| In recent years,steel structure has developed widely in the field of industrial building structure in China,and steel crane beams are particularly prominent.Many steel crane beam structures suffered early damage before their design service lifes due to long-term repeated loads on steel crane beams.In order to ensure the safety of operation,the steel crane beam structure with fatigue cracks needs to be reinforced to increase its service life.Compared with the traditional reinforcement method,which have disadvantages such as increased self-weight and produced new defects,such fatigue reinforcement with carbon fiber reinforced plastic(CFRP)has obvious advantages,but there is no corresponding standard specification for steel crane beam reinforced with CFRP now.Therefore,based on fatigue test,theoretical analysis and numerical simulation,this paper carries out the reinforcement effect,S-N curve,action mechanism and influence factors of CFRP reinforced steel crane beam and its whole process analysis of the life cycle of CFRP antifatigue strengthened steel crane girder.is carried out in this paper.The main work and research results are as follows:(1)Based on the research status of steel crane beams strengthened with CFRP,five steel crane beams strengthened with CFRP were used to carry out fatigue tests under different stress amplitudes.A crack propagation observation method combining beach marking method and eddy current detection technology was proposed.Meanwhile,the S-N curve of steel crane beam reinforced with CFRP and the S-N curve with 95% lower confidence limit are obtained based on the fatigue life obtained from the test.(2)A "three-dimensional entity-cohesion-continuous shell" contact model has been established by ABAQUS software to carry out numerical simulation analyze on the crane beam specimens reinforced with CFRP during this test and comapre and analyze the stress amplitude at the weld toe of the lower end of the mid-span stiffener of the steel crane beam before and after CFRP reinforcement.It is found that CFRP reinforcement can effectively reduce the stress concentration at the lower end of stiffener and improve the fatigue performance of steel crane beam by reducing stress amplitude and inhibiting crack propagation;the stress intensity factor of each steel beam has the same change rule before and after reinforcement,i.e.,it gradually increases in the initial crack propagation,it drops sharply due to the constraint of the lower flange plate when the crack enters the lower flange plate,and it increases rapidly due to the increase of local stress amplitude after the crack completely enters the lower flange.(3)The action mechanism of steel crane beam reinforced with CFRP is analyzed,based on which,the influence of the layers and elastic modulus of CFRP and the elastic modulus and thickness of rubber layer on the stress amplitude in crack initiation stage and the stress intensity factor in crack propagation stage are studied.It is found that in crack initiation stage,the stress amplitude of steel crane beam decreases linearly with the layers and elastic modulus of CFRP and increases linearly with the thickness and the elastic modulus of rubber layer,and the larger the stress amplitude is,the greater the influence of factors;in crack propagation stage,the stress intensity factor is negatively correlated with the layers and elastic modulus of CFRP and the rubber layer while positively correlated with rubber layer thickness,and the degree of reinforcement influence decreases gradually with the increase of various influencing factors.(4)For the steel crane beam reinforced with CFRP,its whole life cycle is carried out,and its remaining life assessment method and guiding suggestions as well as concrete construction technology and related structural measures are proposed.Besides,the common nondestructive testing technology and the rapid removal method of CFRP without damage to the original structure during the operation period of steel crane beams strengthened with CFRP are summarized. |
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