Millions of in-service concrete bridges around the world are exceeding their design life. Corrosion may lead to a sudden fracture of prestressing steels, and understanding the fatigue behavior of corroded prestressed concrete (PC) bridges is essential. Accordingly, an effective fatigue analytical model for corroded PC beams is needed. In this study, an experimental investigation of the fatigue behavior of corroded PC beams, was carried out. Thirteen PC beams had experienced acceleration corrosion before high-cycle fatigue testing. All beams failed due to fatigue fracture of the corroded tensile steel bars, and three-dimensional laser scanning results indicated that the fracture occurred at the minimum cross sections with a severe corrosion pit. A segmented linear analytical model to evaluate fatigue response and predict fatigue life was developed which considers fatigue irrecoverable plastic strain of concrete, stress concentration, and longitudinal variation in the cross-sectional areas of corroded steel bars. There is an acceptable agreement between the numerical and experimental results of corroded PC beams. The proposed model can reasonably predict the evolution of strains in concrete, corroded prestressing steel, and rebars in PC beams under high-cycle fatigue loading, thereby allowing fatigue life prediction. Further analysis studied the influence of degree of corrosion in prestressing wires/rebars, stress concentration and longitudinal variation in cross-sectional areas of corroded steel bars, load ranges, and partial prestressing ratios (PPRs). It was found that, to reasonably estimate the fatigue life of corroded PC beams, the influence of stress concentration must be considered with the proposed impact factor. A higher corrosion degree, load range, or PPR shortens the fatigue life of corroded PC beams. 

Assessment of Fatigue Life for Corroded Prestressed Concrete Beams Subjected to High-Cycle Fatigue Loading

Failure mechanical behaviors and prevention methods of shaft lining in China

Loess is a common soil layer of geological movement. It has macropores, vertical joints, and tubular pores and also low strength and strong water sensitivity. When building a tunnel in a weak loess stratum (Q3 loess or Q4 loess), the poor geological characteristics of loess usually bring great difficulties to the construction of tunnel invert, and it is very easy to cause subsidence at the tunnel base, uneven subsidence at the tunnel bottom, and cracks in the road and lining. The use of jet-grouting piles to strengthen the weak loess foundation is an effective method to improve the geological characteristics of loess. To investigate the effect of jet-grouting piles on the reinforcement of the tunnel foundation in weak loess areas, centrifugal model tests were used to analyze the subsidence and structural mechanics response characteristics of the tunnel base under the influence of jet-grouting pile length and pile diameter. Research shows that subsidence at the tunnel bottom can be reduced effectively and the adjustment time of the surrounding rock stress can be shorten significantly when using jet-grouting piles to reinforce the tunnel foundation. The length of the jet-grouting pile is better than the diameter in improving the strength of the foundation. However, with the improvement in the strength of jet-grouting piles, the efficiency of foundation reinforcement is reduced, the surrounding rock pressure and lining stress gradually increase, and the construction economy and structural safety are gradually reduced. When selecting parameters of jet-grouting pile, consideration should be given to safety, economy, and ease of construction. 

Effects of Jet-Grouting Piles on Loess Tunnel Foundation with Centrifugal Model Tests

Experimental study on the collapse evolution law of unlined tunnel in Boulder-Cobble mixed formation

Tunnel distress occurs often. Tunnel leakage, segment dislocation, and section deformation seriously affect tunnel construction safety and normal operation. Currently, mainly the traditional monitoring technology is used in tunnel distress monitoring. This kind of technology has the problems of low monitoring efficiency, slow speed, inaccurate measuring points, and so on. With the development of science and technology, three-dimensional laser scanning monitoring technology (3D LSMT) has fast acquisition speed, a comprehensive monitoring range, and high acquisition accuracy. This review collected the world’s more advanced monitoring technologies, such as optical fiber sensing technology (OFST), photogrammetry (PT), and so on. Firstly, these technologies were introduced and compared with 3D LSMT. Then the theoretical basis of 3D LSMT was analyzed. Three-dimensional LSMT uses the captured high-density point cloud to extract the tunnel structure information and realizes the rapid processing of point cloud data through automated software. Finally, the use of 3D LSMT for segment dislocation, tunnel deformation, and seepage water was discussed and analyzed further to understand the status of 3D LSMT in tunnel monitoring and provide a reference for tunnel distress monitoring. 

Xuguang Kong

Papers

Local buckling characteristic of hollow π-type steel-concrete composite support in hilly-gully region of loess tunnel

Failure mechanical behaviors and prevention methods of shaft lining in China