Alberni by Kengo Kuma (1550 Alberni) | 133m | 42Fl | Completed

[officedweller]

Originally Posted by Changing City

There are parts of the city where there's rock near the surface, like near QE Park, but that's not generally the case Downtown.

If I recall correctly, they had to do blasting for Shangri-La's excavation, so there's bedrock at that depth.

[Changing City]

Originally Posted by officedweller

If I recall correctly, they had to do blasting for Shangri-La's excavation, so there's bedrock at that depth.

That's possible - the thickness of the glacial cover varies across the Downtown (and elsewhere that it's found). You can only really tell if the colour of the material coming out changes to sandstone - like the cliffs you can see on the far side of Stanley Park. That's the underling bedrock for most of Downtown. If it's grey, it's still glacial. Some of the glacial material can need blasting, when it's more compacted. It can apparently be harder to cut into than the sandstone, which is much older, but not necessarily as compact (as you can tell from the way those Stanley Park cliffs erode). You can also get huge erratics - big granite boulders - that were carried on (or under) the glacier, and deposited. They're often too big to lift out of the hole, and have to be blasted apart.

[mcminsen]

Originally Posted by Changing City

... You can also get huge erratics - big granite boulders - that were carried on (or under) the glacier, and deposited. They're often too big to lift out of the hole, and have to be blasted apart.

Like these at the 410 West Georgia site.



June 22 '18, my pic

[mcminsen]

Okay, I guess I am officially in the market for a selfy stick now. If I could have raised my camera up another 3 or 4 feet this shot would have been much better. This spot is along the Cardero Street side near the alley, on the sidewalk.



July 17 '19, my pic

[logan5]

Thanks for the responses regarding piles. Just not seeing how a 40 plus story tower could go without piles, especially in an earthquake zone. Not only would you need pilings to hold up the weight of the building, the pilings would also stop the bottom of the tower from sliding sideways. You've got 500 feet of tower rooted into the ground by only 50 feet or so? In an earthquake I picture a building doing something similar to trees that are uprooted in high winds. Even if it is dense glacial sediment, that's a lot of force being transferred to the bottom end of the tower that's being held in place by a 50 foot deep hole.

[Changing City]

Originally Posted by logan5

Thanks for the responses regarding piles. Just not seeing how a 40 plus story tower could go without piles, especially in an earthquake zone. Not only would you need pilings to hold up the weight of the building, the pilings would also stop the bottom of the tower from sliding sideways. You've got 500 feet of tower rooted into the ground by only 50 feet or so? In an earthquake I picture a building doing something similar to trees that are uprooted in high winds. Even if it is dense glacial sediment, that's a lot of force being transferred to the bottom end of the tower that's being held in place by a 50 foot deep hole.

No problem, but no piles, either (at least not here). We need an engineer to confirm it, or someone who develops building that hires an engineer to confirm / explain why it's OK.

I'm looking at the pictures of the bottom of the hole for Vancouver House from January 2016. You couldn't keep McMinsen away, so it's extensively recorded. It's glacial till, not sandstone, and they flatten the base, then start pouring big blocks of concrete to anchor the initial rebar, and the crane base - just like in this hole. The stresses on that building must potentially be greater, but there's no sign of any piling. They were still flattening out the edges of the hole when they started erecting the base of the core.

[Zepfancouver]

[QUOTE=mcminsen;8635210]Okay, I guess I am officially in the market for a selfy stick now. If I could have raised my camera up another 3 or 4 feet this shot would have been much better. This spot is along the Cardero Street side near the alley, on the sidewalk.

Pick this up today at Best buy $49 https://imgur.com/0fDiTz1 It has a quick release camera mount, holds my video cam very well. There's a tether for the camera or phone and a tether to your wrist. I like it. https://www.bestbuy.ca/en-ca/product/digipower-digipower-quikpod-extreme-gopro-monopod-tp-qpxt-tp-qpxt/10238716

[jollyburger]

A hundred or so pages on foundation design criteria for super talls

https://link.springer.com/article/10...062-016-0010-2

[Zepfancouver]

A special thank you to Quikpod Selfie Extreme https://imgur.com/0fDiTz1


• Video Link

[mcminsen]

^^^ Excellent!

[Zepfancouver]

[Changing City]

Originally Posted by Zepfancouver

Today...Not sure what's happening here, but it's happening

I'm pretty certain there was another recent building site where they set up similar steel trestles, added another set of woven reinforcing bars in a mat on top, and then filled the whole thing with concrete to create a hugely dense base, but I can't remember where. Maybe McMinsen can recall - although it's possible he's just peered into too many holes to remember just one of them.

[mcminsen]

As soon as I saw Zepfancouver's pic I thought ah, I've seen that before. It was at Vancouver House three years ago. Click on the link in the post below and scroll through to the following posts for some extended discussion about the scaffolding/trestles used amongst the rebar.

Originally Posted by mcminsen

Vancouver House, March 8 '16, my pic

[mcminsen]

For example, this post from Marshal. Perhaps the tensile void described is what's going on now with the foundation at 1550 Alberni.

Originally Posted by Marshal

Forgive me if I am over-explaining, but:
There are two kinds of voids in poured concrete construction. One where no material is required (there is no structural requirement). These can be formed in the standard way, such that when the pour is complete the void includes the wood formwork which is trapped and air, or by other methods, for example, a hard foam shape used to form the void, which is then trapped by the pour and becomes what constitutes the void. It depends on what the engineer is doing at that location, and/or what is cheaper overall (with regard to material and labour costs for construction). A second version is a tensile void. This seems to be the case with Vancouver House. They need a large mass, so they want to fill that whole area. But, there is no need for reinforcing steel in the central part of the volume. So they are using the scaffolding to support the rebar placement above the void until the concrete is added. Once the concrete is in place, the scaffolding is dumbly trapped within but serves no purpose any longer. The end product is a large volume of concrete with an 'empty' box of rebar inside it.

[Zepfancouver]

I see it and get it now, thanks. I'll try to capture the top rebar assembly, in the coming days.

[Changing City]

Originally Posted by mcminsen

For example, this post from Marshal. Perhaps the tensile void described is what's going on now with the foundation at 1550 Alberni.

If you look at the subsequent images on Vancouver House, you'll see that there wasn't actually a 'void' at all - it looks to me that they filled the whole thing with concrete, entombing the blue supports. (Marshall seemed to note that too). It's just mass between the top and bottom sets of steel, without extra reinforcement, although the vertical steel where the elevator cores are obviously goes right through the base concrete. On Vancouver House the base of the crane was in two sections, and the bottom frame was buried in concrete as well; the main mast of the crane bolted on at the level that the concrete was poured to. This one looks the same. Once they've finished putting the upper steel in place I think we can anticipate a huge concrete pour.

[osirisboy]

I took it to mean it's void of rebar etc not concrete

[Changing City]

Originally Posted by osirisboy

I took it to mean it's void of rebar etc not concrete

You're probably right. When I see 'Void' and 'empty' it usually mean a hole, but void of rebar makes more sense.

[Zepfancouver]

Couldn't they have used old scaffolding. Someone would have gladly traded their old sets for these brand new ones.

[mcminsen]

Originally Posted by Zepfancouver

Couldn't they have used old scaffolding. Someone would have gladly traded their old sets for these brand new ones.

That same question came up in the Vancouver House thread...

Originally Posted by cairnstone

Damn thats a few tons of steel. This will be one of the larger pours in the city. Amazing they used new scaffold to support the steel. I would have thought they would have bought old stock from sky hi or aluma.

In the past i have done timber supports when they would be void formed

Originally Posted by Marshal

What do you mean by 'timber supports?' How did you use them? I can understand for voids, but supports?

As for new scaffold, I think the project/contractor insurer would ultimately dictate that. Just imagine the nervous breakdown the night before the pour, of the guy who decided to use old stock. Our lawyers and insurers get prickly if our specifications don't include the worn-out old clause "contractor to supply with all new material." That includes temp materials like formwork. Many times it is downright stupid, but our legal foundations require it regardless. (As an aside, specifying old timber, structural or not, can get pretty tricky.)