Anchoring Wood Rafters to a Steel Beam (Uplift) 2

[medeek]

So instead of a solid sawn or glulam beam a client wants to use a steel beam and complicate matters. I have 4x10 rafters on 48" centers resting on this beam, the roof has a 2/12 pitch with a slight birdsmouth cut. Normally I would use a couple of Simpson H2.5 hurricane ties for uplift of the rafters however the steel beam potentially changes that. Are there any off the shelf products for joist-to-steel beam or rafter-to-steel beam ties for uplift in such a situation.

Another option I was considering was bolting a "sill plate" on top of the steel beam and then rest the rafters on top of this plate and attach the ties to this.

I rarely deal with steel in most of my residential designs (the factor being the cost) so wood/steel interfaces always seem to be my achilles heel. On that note does anyone have any suggestions or resources for standard steel-to-wood connections for residential and light commercial work?

A confused student is a good student.
Nathaniel P. Wilkerson, PE

http://www.medeek.com

 

[KootK]

I think that the bolted plate is the way to go. I've seen connection hardware connected to steel with self tapping screws and even welds but that gets messy and difficult to evaluate pretty fast.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[mike20793]

I almost always bolt the plate to the top flange when it's a repetitive member. When the member is unique, like a truss girder or built up LVL, I've used the welds.

 

[KootK]

The AITC timber design manual might be a useful detailing reference for heavier wood connections. It's mostly wood to wood but many details could be easily adapted to wood to steel.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[Guastavino]

Simpson Strong Tie may have an engineering letter for a clip that you could weld to the steel (They have some of those posted online, but I'd just call them, ask for engineering department and talk to them). Like Kootk said, not ideal to weld them, but could be done if you don't like the "sill plate" idea.

I'm currently using a weld option for top flange hangers to hang some LVL's to existing Steel wide flange shapes to hold new Rooftop units. I put on the drawings to have a CWI inspect the welds, might be overkill, but I don't want to expect the contractor to get it right the first try since it's likely something they haven't done before (not even being cynical about the contractor, just not something they likely do all the time). If you go with the welds, since it's residential, you might just want to say that you want to see the welds yourself before they cover them up if you choose that option. Or at least get them to do a mockup so you can see if it looks OK to you.

 

[jeffandmike]

The "bolted"/attached wood sill plate is the most common solution I've seen in this instance. It allows for relative flexibility with (lateral; along the support) rafter placement in a way that stationary hurricane ties can't. The Simpson "Strong-Drive TB WOOD-TO-STEEL Screw" is a good fastener to use in this situation, assuming it has sufficient capacity for your purposes. It's on page 25 of the current (2015-2016) Wood Construction Connectors catalog.

 

[Archie264]

A connection that used to be common was connecting the wood plate on top of the steel beam by shooting powder-actuated fasteners (i.e., Hilti, Ram-set, etc.) though both the wood and the steel.

 

[KootK]

The PAF's sound attractive. One thing that's always bothered me about the connection is that you can't expect the bolts to miss the framing members. You can use carriage bots and counter sink etc but that stuff always has implications for uplift.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[Triangled]

don't know where you are and how large your forces are, but I'd give a little consideration to the uplift induced cross grain bending in your wood plate, when you select your thickness, grade, bolt location and pattern and connector.

somewhat related article:
Link

 

[medeek]

@KootK

What is the PAF acronym? With the rafters at 48" on center I should be able to arrange the bolts to miss the rafters but I can almost count on the contractor to screw this up.

A confused student is a good student.
Nathaniel P. Wilkerson, PE

http://www.medeek.com

 

[mike20793]

Power Actuated Fasteners. I haven't had many issues with contractors messing up the alignment with the throughbolts. I usually keep the bolts at an increment of the typical rafter spacing.

 

[gte447f]

I prefer a wood nailer (i.e. sill plate) fastened to the top flange of the steel beam with either powder actuated fasteners, through bolts, or Nelson threaded studs welded to the beam flange. msquared48 on this board clued me in to the Nelson stud option for fastening the nailer.