PCR en tiempo real 1. Transcripción reversa

Regarding all FRP structures, so much effort has been made to explore the use of this type of structures. In comparison with the common FRP composites (e.g. FRP sheet and bars), FRP profiles have some specific advantages, such as ease of installation, tailorability of the cross-section and higher flexural behaviour, which are beneficial for developing a time-saving and efficient construction in civil engineering. The most typical all FRP structure is FRP composite bridge, as such this section reviews the development of the FRP composite bridges in the world as well as the most significant issue for all FRP structures in practical application, namely the connection of the FRP profiles.

2.4.1.1 FRP composite bridge

A bridge is the most typical all FRP structure and the first pedestrian FRP bridge in the world was built in Israel in 1975 [46]. Since then, more FRP bridges have been built in North American, Asia, and Europe. For example, the first cable-stayed,

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GFRP deck and pylons bridge was erected at Aberfeldy, Scotland in 1992. This bridge joined two regions of the Aberfeldy golf course and crossed the river Tay. The self-weight of the structure was significantly reduced by using the GFRP profiles, as such no heavy machinery was used when assembling the bridges. The durability performance of this bridge was found to be satisfactory after 16 years [47].

Halgavor suspension bridge, which is one of the longest curved composite structures in Europe, has a 47 m span over the A30 road near Cornwall, England. This bridge was built in July 2001 and was designed for pedestrians, cyclists, and horses. All the components of the bridge were connected with bonded structural joints. The FRP deck had a 4 meter width and was manufactured by using resin infusion with vinyl-ester resin and an ultraviolet resistant gel-coat. The tailorability of the FRP profiles was demonstrated in the project, which is contributed to the easy installation during the construction process.

More constructions regarding FRP composite bridges can be found in other literature, for example, Hollaway [48] presented a review of FRP composites for civil infrastructure applications; Keller has developed a detailed review of all-composite bridges and buildings from 1997-2000 [9]. Based on this review, it is noted that the

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use of all FRP structures is only limited within the small bridges for pedestrians. Regarding using all FRP structures in large bridges, there are still a lot of technical issues to be addressed.

2.4.1.2 Connection of FRP profiles

Although FRP profiles as a type of building material have the distinctive advantages such as high strength-to-weight ratio and tailorability, there are still some difficulties when using the FRP profiles in all FRP structures, for example, the design of FRP joints and connections. A reasonable design of the joints and connections is significant to ensure a good structural performance. Some design standards have been established for steel structures, thus guiding the setup of the bolts or welding points between the different components. Due to the similarity between the steel structures and FRP structures, some designs of FRP joints and connections are copied from steel design practice. However, the intrinsic characteristics of the FRP profiles are apparently different from steel structures, thus requiring a different theory to guide the design of FRP joints and connections.

The influence of geometry has been investigated in several studies [49-53], and the variables involved the ratio of width-to-hole diameter (w/d0), the ratio of end

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results show that when the ratio of end distance-to-hole diameter (e1/d0) was more

than 1.5, which had little effect on the failure strength. With the increment of the ratio of width-to-hole diameter (w/d0), the corresponding ultimate connection

resistance was increased. The coupons cut from different direction of FRP profiles present different ultimate connection resistance, and the larger resistance was found for the coupons extracted from the longitudinal direction.

The fastener parameters were also experimentally investigated [54], and the main parameter involved was the material of the fastener. The preliminary conclusions of this study show that the failure modes and the ultimate load were determined by the mechanical properties of the FRP profiles if the strength of the fastener was stronger than that of the FRP plate. If the fastener was weaker than the FRP plate, the failure modes and the ultimate load were governed by the fastener with little damage to the FRP plates. Similarly, the influence of the angle between applied tension and pultrusion direction, as well as the influence of lateral restraint and the joints with angles have been discussed [10, 55].

Based on the above-mentioned literature review, it could be found that considerable studies have been conducted regarding the connections and joints of FRP profiles. Nevertheless, there is currently no quantitative guidance for the design of

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beam-to-column joints, and the mimicry of bare steel joint configurations is not totally appropriate for the FRP profiles joints due to the orthotropic properties of FRP. Therefore, more investigations are required regarding the connection of FRP profiles in future studies to implement the application of the FRP profiles in civil engineering.