Supports are used to attach structures to the ground or other bodies, thereby restricting their movements under the action of applied loads. The loads tend to move the structures; but supports prevent the movements by exerting opposing forces or reactions to neutralize the effects of loads, thereby keeping the structures in equilibrium. The type of reaction a support exerts on a structure depends on the type of supporting device used and the type of movement it prevents. A support that prevents translation of the structure in a particular direction exerts a reaction force on the structure in that direction. Similarly, a support that prevents rotation of the structure about a particular axis exerts a reaction couple on the structure about that axis. The type of supports commonly used for plane structures are given below.
1) Fixed Support
A fixed support is the most rigid type of support or connection. It constrains the member in all translations and rotations (i.e. it cannot move or rotate in any direction). The easiest example of a fixed support would be a pole or column in concrete. The pole cannot twist, rotate or displace; it is basically restricted in all its movements at this connection. Fixed supports are extremely beneficial when you can only use a single support. The fixed support provides all the constraints necessary to ensure the structure is static. It is most widely used as the only support for a cantilever. The fixed support is also called rigid support. It provides greater stability to the structure as compared with all other supports. To provide good stability to the structure, at least one rigid support should be provided. Beam fixed in the wall is a good example of fixed support.
2) Pinned Support (Hinged Support)
The hinged support is also called pinned support. A pinned support is a very common type of support and is most commonly compared to a hinge in civil engineering. Like a hinge, a pinned support allows rotation to occur but no translation (i.e. it resists horizontal and vertical forces but not a moment). The horizontal and vertical components of the reaction can be determined using the equation of equilibrium. Pinned supports can be used in trusses. By linking multiple members joined by hinge connections, the members will push against each other; inducing an axial force within the member. The benefit of this is that the members contain no internal moment forces and can be designed according to their axial force only. Hinge support reduces sensitivity to an earthquake.
3) Roller Support
It is a support that is free to rotate and translate along the surface on which they rest. The surface on which the roller supports are installed may be horizontal, vertical and inclined to any angle. Roller supports can resist a vertical force but not a horizontal force. The roller supports has only one reaction, this reaction acts perpendicular to the surface and away from it. A roller support or connection is free to move horizontally as there is nothing constraining it. The most common use of a roller support is in a bridge. In civil engineering, a bridge will typically contain a roller support at one end to account for vertical displacement and expansion from changes in temperature. This is required to prevent the expansion causing damage to a pinned support. This type of support does not resist any horizontal forces. This obviously has limitations in itself as it means the structure will require another support to resist this type of force.
4) Simple Support
A simple support is basically just where the member rests on an external structure. They are quite similar to roller supports in the sense that they are able to restrain vertical forces but not horizontal forces. The member simply rests on an external structure to which the force is transferred to. An example is a plank of wood resting on two concrete blocks. The plank can support any downward (vertical) force but if you apply a horizontal force, the plank will simply slide off the concrete blocks.
5) Rocker Support
Rocker support is similar to roller support. It also resists vertical force and allows horizontal translation and rotation. But in this case, horizontal movement is due to the curved surface provided at the bottom as shown in Fig. 5. So, the amount of horizontal movement is limited in this case.
6) Link Support
A link has two hinges, one at each end. The link is supported and allows rotation and translation perpendicular to the direction of the link only. It does not allow translation in the direction of the link. It has a single linear resultant force component in the direction of the link which can be resolved into vertical and horizontal components. In other words, the reaction force of a link is in the direction of the link, along its longitudinal axis.
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