| The orthotropic steel deck(OSD)has been widely used in the bridge construction both at home and abroad with the advantages of lightweight,high bearing capacity,convenient construction and easy maintenance.However,it is a complex structure which has many welds.The welding residual stress and stress concentration are significant.Fatigue cracking may occur at the pronefatigue details under the repeated action of wheel loads.As a common material of the bridge deck pavement,the stiffness of the epoxy asphalt concrete decreases with the increase of temperature,which will lead to rapid increase of the stress of details on OSD and in turn reduce the fatigue life of the OSD.To study the effect of temperature on the fatigue performance of OSD,field tests and finite element analysis of the OSD related to temperature have been carried out from many aspects in this paper.The main works and conclusions are as follows:Temperature field measurements were carried out on the PK section steel box girder during the high temperature period in summer.The temperature distribution patterns of the deck plate,bottom slab and floorbeam were analyzed.The study shows that the temperature variation of the bottom slab is small and temperature variation of the deck plate is significant.But the transverse temperature difference of the deck plate and bottom slab is very small.There is an obvious vertical positive temperature gradient on the floorbeam,with the maximum temperature difference of 19℃ at 15:00.The most unfavorable positive temperature gradient model is proposed in the form of four-fold function.The thermal stress curves of the details on OSD under a closed lane in high temperature period was measured and the effect of temperature on the fatigue life of details was analyzed.The segmental model of steel box girder and OSD sub-model were established.The finite element analysis of temperature field of the box girder and thermal stress of the details were carried out.The study shows that the details exhibit obvious daily cyclic stress,among which the thermal stresses of RF-F and RF-R details are higher,followed by the cutout details,and the thermal stresses of RD and RF-W details are small and can be negligible.The maximum amplitude of thermal stress generated by each detail is less than the constant amplitude fatigue limit during high temperature period in summer,and the number of cycles is much fewer compared to that of the vehicles.As a result,the effect of sunlight temperature alone on the fatigue performance of OSD can be ignored.In order to study the coupling effect of sunlight temperature and vehicles on the fatigue performance of OSD,stress monitoring tests of details on OSD under random traffic were carried out in winter and summer,respectively.The stress characteristics and fatigue life of each detail on OSD in winter and summer were compared,and finite element models were also established to analyze the temperature sensitivity of different details.It was found that,in winter,the stress of the details increased significantly from 9:00 to 14:00,and then gradually decreased.But this trend was not obvious in summer.In addition,the equivalent stress amplitude and equivalent loading times of the details in summer are larger than those in winter,and the RD details are especially significant.For the RD details,the fatigue life calculated based on winter data is more than 100 years,but the lowest fatigue life calculated based on summer data is 19.2 years.Considering the data both in winter and summer,the shortest fatigue life of RD details is 39.1 years.Even in summer,the maximum stress amplitude of RF and cutout details is less than their respective fatigue constant amplitude limit,and the fatigue life is infinite.Finite element analysis shows that full internal bulkheads are the local reinforcement of the OSD,which can decrease the stress at the RF-W and cutout details and improve their fatigue performance.Parametric analysis of the pavement temperature shows that the stress amplitude of each detail increases with the increase of pavement temperature,among which the RD detail is the most obvious.The stress amplitude of the RD-D detail increases by 261.5%when the pavement temperature reaches 70℃ compared with that at 0℃.In order to reasonably reflect the effect of pavement temperature during one year on the fatigue performance of details on OSD under random traffic,the BP neural network method was used to train a network model between the ambient temperature,time and the equivalent stress amplitude,equivalent loading times of each detail.According to the ambient temperature collected in the bridge health monitoring system during one year,the equivalent stress amplitude and loading times at different times of the year can be predicted,and finally the fatigue life of OSD considering the annual temperature effect can be calculated.The study shows that the equivalent stress amplitude and loading times of RD details have strong correlation with the ambient temperature.The fatigue life of RD details is 51.7 years.The fatigue life of RF and cutout details is more than 100 years.RD double-side welded joint was studied based on a truck controlled loading test and refined finite element analysis.The research shows that for RD double-sided welded joints,the maximum stress amplitude at the RD-D and RDR detail of the out weld is greater than that of inner weld,so the fatigue resistance of the inner weld will be better than that of outer weld.Compared with RD single side welded joint,the RD double-sided welded joint reduces the stress amplitude of the RD detail by 10%,and changes the most unfavorable position of the RD detail.But the RD double-sided welded joint has no effect on the fatigue performance of RF and cutout details.The stress amplitude of RD double-sided welded joint also increased significantly with the increase of pavement temperature.When the temperature rises from 0℃ to 50℃,the stress amplitude of the RD-D detail increases by 1.35 times,which is lower than that of RD single-sided welded joint by 1.76 times. |
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