It is desirable to allow yield of the steel at ultimate, but this is only possible if premature failure of the adhesive joint can be prevented, for example, by additional mechanical restraints ( Sen et al., 2001). The modular ratio of FRP to steel is lower than for FRP to cast iron consequently a large amount of strengthening is required to significantly affect a structure's elastic response. A high modular FRP-to-metal ratio remains beneficial, but it may be possible to use a less expensive, lower modulus FRP strengthening material.įRP strengthening has also been used to increase the flexural strength of steel beams, for which different constraints govern the use of FRP strengthening: Failure of cast iron is governed by the tensile strength of brittle cast iron, making a high modular ratio strengthening material particularly beneficial.Īs discussed below, a ductile steel member can be allowed to yield. Preformed UHM plates are available with Young's modulus E = 360 GPa ( Cadei et al., 2004), giving a modular ratio to cast iron of around 4. UHM (ultra-high modulus) CFRP strengthening has the highest axial modulus and is consequently often most economic for strengthening metallic structures. Thicker plates are more expensive to fabricate and install. Whilst a thicker plate of a lower modulus FRP might be used, this increases the peel stresses within the adhesive (see below). STRATFORD, in Strengthening and Rehabilitation of Civil Infrastructures Using Fibre-Reinforced Polymer (FRP) Composites, 2008 Maximising the FRP to metal modular ratioĪ higher FRP-to-metal modular ratio allows the FRP to develop greater stress when the composite section is loaded, and results in a more efficient strengthened section.
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