Corroded RC Beams at Service Load before and after Patch Repair and Strengthening with NSM CFRP Strips
Abstract
:1. Introduction
2. Experimental Program
2.1. Specimen Details
2.2. Material Properties
2.3. Accelerated Corrosion
2.4. Patch Repair Technique
2.5. NSM Strengthening
2.6. Test Setup
3. Experimental Results
3.1. Crack Mapping, Gravimetric Measurements of Steel Mass Loss and Rough Indirect Estimation of Level of Corrosion
3.2. Structural Performance of Non Corroded (B1) and Corroded (BC1) Beams
3.3. Structural Performance of Corroded Beams (BC1,2,3-60, BC1,2,3-75) under Service Loads
3.4. Structural Performance of Patch-Repaired and NSM Strengthened Corroded Beams (BC3-60 NSM, BC3-75 NSM)
4. Conclusions
- Beams BC1-60 and BC1-75 that were subjected to 60% and 75% of yield load of non-corroded beam B1 correspondingly presented a similar mass loss of steel due to the corrosion of measured levels up to 12% mass loss (revealing similar crack widths).
- For the beam loaded under 75% of yield load, further corrosion resulted in higher mass loss (around 24% higher mass loss, at a mass loss level of around 30% for BC3-75 compared to around 25% for BC3-60) as it revealed higher crack widths.
- Beams BC3-60 and BC3-75 presented 35.6% and 68.9% higher deflection (almost double) for the high corrosion level compared to their first loading, respectively. Deflection of BC3-75 surpassed deflection at steel yielding.
- Strengthening of the corroded beams with two NSM CFRP strips, having identical FRP reinforcement but under different service loads, resulted in different structural performances and failure modes. The failure mode of both corroded strengthened beams is mainly characterized by debonding in the form of concrete cover separation, as well as by debonding at the epoxy-CFRP strips interface. The new concrete cover of high strength allowed for further utilization of the NSM material. The strengthened corroded beam subjected to 60% service load had no cut steel stirrups at the old concrete-patch interface, a lower extent of damaged concrete cover, and no steel yielding. The strengthened corroded beam subjected to 75% service load had already entered steel yielding and had extensively corroded and cut stirrups. Beam BC3-75NSM revealed significant load loss after NSM debonding, and at higher deflections, the load remained lower than that of the non-corroded beam.
- The structural performance of both retrofitted beams was as expected according to existing design recommendations or better up to CFRP NSM debonding. Patch repair and FRP strengthening can efficiently restore the capacity of corroded concrete beams. The residual bearing load after CFRP NSM debonding depends on the different localization of damages throughout loading in beams with different mass loss of steel (bars and stirrups) due to corrosion. Even in the case of tensile steel bars yielding, the proposed retrofit was successful. Yet, localization of damage and pitting corrosion should be thoroughly investigated in any case as it can significantly reduce the tensile deformability of steel. The current study may contribute to the identification of the characteristic serviceability limit state for corroded beams (under structural health monitoring) in order to undertake successful retrofit actions or replace them.
- The model by Reference [43] can provide a satisfactory indirect prediction of the steel mass loss at each corrosion phase based on the measured corrosion-induced crack width. The SLS loading cycles seem to further increase the mass loss of steel.
- Further elaborations should be focused on the crack development and potential steel–concrete bond loss at serviceability limit states due to steel corrosion.
Author Contributions
Funding
Conflicts of Interest
References
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Beams | BC1-60 | BC2-60 | BC3-60 | BC1-75 | BC2-75 | BC3-75 |
---|---|---|---|---|---|---|
δ (mm) | 5.53 | 6.16 | 7.5 | 6.79 | 9.04 | 11.47 |
Beams | At Concrete Cracking | At Steel Yielding | At Maximum Load | At Ultimate Load | ||||
---|---|---|---|---|---|---|---|---|
Pcr (kN) | δcr (mm) | Py (kN) | δy (mm) | Pmax (kN) | δPmax (mm) | Pu (kN) | δu (mm) | |
B1 | 45.4 | 1.1 | 243 | 10.9 | 248 | 19.9 | 205 | 69.4 |
BC1 | 62 | 1.4 | 218 | 8.8 | 231 | 23.2 | 225 | 70.8 |
BC3-60 NSM | 40.6 | 3.7 (1.1) 1 | 182 | 9.4 (6.8) | 256 | 20.4 (17.8) | 256 | 20.4 (17.8) |
BC3-75 NSM | 38.5 | 6.8 (1.0) | 201 | 13.5 (7.7) | 272 | 27.7 (21.9) | 272 | 27.7 (21.9) |
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Triantafyllou, G.; Rousakis, T.; Karabinis, A. Corroded RC Beams at Service Load before and after Patch Repair and Strengthening with NSM CFRP Strips. Buildings 2019, 9, 67. https://doi.org/10.3390/buildings9030067
Triantafyllou G, Rousakis T, Karabinis A. Corroded RC Beams at Service Load before and after Patch Repair and Strengthening with NSM CFRP Strips. Buildings. 2019; 9(3):67. https://doi.org/10.3390/buildings9030067
Chicago/Turabian StyleTriantafyllou, Garyfalia, Theodoros Rousakis, and Athanasios Karabinis. 2019. "Corroded RC Beams at Service Load before and after Patch Repair and Strengthening with NSM CFRP Strips" Buildings 9, no. 3: 67. https://doi.org/10.3390/buildings9030067