Determination of load path through concrete crosstie and fastening system: a laboratory and field investigation

US railways move more freight (measured in tonne-kms) by rail than by any other means. This is done over an extensive network of primarily private freight railway lines that also transport passenger trains. To enable the expansion of high-speed passenger rail service using shared passenger/freight infrastructure, the US Department of Transportation Federal Railroad Administration (FRA) sponsored a research project to investigate infrastructure design and performance challenges. This is a multi-faceted research project for which one element is laboratory and field investigation of the load path from rail-wheel to precast concrete crossties. In this research, the behavior of crosstie and fastening system is investigated through material-level, component-level and system-level laboratory and field experiments. The system-level experiments use three primary test setups. One of these setups, referred to as a static single-crosstie and fastening system experiment, enables the application of a downward and outward lateral force from the contact point of an idealize wheel through to the crosstie. Displacements and strains from each component were collected to understand the load path under simplified loading conditions. In addition to examining the factors that influence the flow of forces, a key objective of this work was to calibrate a means of displacement and strain measurements for use in rail corridors to determine the flow of forces from wheels through to crossties. The second test setup uses the full-scale Track Loading System (TLS) to conduct similar tests and measurements over a multi-crosstie system in laboratory. A 22-feet long section of track including eleven concrete crossties that was loaded by vertical and lateral actuators over a 32-inch wheel set with varying ratios of lateral to vertical force from the wheel to rail. The third test setup is the full-scale field experiment performed at the Transportation Technology Center (TTC) in Pueblo, CO. Five adjacent crossties in tangent and curved track were instrumented and loaded by Track Loading Vehicle (TLV) with static wheel loads. Dynamic tests were conducted with passenger and freight train consists at various speeds. Measurements including the wheel-rail interaction forces, rail seat vertical reactions, shoulder lateral reactions, and component strain and displacements. The data collected from the three system-level experiments was used to clarify the load path, target areas of uncertainty, investigate the behavior of each component under extreme static loading and cyclical dynamic loading, as well as calibrate and validate a 3-D finite element model being developed at UIUC. In addition, this research offers suggestions for the instrumentation, testing, data-analysis and current design recommendations of concrete crosstie and fastening systems

Reliability-based structural assessment of historical masonry arch bridges: The case study of Cernadela bridge

Nowadays, several historical masonry arch bridges present a deficient state of conservation due to degradation processes induced by natural or human actions. Usually, these constructions have significant economic, cultural, and heritage value. Therefore, they shall be thoroughly assessed to verify their structural integrity and safety condition. For this purpose, reliability-based structural assessments are typically performed. However, the associated outcomes (i.e., reliability index and probability of failure) highly rely on the accuracy of the structural parameters uncertainty quantification. This work presents a study regarding the influence of the scattering of the arches' thickness dimensions in the load-carrying capacity assessment of the Cernadela Bridge, a historical stone bridge located in Galicia, Spain. The study first involved a comprehensive experimental campaign to characterize the outer and inner bridge geometry through geomatic techniques, i.e., terrestrial laser scanning and ground penetrating radar. Subsequently, a limit analysis model was developed, considering only the arches' outer (visible) data. From this initial structural assessment, a reliability index of 2.38 was obtained. The influence of the uncertain structural parameters, both geometric features and material properties, in the collapse load was investigated through a global variance-based sensitivity analysis (i.e., Sobol' indices) complemented by a surrogate modeling strategy based on the Kriging approach. Finally, the measured inner geometry of the arches was introduced in the computational model through Bayesian inference procedures. Thus, two new structural assessments were performed: first, by considering the updated distributions of all arches thicknesses, and second, by considering only the updated distributions of the non-influential ones. Reliability indexes of 1.51 and 2.33 were derived, thus highlighting the importance of a proper uncertainty quantification process and the relevance of the sensitivity analysis outcomes to identify the critical parameters on the bridge mechanical response.Ministerio de Ciencia e Innovación | Ref. TED2021-130497A-I00Ministerio de Ciencia e Innovación | Ref. RYC2019-026604-

Mems based bridge monitoring supported by image-assisted total station

In this study, the feasibility of Micro-Electro-Mechanical System (MEMS) accelerometers and an image-assisted total station (IATS) for short-and long-term deformation monitoring of bridge structures is investigated. The MEMS sensors of type BNO055 from Bosch as part of a geo-sensor network are mounted at different positions of the bridge structure. In order to degrade the impact of systematic errors on the acceleration measurements, the deterministic calibration parameters are determined for fixed positions using a KUKA youBot in a climate chamber over certain temperature ranges. The measured acceleration data, with a sampling frequency of 100 Hz, yields accurate estimates of the modal parameters over short time intervals but suffer from accuracy degradation for absolute position estimates with time. To overcome this problem, video frames of a passive target, attached in the vicinity of one of the MEMS sensors, are captured from an embedded on-axis telescope camera of the IATS of type Leica Nova MS50 MultiStation with a practical sampling frequency of 10 Hz. To identify the modal parameters such as eigenfrequencies and modal damping for both acceleration and displacement time series, a damped harmonic oscillation model is employed together with an autoregressive (AR) model of coloured measurement noise. The AR model is solved by means of a generalized expectation maximization (GEM) algorithm. Subsequently, the estimated model parameters from the IATS are used for coordinate updates of the MEMS sensor within a Kalman filter approach. The experiment was performed for a synthetic bridge and the analysis shows an accuracy level of sub-millimetre for amplitudes and much better than 0.1 Hz for the frequencies. © 2019 M. Omidalizarandi et al