Structural Supports- Analysis of Structures-Part-2 

In this article I will be talking about main types of structural supports. Essential knowledge about the three types of supports will be explained in such a practical way that the people with limited knowledge can also get benefit from this article. Movement possibilities of Structural Supports, i.e. structural degrees of freedom will be explained in this article. Engineering students and beginner structural engineers are the common beneficiaries of this article.

Structural supports are where a support structure rests. Support defines how the ends of a support structure is connected to a supporting body or foundation. In the example shown above the beam is resting on a hinge support on one end and on roller support on other end.

Simply Supported Structure: A support structure with roller and hinge supports on its ends is called a simply supported structure. Supports of a simply supported structures only support forces, they cannot support any moments. Therefore, associated support reactions are only forces. 

Fixed Supports: Fixed supports do not allow the fixed end to displace neither in any direction nor rotating about any axes.

On the beam column system, the column has a fixed support. Foundation of a regular column is an example for a fixed support.

Cantilever: A support structure with only one fixed support is called a Cantilever. Cantilevers can support both the forces and moments. Associated support reaction can be forces and moments. 

Displacements and rotation possibilities of the structural supports is called Degrees of Freedom. There are altogether six degrees of freedom for a structural support.

By restricting a displacement and or rotations we prepare a roller, hinge or fixed supports. At the restricted degree of freedom a related support reaction develops if any load is applied along or about that related axis.

For example, if a displacement along axis-z is restricted the Fx reaction develops in the support. Similarly, if a rotation about axis y is restricted a reaction moment My develops in the support. Following table shows which degree of freedom is restricted and which is allowed in different common 2D structural supports .

Following figures show how the support reactions develop in different support types depending on application of loads.

In summary, if we have a load on a support structure along one axis then at least one of its supports should not be allowed to displace along that axis. Similarly, if we have a applied moment about an axis then one of the supports should not be allowed to rotate about that axis.

In the next article I will be dealing with determination of support reactions. Previous

Related reading: Loads, Terminology of Structural Analysis, Determination of Bending Moments, Shear Forces and Axial Forces