Abstract:A consolidating method of “shell plate” aiming at the existing right-angle mutational steel crane beam is proposed， where a “shell type” steel plate with an arc is welded on both sides of the web at the variable section of the crane beam for fatigue reinforcement. The stress level of fatigue detail is reduced by increasing the stiffness of the web in variable section areas， thus improving its fatigue strength. In this paper， the fatigue performance of a right-angle mutational steel crane beam reinforced with “shell plate” is studied through a scaled fatigue test， the fatigue failure law of the crane beam reinforced with “shell plate” is analyzed， while the fatigue performance of the reinforced crane beam is evaluated. Meanwhile， taking the principal stress of the most dangerous fatigue detail of the reinforced crane beam as the basic parameter， the Sr，p-N fatigue curves of the reinforced crane beam are given. Moreover， the correctness of crack propagation simulation and fatigue life calculation of the crane beam after reinforcement is verified by the experimental results， and the fatigue crack propagation characteristics of the crane beam damage details after the “shell plate” reinforcement are further analyzed. The influence of the variation in thickness and height of the “shell plate” on the reinforcement effect is studied， which provides the reference for the crane beam reinforcement design.

Abstract:In order to reveal the influence law of the stud spacing on the behavior of steel-UHPC lightweight composite deck structures, variable amplitude fatigue tests were accomplished for three LWCD beam specimens and the stud spacing was chosen as the core parameter in the tests (i.e., 100 mm, 150 mm, 300 mm). In the fatigue tests, the influence of the stud spacing on the fatigue performance of the LWCD was revealed and the combined tension-shear fatigue properties of the steel deck plate at stud root positions were obtained. In the residual capacity test after the fatigue tests, the influence of stud spacing on the cracking evolution mechanism in UHPC and on the residual capacity of the specimens was captured. The fatigue tests indicated that when the stud spacing was 300 mm, the unit-load induced slips at the steel-UHPC interface were much higher than those in the other two specimens, but the slips did not increase significantly during the fatigue testing process. When the stud spacing was 100 mm or 150 mm, the strain at the bottom flange of the U rib did not exhibit significant change, and the strains increased slightly when the stud spacing was 300 mm. On the basis of the calculation method prescribed in the code of “Specifications for Design and Construction of Highway Steel-concrete Composite Bridge” in China, the combined tension-shear fatigue state of the steel deck plate at stud root positions was analyzed, and the results implied that this method could provide conservative results. In addition, the residual capacity test after the fatigue testing showed that the smaller the stud spacing, the smaller the interfacial slip and the higher the residual flexural capacity. On the basis of the elastic-to-plastic theory and plastic theory, the residual capacities of the specimens were predicted. It was revealed that although the specimens experienced a series of fatigue loading, the actual residual capacities obtained in the tests were still higher than the predicted values, and the plastic theory exhibits a better agreement relative to the test results.

Abstract:To study the fatigue properties of HRB500 reinforcing bar in longitudinal connected slab track on bridge, fatigue tests under symmetric axial alternating tension-compression cyclic loads for standard specimens of HRB500 reinforcing bar were conducted, and then the fatigue life and its cumulative failure probability of standard HRB500 reinforcing bar at different stress levels were obtained. On this basis, the correlation coefficient p and Theils inequality coefficient u were used as indexes of estimation accuracy to evaluate three methods which are widely used to estimate parameters of three-parameter Weibull distribution. And the grey prediction method, whose prediction accuracy is the highest among the three methods, was used to estimate the parameters of three-parameter Weibull distribution for the fatigue life of standard HRB500 reinforcing bar, and the distribution functions for the fatigue life of HRB500 reinforcing bar at different stress levels were obtained. Ultimately, the probabilistic S-N curve of HRB500 reinforcing bar in the longitudinal connected slab track on bridge with reliable index of 4.2 based on Kohout-Vêchet equation in the full stress range was established. The research can provide experimental basis for the establishment of fatigue life prediction model of HRB500 reinforcing bar in the longitudinal connected slab track on bridge under combined loads during service life.

Abstract:The mean stress correction model of random-amplitude fatigue stress spectrum and cumulative damage model for HRB500 reinforcing bar used in longitudinally connected ballastless track on bridge in service life under combined loads were studied to provide the support for the establishment of fatigue life prediction model for above mentioned HRB500 reinforcing bar.Through the constant-amplitude fatigue tests on standard specimens of HRB500 reinforcing bar，the influence law of mean stress on fatigue life of HRB500 reinforcing bar was studied，and the applicability of mean stress correction models of random-amplitude fatigue stress spectrum commonly used in practical engineering to HRB500 reinforcing bar was studied.Through the three-level variable-amplitude fatigue tests on standard specimens of HRB500 reinforcing bar，the applicability of Miner’s rule to the calculation of cumulative damage of the HRB500 reinforcing bar was analyzed.The research results show that the fatigue life of standard specimens of HRB500 reinforcing bar decreases with the increase of mean stress，Goodman model widely used in practical engineering is applicable to the mean stress correction of HRB500 reinforcing bar under random-amplitude loading，and Miner’s rule is suitable to calculate the cumulative damage of HRB500 reinforcing bar used in longitudinally connected ballastless track on bridge in service life under combined loads.

Abstract:The fatigue properties of RPC (Reactive Powder Concrete) with different steel fiber ratios of 0%, 1.5% and 3% in volume were investigated with the uniaxial compressive fatigue test.The results showed that the splitting failure mode appeared for pure RPC specimens without steel fiber, but the shear failure mode occurred for those specimens with steel fiber of 1.5% or 3% in volume.The fatigue life and strength increased with the increase of steel fiber ratio; the macroscopic damage, ε-n/Nf curves and the evolution of the fatigue deformation modulus of tested RPC experienced three stages.With the increase of steel fiber ratio, the first and third stages of ε-n/Nf curves lengthened，and the fatigue deformation modulus significantly increased with the increase of the steel fiber ratio corresponding to the same n/Nf.It is suggested that the ratio of fatigue deformation modulus to the initial elastic modulus should be 0.7 and 0.75 for the RPC with a steel fiber ratio of 1.5% and 3%, respectively.