Design for Lateral Loads/Systems
343775 - Evaluation of ASCE 41 for Seismic Retrofit Design
Friday, April 20
11:00 AM - 12:30 PM
In the U.S., ASCE/SEI 41 serves as the primary standard for seismic evaluation of existing buildings, as well as for the design of retrofits of these buildings. In this document, representing first-generation performance-based design concepts, a performance level is chosen, then demands are compared against acceptance criteria for each building component. In order for a building to meet an ASCE 41 performance level, all elements must satisfy these prescriptive acceptance criteria. The component limit states and modeling criteria have been developed based on test data, and several of the tables with modeling parameters and acceptance criteria for various components have been updated and improved in recent years, e.g. (Elwood, et al., 2007). Nevertheless, recent work has suggested that the ASCE 41 element level assessment may be overly conservative (Maison, Kasai, & Deierlein, 2009; Sattar & Hulsey, 2015), indicating that even “well-designed” buildings may not pass the assessment at critical performance levels. Additionally, little work has been done to link ASCE 41 performance levels, which are inherently component-based, to structural level performance metrics, such as median collapse capacity, or estimated losses during future earthquakes. Therefore, it is unclear how well the component-based performance levels align with assessed global performance and metrics of interest to decision makers.
In this study, 3- and 6-story buildings, designed to the Uniform Building Code of 1967, are chosen to represent existing inventory of nonductile concrete frame buildings in the U.S. Although nonductile RC frame buildings are only one category of existing building, they are potentially vulnerable and often subject to evaluation and redesign through ASCE 41 analyses. For each building, multiple retrofit alternatives are considered to meet ASCE 41-13 Collapse Prevention (CP), Life Safety (LS), and Immediate Occupancy (IO) performance levels, respectively. In addition, multiple retrofit techniques are considered for each performance level: column jacketing using steel or concrete jackets, and wrapping columns in fiber-reinforced-polymer (FRP) wraps. Nonlinear models of the original and retrofit buildings are created and analyzed using the OpenSEES software and losses are estimated during a design level event using the SP3 software which is built on FEMA P-58 (FEMA, 2012) methods and fragility functions to estimate repair costs in future earthquakes. Structural performance metrics and estimated losses are then compared to the stated ASCE 41 performance objectives, providing a direct comparison between element-based retrofit strategies and structural-level performance benefits.