•An unitless model for system limit state function is proposed for system reliability analysis.•System reliability of CRTS II track slab on viaduct is evaluated by method of moments.•Influences of ...important factors on the system reliability are investigated.
The safety of supporting structures for high-speed trains has motivated many researchers to develop an effective method for reliability analysis of the structure as a whole. In this study, a unitless model for system limit state function is developed, which enables the system reliability analysis of the CRTS II track slab on viaduct with multiple failure modes. The method of moments is employed to determine the system reliability, and the influences of important variables on the system reliability of the track slab are investigated. It is found that the reliability of the CRTS II track slab would be overestimated if only individual failure modes are considered independently, which vindicates the importance to conduct system reliability analysis for CRTS II track slab. It is also found that the randomness of the number of load cycles significantly affects the system reliability of the track slab. The merit of the developed unitless model for system limit state function is its facilitation of the efficient and accurate analysis of system reliability for the CRTS II track slab with no conditions and constraints.
The mechanical properties of rail fasteners play a key role in rail-structure interaction of urban rail viaduct. To reduce vibration and noise, the damping materials such as rubber cushion pads are ...used as the assemble parts of the rail fasteners in urban rail viaduct. The use of the damping materials causes the mechanical behaviours of rail fasteners to be different from the traditional ones whose longitudinal stiffness can be simplified as linear elastic, elastic–plastic or bilinear models. It is important to capture the mechanical behaviours of the rail fastener for accurately predicting the nonlinear seismic response of urban rail viaduct. In this paper, the quasi-static and dynamic cyclic tests of three kinds of commonly used rail fasteners (Type WJ-2A, Type DTIII2, and Type ZX-3) in China urban rail transit were conducted to explore the mechanical behaviours of rail fasteners. On this basis, the Hardin-Drnevich model is used to simulate the nonlinear behaviours of rail fasteners. Analysis results showed that the Hardin-Drnevich model could describe the quasi-static and dynamic cyclic response of Type WJ-2A and Type DTIII2 rail fasteners with reasonable accuracy, while its prediction accuracy for Type ZX-3 rail fasteners are relatively lower than others. Moreover, the Hardin-Drnevich model can predict the nonlinear dynamic response of Type WJ-2A fastener under earthquake loading very well. The calibrated parameters of Hardin-Drnevich model were used to the rail fasteners in the nonlinear seismic response analysis of the practical urban rail viaduct, and that were compared with that using idealized elastic–plastic model of the rail fastener. Comparison results demonstrated that, the mechanical constitutive relations of the rail fastener have obvious effects on the seismic performance of rail viaduct, and the effects are more distinct in the longitudinal direction than in the transversal direction.
•Domino-type progressive collapse analysis of Hongqi Viaduct is presented.•Detailed 3D FE model has been constructed and non-linear material behaviour is involved.•With a case of Hongqi Viaduct, ...domino-type progressive collapse is captured.•The progressive collapse vulnerability of multi-span simply-supported bridge is discussed.
Hongqi Viaduct, a multi-span simply-supported bridge in Zhuzhou city, Hunan Province, China, collapsed progressively during the mechanical demolishing of the bridge on May 17, 2009. Totally nine spans collapsed in the accident and it is a typical domino-type progressive collapse. The accident resulted in the loss of 9 lives and 16 injuries. Investigations were conducted after the accident to determine the cause of the unexpected progressive collapse. This paper is aimed at presenting a summary of the bridge before and after the incident, the demolishing plans and field investigations after the accident. To better understand the cause and mechanism of the progressive collapse, a numerical simulation is carried out. A detail 3D finite element (FE) model is developed by using the explicit FE code LS-DYNA. The bridge components including the bridge slabs, wall-type piers, longitudinal and transverse reinforcement bars are included in the model. The non-linear material behaviour including the strain rate effects of the concrete and steel rebar are considered. The model is used to simulate the bridge collapse induced by demolishing, and the domino-type progressive collapse of the bridge is clearly captured. Based on the numerical results, the reason for the failure is discussed and better understood. Finally, the possible mitigation methods of such progressive collapses of multi-span viaducts are suggested.
The high profile failure of the Malahide Viaduct in Dublin, Ireland, which is a part of the EU TEN-T network of critical transport links, was caused by foundation scour. Scour is a common ...soil-structure interaction problem. In light of current changes in climate, increasing frequency of flooding, coupled with the increasing magnitude of these flood events, will lead to a higher risk of bridge failure. Moni- toring scour is of paramount importance to ensure the continued safe operation of the aging bridge asset network. Most monitoring regimes are based on expensive underwater instrumentation that can often be subjected to damage during times of flooding, when scour risk is at its highest. This paper presents a critical review of existing scour monitoring equipments and methodologies with a particular focus on those using the dynamic response of the structure to indicate the existence and severity of the scour phenomenon affecting the structure. A sensitivity study on a recently developed monitoring method is also undertaken.
It is necessary to evaluate the construction effect of viaducts and identify the viaducts that play a key role in road networks. Based on the node deletion method, this article proposes a method to ...identify the importance of viaducts in road networks. After applying this method to simulate the importance of viaducts in the highway networks in Yunnan and Guizhou Provinces from 2001 to 2020, the results show the following: (1) The viaducts with high importance were mainly built in 2002, 2009, 2015, and 2016. They are mainly distributed on expressways such as the HUKUN Expressway, HANGRUI Expressway, and YINBAI Expressway. Among the viaducts, the Mengzhai Bridge and Beipanjiang Bridge Hukun are the most important. (2) The importance of viaducts will increase, decrease, or increase first and then decrease. Among the years studied, 2012 and 2016 are important time nodes for change. The trend of changes is affected by the construction of highways and viaducts in other locations. In this road network, there are strong coupling relationships between nodes. (3) The importance of some viaducts is not prominent in the whole region, but that does not mean their construction value is low. They may have a high connectivity effect on specific regions from a local perspective.
This study presents a more realistic modelling of the maglev-based high-speed railway line in Shanghai, China. Focus is placed on an accurate simulation of the two subsystems: the train subsystem ...including the magnets and the viaduct subsystem including the modular function units of the rails. The electromagnet force-air gap model with a proportional-derivative (PD) controller is adopted to simulate the interaction between the maglev train via its electromagnets and the viaduct via its modular function units. The flexibilities of the rails, girders, piers and associated elastic bearings are all considered in the modelling of the viaduct subsystem to investigate their effects on an interaction between the two subsystems. By applying the proposed model to the Shanghai maglev line, the essential characteristics of the coupled system can be duly captured. The accuracy and effectiveness of the proposed approach are then validated by comparing the computed dynamic responses and frequencies with the measurement results. It is confirmed that the proposed modelling with a detailed simulation of the magnets and modular function units can duly account for the dynamic interaction between the train and viaduct systems. Moreover, the effects of the inclusion of the flexibilities of the rails, girders and elastic supports to the response of the coupled system are respectively investigated, the results of which prove that their involvements are essential to the accurate prediction of the response of the coupled maglev train-viaduct system.
Quasi-periodic structures, as found in multi-span bridges, multi-bay and multi-storey buildings, are often characterized by a high modal density, even at low frequencies. This clustering of modes ...poses challenges in operational modal analysis, as well as in finite element model updating, where a pairing of experimental and numerically predicted modes is required. To overcome these difficulties, an alternative method for model updating based on the so-called free wave characteristics has recently been proposed. In this work, this method is applied to calibrate a finite element model of the K032 viaduct of the A11 highway in Bruges, Belgium. Vibration measurements are conducted to experimentally determine the free wave characteristics of the viaduct. In the model updating, the discrepancy between the calculated and identified free wave characteristics is minimized. The results are validated by comparing measured frequency response functions with those obtained from the updated finite element model.
Based on the narrowband 930-MHz measurements taken along the "Zhengzhou-Xi'an" high-speed railway in China, an empirical path loss model is proposed. It is applicable to high-speed railway viaduct ...scenarios, considering the influences of viaduct height H and base station antenna relative height h , which are not well-covered by existing large-scale models. The path loss exponents are investigated, based on which the influence of viaduct on propagation is discussed. The fading depth up to 15.96 dB and the Ricean K -factor with mean value of 3.79 dB are obtained.
Finite element (FE) model updating of bridges is based on the measured modal parameters and less frequently on the measured structural response under a known load. Until recently, the FE model ...updating did not consider strain measurements from sensors installed for weighing vehicles with bridge weigh-in-motion (B-WIM) systems. A 50-year-old multi-span concrete highway viaduct, renovated between 2017 and 2019, was equipped with continuous monitoring system with over 200 sensors, and a B-WIM system. In the most heavily instrumented span, the maximum measured longitudinal strains induced by the full-speed calibration vehicle passages were compared with the modelled strains. Based on the sensitivity study results, three variables that affected its overall stiffness were updated: Young's modulus adjustment factor of all structural elements, and two anchorage reduction factors that considered the interaction between the superstructure and non-structural elements. The analysis confirmed the importance of the initial manual FE model updating to correctly reflect the non-structural elements during the automatic nonlinear optimisation. It also demonstrated a successful use of pseudo-static B-WIM loading data during the model updating process and the potential to extend the proposed approach to using random B-WIM-weighed vehicles for FE model updating and long-term monitoring of structural parameters and load-dependent phenomena.
In the urbanization process, the viaduct has been regarded as an effective way to relieve metropolis traffic pressures in the urban area. However, due to the double emission source from elevated- and ...ground-road vehicles, the viaduct-built environment inevitably deteriorates the street canyon's air quality. Besides, the emitted air pollutants are trapped in such street canyons for extended periods. With this consideration, we used measured data to explore the impact of the viaduct on the vertical distribution of PM2.5 in street canyons. First, the experiments were conducted in a residential building near the inner ring of a viaduct in Shanghai, China. Next, the vertical distribution of PM2.5 and its diurnal variation were revealed based on these data. The results indicated the bimodal distribution patterns in the vertical profiles of PM2.5 mass concentrations, with the lower peak at height of 5 m under the viaduct and the upper peak at height of 10 m above the noise barrier on the viaduct. Further, the impact of the viaduct on the vertical distribution of PM2.5 was investigated. Results from both observation and simulation are consistent, revealing that 21–23% of PM2.5 was trapped beneath the viaduct, and the noise barrier causes the PM2.5 to decrease by 4–5%. The traffic source on the viaduct contributes 20–40% of the PM2.5. This study revealed the dispersion patterns of PM2.5, and the impact of the viaduct on it, which could be beneficial to optimizing the viaduct and the noise barrier to release traffic-related air pollutants in street canyons.
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•Viaduct makes an additional 21%–23% of PM2.5 accumulate under it in street canyons.•The noise barrier on the viaduct reduces 4.5% of PM2.5 at the corresponding height in street canyons.•Emission source from viaduct elevated particles and makes PM2.5 20%–40% higher above noise barrier.
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