Graduation Semester and Year
Fall 2024
Language
English
Document Type
Thesis
Degree Name
Master of Science in Civil Engineering
Department
Civil Engineering
First Advisor
Shih-Ho Chao
Abstract
This study investigates the shear behavior and resistance mechanisms of continuous post-tensioned beams commonly used in one-way slab buildings. Combining experimental and analytical methods, the research focuses on the targeted failure regions of prestressed and non-prestressed continuous beams to gain deeper insights into their shear behavior. The large-scale specimens used in this study featured realistic parabolic tendon profiles and an average prestress level comparable to that used in actual construction. The experimental program includes three test series, with beam designs and setups refined for each series based on observations of shear crack development and progression in the preceding series. This study's setup was specifically designed to ensure that the bending moment in the positive moment region exceeded that in the negative moment region. Consequently, the first flexural crack, followed by shear cracks, developed first in the positive moment region. This approach facilitates a systematic investigation of shear strength evaluation. For future studies, the setup can be easily adjusted to increase the moment in the negative moment region, allowing verification of the findings observed in the positive moment region in this study.
Key findings highlight the significant impact of prestressing on shear strength, with prestressed specimens exhibiting nearly three times the shear capacity of non-prestressed specimens across all test series. The results revealed that the fundamental mechanism of critical shear crack development is essentially the same as that observed in simply supported beams reported in the 1960s. Specifically, the critical shear crack resulted from the interaction of two critical flexural cracks, which eventually led to the failure of the compression zone and the dowel resistance. Mohr’s circle analysis was employed to explain why shear cracks in prestressed specimens are shallower and how the biaxial compression zone enhances shear resistance. The primary reason for the significantly higher shear strength in prestressed beams is the greater cracking moment, Mcr, induced by the prestress, which caused the two critical flexural cracks to form much closer to the maximum moment region than in non-prestressed beams. This resulted in a compression zone depth approximately four times greater than that of the non-prestressed beams. The larger compression zone, subjected to significant biaxial compression, provides high resistance and ductility in resisting the shear force.
The current flexure-shear (vci) and web-shear (vcw) equations in the ACI 318-19 Code, used to evaluate the shear strength of prestressed beams, were derived from simply supported beams and pretensioned members in the 1960s. These equations are very cumbersome to apply to continuous post-tensioned beams and may not accurately represent the actual resistance of such beams. For instance, in real-world continuous prestressed beams with uniform loading, there are no sections with both zero moment and extremely high shear demand, as observed at the supports of simply supported beams. This suggests that the vcw equation may not be necessary for the shear design of continuous prestressed beams, simplifying the design process without compromising safety.
A new shear strength equation is proposed in this study, incorporating experimental observations and fundamental engineering principles, including the role of prestress-induced compression. This equation is much simpler than the current ACI equations, and yet reflects the fundamental mechanism of shear resistance and remains conservative compared to the test results. The conservatism also arises from the fact that the actual loading condition is primarily uniform loading, rather than the concentrated loading applied in this study.
Keywords
Post-tensioned concrete, Prestressed concrete, Shear design, ACI shear design, Flexure-shear, Web-shear, Shear failure, Experimental testing of prestressed concrete, Experimental testing for shear failure in concrete, Shear design for concrete beams
Disciplines
Civil Engineering | Engineering Mechanics | Mechanics of Materials | Other Engineering Science and Materials | Structural Engineering
License
This work is licensed under a Creative Commons Attribution-NonCommercial-No Derivative Works 4.0 International License.
Recommended Citation
Rijal, Suman, "EXPERIMENTAL AND FINITE ELEMENT INVESTIGATION OF SHEAR TRANSFER MECHANISMS AND CAPACITY OF CONTINUOUS POST-TENSIONED CONCRETE BEAMS IN ONE-WAY SLAB BUILDINGS" (2024). Civil Engineering Theses. 455.
https://mavmatrix.uta.edu/civilengineering_theses/455
Included in
Civil Engineering Commons, Engineering Mechanics Commons, Mechanics of Materials Commons, Other Engineering Science and Materials Commons, Structural Engineering Commons