This paper studies for the first time the effect of the spatial variability of ground motions (SVGM) with large intensities on the inelastic seismic response of the pylons which are responsible for ...the overall structural integrity of cable-stayed bridges. The
svgm
is defined by the time delay of the earthquake at different supports, the loss of coherency of the seismic waves and the incidence angle of the ground motion. An extensive study is conducted on cable-stayed bridges with ‘H’- and inverted ‘Y’-shaped pylons and with main spans of 200, 400 and 600 m. The
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is most detrimental to the pylon of the 200-m span bridge owing to the large stiffness of this bridge compared to its longer counterparts. The stiff configuration of the inverted ‘Y’-shaped pylon makes it more susceptible against the multi-support excitation than the flexible ‘H’-shaped pylon, especially in the transverse direction of the response. Finally, the earthquake incidence angle is strongly linked with the
svgm
and should be included in the seismic design of cable-stayed bridges.
This study is conducted within the Gambia River Basin Development Organization Energy Project (OMVG) framework. The construction of a high voltage interconnection network fed by a hydropower station ...to supply electricity to OMVG Member States was done on stable ground. During the installation pits for the pylons in Labé Prefecture, Republic of Guinea, cavities were discovered in the geological formations during the initial planned route. Structurally, the study area is bounded by two major faults to the east and west of northeast direction. The geomorphology is made up of a central plateau, intermountain depressions, piedmont plains, talwegs, and glacis. Geological investigations were obtained by a geophysical Two-dimensional Electrical Resistivity Tomography (ERT) method. The results show that the synthetic lithological profile from top to base was sandy-clayey soil, hard cuirass, and a layer of gravel followed by a mottled zone comprising an indurated part and an imbibed part just before the source rock. The cavities were observed probably because of the dissolution of certain minerals constituting the weathering crust due to the infiltration, underground waters, and the seasonal variation in the level of the surface watercourses. Geophysical results showed a very good agreement with the visual observations.
Realizing autonomous inspection, such as that of power distribution lines, through unmanned aerial vehicle (UAV) systems is a key research domain in robotics. In particular, the use of autonomous and ...semi-autonomous vehicles to execute the tasks of an inspection process can enhance the efficacy and safety of the operation; however, many technical problems, such as those pertaining to the precise positioning and path following of the vehicles, robust obstacle detection, and intelligent control, must be addressed. In this study, an innovative architecture involving an unmanned aircraft vehicle (UAV) and an unmanned ground vehicle (UGV) was examined for detailed inspections of power lines. In the proposed strategy, each vehicle provides its position information to the other, which ensures a safe inspection process. The results of real-world experiments indicate a satisfactory performance, thereby demonstrating the feasibility of the proposed approach.
•Nonlinear dynamic responses of a double-pylon cable-stayed bridge under scour and ship impact are investigated through a high-resolution finite-element simulation process.•The scour effects on both ...the bridge and the ship are identified including those on the structure and the ship-bow.•Research findings may offer insights for guiding the multi-hazard design of long-span bridges considering both hazards of scour and ship collision.
Safety evaluation of a bridge crossing a river under vessel impact is commonly conducted based on the original model of the bridge. However, the bridge may be subjected to local scour within its service time. Therefore, it is necessary to assess the safety of the bridge under multiple hazards: local scour and vessel impact. In this effort, the nonlinear dynamic performance of a double-pylon cable-stayed bridge is investigated by a high-resolution finite-element (FE) method. First, to validate the accuracy of the FE model, a drop-hammer test conducted by previous researchers is simulated, and the numerical results show that the impact force, displacement, and failure modes match with those in the test for each case. Based on the validation, an FE model that constructs a complex colliding system for a double-pylon cable-stayed bridge and a ship is created to conduct nonlinear dynamic analysis. The impact forces, deformation of the pylon and pile foundation, and crush depths of the ship are calculated. The findings indicate that (1) local scour has a small effect on the rising step of ship impact force but affects its descending step; (2) the displacement at the impact point significantly increases with scour depth; (3) scour reduces the crush depth of the ship bow when the ship collides at lower collision velocities; (4) the ship impacts activate the vibration of the high-rise pylon, and the resulting damage severity in the pylon increases with scour depth under the same collision condition. The findings in this study can be used to guide the analysis and design of large-span bridges to resist local scour and ship impact.
The fire effect and performance of bridge pylons under construction were investigated via an analysis conducted on two types of pylons with different wall thicknesses. Three fire scenarios, namely ...internal fire, external ring fire, and external side fire, were established for a 40 m high section of the bridge pylon under construction. The distribution of fire smoke and temperature was obtained using fire dynamics simulation software for different fire scenarios. In addition, a finite element simulation was performed using the thermal–mechanical coupling method to obtain the temperature, stress, and deformation of the columns. The simulation results demonstrate that the average temperature of the internal fire is higher. The chimney effect extends the height range of temperature influence. In the vertical direction, the temperature decrease curve for the internal fire follows a single negative exponential function, while the external fire adheres to a double negative exponential function. The thickness of the temperature influence in the bridge pylon is extended by heating to approximately 200 mm. The stress value considering the thermal expansion coefficient is nearly 27.5 times that without the expansion coefficient, while the deformation value increases by 1 to 8 times. In conclusion, the calculations of the coupled expansion coefficient are helpful in improving the fire safety of bridge pylons.
•Backflashover rate evaluation based on Monte Carlo method.•Backflashover performance comparison between a composite pylon and conventional towers.•Separated grounding down-leads of composite pylon ...to prevent simultaneous backflashover of double circuits.•Strategy on installing surge arresters based on different tower configuration.
A design of a fully composite pylon with external grounding down-leads has been proposed for new-generation 400 kV transmission towers, able to save lines corridors and to reduce visual impact. This paper investigates and compares the backflashover performance of a composite pylon and two conventional metallic towers, which have been widely installed in Denmark. The transient models of overhead lines and all three towers were established respectively and the transient analysis was carried out in PSCAD. Monte Carlo method was used to estimate backflashover rate. The backflashover rate of composite pylon is 0.4526 cases per 100 km per year, which is in the same range, but slightly higher than that of metallic towers. The separated grounding down-leads of double circuits on composite pylon eliminates the danger of simultaneous backflashover of double circuits, which exists in transmission lines supported by metallic towers. After comparing the overvoltages to three phases of the three towers from backflashover, it is worthy considering that the installation of surge arresters at all three phases of composite pylon has a strong impact on the backflashover rather, but for the two metallic towers only the surge arresters at the upper phase has an impact.
Static calculations of experimental models in an elastic formulation were carried out, and the regularities connecting the dependences of forces in the calculated cross-section of punching out from ...the main structural parameters of contacting elements (reinforced concrete slabs and pylons) and from the used concrete class were revealed. This article concerns the safety issues of reinforced concrete slabs under punching with different ratios and combinations of pylon and slab thickness parameters, as well as concrete strength. The objectives of the research are consideration of the fracture pattern of reinforced concrete monolithic slabs due to punching shear; comparative analysis of modern normative calculation methods and flat reinforced concrete slabs due to static punching shear; finite element modelling and analysis of the punching shear calculation results for reinforced concrete floor slabs; and the force distribution over the area of the contacting elements-saw and floor slab. The practical significance of the results lies in the use of the obtained forces in the contacting elements for the calculation and design of reliable structures of beamless floor slabs.
This study aimed to estimate the drag and lift coefficients of the long-span bridge pylon using the finite volume method (FVM). The k-ω turbulence model was applied to analyze the behavior of wind ...flow around the pylon, yielding drag and lift coefficient values with an error of 0.98% compared to a previous tunnel experiment. Four recommended cross-sections were proposed to reduce drag and lift forces acting on the pylon, including concave, convex, crossing, and chamfering cross-sections. The finding indicated that drag and lift coefficient decreased for all cross-sections. Cutting edges of concave, convex, and chamfering cross-sections with a ratio ranging from 0.2 to 0.3 has the greatest impact on reducing drag coefficient, while the crossing cross-section with a cutting ratio ranging from 0.2 to 0.25 has the lowest drag coefficient. The maximum reduction in drag and lift coefficients were 23.69% and 13.14% for concave and chamfering cross-sections. Thus, cutting edges of cross-sections is an effective method to enhance the aerodynamic stability of the pylon. Additionally, we evaluated drag and lift coefficients for different wind direction angles. The angles of 0, 30, and 90 degrees resulted in the highest drag coefficient, while the angle of 0 degrees and the angle of 90 degrees resulted in the lowest and highest lift coefficient, respectively. This study not only provides recommendations for cross-sections that reduce forces acting on the pylon but also provides the intensity of this reduction through corresponding estimation equations. In conclusion, concave and chamfering cross-sections are the most effective in reducing drag and lift coefficients, or, in other words, increasing the aerodynamic stability of the pylon.
Buffeting is a kind of wind-induced vibration phenomenon of long-span cable-stayed bridges which is easy to occur. Balanced cantilever method is widely employed for the construction of cable-stayed ...bridge. The maximum double-cantilever state is the most dangerous state of wind resistance. Through the aeroelastic model wind tunnel experiment, the buffeting response of a cable-stayed bridge in construction under skew winds is studied in this paper. The variation law of buffeting response with the wind yaw angle is compared between the two cases with and without pylon. The experimental results show that for the same wind yaw angle the lateral and vertical buffeting responses of the main girder increase with the wind speed approximately in a quadratic curve, while the torsional buffeting response tends to increase linearly. At the same wind speed, the buffeting response of the main girder presents non-monotonic changes with increased wind yaw angle. Under skew winds, due to the disturbing effect of the pylon and the influence of the three-dimensional flow field, the buffeting response of the main girder will be affected by the aerodynamic interference of pylon. When the wind yaw angle is small, the interference effect is not obvious, with the increase of wind yaw angle and wind speed, the interference effect begins to appear. Generally speaking, the aerodynamic interference of the bridge pylon on the buffeting responses can be ignored.
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