Types of Supports, Reactions and Their Applications in Structures

Support in a structure are members that facilitate the supported structural element to bear or resist the load coming over it. For example, a column supporting a beam, or a beam whose one end is supported on a wall, etc.

Supports in structure can be either of two types:

1. External Supports
2. Internal Supports

Note * The support between the column and beam can be made through connections in many ways. For example, they can be connected as a fixed support, and the connection won't allow any movement of the joint during the action of load. But, if the support joint is a roller joint, rotational and translation movement is allowed. Hence, this derives several types of support.

Read On: Concept of Supports & Restraints in Structural Engineering

1. External Supports in a Structure

Those supports are provided externally, without disturbing the structural members are called the external supports. The types of external supports and their respective support reactions are explained below.

1.1. Fixed Support

Fixed supports are supports that do not allow any rotational or translational movement of the member. It is also called a rigid support. It restrains movement in all directions which would result in support reactions in all directions both in 2D and 3D configurations.

Fixed Support between a Steel Beam and Concrete Wall

If the number of support reactions is represented by re, then for fixed support, re in 2D =3 ( Rx, Ry and Mz) ; and re in 3D = 3 ( Rx, Ry, Rz, Mx, My, Mz)

Support Reactions in a Fixed Support in 3D Structure

You Can Get More Explanation On this Here: Fixed End Support Reactions in 2D & 3D 

1.2. Hinged Support or Pinned Support

A hinged support is support provided to the structural elements that facilitate rotational movement of the structure at that point but do not allow translational movement.

Fig.1. Hinge Support for Bridges

This means the support resist both the vertical and horizontal forces and can't resist moment. As a result of which, reactions are derived in the directions along which the movement are restrained.

Hinged End Support ( 2D ) Reactions

Hence, 

Support reactions at a hinge support in 2D Structure are [Rx, Ry] = 2 nos

Support reactions at a Hinge Support in 3D Structure are [ Rx, Ry, Rz] = 3 nos

The major applications of hinged support are in arched bridges ( three-hinged arches) with two support ends and the third hinge is at the centre of the arch called as the internal hinge. 

Read More: Hinged End Support ( 2D & 3D) Reactions in Structural Analysis

1.3. Roller Support 

Roller support resists only the perpendicular forces and restrains the parallel and horizontal forces and moment. Hence reactions arise along a perpendicular direction as shown below. 

Roller Support 

The number of support reactions for roller support = re = [Ry] = 1;

Roller support can be either a single roller or double roller in various configurations. 

1.4. Rocker Support

Rocker support serves the same purpose as roller support. The only difference is that it facilitates horizontal and translational horizontal direction by means of a curved surface at its support. Hence, the extent of horizontal movement it permits is less compared to roller support.

Rocker Support

Support Reactions of Rocker Support, re = Rx

2. Internal Supports and Reactions in a Structure

Internal supports are supports that are provided internally or within the structural members. This support hence disturbs and divides the structural element into parts. The analysis is hence carried out as separate parts and the external reactions are determined. The internal supports provided can be either an internal hinge or an Internal roller.

2.1. Internal Hinge Support for a Structure

An internal hinge in a member similar to a normal hinge support resists translational movement in both directions ( X and Y) and allows rotational movement. Internal hinges can be provided to axial members, beam members, and arch types of bridges.

Internal hinge provided at the center of an arch bridge. External internal hinge supports are provided at the end

2.2. Internal Roller Support for a Structure

An internal roller support similar to a roller support resists perpendicular translation movement and allows horizontal movement and rotation. It is provided internally.

Internal roller supports are provided for tower cranes or harbor cranes that would allow horizontal movement and carry heavy materials from one position to another.

Also Read: Boundary Conditions in a Structures