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10196597 ECEIVT- Thornton Tomas, i MAY 31 2018 morandum City of Santa Ana Re: Alternative Methods Executive Summary (progress) Page 2 visual condition assessment and field testing for rebar number, size and grade, and concrete strength at limited locations. If a 'knowledge factor' K of 1.0 rather than 0.75 in Table 6-1 is needed to justify performance levels 'c' and 'd' the field testing program will be expanded to follow the spirit of the :comprehensive testing program' in ASCE 41-13 while taking advantage of the repetitive framing patterns of the lateral load resisting system. Testing includes small- diameter concrete cores, Ground Penetrating Radar (GPR) scans of concrete faces for rebar below the surface, local concrete cover removal to calibrate GPR scan readings to actual bar sizes, surface hardness testing of exposed bars to establish rebar grades (rather than cutting out bar samples for tension testing), and limited X-ray scans where they have the potential to provide significant additional information. 4. Site visits for ASCE 41-13 visual condition assessment showed a concrete structural system in good condition, with no significant deterioration at the primary lateral load resisting elements. 5. Foundation elements are not visible and will not be tested or probed. This is considered acceptable because Target Building Performance Levels 'c' and 'd' at 50%/50 year Hazard Level imply low seismic demands for which foundation demands will be small, of comparable magnitude to those already experienced during its 50 year life to date. Subgrade conditions based on recent soil investigations at nearby sites will be discussed for reviewer information. 6. 'Seismic base' is taken at the Ground Floor for computer modeling, with lateral restraint there. Column continuity through the Ground Floor is modeled by one-story basement columns and existing concrete infill walls between them. Significant Ground Floor lateral restraint is provided by a continuous reinforced concrete slab tied to heavy perimeter basement walls, and by infill walls between tower perimeter columns in the basement itself. For Target Performance 'c' and 'd' this modeling approach is appropriate. 7. For alternative improvement models, only viscous diagonal dampers will be modeled as nonlinear elements. All other elements are modeled as elastic (with stiffness modifiers). First story tower perimeter columns will be modeled as linear, but being wrapped with FRP for shear capacity greater than plastic demand Vp, they can have Demand Capacity Ratios (DCRs) higher than 1.0 due to improved ductility after wrapping. 8. Response spectrum analysis (RSA) will be used for determining before- and after- improvement performance. Spectrum modifications to reflect increased damping will follow ASCE 41-13 recommendations. In addition, a limited number of realistic earthquake runs