Influence of concrete differential aging time on the construction phases analysis of the Fenghua River Bridge

The Fenghua River Bridge is a major structure on the highway between Hengzhang and Guojiachi, which is to be built with a four-span prestress concrete (PC) box girder and symmetrical cantilever castings. In this paper, a finite element method (FEM) model is set up to study the effects of concrete differential aging time on the construction phases of the Fenghua River Bridge by calculating the vertical displacement of the folding segment of the middle span and the longitudinal bending moment of Pier 12#. In the model, the girders are classified into 150 changing sections based on the desgn scheme, and their construction is to be carried in 16 phases respectively to build 12 blocks connected by a side folding segment and a middle folding segment, covered with a second dead load and in completion for 20 years. It is found that the internal forces and deformations of the concrete structures at the aging time of 60 d are quite different from those of 0 d aging time while the behaviors of the structures of 120 d aging time is nearly the same as those of 60 d aging time― the differences are so small that can be neglected, suggesting that the creep develops obviously about one month after the cement is hardened and the development fades later on.

Research development of digital maintenance and management system for long-span cable-stayed bridges

Digital cable-stayed bridge maintenance and management system （DCBMS） was developed for the need of maintenance and management of long-span cable-stayed bridges. In this paper, the major functions and theoretical application of eight modules were systematically stated with the background of Harbin Songhua River cable-stayed bridge, which include data management module, inspection and measurement module, assessment module, finite dement analysis module, disease diagnosis and prediction module, maintenance module, query module and help module. By analyzing and calculating the data from manual inspection database, basic database and health monitoring subsystem, DCBMS can accomplish the functions like life prediction, disease diagnosis, comprehensive assessment, maintenance and management of bridges. Therefore, the maintenance and management of long-span cable-stayed bridges can be made digital, professional and scientific. By running this system, a real-time and specific technical guidance can be provided for the maintainers and managers of long- span cable-stayed bridges.

Powell's optimal identification of material constants of thin-walled box girders based on Fibonacci series search method

A dynamic Bayesian error function of material constants of the structure is developed for thin-walled curve box girders. Combined with the automatic search scheme with an optimal step length for the one-dimensional Fibonacci series, Powell＇s optimization theory is used to perform the stochastic identification of material constants of the thin-walled curve box. Then, the steps in the parameter identification are presented. Powell＇s identification procedure for material constants of the thin-walled curve box is compiled, in which the mechanical analysis of the thin-walled curve box is completed based on the finite curve strip element （FCSE） method. Some classical examples show that Powell＇s identification is numerically stable and convergent, indicating that the present method and the compiled procedure are correct and reliable. During the parameter iterative processes, Powell＇s theory is irrelevant with the calculation of the FCSE partial differentiation, which proves the high computation efficiency of the studied methods. The stochastic performances of the system parameters and responses axe simultaneously considered in the dynamic Bayesian error function. The one-dimensional optimization problem of the optimal step length is solved by adopting the Fibonacci series search method without the need of determining the region, in which the optimized step length lies.

Evaluation method research on prestressed concrete bridges

Considering the construction features of prestressed concrete bridge, the comprehensive evaluation method about the bridge damage conditions are studied. Particular attentions are paid on establishing a muhilevel evaluation model for damaged prestressed concrete bridge, and the evaluation indices of the model as well as the rating standards are defined in the model. A normal relative function about the evaluation indices of each element is developed to calculate the relative degree, and for each element which is no sub-level elements. When evaluating the elements in sub-item level or index level of the model, the weights of elements that are pertained to one element are adopted, taking account of their deterioration degree. At the same time, the dam- age conditions of bridge are characterized by relative degree, element evaluation scale and structural technology mark of bridge, so it agrees with Code for Maintenance of Highway Bridges and Culvers.

Dynamic response analysis of ship-bridge collisions experiment

Over the past decades, there has been continual construction of sea-crossing bridges as the technology of transportation improves. The probability of bridge pier being subjected to more vehicular impact is also growing. This study performed scale model tests and analyzed a collision mechanism considering the non-navigable span of a sea-crossing bridge in East China Sea as an engineering background. Comparing the test results with the finite element calculations, the dynamic response of the sample bridge and local damages of the fragile components under impact force were evaluated. Subsequently, the time-frequency characteristics of the vibration signal were analyzed based on wavelet packet analysis, and the multi-resolution characteristics as well as energy distribution of the vibration signal were discussed. It was observed that the impact energy transferred from ship to pier during the period of collision distributed different frequency bands with varying characteristics. The main frequency band(0–62.5 Hz) contains more than 75% of the vibration energy. The analysis can provide a basis for structural damage identification after the collision and anti-collision design of bridges.

Technical challenges in the construction of bridge-tunnel sea-crossing projects in China

Since the year 2000,China has built a number of bridges crossing rivers and seas,including the Hangzhou Bay Bridge,Jiaozhou Bay Bridge,Zhoushan Bridge,and Hong Kong-Zhuhai-Macao Bridge(HZMB).As the longest sea-crossing bridge in the world,the opening of the HZMB(Fig.1)was undoubtedly one of the most significant events in 2018(Jing,2020).With the rapid development of China’s economy,especially in coastal areas,and the concentration of population density,the demand for transportation is increasing.Sea-crossing projects have gradually developed from bridge projects to integrated bridge-island-tunnel projects.

Dynamic Bayesian identification of mechanical parameters of multi-cell curve box girder based on conjugate gradient theory

For multi-cell curve box girder, the finite strip governing equation was derived on the basis of Novozhilov theory and orthogonal property of harmonious function series. Dynamic Bayesian error function of mechanical parameters of multi-cell curve box girder was achieved with Bayesian statistical theory. The corresponding formulas of dynamic Bayesian expectation and variance were obtained. After the one-dimensional optimization search method for the automatic determination of step length of the mechanical parameter was put forward, the optimization identification calculative formulas were also obtained by adopting conjugate gradient method. Then the steps of dynamic Bayesian identification of mechanical parameters of multi-cell curve box girder were stated in detail. Through analysis of a classic example, the dynamic Bayesian identification processes of mechanical parameters are steadily convergent to the true values, which proves that dynamic Bayesian theory and conjugate gradient theory are suitable for the identification calculation and the compiled procedure is correct. It is of significance that the foreknown information of mechanical parameters should be set with reliable practical engineering experiences instead of arbitrary selection.