Size effects in unreinforced and lightly reinforced concrete beams failing in flexure

Augusthus Nelson, L; Lees, J; Weekes, L

Abstract

Fracture-based models commonly use a characteristic length as the basis for
determining size effects in concrete beams. The characteristic length is related
to the concrete fracture process zone and defined in terms of the concrete fracture properties. Semi-empirical constants are then developed to accommodate
any unidentified (geometric or crack bridging) parameters. However, a reliance
on semi-empirical factors can limit the applicability to different systems, concretes and reinforcing materials. The aim of the current work is to formulate an
analytical size effect model based solely on fundamental material and geometric
properties. The particular focus is unreinforced and lightly reinforced concrete
beams that fail in flexure due to unstable crack propagation. The proposed
’generalised’ characteristic length approach is based on the mode-I fracture behaviour of concrete and includes crack bridging forces due to the presence of
longitudinal reinforcement. The theoretical expressions suggest that the geometric shape of a beam, the fracture properties of the concrete and the crack
bridging forces (where present) significantly influence the characteristic length.
Experimental investigations on geometrically similar unreinforced and lightly
reinforced concrete beams in 2-D are undertaken as a means for initial validation. The validation is then extended to a wider dataset of existing experimental results in the literature. The generalised characteristic length approach is able
to capture both the influence of the concrete strength and the size effect mitigation due to the inclusion of longitudinal reinforcement. This confirms that the
generalised approach holds promise and could be expanded to other quasi-brittle
materials and non-conventional reinforcing materials.

Citation

Augusthus Nelson, L., Lees, J., & Weekes, L. (2022). Size effects in unreinforced and lightly reinforced concrete beams failing in flexure. Engineering Fracture Mechanics, 259, 107987. https://doi.org/10.1016/j.engfracmech.2021.107987

• Journal Article Type: Article
• Acceptance Date: Aug 31, 2021
• Online Publication Date: Sep 23, 2021
• Publication Date: Jan 1, 2022
• Deposit Date: Sep 2, 2021
• Publicly Available Date: Sep 23, 2022
• Journal: Engineering Fracture Mechanics
• Print ISSN: 0013-7944
• Publisher: Elsevier
• Volume: 259
• Pages: 107987
• DOI: https://doi.org/10.1016/j.engfracmech.2021.107987
• Publisher URL: https://doi.org/10.1016/j.engfracmech.2021.107987
• Related Public URLs: http://www.journals.elsevier.com/engineering-fracture-mechanics/
• Additional Information: Funders : Overseas Research Studentship;Cambridge Commonwealth Trust