SHAKE TABLE TESTS ON TWO-STORY STEEL BUILDING WITH COLLECTORS IN STEEL ROOF DECK AND COMPOSITE SLAB

Seismic collectors are the structural components that transmit seismic inertia forces to the primary vertical elements of the Seismic Force-Resisting System (SFRS) in a building structure. Failure of collector is potentially catastrophic, as evidenced in several building collapses in recent earthquakes. Despite the critical nature of collectors, little research has been specifically focused on collectors. A series of shake table tests were performed on a half-scale two-story multi-bay steel building by using the NHERI@UCSD large high performance outdoor shake table to investigate: (1) the load path of inertia force transferring from the floor diaphragm through collectors to the SFRS and (2) the seismic response of steel collectors and collector-to-column connections. The test building contained a bare steel roof deck and a composite floor diaphragm on the second floor. Three types of commonly seen collector-to-column connections, including all-flange weld (AFW), top-flange weld (TFW), and bolted-web details, were employed in the specimen. This test program contains two main phases. Phase 1 tests were performed on the “single-story phase”, in which only the first story of the specimen had been constructed. An innovative floor acceleration simulation test (FAST) technique was developed and used in Phase 1 testing to excite the single-story test building to produce floor accelerations mimicking the higher mode dominated floor acceleration responses coming from a multi-story prototype building. Phase 2 tests were conducted after the second story had been added and the conventional earthquake testing method, where the specimen is subjected to scaled historical ground motion records, was used for this phase. The measured collector axial forces form the tests were used to evaluate the adequacy of the current design practice on the collector member design. In addition, test results show that the unintended bending action of collectors could result in significant force demands on the steel connections of the collectors in composite floor diaphragms, indicating that the current design approach may be unconservative. The associated design recommendations for the collector connections are proposed. Other key test results and design implications on the seismic detailing of collectors will also be presented.