Steel Connection | Simple Connections & Moment Connections
Selection of Steel Connection
When it comes to steel construction, steel connection is one of the most crucial design components, in terms of cost as well as integrity of the structure. If connection types and arrangements are not carefully chosen, it can account for upto 65% of total cost of the production. This is because for steel structures, raw material cost is around 30-36%. Remaining is in shop fabrication.
For this reason, the selection of members and sizes should be such that the connection requirements can be simple. Hence increasing size can be allowed if it can simplify the steel connection. Detailing of a connection is equally important as designing a connection.
The assumptions and philosophies used in design should be clearly reflected in the drawings and detailing. This will ease the fabrication process. Based on complexity and force transfer mechanism, the connections can be classified into following categories.
- Simple Connections or Shear Connections
- Simple Moment Connections
- Highly Complex Moment Connections.
Simple Shear Connections.
Simple shear connections are one of the most common steel connections in practice. As the name says, these connections can transfer only shear forces to connected members. Moment transfer or moment continuity cannot be achieved using this steel connection.
The arrangement is less complicated and easy to fabricate in shops. Shear connections are achieved using shear plates, clear angles, fin plates and bolting. Shear connections are widely used as column-to-beam and beam-to-beam steel connection. In beam-to-beam connections, the secondary beam flanges are coped to fit to the primary beam, as shown in the figure.
Simple Moment connections
Moment connections is an advanced type of steel connection, which is used when moment transfer is necessary, in addition to shear transfer, between connected members. The complexity of connection depends on the shape of connecting members, percentage of moment transfer required and application.
The fabrication cost increases exponentially based on the complexity of steel connection. A simple moment connection for a beam-to-beam or column-to-beam connection can be achieved by using an end plate, which is welded to the end face of the section.
For an I section the end plate is butt or fillet welded to both flanges and webs to achieve full restraint. It should be noted that unlike shear connections, flanges are restrained to achieve moment transfer between members. They can achieve upto 80% moment transfer.
Highly Complex Moment Connections
These are full moment connections capable of achieving 100% moment transfer between members. For column to beam connections, additional haunches or cleat angles are introduced to achieve full restraint. Additional tensile stiffeners are introduced and welded to prevent local buckling of elements. The cost of a single complex steel moment connection can be 6 to 9 times that of a simple connection.