Shear Performance of Reinforced Concrete Beams Subjected to Premature Loading and the Effectiveness of CFRP Strengthening
Reinforced concrete elements might be loaded at early ages for many reasons such as early formwork removal or uncontrolled loading scenarios. This research investigates the shear behavior of reinforced concrete (RC) beams subjected to loading prior to attaining the recommended design 28th day’s strength and whether strengthening using Carbon Fibre Reinforced Polymer (CFRP) can partially or totally restore the lost capacity. Four groups consisted of Twenty-Seven RC beams have been cast, loaded at age of 7 days to different levels and then tested until failure at 28 days. All testing have been performed under the “Four-Point loading” setup. Three beam samples of the first group (the control group (G1-7)) have been tested until failure at age of 7 days to determine the ultimate strength of beams at this age. The remaining three samples of the control group (G1-28) were tested at age of 28 days to determine the strength of beams at this age and to estimate the strength gain between the ages of 7 and 28 days. The second to fourth groups have been loaded at age of 7 days up to 25, 50, and 75% of their nominal shear capacity at that age, respectively. All of these loading levels exceeded the experimental and theoretical cracking load of the beams. Half of the beam samples of these groups (G2-28, G3-28 and G4-28) have been tested again until failure at 28 days to determine the effect of premature loading on the shear capacity. The other half of the samples (G2-28CFRP, G3-28CFRP and G4-28CFRP) have been externally strengthened using CFRP sheets at age of 7 days and retested at age of 28 days to determine whether strengthening can restore the lost capacity due to the premature loading. Test results indicated that premature loading of RC beams at age of 7 days and up to 75% of the nominal capacity has negatively affected the shear capacity of beams at 28 days where the capacity has been dropped by about 30% for all loaded beams. At 100% premature loading, the shear capacity of loaded beams has been totally lost at 28 days. CFRP strengthening resulted in restoring the lost shear capacity by about 92%, even for the case of 100% premature loading.