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Ssshhh … Occupants Inside: Putzmeister America Helps Complete Construction of the Partially Occupied Summit Building

Ssshhh … Occupants Inside: Putzmeister America Helps Complete Construction of the Partially Occupied Summit Building

STURTEVANT, Wis. (November 2004) – Once again, construction on the Summit building is in progress. Floors are being added to an existing high-rise in the Summit office building complex located in the heart of Bellevue’s central business district. This special area offers a panoramic view of Seattle, Lake Washington, the Cascades and Mt. Rainier.

Construction of the Summit "Building A" had reached the third of 11 floors when the project was halted due to uncertainty about occupancy. The three-story building was temporarily finished and the existing space leased.

Despite the situation, developer Bentall Capital U.S. Inc. remained hopeful that it would eventually finish the entire 143 ft. tower and add more tenants. That time came when Puget Sound Energy signed an agreement in 2004 to lease the tower upon completion. As a result, the first concrete pour occurred on August 20, 2004, with completion of the 235,000 sq. ft. structure slated for 2007.

With existing tenants of the building (businesses and a daycare) remaining in the structure during construction, the first concrete pour required a great amount of ingenuity. The remaining nine floors – spaced 12 ft., 8 in. apart – had to be constructed without disruption from noise or vibration. This required a new approach for placing concrete.

The general contractor, Sellen Construction of Seattle, relied upon Pacific Concrete Pumping to assist with a plan for minimal noise and no vibration during concrete placement. Pacific Concrete Pumping, with facilities in Redmond, Issaquah and Monroe, Wash., stepped up to the challenge. The 15-year old pumping company is owned by Mike and Julie Cooper and offers a 16-unit Putzmeister pumping fleet, a highly trained staff and the necessary expertise to accommodate this job’s special demands.

Keith Gustafson, general manager of Pacific Concrete Pumping says, "We worked with a lot of different technical people on this project because absolutely everything was re-engineered to ensure the safety of the occupants inside and to avoid construction disruptions during the concrete placing process."

Gustafson also notes, "We especially worked hand-in-hand with the professionals at Sellen throughout the decision-making process. It was definitely a team effort to jointly develop and implement a plan so that tenants are virtually unaware of what is happening around them."

Working with Sellen, Pacific Concrete Pumping suggested detaching a boom from a Putzmeister 36-Meter truck-mounted concrete pump to act as a separate placing boom atop a tower.

For erecting the placing boom tower, the easiest approach would have been to re-shore the floors using the existing 4 ft., 6 in. holes left when construction originally started years ago. Unfortunately, this method was not an option. With no way to appropriately distribute the weight between the roof and the third floor due to the building’s occupancy below, the most effective alternative proved to be a Putzmeister adjustable wall bracket.

Fortunately, engineers determined that the shear wall had enough strength to withstand the forces of a mounted wall bracket. As a result, the bracket was bolted through the 2.5 ft. thick shear wall of the building’s core.

Initially, a 20 ft. tower was erected and 10 ft. tower increments added as needed until reaching 50 ft. Then the tower was disassembled, the wall bracket moved up 50 ft. higher and the process of stacking 10 ft. tower increments repeated itself in a similar pattern.

Of course, safety remains a paramount concern because of the tenants inside the structure. Two full-time construction safety personnel are on site at all times and everyone is doing their part to keep the site safe.

Gustafson comments, "We check the wall bracket bolts at least once a week, which is basically after every third concrete pour. Then Sellen re-torques them when necessary to maintain a safe environment."

To sustain a vibration-free approach, a second placing boom tower is also being utilized, but without a placing boom atop. The tower’s sole purpose is keeping the concrete delivery line away from the building to prevent vibration. Therefore, a 5 in. slick line goes upward past three glass floors without bolting onto the building in any manner. Once on the third floor roof, the delivery line travels 70 ft. to the middle of the structure before eventually going up the shear wall.

In the end, two 50 ft. placing boom towers are stationed inside the middle of the existing building’s shear wall and in front of the building on the sidewalk.

Freestanding the 50 ft. placing boom tower on the sidewalk requires the engineering of the smallest footing possible to fit the modest size of the sidewalk and the obstacle of a fixed tower crane less than five feet away. A typical footing is 16 ft. square and 51 in. high; however, this footing was re-engineered at 6 ft. square and 30 in. high to accommodate the delivery line, but no placing boom.

Meanwhile, a high-pressure Putzmeister BSA 2110 HP-D trailer pumps the slabs using a 3/4 in. mix with an 8 in. slump and pumps the columns and shear walls using a pea gravel mix with a 9 in. slump. Stoneway Redi-Mix of Renton, Wash., is supplying all concrete.

Approximately two floors are completed each month. Concrete placement happens three times a week with a 340 cubic yard deck pour once a week and 45 cubic yard concrete pours for the shear walls and columns occurring twice weekly. Together, the concrete placing equipment combination averages 100 yd/hr – more than adequate volume for the project’s delicate situation.

Concrete placement will be finished by year-end; and upon completion, the second phase of the project will have consumed about 6500 cubic yard of concrete.

Bellevue, where Summit Building A is under construction, is at the apex of Metro Seattle’s technology center and is a major player in the software industry nationwide. Only California’s Silicon Valley rivals it. Bellevue’s technology corridor comprises over 1500 acres of corporate campuses along I-405 that includes aerospace, biomedical technology, computers and service industries.

General contractor: Sellen Construction – Seattle, WA
Concrete contractor: Sellen Construction – Seattle, WA
Pumping contractor: Pacific Concrete Pumping – Redmond, Issaquah, and Monroe, WA
Ready-mix supplier: Stoneway Redi-Mix – Renton, WA
Equipment: Putzmeister 36-Meter detachable placing boom, Putzmeister BSA 2110 HP-D trailer pump, two 50 ft. PM towers and a Putzmeister adjustable wall bracket