UC San Diego

During earthquakes, nonstructural components and other objects of sizeable mass attached to building structures may be subjected to significant levels of seismic excitation. These systems require engineered anchorage systems to resist imposed demands, with the earliest attempts to produce qualitative and quantitative metrics for this process taking place in the early 1990s. Over the next two and a half decades, the provisions the design engineer must follow for determining a suitable anchorage system have rapidly expanded, and while some topics have been thoroughly researched and documented, others have not. One such term, the overstrength factor Ω0 used to modify code demands for ductile versus non-ductile anchorage

into concrete for tension-dominated systems, has suffered from particularly sparse academic and scientific background. The first portion of this dissertation establishes a scientific framework for evaluating existing code values of Ω0 by means of two full-scale testing programs on anchorage systems using a shaking table. Both real earthquake and broadband earthquake motions are used in the testing sequences, and four different major anchorage force-displacement responses are considered: brittle linear-elastic behavior with large initial stiffness, highly plastic ductile behavior with comparable initial stiffness to the brittle anchor, soft elastic behavior with large displacement capacity, and a pull-through anchor with non-material-based plastic response characteristics.

Results from these different anchor types are compared and benchmarked against expected code performance standards.

The second portion of this dissertation presents a highly efficient, customized numerical analysis tool that was developed for simulating the seismic response of seismically-driven oscillators with translational and rotational mass degrees of freedom. This program is validated against the structural testing results and existing finite element programs, and offers run times three orders of magnitude faster than standard analysis methods. Detailed parameter studies are then performed looking at both upright and hanging components, targeting specifically the appropriate values of Ω0 which result in intended system performance.

The structural testing and analytical results are then compiled into recommendations for existing code guidelines related to Ω0. Discussion is provided regarding existing ductility provisions for anchorage into concrete, specifically with respect to the expected benefits versus the real and measured benefits of ductile anchor response.