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10196597 <br />R ECEIVE <br />EThornton Tomasetti MAY 31 2018 -Imorandum <br />City of Santa Ana <br />Re: Alternative Methods Executive Summary (progress) <br />Page 3 <br />using Nonlinear Response History Analysis will be used to support validity of the RSA <br />approach. <br />9. Columns are anticipated to govern acceptance, as combined depth of typical perimeter <br />beams and integral infill panels is several times larger than typical column widths. For <br />columns at Level 3 and higher: acceptance will be based on average capacities and average <br />demands at all columns along a building face since multiple similar elements can redistribute <br />loads as properties change. <br />10. Accidental eccentricity will be studied as a side issue, not integrated into each computer run. <br />The lateral system surrounds the tower, so a 5% mass offset will make only small changes <br />to demands in the lateral system members. The primary focus is on the effect of alternative <br />improvements on the tower structure. <br />11. The tall single-story wings to North and South of the main tower will be modeled using semi- <br />rigid wing roof diaphragms to reflect the mass of roofs and attached walls in tower demands. <br />Modifications to existing wing structural elements and connections are not proposed, <br />considering modest seismic demands at Target Performance 'c' and 'd.' <br />12. Existing structural framing in the vicinity of viscous diagonal dampers will be reviewed for <br />damper-generated forces and strengthened where necessary.