EARTHQUAKE SIMULATOR TESTING ON BEHAVIOR OF SEISMIC COLLECTORS IN STEEL BUILDINGS

Seismic collectors are structural components that transmit inertia forces to the primary vertical-plane elements of the Seismic Force-Resisting System (SFRS) in a building structure. Collector failure can be catastrophic as evidenced in several building collapses in recent earthquakes. The collector load path involves complicated indeterminate assemblages of different materials and geometries, acting at different elevations, and connected by elements which may not be intended for collector action. Complex load paths develop in the floor system as a result not only of collector action, but also interaction with lateral load and the gravity load-resisting system. A series of shake table tests have been conducted on a half-scale, two-story multi-bay steel test frame by using the NHERI@UCSD large high performance outdoor shake table. The main objectives of this test program are to (1) investigate the load path of the inertia force transferring from the floor diaphragm through collectors and their connections to the SFRS, and (2) examine the behavior and performance of steel collectors and several commonly used collector-to-column connection details. The test frame included a composite floor diaphragm at the second floor and a bare metal deck diaphragm at the roof level. Three commonly used collector-to-column connection details included in the specimen design were (1) all-flange weld (AFW) detail, (2) top-flange weld (TFW) detail, and 3) bolted-web connection detail. This testing program was conducted in two main phases. The Phase 1 tests were performed on the "single-story phase" of the test frame, in which only the first story of the test frame with a composite slab had been constructed. An innovative test technique was developed such that the floor absolute acceleration time histories of any floor in a multi-story building could be simulated by this single-story frame through a transfer function approach. Phase 2 tests were conducted after the second story with a bare steel roof deck was added to the test frame. In this phase, the historical ground motions were used as the input motion to study the load path and the cyclic resnonse of collectors and their connections. Kev test results and desisn imnlications are oresented.