This study presents a complex experimental research of a damaged steel railway bridge. Before the reconstruction, the elastic behavior of the material was evaluated using the hole-drilling strain ...gauge method of determining residual stresses at the relevant cross-sections. During the reconstruction project (lifting of the structure), a short-term monitoring system was installed at the critical cross-sections for continuous recording of strain. The aim was to evaluate the quality of the reconstruction intervention and prevent further damages. Following a successful reconstruction, a diagnostic load testing was performed according to Croatian standards. The purpose of the load testing (static and dynamic) was to evaluate the ability of the bridge to carry the design loads and calibrate the finite element models. During static load testing vertical displacement was measured as well as strain. Dynamic load testing of the bridge was performed in order to determine the main dynamic parameters of the structure and to calculate the dynamic factor. In order to select the appropriate measurement parameters and methods used during this experimental research it was necessary to consider the bridge type, materials and reconstruction or strengthening interventions. Especially, since this bridge was an example of insufficient inspection and maintenance during service. A well-designed monitoring and diagnostic load testing needed to be performed in order to obtain useful results for the decision makers involved.
Overhead line system is a vital element of any electrified railway infrastructure. Its performance reflects to all vital parameters such as traction, reliability, availability and safety of railway ...infrastructure. Operator GPP Osijek runs a 27.5 km long tramway network which plays a key role in transit system of the city of Osijek, Croatia. In 2016 GPP Osijek applied to a tender for acquisition of new rolling stock with 85% EU investment. Mayor requirement prior to rolling stock acquisition was to document, analyse and upgrade current infrastructure (including track structure, electric substations and catenary) to an optimal level. Task of measurement and evaluation of tram track structure and catenary has been appointed to University of Zagreb Faculty of Civil Engineering. Overhead line analysis comprised from several measuring procedures, including supporting columns evaluation, catenary stagger, height, shocks and wear. Such extensive analysis included GPS positioning and on-site evaluation of 1214 supporting columns of overhead line, as well as overhead line measurements using an instrumented tram vehicle on 18 km of track. For conducting overhead catenary wire measurements, a tram pantograph has been fitted with equipment for measuring catenary height, accelerometers for shock measurement, camera, ruler and GPS for stagger measurement. Catenary wire wear was checked manually from catenary inspection vehicle. To conduct measurements, power had to be switched off on all electric substation along the route and tram vehicle had to be towed by a catenary inspection vehicle. All the data has been analysed and presented to end user in a user-friendly and intuitive GIS environment capable of further updates and detailed analyses. Evaluation of overhead line based on direct measurement results pointed out all the defects and weak spots on the system. It resulted in a series of recommendations for reconstruction and upgrade of the catenary system to fit the need of existing state and further development of tramway network.
Ultra-high-performance fiber-reinforced cement-based composite (UHPFRC) has been increasingly adopted for rehabilitation projects over the past two decades, proving itself as a reliable, ...cost-efficient and sustainable alternative against conventional methods. High compressive strength, low permeability and high ductility are some of the characteristics that render UHPFRC an excellent material for repairing existing aged infrastructure. UHPFRC is most commonly applied as a surface layer for strengthening and rehabilitating concrete structures such as bridge decks or building slabs. However, its implementation with steel structures has so far been limited. In this work, the UHPFRC strengthening of a steel bridge is investigated both in simulation as well as in the laboratory, by exploiting a real-world case study: the Buna Bridge. This Croatian riveted steel bridge, constructed in 1893, repaired in 1953, and decommissioned since 2010, was removed from its original location and transported to laboratory facilities for testing prior to and after rehabilitation via addition of UHPFRC slab. The testing campaign includes static and dynamic experiments featuring state-of-the-art monitoring systems such as embedded fiber optics, acoustic emission sensors and digital image correlation. The information obtained prior to rehabilitation serves for characterization of the actual condition of the structure and allows the design of the rehabilitation solution. The UHPFRC slab thickness was optimized to deliver optimal fatigue and ultimate capacity improvement at reasonable cost. Once the design was implemented, a second round of experiments was conducted in order to confirm the validity of the solution, with particular attention allocated to the interface between the steel substrate and the UHPFRC overlay, as the connection between both materials may result in a weak contact point. A detailed fatigue analysis, based on updated FEM models prior to and after strengthening, combined with the results of a reliability analysis prove the benefits of adoption of such a solution via the significant extension of the structural lifespan.
The condition of the bridge may deteriorate due to the traffic that passes over it, as well as weather and environmental conditions. To ensure the safety and structural stability of the bridges, ...regular inspections of the bridge elements should be carried out. Recent advances in unmanned aerial vehicles (UAVs) can provide tools for accurate and even autonomous inspection of bridge structures without interrupting normal bridge operations. In this paper, we focus on the determination of the dynamic structural parameters of a suspension bridge. The proposed method is based on the estimation of the natural vibration frequency of the bridge cables using the videos captured by the UAV. We provide a detailed theoretical description of the algorithm and an analysis of the simulation results and the data collected during the experiments in the laboratory and in the real case study. In addition to the vision based method for estimating vibration frequency, we tested the ability of the UAV’s on-board sensors to record structural oscillations when the UAV landed on the surface of the bridge.
•Determination of the dynamic structural parameters of a suspension bridge.•Vision based method for estimating vibration frequency.•Estimation of the oscillation frequency of the bridge cables using the UAV.
In finite element analysis of steel‐reinforced elastomeric bearings (SREB) under compression, modeling of rubber as a nearly or fully incompressible material requires special attention. In this ...study, finite element simulations of circular elastomeric pads and rectangular SREB under compression were performed to analyze the effects of rubber compressibility with respect to different pad geometries and shape factor values. The ratio of the compressive modulus for a compressible rubber to that of an incompressible rubber was also introduced based on the previously derived exact solutions as well as the ad hoc approximations. This ratio accurately represents the influence of compressibility on compressive stiffness in terms of relative compressibility (K/G) and shape factor values. Numerical results were also compared with the experimental results on rectangular SREB with moderate shape factors. Recommended values for relative compressibility of carbon black‐filled rubbers in the range of 50–200 result in underestimated compressive stiffness, especially for bearings with shape factor values greater than five. It is recommended to adjust the relative compressibility, considering the shape factor, so that the compressive stiffness does not decrease by more than 50% compared to the incompressible case.
At the time of designing structures up to date, the density and magnitude of the load have increased, and the requirements for regulation have also become more stringent. To ensure the essential ...requirements, especially the mechanical resistance and stability, the numerical modelling of the structure is carried out according to the current regulations. Due to various assumptions, idealization, discretization, and parameterizations that are introduced numerical modelling, obtained numerical model may not always reflect the actual structural behavior. It is known that these structures have a hidden resistance that can be determined by combining experimental investigations (static or/and dynamic tests) and finite element model updating methods to minimize the differences between the actual and predicted structural behavior. This paper provides a review of the FEMU process and methods used and summarizes the FEMU approach to help future engineers to select the appropriate method for solving some discussed issues. First, the main terms important for understanding FEMU are introduced. The whole process of model updating is described step by step: selection of updating parameters (design variables), definition of the model updating problem, its solution using different FEMU methods. An overview of the following methods is given: sensitivity-based, maximum likelihood, non-probabilistic, probabilistic, response surface and regularization methods. Each of the method is presented with the corresponding mathematical background, implementation steps, and examples of studies from the literature.
Abstract The hangers are the important element on suspension bridges that transfer the forces from the deck to the main cable. To verify their capacity and identify possible risks, the forces ...transferred by the hangers and the corresponding tension must be determined. However, this is often done using standard equations for determining cable forces. Due to the different lengths of the hangers and the way in which their tensioning is achieved, the effects of boundary conditions occur that need to be considered and that require an update of the finite element model at the local level (when the whole bridge structure is observed). This paper presents a method for determining the cable tension of hangers that combines the experimentally determined dynamic properties (natural frequencies and mode shapes) and the numerical model updating. In addition to the usual approach based on the determination of the natural frequency of hangers, this paper presents an approach based on the mode shapes of the hangers. Special attention is paid to the boundary conditions coefficient. The method is applied on suspension bridge case study.
•Shear behavior of reinforced concrete beams without transverse reinforcement.•Analysis of crack shape and kinematics on RC beams based on 3D stereophotogrammetric measurements with high sampling ...frequency.•Comparison of experimental results with calculated contribution to shear resistance of different mechanisms.•Calculation of shear and normal stresses based on the proposed discretization of the critical shear crack.
This paper presents an evaluation of the shear capacity of reinforced concrete beams without transverse reinforcement by comparing the theoretical background with the experimental investigation. It is well known in the research community that the various shear transfer mechanisms contribute to the shear capacity. However, there are ongoing discussions regarding the critical shear crack kinematics that affect the relationship between the contributions of these mechanisms. In this study, 16 RC beams without transverse reinforcement were tested and their shear strength was compared with the predictions of existing codes and mechanical models. The shape of the critical crack was tracked using 3D stereophotogrammetric measurements. To analyze the crack kinematics, its shape was idealized by an optimized polyline with the newly proposed discretization degree. Based on stereophotogrammetric measurements with a sampling frequency up to 25 Hz and using available physical models, the detailed analysis of different shear transfer mechanisms is conducted for 4 tested beams, emphasizing the contribution of aggregate interlock. By comparing the experimental results with the calculated contributions to the shear resistance of each mechanism, a reasonable agreement was obtained. However, the measurements showed that most of the available physical models for the aggregate interlock contribution overestimate both the normal and shear stresses developing across the critical shear crack. Thus, with adequate data acquisition and analysis, digital image correlation has proven to be a viable tool for performing detailed real-time measurements of crack shape and kinematics.
•Finite element model updating (FEMU) problem is formulated and further implemented as a game theory problem.•Three different game models (non-cooperative, cooperative and evolutionary) have been ...considered to cope with FEMU problem.•The performance (accuracy and simulation time) of the different game models has been compared when they are implemented to perform the FEMU of a laboratory footbridge.•Direct determination of the optimal solution for the FEMU problem reducing the simulation time (it is not necessary either to compute the Pareto front or to solve the subsequent decision-making problem) without compromising the accuracy of the solution.
Finite element modelling is performed to numerically predict the behaviour of civil engineering structures. Due to the different assumptions adopted during the modelling phase, this initial model does not always reflect adequately the actual structural behaviour. In this context, the results of experimental structural dynamic properties can be used to improve initial numerical model via the implementation of the so-called finite element model updating method. After this process, the updated model better reflects the actual structural behaviour. Due to its simplicity, for practical engineering applications, the updating process is usually performed considering the maximum likelihood method. According to this approach, the updating problem may be formulated as the combination of two sub-problems: (i) a bi-objective optimization sub-problem; and (ii) a decision-making sub-problem. The bi-objective function is usually defined in terms of the residuals between the experimental and numerical modal properties. As optimization method, nature-inspired computational algorithms have been usually considered due to their high efficiency to cope with non-linear optimization problems. Despite this extensive use, this method presents two main limitations: (i) the high simulation time required to compute the Pareto optimal front; and (ii) the necessity of solving a subsequent decision making problem (the selection of the best solution among the different elements of the Pareto front). In order to overcome these limitations, in this paper game theory has been adopted as computational tool to improve the performance of the updating process. For this purpose, the updating problem has been re-formulated as a game theory problem considering three different game models: (i) non-cooperative; (ii) cooperative; and (iii) evolutionary. Finally, the performance of proposal has been assessed when it is implemented for the model updating of a laboratory footbridge. As result of this study, game theory has been shown up as efficient tool to improve the performance of the updating process under the maximum likelihood method since it allows a direct estimation of the solution reducing the simulation time without compromising the accuracy of the result.
The structural integrity of bridges is susceptible to deterioration caused by traffic loads, environmental conditions, and weather phenomena. To maintain the safety and stability of bridges, regular ...inspections of their elements are required. Recent advances in the field of unmanned aerial vehicles (UAVs) provide a viable option for accurate and autonomous inspections of bridge structures without disrupting normal operations. This study focuses on the determination of the dynamic structural parameters of a suspension bridge. The methodology focuses on determining the natural vibration frequency of the bridge cables using UAV imagery. This paper contains a detailed theoretical presentation of the algorithm used, accompanied by a careful analysis of simulation results and empirical data from laboratory experiments and real case studies. In addition to the image processing-based approach for estimating the vibration frequency, the sensors on board the drone are also scrutinized and their effectiveness in detecting structural vibrations after the drone lands on the bridge surface is evaluated.
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