Xin Ruan

Mesoscopic simulation method of concrete carbonation process

Concrete structures in the atmosphere may suffer from the problem of steel corrosion induced by the carbonation process. Most of previous research on concrete carbonation problems has been performed on the macro-scale. These studies did not consider the influence of the aggregates, which should be involved on meso-scale. In order to extend the present studies on the problems of concrete carbonation from macro-scale to meso-scale, an improved method to simulate the random aggregate structure (RAS) in concrete has been proposed. This method can be divided into two steps: the process of RAS in a three-dimensional model, and the process of numerical analysis in a cross-section. In this method, the effect of the randomness on the results of RAS is analysed. Based on the mass conservation law and kinetic model of chemical reactions, a simplified numerical model of concrete carbonation is developed. The effect of the key parameters in this model such as effective diffusion coefficient of CO2 and carbonation reaction constant is discussed. The comparison of the simulations of concrete carbonation process on macro-scale and meso-scale is discussed as well. Finally, an application of the method to determine the proper composition of concrete in the practical engineering is presented.

Safety Assessment of the Antisliding between the Main Cable and Middle Saddle of a Three-Pylon Suspension Bridge Considering Traffic Load Modeling

AbstractThe antisliding safety of the middle saddle is a key issue for the design of three-pylon suspension bridges. Vehicle load is the main adverse effect, especially unsymmetrical vehicle load. A general mechanical model on the saddle sliding behavior is reviewed and proposed, and then characteristics of load responses of the main cable are investigated to explore a simplified live load computational method. Based on the deterministic approach from codes and a reliability-based approach, the antisliding safety of the middle saddle is discussed and assessed for the Taizhou Yangtze River Bridge, which has two symmetrical spans of 1,080 m. The study shows that geometric nonlinearity caused by dead load has a big effect on the load responses of the main cable, so it must be included in the design. Further, the maximum difference between the geometrically linear and nonlinear cases due to live load is up to 12.71%, whereas in all conditions, the balanced static friction coefficient is smaller without consid...

A site-specific traffic load model for long-span multi-pylon cable-stayed bridges

Abstract This paper proposes a site-specific traffic load model for long-span multi-pylon cable-stayed bridge. Structural effects are primarily investigated based on influence lines, which are identified as either global effect (GE) or partial effect (PE) depending on the effective influenced region. GEs are further categorised as sensitive effect (SE), insensitive effect (ISE) or less sensitive effect (LSE), considering sensitivity to unbalanced traffic loading. Three on-bridge traffic states are simulated, and Weibull extrapolations are utilised to predict the extreme responses. These responses are analysed and compared with several design codes. Results indicate the maximum response is only 75% of the value calculated based on the design code of China (D60), and even lower than other codes. The responses show strong positive correlation with traffic parameters of annual average daily traffic volume and heavy vehicle proportion, and the on-bridge traffic states have significant influence on the responses. Further, the identified effects of ISE, SE and LSE present different responses, which indicate specific load models are needed accordingly. Finally, a site-specific traffic load model consisting of load form, loading pattern, multi-lane factor and load value is recommended, which gives an accurate illustration on the structural effects and traffic responses.

In-situ stress identification of bridge concrete components using core-drilling method

Concrete components of existing bridges often have complex and time-dependent stresses due to external load and internal degradation. The reliable information of the stress state plays an important role in performance assessment, life cycle prediction and strengthening and maintenance strategy. Some key bridge components generally carry predominant uniaxial loads, such as girders, towers and pillars, which make it meaningful to focus on the uniaxial in-situ stresses. This article presents a non-destructive method to identify the uniaxial in-situ stresses in concrete components for existing bridges using core-drilling method based on influence functions (IFs). Axial and tangential IFs are defined and calibrated, followed by numerical identifications of different stress fields and experimental tests on concrete specimens. The influence of inhomogeneity and randomness of concrete in the identification tests are evaluated by comparisons of measured data from various strain gages and reduced by introduction of interpolation functions, synthetical IFs and optimisation solutions. The relationship between identification accuracy and damage cost is also investigated.

Concepts of Developing Traffic Load Model for Multi-Span Cable Supported Bridges

Traffic load effects of multi-span, cable-supported bridges are significantly different from those of small- and medium-span bridges. However, the current traffic load codes are generally specified for small- and medium-span bridges, which are extremely conservative for the design of multi-span, cable-supported bridges. A profound and comprehensive review on existing research of traffic load models for large span bridges is presented, providing theoretical foundation for the concepts of performance-based traffic load models. Different structure performance levels, design states and parameters are discussed under varied traffic load service levels. Novel techniques in related traffic load research fields are introduced to explore the possible performance-based design methodology and process. Application of the traffic load effect analysis is stated by two practical examples. According to the results, it is indicated that concepts of performance-based design are more accurate and efficient for the traffic load effect and provide the structure optimization with favorable conditions.