The mounting configurations of the five placing boom towers varied. A placing boom with a tower on the south side was already in place from the first pour and would be used again and two more towers with ballasted bases were installed outside the mat on the west side.
In addition, two footings were poured for two freestanding towers in the middle of the hole (east side). These two towers, in particular, would become a part of the foundation because after the mat pour was finished, the placing boom and upper tower sections were removed, and the remaining 10-foot (3m) tower section at the bottom ended up buried in the concrete. To be flush with the concrete, any pieces of the tower section sticking above the concrete were sawed off.
Gribble says, "It turned out to be a logical, as well as economical, solution."
Supplying the concrete to the five placing booms were four 61-meter boom pumps at street level. The units used their .16H pump cells, capable of up to 210 cubic yards an hour (160m³/hr) outputs, as well as their standard high-pressure S-Valves, so there was plenty of volume and pressure. Plus, a BSA 2110 HP-D trailer pump, capable of outputs up to 133 cubic yards an hour (102m³/hr), was also utilized to pump the concrete. An extensive amount of pipeline traveled down the sides of the deep hole and went in various directions to reach each placing boom tower.
OSS Solves Setup Dilemma
Another resourceful approach to access the pour involved two 61-meter boom pumps, facing cab-to-cab, that were set up in a narrow alley on the north side. The setup in the extremely tight confines was only possible due to the one-sided support (OSS) outrigger system. OSS reduces the outrigger extension on one side of the unit to create an overall smaller machine footprint. In this case, the outrigger width was reduced by 10 feet (3.05m), which enabled a tight fit in the spot.
OSS has been a standard feature on Putzmeister 61-meter boom pumps since 2006 when the model was introduced, and its benefit has proven beneficial. Gribble says, "This setup would have been impossible without OSS on our Putzmeister boom pumps."
Over 80 mixer trucks from five local concrete plants dispatched a self-consolidating concrete mix that was specified for the bottom 18 inches (457mm) of the foundation to ensure proper concrete consolidation where large concentrations of reinforcing bars occur. The remaining foundation used a low-heat concrete mix to minimize temperature differential between the center of the mat and the exposed top surface.
"Everything went exceptionally well," says Gribble. "Our Putzmeister equipment delivered the necessary volume, as well as provided really smooth concrete outputs during the round-the-clock pour."
Rising with Efficiency
After two successful mat pours, the massive six-level garage that covered the entire footprint, along with a three-level podium commons area and the two skyscrapers rose quickly from the ground. The larger 61-meter boom pumps, with vertical heights up to 197' 2" (61m), were used whenever possible to place concrete for anything within their reach. However, Putzmeister placing systems were the main source of concrete placement for the two skyscrapers, with a crane flying four placing booms among eight strategically placed tower locations.
"For a quicker process of flying the placing booms, Series II is an absolute 'must'," says Gribble. Series II features exclusive hydraulic connection technology where the operator can easily couple and uncouple individual color-coded hydraulic hoses while not under pressure.
Plus, as the placing booms do not require counterweight, time and labor savings were realized.
Other efficiencies were also noted. "With the 50-foot (15.24m) Putzmeister tower, we could pour two floors and then jump the tower compared to only one floor per jump, which is more common with other systems," explains Gribble. "This is significant because, with fewer jumps, it reduces expensive crane costs."
When tackling the high rises, Gribble says, "One of the biggest obstacles was the very hot mixes - high strength, high heat - which made pumping challenging." To accommodate the difficult mixes, two BSA 14000 HP-D trailer pumps with eight-inch (200mm) cylinders and powerful 630 hp (470kW) Cat engines provided the power to reach the top level. They were especially put to the test when they needed to accommodate the 9C mixes, which were super hot. The trailer pumps have the capability to provide both high outputs up to 133 cubic yards an hour (102m³/hr), and high pressures up to 2,176 psi (150 bar) - both on the rod side.
The general contractor, Bellevue-based GLY Construction, Inc. is well known in the region and selected to handle the colossal project. Having worked with Ralph's for decades, their past experience led them again to rely on the company's concrete placing services. The pumper has been in business since 1965 so experience is prevalent, and the fleet is expansive, serving customers from eleven offices across Washington and Oregon. Previously under the direction of Skip Gribble, the company is now owned and operated by his three sons ̶ Jacob, Josh and Isaac who grew up in the business. Skip, although still involved with long-term decisions, is enjoying semi-retirement in Arizona, with his sons carrying on his legacy.