Options for mitigating the seismic deficiencies were developed and studied. Mitigation options for the non-ductile concrete columns consisted of either adding columns to the building to support floor loads if the existing columns were to fail during a seismic event, or confining the existing concrete in the columns by filling in the open C-shape of the column with reinforced concrete and then wrapping the columns with fiber reinforced polymer (FRP). Because of the useable floor space that would be lost by the addition of columns, the FRP wrap was chosen as the preferred option.
The deficiency of the connection of the floor diaphragms to the shear walls was mitigated by removing a portion of concrete slabs in the stairwell and re-casting a thicker, more heavily reinforced slab that was appropriately doweled into the shear walls. The diaphragm was reinforced with steel tubes inside the stairwells in order to transfer load to the offset shear walls. These mitigations did not encroach on the useable floor space and did not obstruct the building’s occupancy.
Design, Documentation and Construction
One of the early key decisions involved how to permit and build the project — a decision that determined how the documents would be developed. The team elected to develop four document packages: demolition, seismic upgrade, shell and core improvements and tenant improvement packages. Four packages allowed for rapid permit submittal and early commencement of construction activities.The mitigations of the two seismic deficiencies were designed and documented in different ways. The upgrade that strengthened the floor diaphragms was fully designed and detailed on the structural drawings, as this mitigation consisted of conventional renovation construction.
Because the design and the application of FRP is a specialty sub-contract, the requirements for the FRP column wrap was specified to be equivalent to a reinforcing steel column spiral of a certain size and pitch and designated as “bidder-designed.” The FRP shop drawings were accompanied by fully engineered calculations that verified the capacity of the FRP to perform equivalent to the specified spiral reinforcement.
The demolition and seismic packages were executed together, followed by the shell and core renovations and the tenant improvements. The construction phase was eight months in duration and required exposing the building during the worst weather months in the Columbia River Valley. Significant snow and rain events coupled with extended cold snaps slowed progress at times. Since construction is often a sequential process, some key aspects of the project were held up due to the exterior wall not being closed up.
The FRP seismic retrofit work was executed by a subcontractor with its propriety system. This entity received design performance parameters and details from the structural engineer, architectural constraints from the architect, as well as the constraints presented by the existing facility. Their scope included demolition to expose the area of work, scaffolding, column surface and corner preparation work and the installation of the FRP wrap. The column rebar reinforcing system and concrete in-fill placement were performed by the general contractor, as was the final column cladding once the FRP installation was complete.
Retrofitting delivers cost savings
The seismic factor in the project, while pivotal, yielded little risk and was completely invisible to the occupants.
Following the successful completion of construction, iQ moved into a nearly 40-year-old building that was given a new life. In comparing the costs between renovating the building and constructing a new facility, the designers found that costs were similar. However, four notable factors made retrofitting the smart business decision: the time to market was nine months shorter; traffic impact fees were virtually zero for renovation versus $500,000 for new construction; design fees were lower as a percentage of the total project cost with renovation; and finding choice urban lots is nearly impossible.
Jim Morrell, the iQ chief information officer, said that while he’s happy his company may have saved some money and a lot of time through the retrofit, perhaps even more important was the attendant peace of mind. “I sleep better at night knowing we’ve done everything we can to make this building as safe as it can be.”