The performance of urban bridges will deteriorate gradually throughout service life. Bridge deterioration prediction is essential for bridge management, especially for maintenance planning and decision-making. By considering the time-dependent reliability in the bridge deterioration process, a Weibull distribution based semi-Markov process model for urban bridge deterioration prediction was proposed in this paper. Historical inspection records stored in the Bridge Manage System (BMS) database in Shanghai since 2004 were investigated. The Weibull distribution was used to characterize the bridge deterioration behavior within each condition rating (CR), and the semi-Markov process was used to calculate the bridge transition probabilities between adjacent CRs. After that, the service life expectancy of urban bridges, the transition probabilities of the deck system and the substructure, and the future CR proportion change caused by deterioration was predicted. The prediction results indicate that the life expectancy of concrete beam bridges is about 77 years. The decay rate of the deck system is the fastest among three major parts, and the substructure has a much longer life expectancy. It suggests that the overall prediction accuracy of the semi-Markov model in network-level is better than the regression analysis method. Furthermore, the proportion of bridges in intact condition will gradually decrease in the next few decades, while the percentage of bridges in the qualified and bad state will increase rapidly. The prediction results show a good agreement with the actual deterioration trend of the urban bridges in Shanghai. In order to alleviate the pressure of bridge maintenance in the future, it is necessary to adopt a more targeted preventive maintenance strategy.

Highlights The problems of high resistance to seed sucking and the poor stability of seed sucking were solved. A mechanical model was established for seeds in a seed stirring device. The optimum parameters of the seed stirring device were obtained. Seeding precision was improved, providing a reference for the seed sucking process. Abstract. To achieve a goal of precision seeding with 1 to 3 seeds per hill and to solve problems in a pneumatic rice seed metering device, including high resistance to seed sucking, poor stability of seed suction, and low seeding precision, a cylindrical seed stirring device was designed. The design was based on the characteristics of the rice seed flow in the seed suction area. A mechanical model of the rice seed in the seed stirring device was established. The relationships between the seed fluidity and the parameters of the seed stirring device were simulated with EDEM software. The effects of seed fluidity on the seed suction area were analyzed under different seed stirring device parameters. To analyze the influences of different parameters of the seed stirring device on seed stirring and to observe the relationships between different parameters and rice seeds, high-speed photography was used to observe the seed sucking and stirring processes. The super hybrid rice Y-2 You 900 was selected as the test material. The seeding precision was tested at different rotating speeds, negative pressures, and parameters of the seed stirring device. The test results showed that an increase in the diameter and thickness of the seed stirring device was beneficial for increasing the seed absorption rate and reducing the missed seed rate but also increased the rate of multiple-seed sucking and reduced the seeding precision. The optimal parameters of the seed stirring device were a cylinder thickness of 2 mm and a diameter of 5 mm. This study provides a certain reference basis for the seed suction process of a pneumatic seed metering device. Keywords: Agricultural machinery, Precision seeding, Rice sowing, Seed stirring device, Seeder.

This paper investigates the degradation law and calculation method for the load-carrying capacity of steel–concrete composite girders under fire exposure based on numerical analysis and mathematical statistics. A finite element model of simply supported box-section steel–concrete composite girders is established using ABAQUS, which is validated against existing scaled test data in terms of temperature field distribution, load-carrying capacity, and mid-span displacement. On this basis, the parametric effects of concrete slab thickness, steel web height, steel plate thickness, and concrete strength on the load-carrying capacity of the girders are systematically analyzed. The results indicate that concrete slab thickness, steel web height, and steel plate thickness exert significant influences on the structural bearing capacity, whereas concrete strength has a negligible effect. Specifically, the load-carrying capacity under fire exposure is substantially improved with the increase in concrete slab thickness, steel web height, and steel plate thickness. Furthermore, a simplified calculation formula for the capacity of box-section steel–concrete composite girders under fire exposure is developed via multiple linear regression analysis, incorporating the three dominant influencing factors of concrete slab thickness, steel web height and steel plate thickness. The proposed formula exhibits satisfactory calculation accuracy and can provide a reliable reference for the fire resistance design and repair decision-making of steel–concrete composite girders.

Pavement roughness is an important performance indicator for urban roads. Existing roughness evaluation methods are adapted from the highway system, which do not consider the pavement partial unevenness of urban roads such as manhole covers or repair patches. Significant differences can easily be found between the actual driving experience and roughness evaluation results. A survey investigated 428 urban roads in central Shanghai was launched, and the results show that manhole covers account for the largest amount of pavement partial unevenness types. By using the original pavement elevation data measured from the laser roughness meter, characteristics of manhole covers are analyzed and the critical thresholds (i.e., 4 mm) are also calculated. The automatic identification, location, and classification of manhole covers in the pavement vertical profile is realized on this basis. Ultimately, an IRI correction formula considering manhole covers is proposed, while a new roughness evaluation method is also established to evaluate the influence of manhole covers.

Moving beyond traditional reactive maintenance decisions, this study explores a preventive maintenance strategy for highway bridges by integrating long-term durability forecasting. This need is addressed by analyzing two decades of historical inspection data from China. Visual condition records were sourced from a management system covering 2854 bridges, while durability parameters were obtained through 31 field tests on 23 bridges. This research introduces an instantaneous carbonation coefficient, which quantifies the carbonation rate specific to each discrete condition rating. The analysis reveals a 700% surge in the carbonation rate for poor condition states relative to intact ones, significantly higher than the 300% increase projected by traditional averaged models. Under the premise that maintenance can restore a bridge’s condition by one rating grade, three maintenance strategies are evaluated. Results indicate that initiating preventive interventions at a qualified condition can reduce long-term maintenance frequency by about 20%, offering a practical, condition-informed framework for optimizing maintenance planning and resource allocation.