•Viaduct redesign using Fiber Reinforced Concrete (FRC) as resisting material.•Case study on the replacement of reinforced concrete by FRC.•FRC replaces conventional reinforcement in transversally ...prestressed viaducts.•Serviceability reinforcement due to light-train loads is fully eliminated with FRC.•FRC improves crack opening for large concrete covers while using ULS reinforcement.
An assessment concerning the structural applicability and performance of fiber reinforced concrete (FRC) is presented for different bridge elements and within a design framework. FRC as the main bearing material in structural members has evolved from low-demand applications to increasingly ones, where bending and shear are the main internal forces. In actual applications, this was reflected with initial slab-on-grade cases, through tunnels, and later moving towards elevated slabs. Past experiences show that FRC has notable features regarding ultimate capacity and serviceability performance (i.e., enhanced crack control). These capabilities allowed for optimizations such as material savings, reduction of intensive labor during construction, or extended durability. Considering FRC's enhancements from previous applications, a case study based on the Metrorrey Line 2 light-train viaduct (Mexico) is developed. The case study aims to assess the structural performance that FRC can deliver within bridge geometries, loads, and specific conditions. Two numerical models considering different transversal post-tensioning configurations are developed based on the reference structure. The use of these two numerical models aims to broaden the applicability of this study to most U-shaped light-train viaducts. The design is based on current and future standards and recommendations, being prEN1992-1-1:2021, EN1992-1-1:2004, and fib Model Code 2010. After the numerical models and structural analysis, different sectional analyses at ultimate and serviceability levels are carried out, considering both conventional and fiber reinforced concretes. From the sectional results, FRC can provide reductions to reinforcement quantities at ultimate load levels, which are tied to the initially required reinforcement ratio (in other words, linked to the internal forces existing in the element). When higher reinforcement ratios are necessary, FRC optimizations point toward serviceability limit states, especially on the crack width reduction and the potential to reduce or suppress any additional reinforcement due to crack limitations.
Abstract Historische Eisenbahnviadukte sind stadt‐ bzw. landschaftsprägende Bauwerke. Aufgrund ihres Charakters als bedeutende Bestandteile der gebauten Umwelt, aber auch als wichtige wirtschaftliche ...Werte, ist der respektvolle Umgang bei Entscheidungen zur Instandsetzung und Weiternutzung dieser Zeugnisse zurückliegender Ingenieurbaukunst unabdingbar. Oft gehen derartige Umbaumaßnahmen mit einer umfassenden Erweiterung der Funktion des Bauwerks einher. Neben einer einfachen Verbreiterung des Fahrwegs können auch zusätzliche technische Einrichtungen, zum Beispiel Oberleitungsanlagen, zu erheblichen Eingriffen in das Erscheinungsbild des Bauwerks führen. Bauen im historischen Bestand stellt sowohl an die Planung als auch an die Bauausführung besondere Anforderungen.
Abstract Heiligenborn viaduct Historic railway viaducts define the cityscape or landscape. The fact that they actively shape and characterise the built environment and are considered important economic assets must, therefore, be taken into account for the restoration and further use of these testimonies of historic civil engineering. Such restoration measures are often accompanied by extensive enhancements of the structure's function. Apart from a simple widening of the track, additional technical installations such as overhead line equipment can have a significant impact on the viaduct's appearance. Thus, the restoration of heritage buildings and structures encompasses specific requirements for construction planning and construction work.
High-rise deep street canyons usually experience poor ventilation and large vehicular pollutant exposure to residents in near-road buildings. Investigations are still required to clarify the flow and ...dispersion mechanisms in deep street canyons and explore techniques to reduce such large pollutant exposure. By conducting computational fluid dynamics (CFD) simulations validated by wind tunnel data and scale-model outdoor field measurements, we investigate the integrated impacts of aspect ratios, first-floor and second-floor elevated building designs, viaduct settings, height variations and wind catchers on the flow, personal intake fraction (P_IF) of CO (carbon dioxide) and its spatial mean value 〈P_IF〉 in two-dimensional (2D) street canyons.
Results show that cases with H/W = 5 experience two counter-rotating vortices, much poorer ventilation and 1–2 orders larger 〈P_IF〉 (43.6–120.8 ppm) than H/W = 1 and 3 (3.8–4.3 and 5.6–5.8 ppm). Moreover, in cases with H/W = 5 the height variation results in three vertically-aligned vortices and much weaker wind, subsequently produces greater 〈P_IF〉 (1402–2047 ppm). To reduce 〈P_IF〉 with H/W = 5, various urban designs are evaluated. The first-floor elevated building design creates more effective ventilation pathways than the second-floor elevated type does and reduces 〈P_IF〉 at H/W = 5 by five orders (1402 to ~0.01 ppm) or two orders (43.6 to ~0.1 ppm) in cases with or without the height variation. However, such reductions at H/W = 1 and 3 are only 76.8%–81.4% and 22.4%–36.2% respectively. Wind catchers destroy the multi-vortex flow pattern as H/W = 5, produce a contra-clockwise main vortex and reduce 〈P_IF〉 by 1–2 orders for cases with or without the height variation.
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•Personal intake fraction (P_IF) in 2D street is ~1 and ~102 ppm as H/W = 1–3 and 5.•Cases with H/W = 5 and height variation attain three vortexes and P_IF of 103 ppm.•Elevated building designs reduce 〈P_IF〉 by 3 or 5 orders as H/W = 5.•Wind catchers break multi-vortex pattern as H/W = 5 and reduce 〈P_IF〉 by 1–2 orders.•Viaducts with one more CO source raise concentration but P_IF only change slightly.
•Propose a framework for simulating maglev trains running over transitional viaducts.•The transitional viaduct is assumed to be realistically deformable, instead of rigid.•Both curve radius and ...height difference of the inner and outer rails are considered.•The motion of train running over a transitional track is expressed by trajectory coordinates.•Analysis results are verified by the experimental ones for the Shanghai maglev line.•Vehicle rolling motions affect significantly the ride quality on transitional tracks.
This paper presents a general framework for the dynamic analysis of high-speed maglev trains running on elastic transitional viaducts, a complicated problem that lacks an efficient analysis tool. Unlike the straight and circular tracks, both the curve radius (CR) and height difference (HD) between the outer and inner rails vary along the transitional track. To start, the motion of each vehicle of the train running over a transitional track is expressed by a set of trajectory coordinates, with their orientations given in the Euler angles as functions of the CR and HD. The elastic transitional viaduct is simulated by finite elements in the global coordinates. For the maglev trains, the electromagnet force-air gap model is used to account for the interaction and coupling effect between the moving vehicles and supporting viaduct. By applying the proposed framework to the Shanghai maglev line (SML), the dynamic responses of the maglev vehicles running on the transitional viaduct are studied and compared with those on the straight and circular viaducts. Moreover, the effects of transitional track length and cant deficiency on the coupled system are investigated. The results show that for vehicles running on the transitional track, the levitation forces and vehicle’s angular velocity are highly related to the rate of change of HD of the track. The length of the transitional viaduct affects significantly all the vehicle’s responses. The increase of deficient cant angle causes a sharp increase in the responses of the transitional viaduct in both the radial and rotational directions.
A numerical simulation and a wind tunnel experiment are performed to investigate the flow field and pollutant dispersion in a two dimensional (2-D) ideal urban street canyon with roofs installed in a ...viaduct at different heights. Two typical roof shapes are taken into consideration: double flat (DF) and double triangular (DT). The simulation results show that when the height of the viaduct is at 0.875H–0.98H for DF and at 0.71H–0.988H for DT, the main flow field in the canyon will be reversed compared to initial flow field. This reversing phenomenon will aggravate pollution for DF and significantly mitigate pollution for DT compared to levels without a viaduct. The wind tunnel experiment is qualitatively consistent with the numerical simulation results which indicates that this reversing phenomenon is not just theoretical. A mechanism is proposed whereby the viaduct obstructing airflow is the key reason for the flow field reversion.
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•Reverse flow occurs if viaduct is fixed in a 2D urban street canyon.•The flow field reversing heights with two roof shapes are acquired.•Pollution will be effectively alleviated for DT cases when flow reverses.•The flow field reversing phenomenon was verified by wind tunnel test qualitatively.
The ground-borne vibration induced by the high-speed train operation in the loess area will adversely affect the safety of surrounding buildings and the daily life of residents. The ground vibration ...responses of the viaduct section and the subgrade-viaduct transition section of the Xi'an-Baoji high-speed railroad in China were measured in the longitudinal, transversal, and vertical directions. The vibration characteristics in time and frequency domains were analyzed based on the Fourier transform and the continuous wavelet transform (CWT). The acceleration levels were further calculated to evaluate the vibration exceedance of the viaduct section and the transition section. The CWT-based energy analysis method was used to analyze the vibration energy transmission pattern and the cumulative rate in the surrounding site. The analysis results show that both the viaduct section and the transition section exists vibration amplification zone, and the degree of vibration amplification in the horizontal direction is more significant than that in the vertical direction. It is also found that the horizontal direction is more prone to amplification than the vertical direction and it has the greater amplification degree because of the wave refraction. Two indicators of energy accumulation level and energy accumulation rate are proposed based on CWT. The two indicators are greater in the amplification zone than in other regions, and greater in the viaduct section than in the transition section. It shows that the acceleration vibration levels of both the viaduct section and the transition section exceed the vibration limits specified in the code. Some effective measures for the track vibration and noise reduction are finally recommended.
•The CWT-based energy analysis method is used to analyze the vibration energy transmission pattern.•The vibration amplification phenomenon is found at 20 m and 55 m in the transition section.•The ground vibration dominant frequencies are characteristic frequencies integer multiples of carriage bogies.•The horizontal direction is more prone to amplification than the vertical direction.•The energy accumulation and energy transfer efficiency are higher at the amplification area.
Vehicular pollutant exposure of residents and pedestrians in high-rise deep street canyons with viaducts and noise barriers requires special concerns because the ventilation capacity is weak and the ...literature reported inconsistent findings on flow patterns as aspect ratios (building height/street width, H/W) are larger than 2. By conducting computational fluid dynamics (CFD) simulations coupled with the intake fraction iF and the daily pollutant exposure Et, this paper investigates the impact of street aspect ratios, viaducts and noise barriers on the flow and vehicular passive pollutant exposure in full-scale street canyons (H/W=1–6, W=24m). iF represents the fraction of total emissions inhaled by a population (1ppm=10−6), while Et means the extent of human beings’ contact with pollutants within one day. CFD methodologies of passive pollutant dispersion modeling are successfully validated by wind tunnel data in Meroney et al. (1996).
As a novelty, the two-main-vortex pattern start appearing in full-scale street canyons as H/W changes from 4 to 5, however previous studies using wind-tunnel-scale models (H=6cm) reported two to five vortexes as H/W=2–5. This finding is validated by both smoke visualization in scale-model outdoor field experiments (H=1.2m, W=0.6m) and CFD simulations of Reynolds number independence. Cases with two main vortexes (H/W=5–6) experience much larger daily pollutant exposure (~103–104mg/m3/day) than those with single main vortex as H/W=1–4 (~101–102mg/m3/day). Moreover leeward-side pollutant exposures are much larger than windward-side as H/W=1–4 while oppositely as H/W=5–6. Assuming a general population density, the total iF is 485–803ppm as H/W=1, 2020–12051ppm as H/W=2–4, and 51112–794026ppm as H/W=5–6. With a single elevated pollutant source, cases with viaducts experience significantly smaller pollutant exposures than cases without viaducts. Road barriers slightly increase pollutant exposure in near-road buildings with H/W=1 while reduce a little as H/W=3 and 5. Two-source cases can experience 2.60–5.52 times pollutant exposure as great as single-source cases.
•Intake fraction (iF) and daily CO exposure (Et) are used for exposure assessment.•Effects of aspect ratios (H/W=1–6), viaduct/noise barriers are studied by CFD.•iF=102–104ppm as H/W=1–4 (one vortex) but iF=105–106ppm as H/W=5–6 (two vortexes).•Viaducts produce less CO exposure if only a viaduct-level CO source is fixed.•Noise barriers slightly reduce vehicular indoor CO exposure as H/W=3–6.
Subways or rapid transit railways can be found in many major cities. These rapid transit railways are typically built above ground whenever possible to avoid the high capital cost of tunneling and ...also the high running cost of air conditioning and ventilation. However, noise from trains running on elevated tracks or viaducts close to residential and commercial buildings or houses is a problem for many cities. Noise barriers have been used extensively to mitigate noise from motorways, heavy trunk roads, and construction sites. On the other hand, relatively few reported studies on the design and performance of noise barriers for elevated railway tracks or viaducts to mitigate rapid transit train noise. The effectiveness of noise barriers on elevated railway tracks or viaducts for the mitigation of train noise may be different and challenging to predict due to complex street canyons and surrounding buildings beside the barrier designs and construction materials. Riding on the Singapore Railway Noise Barrier Programme, the present research conducted on-site measurements of several housing estates in Singapore to investigate the effect of noise barriers on the mitigation of train noise. Comparisons were also carried out to examine the performance of two different designs, Taiwan's Taipei subway track noise barriers and the vertical noise barriers used by the Singapore Mass Rapid Transit (MRT) system. Acoustic mapping revealed that the simulated noise mitigation barriers led to a 5–12 dB(A) reduction in noise levels reaching the resident apartments.
As the requirements for reduced vibration of URT viaduct lines continue to increase, low-stiffness structures have been used extensively. When the TSI are adversely affected by low-stiffness ...structures, the TGI maintenance workload increases sharply. Therefore, it is necessary to predict and evaluate the TDGS of low-stiffness URT viaduct to resolve the conflict between vibration-reduction design and track maintenance. First, the train-steel spring floating slab track-U-beam viaduct model is established. Second, virtual track inspection method is used to obtain the virtual dynamic irregularities. After comparing with actual measurement results, we investigated the influence of linetype, bridge span, and static irregularities on the security indexes and the TDGS. The results showed that for curved viaduct, in addition to vertical dynamic irregularities, alignment/horizontal dynamic irregularities also have characteristic wavelengths at 1/n times bridge span. The time-domain peak values were larger than those of the straight viaduct. Moreover, as the bridge span increased, the TDGS degradation of the curve viaduct was more significant than straight viaduct. The vehicle security indexes of the low-stiffness viaduct lines have large safety margin, while TDGS indexes are close or even exceed the limit when structures are improperly designed. This could bring insurmountable difficulties to the track maintenance.
This article focuses on multiobjective optimization in the design of bridges and viaducts. The problem is characterized as a multi-objective optimization, with the objective functions being the ...construction cost, the environmental impact (CO2 emissions) and the design service life. For optimization, three commonly used metaheuristics in structural optimization problems were tested: Multiple Objective Particle Swarm Optimization (MOPSO), Nondominated Sorting Genetic Algorithm II (NSGA-II) and Strength Pareto Evolutionary Algorithm 2 (SPEA2). The results showed that MOPSO outperformed the other methods, achieving the highest hypervolume and Pure Diversity values. Once the best performing metaheuristic was defined, the calibration of the MOPSO parameters was then developed to improve the quality of the solutions found, reduce the execution time and increase the robustness of the algorithm. Using the Taguchi method with an orthogonal matrix consisting of 54 experiments, five parameters were evaluated at three different levels, totaling 270 analyses. The results indicated that parameter calibration led to an increase in the average hypervolume compared to the results before calibration. Moreover, the coverage of two sets revealed the superior performance of the calibrated set, demonstrating better trade-offs among the objective functions.
•Optimization of bridge and viaduct design are reviewed.•Comparing MOPSO, NSGA-II, SPEA2 for real-world viaduct design.•Calibrated MOPSO yields improved trade-off solutions for real-world viaduct design.
