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6 of 234 Thornton Tomasetti PROJECT 888 N Main St Santa Ana SUBJECT ASCE41-13 Alternative Methods Summar, PROJECT NO S18003.00 REVIEWER LJ/CS/JP DATE 8/13/2018 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 thref Limited Performance Objectives of which are satisfied and the final will be confirmed during the on-going connection design. Target Building Performance At the 50%/50year mean recurrence interval (MRI) event, the Collapse Prevention (S-5) and Life 2.3 Levels Safety (S-3) Levels will be achieved. See Table C2-4 for Concrete frames. 2.42.2 3.2.1 3.2.2 Ground Motion Acceleration Histories Building Type Building Configuration Evaluation of the existing structure is being conducted with four separate acceleration histones (each with two horizontal components). spectrally matched to a site-specific 72yr (50%/50yr) MR Response Spectrum. See Wood PLC geotechnical report 225yr MRI acceleration histories are used only to confirm dampers and their connections can sustain greater-than-72yr event demands. Cl Classification - Concrete Moment Frames The tower floor geometry is regular at all levels. Continuous concrete diaphragms are integrated with penmeter 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. Because all perimeter columns are captured to an extent by a penmeter concrete infill panel, no irregularly captured columns are present. The effect of capture is renecte in beam modeling and use of 50% rigid offsets. Column/Beam Bar Splices: From field testing at Level 1, column splice extents appear to follow column compression splice practice of the 1960s. Flexural demands are well below yield so this is not a concern. Column Tie Spacing Field testing of multiple columns at multiple floors shows ties typically at 18 or doser. Shear capacity is checked using the ASCE 41-13 formula. At those columns receiving damper connections, Fiber-Reinforced Polymer (FRP) wrap will provide additional column confinement and shear capacity from ground floor to underside of L3 spandrel beams to address possible increased column stiffness from the connections Diaphragm Continuity: Visibly satisfied as mentioned above. Wing Buildings: GPR scanning detected vertical and horizontal reinforcement in the wing end walls. Tapered wing girder ends have bolted connections to the wing end walls and tower columns. The Tier 1 checklist is used to help Identify structural deficiencies in existing buildings Considering this structure's limited performance objective, the pnmary components of interest art 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 adequacy of penmeter moment frame columns 54 54.22 5.52.1 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 k 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 Soft Story Irregulanty 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 pnmary retrofit measure c introducing strategically-positioned viscous diagonal dampers aims to mitigate this primary deficiency. As mentioned above, no significant irregulanties are present in this predominantly symmetric, continuous structure. General checks to be carried out for moment frames indude drifts and axial stress (in conjundior 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 capadty studies will be performed via the Tier 3 Nonlinear time history analyses.