Simple Connection Design Philosophy

Simple connections are defined as connections which transmit end shear only. This definition underlines both the connection design and the analysis of the overall structure, with beams being designed as simply supported and columns being designed for axial load and nominal moments which results from the end reactions of the beams considered with a nominal minimum eccentricity relative to the column. To accommodate the potential rotation of the joint, end plates, where used, need to be thin. In beam to column connections, to prevent the bottom flange of the beam bearing directly against the column when under going rotation, a minimum end gap is specified.

The connection design is based on a component based model, where each part of the connection is considered as an individual component, with each component checked for the load transfer through the connection elements including welds, plates, bolts and section webs or flanges. The capacity of each component is calculated. For each component to be considered to be satisfactory, the calculated capacity of the component must be greater than the applied force. The SCI Green Book checks each connection component in a series of design procedure checks. These Checks are used in the MasterKey: Simple connections module, as noted in the design output for each connection.

The Green Book design methodology covers only vertical shear design, where the orientation of the member is such that the vertical shear results from loading the beam about its major axis. Shear due to loading about the minor axis is not covered. Lateral loading, say due to wind load, is assumed to be resisted by other means, such as transfer of the load into a floor diaphragm. Torsional resistance is also not considered as part of the Green Book methodology.

The Green Book SCI P358 provides a design method for the following connection types to EC3:

Partial depth end plates, beam-to-column and beam-to-beam connections
Fin plate connections, beam-to-column and beam-to-beam
Column Splices
Column Bases
Bracing connections

The design of double-angle cleats was excluded form SCI P358, but these connection types were included in the earlier Green Book P212. MasterKey: Simple Connections has retained the double angle cleats in the EC3 design, by adapting the methods for the British Standard design in line with the requirements of BS EN 1993-1-8. The SCI Steel Designer's Manual also includes a method for the design of double-angel web cleats.

When designing tying forces in simple connections, the check for tying resistance is entirely separate to the check for vertical shear capacity and the tow forces are not considered to occur simultaneously. The tying force design is based on the ultimate material strengths, with an appropriate material factor. When calculating the tying resistance, only the ultimate strength is considered and significant permanent deformations are anticipated. For these reasons, the tying force calculation is not appropriate for the design of simply supported members with axial forces.