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Open Joist™Effects of "Strongback" Bridging

Open Joist™ recommends the use of strongback bridging to enhance the performance of floor systems. While such bridging does not affect the strength or structural integrity of a floor system and, therefore is not a required component of Open Joist floor systems, it is strongly recommended because of the positive effect it has on “comfort” factors perceived by individuals on a floor system.

ANSI/TPI 1-2002 includes information in the commentary to Section 7.5.2.4 regarding the use of strongback bridging to reduce the effects of differential deflection in floor trusses:

7.5.2.4

Strongbacking is recognized for serving two purposes: reducing floor vibrations and limiting differential deflection. Strongbacking does not, however, contribute to or enhance the strength or structural integrity of the system.

Strongbacks are typically used to control potential vibration problems, as the addition of strongbacks has proven to stiffen the trusses and increase the dampening of transient oscillations. Vibration in a floor joist due to normal human activity (e.g. walking) includes vibration movements from side to side, and while floor sheathing prevents lateral vibration of the top chord, the bottom can still vibrate back and forth. Thus, placing a strongback at the bottom of the floor truss helps control the side-to-side movement at the bottom and improves the overall perceptible performance of the floor. Even when there is a ceiling on the bottom of the trusses, in which case the drywall will reduce lateral movement, the addition of strongbacks can still help to further restrict vibration. It should be recognized that, while it will not affect the structural integrity of the system, cutting, removing or failing to provide such strongback bracing can result in degradation of the floor system’s ability to dampen vibration.


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  Bridging – Standard - DWG / PDF
Bridging – Alternate - DWG / PDF
Bracing Under Non-Bearing Parallel Wall - DWG / PDF