Experimental Test And Finite Element Analysis Of Fatigue Performance Of Steel-thin UHPC Lightweight Composite Deck Structure

In order to address two typical problems of conventional orthotropic steel deck(OSD)systems,i.e.,fatigue cracking of OSD and damage of asphalt overlay,Prof.Xudong Shao at Hunan University proposed the steel-thin UHPC lightweight composite deck(LWCD)structure,in which short headed studs are used at the steel-UHPC interface.The research team at Hunan University accomplished plenty of pioneer researches for the LWCD.However,the fatigue properties and mechanism are still under investigations.On the one hand,currently the stud spacing for headed studs in the LWCD is generally 150 mm and the influence of stud spacing on the fatigue damage evolution mechanism and residual capacity of the LWCD under flexural loads is unclear.On the other hand,the steel plate at negative moment zones under local vehicle loads is in tension and the short headed studs should resist shear stress,resulting in a complex tension-shear coupled stress state at the stud root position of the steel plate,and the fatigue properties at this position also needs to clarify.Thus,this paper presents a series of fatigue tests and finite element(FE)analysis with concentrations on the above two aspects.The details are as follows:(1)Flexural fatigue tests were performed on three LWCD strip specimens to reveal the influence of stud spacing on the fatigue damage evolution properties of LWCD.The stud spacing was 100 mm,150 mm,and 300 mm for the three specimens,respectively,and the tests were implemented via variable amplitude fatigue loads.The test results indicate the following observations.The thin UHPC layer exhibited excellent anti-cracking performances.By taking the specimen with a stud spacing of 300 mm as an example,the thin UHPC layer did not develop cracks after experiencing 20 million cycles of loading under a tensile stress range of 4.4 MPa.The maximum cracking width raised to 0.02 mm after a consequent cyclic loading of 10 million cycles under a tensile stress range of 8.8 MPa,and after a subsequent fatigue loading of 2 million cycles under a tensile stress range of 13.2 MPa,the maximum crack width was only 0.06 mm.Further,when the stud spacing was 100 mm and 150 mm,the specimens did not exhibit significant change of deflection during the fatigue test,while for the specimen with a stud spacing of 300 mm,the deflection increased rapidly.In addition,when the stud spacing was 300 mm,the unit-load induced slips at the steel-UHPC interface was much higher than that in the remaining two specimens,while the slips did not increased significantly during the whole fatigue testing processes.(2)Residual flexural capacity tests were carried for the two specimens that did not failed during the fatigue tests,and the two specimens have stud spacings of 150 mm and 300 mm,respectively.The test results show that the smaller the stud spacing,the higher the residual bending capacity,and the smaller the ultimate slip at the steel-UHPC interface.On the basis of the elastic-to-plastic theory and plastic theory,two methods were proposed to calculate the residual flexural capacity of LWCD.Comparisons show that the actual capacities of the specimens were higher than the predicted capacities,showing that although the specimens experienced fatigue damage,the residual capacity would not be reduced significantly.Specifically,the test results are32%～54% and 15%～35% higher than the theoretical results predicted from the elastic-to-plastic theory and plastic theory,respectively,indicating that the calculation method basing on the elastic-to-plastic theory is more conservative and the method basing on the plastic theory has higher agreement.(3)On the basis of the Miner linear fatigue damage principle,the stresses in the aforementioned fatigue tests were converted into equivalent stress ranges under 2 million loading cycles.The results were compared to the fatigue strength calculation equations in the design code of《Specifications for Design and Construction of Highway Steel-concrete Composite Bridge》.It was revealed that although the equivalent fatigue stresses in the tests exceeded the fatigue strength in the design code,no fatigue damage developed in the steel deck plate at the stud root positions,indicating that the calculation method in the design code for conventional steel-concrete composite bridges should be applicable for LWCD.A local FE model was established basing on the Dong Lake Bridge on the Hangzhou-to-Ruili national expressway.According to the analysis results,for headed studs with high shear stresses,the corresponding tensile stress in the steel plate at the stud root position is also high,and this implies that the tension-shear coupled fatigue effect at the stud root position of the steel plate should not be neglected.Further,the maximum values of tension-shear coupled fatigue effect in the transverse and longitudinal directions for the steel plate were 0.85 and 0.70,respectively,implying that the transverse direction is more unfavorable.However,both the values of the tension-shear coupled effect along the longitudinal and transverse directions could meet the design requirement(≤1.3).(4)A series of parametric analysis was performed to reveal the influence of stud spacing,stud diameter,and thickness of steel plate on the tension-shear coupled fatigue effect of the steel plate.The analysis results show that the coupled effect increased with the increasing of stud spacing and stud diameter or decreasing of thickness of steek plate.Among the three parameters,the influence of stud spacing is most significant.When the stud spacing was 100 mm or 150 mm,the peak values of the coupled effect are 0.51～0.85,and when the stud spacing was 300 mm,the corresponding peak values are 1.08～1.24,nearly equaling the limit value of the design code(1.3).Thus,the stud spacing in the LWCD should not be too large.