Zhongzhao Guo

Under cyclic moving load action, tensile-dominant structures are prone to crack initiation due to cumulative damage effects. The presence of cracks leads to structural stiffness degradation and nonlinear redistribution of dynamic characteristics, thereby compromising str18uctural integrity and service performance. The current research on the dynamic behavior of cracked structures predominantly focuses on transient analysis through high-fidelity finite element models. However, the existing methodologies encounter two critical limitations: computational inefficiency and a trade-off between model fidelity and practicality. Thus, this study presents an innovative analytical framework to investigate the dynamic response of cracked simply supported beams subjected to moving loads. The proposed methodology conceptualizes the cracked beam as a system composed of multiple interconnected sub-beams, each governed by the Euler–Bernoulli beam theory. At crack locations, massless rotational springs are employed to accurately capture the local flexibility induced by these defects. The transfer matrix method is utilized to derive explicit eigenfunctions for the cracked beam system, thereby facilitating the formulation of coupled vehicle–bridge vibration equations through modal superposition. Subsequently, dynamic response analysis is conducted using the Runge–Kutta numerical integration scheme. Extensive numerical simulations reveal the influence of critical parameters—particularly crack depth and location—on the coupled dynamic behavior of the structure subjected to moving loads. The results indicate that at a constant speed, neither crack depth nor position alters the shape of the beam’s vibration curve. The maximum deflection of beams with a 30% crack in the middle span increases by 14.96% compared to those without cracks. Furthermore, crack migration toward the mid-span results in increased mid-span displacement without changing vibration curve topology. For a constant crack depth ratio (γ_i = 0.3), the progressive migration of the crack position from 0.05 L to 0.5 L leads to a 26.4% increase in the mid-span displacement (from 5.3 mm to 6.7 mm). These findings highlight the efficacy of the proposed method in capturing the complex interactions between moving loads and cracked concrete structures, offering valuable insights for structural health monitoring and assessment.

This paper systematically performed fatigue crack propagation (FCP) tests to investigate the corrosion fatigue crack propagation (CFCP) behavior of HRB400 steel bar. The fatigue loading scheme involved the constant amplitude loading and stepwise decreasing amplitude loading. The load ratio, the ratio of the minimum load to the maximum load, was designed as 0.1, 0.2, 0.3, 0.5, and 0.7. The test environments included air, pure water, 3.5% NaCl solution, and an electrolytic erosive environment. The FCP rate and threshold stress intensity under the test conditions were obtained and compared. An empirical model for predicting the CFCP rate was proposed, where the influences of load ratio and environment type were incorporated. The proposed model was validated using the test results. The results showed that the CFCP behavior of the rebar showed the feature of true corrosion fatigue. Increasing the environmental erosion level and load ratio increased the FCP rate and decreased the threshold stress intensity, indicating that the steel bar’s resistance to fatigue crack growth decreased. The predictions of the proposed model agreed well with the test data. This paper provided experimental and theoretical references for the corrosion fatigue life prediction of concrete structures.

Shear strength is a widely investigated parameter for reinforced concrete structures. The corrosion of reinforcement results in shear strength reduction. Corrosion has become one of the main deterioration factors in reinforced concrete beam. This paper proposes a shear strength model for beams with inclined bars based on a limit equilibrium method. The proposed model can be applied to both corroded and uncorroded reinforced concrete beams. Besides the tensile strength of longitudinal steel bars, the shear capacity provided by the concrete on the top of the diagonal crack, the tensile force of the shear steel at the diagonal crack, the degradation of the cross-sectional area and strength of the reinforcements induced by corrosion are all considered. An experimental work on two groups accelerated corroded beams was performed. Good agreements were found between the proposed theoretical predictions and experimental observations.

This paper investigates the effects of stress ratio and microstructure on the fatigue crack growth (FCG) behavior of HRB400 steel bars widely used in concrete bridges. A constant stress–controlled FCG test with different stress ratios is performed on compact tension specimens. Test specimens are machined from rebar in two directions, i.e., cracks propagate in the radial and axial directions of the steel bar. The FCG rate versus stress intensity factor range under different stress ratios and different crack orientations are obtained. The morphology of the fracture surface and the FCG path are examined by scanning electron microscope and optical microscopy. Following this, the FCG curves, fracture characteristics, and FCG paths are compared. The experimental results show that the radial and axial crack predominantly present the transgranular and intergranular fracture mode, respectively. The material presents a higher resistance to FCG in radial orientation than that in axial direction.

Pitting corrosion is one of the most common forms of localized corrosion. Corrosion pit results in a stress concentration and fatigue cracks usually initiate and propagate from these corrosion pits. Aging structures may fracture when the fatigue crack reaches a critical size. This paper experimentally simulates the effects of pitting morphologies on the static and fatigue behavior of steel bars. Four artificial notch shapes are considered: radial ellipse, axial ellipse, triangle and length-variable triangle. Each shape notch includes six sizes to simulate a variety of pitting corrosion morphologies. The stress-strain curves of steel bars with different notch shape and depth are obtained based on static tensile testing, and the stress concentration coefficients for various conditions are determined. It was determined that the triangular notch has the highest stress concentration coefficient, followed by length-variable triangle, radial ellipse and axial ellipse shaped notches. Subsequently, the effects of notch depth and notch aspect ratios on the fatigue life under three stress levels are investigated by fatigue testing, and the equations for stress range-fatigue life-notch depth are obtained. Several conclusions are drawn based on the proposed study. The established relationships provide an experimental reference for evaluating the fatigue life of concrete bridges.