Behavior, modeling, and impact of bond in steel reinforced high-performance fiber-reinforced cement-based composites [electronic resource]

High-performance fiber-reinforced cement-based composites (HPFRCCs) are a class of cement-based materials that exhibit a psuedo strain-hardening behavior in uniaxial tension after first cracking, and retain residual strength in compression after crushing. The unique mechanical properties of HPFRCCs have led researchers to investigate their use in structural applications where damage tolerance and energy dissipation is needed. Research on structural applications of steel reinforced HPFRCCs members has shown enhanced damage tolerance, shear capacity, flexural strength, inelastic deformation capacity, and life cycle performance. Recent research has focused on the interaction between mild steel reinforcement and HPFRCCs for modeling and design purposes. When reinforced HPFRCCs have been subjected to direct tension, early strain hardening and reinforcement strain localization have been observed caused by short debonded lengths, as opposed to long debonded lengths in traditional reinforced concrete. Short debonded lengths caused the HPFRCC reinforcement to fracture at lower levels of specimen deformation compared to reinforced concrete. This recent research indicates that bond strength between reinforcement and HPFRCCs may be higher than that of traditional reinforced concrete. Additionally, reinforcement tensile strains may be an important consideration for design and modeling of reinforced HPFRCC structural components. In this dissertation, the bond behavior between steel reinforcement and HPFRCCs is presented through experimental testing and numerical simulations. Bond experiments were conducted under monotonic and cyclic loading conditions where the HPFRCC material surrounding the reinforcement was in a flexural tension stress state. Monotonic test results show that bond strengths are 37% higher, on average, in reinforced HPFRCCs than in reinforced concrete. Additionally, bond-slip toughness (i.e., the area under the bond stress versus reinforcement slip curve) is higher in reinforced HPFRCCs than in reinforced concrete. Cyclic bond-slip experiments were performed for two types of HPFRCCs and compared to monotonic behavior using beam-end specimens. Results show that bond deterioration occurs in HPFRCCs after the maximum bond stress is reached, causing bond stress to reduce by 60%, on average. The loss of bond capacity and bond-slip toughness is due to combined crushing and splitting of the interface. The effects of bond on structural performance are examined through a study on monotonic and cyclic performance of reinforced HPFRCC beam specimens with varying reinforcement ratios. It is shown that cyclic deformation histories can decrease deformation capacity by up to 67%. Unlike traditional reinforced concrete, deformation capacity of reinforced HPFRCCs is shown to increase with increasing longitudinal reinforcement ratio. Results show that the difference between monotonic and cyclic deformation capacity becomes smaller as reinforcement ratio increases. Suggestions are made for providing a moderate amount of reinforcement to take full of advantage of the HPFRCC material toughness and improve structural performance and deformation capacity. An interface bond-slip material model is proposed based on the experimental results to model the interaction between steel reinforcement and HPFRCC materials. Simulations with the proposed interface model are compared with perfect bond models in finite element simulations by comparing numerical and experimental responses of reinforced HPFRCC structural members. Simulations are conducted on reinforced HPFRCC components under monotonic and cyclic deformation histories, and on members with varying reinforcement ratios. Including the proposed interface material model reduces variability in simulated deformation capacity, and leads to a consistent response in terms of cracking patterns and deformation capacity. A methodology is proposed to predict reinforced HPFRCC deformation capacity by examining reinforcement strains, modeling the interface conditions, and implementing a cyclic fracture energy material parameter from test data. The dissertation concludes with suggestions for future research that can extend the work presented herein. Suggestions for future work include additional experimental, numerical, and design-related research.

Keywords: Civil and Environmental Engineering.
Advisor: Billington Sarah L. (Sarah Longstreth)
Deierlein Gregory G. (Gregory Gerard)
Lepech Michael advisor. Thesis advisor