Times change on Rincon Hill; Tower 1 to top-off this month

07/01/2007 http://www.concretemonthly.com/monthly/art.php?2835

While most of the country figuratively shakes in its civic boots at the thought of an earthquake, San Francisco just keeps building up without fear.

One of the latest changes to the city's skyline is Rincon Hill - once home to the 183-foot Bank of America clock tower that became an icon for the area around First and Harrison streets, adjacent to the entrance to the San Francisco-Oakland Bay Bridge. When complete, the old clock tower will be replaced by a two-tower high-rise condominium development known as One Rincon Hill.

Those in favor of the new development call it an instant landmark because it is the first thing people will see coming into the city from the East Bay. Located near the city's financial center, One Rincon Hill is one of several developments that are transforming San Francisco, bringing a new and high-priced lifestyle to a somewhat-run-down area.

Ironically, this project is establishing a new construction benchmark by beating the clock. The combined efforts of the concrete contractor, San Mateo-based Webcor Builders and the concrete pumping company, Interstate Concrete Pumping of Hayward have achieved the first three-day floor cycle on the West Coast.

The placing boom went up Sept. 18, 2006 and the first tower will top off this month with a total of more than 45,000 cubic yards of concrete, including the mat pour.

Developed by Michael Kriozere of Urban West Associates with headquarters in La Jolla and under the construction management of Bovis Lend Lease, groundbreaking on this $290 million project occurred in November of 2005 on the first of two elegantly slender towers. There will be 376 condominiums in the first tower with prices ranging from $600,000 for a small one-bedroom condo to $2.5 million for a penthouse.


Strength in Design

There's no arguing that the views are spectacular. But one view that comes quickly to mind of people around the world, is the part of the Bay Bridge that collapsed during one of San Francisco's recent earthquakes.

Designed for strength and stability in a notoriously unstable part of the country, the design of One Rincon Hill features a central core providing the main support for the structure as opposed to an exterior frame. Outside of the core, tall columns made of steel-reinforced concrete, will function like outriggers to provide extra strength. Buckling restrained braces provide added seismic safety.

The first eight levels are for parking, providing the residential floors with vistas across the Bay and the Golden Gate Bridge.

Based on bedrock, the concrete and steel foundation at One Rincon Hill is 12 feet thick.

Interstate vice president and estimator for this job, Andy Paulazzo, said that for the mat pour, the pumps provided the reach needed and took the concrete provided by Bode Gravel as fast as it could be delivered.

Bode provides several different mix designs for One Rincon Hill. This includes a 5,000-psi mix for the foundation and a combination of 8,000-psi and 6,000-psi for the core walls and columns. The post tension slabs are a 5,000-psi early strength mix that enables post tensioning in three days.


A Tight Spot

The fact that the project is directly adjacent to San Francisco's dramatic Bay Bridge made this project not only spectacular in terms of the views it will offer, it also made the logistics of getting concrete to the site a challenge.

Positioned near the entrance ramp for the bridge on a footprint of only 9,800 square feet, the 52- and 63-story two-tower condo project will reach 629 feet when complete.

"Since the buildings sit on less than an acre and a half of land, there are only about four feet between the first 63-story tower and the bridge," Paulazzo said. "While this location will be great for residents, it definitely posed issues in terms of how we would be able to get the concrete for the foundation onsite."

Because the city of San Francisco would not grant a traffic lane for the ready mix trucks, Interstate came up with a plan to use five of its Putzmeister truck-mounted concrete boom pumps, both onsite and offsite for the original mat pour. Starting early in the morning on Feb. 4, 2006, the Interstate fleet began the 6,011-cubic-yard job.

"It was a very coordinated effort between our operators and the ready mix company," Paulazzo said. "Onsite, we had a 58-meter pump on a steep ramp adjacent to the bridge's on-ramp, as well as a 52Z-meter over a corner and onto the mat. We also used our 42-meter to pump concrete into the hopper of a 46-meter down in the hole. In addition, we had a 55-meter offsite with its boom extended over a hill and onto the mat."


Placing Boom Expertise

Founded in 1996, Interstate Concrete Pumping has developed a strong industry following, especially in the use of placing booms. "Bucketing just eats up crane time," Jim Nolan, president of Interstate, said. "A placing system is much more efficient. Now, our competitors are catching on to this method."

Ten years ago, Interstate and Webcor Builders started the age of the modern placing boom in San Francisco, when the two companies worked together on 388 Beal St.

"Placing boom jobs continue to grow in our area," he said. "We work jobs with freestanding tower, outside tie-in and inside self-climbing, like One Rincon Hill. In fact, we recently had seven placing booms for Webcor on various projects at the same time."

Jack Harrington, Webcor's concrete project manager, said that by using placing booms, the tower crane is available for other critical tasks in the pouring cycle. "The increased crane availability has been one of the key elements for achieving the historic three-day pace," Harrington said.

Construction of One Rincon Hill is progressing quickly. Interstate is pouring a concrete floor every three days, compared to the usual standard in San Francisco, which is one floor every five to six days. "This three-day cycle will save 60 working days on the project, and the labor and material costs that go with it," notes Harrington.

At the foot of the building, a 680 horsepower Putzmeister high pressure trailer pump delivers the concrete to the waiting 34/38Z-meter placing boom on 30 feet of tower at the top of the structure, more than 500 feet above the summit of Rincon Hill.
Paulazzo said: "We have years of experience in pumping concrete and knew we could rely on our equipment and operators like Al Valdez, Randy Boychuck and Robert Turner Sr. to make this project happen in the 16 months we had to do it."

In a typical three-day cycle, Interstate pumps the 160-cubic-yard core wall on day one. Day two starts early with a 23-cubic-yard deck pour in the morning followed by clean out and pouring another 50 cubic yards for the columns in the afternoon. The third day is left open to prepare for the next deck.

From truck-mounted concrete boom pumps for the mat pour to powerful Thom-Katt TK 50s for small jobs like stairs, to its high pressure pump and placing boom system, Intestate has used practically every size pump in its Putzmeister fleet.

The building will be completed in April 2008, ready for occupants of the expensive condos with very stable views over the city and beyond, from the Bay Bridge on the east to the Pacific Ocean on the west. CM


This article appears in the July 2007 issue of Concrete Monthly.

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