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Tomasetti PROJECT 888 N Main St Santa Ana SUBJECT ASCE41-13 Alternative Methods Summary PROJECT NO.S18003.00 REVIEWER LJICSMP DATE 6/28/2018 CODE REFERENCE TOPIC RESPONSE 2.2 2.2.3 From Table C2-2, Target Building Perofrmance Levels 'c' and 'd' apply to the tower concrete Performance Objective frame building structure. These levels correspond to Limited Objectives of Life Safety and Collapse Prevention at the 50%/50 year Seismic Hazard Level. The code lists four stipulations when achieving the Limited Performance Objective. The first three Limited Performance Objectives of which are satisfied and the final will be confirmed during the on-going connection design. 2.3 Target Building Performance Levels At the 50%/50year mean recurrence interval (MRI) event, the Collapse Prevention (S-5) and Life Safety (S-3) Levels will be achieved. See Table C2-4 for Concrete frames. 2.4.2.2 3.2.1 3.2.2 Ground Motion Acceleration Histories Building Type Building Configuration Evaluation of the existing structure is being conducted with three separate acceleration histories (each with two horizontal components) scaled to match a 100yr (39%/50yr) MRI Response Spectrum. Ultimately we will use a suite of 72yr (50%/50yr) time histories as provided by the geotechnical engineer. Cl Classification - Concrete Moment Frames The tower floor geometry is regular at all levels. Continuous concrete diaphragms are integrated with perimeter moment frames with few obstructions or irregularities. 4.4 Tier 1 Checklist Referencing the checklist for Cl Concrete Moment frames in 16.9LS in high seismicity, certain applicable items are addressed below: Redundancy: entire perimeter moment frame system contributes to lateral resistance. Column Axial Stress Check: Under the Tier 3 Nonlinear Time History Analysis, moment frame columns will be assessed under axial and fiexural combined stresses to determine adequacy. Likwise, column shear stress will be evaluated. Captive Columns: All perimeter columns are captured to an extent by a perimeter concrete infill panel. No irregularly captured columns are present. Column/Beam Bar Splices: Field testing is on-going to confirm splice extents. Column Tie Spacing: With application of Fiber-Reinforced Polymer (FRP) wrap, additional column confinement, shear capacity, and ductility will be provided for all columns extending from the ground floor to L3. Diaphragm Continuity: Visibly satisfied as mentioned above. The Tier 1 checklist is used to help identify structural deficiencies in existing buildings. Considering this structure's limited performance objective, the primary components of interest are the tower moment frame columns: MF beams will be checked to not control due to much greater effective depth. Therefore this building performance will be evaluated at a Tier 3 level for Once deficiencies are identified in a Tier 1 screening, they are specifically addressed in Tier 2. In the case of this project, the design team recognizes that the following potential deficiencies are to 5.4 Tier 2 Deficiency-Based Evaluation be evaluated within the eventual Tier 3 analysis: tower perimeter Ll -L3 column moment and shear capacity, tower perimeter L3 through roof column moment and shear capacity. 5.4.2.2 Soft Story Irregularity The nearly-double height moment frame columns extending from the ground floor the Level 3 introduce a stiffness discontinuity which tends to form a soft story. The primary retrofit measure of introducing strategically-positioned viscous diagonal dampers aims to mitigate this primary deficiency. As mentioned above, no significant irregularities are present in this predominantly symmetric, continuous structure. 5.5.2.1 General checks to be carried out for moment frames include drifts and axial stress (in conjunction with flexural). Deep perimeter moment frame beams combined with a thinner concrete infill panel General Moment Frame Checks preclude this system from obeying the traditional strong column-weak beam framing proportions. Thus, as noted in C5.5.2.1.5, additional column shear capacity studies will be performed via the Tier 3 Nonlinear time history analyses. 5.5.2.3 Specific checks pertaining to Concrete moment frames: No Shear Failures - per C5.5.2.3.4, members that cannot develop the flexural capacity in shear shall be checked for adequacy against calculated shear demands. For columns, the shear capacity is dependent upon the level Concrete Moment Frame Checks of axial stress and therefore will be evaluated for all pertinent load combinations to determine the most critical. Bar splices - not considered critical as 50%/50yr demand/capacity is typically well below 1.0 and likely bar splice locations are at the elevations of infill panels 'capturing' columns.