Regaining Structural Performance of Thermally Damaged Beams Using NSM CFRP Strips: A NLFE Study

A non-linear finite-element model was developed to evaluate the flexural behavior of concrete beams, heat-damaged by exposure to elevated temperatures (300-600 degrees C) before being repaired using different configurations of near surface-mounted carbon-fiber-reinforced polymer strips. The model was validated using reliable experimental data before being employed for predicting flexural performance of heat-damaged beams, cast originally using normal, weight concrete of varying strength grades (25-55 MPa), then repaired with different numbers, spacings, locations (at soffit and on sides) and extension lengths (100-450 mm) of the composite strips. The repaired and heat-damaged concrete beams performed significantly better when being originally cast with a higher strength class of concrete. The results indicate that using a higher number of strips is more beneficial for intact beams and those heat-damaged at intermediate temperatures of 300 and 400 degrees C with residual ranges for load capacity of (111-121), (108-128) and (126-148) % for the cases of 1, 2 and 3 strips, respectively. It was asserted that inserting two composite strips at a groove spacing less than 50 mm undermined the benefit from repair, especially for heat-damaged beams. The study accentuated the advantages of inserting the composite strips on the sides of the beams instead of their soffits, as well as extending these strips towards the end supports, especially in heat-damaged beams.