Strengthening prestressed concrete with prestressed CFRP

This paper presents the effect of unevenly prestressed carbon-fibre-reinforced polymer (CFRP) sheets used for strengthening a prestressed concrete beam (L = 3·6 m). An integrated anchor system, consisting of steel brackets and anchor plates, is used to prestress the sheets. To predict the behaviour of the CFRP sheet during a prestressing operation, a three-dimensional finite-element analysis model is built. The model includes the reinforced concrete element, structural solid element and elastic shell element to represent the concrete, anchorage and CFRP sheet respectively. The model shows good agreement with test data, including a maximum error of less than 5%. Stress concentrations in the CFRP sheet are predicted near the tip of the anchor plates. Uneven prestressing effects are observed across the CFRP sheet because of the anchor geometry and uneven bonding of the sheet in the laboratory. These effects cause uneven rupture of the sheet when the strengthened beam is flexurally loaded to failure. To avoid such a failure mode, care should be exercised when the strengthening system is prepared with adequate anchorage.