Structural systems using open-web steel joists are popular due to their cost effectiveness, flexibility, and ease of installation. Because these systems have high strength-to-weight ratios, human-induced vibration often controls the member sizes, especially when traditional seats are used. One significant improvement is to change from traditional seats to flush-framed connections.

In the November 2024 SEU Session, Brad Davis, Ph.D., S.E., from Davis Structural Engineering, presented Vibration Analysis of Steel Joists / Concrete Floors. Brad reviewed the AISC Design Guide 11 and SJI Technical Digest 5 methods for evaluating floors for vibration and discussed recent innovations in open-web steel joist floor systems. He noted key improvements in the vibration evaluation methods and discussed research efforts regarding hybrid mass-timber / open-web steel joist systems.

Flush framed connections of steel joists to girders may not be a new concept, however, using this connection for its vibration mitigation benefits is a novel approach to vibration design. To hear Brad discuss the geometry and advantages of this type of joist connection, click below to watch this short video:

When using traditional joist seats, the joists cannot be considered continuous with the girder.  Using flush framed connections may allow for a shallower structural system, permit the system to act compositely, and increase the continuity factor and the Cg factor in the girder effective panel weight calculation.  All of these changes benefit the overall vibration performance of the structural framing system.  Flush framed connections and the equations Brad discussed are covered in AISC Design Guide 11 Section 4.1.2 and SJIs Technical Digest 5 Chapter 3.  Using these connections may be an option to reduce vibrations in your future design projects.