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Mr. Mark Thunberg <br />Snohomish County Property Management <br />Plan Check Number: B1802-011, First Review (Structural) <br />June 18, 2018 <br />23. Continuing with the previous comment, the following comments shall be addressed if a modal <br />analysis is performed for this project: <br />a. Seismic participating mass definitions, calculated building masses, and modal analysis load <br />cases. <br />b. Modal -response output showing the building periods and associated participating mass. <br />The combined modal participating mass for each of the lateral, overturning, and torsional <br />responses shall shall meeting the minimum 90% threshold per ASCE 7-10 Section 12.9.2. <br />c. Calculation of scaling factors for seismic loads, including scaling modal base shear to a <br />minimum of 85% of the ELFP per ASCE 7-10 Section 12.9.4.1. The scaling factors shall be <br />included in the applicable seismic load case definitions. Scaling factors should match <br />seismic load case input files. <br />d. Calculated seismic base shears. <br />24. The lateral design has been performed considering a response modification factor of R=5 for <br />special reinforced concrete shear walls (SRCSW). The lateral system includes the existing <br />concrete shear walls, which must also qualify as SRCSW. Documentation substantiating that <br />the existing walls have adequate detailing to qualify as SRCSW shall be submitted for review. <br />Alternatively, the lateral system shall be designed using R=4 for ordinary shear walls. The new <br />walls must still meet the seismic detailing requirements for SRCSW because the construction of <br />new ordinary walls is not permitted in Seismic Design Category D per ASCE 7-10 Table 12.2-1 <br />Item A.2. IEBC Sections 1103.3 and 301.1.4.1 Item 1, IBC Section 1613.1, and ASCE 7-10 <br />Section 12.2.3. <br />25. Section 2.8 of the structural calculations provides an evaluation of the existing building in <br />accordance with the requirements of IEBC Section 1103.3 Exception 2. <br />a. Documentation for the FEM demonstrating its lateral performance shall be submitted for <br />review. Additional documentation demonstrating the model construction is not required <br />unless it differs with the information provided for the combined FEM; see additional <br />comments above. The comments for the combined FEM shall be applied to this comment <br />where applicable. See IBC 1613.1 and ASCE 7-10 Section 12.7.3. <br />b. Calculations substantiating the lateral seismic load on the existing structure shall be <br />submitted for review. Full seismic loads shall be considered per IEBC Section 301.1.4.1. <br />The calculations shall verify a response modification factor of R=4 has been used unless <br />the existing concrete shear walls are substantiated as SRCSW. <br />c. Revised DCR ratios for the pre- and post -addition structure shall be submitted considering <br />R=4 unless the existing concrete shear walls are substantiated as SRCSW. <br />26. Seismic weights for the structure are provided in Section 2.3 of the structural calculations. <br />Calculations substantiating the weights shall be submitted for review. The building appears to <br />include existing and new areas with dissimilar construction. The weights for each area shall be <br />determined. The weights shall be spatially distributed in the lateral analysis to model the <br />structure's construction; see additional comments below. See IBC Section 1613.1 and ASCE 7- <br />10 Sections 12.7.2 and 12.7.3. <br />Pag:e7:o 11 <br />CITY OF EVERETT . 3200 Cedar Street • Everett, WA 98201 . (425) 257-8810 • Fax (425) 257-8857 <br />