Are you aware of the many advantages of using flush-frame connections for open web steel joists?  Not only are flush-frame connections an excellent solution to improve the composite action of girders, they also facilitate panelized erection which can reduce multi-story erection times by half.  The floor-to-floor heights are also reduced and flush-frame connections eliminate the need for blocking between joists to transfer shear since the slab is in direct contact with the girders. 

In the August 2025 SEU session, Joe Pote, PE, from New Millennium, and Dave Samuelson, PE, retired from Nucor, presented Composite Floor Joist Systems.  Joe and Dave explained what spacings and depths work best for open web steel joists in floors and how to decrease the floor-to-floor height while increasing the joist depth.  They compared the performance of composite and non-composite joists, and they discussed the advantages of flush-frame joist connections in floor construction.

The significant increase in the use of flush-frame joist connections in the post-Covid boom of e-commerce multi-story office buildings resulted in every major US joist manufacturer learning to mass produce this new joist connection.  Using flush-frame joist connections allows the steel deck and concrete slab to be in direct contact with the girder top flange, thus developing the full composite moment of inertia with no reduction from an elevated concrete slab as is the case with a standard joist seat.  This results in a more effective girder size and improves the vibration performance of the floor system.

Joe noted there is no standard design procedure offered by SJI for flush-framed connections, however all major joist manufacturers have developed their own design procedures, and many resources are available to aid in the design of flush-frame connections.  Joe walked through the process used by New Millennium, and offered some design considerations for the EOR.

Under-flange and extended tab connection tables, as shown below, are offered by joist manufacturers which can be used as design aids to expedite the design process.   Although the EOR is solely responsible for the design of the joists and its connections, the joist manufacturer can provide calculations for each of their standard flush-frame connection details to the EOR.  New Millennium also offers a Flush-Frame Design Guide on the use of these connections which can be downloaded from their website.  

Flush-frame joist connections are used in up to 90% of composite joist floor construction in the US today.  Their ability to reduce floor-to-floor heights while improving floor vibration performance, and facilitate the use of  panelized erection during construction has prompted a major shift in the design of large scale, multi-story office floor systems.