San Francisco Nonductile Concrete Buildings Part Ⅱ: Analysis, Assessment and Comparison of Older San Francisco Concrete Buildings

摘要

The building stock of large metropolitan areas comprise buildings of various materials constructed over the course of many years. A significant number of these buildings utilized concrete construction with details drastically different than modern methods of construction. For existing buildings, nonductile concrete (NDC) buildings have been identified in numerous studies as a potential seismically-vulnerable existing building type within California communities. Recently the City of San Francisco, in collaboration with the Structural Engineers Association of Northern California (SEAONC) Existing Buildings Committee (EBC) completed an initial inventory of all the concrete buildings in San Francisco. Based on recent inventory work, previous work by the Concrete Coalition, and retrofit experience with San Francisco buildings, there are several common pre-1980 concrete building types that can be identified in the San Francisco inventory. This paper attempts to answer several questions including: 1. How vulnerable are certain types of San Francisco concrete buildings? 2. How do different evaluation methodologies compare in identifying vulnerabilities? 3. Does one evaluation methodology stand out as being more economical or efficient in determining if a detailed building evaluation should be performed? 4. What is the potential vulnerability of the entire San Francisco pre-1980 concrete building inventory? 5. Should a potential ordinance target specific vulnerabilities (e.g. soft-story) or will fixing one vulnerability shift the problem to another part of the building (e.g. second-story columns). To answer these questions, the NDC Subcommittee of the SEAONC EBC performed analysis on typical concrete buildings constructed during certain eras using a range of analysis methodologies, including: the Hassan & Sozen Priority Index, ATC-14, ASCE 41 (Tiers 1, 2 and 3), FEMA-154, ATC-78, and FEMA P-58 implemented in the Seismic Performance Prediction Program (SP3).