Posted on 02/15/2014 5:09:06 PM PST by BenLurkin
The marathon concrete pour begins Saturday evening and is expected to last 20 hours without interruption. The attempt will be verified by an official from Guinness World Records.
About 2,000 truckloads of concrete will be driven throughout the weekend to the construction site in downtown LA where a skyscraper called the New Wilshire Grand will be built.
... For the past several months, crews have prepared the site by digging an 18-foot-deep pit and lining it with 7 million pounds of reinforcing steel. They will then add 84 million pounds of concrete.
Because the concrete must be poured within 90 minutes of being mixed, trucks must arrive on time. In case of freeway jams, alternate routes have been mapped.
(Excerpt) Read more at losangeles.cbslocal.com ...
water.
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Additives can be mixed into the concrete to give a fast-high cure. This greatly increases to initial cure rate although it does take the same amount of time to achieve final cure. In addition, you can use a higher strength concrete so that you can more rapidly get to a required strength needed for ongoing construction tasks.
Dam few, if any, were continuous pour, though.
Hoover Dam? No way, Jose. Many many individual pours.
I remember when the fire happened. IIRC the building came very close to being destroyed by failure of the steel, but fortunately LAFD was able to control the blaze in time.
Respectfully, they have pretty much mastered how to build skyscrapers in SoCal that withstand quakes. I was in one, in 1990 during a seismic event, it shook like crazy, but no damage. They are built on gigantic rollers. You may recall the ‘94 event in Northridge. Most of the fatalities were in a three story apartment building. There were freeway collapses, the scoreboard at Anaheim Stadium tumbled into the seats, damage occurred as far as 80 miles from the epicenter, and it was felt in Las Vegas, nearly 300 miles away. None of the high rise buildings in the zone were catastrophically damaged.
“All concrete can crack.” - My Contractor
“All motorcycles can catch on fire.” - Me
Uh oh....A skyscraper!!!!
lol..
Some of these people seem rather medieval when it comes to skyscrapers. The west coast has many highrises and they've been up for many decades....Trying to recall the last time a skyscraper fell down in CA.
I can understand the sentiment, that was my opinion, when I first moved out here, but, as you posted, the facts say otherwise :)
Not sure if it was continuous or not, it was poured in triangular sections with cooling pipes running through it to draw off the heat of curring.
There have been many longer duration continuous concrete pours but I know of none larger.
Does anybody know what, if any, are the benefits of a continuous pour of concrete? Any drawbacks?
I don’t but one of the knowledgeable FReepers who have replied on this thread may.
“An 1,100 foot skyscraper in middle of earthquake country. What could go wrong?”
The tallest building in the San Fernando Valley is the 506 foot tall 10 Universal City Plaza skyscraper. It weathered the San Fernando Valley earthquakes wery well on the shock absorbers and rollers built into its foundation for earthquake resistance.
Certain types of buildings are more suited to a giant mat slab or single deep mass foundation due to the surrounding soils or the mass of the structure above.
Those characteristics lead to a placement like this — one giant mass of reinforced concrete. It has no seams or joints leading to a place where the segments would have to transfer forces, instead it is all one giant mass performing as a unit. The reinforcing makes it work as a single unit — think of a hammer head — an item cast that takes forces and transmits them as a whole.
That outlines the benefits. The drawbacks are that such a placement takes a very long time to reach its design strength. A footing, wall, beam or slab is typically designed for its cured strength at 28 days. It does continue to chemically cure and develop crystalline structure past that point, but most of the curing has occurred by that point. A giant mass placement (or pour if you will) stays slowing curing in the center for an extremely long time, months to take full load and years for the ultimate curve to be reached.
Dangers are batch plant failures, design mix mistakes or equipment failures in delivery or in the pumps that distribute it. Usually a number of plants are involved in the supply for just that reason. A fire on the only highway leading to a job sight can cause entire loads to be delayed and wasted and the placement to begin to set without supply to keep the placement underway as a single mass.
Can you imagine a placement where the batch plant calls in the middle and says, “we have found some of our trucks used to supply aggregate to the batch plant were used to haul soy beans and we have contaminated some of the loads of mixed concrete with soy beans — STOP the pour!!!” Such things have happened — that comes from a project where I knew the superintendent — he destroyed his cell phone he took the call on by throwing it at a wall.
I don't believe this current pour will set up in two weeks. Two months...maybe.
Right about the interlocking blocks but I rather doubt that breaking up the pour into increments had much effect on heat dissipation or curing time. The design of the dam included miles of iron pipe which was placed in the cubical forms. The pipes are connected together and to an extremely large refrigeration plant which supplies the pipe network with water at near freezing temperatures. There is also a network of thermocouples (heat sensors) throughout the mass of concrete. The current temperature is about half of what it was when the pouring was finished. It is estimated that the structure will reach thermal equilibrium about 300 years after the concrete work was complete.
I had the chance to take the ten dollar tour about 12 years ago. They took us into places the public seldom sees on the three dollar tour. We were allowed to walk out to the canyon rock face and see the seepage creeping along the rock face and concrete boundary. We also went below the generator gallery floor to see the operating turbines. I would think that the security people no longer allow public entry into those places.
Regards,
GtG
PS I'll never forget the time I spent on that tour, quite the thrill for an old mechanical engineer. That was a unique Federal project in that it came in under budget, ahead of schedule, and it has sold enough power to pay for itself many times over.
I know about vibrating the casting to take out the air pockets. Do they do this with a fast pour? (I’m an electrical engineer, not a civil). I have seen the results of not vibrating the forms while working on a water treatment plant. All the resulting voids made for a lot of leaks.
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