Building Aspect Ratio Research Articles

Research on the air-infiltration rate shelter coefficient of building complexes based on building parameter clustering

The configuration of a building complex can significantly influence the air-infiltration rate, which subsequently affects the energy consumption for heating and cooling. Given the diversity of parameters associated with a building complex, it is challenging to study all combinations. This study proposed the k-means clustering method to identify representative building clusters, thereby facilitating the derivation of correction coefficient for the air-infiltration rate within a complex. Initially, data pertaining to district characteristics, such as the complex density, height, and building aspect ratio, were collected and clustered to obtain several representative groups of building clusters. Subsequently, a validated computational fluid dynamics program with the renormalization group (RNG) k–ε turbulence model was employed to investigate the spatial characteristics of the pressure coefficient (Cp) on building surfaces across various groups within the complex. Finally, the shelter coefficient (SAIR), which represents the ratio of an individual building to those in different groups, was determined to correct for the air-infiltration rate in diverse district types. The results show that SAIR varies considerably (from 0.15 to 0.53) owing to the different densities, heights, and layouts between buildings. The applicability of SAIR was further demonstrated and verified in a case study of a building in Dalian, China. The research results can provide a method for predicting the air-infiltration rate of building complex.

Gust Factor Approach for Estimating Maximum Response and Control Force in High-Rise Base-Isolated Buildings with Active Structural Control

This paper devises a new method for estimating the maximum response and maximum control force for high-rise base-isolated buildings with active structural control (active base isolation) to simplify the conventional complex design procedure. While active base isolation has emerged as a prominent solution for achieving high control performance, its design process is inherently complex, particularly when applied to high-rise buildings where wind loads become prominent. To address this problem, we propose a streamlined method inspired by the gust factor methodology widely used in conventional passive wind-resistant designs. This method estimates the maximum response and maximum control force without the need for numerical simulations. We first construct an equivalent passive model of a multi-degree-of-freedom control system to theoretically compute the dynamics of the system. Based on the constructed equivalent passive model and then propose a method to calculate the mean displacement and mean control force using only the static equilibrium of this model. Furthermore, we extend the conventional gust factor approach to active base isolation to estimate the maximum displacement and maximum control force for active base isolation without the need for numerical simulations. We validate our methods through a series of numerical examples, incorporating key parameters such as feedback gain, aspect ratio of building, return period of wind force, and stiffness of isolation. Numerical verifications show that the mean response and mean control force are estimated by the static equilibrium of the proposed equivalent passive model. Moreover, the maximum response and maximum control force can be estimated by the proposed gust factors. Our methods can be applied for feedback control systems using a given feedback gain.

The impact of aspect ratio of buildings implementing Horizontal light pipe and shading systems on daylight performance

ABSTRACT Deep-plan buildings limit daylight use in spaces far from the building perimeter, leading to uneven daylight distribution. Integrating a Horizontal Light Pipe (HLP) as an optical daylighting system, reflective light shelves, and blinds as shading systems can reduce excessive daylight levels at the perimeter area of a building and improve daylight uniformity. Earlier investigations of HLP daylight performance concentrated on fixed building geometries, but few studies focused on the building aspect ratio, one of the design variables of building geometry that greatly influences daylight performance. This study aims to investigate the impact of the aspect ratio of buildings implementing HLP and shading systems on daylight performance. The research method was experimental, using IES-VE simulation as a tool. The daylight factor (DF), uniformity daylight factor (UDF), and useful daylight illuminance (UDI) of various aspect ratios and depths of office buildings implementing HLP and shading systems were analyzed. The results show that increasing the building aspect ratio from 1:1 to 2.1:1 sequentially increased the average DF and UDF values by 18.47% and 17.2%, respectively. Improving the building aspect ratio from 1:1 to 2.1:1 along the east-west axis improved the UDI by 3%, whereas the north-south axis decreased it by 10.2%.

The NOx-O3 photochemical reactive air pollutant dispersion around an isolated building—the role of turbulence model and building aspect ratio

The NOx-O3 photochemical reactive air pollutant dispersion around an isolated building bears significant scientific and engineering implications. The present work extends the investigation to the role of turbulence models and building aspect ratio, providing valuable insights for future numerical investigations and building complex design. Validated against wind tunnel experiments, a serial Computational Fluid Dynamics (CFD) investigation was conducted with physiochemical coupling, including one large eddy simulation with near-wall resolution (LES-NWR) and three Reynolds-averaged Navier-Stokes (RANS) viscosity models (i.e., standard k-ε model (STK), renormalization group k-ε model (RNG), realizable k-ε model (RLZ)). The numerical models were assessed regarding the predictive capability of the mean pollutant concentration and velocity fields. Results show that the areas of high NO concentration are generally indifferent to the selection of turbulence models. Elsewhere, the RLZ provides the most comparable results to the LES-NWR, whereas the RNG and STK underestimate the reverse flow in the building wake and produce subpar predictions at the roof. The RNG also yields the weakest prediction by overestimating the lateral separation bubbles’ influence. Furthermore, changing the aspect ratio has negligible effects on the stream and spanwise dispersion of the highly concentrated pollutant. However, the building width plays a more decisive role in constraining the streamwise dispersion than the building height. Doubling the building length also slows down the shrinkage of recirculation, leading to a steep deduction in the streamwise dispersion along the building height.

Analysis of single-sided ventilation flows of a generic isolated building using particle tracking method in LES simulation

The main objective of this study is to investigate the airflow patterns in single-sided ventilation of isolated buildings in which the ventilation rate can not be easily predicted by the conventional Orifice equation. The research focuses on buildings with two openings located either at the front or back external wall, with building aspect ratios of 1:1 and 1:2.The study utilizes Large Eddy Simulation (LES) with the particle tracking technique validated by velocity data obtained from a wind tunnel experiment. Ventilation performance is evaluated by Airflow Rate (AFR) and Purging Flow Rate (PFR). AFR was obtained based on the instantaneous velocity over the openings, and PFR was determined by the tracer gas method. The results show that the influence of pulsation flow and eddy penetration both exist in single-sided ventilation. The comparison of AFR and PFR indicates part of the airflow through the opening does not contribute to effectively removing the indoor contaminants, which is quantitively evaluated by ventilation efficiency (εv) defined as the ratio of PFR and AFR. In order to explicitly observe and depict the airflow, the massless particles were emitted at the opening, and the trajectories were analysed. The Probability Density Function (PDF) of indoor residence and indoor travel distance was calculated. The high probability of short indoor travel distance and the residence time, which is mainly caused by the eddy at the openings and time-variant pulsation flow, can explain the difference between AFR and PFR.

Effect of Building Aspect Ratio on Blast Response: A Hypothetical Case Study

Effect of Building Aspect Ratio on Blast Response: A Hypothetical Case Study

Satellite-based daytime urban thermal anisotropy: A comparison of 25 global cities

Remotely sensed land surface temperature (LST) has become one of primary observational sources for urban climate research. However, LST is subject to considerable angular variation, particularly in urban areas caused by a large variation of sensor viewing angles and non-isothermal façades of 3D urban structures. Anisotropy varies seasonally and diurnally, and is sensitive to sensor viewing geometry, solar angles, and urban surface properties. Current studies focus on urban thermal anisotropy of individual cities, comparative study and the resultant driving factor analysis are still lacking. To bridge this critical knowledge gap, a systematic comparative assessment of satellite-based urban thermal anisotropy is required. Here, we modify and validate a satellite-based anisotropy estimation approach and compare the seasonal and diurnal anisotropy variations over 25 global cities to answer the following research questions: 1) How do the anisotropy magnitude and profile shapes vary among different cities? 2) What are the factors influencing the anisotropy? The results show that off-nadir observations are up to 3.5 K cooler on average than nadir LST during summer whereas the effective anisotropy ranges between 2.1 K and 5.8 K for all cities. Winter anisotropy is much smaller (∼ 1 K), where the warm or cold bias is determined by solar zenith angle (morning/afternoon overpasses), and its bias magnitude is linearly proportional to the sensor zenith angle. Urban thermal anisotropy is partly influenced by geographic location (e.g., latitude, longitude), urban vegetation (measured by NDVI) and urban geometry (building height-street width ratio, h/w), where low latitude cities or cities with less vegetation tend to have a greater angular variation in summer, and the anisotropy tends to increase with more complex urban morphology (i.e., higher building aspect ratio). High vegetation cover makes the anisotropy distribution shape more asymmetric along the cross-track direction (or sensor zenith angle). Our findings help understand the seasonal and diurnal impact of anisotropy for wide-swath LST applications in cities and offers insights for addressing anisotropy in future satellite products.

Validity of Orifice equation and impact of building parameters on wind-induced natural ventilation rates with minute mean wind pressure difference

Natural ventilation is gaining more popularity in recent decades as a sustainable strategy to reduce energy consumption and improve indoor air quality. Due to variable turbulent characteristics, there is a lack of a practical guide that helps engineers accurately predict and maximize wind-induced ventilation rates. The current work intends to investigate the factors that influence the ventilation rates by focusing on cases that have a minor wind pressure coefficient difference. This paper presents an experimental study of single- and double-sided wind-induced ventilation mainly through two openings of a reduced scale building with three different building aspect ratios in a boundary-layer wind tunnel. A continuous dose method of tracer gas technique was used to evaluate the ventilation rate. Important factors that affect ventilation rates such as velocity in the vicinity of the wall where the opening is assumed to exist (expressed as “nearby velocity”) and surface wind pressure were measured. Flow visualization was also performed to help to understand the ventilation mechanism caused by turbulence.The experimental results showed that building aspect ratios of 1:2 and 1:3 generally led to higher ventilation rates than that of 1:1. Linear correlation between aperture separation and ventilation rates was reconfirmed regardless of openings symmetry. We noticed that the Orifice equation works well when the wind pressure coefficient difference is higher than 0.1. There is a positive correlation between the fluctuation of wind pressure coefficient and ventilation rates. The nearby velocity of the sealed model was uncorrelated with ventilation rates in this experiment.

Investigation of local severe suction on the side walls of a high-rise building by standard, spectral and conditional POD

Local severe suction greatly determines the safe and economic wind-resistant design of cladding system in the façade of buildings. This study focuses on two localized regions with severe suction of a building, i.e., the lower windward corner of side wall and the region immediately upstream of trailing edge. The aspect ratio of building is 3. The characteristics and mechanism of wind peak pressures are investigated by standard, spectral and conditional proper orthogonal decomposition (POD). Spectral POD extracts the space–time modes which oscillate at the single frequency of the anti-symmetric vortex shedding, where the pressure distributions have the shape of ‘dragonfly’ wing and opposite signs on two side walls. Conditional POD is demonstrated to be a powerful tool to study the average evolution of peak pressures. By inspection of conditional POD modes, high positive fluctuating pressure is observed in the trailing portion of the lower side wall, accompanied by the minimum pressure in the windward corner. The identified pressure behaviors provide the statistical evidences for flow reattachment and shear-layer roll-up which were observed by instantaneous flow visualization in the literature. The trailing-edge peak pressure in the middle-height region is induced by trailing-edge vortex of great vorticity concentration. The flow mechanism and occurrence phase of trailing-edge peak pressures are similar to those of infinite-length cylinders.

Buoyancy-driven natural ventilation characteristics of thermal corridors in industrial buildings

The continuous setup of heating plants such as kilns and boilers may form thermal corridors in industrial buildings resulting in high air temperature, which could be harmful to workers. To solve these problems, this study presents an investigation of the buoyancy-driven natural ventilation of a high-temperature corridor via computational fluid dynamics (CFD) simulation. First, a field measurement was conducted in a typical thermal corridor of a ceramic factory to define the boundary conditions for the simulation. Then, a CFD model was established and validated using reduced-scaled model experimental data. Next, the flow and temperature fields of the thermal corridor under buoyancy-driven natural ventilation were examined using the verified model. It was shown that the natural ventilation in the side corridor is generated by an asymmetric heat channel, and the flow in the main corridor belongs to the natural convection of a semi-closed square heating cavity. Finally, the single-story industrial building aspect ratio was fixed at 3.3, and five different parameters of building and heating plant setups on the natural ventilation in corridors were analysed. For example, the heat source and air opening aspect ratios varied from 12.5 to 50 and from 25 to 100, respectively. The results indicated that the height of the heat source bottom has a more significant effect on the indoor thermal environment than other situations. The maximum ventilation flow rate was observed at the heat source position zs/H = 0.04 and opening position H0/H = 0.05. When the overhead height zs/H reached 0.08, the flow in the main corridor turned to a symmetric heat channel, and the temperature in this region decreased sharply. This research can provide a reference for the natural ventilation design of high-temperature corridors in factories.

Climate characteristics and the adaptation level to formulate mitigation strategies for a climate-resilient archaeological park

The urban form representation to apply in studies of urban climate is a challenge especially in cities of developing countries. These cities lack planning, thus the urban fabric is heterogeneous and several types of buildings are mixed in the same area. Considering this reality, the paper will compare three methods to calculate urban surface parameters. These parameters were compared with the WUDAPT classification. The software QGIS was used to develop models to calculate the following urban surface parameters: plan area ratio (λp), complete building aspect ratio (λbc), and mean height of buildings (hm). Three grid size were applied for calculations: 100 m, 500 m, and 1 km. λbc was the only geometric property able to express the difference of density and the absolute size of the active surface of buildings as a unique parameter. The methods developed have some advantages: (a) they are based on realistic shapes of buildings, (b) they were developed in a free and open source system, (c) and it is possible to vary the calculation grid size.

Methods to calculate urban surface parameters and their relation to the LCZ classification

The urban form representation to apply in studies of urban climate is a challenge especially in cities of developing countries. These cities lack planning, thus the urban fabric is heterogeneous and several types of buildings are mixed in the same area. Considering this reality, the paper will compare three methods to calculate urban surface parameters. These parameters were compared with the WUDAPT classification. The software QGIS was used to develop models to calculate the following urban surface parameters: plan area ratio (λp), complete building aspect ratio (λbc), and mean height of buildings (hm). Three grid size were applied for calculations: 100 m, 500 m, and 1 km. λbc was the only geometric property able to express the difference of density and the absolute size of the active surface of buildings as a unique parameter. The methods developed have some advantages: (a) they are based on realistic shapes of buildings, (b) they were developed in a free and open source system, (c) and it is possible to vary the calculation grid size.

Numerical study of stable stratification effects on the wind over simplified tall building models using large-eddy simulations

Atmospheric stratification is a critical factor affecting wind around buildings. However, very few studies have dealt with the atmosphere under stable stratification. In addition, the building model is typically simplified as a cubic block in previous studies concerning stable stratifications; however, the building aspect ratio (height/width) in the downtown area is often larger than 1. Furthermore, the spatial correlation of the velocities in tall buildings, which is important in determining the length scale of the flow and in evaluating pollutant dispersion, has seldom been studied. Therefore, in the present study, the flow around a simplified tall building and the flow around two groups of buildings with the plan area densities of 12.5% and 25.0%, were investigated under stable stratifications with stratified numbers K equaling to 0, 1, 2, and 3, using large eddy simulations (LES). The aspect ratio of the building models is 2. It was found that, for a single building model, the average wind acceleration above the building is directly proportional to K. Regarding the fluctuating wind velocity, the stratification effect has a weak impact. For building groups, the impact region of stratified flow usually appears when z/H < 1.2. A higher building density reduces the streamwise fluctuating wind velocity and the streamwise velocity spatial correlation.

A Street Graph-Based Morphometric Characterization of Two Large Urban Areas

Urban microclimate modelling, both numerical and in the laboratory, has strong implications in many relevant health and life-style management issues e.g., in studies for assessment and forecast of air quality (for both outdoor and, as boundary conditions, indoor investigations), for thermometric trend analysis in urban zones, in cultural heritage preservation, etc. Moreover, the study of urban microclimate modelling is largely promoted and encouraged by international institutions for its implication in human health protection. In the present work, we propose and discuss an adaptive street graph-based method aimed at automatically computing the geometrical parameters adopted in atmospheric turbulent flow modelling. This method has been applied to two real cases, the Italian cities of Rome and Cagliari, and its results has been compared with the ones from traditional methods based on regular grids. Results show that the proposed method leads to a more accurate determination of the urban canyon parameters (Canyon Aspect Ratio and Building Aspect Ratio) and morphometric parameters (Planar Area Index and Frontal Area Index) compared to traditional regular grid-based methods, at least for the tested cases. Further investigations on a larger number of different urban contexts are planned to thoroughly test and validate the proposed algorithm.

Identifying key determinants for building energy analysis from urban building datasets

Urban and building morphologies, usually determined at the design stage, have been proven as important determinants of energy usage at later operational stages. However, questions remain regarding the identification of the key determinants that influence urban building energy usage. To address this, in this study, an urban building dataset of 539 residential buildings and 153 public buildings was used to extract the building morphology factors as the determinants. A principal component analysis was performed to identify the key determinants for three buildings groups—residential buildings, residential blocks, and public buildings. The results show that the key determinants for residential buildings are their orientation, ratio of obstruction height to the canyon width from the south and west directions, shape coefficient, perimeter-to-area ratio, and building aspect ratio. The key determinants for public buildings are similar to those for residential buildings with the exception of the ratio of the obstruction height to the canyon width from the south direction. The key determinants for residential blocks are the ratio of the obstruction height to the canyon width from the south and west directions, mass space proportion, building aspect ratio, and floor area ratio. The findings of this study provide insights into the key drivers of urban building energy usage and the strategies that could be used to improve urban energy planning.

Investigation of Lightning Attachment Risks to Small Structures Associated With the Electrogeometric Model (EGM)

A 3-D Monte Carlo-type random walk model was constructed for the assessment of lightning attachment probabilities to small structures. The simulation assumed buildings had a negligible impact on the propagation of lightning. A purely stochastic propagation model based on a previously proposed gas and charged particle diffusion process was employed. The attachment was based on the electrogeometric model in which striking distance is determined by return stroke peak current. This model allows for hundreds of thousands of samples to be evaluated in the window of a few minutes on readily available consumer computing hardware. Using this model, it became possible to enable characterizing building protection as a probability distribution of striking distance. Such was done to provide a deeper understanding of the impact of building protection design choices than is readily available from binary testing. The model was calibrated for minimum input resolution, which is found to be insensitive to variations in step length and moderately insensitive to variations in propagation angle distribution, resulting in normalized errors of less than 15% (rms). A parametric sweep of geometric features was performed for a large (100 m $\times $ 50 m) rectangular building with catenary wire protection. For heights of less than 30 m, lightning was found to bypass protection structures and strike to the building itself at rates that were insensitive to variations in building height. The extent to which the protection may be recessed from the building’s perimeter was found to have a significant impact. Variations in building aspect ratio were found to be of limited impact except for cases of extreme aspect ratio where competition with the ground appears to have resulted in much better lightning protection performance.

Flow Characteristics Around Step-Up Street Canyons with Various Building Aspect Ratios

We investigate the flow characteristics around step-up street canyons with various building aspect ratios (ratio of along-canyon building length to street-canyon width, and upwind building height to downwind building height) using a computational fluid dynamics (CFD) model. Simulated results are validated against experimental wind-tunnel results, with the CFD simulations conducted under the same building configurations as those in the wind-tunnel experiments. The CFD model reproduces the measured in-canyon vortex, rooftop recirculation zone above the downwind building, and stagnation point position reasonably well. We analyze the flow characteristics, focusing on the structural change of the in-canyon flows and the interaction between the in- and around-canyon flows with the increase of building-length ratio. The in-canyon flows undergo development and mature stages as the building-length ratio increases. In the development stage (i.e., small building-length ratios), the position of the primary vortex wanders, and the incoming flow closely follows both the upstream and downstream building sidewalls. As a result, increasing momentum transfer from the upper layer contributes to a momentum increase in the in-canyon region, and the vorticity in the in-canyon region also increases. In the mature stage (i.e., large building-length ratios), the primary vortex stabilizes in position, and the incoming flow no longer follows the building sidewalls. This causes momentum loss through the street-canyon lateral boundaries. As the building-length ratio increases, momentum transfer from the upper layer slightly decreases, and the reverse flow, updraft, and streamwise flow in the in-canyon region also slightly decrease, resulting in vorticity reduction.

On the Flow Past an Array of Two-Dimensional Street Canyons Between Slender Buildings

The flow above idealized, two-dimensional series of parallelepipedal buildings is examined with the aim of investigating how the building width to height aspect ratio affects the turbulence in the roughness sublayer and the ventilation of the underlying street canyons. We compare the case of buildings with a squared section with a configuration with slender buildings both in the case of unit canyon width to height aspect ratio and in the case of AR = 2. The former corresponds to skimming flow and the latter to wake-interference regime. Measurements are performed in a water channel, measuring velocity on a vertical mid-plane using a particle image velocimetry technique. The mean flow, its second-order turbulence statistics, the exchange fluxes, and the integral time scales investigated, with results showing that slender buildings enhance turbulence production and yield longer integral time scales in the region just above the building roof. The combined analysis of the turbulence production fields and the snapshots of the flow during sweep and ejection events demonstrate that the shear layer between the canyon and the external flow is significantly more unstable with slender buildings, mainly because the damping effect of the vertical velocity fluctuations from the flat roof of the upwind building is substantially missing. Consequently, a larger (downstream) portion of the interface is prone to the direct interaction of the external flow structures. The higher turbulence intensity promotes the ventilation at the canyon interface. In summary, the present experiments show that the effect of the reduced building aspect ratio is particularly significant when the urban canopy consists of narrow canyons. The result is of interest since narrow street canyons are typically bounded by slender buildings in the urban texture of the old European city centres.

Seismic shear and acceleration demands in multi-storey cross-laminated timber buildings

A realistic estimation of seismic shear demands is essential for the design and assessment of multi-storey buildings and for ensuring the activation of ductile failure modes during strong ground-motion. Likewise, the evaluation of seismic floor accelerations is fundamental to the appraisal of damage to non-structural elements and building contents. Given the relative novelty of tall timber buildings and their increasing popularity, a rigorous evaluation of their shear and acceleration demands is all the more critical and timely. For this purpose, this paper investigates the scaling of seismic shear and acceleration demands in multi-storey cross-laminated timber (CLT) buildings and its dependency on various structural properties. Special attention is given to the influence of the frequency content of the ground-motion. A set of 60 CLT buildings of varying heights representative of a wide range of structural configurations is subjected to a large dataset of 1656 real earthquake records. It is demonstrated that the mean period (Tm) of the ground-motion together with salient structural parameters such as building aspect ratio (λ), design force reduction factor (q) and panel subdivision (β) influence strongly the variation of base shear, storey shears and acceleration demands. Besides, robust regression models are used to assess and quantify the distribution of force and acceleration demands on CLT buildings. Finally, practical expressions for the estimation of base shears, inter-storey shears and peak floor accelerations are offered.

Characteristics of pedestrian-level Mean wind speed around square buildings: Effects of height, width, size and approaching flow profile

A series of wind-tunnel tests were carried out to investigate the characteristics of pedestrian-level wind around square buildings with various dimensions, in particular, to examine the effects of building height, building width, building aspect ratio, approaching flow profile and turbulence intensity. It was found that the downwash effect on pedestrian-level wind is significant for a building in boundary layer flow. The maximum speed-up ratio and speed-up area in boundary layer flow (BLF) are much larger than those in a uniform turbulent flow (UTF). The maximum speed-up ratio and speed-up area for a building with constant width in BLF shows an increasing tendency with building height, but this becomes less significant for higher buildings. For a building with constant height in BLF, increase in building width results in smaller aspect ratio, stronger blocking effects, and enhanced downwash effect and Venturi effect. Thus, the speed-up area increases exponentially with building width. For a building with constant aspect ratio in BLF, Venturi effect and downwash effect cause an exponentially increasing speed-up area with building size.