State-of-the-art review on FRP strengthened steel structures
Introduction
A large number of steel structures, such as bridges, offshore platforms, large mining equipment and buildings, need retrofitting. The conventional method of repairing or strengthening steel structures is to cut out and replace plating, or to attach external steel plates. These plates are usually bulky, heavy, difficult to fix and prone to corrosion and fatigue [48]. There is a need to look for alternatives. The use of FRP (Fibre Reinforced Polymer) appears to be an excellent solution [16], [51], [3].
FRP has high strength to weight ratios, and excellent resistance to corrosion and environmental degradation. It is very flexible and forms all kinds of shapes, and is easy to handle during construction [2], [28], [50]. FRP has been widely used in strengthening concrete structures, and extensive research has already been conducted (e.g. [50], [30], [29], [35], [38], [33]). Recent experience in the USA [48], [49], [26], [20], [36], [6], [27], the UK [17], [31], [5], [24] Japan [46] and Switzerland [4] showed that there is a great potential for CFRP to be used in the retrofitting of steel structures. However, many issues need to be resolved before this advanced material can be fully utilised to provide confident retrofitting of existing structures.
Hollaway and Cadei [17] wrote an excellent state-of-the-art review article on “Progress in the Technique of Upgrading Metallic Structures with Advanced Polymer Composites”. It had in-depth coverage on the following aspects:
- (1)
In-service problems associated with advanced polymer composite and metallic adherents
- (2)
Adhesive bonding in terms of surface preparation and durability
- (3)
Durability of FRP composites in the civil environment
- (4)
Prestressing FRP plates before bonding to metallic beams
- (5)
Field applications.
- (1)
Retrofit of steel girders
- (2)
Fatigue life improvement
- (3)
Surface preparation and other means to avoid debonding
- (4)
Durability of steel members retrofitted with FRP
- (5)
Field applications.
- (1)
Materials (metallic materials including cast iron and wrought iron, and FRP strengthening materials)
- (2)
Conceptual design
- (3)
Structural behaviour and analysis, especially I-sections with FRP
- (4)
Design detailing to reduce the stress concentration at the end of a plate
- (5)
Installation and quality control
- (6)
Operation (inspection and maintenance, owners’ responsibilities).
Section snippets
Bond test method
Different bond testing methods were adopted by various researchers for different purposes of study, as shown in Fig. 1. They can be categorised into four types:
- Type 1:
Loading is indirectly applied to the FRP and the steel plate in a beam (see Fig. 1(a))
- Type 2:
Loading is directly applied to the steel element without any gap (see Fig. 1(b))
- Type 3:
Loading is directly applied to the steel element with a gap (see Fig. 1(c))
- Type 4:
Loading is directly applied to the FRP (see Fig. 1(d)).
The Type 1
Compression members
Local buckling may occur in steel hollow sections in compression if the width-to-thickness ratio is larger than a certain value (e.g. [54]). It is also well known that interaction of local buckling and overall buckling occurs in steel hollow section columns (e.g. [56]). Tests were conducted by [40] to strengthen short and long steel hollow section columns using CFRP sheets. The major parameters varied in the testing program include the number of CFRP layers and the fibres’ orientation
Fatigue crack propagation in FRP–steel system
The improvement of the fatigue life of existing structures (e.g. steel girder bridges and tubular signboard columns) due to FRP strengthening has been well documented in the literature [5], [42]. This section reviews the recent research on the influence of fatigue loading on bond strength and crack propagation behaviour in CFRP–steel composite system.
Matta [25] and Liu et al. [21] conducted tests to understand the influence of fatigue loading on the bond between steel and CFRP. CFRP plate was
Conclusions
This paper has provided a review of current research on FRP strengthened steel structures. It complements the existing review documents of [17], [42] and [5] by focusing on the following areas that have received only small coverage, but which have developed rapidly: the bond between steel and FRP, the strengthening of steel hollow section members, and fatigue crack propagation in the FRP–Steel system. Future research topics have been identified as: the bond–slip relationship, the stability of
Acknowledgements
This paper was prepared during the first author’s sabbatical leave at The Hong Kong Polytechnic University. The authors are grateful to Professor Jin-Guang Teng for his many discussions and for his comments on drafts of the paper. The authors are grateful to Prof. Len Hollaway for his discussions on some of the topics presented in this paper. Thanks are given to Mr. Mark Ayers (a former student at Monash University) for his assistance in collecting and summarising some of the references
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