Structural behavior and modeling of high-performance fiber-reinforced cementitious composites for earthquake-resistant design

摘要

For earthquake-resistant design, adequate concrete confinement is vital for a ductile structural response and for providing a stable energy dissipating mechanism. Since concrete materials generally exhibit quasi-brittle failure and a low tensile strength, designers of traditional reinforced concrete often specify extensive transverse reinforcement with thorough detailing to ensure that appropriate confinement to the concrete and the longitudinal reinforcing bars is provided. This approach often results in such a large amount of reinforcing steel that construction of the design can be congested, costly, and even impractical. This effect is particularly pronounced in critical shear and/or moment regions of structural concrete coupling beams and pile-wharf connections, as well as in plastic hinge regions of reinforced concrete beams, columns, and structural walls. To address this problem, the development and modeling of High Performance Fiber-Reinforced Cementitious Composites (HPFRCC) for use in key shear and/or moment regions of damage-critical structural concrete elements has been investigated. An experimental program was conducted to further understand the behavior of HPFRCC under general multi-axial stress states, such as would be expected at various key locations in a damage-critical structural component. Concrete plate specimens comprising mixes containing from one to two percent volume fraction of hooked steel fibers and Spectra (polyethylene) fibers were tested. After exploration of these different fiber types and volume fractions, a 1.5% volume fraction of hooked steel fibers was selected as the concrete mix for more comprehensive examination, based in part on a study to create self-consolidating fiber-reinforced concrete. The stress-strain behavior of the various HPFRCC mixes was examined, and biaxial failure envelopes have been developed. The plate specimen tests showed that HPFRCC exhibits a confined compressive behavior with a significantly increased damage tolerance and deformation capacity. Using the knowledge and behavioral trends gained from the laboratory tests of HPFRCC materials, it was possible to create a phenomenological HPFRCC finite element material model, with a smeared crack representation, that was calibrated to the experimental data. In addition to small-scale structural / material testing and modeling, the same HPFRCC hooked steel fiber mix was tested in large-scale coupling beam component tests by project partners at the University of Michigan. After completion of these large-scale tests, the material model was validated at the structural component level with their experimental coupling beam results. Finally, a full-scale structural concrete pile-wharf connection was tested at the University of Illinois, and the behavior of this damage-critical component was thoroughly analyzed. The HPFRCC model was then implemented into the pile-wharf connection application. Overall, it was found that the increase in structural component damage tolerance through a ductile response obtained by the tensile strain-hardening and confined compressive behavior from the use of HPFRCC makes it a potentially viable solution as a replacement for some steel confinement reinforcement and as an additional shear resistance mechanism. With the development of an HPFRCC modeling tool, insight into the levels of damage experienced by structural elements can inform performance-based design decisions regarding the use of HPFRCC in critical structural components.