Design for FRP-Based Structural Strengthening: How Safe Is Safe Enough?
FRP-based structural strengthening has emerged as a popular approach for rehabilitating the distressed and underperforming concrete structures. Design of FRP-based structural strengthening systems involves an interesting interplay of uncertainties between those inherent in the existing structure being strengthened and those arising from the lack of complete knowledge and time testimony of using FRP composites for structural strengthening. The safety formats prescribed by most strengthening design standards remain largely cloned from that used for the design of new concrete structures, with a set of safety factors which are significantly higher (up to 2–3 times) than the conventional norm in design of concrete structures. These higher safety factors are proposed to account for the additional uncertainties associated with FRP composites. However, FRP composites in general, and their use as externally bonded reinforcement for strengthening in particular, involve substantially peculiar characteristics compared to reinforced concrete (RC). Therefore, the design processes for strength (for new RC structures) and additional strength (for strengthening existing RC structures) have conflicting design requirements and objectives. Under these conditions, a blind extension of the conventional safety format to design for FRP-based structural strengthening will not only fall short in providing the required safety margins, but could also instigate negative implications and undesirable side effects under some design scenarios. This paper highlights important sources of conservatism in strengthening design arising from the design treatments of uncertainties and mechanics of FRP, and their implications on the course and quality of strengthening design solutions and that on their resultant safety contents are discussed.
KeywordsFRP Strengthening Design conflicts Concrete ACI440 TR55
- 1.Maruyama K, Ueda T (2001) JSCE recommendations for upgrading of concrete structures with use of continuous fibre sheets. In: Teng J-G (eds) FRP composites in constructionGoogle Scholar
- 2.Nanni A (2001) North American guidelines for concrete reinforcement and strengthening using FRP composites. In: Teng J-G (eds) FRP composites in constructionGoogle Scholar
- 3.Darby A et al (2007) Gaps in current knowledge for FRP strengthening of RC structures. In: Proceedings of advanced composites in construction, Bath, UK (2007)Google Scholar
- 5.ACI440-2R (2008) Guide for the design and construction of externally bonded FRP systems for strengthening concrete structures. American Concrete Institute, (2008)Google Scholar
- 6.TR55 (2004) Design guidance for strengthening concrete structures using fibre composites materials. Concrete Society, UKGoogle Scholar
- 7.TR55 (2012) Design guidance for strengthening concrete structures using fibre composites materials. Concrete Society, UKGoogle Scholar
- 8.fib14 (2001) Externally bonded FRP reinforcement for RC structures. International federation of structural concrete (fib), SwitzerlandGoogle Scholar
- 9.HKG (2010) Guide for the strengthening of concrete structures using FRP composites. Hong Kong Polytechnic University, Hong KongGoogle Scholar
- 11.Kansara K, Ibell T, Darby A, Evernden M (2016) Limitations of the safety formats used in design of FRP-based structural strengthening systems. In: Forde M (eds) Proceedings of structural faults and repairs, (2016)Google Scholar
- 12.Kansara K (2012) Assessment of conservativeness in design of FRP-based structural strengthening systems. Ph.D. Thesis, University of Bath (2012)Google Scholar