Bondek (or equiv.) & Continous Lateral Restraint

[Trenno]

Hi all,

Would like the industry's opinion on my question and Bluescope's response in regards to the following:


"Just confirming that full lateral restraint can be achieved using Bondek, WITHOUT implementing shear studs?

Therefore either spot welding and/or fasteners prevent lateral-torsional buckling of the steel beam and thus allow the beam to develop Sectional Capacity (phi Ms)?

Thanks for the help, much appreciated. "


"It has always been assumed by the industry that the deck fixed to the steel support using screws/pins/nails/spot welds provide adequate restraint. However no testing data is available to provide numerical data.
It is upon the designer to use Engineering judgement."

 

[slickdeals]

I think what they say is true. On a roof, for example, you would only have a puddle weld or pins to connect the metal deck to joists or beams and it is adequate to brace the compression flange for gravity loads.

 

[asixth]

Yeah, restraint to the top flange which would be the compression flange for normal load scenarios. Spot welding or fasteners that can achieve the required bracing restraint as required in AS4100, should be 2.5% of the flange compression force. I would actually put a note on the drawing for how much weld you want to achieve that.

 

[asixth]

Actually at some consultancy's I have worked, studs are nominated at a typical 2 or 3m centres even when the beam is designed to be non-composite. Typical notes read like this:

ALL NON-COMPOSITE SECONDARY BEAMS TO HAVE 19mm DIA. x 90 LONG
STUDS AT 1.5m CRS TOP FLANGE RESTRAINTS. PERIMETER BEAMS TO HAVE
19mm DIA. x 90 LONG STUDS AT 1.0m CRS.

19.2mm SHEAR STUDS AT QUARTER POINTS. REFER PART PLAN FOR LOCATIONS

 

[Trenno]

Thanks for the helpful info there, Asixth. I'm guessing it would be a stretch for them to provide capacities of their standard spot welds and/or fasteners (with no testing been done).

To add to my original post - for the beam's top flange (critical) to torsionally buckle I envisaged the top flange would need to rotate and displace "into" the slab above. Therefore weight and stiffness of the slab above then prevents this rotation??

 

[asixth]

Yeah, I reckon you would need to go to the codes for estimating the capacities of the weld or fasteners. I wouldn't think there would be much when welding to a 1.0mm metal deck (guessing that your calling up 1.0mm BMT, That's the thickness I always called up when doing Bondek).

As soon as it get's into the slab it's fine. The 120mm thick slab will have ample capacity in compression or diaphragm shear to get back to your main lateral system (again guessing your calling up 120mm slab cause that's what I use to call up).

 

[Trenno]

Yeah, I stick to 1mm BMT - why not!

Found a reference online that also hints at friction helping transfer the lateral force (shown below). However in this case it's metal on metal...