Abstract
Steel bridges are extremely damaged by fatigue subjected to cycling load. Therefore, it is often necessary to put forward effective reinforcement to strengthen steel structures during the daily maintenance. In this study, two repairing methods of high-strength bolts and high-modulus CFRP strips on the basis of stop-hole repair method were introduced, respectively, to investigate fatigue improvement of cracked steel plates. First of all, numerical analysis was conducted to predict the repair efficiency and investigate the optimal parameters of each method. Variables studied were stop-hole diameter, pretightening force of bolt, and size of CFRP patch. Subsequently, a total of 12 specimens were tested to study the repairing efficiency of cracked steel plates with various strengthening methods through cyclic loading. At the same time, the failure mode and fatigue life were analyzed to present the improvement of fatigue performance. In addition, the experimental results were compared against the S-N curves of this strengthened fatigue detail. The outcomes of this study revealed that an improvement in the influence of fatigue-crack repair with the adoption of these two strengthening methods was evident. Numerical results showed that the addition of these materials could significantly diminish stress concentration factor around hole edge and improve their fatigue performance in comparison with only stop-hole method. Fatigue test results indicated that the crack initiation life of specimens repaired by stop-hole method was more than 20 times that of the unrepaired specimens. The high-strength bolt reinforced stop hole and CFRP patched stop hole can extend the crack initiation life by 9 and 8 times, respectively, in contrast to control specimens with sole stop-hole method. Finally, it was demonstrated that repairing damaged steel plates with stop-hole method alone was not enough to satisfy the fatigue strength requirements of various countries. But the fatigue strength category of damaged steel plates after further repairing with high-strength bolts and high-elastic-modulus CFRP, respectively, was higher than category A of AASHTO.
Highlights
A number of steel bridges built in earlier ages are still in existence and in service
In order to reduce the damage of fatigue cracks, it is of great significance to conduct fatigue strengthening in order to eliminate fatigue cracks or retard further crack propagation in addition to early preventive maintenance. e traditional repairing methods of steel structures include stop-hole method, rewelding, and new plate attachment/replacement, while these methods might not be feasible in all cases
The stop-hole method, as a temporary or emergency treatment, can effectively repair fatigue cracks caused by stress concentration at the tip of cracks and extend the fatigue life of cracked structural components [2,3,4]
Summary
A number of steel bridges built in earlier ages are still in existence and in service. Carbon fiber reinforced polymers (CFRP), recognized as an advanced composite material, possess excellent mechanical properties, such as high strength-to-weight ratio, good antifatigue performance, and convenience of installation. Because of those excellent properties, the method using CFRP for retrofitting aging metallic structures is a research hotspot developed in recent years [15, 16]. The stress variation of 12 mm thick cracked steel plates affected by the key repair parameters was analyzed by finite element method On this basis, a series of experimental tests were conducted to determine the fatigue enhancement with various strengthening method through cyclic loading. The test values of repaired groups were compared against the fatigue strength curves
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