Wheel diameter is a significant geometric parameter related to the safe operation of trains, and needs to be measured dynamically. To the best of the authors’ knowledge, most existing dynamic measurement methods and systems do not meet the requirement that the wheel diameter measurement error for the high-speed vehicle is less than 0.3 mm. In this paper, a simple method for dynamically and precisely measuring train wheel diameter using three one-dimensional laser displacement transducers (1D-LDTs) is proposed for the first time, and a corresponding measurement system which was developed is described. The factors that affect the measurement accuracy were analyzed. As a main factor, rail deformation caused by the wheel-rail interaction force at low (20 km/h) and high (300 km/h) speeds was determined based on the combination of multi-body dynamics and finite element methods, and the effect of rail deformation on measurement accuracy is greatly reduced by a comparative measurement. Field experiments were performed to verify the performance of the developed measurement system, and the results of the repeatability error and measurement error of the system were both less than 0.3 mm, which meets the requirement of wheel diameter measurements for high-speed vehicles.
To study the influence of urban heat island effect on sulphate attack on concrete, three environments are designed to simulate both sulphate attack underground and crystallisation attack on the ground surface. Experiments last for 1 year and then all specimens are taken out to conduct macro-observations and micro-observations. Results indicate the following: after attack, the micro-structural change of concrete is in accord with the macro-mechanical behaviour; under the influence of urban heat island effect, the visual degradation mainly induced by ettringite is much more serious and the crystallisation attack mainly induced by thenardite crystal is extended to greater range, and therefore the compressive strength is decreased more obviously. The degradation is particularly prominent for C20 concrete, this should be paid more attention, because in China, C20 concrete was often adopted by relatively early building foundation and underground pipeline. This research will provide good basis for further putting forward repair techniques to the attacked concrete material.
Performance tests are conducted on pervious concrete mixed with Polypropylene Split Fiber (PPSF), in which basic indexes such as compressive strength, splitting strength, flexural strength, porosity, permeability coefficient are measured. Results indicate: mixed with certain amount of PPSF in ordinary pervious concrete is feasible, and during mixing PPSF is split into uniformly distributed monofilament fiber without occurrence of agglomeration or rustiness; incorporating 3kg PPSF in 1m3 pervious concrete is proper, under which compared with the ordinary pervious concrete, both porosity and permeability coefficient are decreased, but application requirements are still met, while strength is increased obviously; the pervious concrete mixed with PPSF can be used in ordinary light traffic pavements.
One 6-stories brick-concrete structure was built in the late of 1990s. The uneven settlement of the foundation had occurred and the average concrete compressive strength of the foundation was close to C30 standard. Apparent observations indicated that some white powdery substance which was not adhesive was precipitated at the aggregate/mortar interface, pores and cracks. Micro observations by means of a Scanning Electron Microscope equipped with a Energy Dispersive Spectrometer showed the coexistence of ettringite and small amount of alkali–silica gel, which proved that the foundation had suffered from sulfate attack and alkali–silica reaction.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.