Appeal 34817

ASCE 7-16 Section 12.13.9

OSSC 3405.2.1 requires that an addition meet the code provisions for new construction, which includes OSSC 1613. OSSC 1613 references ASCE 7-16, Chapter 12. ASCE 7-16 Section 12.13.9 requires that buildings on liquefiable sites meet shallow and/or deep foundation requirements, and in some cases prohibits the use of shallow foundations.

Due to the low risk to life safety, the intent of the appeal is to waive the requirements of ASCE 7-16 Section 12.13.9 on the existing concrete structure.

The existing structure, built in approximately 1996 under permit 95-01987-BLD (see relevant drawings and photograph, attached) consists of a concrete structure that is mostly below grade but that extends above grade by approximately 5 feet. A steel pre-engineered metal building canopy structure currently covers the eastern-half of the existing concrete structure. The original permit drawings reference a future cover over the western-half of the concrete structure, and an upcoming project intends to construct a steel-framed canopy structure in order to provide shade and rain protection for maintenance workers. The facility houses the water reuse system at the Columbia Boulevard Wastewater Treatment Plant, which is a recycling process that takes already-treated wastewater that would otherwise be discharged to the Columbia River and applies a chemical and filtering process to the water such that the water can be reused for plant operations rather than purchasing the needed water from the City water supply. The system is existing but will be replaced in an upcoming capital improvement project, and BES wants to take this opportunity to add the canopy structure for shade and rain protection for its operations and maintenance staff.

The proposed new open-sided steel-framed column and roof canopy structure will attach to the top and sides of the existing concrete structure, and the columns will cantilever upward to support the roof. No new foundations will be constructed, and there will not be any ground disturbance with the proposed design.

The site is located within approximately 50 feet of the Columbia Slough. Geotechnical investigation conducted as a part of recent construction at the Plant indicates that lateral spreading at that distance from the Slough could be between 2.5 and 9 feet, depending on the calculation method used. Similarly, liquefaction-induced total settlement could be between 10 and 22 inches, with differential settlement across the structure expected to be less. The ability of the existing concrete and steel framed canopy structure to withstand the anticipated liquefaction-induced settlement and lateral spreading without potential failure is questionable at best. Upgrading the existing concrete structure to withstand the anticipated movements is not practical without probable demolition and reconstruction, support on piles and ground improvement.

The area of the existing concrete structure that houses the recycling process equipment will not be occupied full-time. The only time occupancy will occur is during normal maintenance operations by a team of two workers. The anticipated maintenance frequency and duration is as follows: weekly inspections taking less than 30 minutes; monthly lubrication of pumps, drives and gear boxes taking approximately 1 hour; and every 7 to 10 years, filter cloth replacement taking approximately 2 days.

Based on the infrequent occupancy, the change in the risk to life safety is minimal. Further, if the new equipment were installed during the upcoming project without the sun and rain canopy structure added, the change in the risk to life safety would be zero since the maintenance would occur whether or not a canopy is present.

Since the change in the risk to life safety due to the infrequent occupancy is minimal, and the impracticality of rehabilitating the existing structure to address liquefaction issues, we propose that the steel framed canopy structure be allowed to be constructed as an addition to the western-half of the existing concrete structure without provisions made to address ASCE 7-16 Section 12.13.9.