Shear Behaviour in Slender Reinforced Concrete Beams with and without Transverse Reinforcement

This study investigates shear crack behaviour in slender reinforced concrete (RC) beams, focusing on the critical shear crack (CSC) geometry and its impact on crack kinematics and shear transfer mechanisms. Existing models often oversimplify CSC shape assumptions, potentially leading to inaccuracies in shear capacity predictions. Through a comprehensive experimental program of testing nine large scale RC beams in three point bending, this research systematically investigates the influence of flexural reinforcement ratios on CSC shape variability. The findings show how varying reinforcement ratios between 0.84% and 2.35% impact the overall behaviour of the CSC and subsequently affect shear capacity. A novel crack kinematic model is proposed based on literature and refined through successive stages, transitioning from a one-end rotation mechanism to a more realistic two-end rotation mechanism. This iterative development process is guided by experimental observations, particularly from digital image correlation (DIC). The study investigates the choice of strains to input into the two-end kinematic model for beams with and without transverse steel. Comparisons with DIC and fibre optic sensors (FOS), experimental strain measurements are used to inform the selection of representative values. The RC beams without transverse steel utilise the average concrete strain within the web from the simplified modified compression field theory (SMCFT), whereas those incorporating transverse steel rely on average steel strains in the transverse direction from SMCFT to determine the rotation at the crack tip. The proposed model’s effectiveness is verified across slender RC beams, both with and without transverse reinforcement yielding adequate results with an *R²* of 0.8769 for crack width and an *R²* of 0.7324 for crack slip. Particularly, the model’s applicability to cases involving transverse steel reinforcement is a significant advancement, since existing models largely address beams without shear reinforcement. The innovative approach presented here represents a significant step towards improving the shear capacity prediction accuracy for slender RC beams where the ratio of estimated shear capacity and the experimental failure exhibiting a coefficient of a variation of 9%. The methodology underscores the significance of accurate consideration of the CSC shape and opens avenues for forward prediction due to the capability for crack shapes to be used as input parameters. This sensitivity was used to compare simplified crack geometries against best-fit polynomial approximations, concluding that when the polynomial curve is fitted on the combined primary and secondary cracks observed in experiments, the 5th- degree polynomial performs better. Consideration of the secondary crack and the primary flexuralcrack was significant to help facilitate the identification of the surrounding rigid body equilibrium and to explain changes in resultant crack kinematics. This integration has been successfully incorporated into the proposed two-end rotation model. Overall, this research contributes to the understanding of shear behaviour in RC beams, offering a practical framework for designing slender RC beams with more accurate shear predictions. This work paves the way for forward prediction of shear, ultimately advancing the state of the art research for concrete shear performance.

Name dc:type.qualificationname

Doctor of Philosophy (PhD)

Level dc:type.qualificationlevel

Doctoral

Grantor dc:publisher.institution

University of Cambridge

Year dc:date.issued

2023

Author dc:creator

• Weerasinghe, Hasini C

Advisor dc:contributor.advisor

• Lees, Janet

• Crack Kinematics
• Critical Shear Crack
• Shear behaviour
• Shear Transfer Actions

Licence

• https://www.repository.cam.ac.uk/bitstreams/726db05c-ad49-431f-8bc9-e61838a88ead/download
• https://www.rioxx.net/licenses/all-rights-reserved/

Language dc:language

eng

DOI dc:identifier.doi

https://doi.org/10.17863/CAM.106586

OAI identifier oai:identifier

oai:www.repository.cam.ac.uk:1810/365197