Study On Fatigue Behavior Of SMA-CFRP Composite Strengthened Deged Cracked Steel Plate

Orthotropic steel bridge is widely used in long-span bridges at home and abroad;the U-rib and diaphragm are prone to produce slender fatigue cracks at different angles,leading to structural failure The number of fatigue cracks at this position accounts for a large proportion of the total number of bridges,there are many inconveniences in existing reinforcement methods.Thus,using SMA-CFRP to reinforce cracks can give full play to the advantages of the two materials and obtain an excellent reinforcement effect,Refer to the size of cracks at u-rib and diaphragm in actual engineering,only the in-plane tensile stress is considered,the static load and fatigue tests of steel plates with 0° and 30° unilateral crack reinforced with SMA-CFRP composite were carried out to compare and analyze the effects of CFRP,SMA and SMA-CFRP composite reinforcement on specimens.The main research contents and conclusions are as follows.(1)The tensile strength tests of single-side cracked steel plates with different reinforcement methods were carried out.The results show that the bearing capacity of specimens with 0°unilateral crack is increased by each reinforcement method more than that of specimens with30° unilateral crack,The yield load,ultimate load and failure displacement of specimens enhanced by SMA-CFRP composite reinforcement are greater than the sum of single reinforcement effects,The yield load,ultimate load and failure displacement of the composite specimen with 0° crack were increased by 100.55%,26.36% and 121.94%,respectively,and the composite specimen with 30° crack was increased by 89.77%,20.57% and 109.88%,respectively;Compared with the specimens with 0° crack,the composite reinforced specimens with 30° crack showed a higher sum of lifting ratio and showed a better synergistic lifting effect of SMA-CFRP.The sum of yield load and ultimate load of the composite reinforced specimens with 0° crack increased by 1.13 times and 1.04 times compared with the single reinforced specimens.For specimens with 30° crack,the ratio is 1.49 times and 1.40 times.(2)Fatigue tests on single-side cracked steel plates with different reinforcement methods show that the specimens with 30° crack have longer fatigue life and better fatigue performance than those with 0° crack.The fatigue life improvement ratio of specimens reinforced with SMA-CFRP is higher than the sum of single reinforcement of SMA and CFRP.The effect of SMA-CFRP on fatigue life improvement is more significant in specimens with 30° crack.(3)SMA-CFRP composite reinforcement can not only inhibit the crack initiation extension,improve impact fatigue crack opening and constraint of crack tip stress field under load fatigue stress amplitude and can reduce the crack,under the collaborative work with SMA with CFRP,further reduce crack propagation rate,increase the stability of crack extension area of the specimen length,reduce the specimen stiffness degradation rate.The mechanical properties of specimens under static and fatigue loads are improved better than that of single reinforcement method.