The primary research objective of this project is to investigate the behavior and design of reinforced concrete (RC) wall structures under elevated temperatures due to fire. To achieve this objective, the research will: (1) experimentally investigate the out-of-plane axial-load-moment-curvature-temperature behavior of RC wall cross sections under elevated temperatures; (2) evaluate the effects of geometric, material, reinforcement, and loading parameters on these structures; and (3) develop a rational, predictive fire-resistant structural design procedure based on the test results. The project will result in experimental evidence demonstrating the fire performance of RC walls and validated design models using the test data. In addition, the experiments will investigate the application of a cost-effective test method using ceramic fiber radiant heaters to subject the specimens to elevated temperatures. The ultimate project deliverables will be the ability to evaluate the structural performance of a RC wall under fire and the ability to design a wall that can withstand uncontrolled fires until burnout.
The successful completion of the project tasks will provide important data for fire-resistant design of reinforced concrete walls commonly used in building structures, with ancillary contributions to fire engineering and materials engineering/science fields. Wall structures designed using this information will facilitate emergency response activities by protecting elevator cores and stairwells, and contribute towards the resistance of buildings to prevent catastrophic overall collapse. The project will train a graduate student in fire resistant design of structures and encourage undergraduate students to study structural fire engineering, strongly focusing on underrepresented groups. The researchers will utilize the project to educate future engineers through K12 activities as well. The research results will be disseminated widely for utilization by practicing engineers, other researchers, and other end users.
Reinforced concrete (RC) bearing walls are one of the most common primary lateral and gravity load carrying systems in U.S. building practice. The project considered the importance of these walls on the axial load capacity of building structures and the challenges from compartment (one-sided) fires. While RC walls are robust and can restrain the spread of fires for multiple hours, the structural load-bearing capacity of the overall system can be greatly hindered by one-sided heating and the resulting steep thermal gradients and unsymmetric degradation of the concrete and reinforcing steel across the wall thickness. Severe exposure to fire can compromise the out-of-plane stability of these walls under service-level gravity loads, causing catastrophic overall or disproportionately large failure of the structure. The previous fire engineering research on RC wall structures is limited and does not address these issues. Considering the current research needs, this research project, conducted at the University of Notre Dame in collaboration with the University of Texas at Tyler, involved unique full-scale experiments and monitoring of RC bearing walls and accompanying numerical studies resulting in new technical knowledge, physical resources, know-how, and human resources for the testing, analysis, and design of RC bearing wall structures under fire. The response of RC structures to fire is a complex phenomenon and previous research in this area is very scarce. As such, the development of rational methods to improve the design and analysis of structural components for fire represents a major long-range and transformative, seminal rather than incremental, advance on the development of fire-resistant buildings. The main intellectual outcome from the project resides in its specific contributions to this area by: 1) developing experimental evidence demonstrating the structural fire performance and design of RC bearing walls in the out-of-plane direction, which is the most critical direction for the overall stability of the building system; 2) investigating the influence of the underpinning parameters (e.g., geometric, material, reinforcement, and loading parameters) on the axial-flexural-fire behavior of these structures; and 3) investigating validated design and analysis models and tools using the test data. The intellectual outcomes from the project also include the development of a one-of-a-kind portable gas fire furnace that can potentially lead to a paradigm shift in structural fire engineering research. The furnace that was constructed is a skid-mounted furnace that can reach temperatures as high as 3000 degrees F following a user-specified time-temperature curve. Different from conventional gas fire furnaces, the specimen is kept outside the furnace allowing easier visual inspections, monitoring of behavior, and application of gravity and lateral loads. The new furnace allowed the use of advanced monitoring systems that were not possible in fire research before, resulting in unprecedented experimental measurements. Additionally, since the furnace only heats a small volume, it is considerably more energy efficient than a traditional furnace. The burner and gas train skid assemblies can be conveniently moved and stored when not in use. Ultimately, the results from this project can form the foundation for codified regulatory structural fire design standards and specifications for RC bearing walls. Wall structures designed using these results can contribute towards the resistance of a building to prevent catastrophic overall (or disproportionately large) collapse during an uncontrolled fire and to facilitate emergency response activities by protecting elevator cores and stairwells. As a major broader outcome, this could contribute to the general public welfare by mitigating loss of life and property, and improving the performance of structures under extreme fire exposures. The project played a significant role on the professional career development of the Faculty Principal Investigator as a researcher and educator in structural fire engineering, which is a relatively new field of study for him. Additional contributions and broader impacts of the project to human resource development in science, engineering, and technology included the involvement of a young assistant professor, one Ph.D. student, and ten undergraduate students at the University of Notre Dame. Four of these undergraduates were female, two were Hispanic, and one student was from a predominantly undergraduate institution. Six of the undergraduate students have already received their B.S. degrees in Civil Engineering and are currently pursuing graduate degrees. Two other students are planning to conduct graduate studies in structural engineering after they receive their B.S. degrees. Thus, the project was successful in attracting a significant number of students to carry out advanced studies. Through an NSF EArly-concept Grants for Exploratory Research (EAGER) grant, the project also provided advanced research, education, and training opportunities for an assistant professor and undergraduate students at the University of Texas at Tyler, which is a predominately undergraduate institution with a fledgling Civil Engineering Department (established in 2005). This may ultimately provide an impetus for the creation of a research center of excellence in East Texas.
