888 N Main St - Soils Report - Laserfiche WebLink

Home Browse Search

10/96597 R ECEIVE D Thornton Tomasetti MAY 31 2018 Memorandum City of Santa Ana TO COMPANY RE CC Michael Harrah Caribou Industries Alternative Methods Executive Summary (in progress) Cam Simsir, Jackson Pitofsky, Dean Schoenberg FROM Leonard Joseph DATE May 21, 2018 PROJECT NO S18003.01 PROJECT 888 N Main Santa Ana tower NAME The City of Santa Ana Building Safety Division requested that an alternative seismic improvement program proposed for the 888 North Main 10-story tower be developed and documented within the framework of a recognized standard. This executive summary (in progress) is intended to accompany Alternative Materials,Design and Methods of Construction form APP-09 under CBC 2016, along with supporting documentation as it is developed. ASCE 41-13 was suggested as a framework for developing the alternative seismic improvement program. The owner and design team agrees with this approach with modifications appropriate to the limited nature of proposed improvements.' 1. Target Building Performance Levels 'c' and 'd' will apply to the tower concrete frame building structure after alternative seismic improvements have been completed. These levels correspond to'Limited Objectives' of Life Safety and Collapse Prevention performance at the 50%/50 year Seismic Hazard Level as shown in ASCE 41-13 Table C2-2. This level is proposed as practical and achievable while still providing a significant performance improvement compared to building performance before retrofit. For building department information we will present both before- and after-improvement performance measures. 2. Tier 1 and Tier 2 study approaches and flow charts in ASCE 41-13 will be addressed in brief narrative form. With visibly robust and regular building geometry, and continuous concrete floor slab diaphragms, most questions about load paths, transfers and connections are not relevant. Building performance will be evaluated at a Tier 3 level using computer models reflecting concrete section geometry, with appropriate modifiers for cracked sections, etc. following established standards. Overall modeling will use simplified members with properties and offsets calibrated to simulate behavior of more complex partial models reflecting as-measured geometric conditions. 3. A field testing program is underway. The extent of the program will depend on the findings and analytical results. While no existing structural drawings have been found, existing architectural drawings show member profiles consistent with field measurements. If member capacities reflecting a 'knowledge factor' K of 0.75 in Table 6-1 are sufficient to justify after- improvement performance levels 'c' and 'd' the field testing program extent will include a 707 Wilshite Blvd, Suite 4450 1 Los Angeles CA 90017-3618 1 T 213.330.7000 1 F 213.330.7001 1 WWW.ThornionTomasetti.com