| Orthotropic steel bridge deck is one of the main structural forms of modern steel bridge deck,which is widely used in large-span bridges.Due to the local stress concentration effect and welding defects,orthotropic steel bridge decks,under fatigue alternating load,fatigue damage or even damage may occur under working conditions where the working stress is lower or even lower than the static strength.The normal work and safety performance of the system pose a serious threat.The existing fatigue performance research methods still have the following problems to be further studied:(1)There is a large gap in the fatigue life calculation results of different calculation methods and these methods cannot be unified;(2)The influencing factors of the optimization design method of weld details have not been targeted;(3)Theoretical studies and experimental calculations are mostly based on the uniaxial effect,which cannot truly simulate the multiaxial stress state of actual projects;(4)There is no perfect fatigue performance optimization design scheme.This paper focuses on the topic of research and optimization of the U-rib fatigue performance of the orthotropic steel bridge deck top plate.Through theoretical calculation,numerical simulation,and integrated analysis of existing test data,the notched stress range is used to evaluate the orthotropic steel bridge.With regard to the parameters of fatigue life and fatigue performance of the panel,a series of research work on the fatigue performance and optimal design of the weld details of the orthotropic steel bridge deck under uniaxial and multiaxial effects have been carried out,and the following main research results have been achieved:1.Combine the test data results to analyze the applicability and limitations of the nominal stress method,hot spot stress method and notch stress method to evaluate the fatigue life,and propose modeling parameters suitable for the notch stress method.The finite element model was established and compared with the test data results of the existing orthotropic steel bridge deck 3U specimens of the research group.Under different plate thicknesses,different weld detail sizes,and different working condition combinations,the nominal stress method,hot spot stress method,and notch stress method are used to calculate the fatigue life of the component,which can be found by comparing with the test results : The key factor to study the fatigue problem of orthotropic steel bridge deck is whether it can accurately restore the stress concentration level at the weld detail.When using the nominal stress method for life prediction,the load and weld details must be consistent with the S-N curve data corresponding to the working conditions and structure.If there is no S-N curve corresponding to the details concerned,the test must be conducted before use to obtain the applicable S-N curve,the workload is more complicated;the hot spot stress method can not accurately simulate the stress concentration at the root of the weld,so that the fatigue problem originating from the weld root cannot be calculated;the notch stress method can solve the problems of the above-mentioned nominal stress method and hot spot stress method.The problem,however,when using the notch stress method to calculate the fatigue life of the details of the longitudinal ribs of the roof plate of orthotropic steel bridge decks,the notch modeling method needs to be further verified.This paper combines a large number of orthotropic steel bridge deck fatigue test data to explore the modeling and use of the notch stress method in the orthotropic steel bridge deck,and finally obtains the notch form and the radius value,this modelling method can more accurately predict the fatigue life of the U-rib detail of the orthotropic steel bridge deck top plate than the modelling method specified in the specification.2.Based on the notch stress method,the fatigue performance optimization scheme of orthotropic steel bridge deck is discussed,and the influencing factors of the optimization performance are analyzed.Through comparison,we can find that the optimization effect of fatigue performance under the double-sided welding structure is better than that of the other two structures.To further investigate the effect of detail size on the fatigue performance in the double-sided welding structure,it is found that the fatigue performance that is different from the existing research conclusions increases with the increase of the length of the top plate welding legs,when the length of the top plate welding legs increases At this time,the stress of the welding toe at the top plate will decrease,and the stress of the welding toe at the U rib will increase.When the length increases to a certain extent,the U rib welding toe will replace the welding toe of the roof plate as a location of fatigue cracking,and cause an increase in fatigue damage stress.In the same way,the increase in the length of the U-rib welding foot will also cause the corresponding fatigue failure stress change and the location of the failure.Therefore,the optimal size of the double-sided welding seam details is not as long as possible within the scope of the construction requirements,but should be analyzed in conjunction with the working conditions.3.Analyze the influence of the multi-axis effect on the fatigue life calculation results.A multi-scale model of orthotropic steel bridge deck was established to analyze and calculate the multi-axis fatigue life under proportional loading in actual engineering.The results of fatigue life calculated by considering the uniaxial effect and the multi-axis effect were compared.The stress level is very low compared to the normal stress level,but the reduced fatigue life will reach 10% to 15%,so a multi-axis analysis of the fatigue performance of orthotropic steel bridge decks is necessary.4.Propose an optimized design scheme of weld details based on notch stress method under multi-axis analysis.An orthotropic steel bridge deck multi-scale model was established,and the multi-axis effect was considered,and the two-sided welding of the orthotropic steel bridge deck was optimized.Based on the cumulative fatigue damage model,the damage variable per unit time is introduced as a measure to evaluate the fatigue performance of weld detail.First select the optional detail size according to the construction requirements,calculate the maximum unit time damage variable in each weld detail of the weld size details of different sizes under the given working condition combination,so that the maximum unit time damage variable takes the smallest size This is the optimal size.Through calculation and analysis,it can be found that the fatigue life increased by the optimization method proposed in this paper is more than 10%compared with the existing theory.The research work and results of this paper can provide references and suggestions for the fatigue performance study of the U-rib detail of the orthotropic steel bridge deck roof and the design and optimization of the double-sided welding structure. |
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