The principal research objective of this Rapid Response Research (RAPID) award is to identify and understand the conditions that could cause an earthquake-induced fracture in eccentrically braced frame (EBF) steel buildings. For this purpose, multi-scale forensic analysis of the first earthquake failure worldwide of an EBF structure will be conducted. Such a failure occurred in the Christchurch Hospital during the February 2011 Christchurch, New Zealand earthquake. The perishable data to be collected under this RAPID are material specimens from the failed frame before repairs begin. The forensic analysis involves simulations encompassing several scales (from building scale to micromechanical fracture), and will feature mechanical and chemical material tests from the failed frame. The research, if successful, will result in the discovery of new failure modes of EBFs with direct implications for design safety.
The broad significance of this research will include the discovery of new failure modes and the consequent enhancement of design considerations, resulting in safer buildings. Outside the immediate discipline of structural engineering, a significant impact is the modeling of a comprehensive end-to-end simulation (encompassing several scales) of an observed field failure. In addition to revealing deficiencies in such end-to-end simulation methodologies, and thus spawning new research, this will have high educational and training value across various levels of academic accomplishment, including technology transfer to industry.
The Christchurch, New Zealand earthquake of February 2011 created widespread damage in the city of Christchurch and surrounding areas. As a result of the intense shaking, the first observed failures worldwide of steel Eccentrically Braced Frames (EBFs) were observed in the St. Asaph Street parking structure adjacent to Christchurch Hospital in downtown Christchurch. These failures are especially important because EBFs (very similar to the ones that failed in Christchurch) are very common construction in major urban areas in seismic regions of the United States, such as the Los Angeles region or the San Francisco Bay area. The main purpose of this research project was to determine the reasons behind the Christchurch failures such that similar systems in America could be better protected based on the findings. For this purpose, the research team acquired the failed specimens from New Zealand and conducted material testing on these specimens. The material testing was complemented by computer simulation to ascertain the cause of fracture. The main outcomes of the project were – 1. It was found that the materials used in the link construction were of a very high quality. While this may sound like good news, it suggests caution because similar high-quality materials are used for construction in seismic regions of the United States. 2. Thus, a key outcome was the recommendation that design standards in North America must be updated to not only improve construction practices, but also to better characterize the nature and magnitude of expected ground shaking. 3. The broader impacts of the study may be observed in three areas – - The study provided an opportunity to demonstrate a method to predict failure, and more importantly to apportion "blame" to various causes that may have contributed to failure. - This method may be used in a general sense areas outside civil/structural engineering for more effective performance assessment - The study trained two students (both Masters); one is continuing to do his doctoral work at UC Davis, whereas another has accepted a position in industry. Thus, within a modest scope, the proposal had a significant impact in human resource development.
