Resolution No. 4814 - Laserfiche WebLink

Home Browse Search

Eugene City Hall R32.19.04 Rev. B. September 9, 2003 5.0 Fragility and Cost Information Section 5 presents fragility and cost information to be used for benefit cost analysis purposes. The information in Section 5 may not be complete enough for final design purposes. 5.1 Costs As highlighted in Section 4 of this report, the existing capacity of the building is probably not much more than what was envisioned in the original design of circa 1962. Most likely, the nominal elastic lateral limit of the building is in the range of PGA = 0.05 to 0.07g or so. If in fact the existing masonry walls at the main floor level are unreinforced and ungrouted, the existing capacity could be lower than these amounts. As part of any seismic retrofit measures, it is recommended that a in-sim test program be included at the project outset, in order to verify the style of construction of the in-situ masonry walls on the main floor level, both in the wings as well as the city council chambers areas. This test data will necessarily be partially destructive, but only in so far as to uncover the interior style of construction (rebar, grout) and connection systems. The test data would be used for two main purposes: assess the tree as-built capacity of these walls; and to assess how these walls can be re-used in the final upgrades, and / or connected thereto. Any testing effort would include a task to rebuild the damaged walls immediately after the testing process, so that there is no degradation of the structural capacity or significant adverse architectural degradation for the interim period until the final retrofits are installed. The ultimate seismic retrofit for this building is based upon a design upgrade equal to about V = 0.14W (suitable for this type of building in zone 3), using I= 1. About one- third of the total seismic capacity will come from the existing elements, and two-thirds will come from the new structural elements added to the building. Based upon V = 0.10W, and allowing for good ductile detailing of the new structural elements, then the following new elements would be added to the building: o New shear walls in the North-South and East-West directions (14 to 16 walls total). Each wall would run full height of the building (parking level to roof). Most walls would be about 35 feet long, 1 foot wide, and include suitable boundary elements (existing columns with additional reinforcement). Floor diaphragms might be thickened locally as needed to make for a good transfer of floor loads to the walls. The walls would have suitable new foundations, along with tie beams as needed to adjacent elements. o An allowance is provided to provide improved structural load capacity for the council chambers. G&E Engineering Systems Inc. Page 27