Simulation on metro railway induced vibration. Part I: effect of out-of-round wheels

This paper discussed the effect of out-of-round wheels on simulation of rail dynamic behavior in the frequency range for ground vibration and ground-borne noise. A train-track interaction model was built by software Simpack and Abaqus. The input roughness was measured from a worn wheel and was applied moving on perfect smooth rail surface in different train speeds. Simulation results indicated that out-of-round wheel would affect the calculation result that could not be neglected, as the affected frequency range would be lower enough to influence the ground vibration (1-80 Hz) and ground-borne noise (16-250 Hz)

Effects of CNT and MgO–Type Expansive Agent on the Cracking Resistance of Face-Slab Concrete of CFRD

Concrete face rockfill dam (CFRD) is a commonly used and cost-effective type of dams. However, random cracks are often seen in the face slab concrete (FSC) of a CFRD during construction, largely due to the shrinkage caused by concrete temperature gradients, drying, and cementitious hydration. This study aims to improve the cracking resistance of FSC by using shrinkage compensating and cracking control materials. In this study, 5.0% by weight MgO-type expansive agent (MEA) or 0.1% by weight carbon nanotube (CNT) was added to a reference FSC (FSC-REF) selected from a CFRD. Fresh and hardened state properties of the developed concrete were tested. Different properties such as hydration heat, capillary pressure, mechanical properties at various ages, drying and autogenous shrinkage, thermal expansion coefficient (CTE), pore structure, and cracking resistance at early age of the FSC mixes (FSC-REF, FSC-MgO, and FSC-CNT) were determined. The results showed that the CNT addition lowered the capillary pressure and reduced the risk of plastic shrinkage cracking, while it also reduced drying and autogenous shrinkage of FSC. The addition of both CNT and MgO had little influence on the heat of hydration of FSC, but these slightly improved the axial tensile properties of FSC. CNT reduced the thermal expansion coefficient of FSC, whereas MgO increased it. Both CNT and MgO decreased the total porosity of the FSC, and the CNT addition significantly reduced the number of mesopores. The temperature-stress test results showed that MgO/CNT improved the cracking resistance of the FSC at early age under both temperature matching curing mode and constant temperature curing mode. Based on measured properties, CNT can be considered a promising additive for cracking control of FSC.This is a manuscript of an article published as Zhao, Zhifang, Hougui Zhou, Kejin Wang, Xu Wu, and Surendra P. Shah. "Effects of CNT and MgO–Type Expansive Agent on the Cracking Resistance of Face-Slab Concrete of CFRD." Journal of Materials in Civil Engineering 34, no. 12 (2022): 04022331. This material may be found at DOI: 10.1061/(ASCE)MT.1943-5533.0004497. Copyright 2022 ASCE. Posted with permission. This material may be downloaded for personal use only. Any other use requires prior permission of the American Society of Civil Engineers