Tilt Up Panel Base Connection

[ikka]

Hi all,
Just wanted to know whether there are any problems in providing a tilt up panel at structural slab level (floor level) with anchors on to footing at floor level. (Top of footing and top of slab are at same level)

 

[EZBuilding]

You are asking the erector to slide these heavy panels into these tiny dowels through a narrow hole. I expect you are going to end up with multiple bent dowels, followed by the erectors sawcutting the dowels.

Would recommend an embedded plate in the panel and some kind of post installed attachment adjacent to the panel. Grout bed to remain.

 

[JAE]

Here's a detail I've seen used in the past.

It uses a post-drilled installed all thread rod and an embedded steel angle clip.

 

[human909]

You are asking the erector to slide these heavy panels into these tiny dowels through a narrow hole. I expect you are going to end up with multiple bent dowels, followed by the erectors sawcutting the dowels.

Would recommend an embedded plate in the panel and some kind of post installed attachment adjacent to the panel. Grout bed to remain.

This is a fairly common detail in Australia where @ikka is from.

The detail is straight out for the CCAA guide:

Guide to Tilt-up Design and Construction

CCAA T55-2005/CIA Z10-2005: The Guide uses an 'issues-based' approach and therefore comments on matters peculiar to the design of tilt-up construction.

www.ccaa.com.au

I don't see an issue with this detail. Though some people might want a rebate to provide better prevention against moisture ingress or for other reasons.

 

[Tomfh]

Agree. common detail. 50 tube onto a 20 pin is easy enough. and yeah, rebate for waterproofing.

 

[KootK]

I did wall panels with a midwestern precaster for five years that did nothing but this detail. It was their preferred detail and I don't recall any instances of problems. Maybe there were problems and they just didn't tell me about it.

These things always leave me a bit conflicted:

1) In the absence of my particular experience, I would be inclined to agree with @EZBuilding regarding the potential for constructability problems.

2) A good precaster will want to do good work and avoid rework. To an extent, it seems that one can rely on this to a greater degree than one might expect.

3) I still have some doubts about the quality of the finished connection. If we're talking about a nominal shear pin in Indiana... sure. If we're trying to develop a plastic hinge in a San Diego shear wall panel, I'm probably going with something else.

 

[haynewp]

How can you verify the grout completely filled the void space with that detail?

I have used NMB splices for precast before, they are pressure grouted and the grout will flow out of the top tube so you know it has fully filled the splice. I've never tried it with tilt-up.

 

[EZBuilding]

Thank you everyone for the insight.

Looking back at the post and I noticed it does mention tilt-up construction.

The detail identifies it as a precast panel - so in my head I imagined a multi-level construction with panels in-between floor levels. Would the group here still have the same level of confidence regarding that detail for that type of erection sequencing (i.e. more restriction at the top floor level in setting the panel).

 

[Lomarandil]

This is a minor thing, but I'd detail the grout tube longer than the pin length so that the pin binding at the bend in the tube doesn't affect your ability to get the panel placed at the desired height.

 

[JoshPlumSE]

The only issue I have is that I usually see a this foundation a little below the slab and then a "closure pour strip" that connects the wall to the slab. Maybe this is detail used more in seismic country compared to the rest of the world?

Something like the following:

 

[human909]

The only issue I have is that I usually see a this foundation a little below the slab and then a "closure pour strip" that connects the wall to the slab. Maybe this is detail used more in seismic country compared to the rest of the world?

Yes details like the above can offer better behaviour. And they are often used in Aus and also are including the the guide I linked above.

In many of these precast designs (at least in Australia) the lateral load path is often take care of by steel. So seismic and other lateral loads are dealt with there. However there are also specific requirements regarding fire and these panels. To put loosely, in the event of a fire and internal steel integrity is lost the panels fall outwards. This puts fire fighters and neighbours at risk. This requirement drives a fair bit of the connection design at the base and at the connectors to the internal steel.

For what it is worth. I'm mostly ignorant of precast design having never done it myself. But I've been around enough projects to understand some of it.

 

[Brad805]

Meadow Burke and Dayton Superior make an anchor like JAE shows. These are tested for the minimum anchorage force. It is hard to find a cheaper option than the grout tube.

It is common to see the panel sit directly on the footing and they form a blockout in the slab for the wall. If only anchoring to the slab for shear forces welded connections can be used as well. I have never liked the welded joints given the repair extra steps, but they are quite common.

In NZ and AUS they have better dowel details. You can find many of their tests online and standard details.

The dowel detail you show is not quite correct. You need a fill hole and a vent. Fill until grout oozes out the vent hole. Easy peasy. Our crew has grouted thousands of these. The greater the quantity of dowels the less you can move the panels unless your grout tubes are oversized more than the norm.

 

[Greenalleycat]

These are extensively used in NZ - page 7 & 8 of this brochure has some example details
They aren't perfect and have their risks (reduced concrete cover encourages spalling under seismic, lack of surety about grouting) but they're pretty good

https://reids.co.nz/upload/modules/document_loader/CB0091_Reid_Precast_Connection_Application_Examples.pdf

Post-quake the standard details changed a lot to address the spalling issue, and standardisation of duct lengths + improvements in QA is addressing the grouting issue

 

[human909]

And one could ar

These are extensively used in NZ - page 7 & 8 of this brochure has some example details

Good detail to know. And one could point out that in the English speaking world NZ has the most recent first hand learning experience regarding seismic behaviour and detailing.

(Of course in a perfect world it shouldn't take first hand experience for codes and practices to be updated to reflect best practice.... But I've yet to visit a "perfect world". One day California will likely teach the US some further important lessons! Here in Australia we have poor historical data and a low recurrence rate of significant seismic events. But we are seismically active and could still get taught a brutal lesson if we are highly unlucky.)

 

[Greenalleycat]

@human909 unfortunately that shake in Melbourne a few years back highlighted that you guys are royally f'ed if there is ever a proper shake....

@ikka I forgot to say - I am not a fan of drill and epoxy for these details. It -can- work depending on your loading condition, but those bars really should be cast in. Also 500mm seems way too short for a 20mm bar - how is that getting developed with the non-contact lap to the reinforcement in the wall? 600mm centres is also very close - that will be hard to construct. Normally we'd favour reducing the number of bars and using larger ones (within reason, of course).

What loading is this thing subject to? Out of plane? In plane? Nominal tie loads only?

 

[human909]

@human909 unfortunately that shake in Melbourne a few years back highlighted that you guys are royally f'ed if there is ever a proper shake....

Yep. Certainly plenty of old masonry apartments from the 30s in Sydney and soft storey masonry apartments from the 60s in Melbourne.

I'm heard by value the largest reinsurance risk that insurers in Australia have is a serious seismic event in Melbourne or Sydney. (Which isn't surprising when you think about it. And it might be the largest in value, but risk adjusted it would be much lower. We really don't have enough data on the recurrence intervals and the magnitude of tail end events. Though Australia and I'm sure other parts of the world have been waking up to this.

Of course if we as structural engineers mention seismic loads to our clients then the response can readily be "Nah, you don't need to design for that mate".

That said most of Western Victoria (west of Melbourne for those who don't know Australian states) is VOLCANICALLY active but the recurrence interval of a major event is on the order of every 4000-5000 years. The last event was 6000 years ago. But I digress.

 

[Greenalleycat]

Yep. Certainly plenty of old masonry apartments from the 30s in Sydney and soft storey masonry apartments from the 60s in Melbourne.

I'm heard by value the largest reinsurance risk that insurers in Australia have is a serious seismic event in Melbourne or Sydney. (Which isn't surprising when you think about it. And it might be the largest in value, but risk adjusted it would be much lower. We really don't have enough data on the recurrence intervals and the magnitude of tail end events. Though Australia and I'm sure other parts of the world have been waking up to this.

Of course if we as structural engineers mention seismic loads to our clients then the response can readily be "Nah, you don't need to design for that mate".

That said most of Western Victoria (west of Melbourne for those who don't know Australian states) is VOLCANICALLY active but the recurrence interval of a major event is on the order of every 4000-5000 years. The last event was 6000 years ago. But I digress.

Sounds a bit like Dunedin. I was reading the seismic hazard report for it one day, I think there's a ginormo faultline off the coast that goes every ~7500 years so the time-weighted risk is very low at our typical 1/500 deisgn level but, if it does go, the whole city is basically going to be flattened....especially as the city is hugely built from brick, masonry, and shitty old concrete

 

[Tomfh]

unfortunately that shake in Melbourne a few years back highlighted that you guys are royally f'ed if there is ever a proper shake....

We get the odd fatal quake, and yeah, worse ones could happen, but our intraplate quakes just don’t have the energy to wipe out cities like plate boundary quakes. Sure, there’s always a tiny chance there’s some fault right under Sydney or Melbourne that’s been flying under the radar, but honestly, it’s a long shot. Risk isn’t just about how bad it could be, it’s how likely it is too, and in our case, the odds are pretty low.

A lot of facades will fall off though if we get a newcastle quake in sydney. All that old junk that the heritage people make us keep.

 

[Greenalleycat]

We get the odd fatal quake, and yeah, worse ones could happen, but our intraplate quakes just don’t have the energy to wipe out cities like plate boundary quakes. Sure, there’s always a tiny chance there’s some fault right under Sydney or Melbourne that’s been flying under the radar, but honestly, it’s a long shot. Risk isn’t just about how bad it could be, it’s how likely it is too, and in our case, the odds are pretty low.

A lot of facades will fall off though if we get a newcastle quake in sydney. All that old crap that the heritage people make us keep.

Apart from 2 significant building collapses, the deaths here were basically due to URM buildings and primarily their facades
So I don't agree with your flippant attitude towards that risk - given a) how many such facades Melbourne has b) the laneway culture c) large population, even a moderately large quake could kill a lot of people

I had to help my Dad post quake as he got called into a Royal Commission inquiry into facade deaths down one of the main streets of Chch
Dad had previously strengthened a facade in a row building down there so every engineer got dragged in who had touched something in that block
Luckily, I found a video someone had taken during the February 2011 earthquake in which you could see that his facade held on longer than the unstrengthened ones either side, only getting pulled down when the ones either side (which were structurally integral) collapsed
So, he was able to navigate that situation well....unlike the poor suckers who got crushed by facades that collapsed

I can't find that old video any more but here's one taken in the same street - you can see that the buildings themselves stayed up a lot better than the facades
I've also included a few photos I took myself from working in the central city cordon
It's not a risk to be scoffed at

 

[Tomfh]

Yes, I’m familiar with the Newcastle quake which did similar damage to masonry facades, and I completely agree—facades will fall off and kill people in sydney and melbourne in the event of a moderate quake. You won’t find a stronger critic of our quaint old brickwork than me. If I ruled Sydney, the heritage crowd would be out on their arse and every loose brick facade would be coming down. For me it is outrageous that we are expected to preserve these deathtraps. All this business of ductile frames, while "heritage" parapets adorn every street.

What I’m being "flippant" about is the idea of a massive quake flattening Sydney or Melbourne and killing tens of thousands—like what happens in places with serious seismic activity. That kind of scenario just isn’t on the table for the eastern seaboard. Our geology doesn’t allow it.