Project Description

Pittock Block

Portland, Oregon
Service:
  • Seismic Design & Evaluation, Structural Design & Retrofit
Market Sector:
  • Mixed-Used Residential, Commerical

Pittock Block is a National Register of Historic Places landmark that occupies an entire city block in downtown Portland, Oregon. The 302,000-square-foot building is a networking hub for many telecom providers, a data center and has expansive office space.

The engineering team at Frost was enlisted to carry out a seismic evaluation, retrofit design, and retrofit cost estimate of this historic, 8-story structure originally constructed in 1913. The estimated seismic retrofit costs were approximately $30 million and were determined for purposes of informing a client regarding their pending ~$330 million purchase of the building. Risk category IV was voluntarily chosen by the owner for the retrofit of this building. Based on the selected performance level, seismicity level, risk category, and building type, a sophisticated Tier 3 analysis was required per ASCE 41 as part of the final seismic risk assessment including an evaluation of all components of the building by explicitly recognizing non-linear response. Frost directed and carried out a nonlinear analysis in order to evaluate the original reinforced concrete building columns. This effort included precise quantification of damping, ductility demands, and performance for two different BPOE target levels, 1-B (i.e., structural IO) for the 20%/50 years (i.e., 1-in-225 year) earthquake and 3-D (i.e., structural LS) for the 5%/50 years (i.e., 1-in-975 years) earthquake.

Frost applied the provisions of the following codes, standards, and guides in this evaluation and retrofit design and cost estimate: TIA-942 Data Center Standards, the building regulations for the City of Portland, the Oregon Structural Specialty Code (OSSC), ASCE 7, ASCE 41, ASTM E2026, ASTM E2557, and FEMA 156. Frost applied cracked section inertial reduction to all columns and proposed shear walls for both the IO and LS targets. Frost formulated nonlinear “backbone” capacity curves for the columns in accordance with ASCE 41. Shear strength, bar buckling, and bidirectional loading were determined by Frost to not limit the representative columns backbone capacities in the current assessment. Considered retrofits to limit interstory displacement and increase strength in targeted areas of the building included reinforced concrete shear walls with corresponding foundations and targeted use of FRP wraps, which Frost included in different version of the structural model and cost estimated per the aforementioned ASTM and FEMA standards, as well as RSMeans.

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