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<br /> <br /> <br /> <br /> <br /> <br />3rd & Broadway, Santa Ana, CA <br />Volume 1 - Basis of Design June 17, 2024 | Project # S21043.00 <br /> pg. 29 <br />2.5.3 SEISMIC CRITERIA <br /> <br />2.5.3.1 RESIDENTIAL BUILDING <br />The structural (seismic) design for the Residential building is based on modal response spectrum <br />analysis. A model of Residential building is constructed in ETABS. <br />Note that modeling a portion of the basement with an ‘open end’ conservatively minimizes any <br />helpful backstay effect from the basement and L1 slab. In ETABS the parking ramps are simplified <br />as flat floors aligned at the upper most slab elevation, which ensures maximum acceleration and <br />delivers all seismic load to the core rather than allowing the ramps to provide potentially fictious <br />bracing. <br />The defined building mass, material properties, and geometry of the structure contribute to a <br />calculated set of periods and shapes for 30 modes using Ritz-vectors analysis, where the number <br />of modes analyzed must result in a mass participation ratio greater than 90%. The site -specific <br />response spectrum function shown in Figure 2.6-1 is defined and applied to the model in two <br />orthogonal directions as response spectrum load cases. Along with a scale factor inversely <br />proportional to the response modification factor R/I, this produces applied story shears and an <br />overall base shear. Response spectrum forces must be scaled per ASCE 7-16 section 12.9.1.4, <br />which stipulates that the response spectrum base shear must be scaled up to 1.0 times the <br />equivalent lateral force procedure base shear for strength design purposes. <br />Calculations of the equivalent lateral force procedure base shear and subsequent response <br />spectrum base shear are shown below. A more detailed description of the ETABS models is also <br />shown in Volume 2 Section 4.2. <br /> <br />Figure 2.5-2: ETABS 3D View for Residential building.