Deformation behavior of reinforced ECC flexural members under reversed cyclic loading conditions.

Abstract

In this dissertation, the use of engineered cementitious composites (ECC) in reinforced members and model seismic resistant frames is investigated. The development from composite material to structural system behavior is presented, bridging the dimensional scales associated with microstructures, composite materials and composite structures. The fundamental cause of damage in reinforced concrete (R/C) structures is the brittle deformation behavior of concrete in tension. Engineered cementitious composites (ECC) are fiber reinforced cementitious composites designed to achieve a deformation behavior analogous to that of metals, specifically strain hardening and multiple cracking behavior. The combination of such a ductile ECC with ductile reinforcing steel in direct tension results in deformation compatibility of these R/ECC components, leading to a reduction of interfacial bond stresses and bond splitting cracks while maintaining composite integrity. Test results show that the performance of R/ECC structural composites in reversed cyclic flexure benefits from this deformation compatibility, resulting in a decrease of peak curvature at a given flexural deformation. It is further observed that beyond localization of cracking in ECC, enhanced confinement, shear strength and buckling resistance in R/ECC members make transverse steel reinforcement redundant and lead to stable energy dissipation by yielding of longitudinal steel reinforcement. Furthermore, R/ECC members with longitudinal FRP reinforcement show reduced residual displacements after unloading. On the structural system scale, the particular interaction of R/ECC members reinforced with steel and FRP reinforcement in a moment resisting frame is found to result in a structural system with considerable energy dissipation capacity and reduced residual displacement. This composite structural system shows a bi-linear elastic load-deformation behavior and intrinsic stiffness modification capabilities, which are expected to reduce the base shear forces on this system in case of a seismic event. The work presented in this dissertation may serve as a basis for development and design of seismic resistant structures using reinforced ECC members and subsystems for improved structural performance in terms of seismic response, reinforcement detailing requirements, damage tolerance, and repair needs.