Resolution No. 4814 - Laserfiche WebLink

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Eugene City Hall R32.19.04 Rev. B. September 9, 2003 o Given these issues, for the current effort we apply the K&T findings as follows: the building will likely remain nearly elastic under lateral loading of about V = 0.05W to 0.06W (this assumed the masonry walls are reinforced and mostly grouted). o The 2001 URS report presents a probable maximum loss estimate for the City Hall complex. Loss models were based on ATC-13 coupled with on-site inspections and adjustments. Losses were calculated for two earthquake events, corresponding to a 10% chance of exceedence in 50 years (PGA = 0.137g) and a 2% chance of exceedence in 50 years (PGA = 0.296g). URS suggests characterizing the site as soil profile type SD, in accordance with the nomenclature used is the 1997 UBC and 2000 IBC codes. The projected median losses for the City Hall Complex were 28.3%, and 53.9%, for these two earthquakes, respectively. 4.0 Seismic Hazards The understanding of the seismic hazard for Oregon City has changed substantially over the past 20 years. Prior to 1980 (or so), The central regions of Oregon were considered to be largely aseismic. Studies suggested that the area of Eugene could experience ground motions, as measured by Peak Ground acceleration, of about 0.05g once every 500 years or so. At this very low level of shaking, damage is uncommon or limited even to poorly constructed buildings, and in all practicality, local building codes excluded seismic forces as a design requirement; or if required, set at such a low level that wind-level design forces would exceed those from seismic. As of 2003, it is now understood that Eugene faces three distinct types of seismic hazards. First, a great subduction magnitude (M) 8 to 9 earthquake under the Pacific Ocean, near the Oregon coastline about 110 km west of Eugene, can cause strong shaking of perhaps PGA = 0.20 to 0.35g for 60 to 90 seconds in Eugene. Second, a very large M 7 to 7.5 earthquake within the subducting plate (so-called Intra-plate) could occur directly beneath Eugene, but at substantial depth or possibly 60 to 75 kin. While smaller in magnitude, this event will still cause ground shaking in the range of PGA = 0.20 to 0.35g in Eugene. Third, a moderate M 5.5 to 6.5 earthquake can occur in the top 10 to 20 km of the earth's crust, rather near Eugene. While smaller in magnitude, this event can cause ground shaking in the range of PGA = 0.10 to 0.60g (or higher) in Eugene, depending upon exactly where the earthquake occurs. G&E Engineering Systems Inc. Page 24