An Assessment of Reinforced Concrete Members in Tension Strengthened with Near Surface Mounted CFRP Strips

The strengthening of structural elements by bonding Near Surface Mounted (NSM) Fibre Reinforced Polymer (FRP) strips and bars with epoxy resin into grooves cut in the concrete cover is an emerging technique which has recently... [ view full abstract ]

The strengthening of structural elements by bonding Near Surface Mounted (NSM) Fibre Reinforced Polymer (FRP) strips and bars with epoxy resin into grooves cut in the concrete cover is an emerging technique which has recently attracted world-wide interest. FRP materials are well suited for applications in strengthening owing to their favourable properties such as their high stiffness and strength. However, existing knowledge on the technique is limited and this is reflected by the absence of relevant design guidance in existing international codes. In this regard there is a need for further research into the area. The experimental programme developed for this study involved the design and testing of six reinforced concrete beams in flexure that were strengthened using the NSM technique. The test-beams were taken to failure under two monotonically increasing point loads. The section of the beam under the neutral axis, located between the two point loads was considered to be in tension. Three different sizes of Carbon Fibre Reinforced Polymer (CFRP) strip measuring 10 x 3mm; 15 x 2.5mm and 20 x 2.5mm were used for strengthening. Enhancement ratios of 2.3 times the moment capacity of an un-strengthened member were recorded for the study. The results further indicate that a doubly-strengthened beam offers approximately one third extra capacity over a member which is strengthened using a single CFRP strip of similar dimensions. The 3D nonlinear finite element (FE) model developed from the experimental data can accurately simulate the structural behavioural responses of a CFRP-strengthened reinforced concrete member in flexure, under applied loading. It is concluded that strengthening reinforced concrete members with NSM CFRP strips significantly enhances the tensile and flexural capacities of the structural element.