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Dept. of Civil Engineering
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Minneapolis, MN 55455
Projects › Current
NEESR-CR: Steel Truss Systems with Enhanced Seismic Safety and PerformancePrincipal Investigators: Chao, Univ. of Texas-Arlington
This award is an outcome of the NSF 09-524 program solicitation .George E. Brown, Jr. Network for Earthquake Engineering Simulation (NEES) Research (NEESR). competition and includes the University of Texas, Arlington (lead) and Valparaiso University (subaward). This award will utilize the NEES equipment site at the University of Minnesota, named the Multi-Axial Subassemblage Testing (MAST) Laboratory. The goal of this research is to advance seismic safety and design of building structures by studying two steel truss systems: special truss moment frames (STMFs) and staggered truss frames (STFs). Due to their ability to achieve large column-free floor spaces, STMFs and STFs are unique, valuable options for structural engineers. However, although STMFs and STFs offer a wide range of structural, architectural, and economical benefits, limited research data is available on the seismic performance of these systems. Because previous tests on STMFs do not adequately reflect the current practice in design and detailing, substantial improvement in design methodology and confidence could be gained for STMFs by further research. Despite the strong interest among the engineering community, the application of STFs to seismic regions has been restricted due to lack of research. The project will advance knowledge about the system behavior of STMFs and STFs and recommend innovations to improve the seismic performance of these two truss systems.
NEESR-CR: Unbonded Post-Tensioned Rocking Walls for Seismic Resilient StructuresPrincipal Investigators: Sritharan, Iowa State
The motivation for this research is that damage caused by earthquakes, and the subsequent economic losses, underscore the need to focus on developing earthquake resilient buildings. One method of achieving resilient buildings is to design them with self-centering structural systems to resist earthquake lateral loads. Using unbonded post-tensioning tendons, a cost-effective, self-centering wall system known as PreWEC (i.e., Precast Wall with two End Columns) was developed at ISU, which has been proven analytically and experimentally to have excellent seismic performance with minimal structural damage. In this system, as well as in single rocking walls (SRWs) designed with unbonded post-tensioning, the response is dominated by a rocking mode. However, the energy loss caused by the wall impacting the foundation during rocking has not been given consideration in design due to lack of knowledge on this subject. Significant evidence suggests that this mechanism alone may be sufficient to dissipate the seismic energy. Furthermore, the resilience of a building containing rocking walls is also dependent on the behavior of surrounding structural components, especially floors and gravity columns, and their interactions with the seismic resistant systems. To ensure a fully resilient structure, these interactions should be addressed by understanding the wall-floor connection responses.
NEESR-CR: Full-Scale RC and HPFRC Frame Subassemblages Subjected to Collapse-Consistent Loading Protocols for Enhanced Collapse Simulation and InternalPrincipal Investigators: Chao, Univ. of Texas-Arlington
Reinforced concrete (RC) structures comprise a large number of the buildings and bridges around the world. The collapse resistance of RC structures is not well understood, even though the collapse resistance is fundamental to the life-safety of building occupants during earthquakes. One of the primary problems is that currently available experimental test data are insufficient to allow researchers to comprehensively understand the collapse behavior of a building and develop accurate computer simulation models to predict when a building would collapse in an earthquake. The objective of this research is to advance knowledge about the collapse behavior and safety of both modern RC frame buildings and high performance fiber reinforced concrete (HPFRC) frame buildings when subjected to extreme earthquakes. This research project involves testing a comprehensive set of full-scale RC components and subassemblages all the way to collapse (nearly all currently available test data stop short of collapse); this comprehensive set of tests has been specifically planned for the purpose of better understanding collapse behavior and creating improved computer simulation models to predict the collapse safety of RC buildings. To improve understanding of how internal damage develops at small scales within the materials, advanced imaging technology (ultrasonic tomography) will be utilized during testing to characterize the progression of internal damage. To improve understanding of the collapse behavior of full large-scale RC buildings, improved computer simulation models will be developed and the collapse of RC building models will be directly simulated. The following technical contributions are anticipated: (1) new calibrated RC/HPFRC component models, (2) new understanding of collapse resistance behavior of RC frame buildings constructed with RC and HPFRC materials; (3) development of internal imaging technology that could be used as an on-site structural assessment tool; and (4) understanding of the internal damage development and mechanisms for RC columns and slab-beam-column connections subjected to cyclic loading. Results from this study will provide comprehensive information for collapse assessment of newly constructed RC moment frames, as well as moment frames constructed from an emerging high performance material (HPFRC). Such information will be necessary to support widespread use of HPFRC. The development of advanced imaging technology for concrete structures will provide new diagnostic capability to ascertain structural damage within concrete members, for example immediately after an earthquake event. The collapse simulation and imaging techniques developed in this research will be incorporated into educational tools to introduce undergraduate students to earthquake engineering research, the significance of earthquake effects, and the behavior of building structures subjected to collapse-level ground motions.