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5 of 234 <br />Thornton Tomasetti Memorandum <br />Re: Alternative Methods Executive Summary <br />Page 3 <br />11. Column acceptance will be studied on a column by column basis, but average capacities and <br />average demands at all columns along a building face will also be considered since multiple <br />similar elements can redistribute loads as properties change. <br />12. Accidental eccentricity will be studied as a side issue, not integrated into each computer run. <br />Because the lateral system surrounds the tower, torsion from a 5% mass offset will make <br />only about a 5% change to demands in the lateral system members. The primary focus is on <br />the effect of alternative improvements on the tower structure. <br />13. The tall single-story wings to North and South of the main tower are modeled using semi- <br />rigid wing roof diaphragms and reduced wall shear stiffness to maximize the amount of roof <br />and attached wall mass generating tower seismic demands. No modifications to existing <br />wing structural elements and connections are proposed, since seismic demands at Target <br />Performance 'c' and 'd' are modest. <br />14. Existing structural framing in the vicinity of viscous diagonal dampers will be reviewed for <br />damper-generated forces and strengthened where necessary. Damper forces used in these <br />checks will reflect velocities 200% of those used in the nonlinear analysis per ASCE 41-13 <br />and damper coefficient variability based on damper vendor experience rather'than generic <br />values in ASCE 41-13.