Impact of loading protocol on the repair efficiency of heat-damaged concrete beams with SNSM CFRP ropes

The influence of static-load distribution and symmetry on the flexural performance of reinforced concrete beams, strengthened/repaired using side near-surface-mounted (SNSM) carbon fiber reinforced polymer (CFRP) ropes with parabolic and straight profiles is investigated. For this, eighteen reinforced concrete beams (150 × 250 × 1600 mm) were fabricated using a ready-mix concrete of 35 MPa strength grade before cured in wet burlap for 28 days. Nine beams were exposed to an elevated temperature at 450 °C for three hours, while the remaining ones were left in laboratory air, as controls. Six specimens from each group were retrofitted using SNSM of straight and parabolic profiles then tested with references ones under four- and six-point symmetrical and six-point asymmetrical loadings with load response versus deflection and strain in SNSM ropes acquired. Furthermore, cracking initiation and propagation leading to failure was monitored and reported. Generally, the study revealed that the mechanical performance of the concrete beams was influenced by the loading regime as well as by the rope profile (straight, parabolic) as well as heat-damage. The performance factor (PF), computed based on strength and deformability performances, varied from 5.4 to 7.9 for strengthened compared to 10.9–16.3 for repaired and heat-damaged specimens. Furthermore, all strengthened/repaired beams failed by concrete-cover separation following the sudden rupture of the SNSM CFRP ropes except for that repaired with a straight profile of SNSM CFRP rope and subjected to asymmetrical loading.