Feb 28 2015
Architects, engineers and construction workers building Bellevue’s Lincoln Square Expansion project will witness the state’s largest continuous concrete pour starting Feb. 28 at 3 a.m.
The continuous pour of 13,690 yards of concrete will last 24 hours and will form the structural base for the 41-story luxury hotel-residential tower.
“This massive mat of concrete and rebar is the foundation for what will become Bellevue’s premier luxury hotel-residential tower,” said Michael Chaplin, principal at Sclater Architects, the lead architect for the 1.5 million-square-foot, mixed-use Lincoln Square Expansion project. “In coming months, Bellevue residents will witness this tower and an adjacent office tower climb upward into the Bellevue skyline.”
Built atop six levels of underground parking, the tower will feature a designer hotel and luxury high-rise rental residences with unequalled views.
The concrete and rebar structure that will take shape Feb. 28 will anchor the 450-foot tower and play a critical structural role in supporting the cast-in-place concrete and steel structure. After removing more than 485,000 square feet of earth over the past year, workers recently installed more than 3 million pounds of rebar in the construction pit located at the corner of NE 4th Street and Bellevue Way.
“The mat is designed to carry the weight of a 47-level structure and resist wind and seismic forces from the tower above. The design also provides a number of opportunities to implement creative and constructible solutions,” said Mark Whiteley, P.E. S.E., Principal at CKC, the structural engineering firm working on the Lincoln Square Expansion. “The mat foundation utilizes high-strength steel reinforcing (80 ksi) to minimize congestion and reduce total steel tonnage.”
A self-consolidating concrete mix is specified for the bottom 18 inches of the foundation to ensure proper concrete consolidation where large concentrations of reinforcing bars occur. The remaining foundation will use a low-heat concrete mix to minimize temperature differential between the center of the mat and the exposed top surface.
“A tremendous amount of complex planning and coordination is required to execute a pour of this size,” said GLY’s Executive Vice President Ted Herb. “The north tower pour took hundreds of hours of teamwork between our employees, project partners, the City of Bellevue, and our subcontractors and suppliers to map out each and every detail.”
Saturday’s mat pour is the second on the site this year. Workers completed the first pour for the 450-foot office tower of the Lincoln Square expansion project on Jan. 31. More than 13,400 yards of concrete were pumped into the site over the course of 16 hours.
Quick Facts / North Tower Concrete Mat Pour
- The concrete mat foundation provides stability and strength to the building and is 10 feet thick at its deepest point. Approximately 13,690 cubic yards of concrete and 1,470 tons of high-strength reinforcing steel go into the slab.
- The 76,000-ton building above the foundation is supported by columns constructed of high-strength concrete with a capacity of 14,000 pounds per square inch. These columns are in turn supported by the mat foundation, creating pressures of 12,000 pounds per square foot on the underlying soil.
- The size of a mat foundation is determined by the size and weight of the building, the soil bearing capacity, and the forces on the building during an earthquake or wind storm.
- The temperature at the center of the mat will reach 150 degrees Fahrenheit 24 hours after the pour as a result of a chemical process called cement hydration, the reaction of water to other components of the concrete mixture. The process is what ultimately strengthens the concrete. The slab temperature typically cools down over the course of a week after the pour. Three thermometers placed respectively at the bottom, middle and top of the mat are used to monitor the temperature.
- Eighty-one trucks will run continuously between the site and 5 local concrete plants starting at 3:00 a.m. Seven concrete pumps will be used at the job site.
Source: http://sclaterarchitects.com/