September 27, 2019

High-rise structures

Photo provided by WACA

The W Hotel tower's innovations included the use of high-strength steel fiber reinforced concrete in the shear wall coupling beams, the largest use ever in North America.

W Hotel tower

Location: Bellevue

The 41-story W Hotel tower features luxury hotel rooms and upscale apartments atop a three-level podium, with six subterranean parking levels below. The retail podium includes boutique shops, an upscale theater and a wide variety of restaurants.

The subterranean parking provides 2,200 spaces and connects to the adjacent Lincoln Square parking via a tunnel.

The W Hotel tower incorporated numerous innovative design features. These included the use of high-strength steel fiber reinforced concrete (SFRC) in the shear wall coupling beams, the largest use ever in North America. The building also incorporated a unique long-span framing system throughout the subterranean garage, 14,000 pounds per square inch column concrete to minimize the number and size of columns and Grade 80 rebar to reduce steel tonnage and improve constructability.

The W Hotel tower is fully constructed of cast-in-place concrete, with two-way flat plates in the hotel and residential tower, and a combination of one-way and two-way post-tensioned slabs in the podium and subterranean parking.

Concrete shear walls resist seismic loads for both the tower and podium. In the tower, flat-plate post-tensioned slabs enabled the use of long perimeter cantilevers, as well as generous balconies that were cast integral with the slabs, the most efficient system for balcony construction.

The subterranean parking utilizes one-way post-tensioned slabs with wide-shallow beams to create expansive open space and user-friendly parking. The placement of the concrete basement walls were delayed and taken off the critical path, which allowed the concrete frame of the tower to advance ahead with greater speed.

This also allowed the shrinkage of the concrete deck to essentially complete prior to the placement of the basement walls, resulting in parking slabs that are virtually crack free. In addition to creating longer spans, the use of post-tensioned slabs reduced the subterranean floor-to-floor height, which minimized the excavation and shoring depth.

The use of SFRC in the shear wall coupling beams streamlined construction by eliminating all diagonal beam reinforcing bars, the most difficult bar in a concrete frame to install. In addition, SFRC significantly reduced the quantity of the remaining horizontal beam bar and stirrups.

The W Hotel tower is the largest-ever use in North America of SFRC for shear wall coupling beams in high seismic regions. SFRC, a new method of designing and constructing shear wall coupling beams, reduces total beam rebar by up to 40% and improves shear wall constructability. This creates an overall cost savings and accelerates construction, compared with traditional coupling beam design.

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