[CCoE Notice] Dissertation Announcement: Abdulrahman Salah, "Characterizing the Shear Behavior of Ultra-High-Performance Concrete through the Universal Panel Tester"

[Greenwell, Stephen J]

[Dissertation Defense Announcement at the Cullen College of Engineering]
Characterizing the Shear Behavior of
Ultra-High-Performance Concrete through the Universal Panel Tester
Abdulrahman Salah
April 28, 2025, 9 a.m. to 11 a.m. (CST)
Location: N137 Conference Room - Civil & Environmental Engineering Department
Committee Chair:
Dr. Dimitrios Kalliontzis, Ph.D.
Committee Members:
Dr. Abdeldjelil Belarbi, Ph.D. | Dr.Yi-Lung Mo, Ph.D. | Dr. Theocharis Baxevanis, Ph.D. | Dr. Tian Chen, Ph.D.
Abstract
The limited understanding of the shear behavior of Ultra-High-Performance Concrete (UHPC), especially under axial load and varying structural scale, poses challenges to the formulation of reliable design models. Although UHPC is being increasingly utilized in structural applications, owing to its superior compressive strength and post-cracking tensile strength, its complex behavior under combined stress states and the influence of fiber alignment are yet to be well characterized. This dissertation presents a comprehensive experimental and analytical investigation of the shear behavior of UHPC, considering axial load, size, and fiber alignment effects.

The experimental program consists of three phases. During the first one, pure shear and combined shear-axial load tests were conducted on rebar-free UHPC panels using the Universal Panel Tester (UPT). The post-peak behavior and the effect of fiber alignment were evaluated. A series of material companion tests were performed along with large-scale Tension Strip Tests (TSTs). The second phase examined the contribution of bar reinforcement in UHPC shear resistance by testing bar-reinforced UHPC panels. Results indicated that axial loads have a significant effect on shear strength of UHPC, more than conventional concrete. A correlation was observed between fiber alignment and tensile strength, which influenced UHPC's shear strength.

In the third phase, a set of shear panel tests was used to investigate size effects in the shear behavior of UHPC. Two sources of size effect were observed: (1) the classical depth size effect observed in conventional concrete and (2) a fiber alignment-related size effect which is dependent on formwork geometry and boundary layer effects during casting. Comparisons with uniaxial tension tests and beam shear datasets provided additional evidence for UHPC's scale-dependent behavior related to fiber alignment.

The experimental findings informed improvements to the Softened Membrane Model for UHPC (SMM-UHPC) to capture the effects of fiber alignment and axial loads. Combining experimental and analytical findings led to the proposal of a one-way shear design model for UHPC beams that contain no transverse reinforcing bars. The model integrates material, geometric, and fiber alignment parameters within a framework that is compatible with the current ACI 318 provisions. Overall, this work contributes to a better understanding of UHPC shear behavior.
[Engineered For What's Next]


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