.
Plane

The joints are said to be rigid if the angles between the members remain unchanged during the deformation of the structure. The members of a rigid jointed plane frame carry axial forces, shear forces, and bending moments. During deformation the members of a rigid jointed frame assume a curved shape. As the axial displacements of the members of a rigid jointed frame are much smaller than the transverse displacements, it is a common practice in structural analysis to ignore the axial displacement of the members. Thus all members of a rigid jointed frame are considered inextensible. This basic assumption will be utilized in the development of the force and displacement methods of matrix analysis of rigid jointed