Dance of the concrete
San Francisco: Pouring the floors for the 600-foot One Rincon Hill tower involves a blend of high technology and old-fashioned muscle -- it's also a race against the clock
Carl Nolte, Chronicle Staff Writer
Monday, April 16, 2007
This is the way they build a high rise: 14 men in hard hats, 45 stories above Rincon Hill in San Francisco, pushing, smoothing, shoveling, their feet ankle-deep in wet concrete.
The crew is pouring the floor of what will be the 45th story of a 600-foot-tall condominium tower called One Rincon Hill. When the building is finished, it will be the tallest residential building west of the Mississippi.
The work pouring the concrete floor is like a slow ballet, a combination of advanced construction technology and human muscle.
The technology gets the wet concrete from a plant near Hunters Point to the job site two miles away to be pumped more than 500 feet above the summit of Rincon Hill and poured in place.
At the foot of the building, a Putzmeister cement pump with 680 horsepower forces the cement through a six-inch pipe called a "slick line" in the center of the high rise, then into a pouring tower that looks like the neck of some enormous insect, then through a wide hose to plop out on the roof of the floor below. It is a wet mix, gray in color, like oatmeal with rocks and gravel in it.
Then the workers take over, shaping the concrete, smoothing it. It is a race against time: The concrete will set in 31/2 to 4 hours. There is no time to waste.
"This is not fun,'' said Donald Sampson, a superintendent of the job. "This is hard work.''
"This stuff is heavy,'' said Randy Boychuck, who positions the pump nozzle using a radio transmitter. "Pick up a bucket of concrete and you'll see.''
This is young men's work. The concrete crew is all men, all in their 20s and 30s, laughing and joking. The older men are on the fringes, watching, inspecting, supervising.
The view from the 45th floor is impressive -- the city and the Bay Bridge seem to be at the feet of the workers.
There are no walls on the 45th floor yet, and the edges where the floor-to-ceiling glass windows will go are protected only by wooden rails; a chill wind whips through a curtain of gray mesh fabric. Outside that, there is nothing but air.
Crane towers above tower
Above the top of the building is a huge tower crane, maybe 100 feet taller than the top of the building. It looks like a giant version of those old toy Erector sets, like a steel exclamation mark on the skyline.
People in cars whizzing by the tower can get only a fast glimpse of the building, which seems to be growing like a weed in the spring. And it is -- a new floor is poured every three days.
The steel core of the building, a web of reinforced concrete bars soon to be enclosed in concrete, has reached 50 stories. Later in the week, crews poured the 46th floor.
It is a landmark already, the green window facings -- called curtain wall -- gleaming in the sun. At night, lights burn high up in the building, making the empty tower look ghostly.
Five months ago, the building was half as tall. There is still more to go: it will top off at 60 stories.
Mixing the concrete
On days when concrete is poured, the work starts at the Bode Gravel Co. plant near Pier 96. Here the concrete, made of cement, sand, gravel and rock, is mixed and poured wet into big red and yellow trucks. Each truck weighs 60,000 pounds loaded, said Arvell Williams, one of the drivers.
Bode is an old company, as construction companies go. It has been in San Francisco for 92 years.
With so many construction projects going on in San Francisco these days, the trucks are a familiar sight, their big drums rotating to keep the fresh concrete wet.
Williams figures it takes him 15 minutes or so to make it from the plant to the job site at the dead end of First Street, more if there is a baseball game at AT&T Park or a lot of other traffic. The big concrete truck growls up Rincon Hill, up Harrison Street. The street feeds a major on-ramp for the Bay Bridge, so the going is often slow.
The driver turns into the stub end of First Street and backs the truck up to the Putzmeister pump. He pulls out the pouring ramp, and the concrete is on its way -- up the slick line pipe onto the top of the pouring tower. Each truck carries 10 cubic yards of concrete. It takes 23 trucks per floor.
Boychuck, the pump operator at the top of the building, guides the arm of the pump device, and then the men, wearing rubber boots, smooth out the concrete. Some use shovels, others smoothing devices like big trowels. One man carries a gas-powered vibrator and moves it through the concrete. He's getting the air bubbles out.
Underneath the concrete is a spider web of reinforced steel bars, called rebar. There also is a conduit for electrical connections and cables faced with green plastic. The cables will be used later to pull the concrete and tighten it when it sets.
Checking the strength
Tim Farley, an inspector with Construction Testing Services, watches carefully. His job is to take samples of the concrete to ensure it has the required strength.
This is no plain slab of concrete. Here and there are green objects that look like upside-down coffee cans sitting above the concrete base and between the rebar. These mark the spots where water and gas connections will go in.
"Look,'' says Mike Gomez, a 25-year-old plumber. "Here is the connection for the kitchen sink, here is the shower.'' There, covered by a hood of white plastic, is the place for the toilet. "See that big square spot?'' Gomez says. "That is where the bathtub will go.''
All of this will be buried in concrete, but the water and gas connections will be covered by a thin layer of concrete, to be punched out from below later. Then the plumbers will install the pipes.
A year from now, if all goes well, the building will be completed and the elevators in its center will open, and people will step out into the 45th floor, into expensive condos with views over the city and beyond, from the Bay Bridge on the east to the Pacific Ocean on the west.
A variety of trades and contractors is working on the concrete. The general contractor is Bovis Lend Lease, Webcor Concrete is doing the pouring, Dolan Concrete is putting it in place, and RPS Inc. does the rebar work.
Ground was broken for One Rincon Hill right next to where the Bay Bridge lands in San Francisco in the late fall of 2005.
Transforming the city
One Rincon Hill -- two towers side by side -- will be one of those projects that are transforming San Francisco, turning the somewhat-run-down area into a residential neighborhood of pricey high-rise buildings.
There will be 376 condominiums in the first tower. The prices range from $600,000 for a small condo to $2.5 million. The condos have been selling well for a building that is not yet completed -- only 27 remain to be sold.
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