113. SM Structural Feature on 181 Freemont

From a Space Program Hall of Fame induction to one of the tallest, mixed-use buildings in San Francisco, Taylor Devices continues to provide the most efficient, effective and innovative structural protection products on the planet.

108. Seismic Retrofit of the Tower of Hope – Preservation of a Masterwork of Mid-Century Modernism

The two frame office towers, constructed in the 1970s per the 1967 edition of the UBC, use perimeter reinforced concrete moment frames to resist seismic loading. The buildings are rectangular in plan and have certain characteristics that adversely affect their seismic performance, in particular the presence of a soft-story response at the first floor (approximately 50% taller than typical floors), and limited ductility typical of buildings of that era. Risk analysis showed that for the towers the PML exceeded 20%. Nonlinear response history analysis (NLRHA) of the towers was conducted and showed that in the existing configuration, the story drift ratios (SDRs) at the first floor exceeded 2%, shear hinging of the first floor beams was expected and that the SDRs would need to be reduced to approximately 1.4% for the first floor to limit the extent of nonlinear response. Seismic retrofit included addition of 300-kip viscous dampers in both directions to the first floor of the building.

105. SUSTAINABILITY IN SOFT WEAK OPEN FRONT BUILDINGS

Soft weak open front (SWOF) buildings often perform poorly in earthquakes. Two examples are buildings with a street facing garage, or commercial facilities with extensive open display windows. The poor performance of SWOF structures can consist of complete loss of use or even total collapse. This paper presents an approach to protecting such structures via the addition of an energy dissipation system (viscous dampers) such that peak inter-story drifts are limited to about 1% under relatively severe seismic events, thus keeping the deformations within the elastic range. With this addition of damping, earthquake survivability of this class of structures increases significantly. A series of seismic analyses are presented herein to demonstrate the potential performance of the damping system. In addition, a variety of damper installation configurations that provide enhanced energy dissipation are discussed.

102. TORSIONAL CONTROL OF TWO ADJACENT OFFICE BUILDINGS USING VISCOUS DAMPERS

Two adjacent wings of a three story office building in Southern California were found by analysis to be excessively responsive in torsion under an earthquake on the near-by Newport-Inglewood fault, some five miles from the site. The generous 4.5″ seismic separation between the two office building segments was found to be inadequate to prevent heavy pounding even in a moderate event, having a high probability of occurrence at this location. A variety of structural retrofit schemes were evaluated to mitigate the excessive torsional responses of the two building segments. These included converting the perimeter gravity frames to moment resisting frames, adding diagonal bracing to the perimeter frames, tying the two structures together at each floor level, and using viscous dampers as attachments between the buildings. The best solution from a cost, schedule, construction disruption, and earthquake performance standpoint, turned out to be joining the two building segments with horizontally oriented viscous dampers at a single floor level. This paper describes the analysis and retrofit solution that was used, and discusses the advantages and disadvantages of the retrofit options studied.