Floor Truss Strongback
Floor Truss Strongback
(OP)
When is it a REQUIREMENT to install strongbacks ? Most publications list it as a RECOMENDATION and not required.
When L/480 or L/600 is specified, does that require strongbacks ? Are the building codes specific on this ?
Thanks for any feedback.
When L/480 or L/600 is specified, does that require strongbacks ? Are the building codes specific on this ?
Thanks for any feedback.





RE: Floor Truss Strongback
Garth Dreger PE
AZ Phoenix area
RE: Floor Truss Strongback
RE: Floor Truss Strongback
RE: Floor Truss Strongback
IF they do - you probably don't have a snowball's chance in Hell changing their mind - unless the truss plate engineer gives you a new drawing.
Why not just do it?? It can't cost that much?? And it does serve a purpose.
RE: Floor Truss Strongback
RE: Floor Truss Strongback
RE: Floor Truss Strongback
RE: Floor Truss Strongback
It's currently the builder's problem; let it remain so.
RE: Floor Truss Strongback
Where adjacent trusses can expect differential deflections, the need for strongbacks to reduce sheetrock cracking is justified. The need is greater for high climatic/humidity changes, large snow load variations, and/or different interior bearing conditions. The truss engineer can justify specifying strongbacks rather than being subject to future expense for callbacks to fix sheetrock problems.
RE: Floor Truss Strongback
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: Floor Truss Strongback
They are typically not required for strength of the floor system. Your floor will not collapse if you don't install them :)
Where strong-backs come into play is in the serviceability
aspect of design. Codes usually require X-bridging or blocking in between joists at certain intervals to help resist vibration and create a "system action" for performance of the floor system.
Strongbacks are easier to install than X-bridging and as a result have become the predominate vibration resisting mechanism for open web floor joists.
There is no set rule for strong back size or spacing. Depending on the methodology used for calculating vibration characteristics of floors, engineers will use the stiffness of the strong backs in the calculations.
Strongbacks perform better at mid span and areas of max. deflection. The deeper the strongback the better it resists the effects of floor vibration.
If you have forgotten to install, and the engineering drawings show them, contact the truss designer so that they can provide an alternate detail. If you have short span engineered open web joists, (<10 or 12 ft) its not as critical to have strongbacks.
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C
RE: Floor Truss Strongback
RE: Floor Truss Strongback
Truss Calc design as shown. Many times truss designers run that CSI up to high levels to be competitive so using the strongback is a must. Strongbacks are not x-bridging. Strongbacks are for the structural integrity of the (diaphragm) system. X-bridging is never called out on a truss diagram and is specified the SE. One time I had a contractor scream at me how the strongbacks are there to transfer lateral load....so he could ignore the x-bridging, well it was a $15,000 mistake when the sheetrock came back down to install it.
RE: Floor Truss Strongback
Also if the drawing was sealed and the jobsite is in an area in which a seal is required, they are required if they are designed to be in there. You may be able to get another PE to seal the drawings without them "if" they pass all appropriate calculations.