Joints or connections are specific points in a structure where members are connected. For example:
- It is the point at which the beam meets a column
- The point where the column meets the ground
- Points where members of the truss connect at their ends
Connections influence the structure's behavior. It is essential to know how it resists forces and affects the structure's deflected shape.
What are the Different Connections?
There are three types of connections in terms of rigidity: (1) rigid, (2) flexible (pinned or hinge), and (3) semi-rigid.
Rigid
Rigid joints are stiff connections. These joints can resist both force and moment/torsion imposed on them. For example, if we rotate it by angle \(\theta\), the angle between members should remain the same to maintain rigidity. For example, turning a 90º joint must still be a 90º joint after rotation. An excellent example is an ideal monolithic reinforced concrete beam and column connection.
Flexible (Pinned or Hinge)
Flexible joints (or pinned/hinge joints) are the opposite of rigid joints in terms of rotation. These joints can resist forces but not moment/torsion. Going back to our example, if we rotate a 90º joint by an angle \(\theta\), it doesn't need to be the same 90º after rotation. Pinned connections of ideal trusses are another excellent example of this connection.
Semi-Rigid
A semi-rigid joint occurs when connections exhibit both properties from rigid and flexible connections. When a 90º joint rotates by an angle \(\theta\), for example, it doesn't necessarily maintain a perfect 90º similar to hinged connections; however, it does offer some stiffness and resistance to rotation like rigid connections.
Most structural joints, in real-life, are semi-rigid by nature; however, in analysis, we assume either a perfect rigid or flexible joint.
Summary
Joints or connections are specific points in a structure where members are connected.
Connections influence the structure's behavior.
There are three types of connections in terms of rigidity: (1) rigid, (2) flexible (pinned or hinge), and (3) semi-rigid.
Rigid joints are stiff connections. These joints can resist both force and moment/torsion imposed on them.
Flexible joints (or pinned/hinge joints) are the opposite of rigid joints in terms of rotation. These joints can resist forces but not moment/torsion.
A semi-rigid joint occurs when connections exhibit both properties from rigid and flexible connections.
