After recent high profile failures, the spotlight has settled on the nation's aging infrastructure. The prevalent means of damage evaluation is a qualitative visual inspection which can identify some external but no internal damage. The goal of structural health monitoring is the determination of damage state, or "health," at any given time. Any damage increases local stresses as well as overall motion such that a structure is less likely to resist another abnormal event. Experimental studies can contribute to understanding progressive collapse resulting from this damage accumulation. The goal is to limit the total damage caused by all abnormal events as well as aging throughout the structure's lifetime, allowing more effective condition-based maintenance and increasing public safety. Longer term goals include in-field testing and required reinforcements. Future expansion areas include hazard resistance, non-destructive testing, and design revisions.
The overall objective is to synthesize research and educational activities through an experimental structural health program. The three project objectives are initiation of research on structural health management, creation of unique laboratory experiences for a diverse population, and further development of the PI as a role model for underrepresented groups. Through a laboratory-based research and educational plan, a cross-disciplinary vision exists for a practical research facility that doubles as an innovative classroom. Five currently active outreach programs will incorporate this project's activities to produce a positive scholastic impact on pre-college, undergraduate, and graduate students as well as educators and professionals. Considering diverse perspectives, every student can benefit from an experimental encounter with dynamics: the excitement of demolishing a structure is unfailing.
This project’s major research thrust is the experimental development of structural health evaluation. The ultimate aim of this infrastructure protection method is increased public safety. Improved structural health evaluation techniques can create maintenance-based inspection rather than less efficient routine inspection. The identification of at-risk structures can prevent loss of infrastructure and perhaps loss of life after aging or severe events. Residual strength determination can help in the prevention of progressive collapse and the rehabilitation of damaged structures. The vision to improve response and recovery efforts by answering the question: how do engineers cost-effectively determine a "dangerous" threshold for any building in real-time? Current damage evaluation consists of visual inspection that identifies only external damage. Global internal damage quantification is underway herein in a manner that can be used on common infrastructure. A structural health algorithm requires damage indicators for measuring extent and identifying location. To this end, a series of laboratory experiments have been performed as a part of this work. One additional research project and several educational activities have also been undertaken. As an initial investigation, experiments on a stainless steel cantilever beam are used to determine potential parameters for damage detection. The next step in higher order analysis has been measuring and studying the damage trend behaviors of a student-constructed tower. The incrementally damaged responses show a decreased first modal frequency as well as characteristic coupling and splitting in the higher modal frequencies. In fact, the first natural frequency lowered by a surprising 27.75% and 34.60% with increasing damage. The location of the damage will require a more complex structure, which has been the latest focus. A three story metal frame structure was constructed. A significant amount of time was devoted to comparing data from traditional sensors and high-speed video analysis: displacement is well tracked visually by Xcitex’s ProAnalyst, but acceleration is better monitored by contact transducers. Dynamic structural parameters were obtained from the measured response using a specialized software suite called STAR Modal. After the baseline, "healthy", or undamaged state of the structure was established, damage was incrementally applied to the building by removing various members one at a time. With this data, damage detection algorithms can be applied. The survey is complete, and future research will concentrate on this step. Additionally, the related work on impact mechanics, model verification, and model reduction has produced important findings on influential parameters. The ultimate goal of this work includes the generation of reduced order models for structure-to-structure contact and debris impact. In addition to the research advancement, two courses, Structural Dynamics and Advanced Structural Dynamics, were redesigned and create, respectively. In both courses, each student completed an individual project, and the results will be posted to the PI’s website. Three balsa wood test sessions have been performed on student-built structures, both building and water towers. In order to help students visualize vibration as well as inspire the interest of high school students, a MATLAB Graphic User Interface (GUI) program has been formulated. Two journals, six one-time publications, and eight proposals have been enhanced through this grant. The knowledge of modal testing, data acquisition, and health evaluation has been augmented in the Multi-Function Dynamics Laboratory at the University of Mississippi. Laboratory and demonstration equipment have been greatly improved through this grant; specifically, the DURIP high-speed camera grant has provided a unique capability that is in great demand. No other organizations have partnered in this work, but connections have been developed with the Office of Naval Research, the Department of Homeland Security, and the Army Corps of Engineers Engineering Research Development Center. In addition to the PI, three female graduate students have been employed on this project: Ling-Yu Su, M.S., graduated May 2009; Weiping Xu, Ph.D., to graduate in December 2010; and Samantha Sabatino, M.S., to graduate in May 2011. Thus, the use of this facility as both a research resource and an innovative classroom has been advanced.
