Experimental Investigation of Bond between Near-Surface-Mounted CFRP Strips and Concrete under Freeze-Thawing Cycling

This paper presents an investigation of the bond mechanism between carbon fibre reinforced polymer (CFRP) laminates, concrete and steel in the near-surface mounted (NSM) CFRP-strengthened reinforced concrete (RC) beam-bond tests. The experimental program consisting of thirty modified concrete beams flexurally strengthened with NSM CFRP strips was published in. The effects of five parameters and their interactions on the ultimate load carrying capacities and the associated bond mechanisms of the beams are investigated in this paper with consideration of the following investigated parameters: beam span, beam depth, longitudinal tensile steel reinforcement ratio, the bond length of the CFRP strips and compressive concrete strength. The longitudinal steel reinforcement was cut at the beam mid-span in four beams to investigate a better assessment of the influence of the steel reinforcement ratio on the bond behaviour of CFRP to concrete bond behaviour. The numerical analysis implemented in this paper is based on a nonlinear micromechanical finite element model (FEM) that was used for investigation of the flexural behaviour of NSM CFRP-strengthened members. The 3D model based on advanced CFRP to concrete bond responses was introduced to modelling of tested specimens. The FEM procedure presents the orthotropic behaviour of the CFRP strips and the bond response between the CFRP and concrete. Comparison of the experimental and numerical results revealed an excellent agreement that confirms the suitability of the proposed FE model.

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Activated Ductile CFRP NSMR Strengthening

Materials ◽

10.3390/ma14112821 ◽

2021 ◽

Vol 14 (11) ◽

pp. 2821

Author(s):

Jacob Wittrup Schmidt ◽

Christian Overgaard Christensen ◽

Per Goltermann ◽

José Sena-Cruz

Keyword(s):

Failure Modes ◽

Elastic Response ◽

Applied Theory ◽

Strengthening Effect ◽

The Novel ◽

Near Surface ◽

Linear Elastic ◽

Near Surface Mounted ◽

High Elongation ◽

Strengthened Beam

Significant strengthening of concrete structures can be obtained when using adhesively-bonded carbon fiber-reinforced polymer (CFRP) systems. Challenges related to such strengthening methods are; however, the brittle concrete delamination failure, reduced warning, and the consequent inefficient use of the CFRP. A novel ductile near-surface mounted reinforcement (NSMR) CFRP strengthening system with a high CFRP utilization is introduced in this paper. It is hypothesized that the tailored ductile enclosure wedge (EW) end anchors, in combination with low E-modulus and high elongation adhesive, can provide significant strengthening and ductility control. Five concrete T-beams were strengthened using the novel system with a CFRP rod activation stress of approximately 980 MPa. The beam responses were compared to identical epoxy-bonded NSMR strengthened and un-strengthened beams. The linear elastic response was identical to the epoxy-bonded NSMR strengthened beam. In addition, the average deflection and yielding regimes were improved by 220% and 300% (average values), respectively, with an ultimate capacity comparable to the epoxy-bonded NSMR strengthened beam. Reproducible and predictable strengthening effect seems obtainable, where a good correlation between the results and applied theory was reached. The brittle failure modes were prevented, where concrete compression failure and frontal overload anchor failure were experienced when failure was initiated.

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Inorganic adhesive based near-surface-mounted fibre reinforced polymer for strengthening of concrete structures: An overview

Structures ◽

10.1016/j.istruc.2021.04.017 ◽

2021 ◽

Vol 33 ◽

pp. 2099-2120

Author(s):

Jin-Guang Yu ◽

Liang Cheng ◽

Shu Liu ◽

Bing Fu ◽

Bo Li

Keyword(s):

Concrete Structures ◽

Near Surface ◽

Reinforced Polymer ◽

Fibre Reinforced Polymer ◽

Near Surface Mounted

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Near-Surface Mounted Reinforcement of Sawn Timber Beams-FEM Approach

Materials ◽

10.3390/ma14112780 ◽

2021 ◽

Vol 14 (11) ◽

pp. 2780

Author(s):

Izabela Burawska-Kupniewska ◽

Piotr Beer

Keyword(s):

European Standard ◽

Near Surface ◽

Bending Tests ◽

Starting Point ◽

Structural Applications ◽

Bending Stresses ◽

Complex Models ◽

Near Surface Mounted ◽

Sawn Timber ◽

Timber Beams

The demand for timber has increased significantly in recent years. Therefore, reliable tools are needed to predict the mechanical properties of sawn timber, especially for structural applications. Very complex models require a lot of input data for analysis, which cannot always be guaranteed, especially in industrial practice. Thus, a simplified model for material description was developed and assessed with experiments (static bending tests carried out in accordance with the guidelines suggested in the European standard EN 408) and an analytical approach (gamma method according to the guidelines given in the European standard EN 1995). The effective stiffness was calculated as a major parameter, which has an influence on the elements’ behavior. The model included a near-surface mounted (NSM) local reinforcement technique, with CFRP strips of Scots pine timber beams being subjected to bending stresses. It is anticipated that the developed model can be a starting point for the repair engineering field, contributing to decision-making regarding conservation technique selection and range. Next, improvements of the model will provide more and more realistic results for numerical analysis in terms of the obtained failure mechanisms for sawn timber elements.

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