Modal characterization of a three-story buckling-restrained braced frame steel building by non-destructive field testing

A full-scale, reconfigurable, three-story steel building was constructed and its modal properties identified prior to shake table testing on the UC San Diego Large High Performance Outdoor Shake Table (LHPOST6). The aim of this pre-shake table test erection was to demonstrate the rapid constructability of the building and identify construction fit issues prior to its assembly on LHPOST6. This posed a unique opportunity to characterize the building's modal properties using a variety of non-destructive, low-amplitude techniques. To this end, two novel, non-destructive methods were used, namely: (1) impact tests conducted by swinging a tire from a crane to impact strategically selected locations, and (2) dynamic base vibration tests, induced by driving heavy machinery in the vicinity of the base of the structure. A system of accelerometers located throughout the structure captured waves propagating from each test to characterize the as-built dynamic properties of the building. Results from various system identification methods are presented and compared to theoretical and numerical analysis. Comparisons indicate that the theoretical, numerical, and experimentally determined periods are nominally within 15% of each other. The erection of the structure was complete over the course of 3 days and construction fit-up issues were addressed. The structure was then rapidly deconstructed and stored prior to erection for full-scale shake table testing. This pre-shake table test exercise demonstrated the viability of two, simple, low-amplitude excitation approaches for use in the dynamic characterization of full-scale buildings, with results consistent with theoretical and numerical models.