Citation: Zhou, B.; Wu, R.-Y.; Yin, S.
Stress Field Approach for Prediction
of End Concrete Cover Separation in
RC Beams Strengthened with FRP
Reinforcement. Polymers 2022, 14, 988.
https://doi.org/10.3390/
polym14050988
Academic Editors: Alberto
Campagnolo and Alberto Sapora
Received: 23 January 2022
Accepted: 24 February 2022
Published: 28 February 2022
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Article
Stress Field Approach for Prediction of End Concrete Cover
Separation in RC Beams Strengthened with FRP Reinforcement
Binbin Zhou
1,2,
*, Ruo-Yang Wu
3,
* and Shiping Yin
1,2,
*
1
Jiangsu Key Laboratory of Environmental Impact and Structural Safety in Engineering, School of
Mechanics & Civil Engineering, China University of Mining and Technology, Xuzhou 221116, China
2
State Key Laboratory for Geomechanics & Deep Underground Engineering, China University of Mining
and Technology, Xuzhou 221116, China
3
Wilson and Company, South Jordan, UT 84096, USA
* Correspondence: wwwzb623@163.com (B.Z.); rywuandrew@gmail.com (R.-Y.W.);
yinshiping7808@aliyun.com (S.Y.); Tel.: +86-516-88912003 (B.Z.)
Abstract:
End concrete cover separation is one of the most common failure modes for RC beams
strengthened with external FRP reinforcement. The premature failure mode significantly restricts the
application of FRP materials and could incur serious safety problems. In this paper, an innovative
stress field-based analytical approach is proposed to assess the failure strength of end concrete cover
separation and the conventional plane-section analysis is extended to evaluate the corresponding
carrying capacity of FRP-strengthened RC beams. First, the dowel action of reinforcement and the
induced concrete splitting, reflecting the interaction between concrete, steel and FRP, are consid-
ered in establishing the geometrical relationships of stress field for cracked concrete block. Then,
the cracking angle and innovative failure criterion, considering the arrangement of steel and FRP
reinforcement and cracking status of concrete and its softening effect, are derived to predict the
occurrence of concrete cover separation and related mixed modes of debonding failure. Subsequently,
an extended sectional analytical approach, in which the components of effective tensile strain of FRP
resulted from flexural and shear actions are both considered, is presented to evaluate the carrying
capacity of strengthened beams. Finally, the proposed calculational model is effectively validated by
experimental results available in the literature.
Keywords:
end concrete cover separation; stress field approach; cracked concrete; failure strength;
dowel action; concrete splitting
1. Introduction
Due to the pronounced advantages, such as high strength, light weight, electromag-
netic transparency, non-corrosive, and nonconductive properties, externally bonded (EB)
fiber-reinforced polymer (FRP) and near-surface-mounted (NSM) FRP have become the
prevailing techniques over the last three decades for flexural strengthening of existing
reinforced concrete (RC) members [
1
–
4
]. Extensive experimental and analytical research
has been performed to investigate the structural performance of FRP-strengthened RC
members and to assess the retrofitting efficiency. Accordingly, numerous study findings
indicated that premature reinforcement debonding failure restricts the sufficient application
of FRP materials and furthermore, the brittle failure could incur serious safety problems of
RC members or structures [
5
,
6
]. According to the failure mechanism, debonding failure can
be divided into interfacial debonding (ID) that happens at or near a bi-material interface
and concrete cover separation (CCS) that occurs along the level of internal tensile steel
reinforcement. Moreover, debonding failure can be also categorized into reinforcement end
debonding and intermediate crack-induced debonding in terms of failure location [
6
,
7
],
which are schematically shown in Figure 1.
Polymers 2022, 14, 988. https://doi.org/10.3390/polym14050988 https://www.mdpi.com/journal/polymers
