Roof Edges Research Articles

3D Building Modelling from ALS Point Clouds by Delaunay Triangulation and Graph Theories

Abstract. As an important task in 3D building reconstruction, 3D roof reconstruction attracts increasing attention. Existing methods have the issue of additional errors caused by multi-step processes, resulting in relatively high uncertainty and potentially affecting the reconstruction accuracy. Deep learning-based methods to achieve the direct extraction of roof vertices and edges for reconstructing 3D roof structures tackle the issue of additional errors while leading to another problem: the reliance on large labeled datasets for training. In this study, a fully rule-based method is proposed to achieve automatic 3D roof reconstruction. Roof vertices with their edges parallel to the x-y plane are first extracted from the point clouds, and subsequently, the left roof edges connecting vertices are inferred by using Delaunay triangulation. Finally, the 3D roof structure is reconstructed by using graph analysis based on the information of roof vertices and edges. This method simplifies the process of 3D roof reconstruction, and the experiment results demonstrate that the proposed method can effectively reconstruct 3D roof structures from point clouds.

Flow characteristics over flat building roof with different edge configurations for wind energy harvesting: A wind tunnel study

The impact of climate change and global warming makes it imperative to seek sustainable solutions for the built environment. To facilitate the design of future sustainable buildings, wind tunnel tests are conducted in this study to investigate the flow characteristics and wind energy potential over a flat building roof with different edge configurations. Specifically, this study addresses the effect of parapet walls and roof edge-mounted solar panels on the wind flow over a flat-roof tall building. The results show that parapet walls generally slow down the wind speed and increase turbulence intensity as well as skewness angle, which compromises the efficiency of traditional turbine-based wind energy harvesting. On the other hand, the presence of solar panels on the roof edge (or on the top of the parapet wall) further alters flow separation and has the potential to enhance wind energy harvesting over the roof, especially for the solar panel inclined at 30°. In addition to providing valuable data for validating computational fluid dynamics (CFD) simulations, this study could also help to guide the design of wind energy harvesting devices on the building roof and explore the promising synergy with solar panels.

Re-evaluating falls through skylights in the USA: has anything changed?

Purpose With proper design and work planning, falls through fragile skylights are preventable. Skylights pose a hazard to workers when their work tasks for operations, maintenance and repair require them to be on roofs. The National Institute of Occupational Health and Safety produced guidelines and special alerts to address the dangers that are present around skylights, and the Occupational Safety and Health Administration regulations have prescriptive requirements for work performed around skylights, and yet incidents still occur. The purpose of this study is to investigate and raise awareness for the causality of the incidents involving skylights in the USA. Design/methodology/approach The authors investigated and analyzed 204 incidents involving skylights recorded by the Bureau of Labor Statistics to characterize their nature and to determine any correlation with the roof environment or the nature of the work performed. Using Google Earth and Google Maps roof geometry, proximity of skylights to roof edge and rooftop mechanical equipment was determined. Findings The majority of falls through skylights occur during roof maintenance and repair activities. Falls through skylights are underreported. Because of a general lack of good design to reduce or eliminate the risk of falling through skylights, facility managers carry the burden to properly assess work and access on roofs where fragile skylights are present. Originality/value The phenomenon of falling through skylights was made aware on a national level in the USA in 1989; however, little has been done from a design and planning perspective to reduce these incidents. This paper presents a unique perspective on the role of facility managers in understanding the hazards associated with roof maintenance near skylights.

Fundamental Characteristics of Wind Loading on Vaulted-Free Roofs

The present paper investigates the fundamental characteristics of wind loading on vaulted (cylindrical) free roofs based on a wind tunnel experiment and a computational fluid dynamics (CFD) analysis using Large Eddy Simulation (LES). In the wind tunnel experiment, wind pressures at many points, both on the top and bottom surfaces of rigid roof models, were measured in a turbulent boundary layer. The wind tunnel models, including the tubing system installed in the roof and columns, were made using a 3D printer, which made the roof thickness as small as 2 mm, whereas the span B was 150 mm and the length L ranged from 150 to 450 mm. The rise-to-span ratio f/B ranged from 0.1 to 0.4. Pressure taps were installed along the center arc and an arc near the roof edge (verge) of an instrumented model with a length-to-span ratio of L/B = 1. The value of L/B of the tested models was changed from 1 to 3 using one or two dummy models, which had the same configuration as that of the instrumented model but no pressure taps. The wind direction θ was changed from 0° (perpendicular to the eaves) to ±90° (parallel to the eaves). The CFD simulation was carried out only for limited cases, that is, f/B = 0.1 and 0.4 and θ = 0° and 45°, considering the computational time. The effects of f/B, L/B, and θ on the mean (time-averaged) and fluctuating wind pressures acting on the roofs were investigated. In particular, the flow mechanism generating large wind forces on the roof was discussed. An empirical formula was provided for the distribution of mean wind force coefficients along the center arc (Line C) at θ = 0° and 30° and along the edge arc (Line E) at θ = 40° for each f/B ratio. Note that these wind directions provided the maximum and minimum mean wind force coefficients within all wind directions for Lines C and E. Furthermore, the maximum and minimum peak wind force coefficients on the two arcs were presented. The effect of turbulence intensity of approach flow on the maximum and minimum peak wind force coefficients was investigated. The experimental results were compared with those estimated using a peak factor approach, which showed a relatively good agreement between them. The data presented here can be used to guide the design of the main wind force-resisting systems and the cladding/components of vaulted-free roofs.

Effects of Cornices on Wind Loads of Solar Panels Mounted on Gable Roof Building

The effects of various parameters of the solar panel and surrounding structure on wind loads acting on solar panels have been extensively investigated in prior studies. However, the parameter of cornice length has not been considered. With varying lengths of cornices, solar panels can be positioned either near or far away from the roof corner and edge, which are the locations where the largest wind-induced suction forces are likely to occur. To examine the effects of cornices, a wind tunnel test was conducted to measure the wind pressures on a solar module installed on a residential gable roof building. The cornice lengths varied from 0 m to 1.6 m, with an interval of 0.4 m. The results show that when wind blows perpendicular to the roof ridge, cornice can reduce the mean, STD, and peak pressure coefficients on the upper and lower surfaces and resulting net values. However, it should be noted that the most unfavorable area-averaged minimum peaks in the middle and trailing zones exhibit a gradual increase with the growing cornice length. Considering the potential risk of solar module failure resulting from high wind-induced suction forces, more caution is needed when installing solar modules on roofs with larger cornices.

Wind loading on commercial roof edge metals: A full-scale experimental study

Roof edge metal systems provide an effective interface between the roof of a building to its walls and are used to secure and protect the edge of the roof membrane. Previous studies show that damage involving roof systems mostly occurs because of their failure at perimeter edges under high winds. This study presents an effort to evaluate wind loads on these edge metal elements by conducting full-scale experiments at the NHERI Wall of Wind (WOW) Experimental Facility (EF) at Florida International University. In addition to full-scale aerodynamic and failure assessment test protocols, the experimental campaign, for the first time to the authors’ knowledge, consisted of investigating the effect of wind-induced vibrations on these dynamically sensitive systems. Pressure measurements were conducted at different layers of the edge metals systems by considering the most common installation practices in the industry. The results showed that these roofing elements experience high suctions due to near-parallel wind flows and are susceptible to significant vibration even at low wind speeds, which is a phenomenon not captured in current static pull testing. Moreover, peak pressure coefficients were also observed to increase with wind speeds due to increased dynamic contributions which may amplify the aerodynamic loads by more than about 25%. Furthermore, utilization of edge metal configurations with a higher degree of flexibility was observed to possibly reduce suction on roofing components and appurtenances.

Effect of the Innominate Bone Horizontal Rotation on Acetabular Version: A Retrospective Radiological Study on a Middle Eastern Population

Background: The impact of acetabular horizontal rotation on the development of femoroacetabular impingement and subsequently osteoarthritis is well-studied in the literature. However, there is not a clear relationship between the rotation of the hemipelvis and the version of the acetabulum. Purpose: The purpose of this study was to evaluate the influence of the rotation of the hemipelvis on the version of the acetabulum. Methods: Through a retrospective study, three-dimensional reconstructions of high-resolution CT (computed tomography) scans of 154 patients receiving pelvic scans for non-orthopedic causes were selected from our institution’s database. The horizontal rotation of the different parts of the hemipelvis was evaluated using the following parameters: superior iliac spine angle (SIS), inferior iliac spine angle (IIS), roof edge angle (REA), equatorial edge angle (EEA) and ischiopubic angle (IPA). Results: The results showed a significant positive correlation between the different angles of the innominate bone and the version of the acetabulum such as when the proximal innominate bone rotates, the cranial part of the acetabulum rotates in the opposite direction. Increased anteversion angles in females compared to males were also observed. Conclusion: The observations suggest that, in an asymptomatic population, the acetabulum should not be considered a separate entity independent from the rest of the innominate bone and that the version of the acetabulum correlates with the rotation of the hemipelvis.

Investigation of peak wind loading on a high-rise building in the atmospheric boundary layer using large-eddy simulations

Significant negative peak pressures have been observed in two recent wind tunnel experiments of a high-rise building for certain wind directions. This peak wind loading is crucial for the design of cladding systems. However, the governing flow physics is not well understood. In this study, large-eddy simulations with sufficient resolution are performed to capture and analyze these peak pressure phenomena. The atmospheric boundary layer flow is generated using a divergence free synthetic turbulence inflow generator before the high-rise building is placed in the flow at various wind directions. The mean, standard deviation, and peak pressure coefficients are shown to agree well with the experimental measurements. The strongest negative peak pressures near the top trailing corner on the leeward surface are captured by simulations with the resolved scale between the Taylor microscale and Kolmogorov scale. The probability density function of the pressure at the top trailing corner is well approximated using a log-normal distribution, which is a signature of the effect of small-scale turbulence intermittency. Flow visualization indicates that the strong negative peak values result from the interaction between small eddies shed from the separated flow region at the upwind roof edge and larger eddies downstream of the leeward roof edge.

Active flow control of the airflow of a ship at yaw

This paper implements the steady Coanda effect active flow control (AFC) on the Chalmers ship model (CSM) to study its influence on the ship’s side force and airwake under the yaw effect. The study is conducted numerically using Large Eddy Simulation (LES) with Wall-Adapting Local-Eddy Viscosity (WALE) model. Numerical methods are validated by the experimental data acquired from the baseline CSM under 10∘ port-side wind. The model with AFC is created by modifying the square-shaped hanger base to the Coanda surface and added with injection slots along the base’s roof edge and two side edges. The results show that the base-shape modification significantly alters the vortex structure on deck from z-direction vortex (ZV) to streamwise vortex (SV), and the steady Coanda effect with a momentum coefficient (Cμ) of 0.02 further enhances the SV with the removal of port-side vortex (PV). The side force and yaw moment are reduced by 5.27% and 7.97%, respectively in the AFC case due to the reduction of port-side (windward) ship-surface pressure. Furthermore, the current AFC can suppress the low-speed region and alleviate the velocity gradient in the lateral direction, which mitigates the regions of high TKE (turbulent kinetic energy) and high shear stress along the port-side deck.

Wukro Medhane Alem: A Medieval Rock-hewn Church in Historic Gondar, Ethiopia

This study explores the historical and architectural heritage of Wukro Medhane Alem, a least-known monolithic rock-hewn church in South Gondar. Primary and secondary sources of the study were collected through fieldwork, interviews, and literature review. The study shows that it is one of the medieval churches traditionally attributed to King Lalibela (r. 1181-1221). The hypogeum has a rectangular plan being deeply excavated out of bedrock. There is a built-up feature added over the roof's edge of the rock-hewn church. It imitates a Gondarine architectural tradition, implying the transition from the earlier rock-hewn tradition to the building architectural orientation of the Gondarine period (1636-1769). Its hypogeum reflects an Aksumite and medieval architectural tradition. Internally, the basilica is partitioned into kine mahilet (chanting), kiddist (holy) and mekides or kiddiste kiddusan (sanctuary) rooms through the arranged rock-hewn pillars, which are refined with arches, capitals, and entablatures that create the ceiling of the roof which is also decorated with engraved cruciform, geometrical, quadrifoliate, and crown-like protruding features. The kiddiste kiddusan has six sub-sanctuaries with doubled circular domed roofs and rectangular altars cut from the main rock. The hypogeum, thus, has such potential values to be promoted as an alternative tourist site in historic Gondar, which is mainly known to tourists for its built palaces.

Wind loading characteristics and roof zoning of solar arrays mounted on flat-roofed tall buildings

Effects of building height (24, 48, 72, and 96 m) and panel tilt angle on wind loads of solar arrays on sharp roofs were investigated through wind tunnel testing. The largest mean and negative peak module force coefficients among all modules and wind angles tended to decrease as building height increased. This is attributed to that approaching flows tend to separate from roof edges rather than building sides of low-rise buildings. Moreover, building height exerted a more significant influence on the largest mean and negative peak module force coefficients among all wind angles on modules at roof corners than those at roof edges and centers. Roof zoning of solar arrays was conducted using the k-means algorithm. The roof zoning scheme helps to balance the design cost and structural safety of rooftop solar arrays. Roofs can be divided into three categories based on k-means clustering analysis, i.e., corner, edge, and interior zones. Besides, regression analysis of mean and negative peak loads with building height at various roof zones was conducted. This study provides recommendations for design wind loads on solar arrays mounted on roofs with different heights.

Large eddy simulation of ship airflow control with steady Coanda effect

This paper numerically studies the steady Coanda effect for drag reduction and airwake manipulations on the Chalmers ship model (CSM) using large eddy simulation with wall-adapting local-eddy viscosity model. Numerical methods are validated by experimental data acquired from the baseline CSM. In creating the flow control model, the hanger base of the baseline CSM is modified with Coanda surfaces and injection slots along its roof edge and two side edges. Four representative cases are studied: a no-jet case and three cases with the same momentum coefficient of the jet flow activated at different locations (roof, sides, and combined). The results show that the four cases have various performances in drag reduction and vortex structures on the deck. They are also different in mean and turbulent quantities as well as POD (proper orthogonal decomposition) modes in their airwake. It is found that the roof-jet has a stronger Coanda effect and is more vectored toward the low-speed area (LSA) on the deck than the side-jets that detach earlier from the Coanda surface. The energization process is, therefore, different where the roof-jet is more effective that directly brings high momentum to LSA and side-jets manipulate shear layers for mixing enhancement. The cases with roof-jet achieve better mitigation of flow re-circulation and higher recovery of streamwise velocity with lower turbulent fluctuation in the airwake. POD analysis suggests that the roof-jet can stabilize the wake.

Mechanism of Icicle Formation at Folded-plate Roof Edges

Mechanism of Icicle Formation at Folded-plate Roof Edges

Wind loading on a low-slope gabled roof: Comparison of field measurements, wind tunnel data, and code provisions

The current wind load provisions for low-slope roofs in the NBCC were established in the 70 s with wind tunnel experiments using analog data technology. These coefficients have remained almost unchanged. As the wind pressure measurement tools have significantly improved during the past 50 years, verification of the original pressure coefficients is required. The National Research Council of Canada (NRC), in collaboration with the Special Interest Group on Dynamic Evaluation of Roofing Systems (SIGDERS) consortium, conducted a wind load investigation to verify the suitability of the current wind load provisions. The investigation was carried out using both field measurements and wind tunnel simulations. An ideal full-scale representation of the low-slope roof specified in building code was instrumented and continuous data was collected for four years. A duplication of the building was evaluated by two wind tunnels to investigate the effect of critical wind directions. The paper presents the efforts made to make field measurements comparable to wind tunnel data and code provisions. It was observed that records with mean wind a speed above 22 mph (10 m/s) reduce the data variability and maximize reliability, which are important features for the code verification process. The goal of this research is to combine multiple sources of data to verify the suitability of wind load provisions on low-slope roofs. The research focuses on NBCC-2020 as an application. Evidence is presented that the NBCC-2020 provisions for the Roof Edge Zone is currently underestimated and needs to be increased. The study suggests taking the opportunity of Edge provision enhancement to merge Corner and Edge into a unique “Perimeter” load provision. The suggested code change addresses the current underestimation of the Edge Zone coefficients (wind load upgrade), and provides construction simplification to minimize roofing failure associated with labour-induced errors during cladding system installation (constructability upgrade).

Investigation of effects of repose angle and critical sliding angle of snow on curved roofs

Accompanied by extreme snowy weather occurred frequently, the number of collapse accidents of structures which are caused by uneven snowdrift is increasing. The formation of uneven snowdrift on the roofs is substantially related to snow profile. Especially to curved roofs, snow profile has certain peculiarity due to curvature of roof edge. The inter-particle properties such as repose angle and critical sliding angle of snow also affect snow profile on curved roofs. This study is to systematically investigate laws of inter-particle properties with measuring, provide a revision approach to accurately restore snow profile considering inter-particle properties, and validate the feasibility of approach by comparing simulation results with that of wind tunnel test. Firstly, a series measuring of repose angle is conducted and results show that repose angle is about 60°. Then the wind tunnel test on curved roofs is carried out to investigate properties of critical sliding angle and found that critical sliding angle is around 60°. Based on inter-particle properties, a revision approach of snow profile is proposed. Snow distribution of numerical simulation with revised snow profile is more in line with wind tunnel test. It is found that snow profile which is revised by inter-particle properties influences characteristics of flow field around roofs and snowdrift on curved roofs.

Air pollutant dispersion around high-rise buildings due to roof emissions

Air quality in the built environment has a significant impact on public health, particularly in densely populated cities where residents live in closely-packed high-rise buildings. In this case, communicable respiratory diseases are apt to spread through vent pipe emissions on the building roof and facilitate community transmission. This study applied computational fluid dynamics to simulate the dispersion of the pollutants discharged from the roof vent pipes around high-rise buildings. The results show that the dispersion process is dominated by wind-structure interaction, wind incidence angle, air pollutant discharge location, and vent pipe height, and the dispersion is more complex around crucifix-form buildings than cubic ones. When the wind incidence angle reaches around 90°, the air pollutants are entrained in the re-entry of the building, thus impeding the dispersion process. The building areas most adversely affected by air pollutants are located on high floors near the vent pipe. Changing air pollutant discharge location and increasing the height of the vent pipe can significantly reduce the affected area. Where the height of the vent pipe is restricted, parapets at the roof edges are suggested to further reduce the adverse effects of air pollutants. These research findings can help to reduce the risk of airborne contaminants/diseases spreading in current and future built environments.

An experimental investigation of a roof-mounted horizontal-axis wind turbine in an idealized urban environment

Wind-tunnel experiments are performed to investigate the effect of minor modifications to the roof edge shape on the power performance and wake characteristics of a horizontal-axis wind turbine sited on a cube-shaped building. Three roof edge shapes are considered: a sharp edge, a rounded edge, and a solid fence. The power performance of the turbine is dependent on its streamwise position, and on the roof edge shape due to the difference in the flow shear induced by different roof edges. The sharp edge and solid fence cases show high variation in power with the turbine position, which is reduced significantly in the rounded-edge case. The turbine shows the worst power performance regardless of its position in the fence case. The roof edge shape is also found to affect the wind turbine wake. Specifically, the wake recovery and expansion rates are found to be greatest for the fence case, and they decrease with the increasing smoothness of the roof edges. This is related to the difference in the base flow turbulence induced by different roof edge shapes. Compared to the base flow, turbulence intensity in the wake is reduced on the building, except at the rotor top tip level.

Wind Loading of Photovoltaic Panels Installed on Hip Roofs of Rectangular and L-Shaped Low-Rise Buildings

Many residential houses in Japan have hip roofs with pitches ranging from 20° to 30°. Recently, roof-mounted photovoltaic (PV) panels have become popular all over the world for environmental conservation. The design of PV systems in Japan is usually based on the Japanese Industrial Standard (JIS) C 8955 (2017). However, the standard does not provide wind force coefficients for PV panels installed near roof edges (up to 0.3 m from the edge) because flow separation at the roof edges causes large up-lift forces on such panels. In this paper, we investigated the wind force coefficients for designing PV panels installed on hip roofs of rectangular and L-shaped low-rise buildings. The roof pitch was set to 25° as a typical value. Rectangular panels were installed almost over the whole roof, including the edge zones. Because the thickness of PV panels and the distance between PV panels and the roof are both as small as several centimeters, it is difficult to make wind tunnel models of PV systems with the same geometric scale as that for buildings. We focused on a numerical simulation using the unsteady Bernoulli equation to estimate the pressures in the space between PV panels and the roof. In the simulation, we used the time histories of wind pressure coefficients on the bare roof, which were measured in a turbulent boundary layer. We propose installing PV panels with small gaps between them along their short sides. The gaps may reduce the wind loads not only on the PV panels but also on the roofing due to pressure equalization. We discuss the optimum gap width from the viewpoint of wind load reduction.

Multi-antenna 3D pattern design for millimeter-wave vehicular communications

The transformation of the automotive industry towards ubiquitous connection of vehicles with all kind of external agents (V2X) motivates the use of a wide range of frequencies for several applications. Millimeter-wave (mmWave) connectivity represents a paramount research field in which adequate geometries of antenna arrays must be provided to be integrated in modern vehicles, so 5G-V2X can be fully exploited in the Frequency Range 2 (FR2) band. This paper presents an approach to design mmWave vehicular multi-antenna systems with beamforming capabilities considering the practical limitations of their usage in real vehicular environments. The study considers both the influence of the vehicle itself at radiation pattern level and the impact of the urban traffic on physical layer parameters. Connectivity parameters such as Signal-to-Interference-plus-Noise Ratio (SINR) and outage probability are optimized based on the array topology. A shaped beam in the vertical plane based on three preset radiating elements is proven to be robust enough against self-scattering effects on the vehicle body. Regarding the horizontal geometry, four panels on the roof's edges provide good coverage and link quality. The number of horizontal antennas per panel tightly depends on the required values of the link quality metrics, potentially leading to a non-uniform geometry between sides and front or back panels.

Application of a Numerical Simulation to the Estimation of Wind Loads on Photovoltaic Panels Installed Parallel to Sloped Roofs of Residential Houses

Many residential houses with sloped roofs are equipped with photovoltaic (PV) systems. In Japan, PV systems are generally designed based on JIS C 8955, which specifies wind force coefficients for designing PV panels. However, no specification is provided to the PV panels installed near the roof edges where high suctions are induced. When installing PV panels in such high-suction zones, we need to evaluate the wind loads on the PV panels appropriately, usually by performing a wind tunnel experiment. However, it is difficult to make wind tunnel models of PV panels with the same geometric scale as that for the building, e.g., 1/100, because the thickness of PV panels and the distance between PV panels and a roof are both several centimeters. Therefore, in the present paper a numerical simulation is applied to the estimation of pressures in the space between the lower surface of PV panels and the roof surface, called “layer pressures”, using the unsteady Bernoulli equation and the time histories of external pressure coefficients obtained from a wind tunnel experiment. An assumption of the weak compressibility of the air and an adiabatic condition is made for predicting the layer pressures from the flow speed through the gaps. The simulation method is validated by a wind tunnel experiment using a model of square-roof building.