Application of the Next Generation Building Codes to the Seismic Retrofit of a Historic Building

摘要

A historic three-story building located in Old Sacramento was selected for seismic retrofit. The building, constructed in the 1880's, served as a packing and shipment center due to its proximity to the rail lines. This structure is the last remaining non-retrofitted unreinforced masonry (URM) building in this historic town. It consists of wood post and beam construction and URM walls. Preliminary investigations revealed several critical seismic deficiencies. These deficiencies ranged from soft story response to degraded timber posts, and from heavily cracked URM walls to an incomplete load path for resisting seismic forces. The building is scheduled for seismic rehabilitation to bring it into compliance with the code prior to allowing full occupancy. This provided the opportunity to apply the provisions of two code documents for its seismic retrofit. The 2007 edition of California Building Code (CBC) devotes two chapters to existing buildings. The provisions in the California Historic Building Code (CHBC) references the California Code for Building Conservation (CCBC), which utilizes evaluation and retrofit methodologies in effect prior to 2007. Alternate provisions are presented in the California Existing Building Code (CEBC). Both CHBC and CEBC propose to provide means for preservation and utilization of existing buildings; an enhanced level of safety is provided without having to meet the full design and detailing requirements listed in the current building codes, such as the CBC. Although similar in scope, the codes employ different methodologies for evaluation, rehabilitation, and occupancy change for existing buildings. For example, CHBC utilizes working stress design, whereas load factor design is used in CEBC. The force requirements for the CHBC are less restrictive because the intent is to allow for preservation of a greater number of historical structures. A case study between the two codes was conducted to determine the impacts of the new code for seismic rehabilitation of an existing historic URM structure. For clarity, the CHBC is used as reference when CCBC equations are used in this paper.