Rafter to Pole Plate Concealed Connection 1

[jrbaus]

I have a small project at the moment where the client wants to install a leanto off the front of an existing dwelling. The site is located in Australia with a very dry, hot climate and low wind loads.

The client does not want to use metal hangers to make connections between timber elements as they will be left exposed. I could not find a suitable connection in the residential framing code AS1684.2 so designed the connection for shear, bending & bearing taking the reduced section properties into consideration. I am not sure what effect notching the hardwood will have in such environment though and am concerned about potential splitting. Can you please share your thoughts on the attached detail?

I guess the other (safer?) option would be to use something like this:

http://www.dhcsupplies.com/store/p/3739-CJT6S-Concealed-Joist-Ties-Short-Pins.html#.VHz8psn8IuQ

Kind regards,
Jake

 

[Ingenuity]

jrbaus: A sketch of the proposed framing would help? Is it cantilevered construction, post-and beam framing, approx plan size etc?

Just so we can get a 'feel' for the magnitude of actions.

 

[jrbaus]

Ingenuity, sorry my attachments didn't upload correctly first time around. Please see client sketch attached & I will upload connection detail in a subsequent post.

Plan size = 12m long x 2.5m span

Regards Jake

 

[jrbaus]

Sketch of proposed connection attached.

 

[chicopee]

Yeah, it will probably split where you show the red line. Tell you client of that potential problem. If there is no load then may be there will be no splitting. I have seen the type of problem several times with no occurences, probably because the superimposed loads were light.

 

[jrbaus]

Hi chicopee,

Thanks for your input and confirming my suspicions. There is indeed little long term load on the connection since it is only supporting the dead load of the roof however any splitting is obviously going to be just as aesthetically displeasing (if not worse) than joist hangers in my opinion.

Regards Jake

 

[azcats]

Could you use the joist hangers then add an additional 'decorative' notched ledger/plate to conceal them?

Or bear the joist directly on a smaller ledger/plate below the joist and infill with blocking between the joists?

Or use a deeper ledger/plate and fully notch it for the joists to insert? Have to make sure all your attachment to the wall is below the joist and that the reduced section can x-fer load.

Just some ideas...

 

[KootK]

You could reinforce the notch with a vertical wood screw through the bottom.

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

 

[Ingenuity]

@jrbaus: It is not clear to me from your 'perspective view' sketch, but is this 'leanto' cantilevering?

 

[jrbaus]

@azcats: thank you for the suggestions. I am limited to having the pole plate at about 140mm deep. 'The decorative' option might be a better way to go.
@KootK: interesting suggestions - I will examine that option further
@Ingenuity: leanto rafters are simply supported, not cantilevered. Pole plate one end, veranda beam the other end.

 

[JAE]

Wow - KootK - we must think alike. I was going to suggest the same idea as I used it once on a set of exterior glue-lam beams which were hit by a rental van trying to drive under a canopy which was too low.

What we did was drill lead holes vertically from the bottom of the beam up past the theoretical horizontal crack line (in our case the cracks were already there).
We then drilled larger diameter countersink holes for the lag screw heads and washers.
Then we installed lag screws up into the lead holes and used long enough screws to "develop" past the crack and draw the crack together.
Then a wood plug in the bottom to close it up and leave a "wood" beam.



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[hokie66]

This may be a low wind region theoretically, but the most common method of failure of this type roof in Australia is by being blown away in a thunderstorm. Thunderstorms can occur anywhere. I would want a better connection for uplift.

 

[woodman88]

What type of wall is it? In new construction I have ran the beam into the wall and bolted/lag screwed them to studs each side. If you cannot do this, I would perfer to use the "decorative option" that azcats mentioned.

Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.

 

[KootK]

@JAE: like your scenario, I've only ever done this in response to a horizontal shear crack. If the member were reinforced pre-emptively, you'd still get the crack, right? I'm thinking of this similarly to concrete reinforcement: marginally active until after cracking.

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

 

[msquared48]

I do not like the idea of trying to prevent splitting with a wood screw. It just encourages splitting in another plane, particularly at the end of the member.

The attached sketch is more complicated, but splitting is minimized.

Mike McCann, PE, SE (WA)

 

[manstrom]

Simpson makes a concealed hanger

http://www.homedepot.com/p/Simpson-...VdxFzNIDCeSuxWuz4ykcyY07DmCqhd9JgXRoC7vrw_wcB

When I am working on a problem, I never think about beauty but when I have finished, if the solution is not beautiful, I know it is wrong.

-R. Buckminster Fuller

 

[msquared48]

This connector is only "concealed" for 4X rafters and joists though. You will see it for 2X to either side of the joist.

Mike McCann, PE, SE (WA)

 

[JAE]

Mike - I don't know about your assertion. My three gluelam beams using the vertical lag screws have performed very well for perhaps 7 years.

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[msquared48]

JAE...

Glue lam beams are one thing and less susceptible to splitting than a solid stick. However, they can and do split. These are 35 mm joists - less than 1.5 inches wide. These are far more susceptible to splitting than a glue lam that does not come less than 3.125" wide.

Perhaps I am missing something here? I will have to check the AITC tomorrow, but I d not think this would be a good fix for a split 2x joist.

Mike McCann, PE, SE (WA)

 

[jrbaus]

@hokie66: I tend to agree with you. A stronger tie down is cheap insurance.
@woodmain88: It is an existing hardwood stud wall with weatherboard on the outside.
@manstrom: thanks for taking the time to put a sketch together. Most appreciated. I might run this option by the client and see if he still wants to pursue the ‘concealed’ arrangement.
@msquared48: thanks for the link to the Simpson hanger with pricing. I am waiting for confirmation of availability in Australia from the manufacturer.

Thanks all for your comments. It is reassuring to get advice on some of these issues that are outside my area of normal practice (have mainly worked with steel up to this point).

Regards Jake