Cast-in-Place Structures

Location: 401 Terry Ave. N., Seattle

Owner/developers: Schnitzer Northwest and Vulcan Inc.

Project team: Lease Crutcher Lewis, general and concrete contractor; NBBJ, architect; DCI Engineers, structural engineer; Stoneway Concrete, ready-mix supplier

Interurban Exchange 3 is part of a five-building development in Seattle’s South Lake Union neighborhood. The four-story, 250,000-square-foot building contains office and biotech space with three levels of underground parking.

The project uses a cast-in-place concrete slab system with one-way post-tensioned beams and one-way mild reinforced slabs to meet the biotech tenant’s needs for a low-vibration floor system. It has a limited number of post-tensioned tendons to allow greater flexibility in locating future slab penetrations.

DCI Engineers, the project’s structural engineer, developed a model to verify 40-foot exterior concrete spans could be used for the floor system without adding interior structural steel or concrete supports.

Challenges faced in the building’s underground levels included a water table that is 2 feet above the lowest garage level and fill material on part of the site. Caltite concrete was used in the slab-on-grade and perimeter basement walls to keep the building dry below the water table. Auger-cast concrete pile foundations were used in the fill areas.

Form liners and special finishing techniques were used on several cast-in-place concrete walls and precast concrete panels.