Date of Award
Doctor of Philosophy in Civil Engineering - (Ph.D.)
Civil and Environmental Engineering
Matthew J. Bandelt
Shawn Alexander Chester
Matthew P. Adams
Bruno M. Goncalves da Silva
Structural components constructed with ductile concrete composites, such as high-performance fiber-reinforced cementitious composites (HPFRCC), are known to perform exceptionally well under extreme mechanical and environmental loading conditions compared to traditional concrete. HPFRCC flexural components exhibit enhanced performance in terms of displacement ductility, energy dissipation capacity, and damage tolerance capacity. However, recent research suggests that the flexural behavior of reinforced HPFRCCs in terms of crack progression, reinforcement plasticity, and failure mechanism is significantly different than conventional reinforced concrete. Specifically, the failure mode of flexural members is found to be predominantly through the fracture of longitudinal reinforcement rather than compression crushing of HPFRCC matrix. Further, the influence of cross-section properties on the deformation capacity of reinforced HPFRCC beams has been found to be opposite to that in reinforced concrete beams.
To that end, an extensive numerical simulation study is carried out with variations in material and structural properties to identify the fundamental variables affecting deformation capacity and plasticity in reinforced HPFRCC beams. The results of the study indicate that increasing tensile strength of HPFRCCs can significantly decrease component deformation capacity. The influence of other factors such as reinforcement ratio, boundary conditions, and shear span-to-depth ratio are also investigated. Statistical analyses are performed to understand the relative impact of these factors on deformation capacity, and recommendations are given to predict deformation capacity in reinforced HPFRCC beams under monotonic loading condition.
In the next phase of the research, an investigation of plastic hinge behavior in reinforced HPFRCC flexural members is performed. Variations in mechanical properties, boundary conditions, and geometric properties are considered. The reinforcement yielding region, plastic strain distribution region, and curvature localization region are particularly explored. New expressions are developed to compute the equivalent plastic hinge length, Lp, using variables such as shear-span, tensile strength of HPFRCC, reinforcement ratio, yield strength of the reinforcement, boundary condition, and loading scenario. A simplified mechanics-based approach is developed to compute flexural strengths and rotation capacities at multiple damage states. The proposed approach is validated using a large experimental database found in the literature for wide range of HPFRCC classes.
To further validate the robustness of the analytical framework, an experimental program is carried out using two reinforced HPFRCC beams with variation in fiber volume fraction. The experimental results show that the plasticity length in steel reinforcement bar increases with a decrease in fiber volume fraction from 2% to 1%. The plastic hinge region of the HPFRCC specimen with 2% fiber content has crack localization over a short region compared to the specimen with 1% fiber content. The analytical approach developed in the previous research phase is used to predict the flexural strengths and rotation capacities at different limit states.
While the research presented represents significant advancement in the numerical analysis and design of reinforced HPFRCC members, additional experimental work is necessary to further improve the framework presented herein. Therefore, an experimental program is outlined considering two variants of HPFRCCs under monotonic and cyclic loading.
Pokhrel, Mandeep, "Numerical and analytical methods to predict behavior of reinforced ductile concrete composites" (2020). Dissertations. 1461.