Research On Fatigue Analysis Methods Applied For Typical Welds Of Orthotropic Steel Deck

Nowadays,the orthotropic steel bridge decks are widely used in large and medium span bridges at home and abroad.However,Fatigue cracks more or less were founded in some bridges.Undoubtfully,the cracks shorten the service life of the bridges.However,there are few methods to accurately evaluate the fatigue of welded joints.When using nominal stress method to evaluate fatigue life,it is difficult to get accurate S-N curve,So the discreteness of results will be very large.When using hot-spot stress method,the results varied largely because of different element size.This article applied these methods to analyze the weled joints in orthotropic steel bridge deck.(including hot spot stress method,zero stress method,the effective notch stress method,the stress intensity factor method,the strain energy density method,etc.).Some key points of the method when being applied to the bridge deck are explained,and some improvements are provided.Therefore,the parameters for evaluating the weld fatigue can be selected.Finally,parametric analysis was conducted to improve the cost performance.Main work contents are as follows:(1)According to the standard fatigue vehicle load mentioned in the specification,make the preliminary finite element calculation.So,the stress concentration of weld toe and weld root in Rib-to-deck area,in transverse diaphragm incision area and Rib-to-Floorbeam welding toe can be obtained.(2)The stress integral method can be used to replace the nodal force method in the deck area.A detailed analysis was also made on the element size-insensitive problem when using the stress integral method.The fatigue problem of weld throat was also analyzed.(3)The zero-point stress method and 1mm stress method were also analyzed.The stability of 1mm is also verified.when this method is used in orthotropic steel bridge decks.(4)In the direction of deck thickness,according to the theory of stress analysis and calculation,the stress distribution can be accurately expressed.Furthermore,the notch stress intensity factor K will be calculated to verify whether there exists a stable relationship within a certain range.(5)The current mainstream methods of considering the notch effect were analyzed in this article.Firstly,the fatigue life curve of the weld toe and weld root of the bridge deck will be discussed when using the stress intensity factor method.Secondly,the peak stress method was used in Abaqus to verify can this method be used in orthotropic steel bridge.Finally,analysis whether there exists a relationship between the effective notch stress method and other methods.This relationship may let stress intensity factor method,fictious notch round method and strain energy density method build a relationship by the numerical value.(6)By response surface analysis of the design parameters,the optimization value of the traditional orthotropic bridge deck can be obtained in consideration of fatigue performance and economic benefits.