A Non-Linear Dynamic Evaluation of a Five-Story, Steel Moment Frame Building with Pounding against an Adjacent Structure

摘要

With the passage of California Senate Bill 499 in the fall of 2009, a new code path came into existence for certain existing acute care hospital buildings classified at the lowest structural performance level, SPC 1, to be reassessed and potentially have their useable life extended until 2030. The reassessment approach is based upon the risk-based loss estimation tool, HAZUS, developed by FEMA. By allowing building owners to mitigate structural deficiencies in buildings before reassessment, voluntary seismic improvements addressing significant structural deficiencies can be used to achieve a cost-effective extension of the useable life of some acute care hospital buildings. This paper summarizes the evaluation and design approach of a voluntary seismic improvement of a five-story steel-frame hospital building designed circa 1959. The longitudinal frames of the building are steel moment frames with a tall, soft and weak first-story. The moment frame connections consist of welded flange plate moment connections used at all beam-to-column connections in the longitudinal direction. The resulting seismic improvement includes mitigating the soft and weak story deficiencies and improving the seismic performance through the addition of three buckling restrained braces (BRBs) at the first story. The design of the seismic improvement and evaluation of existing structural components of the building follows the performed-based approach of ASCE/SEI 41-06, Seismic Rehabilitation of Existing Buildings (ASCE 41) using non-linear static pushover and non-linear dynamic procedures. Comparison of linear, non-linear static and non-linear dynamic evaluation results are presented as a case study of the potential benefits of advanced analysis techniques when following a performance-based design approach. One challenge of this seismic improvement is the proximity of an existing concrete and masonry building close to one end of the building being improved. Investigations into the building separations, including the modeling and effects of pounding, are summarized.