Xinglang Fan

A numerical method is proposed for evaluating the axial stress–strain relationship of FRP-confined concrete. In this method, empirical formulae for the compressive strength and strain at peak stress of confined concrete are obtained by fitting experimental data collected from the literature. It is then assumed that when FRP-confined concrete and actively confined concrete are subjected to the same lateral strain and confining pressure at a specific loading stage, their axial stress–strain relationships are identical at that stage. Based on this assumption, a numerical method for the axial stress–strain relationship of FRP-confined concrete is developed by combining the stress–strain model of actively confined concrete with the axial–lateral strain correlation. Finally, the validity of this numerical method is verified with experimental data with various geometric and material parameters, demonstrating a reasonable agreement between predicted stress–strain curves and measured ones. A parametric analysis is conducted to reveal that the stress–strain curve is independent of the specimen length for strong FRP confinement with small failure strains, while the specimen length exhibits a significant effect on the softening branch for weak FRP confinement. Therefore, for weakly FRP-confined concrete, it is recommended to consider the specimen length effect in evaluating the axial stress–strain relationship.

Creep is an important physical property of concrete and can lead to additional displacement, stress redistribution, and even cracking in concrete structures, inducing prestress loss of large-scale prestressed concrete structures. When an exponential algorithm is used to calculate the long-term creep of concrete, it is usually necessary to apply the continuous retardation spectra of the material. In the improved approach proposed here, the continuous retardation spectra can be obtained by the Weeks inverse Laplace transform. The CEB MC90 creep model is taken as an example to analyze the computational process, efficiency, and error of the approach. The improved approach is further applied to the ACI 209R-92, JSCE, and GL2000 concrete creep models. Through comparison with other methods, the advantages of the improved approach are illustrated, and some useful conclusions are drawn.

Cement asphalt mortar (CAM) in high‐speed lines is subjected to varying environmental conditions, which lead to the deterioration of CAM. The nanoparticles of nano‐SiO₂ and nano‐TiO₂ are added to improve the performance of CAM, and the temperature sensitivity of CAM with nanoparticles is primarily studied in this paper. The flexural strength and compressive strength of CAM with and without nano‐SiO₂ and nano‐TiO₂ were measured and compared to study the effect of nanoparticles on the performance of CAM subjected to different temperatures. Temperature sensitivity factors of flexural and compressive strength based on Arrhenius model were proposed to evaluate the temperature dependence of CAM by nanoparticles. Furthermore, the microstructure of hardened CAM was studied using scan electronic microscope (SEM) to investigate the mechanism of temperature sensitivity of CAM with and without nanoparticles. The results indicated that the flexural and compressive strength of CAM with and without nanoparticles decreased with the increasing temperature; however, the decreasing rate of strength with temperature was different in CAM with and without nanoparticles. The reduction in the decreasing rate of strength was obtained by using nano‐SiO₂ rather than nano‐TiO₂ in CAM. Based on the SEM results, the free asphalt was seen to be greatly reduced in the CAM with nano‐SiO₂, suggesting a positive effect of nano‐SiO₂ on the mitigation of temperature sensitivity of CAM.

The viscosity of Retard-Hardening Adhesive (RHA) varies with the hardening of resin-based materials and greatly affects the workability and prestress loss of retard-bonded prestressed systems. So far, the effect of aging time on the viscosity of the RHA has not been revealed, which hampers the further application of Retard-Bonded Prestressed Reinforcements. In the current article, therefore, an experimental study is developed to evaluate the effect of aging time on the viscosity of RHA. Different exposure temperatures and hardening periods of RHA are considered in the rheological test. Test results show that when the aging time and exposure temperature remain the same, and as the shear rate increases, the viscosity of the RHA firstly decreases rapidly and then remains basically constant. The peak viscosity increases with the aging time, exposure temperature, or both. The effects of temperature on the peak viscosity are different at different stages of aging. The effect of the hardening period on the peak viscosity can be eliminated by introducing the relative aging time. Finally, an empirical model is suggested to predict the peak viscosity of the RHA at different aging times, and the results show that the proposed model agrees well with the experimental results.

The bond strength of plain bars plays an important role in assessing the anchorage capacity of historical buildings. For plain bars, the bond strength greatly depends on the frictional effect, and can easily be affected by the lateral stress around the bars. For bars located in the beam–column joint, the lateral compressive–tensile stresses from gravity and earthquakes might be applied simultaneously. To date, the effect of such biaxial stresses on the bond strength of plain bars has not been evaluated in an analytical manner. Consequently, an analytical approach combining both theoretical and numerical solutions to the bond strength of plain round bars under biaxial tensile compressive stresses is developed. Comparison between test data and the results calculated by the proposed analytical model shows that the model is well capable of predicting the bond strength for different concrete and bars. Moreover, the comparative studies between the proposed analytical model and closed-form solutions show that the partial separation of the bond interface due to the biaxial stresses cannot be ignored in predicting the bond strength of plain bars. Finally, a simplified model with acceptable precision is suggested to substitute for the numerical procedure in the proposed analytical model.

Owing to its light self-weight, low heat capacity and large thermal expansion coefficient, the application of the curved steel box girder bridge with small and medium spans has gained popularity for the construction of urban infrastructure. However, sun exposure could easily increase the maximum temperature difference at the bottom of steel box beam by 25°C. With the effect of nonuniform temperature field and overloaded vehicles, the edge inside the curved steel box girder bridge may be separated from the remaining structure, resulting in overturning. Thus, more attention needs to be paid in order to prevent the separation. In this paper, an overturning resistance analysis of a three-span curved steel box girder bridge located in Hangzhou, China was performed. A model was proposed based on the measurement of temperature field to the steel box girder. The separating displacement due to temperature variations was predicted and verified by the measurement results. As a result, changes in supporting r...