Studies on urban shrinkage in eastern China lack relevant contributions. This study investigates population dynamics in Jiangsu Province, focusing on county-level cities to understand the factors influencing urban population size. It developed a multidimensional indicator system per 2014, 2017, 2020, and 2023 statistical data, incorporating road network accessibility, socio-economic levels, resident income, public services, and the built environment. Employing static fixed effects models and dynamic panel regression models, it analyses trends and evolutionary patterns of permanent population changes. The findings indicate an overall increase in the permanent population over the past decade, although the growth rate has slowed in the last five years. Notably, there is a significant spatial clustering of population growth and contraction, often aligned with high-speed transportation corridors. Unlike existing research findings, the urban shrinkage pattern in Jiangsu Province is unique. Some cities in northern Jiangsu exhibit a ‘relative contraction’ pattern, where population decline coexists with high economic growth and spatial expansion. Key short-term factors influencing population size include the city’s economic level and residents’ disposable income, while long-term factors encompass city level, industrial structure, and transportation networks. Small towns exhibit ‘close-range mobility’, with primary short-term influences stemming from residents’ income, public service quality, and intercity transportation accessibility. Indeed, long-term factors primarily reflect economic development quality and urban employment rates.

This study theoretically and numerically examines the differences in shear performance between tapered and prismatic girder configurations with corrugated steel webs (CSWs) and investigates the influence of the Resal effect on the shear performance of tapered girders with CSWs. The vertical components of the inclined bottom slab forces (which are zero in prismatic cases) may decrease or increase the effective shear force on the CSWs, reflecting the positive and negative influences of the Resal effect. Based on these influences, this study introduces the concepts of positive and negative Resal effects and proposes an improved shear method to predict the effective shear forces acting on tapered CSWs. The results of the theoretical and finite element (FE) analyses show that the traditional shear method, which assumes CSWs bear all the shear force, is not applicable to tapered girders. The improved shear method significantly reduced the error in predicting shear forces within the CSWs, decreasing the maximum error from 42.25% (traditional method) to 7.71% (improved method) in specific sections. Quantitative analyses of three different types of girders with CSWs indicate that the Resal effect is influenced by both the internal forces and the structural form of the box girder. In cases of a positive Resal effect, the inclined bottom slab shares a considerable portion of the shear force with CSWs, resulting in a surplus shear capacity in the CSWs; conversely, under a negative Resal effect, there is an increase in the effective shear force on the web, which could lead to an overestimation of the shear buckling strength of CSWs. These findings highlight the necessity of incorporating Resal effects for accurate shear force predictions in tapered girders. By accurately predicting shear forces, engineers can enhance the performance and reliability of these structures, avoiding both overestimation and underestimation of shear capacities.