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A number 11 bar is 5.31 lbs per linear foot. 

 

25,000 tonnes would be roughly equivalent to 9.4 million lineal feet of No. 11 bar. A standard Houston block is 330ft by 330 ft. Even if I had 1 foot spacing, both ways, and 2 mats that adds up to 435600 lineal feet- or 1,000 tonnes. 25,000 tons, seems like too much even for the full tower. B/c they likely be using Number 11 bars after the first few floors. 

 

No 18 bars are 13.6 lbs per linear foot. Based on the pictures it doesnt look like No. 18 bars to me. But I could be wrong! I'm totally playing armchair engineer right now without any knowledge on the load calculations for the foundation. Thanks for the pictures again though... keep em coming!

Edited by Purdueenginerd
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From Hines' fb page

609 Main at Texas, Hines next iconic building in downtown Houston, is 3 days away from the “mat pour.” On Saturday, 180 concrete trucks will line up to continuously pour 14,000 cubic yards of concrete for more than 17 hours. The 48-story office tower is scheduled for completion in early 2017. http://bit.ly/1mlG2J2

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I wish the oxblue construction cam featured 24 hour live flow. If I remember correctly it seems that you only get a shot every once in a while every day, but live feed would be interesting to see. They do have a feature that allows you to watch the time lapse images but I don't think there will be enough of them to see the trucks going in and out. I wish I could be there to watch but will be at work.

I'm really not sure how their cameras work but I do know you don't see movement in the images. Anyone know for sure.

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This is for sure the foundation slab for the high rise. Parking garage loads are puny compared to the skyscrapers. 

 

So on a building like this, I always thought there were piers that went down deep into the ground, from which the building frame was constructed. With this giant slab, it looks like they're essentially building the building on top of a giant concrete raft floating on the clay 30 feet below ground. Can you explain it?

 

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When I went by on Sunday and talked to a supervisor, he said 1 tower crane will be in the center north section of the office tower( if you look closely in the pic you can see the foundation), 1 on the southwest corner and 1 for the north side parking garage.

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So on a building like this, I always thought there were piers that went down deep into the ground, from which the building frame was constructed. With this giant slab, it looks like they're essentially building the building on top of a giant concrete raft floating on the clay 30 feet below ground. Can you explain it?

 

Pretty sure this is the way all highrises are built in Houston.  There is no bedrock on which to set piers.

 

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From Hines Facebook page:

609 Main at Texas, Hines' next iconic building in downtown Houston, is 3 days away from the mat pour. On Saturday, 180 concrete trucks will line up to continuously pour 14,000 cubic yards of concrete for more than 17 hours. The 48-story office tower is scheduled for completion in early 2017. http://bit.ly/1mlG2J2

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So on a building like this, I always thought there were piers that went down deep into the ground, from which the building frame was constructed. With this giant slab, it looks like they're essentially building the building on top of a giant concrete raft floating on the clay 30 feet below ground. Can you explain it?

 

Piles arent needed if you the bearing and uplift pressures in the soils can be achieved within the depth they dug down. Piles would still need a transfer slab/foundation at the top of the piles to distribute loads to each pile. I didnt see if they installed piles on this project. but lets assume that foundation doesnt have piles and that the footing they poured is 300 ft by 150 ft and their soil tests showed that the bearing pressure is 4000 PSI. Off the cuff, calc without any adjustment factors shows that the soil will support 2,160,000,000 lbs- before it starts to move. Reinforced Concrete is 150 lbs per cubic foot.  Which means I could pour 300 ft x 150 ft x 320 foot (tall) Solid Block of reinforced concrete before the soil could fail in bearing, just from its weight-- and as you know buildings are mostly hollow. Now, thats just vertical weight. I doubt it controls. Wind loads and overturning moment are probably the controlling factor regarding geotech design. 

 

Someone mentioned piles arent used because bedrock is too deep. Thats not entirely true. Bedrock is, in fact, probably too deep. but really think about this. Say the Geo tech testing determined that at 40 feet deep, the soil pressure capacity is 4000 psi. But at 80 feet deep. Its only 5000 psi. How many piles (with their small cross sectional area) driven to 80 feet do I need to reach the same capacity has a gigantic footing at 40 feet? Where his/her degree of truth comes in, is that if bedrock was at 40 ft depth and had a pressure capacity of 13000 psi. In which case yeah, piles might be worth it. 

 

Basically, like many things it depends. I actually, would have assumed some piles would have been installed: but it all depends on the geotech conditions. No geotech site in Houston is the same. 

 

 

Disclaimer: Armchair engineering & and most of my foundation design is substantially smaller than this. 

Edited by Purdueenginerd
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Maybe. So, Chase tower is taller, and I think has a smaller foot print than 609 Main. Which means two problems. Higher pressure on the soil due to less area & and more windloads due to taller height. Its hard to speculate, but maybe they dug down 60 feet, instead of 30 feet to achieve their footing. Maybe they drove piles & built a large footing. I think chase tower is also a steel frame, which makes it could make it lighter than a reinforced concrete structure of similar height. 

So look, Burj Khalifa, Tallest building in the world had a footing, but also had a shit ton of piles that went a whopping 160 feet down. Their soil conditions are sandy- which performs worse than clay. (Link below for UAE soil maps). My most recent geotech design project, I designed a foundation 30 feet from the ship channel-- Soil samples hit 3000 psi--- within 5 feet depth (and totally saturated in water). No soil condition is the same, but clay soils arent as bad as many think. 

 

https://www.uaesis.ae/imf/imf.jsp?site=ADSIS&u=everyone&p=everyone&Submit=Submit

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Doesn't the clay kind of move over time? I remember in College Station reading that the clay underground had sort of a current to it, emanating away from the Brazos River, with waves that moved over decades. This was the reason why so many of the older buildings there had cracks. Does the clay downtown do something like this perhaps?

 

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Here are two photos from yesterday afternoon, You can see the base of the crane being installed.....

 

There are about 6-7 feet between the layers of rebar (enough for construction men to work underneath the top layer), and the top layer is elevated by small groupings of rebar placed vertically. During the mat pour, how are the engineers going to ensure that the concrete can get through the top, dense layer of rebar, enough to completely to cover the bottom, dense layer of rebar? In other words, how will the engineers ensure that the concrete will be solid throughout?

 

Pardon my ignorance, I am not an engineer and have never seen a mat pour. I am looking forward to watching it this weekend though!

 

Go Coogs! Beat UTSA!

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All Soil moves over time. Geology is not my specialty. Soil Sublimation can be a problem in this area because of oil extraction and water extraction, which changes soil characteristics. Clay, sand, etc will move, if a load is applied. As an engineer, other than rapid seismic loads, I can't account for the geology of this area. The only load I can design for is, the loads from the building into the soil. I have to calculate weather the soils will move, if I apply a load to it. If the answer is no- then my design is sufficient. If an unknown underground river 600 feet below the building, collapses thus moving all the clay above it--- "Well, shit that sucks" is going to be my response. :)

 

But soil acting like a wave, thus slowly moving. Yeah- that makes sense. But none of the buildings in downtown houston are design to last throughout the geological era of this region. 

 

Thats a tough question. 

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Wow those pictures do a lot of justice to just how much rebar is actually going into this thing.  That's incredible.

 

As far as making sure the concrete is evenly distributed throughout...I would think gravity is doing most of the work.  There is going to be a LOT of concrete and the weight of all that alone will force the nooks and crannies to be filled in.  Also, and Purdueenginerd can school me here if I'm wrong, but there will be workers following the pump hose ensuring that the concrete is getting down where they need it.

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That's very interesting thanks for the insight PurdueEngineer. If I may ask, what kind of engineer are you? Structural or Civil?

And one more question, those piles that surround the shaft, are those similar to piles that go deep into the soil or do they not provide and large load bearing support at all?

Edited by BigFootsSocks
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Great question Grizz,

 

So to answer this question, I'm going ask you to imagine you have just squeezed a pile of ketchup on your plate. That pile is maybe 1'' high. Even though Ketchup could be classified as liquid, why doesnt it  spread out like say water, or oil would on your plate. There is property of liquids called "viscosity". The property deals with internal stresses between the molecules that can be summed as Viscosity is quantified measure of resistance to internal stress. Water flows, because its internal stresses are not strong enough to overcome the force due to gravity. Ketchup internal stresses, can sort of beat out gravity.  Say you want to spread the ketchup out without touching it. Youre going to pick up your plate, and vigorously vibrate the plate (not violently). As you apply that vibration, you are adding more internal stresses to the pile.  What happens? Your ketchup pile spreads out. 

http://en.wikipedia.org/wiki/Viscosity

Now concrete, is a little similar (though not as delicious). ASTM, ACI standards generally indicate that concrete shouldnt be dropped from a pump hose end for over 4'-6'. The crews are <likely> going to take the pump hose to the bottom of their reinforcement. Concrete will be pumped there and form a pile. ACI and ASTM standards will then dictate that they have to vibrate it. We often use a concrete vibrators, dubbed nicely by crews as a "donkey dicks". (http://www.harborfreight.com/power-tools/concrete-vibrators.html). This spreads out your concrete and helps consolidate the material around the reinforcement. At THAT point, its just a matter of keep pumping, and keep "filling up" your form. 

The next issue comes on the engineering side. There are very accurate scientific tests, performed to determine a viscosity of the a liquid. In construction, I dont care for that accuracy. A test is often performed in the field called a slump test(http://en.wikipedia.org/wiki/Slump_test). The drop in concrete after the test is performed is a method used to 'sort of' determine how workable or flowable the concrete is. A highway might use a 1'' slump, thats very low. If the engineer specified a 1'' slump for say, this pour... the crew would mutiny and murder him. So the engineer knows the mix design he needs and will specify a slump based on that. 6'' slump is pretty workable. Mix design/slump can be altered with a chemical additives such as plasticizers (http://en.wikipedia.org/wiki/Plasticizer) and superplasticizers. Aggragate selection and water content also can alter material properties. 

Finally there's another option. If rebar density is SO dense, that proper vibration is difficult or impossible. The engineer might specify whats called a self consolidating concrete (SCC). THis concrete is so liquid-y that its slump  could be considered 10''-11''.  The beauty of those concretes are that its material properties allow for the suspension of the coarse aggregate during placement--- IE... the rocks won't sink! If they select that concrete, at that point its just a matter of 'filling up' the tub. 

 

Edited by Purdueenginerd
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That's very interesting thanks for the insight PurdueEngineer. If I may ask, what kind of engineer are you? Structural or Civil?

And one more question, those piles that surround the shaft, are those similar to piles that go deep into the soil or do they not provide and large load bearing support at all?

 

 

Structural and Forensic Engineering are about 70 percent of my work day. Civil and Mechanical (not very advanced mechanical) are probably the other 30 percent. 

 

I don't do much 'new construction'. Most is fixing things that are failing/failed.

 

The perimeter piles are probably utilized as retaining structure. Designed to resist the lateral load of the soil below the street surface and provide a safe working environment for the crews working below grade. For load bearing, in regards to the building-- I doubt they'll be utilized for that purpose---at this interval. But we'll know within a few weeks. Those piles can go pretty deep. But how deep?  Say the hole in the ground is 20'. That means, it has to resist 20' deep of lateral soil pressure. The pile will try to rotate when the lateral soil pressure presses on it, what prevent its from rotating?--- More soil below the hole. So... those things probably go another 35-40 feet below the street. I'm simplifying the calculation massively as there's a lot more to take into account, but conceptually that is essentially their purpose. 

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Thanks for the structures class. I always learn something on this site. I'm not an architect, but I know many that attend seminars and lectures for credit. Does this count towards those necessary credits?  tongue.png

Also I mentioned on the Marriot site, but they have a big pour this weekend also. Should be a busy Saturday downtown.

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^Much like the Main St. side of 1111 Travis St., I'm sure the perimeter beam stub-outs will get tied & formed when the basement walls reach that height (maybe sidewalk grade?). Be sure to look for them on the north side of the tower as that's where it will tie into the garage too. 2929 Wesleyan had some funky stub-outs on it's podium as well.

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So look, Burj Khalifa, Tallest building in the world had a footing, but also had a shit ton of piles that went a whopping 160 feet down.

Some of the early photos of the construction of Kingdom Tower in Jeddah seem to indicate a rather shallow foundation with no piles. Not sure whether piles are being eschewed for other reasons or whether soil in Jeddah is more stable than Dubai. But the gumbo underlying Houston is certainly a design challenge.

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Thanks, Purdueenginerd, for all the great insight! I'm always fascinated by this stuff and still can't fully grasp how it all works. To me, it appears that the foundations for buildings such as 609 Main are just too puny to hold those giant structures above perfectly in place over long periods of time. It would only make sense to me if the foundations were like tree roots - equal, or at least close to the size of the structure above. But, this is why I'm not an enginerd!

 

tree_mirror.jpg

 

 

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  • The title was changed to 609 Main at Texas

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