Roof Beam to Tilt up panel Connection

[civeng80]

This is a roof beam to tilt up concrete panel connection that I am proposing on a job. I thought this was a fairly typical connection detail at least in Australia.

Comments from checking engineers are that it will not act as a pin connection (even though it is designed as a pinned connection) and that significant moment will be transfered possibly damaging the panel. I always thought that this was the closest (or one of the closest) type of panel to beam connections to represent a pin.

Any ideas or suggestions or modifications on this would be appreciated.

 

[humanengr]

The connection of the upper channel girt to wall panel is not shown.
If you can use the seat angle to transfer rafter vertical load to the panel, as well as panel lateral
loads to the rafter, you can eliminate the channel girt. This would be much closer to a "pinned" connection at the
top of the panel and avoid bending moment in the panel.
You will probably need to modify the seat angle details or sizes to transfer both lateral and vertical loads.

 

[hokie66]

civeng80,
What shelf angle? I didn't see a shelf angle in your detail.

 

[civeng80]

hokkie my apology,

That should be "angle seat".

 

[hokie66]

So what does the "checking engineer" recommend? No good to be critical without participating in solving the problem.

 

[civeng80]

Recomends portalising roof beams with panels. Different system altogether.

 

[hokie66]

Yes, different system. More robust, though.

 

[rowingengineer]

but more of a fire risk

http://www.nceng.com.au/

"Programming today is a race between software engineers striving to build bigger and better idiot-proof programs, and the Universe trying to produce bigger and better idiots. So far, the Universe is winning."

 

[rowingengineer]

make that more of a risk in a fire

http://www.nceng.com.au/

"Programming today is a race between software engineers striving to build bigger and better idiot-proof programs, and the Universe trying to produce bigger and better idiots. So far, the Universe is winning."

 

[civeng80]

Let me elaborate.

Not a steel portal frame with steel columns and beams.

Use the panel as a beam column and connect the roof beam with moment connection to panel.

It sounds OK in theory but I don't have enough literature on this type of construction to be comfortable with it

Definitely like steel portal frame though.

 

[CELinOttawa]

Panels as beam-columns with a Rafter's moment capacity is not going to work with an economical thickness of panel. You're going to wind up face casting a second lift to actually produce a column beneath the rafter. This is sounding wasteful and unnecessary.

I have seen this a couple of times, but only with very large (read: tall) panels indeed....

 

[rowingengineer]

I don't like the sounds of it. a thin panel taking moment loads from a rafter sounds like hard work.

I would look to adjust your connection, I have made a few suggestions, if this is heavily loaded and the vertical angle is transferring to much I may look at the vertical angle and replace with a horizontal angle that sits on two angles/castin plates.

http://www.nceng.com.au/

"Programming today is a race between software engineers striving to build bigger and better idiot-proof programs, and the Universe trying to produce bigger and better idiots. So far, the Universe is winning."

 

[hokie66]

I thought your tormenter was worried about distress in the panel. Now he want you to do a moment connection to it? Makes no sense.

RE, why do you think the steel portals present more of a risk in a fire than the concrete bearing wall system?

 

[CELinOttawa]

Probably getting at the fact that the concrete cover protects from fire issues, but the steel portals would have to be competently protected.

Alright, I'll bite as well: RE - What Hokie said!

 

[rowingengineer]

Steel portals by themselves do not present more of a problem but when you clad with concrete panel this can be a higher risk in my opinion (however this risk can be handled by proper detailing, Fire ties to columns would be one such detail).

Reason is that the panels and steel portal will naturally want to bend away from the fire in the first instance in both forms of construction; however when the steel starts to sage the idea is that the steel pulls the panels back into the building reducing the risk to structures or property outside the building.

For the concrete panel option you are normally detailing a pin type joint at the bottom or allowing for plastic failure of the panel for this pull-in to occur before the rafters pull off the wall, there is a clause in the BCA to handle this connection capacity requirement to assume this happens.

For the steel portal option you need the columns and panels to form this plastic hinge for them all to fall in. I don't see this as very easy thing to make happen compared to the single panel, however if you detail fire ties at the top of the columns to allow the panels to blow off the columns and form independently the plastic hinge, I think there is a chance.

http://www.nceng.com.au/

"Programming today is a race between software engineers striving to build bigger and better idiot-proof programs, and the Universe trying to produce bigger and better idiots. So far, the Universe is winning."

 

[civeng80]

Hokkie,

I have a lot of respect for this engineer.

His idea is either beam pinned to the panel or fully fixed to the panel.

According to him a pinned connection is statically determinate which is good for analysis and design but not so good for limit state design as failure could be catastrophic if one element fails e.g. a roof bracing member.

So his theory is make the structure statically indeterminate e.g. fixed beam connection to panel and to base and use this redundancy as a backup safety measure and moment redistribution, so that the structure would not fail catastrophically under extreme loads including any unforeseen loads e.g. blast loads, earthquake or impact load from vehicles (they do occur in industrial buildings).

It sounds good in theory but in practice I don’t know as there is not enough literature on this method including the economic viability of construction.

I must admit that there are some pretty poor tilt up panel buildings with a lot of problems out there, of which owners and builders remain silent on.

But then there are some pretty good ones (or so it seems) like the Bunnings warehouses.
I choose to make the connection pinned and statically determinate structure with roof bracing to hold the building stable (in reality of course no structure is truly statically determinate) . I think that these type of buildings and the Industry that developed them have been around long enough now to seriously consider them viable alternatives to the steel portal frames. I know AS3600 does not say much about tilt up and if read to the nth degree require more rebar in panels than what’s actually put in by the industry. (Mu > 1.2*cracking moment)

Rowingengineer thanks very much for going to the trouble of detailing alternative connection.
Thanks all for some pretty good thoughts on this topic.

 

[hokie66]

The concept of redundancy due to portal action is great for steel structures, and arguably to a lesser degree for concrete structures. I just don't see that it is applicable to tilt up concrete panels.

 

[CELinOttawa]

Agreed! This is someone trying to fit a theoretical model to a practical reality... I like to have the panels be robust, the connections be of the seismic yielding type to the foundations, and the steel to panel connections be well overdesigned.

 

[civeng80]

I agree, good in theory but in practice, got my strong reservations.

 

[CELinOttawa]

Well remember: Review Engineer or no Review Engineer, this is your design. Never allow something to go out that you don't believe in...