Search Results (8)

In modern society, distributed photovoltaics are widely used, and overhead photovoltaic roofs are favored for their many advantages; however, they are vulnerable to failure during high-wind events. Parapets are common auxiliary structures on building rooftops. Wind tunnel testing was employed to investigate the effects of parapet configurations on wind pressures acting on overhead photovoltaic (PV) roofs. Results show that wind suction dominates, with maximum negative pressure consistently at the windward corner leading edge. A solid parapet significantly increases the maximum mean pressure coefficient, whereas perforated parapets have little effect. In most cases, parapets reduce fluctuating pressure coefficients. Extreme pressure distribution exhibits significant regional characteristics, with the most unfavorable area at the roof corner. The solid parapet increases unfavorable extreme values at the corner. Horizontal and rectangular grid parapets reduce extreme pressure coefficients at the high-eave corner with minimal impact on the low-eave corner, while the vertical parapet increases values at the low-eave corner. Under the conditions of this experiment, among the four parapet types, the horizontal and rectangular grid parapets have little effect on the mean wind pressure and significantly reduce the peak wind pressure, thereby helping to ensure the wind resistance safety of the photovoltaic roof. Full article

Electrified roads represent an emerging transportation solution in the context of global energy transition. These systems enable vehicles equipped with roof-mounted pantographs to draw power from overhead contact lines while in motion, allowing continuous energy replenishment. The effectiveness of this energy transfer—namely, the quality of pantograph–catenary interaction—is significantly influenced by the pantograph’s equivalent mechanical parameters. This study develops a three-dimensional overhead catenary model and a five-mass pantograph model tailored to electrified roads. Under conditions of road surface irregularities, it investigates how variations in equivalent pantograph parameters affect key contact performance indicators. Simulation results are used to identify a new set of equivalent pantograph parameters that significantly improve the overall quality of pantograph–catenary interaction compared to the baseline configuration. Sensitivity analysis further reveals that, under road-induced excitation, pan-head stiffness is the most critical factor affecting contact performance, while pan-head damping, upper frame stiffness, and upper frame damping show minimal influence. By constructing a coupled dynamic model and conducting parameter optimization, this study elucidates the role of key pantograph parameters for electrified roads in determining contact performance. The findings provide a theoretical foundation for future equipment development and technological advancement. Full article

In the high-speed rail industry, the overhead contact line erected along the railroad is used to supply the electricity to the high-speed train via a pantograph on the carbody’s roof. This work attempts to explore the effect of contact line pre-sag on the contact quality between the pantograph and the contact line. A nonlinear finite element approach is implemented to build the overhead contact line system with accurate description of the pre-sag of the contact line. Through a nonlinear solution, the effect of contact line pre-sag on the contact force is analysed with different train speeds and tension classes. The analysis result indicates the feasibility of tuning the pre-sag to improve the interaction performance at a given speed and tension class. In the low-speed range, the change of pre-sag does not have a significant effect on the interaction performance. However, when the speed increases up to a certain value, the effect of pre-sag on the contact force is nonnegligible. The increase in tension can reduce the sensitivity of the interaction performance to the pre-sag. An optimisation procedure is implemented to obtain the optimal amount of pre-sag for different train speeds and tension classes. The results indicate a necessity to include a certain amount of contact line pre-sag to maintain an excellent interaction performance at high speed. Full article

A steel-batten ribbed cable dome structural system is proposed. By replacing the upper flexible cables with semi-rigid steel battens, rigid roofing materials were conveniently installed overhead via non-bracket or less-bracket technology. Additionally, an 8 m diameter test model was designed, and a ‘ω’ shaped less-bracket consequent hoist-dragging system was adopted. Finally, the test model was tested under symmetric and asymmetric uniform loading arrangements, while a finite element model was established to verify the test values. The results indicate that the measured values are basically consistent with the finite element values. In the early steps of hoisting and dragging, the structure establishes a prestress, accumulates stiffness, and found its internal force balance, while the entire structure keeps a “ω” shape to guarantee stability. As the internal forces of the components increase, the structure turns from “ω” to “m” and finally reached its designed shape. With increasing symmetric uniform load, the internal forces of the cables decrease, the bending stresses of the steel battens increase, and the steel battens remain in the elastic stage. Under an asymmetric uniform load, the high loaded area is displaced downward, and the low loaded area behaves upward, twisting the overall structure. Full article

According to existing rigid roofing projects, a new structure called the Levy hinged-beam cable dome is proposed. By replacing the upper flexible cables with hinged beams, rigid plates can be installed overhead. To fulfill the requirements of integral tow-lifting construction, the setting criteria for the temporary hinged joints on ridge beams were presented. An 8-m diameter specimen was manufactured and monitored to investigate the structural configurations during the accumulative traction-hoisting construction process. Finally, the specimen was tested under full-span and half-span loading conditions, while a numerical model was built to verify the experimental values. The results show that in the early stages of traction-hoisting, the structure establishes the overall prestress and finds its internal force balance, while the entire structure is in a shape of “ω”. As the component’s internal force increases during the construction steps, and the local deformations of the hinged beams gradually decrease, with the entire structure changing from “ω” to “m”, and finally reach their designed states. Under full-span loads, large local deformations occurred at the HB-3 hinges, while the bending stresses of these hinged beams were relatively small. Under half-span loads, the loading part exhibits a downward appearance, while the unloading part exhibits upward deflection. Full article

Poultry production requires electricity for optimal climate control throughout the year. Demand for electricity in poultry production peaks during summer months when solar irradiation is also high. Installing solar photovoltaic (PV) panels on the rooftops of poultry houses has potential for reducing the energy costs by reducing the electricity demand charges of utility companies. The objective of this research was to estimate the rooftop areas of poultry houses for possible PV installation using aerial images acquired with a commercially available low-cost unmanned aerial vehicle (UAV). Overhead images of 31 broiler houses were captured with a UAV to assess their potential for solar energy applications. Building plan dimensions were acquired and building heights were independently measured manually. Images were captured by flying the UAV in a double grid flight path at a 69-m altitude using an onboard 4K camera at an angle of −80° from the horizon with 70% and 80% overlaps. The captured images were processed using Agisoft Photoscan Professional photogrammetry software. Orthophotos of the study areas were generated from the acquired 3D image sequences using structure from motion (SfM) techniques. Building rooftop overhang obscured building footprint in aerial imagery. To accurately measure building dimensions, 0.91 m was subtracted from building roof width and 0.61 m was subtracted from roof length based on blueprint dimensions of the poultry houses. The actual building widths and lengths ranged from 10.8 to 184.0 m and the mean measurement error using the UAV-derived orthophotos was 0.69% for all planar dimensions. The average error for building length was 1.66 ± 0.48 m and the average error for widths was 0.047 ± 0.13 m. Building sidewall, side entrance and peak heights ranged from 1.9 to 5.6 m and the mean error was 0.06 ± 0.04 m or 1.2%. When compared to the horizontal accuracy of the same building measurements taken from readily available satellite imagery, the mean error in satellite images was −0.36%. The average length error was −0.46 ± 0.49 m and −0.44 ± 0.14 m for building widths. The satellite orthomosaics were more accurate for length estimations and the UAV orthomosaics were more accurate for width estimations. This disparity was likely due to the flight altitude, camera field of view, and building shape. The results proved that a low-cost UAV and photogrammetric SfM can be used to create digital surface models and orthomosaics of poultry houses without the need for survey-grade equipment or ground control points. Full article

Cable-stayed structures are widely employed in several fields of civil, industrial, electrical and ocean engineering. Typical applications are cable-stayed building roofs, bridges, guyed masts, overhead electrical lines, and floating device anchorages. Since the cable behavior is often highly nonlinear, suitable equivalent mechanical cable models are often adopted in analyzing this kind of structures. Usually, like in the classical Dischinger’s approach, stays are treated as straight rods offering an equivalent axial tangent stiffness, so that each of them can be substituted with an appropriate equivalent nonlinear spring or truss element. Formulae expressing equivalent stiffness provided by classical methods are satisfactory only when the cable is highly stressed, and therefore its sag is small with respect to its chord; on the contrary, when the cable is slack, they give often contradictory or meaningless results. Aiming to remove that limitation, a more refined approach based on the application of the virtual work principle is discussed. Important products of that original rational criterion are accurate and closed form innovative expressions of the tangent stiffness of the cable, whose field of application is independent on the sag to chord ratio of the cable, as well as on the magnitude of the normal stresses. Referring to some relevant case studies, the results obtained applying these new formulae are critically discussed for cables made of different materials, also in comparison with the approximate expressions provided by simplified methods. Full article

Prior research on extrication of victims entrapped in stored grain has measured the vertical forces applied to a representative victim (i.e., mannequin) using an anchor point that is mounted directly overhead. However, primarily because of how most grain storage structures are designed, the forces applied would more likely be coming from an angle. This is due to the victim typically being entrapped in the center of the grain mass while the access point is at the perimeter of the roof. The objective of this study was to measure the peak forces required to pull a mannequin at an angle and compare it to vertical pull. An adult-size mannequin was pulled out of dry corn and soybean masses from various depths and at various angles. It was found that both corn and soybeans were comparable regardless of depth or angle with the exception of 15° angle. It was also found that, at pulling angles of 60° and 75°, the loads were comparable to those required at 90° or directly overhead. Only at the sharper angles of 15° and 30° did the peak forces significantly increase. The results highlight that there is some flexibility in the placement of the anchor point and that extrication forces on the body will increase at sharper pull angles. Full article