Multi-storey steel-concrete composite buildings that are braced against sidesway but not subjected to significant lateral and earthquake loads often use simplified joint details, such as fin plate bolted connections, in beam-to-column and beam-to-beam joints to speed up construction. While these joints are relatively easy to install on-site and are preferred for their simplicity, modern commercial buildings with long span and open space floor beam layouts may require a structural framework with semi-rigid connections for greater economy, without the need for complicated rigid joint detailing.

According to EN 1993-1-81, steel joints can be classified as pinned, semi-rigid, or rigid based on their initial rotational stiffness and moment resistance, depending on the analysis methods used in the design. Composite joints, as defined in EN 1994-1-12, are joints in which slab reinforcements are considered to calculate the rotational stiffness and moment resistance if the reinforcements are continuous or anchored at the joints. Thus, some of the simple steel joints defined in EN 1993-1-8 can be classified as semi-rigid composite joints, in accordance with EN 1994-1-1, if the reinforcing bars in the floor slab are continuous or anchored at the joints and some degree of rotational restraint can be provided.

The previous edition of the design guide3 only applied to beam-to-beam composite joints, where both primary and secondary beams are designed to act compositely with the floor slab. It proposed a contact type of semi-rigid composite joint that can develop higher rotational stiffness and moment resistance.

A mechanical model assumed that the tension force is transferred by reinforcing bars, and the compression force is transferred by contact plates inserted at the bottom flange of the steel beam to enhance rotational stiffness and moment resistance.

This new design guide extends its scope of application to include beam-to-beam joints, steel beams connecting to reinforced concrete primary beams, beam-to-column joints, and beam-to-reinforced concrete wall joints with contact plates to enhance semi-rigidity in the connections. The design methods for contact-type semi-rigid joints have been validated based on finite element analyses and full scale tests conducted at the Steel Structures Research Laboratory at Nippon Steel Corporation in Japan.

The design guide aims to give structural engineers the confidence to use semirigid composite joints safely and economically in the design and construction of steel-concrete composite buildings. With this updated guide, designers can now expand their use of semi-rigid joints, potentially reducing construction time and costs while maintaining the necessary level of structural performance.

To download the design guide, please click here.