Urban Campus: PBD office tower will energize Bellevue’s central business district

When complete,The Artise will be a 25-story office tower in Bellevue’s central business district appealing to high tech businesses and professionals. DCI Engineers is the structural engineer of record for the project. The 1,040,000-sf tower will consist of a steel framed gravity and lateral structure with buckling restrained mega braces and steel moment frames. The lateral system stops at Level 1 and completely transfers lateral forces to the basement walls, which allows the entire basement level to be open, unobstructed space. This project is being peer reviewed for performance based design for resiliency and economy.

• An aquifer limited the depth of excavation and to avoid contaminating it, DCI determined a way to maximize the available parking below grade, which was paramount in serving the office occupants on the above levels.
• The development of a unique, recognizable, yet economical, building with open floor plates was essential to attract tech tenants.
• Transitioning the performance based design of the building from a category 2 building to a category 3 building (more than 5,000 occupants) very late in the design process required innovation to keep the aesthetics consistent.

• To optimize the below-grade parking, DCI decided to eliminate all lateral shear resisting elements below-grade. Traditional concrete cores and even braced frames typically carry all the way down to the foundation. On the Artise, perimeter Buckling Restrained Braces (BRBs) were used to support the tower lateral forces. The lateral braces stop at Level 1, where lateral forces completely transfer to the basement walls. This design solution completely opened up the basement levels for maximum parking.
• The typical office spans in the tower transitioned to a shorter span, and shallower depth, framing system in the garage which required interior columns to slope to transition the column grid. This approach, combined with the efficient BRB system that stopped at level 1, eliminated the need to excavate an additional below-grade floor - bringing cost savings to the client.
• The BRB lateral system is a super brace system, meaning the braces connect at either every 3 floors or every 4 in some cases, skipping floors along the way. The lateral forces on the skipped floors span between braced floors with a unique moment frame system. This allowed the architect to create patterns around the four sides of the building that play off of each other - creating consistency in the expression. On the western façade at the base, a transitional pattern of braces transfers out the frame and columns, and creates a distinguishable entrance.
• Late in the design, the tenant finally signed on and decided to change the building to a category 3 building for more flexibility. Since drift governs the structural design of the BRBs, and a category 3 building requires more stringent drift limits, DCI was able to add fluid viscous dampers (big shock absorbers) in parallel with the buckling restrained mega braces to reduce the drift to acceptable limits and keep all of the brace configurations and the architectural integrity intact. This is the first time fluid viscous dampers have been used in Bellevue.