PhD Defense by Timothy R. Wright
School of Civil and Environmental Engineering Ph.D. Thesis Defense Announcement Full-Scale Seismic Testing of a Reinforced Concrete Moment Frame Using Mobile Shakers ByTimothy R. Wright Advisor:Dr. Reginald DesRoches (CEE) Committee Members:Dr. Lawrence F. Kahn (CEE), Dr. Roberto T. Leon (Virginia Tech), Dr. Yang Wang (CEE), and Dr. Russell Gentry (ARCH) Date & Time: Monday, November 2nd, 2015 (8:00 am)Location: Sustainable Education Building (SEB) Room 122AbstractTo date, research on the seismic vulnerability of nonductile reinforced concrete moment frames has been limited in a variety of ways. Most of the research has focused on single components – often isolating individual resistance mechanisms for study. While this has provided a wealth of knowledge about the behavior of individual elements, it has inherently failed to address the interaction between multiple components that comprise a full structural system. For system level testing, the two primary testing techniques found in the literature are shake table tests and psuedostatic testing using actuators. While the existing shake table tests provided credible earthquake input forces, they were performed on reduced scale models due to table constraints. The primary limitation of the reduced scale is that some of the critical resistance mechanisms such as the bond between the concrete and the reinforcing bars are not well replicated at reduced scale. Most pseudostatic tests have also been conducted at reduced scale, however suffered from the added limitations of having applied pre-determined displacement profiles to the structure at slow rates. The research presented herein attempts to overcome these limitations by presenting a method that can apply broadband seismic excitations capable of generating multimodal response to full-scale structures. Additionally, the test method has the potential to be mobilized and used to test in-situ structures. Specifically, this dissertation examines the use of the nees@UCLA mobile shakers to seismically excite a full-scale reinforced concrete moment frame. The frames were representative of structures built in the Central and Eastern United States between 1950-1970 when seismic loads were not adequately considered in design. Accordingly, the specimens were characterized by numerous details that are now known to result in poor structural response during earthquakes (e.g., minimal transverse reinforcement in the columns, short column lap splices, unreinforced beam-column joints). The specimen was instrumented with a dense array of sensors, including 167 metal foil strain gages, six string potentiometers, 38 linear variable differential transformers, and 42 accelerometers to monitor its behavior during testing. The frame was subjected to a total of 25 forced vibration tests consisting of two basic excitation waveforms –one a broadband earthquake record, and the other a series of sinusoidal cycles intended to generate an isolated first mode response. The structural failure was controlled by pullout failure of the positive moment reinforcing bars at the beam-column joints and ultimately by the simultaneous splice failures within all columns at the foundation level. Additionally, shear damage was observed within the column splice regions – a phenomenon not noted elsewhere in the literature for such slender columns. The development of a unique testing system for the evaluation of four nominally identical frames using the nees@UCLA shakers, the use of a new test method to destructively test the first frame, an evaluation of that method, and the documentation and public curation of the full experimental data set for use by future researchers make up the primary contributions of this dissertation.
- Workflow Status: Published
- Created By: Tatianna Richardson
- Created: 10/19/2015
- Modified By: Fletcher Moore
- Modified: 10/07/2016