A strengthening theory to prevent fatigue crack initiation in old metallic bridges

Analytical solutions were developed to determine the fatigue resistance of metallic members retrofitted by bonded carbon fiber-reinforced polymer (CFRP) laminates. Different fatigue failure criteria based on the constant life diagram (CLD) approach were introduced to predict the strengthening properties that would prevent fatigue cracks in metallic members. The use of normal modulus (NM), high modulus (IIM) and ultra-high modulus (UHM) CFRP laminates with different pre-stress levels was considered in the modeling. To validate the model, a series of fatigue experiments were performed on four steel beams strengthened with bonded NM, HM and UHM CFRP laminates. The results have shown that there are two main mechanisms that can transition the detail from a risky finite-life regime to a safe infinite-life regime. In particular, UHM laminates have been shown to be effective to prevent fatigue crack initiation in steel members. In this paper bonded CFRP laminates were used for strengthening, however, the method can be applied for other retrofit elements such as un-bonded laminates, bolted steel plates and pre-stressed steel tendons.