How is the durability of steel bridges assessed?

2025-03-27 14:46:45

Inside the steel box girders of the Hong Kong-Zhuhai-Macao Bridge, nano-sensors are monitoring the aging rate of the coating in real time; along the Qinghai-Tibet Railway, autonomous inspection robots are capturing the crack expansion signals along the steel trusses; at the mouth of the Yangtze River, the digital twin system predicts the corrosion process of the Steel Structure under the salt spray environment. These scenes reveal that the durability assessment of steel bridges has entered the era of multi-dimensional and full-cycle intelligent diagnosis.

I. Research on degradation mechanism of material performance

The durability decay of steel bridges presents multi-factor coupling characteristics. The tracking data of steel box girders of a cross-sea bridge show that the fatigue life of Q345qD steel is shortened by 38% under the joint action of chloride ions, humidity and heat cycles and traffic loads. The “environment-stress” biaxial accelerated corrosion model established by a research institute has successfully reproduced the typical damage pattern of steel bridge connectors in the salty soil area in the west, and the prediction error is controlled within 5%.

Breakthrough in microscopic damage detection technology. When analyzing the welds of a Yangtze River Bridge, transmission electron microscope (TEM) found that sulfur agglomeration at the grain boundaries led to a 300% increase in stress corrosion susceptibility. Synchrotron X-ray imaging technology can detect hydrogen-caused cracks at 0.1μm level, providing direct evidence for assessing the risk of delayed fracture in high-strength steel bridges.

Second, the quantitative assessment system of environmental erosion

Atmospheric erosion grade zoning refinement management. The corrosion atlas constructed based on data from 352 monitoring stations across the country shows that the average annual corrosion rate of steel bridges along the southeast coast reaches 0.12mm, which is six times higher than that in the dry northwestern region. A coastal bridge project using micro-environmental monitoring devices, found that the bridge deck system of steel components of salt spray deposition is 8 times the amount of abutment parts, to guide the design of anti-corrosion targeted strengthening.

Water environment erosion dynamic modeling technology innovation. The fluid-structure coupling model established for a river-crossing bridge shows that when the water flow rate reaches 3m/s during flood season, the scour corrosion rate of the steel pile foundation is raised to 4.2 times of that in the dry season. In the Pearl River Estuary bridge project, the chlorine ion permeation prediction model based on machine learning improved the corrosion risk warning accuracy of concrete-encased steel columns to 92%.

Third, intelligent monitoring technology cluster application

Distributed fiber optic sensing network to achieve full coverage. The 6,000 strain monitoring points deployed in a cable-stayed bridge successfully captured the abnormal vibration signals of steel box girders during a typhoon. The resolution of its demodulator reaches 1με, which can recognize the deformation difference of 0.01mm level. In the freeze-thaw cycle region of Northeast China, the FBG sensor array of a steel bridge accurately monitors the process of bolt preload decay due to temperature stress.

Life Prediction and Repair Technology

The remaining life prediction model based on big data is getting mature. A provincial bridge management platform integrates 100,000 sets of inspection data, and the neural network model constructed narrows the fatigue life prediction error of steel beams from ±25% to ±8%. In the maintenance decision-making of Humen Second Bridge, the maintenance program guided by the model reduces the whole life cycle cost by 35%.

Self-healing protection technology opens a new era. A research team developed a microencapsulated self-repairing coating that releases repair agents and restores 92% of the corrosion protection performance when cracks in steel bridge decks expand. Shape memory alloy reinforcement technology was applied in the repair of a bridge in Chongqing, restoring the geometry of deformed components through thermal activation, and increasing the repair efficiency by three times.