Abstract
Most research on fatigue strengthening of steel has focused on carbon fiber-reinforced polymer (CFRP) strengthening of steel members with existing cracks. However, in many practical cases, aging steel members do not yet have existing cracks but rather are nearing the end of their designed fatigue life. Therefore, there is a need to develop a “proactive” retrofit solution that can prevent fatigue crack initiation in aging bridge members. Such a proactive retrofit approach can be applied to bridge members that have been identified to be deficient, based on structural standards, to enhance their safety margins by extending the design service life. This paper explains a proactive retrofit design approach based on constant life diagram (CLD) methodology. The CLD approach is a method that can take into account the combined effect of alternating and mean stress magnitudes to predict the high-cycle fatigue life of a material. To validate the retrofit model, a series of new fatigue tests on steel I-beams retrofitted by the non-prestressed un-bonded CFRP plates have been conducted. Furthermore, this paper attempts to provide a better understanding of the behavior of un-bonded retrofit (UR) and bonded retrofit (BR) systems. Retrofitting the steel beams using the UR system took less than half of the time that was needed for strengthening with the BR system. The results show that the non-prestressed un-bonded ultra-high modulus (UHM) CFRP plates can be effective in preventing fatigue crack initiation in steel members.
Highlights
The results show that the non-prestressed un-bonded ultra-high modulus (UHM) Carbon fiber-reinforced polymer (CFRP) plates can be effective in preventing fatigue crack initiation in steel members
The first method takes advantage of the compressive force achieved from the pre-stressed CFRP plate, In this paper, two retrofit techniques for steel members subjected to cyclic loads were discussed
Strengthening the steel beams using the un-bonded CFRP plates took less than half the time
Summary
Carbon fiber-reinforced polymer (CFRP) has great potential to enhance steel structures in terms of increased strength, ductility, energy absorption and fatigue life [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20]. Tavakkolizadeh and Saadatmanesh [18] investigated the performance of notched steel beams retrofitted with CFRP patches under medium cycle fatigue loading. Rizkalla et al [14] conducted fatigue tests on CFRP-strengthened steel-concrete composite beams The test results for a four-point bending test scheme with a cyclic loading frequency between 5 and 10 Hz showed that the CFRP patch extended the fatigue life more than threefold.
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