Experimental Research of Technology for Strengthening Reinforced Concrete Columns with Carbon Fibers

Reinforcement of columns (piers) is usually accomplished by increasing  cross-section through building-up, injecting reinforcing solutions and external reinforcement. The most and progressive method for strengthening is currently external reinforcement, its essence is to glue high-strength sheets, plates or strips (lamellas) onto structure surface with the help of special adhesives. Scientists pay special attention to theoretical and experimental studies of design solutions for external reinforcement of vertical load-bearing  structures. Unfortunately,   the results  of  such  studies, for example, influence of technology for execution of works on strengthening efficiency are virtually absent. Therefore,  the objective of this paper is to carry out experiments with the purpose to study influence of technological factors on efficiency in strengthening of reinforced concrete structures, which absorb compressive forces. The experimental studies have been made in six series that changed the technology of executed works while using various technological factors. Among the main factors are the following: presence/absence of acute angles; preparation of a base (surface coating); method for gluing reinforcing materials to a structure. A criterion for evaluation of  technology efficiency  has been breaking strength for axial  compression  of  reinforced  samples. Analysis on the results of experimental studies has shown that the highest load-bearing  capacity  is achieved while using samples of columns with rounded edges, provided that an adhesive is applied to sample base and carbon fiber (40.6 tons). The compressive strength of such samples is by 82.2 % higher than the strength of control samples. The strength of reinforced specimens with non-rounded edges has appeared to be the lowest one, namely 34.0 tons. Strengthening of the samples with fiber impregnated with an adhesive has increased the indicator by 74.3 % compared to the control samples. The compressive strength of samples reinforced with carbon fiber adhered to the adhesive which is preliminary spread on the basis  is equal to 38.6 tons, which is by 73.4 % higher than the strength of the control samples.

1. . State Standard of Ukraine В.3.1-2:2016. Repair and Strengthening of Load-Bearing and Protective Building Structures and Foundations of Buildings and Structures. Kiyev, Ukrainian Research and Training Center of Standar-dization, Certification and Quality, 2017. 72 (in Russian).

2. Savyovskiy V. V. (2018) Reconstruction of Buildings and Structures. Kiyev, Lira-K Publ. 320 (in Russian).

3. Omar Ahmed Farghal Ahmed, Abd El-Rahman Megahid (2006) Behavior of Axially Loaded Circular RС Column Confined with CFRP Wrapping Sheet. Journal of Engineering Sciences, Assiut University. 34 (4), 1027–1047.

4. Campione G., Miraglia N., Papia M. (2004) Strength and Strain Enhancements of Concrete Columns Confined with FRP Sheets. Structural Engineering and Mechanics, 18 (6), 769–790. https://doi.org/10.12989/sem.2004.18.6.769.

5. Rocca S., Galati N., Nanni A. (2008) Review of Design Guidelines for FRP Confinement of Reinforced Concrete Columns of Noncircular Cross Sections. Journal of Composites for Construction, 1 (12), 80–92. https://doi.org/10. 1061/(asce)1090-0268(2008)12:1(80).

6. Holmes N., Niall D., O'shea C. (2014) Active Confinement of Weakened Concrete Columns. Materials and Structures, 48 (9), 2759–2777. https://doi.org/10.1617/s11527-014-0352-1.

7. Ghanem S. Y. (2016) Сircular RC Columns Partially Confined with FRP: Theses and Dissertations. Kentucky. 201.

8. Ovchinnikov I. I., Ovchinnikov I. G., Chesnokov G. V., Mikhaldykin E. S. (2016) Analysis of Experimental Studies on the Reinforcement of Reinforced Concrete Structures with Polymer Composite Materials. Part 1. Domestic Experiments under Static Loading. Internet Journal “Naukovedenie”, 8 (3). Available at: https://naukovede nie.ru/PDF/24TVN316.pdf.

9. Hayder Lateef Al-Khafaji (2016) Experimental Investigation of CFRP Wrapped Square Non-Ductile Reinforced Concrete Columns. Dissertations and Theses. Portland State University Pdxscholar. 212.

10. Saviovs'kii V. V., Moloded A. S., Malets N. A. (2017) Reinforcement of Reinforced Concrete Beam Structures with External Reinforcement. Upravlenie Razvitiem Slozhnykh System [Management of the Development of Complex Systems], (29), 198–204 (in Russian).

11. Technological Map for the Implementation of Work on the Restoration of Brick, Reinforced Concrete Structures and their Protectionj. Kiev, LLC “COMPOSITE”, 2009. 7 (in Russian).