Low-Rise Buildings

The paper presents a numerical methodology to assess the natural ventilation. UrbaWind is an automatic computational fluid dynamics code. It was developed to model the wind in urban environments. The turbulence modelling, namely the dependence of turbulence length on the distance from wall, and the model constants were calibrated in order to reproduce with good agreements flow separation around buildings walls and pressure coefficient field on façades. Numerical results match well with the experiments: separation patterns and pressure field on walls in dense urban areas. Examples are presented at the end of the paper in order to show the advantages of the methodology for urban designers as they need pressure coefficients to assess the air change rate of buildings.

This thesis describes an investigation into the wind loading on access scaffolds erected around a cubical building, clad by impermeable sheeting or permeable debris netting. The subject was investigated experimentally by tests in a wind-tunnel and theoretically using computational fluid dynamics techniques. The results were verified from the wind tunnel tests and computational analyses on the Silsoe Experimental Building (SEB) using data from the full-scale tests made in 1993-94 at Silsoe, U.K. The lower portion of the Atmospheric Boundary Layer exhibits different flow properties to the upper elevations. A procedure is presented for modelling the atmospheric surface layer flow properties in a boundarylayer wind-tunnel at useful model scales. The full-scale data available from the cubical 6m x 6m x 6m SEB was used to validate the results presented in this study. A model scale of 1:30 were used both for experiments in a wind-tunnel and in the computational analyses undertaken in the study. Pressure data obtained from the windtunnel experiments on the SEB model were compared to full-scale data with good agreement. These data were also compared with various computational fluid dynamics techniques available commercially and the conclusions drawn on the use of the different techniques. The wind-tunnel simulations on an SEB model and on a sheet/elevated sheet clad scaffold models were undertaken based on a duplication of the turbulence intensities and small-scale turbulence of the incidence flow. It is very difficult to achieve equality of Reynolds number in the wind-tunnel as it is very difficult to achieve exactly the same integral scales of turbulence. Two different types of terrain and inflow boundary conditions were simulated in the wind-tunnel for the models and results are reported here. Large suctions (separation of flows) occur near the leading edges and roof corners. The modelling of these phenomena in the wind-tunnel remains a problem. Because of the limited space near the corners and leading edges, it is difficult to make reliable measurements by introducing probes in these areas. This difficulty can be overcome by modelling the flow with Large Eddy Simulation (LES) numerical techniques. However, the disparity between the large and small scales, especially under extreme wind conditions, makes it extremely difficult to resolve the entire range of dynamic scales. The pressure force on bare pole access scaffolds are further influenced by the presence of the building façade which induces a shielding effect. A 2-D model of bare pole scaffolds surrounding the SEB using CFD techniques was successfully achieved whereas a 3-D model could not be produced because of the limitations of the meshing-software GAMBIT available to the author. Cladding increases the wind loads on scaffold structures above the pressure force on bare pole access scaffolds. To determine the wind forces on net/sheet clad scaffolds the Silsoe Experimental Building was used as a base model and simulated scaffolds erected around it. Although, sheeting/netting exhibits aero-elastic behaviour under wind load, an assumption was made to treat the cladding (sheeting/netting) surrounding the scaffold as being made of static solid thin plates. Models were tested in a wind-tunnel and the same assumptions were used in the computational fluid dynamics analyses. For the sheet clad scaffolds, two models were made, one with sheeting touching the ground and the other with an elevated sheet surrounding the building. These models were tested in a wind-tunnel to determine the pressure coefficients on the outer and inner faces of the sheeting. The permeability of the two types of net were successfully obtained from wind-tunnel tests. The simulated data from the wind-tunnel tests were used as input for different computational techniques with good agreement. A new procedure was developed to extend the computational model to net clad scaffolds (both elevated and touching the ground) with the netting simulated as porous media. The author presents new results of the pressure coefficients on sheeted scaffolds obtained using CFD and wind-tunnel techniques and also CFD results on netted scaffold structures. This thesis is the result of research undertaken to assess various methods available for the numerical simulation of turbulent fluid flow using the Fluent Software Package and to see their applicability in computational wind engineering. Investigations have concentrated on analysing the accuracy and numerical stability of a number of different turbulence models including both widely available models and state of the art techniques. Furthermore, Large Eddy Simulations using the dynamic kinetic energy sub-grid-scale model have been completed on some models, in order to account for the four dimensional nature of turbulent flow and to show the best correlation between wind-tunnel, full-scale and sheeted scaffolds. The author has detailed and tested all the above techniques and gives recommendations on the appropriate turbulence model to be used for successful computational wind engineering. Finally the author has given recommendations on the wind pressures to be used in analysing the scaffold structures.

The investigation of wind pressure distribution on a façade of an atypically shaped 162 m tall building is discussed in this paper. The horizontal cross-section was changed with the height of the structure (the square in the bottom part and the polygon in the top). The surface of the structure was smooth. A structural system was created using a combination of the tube structural system and exoskeleton structure. The building was stand-alone, located in urban terrain. In this case, the information in standards were not sufficient for its design. Therefore, other available tools had to be used for the determination of required input parameters (mean external pressure coefficients). At first, wind tunnel tests (WT) were performed on a reduced-scale model (1:300). Then, the obtained results were compared with data from a computational fluid dynamics (CFD) simulation. The accuracy of the simulation was evaluated by the method of three metrics. Short descriptions of the reduced-scale mode...

This paper presents the results of a set of wind tunnel tests carried out to examine wind-induced overall structural loads on rectangular medium-rise buildings. Emphasis was directed towards torsion and its correlation with peak shear forces in transverse and longitudinal directions. Two building models with the same horizontal dimensions but different gabled-roof angles (0o and 45o) were tested at different full-scale equivalent eave heights (20, 30, 40, 50, and 60 m) in open terrain exposure for all wind directions (every 15o). Wind-induced pressures were integrated over building surfaces and results were obtained for along-wind force, across-wind force, and torsional moment. Maximum wind force component was given along with the other simultaneously-observed wind force components normalized by the overall peak. The study found that for flat-roofed buildings maximum torsion for winds in transverse direction is associated with 80% of the overall shear force perpendicular to the long...

Full-scale experiments were conducted to investigate wind loading on roof tiles in hip, ridge, and perimeter locations, identified from past storms as main points of damage initiation. The objectives were to: (i) provide test-based data on wind-induced loads for tiles, and (ii) evaluate characteristics of nearsurface flows to assess tile loading models. The experiments included pressure measurements on the external surface and in the cavity underneath the tiles, and wind speed measurements near tile surfaces. The highest net uplift pressure (computed as external pressure minus the cavity pressure) was observed on the gable end ridge tiles. Except for a few non-critical cases, due to effects of pressure equalization net uplift was lower than external surface uplift. Mean wind speeds at tile surfaces were recorded that were up to 55% higher than the mean wind speed at mid-roof height in the approach flow. Two alternative models that use wind speeds near the tile surface to determine net design wind loads on tiles were investigated. The results showed that the models can underestimate wind loading. However, when used with appropriate parameters, the models can produce results comparable to those obtained using ASCE's external pressure coefficients in conjunction with pressure adjustment factors.

Understanding the flow field developed in the proximity of a building due to the wind flow over it is a prerequisite for designing a building. The wind environment around buildings plays a pivotal role not only from the point of view of structural integrity but also impacts the ventilation performance, pedestrian comfort and dispersion of pollutants. With the emergence of the green building concept in the light of the sustainable living, modern buildings are equipped with various openings such as doors, windows and ventilators. These openings change the flow characteristics in and around the building remarkably and make the flow field much more complex. The current study seeks to improve the understanding of both the internal and external flow fields around the buildings with openings. In this work, an attempt has been made to investigate the influence of wind direction on the flow behavior of wind in and around gable roof buildings with six different opening configurations. Commerc...

The use of steel fiber-reinforced concrete (SFRC) for low-rise walls in low-seismicity regions is evaluated experimentally. Shake-table tests of SFRC and conventionally reinforced concrete walls with an aspect ratio of 1.0 under several ground motions to failure were conducted. Main variables studied were fiber aspect ratio (64 and 80) and fiber volume content (0.55%, 0.75%, and 1%). Wall performance is assessed in terms of crack patterns, failure modes, lateral resistance and hysteretic response. The results showed that SFRC walls exhibited superior performance than that observed for the wall with welded wire reinforcement in the web. Furthermore, SFRC walls containing 0.75% or 1% fiber volume content exhibited a response that was as good as that observed for the wall reinforced with deformed bars as web reinforcement in terms of lateral strength and drift capacity.

Full-scale experiments were conducted to investigate wind loading on roof tiles in hip, ridge, and perimeter locations, identified from past storms as main points of damage initiation. The objectives were to: (i) provide test-based data on wind-induced loads for tiles, and (ii) evaluate characteristics of nearsurface flows to assess tile loading models. The experiments included pressure measurements on the external surface and in the cavity underneath the tiles, and wind speed measurements near tile surfaces. The highest net uplift pressure (computed as external pressure minus the cavity pressure) was observed on the gable end ridge tiles. Except for a few non-critical cases, due to effects of pressure equalization net uplift was lower than external surface uplift. Mean wind speeds at tile surfaces were recorded that were up to 55% higher than the mean wind speed at mid-roof height in the approach flow. Two alternative models that use wind speeds near the tile surface to determine net design wind loads on tiles were investigated. The results showed that the models can underestimate wind loading. However, when used with appropriate parameters, the models can produce results comparable to those obtained using ASCE's external pressure coefficients in conjunction with pressure adjustment factors.

The industrialized building system has specific characteristics that set it apart from the conventional concrete wall system, namely, a reduced wall thickness, the use of electro-welded wire mesh, and a lack of boundary element confinement. These conditions have attracted the interest of researchers, who have developed various experimental programs to evaluate the behavior of these walls. However, evidence on the seismic performance of buildings remains scarce. In this study, the performance of 5-, 8-and 12-story buildings was evaluated by nonlinear chronological analysis. Numerical models were constructed using the Shell Layered element of the ETABS software and adjusted based on the results from tests of isolated walls and the periods of one of the buildings identified in an ambient vibration test. The findings suggest that these buildings may fail to meet the life safety performance level in high seismic hazard areas.

h i g h l i g h t s Tensile mechanical properties of welded wire meshes available in Colombia is assessed. Strain, area reduction and ultimate-to-yield strength ratio of wires are also assessed. Parameters are compared to those specified by American and European codes. Stress-strain curves of wires are proposed for code-base design. Limitations of the use of electro-welded cold-drawn wire mesh are identified.

Peak bending moments are compared for a set of steel portal frames of industrial buildings in open terrain, calculated using database-assisted design (DAD) techniques and ASCE 7-05 Standard plots. The comparisons indicate that, depending on building dimensions, the peak bending moments at the knee based on DAD techniques are generally larger by 10 % to 40 % than their counterparts based on the ASCE 7-05 plots. (In one case with a relatively steep roof slope of 26.6 ° the discrepancies exceed 90 %.) Discrepancies increase with increasing roof slope and with increasing eave height. CE Database subject headings: Aerodynamics; Buildings, low-rise; Databases; Structural design; Wind forces; Wind tunnel tests. Introduction This note compares peak bending moments in steel portal frames of industrial buildings in open terrain calculated using database-assisted design (DAD) techniques on the one hand and by using the Analytical Procedure from American Society of Civil Engineers (ASCE) Standa...

Coastal areas of the US are affected by extreme wind events, including hurricanes. Roofs are the most vulnerable building components as they are often damaged by high wind uplift forces acting on the edges and corners. This study investigates the application of a mitigation strategy, in the form of an Aerodynamics Mitigation and Power System (AMPS) (US Patent, Gan Chowdhury et al., Patent Number: US 9,951,752 B2, April 2018), designed to simultaneously reduce wind damage and provide power to buildings. The system consists of horizontal axis wind turbines, integrated to roof edges with or without gutters. Four sets of testing on a flat roof low rise building model (without gutters)-including a bare deck configuration (i.e. without AMPS) and three cases where the roof corner was fitted with AMPS-were conducted at the Wall of Wind Experimental Facility at Florida International University. In one of the configurations, the wind turbines were placed slightly above the roof edge, while in the other two configurations, the turbines were placed closer to the roof edge. Wind directions tested ranged from 0 • to 90 • (considering roof geometric symmetry). Estimation of areaaveraged mean and peak pressure coefficients were made for various locations on the roof for the three different configurations, and compared with the case of no mitigation. Results show that for wind directions tested, significant reduction in mean and peak pressure coefficients (reduced suction) were obtained in those cases where the wind turbines were placed closer to the roof edge as compared to the bare roof deck case. Flow visualization studies showed that the turbines helped to disrupt the conical vortices caused by cornering winds, thereby reducing the wind uplift forces on the roof. This study shows that the AMPS can be utilized to prevent wind-induced damage to the roof. Future research will include estimation of the: (1) potential wind energy production using the mitigation system under various wind conditions, (ii) effectiveness of AMPS in mitigating wind loading on other kinds of buildings (e.g., gable and hip roof buildings), and (iii) load transferred from the system to the roof.

The use of steel fiber-reinforced concrete (SFRC) for low-rise walls in low-seismicity regions is evaluated experimentally. Shake-table tests of SFRC and conventionally reinforced concrete walls with an aspect ratio of 1.0 under several ground motions to failure were conducted. Main variables studied were fiber aspect ratio (64 and 80) and fiber volume content (0.55%, 0.75%, and 1%). Wall performance is assessed in terms of crack patterns, failure modes, lateral resistance and hysteretic response. The results showed that SFRC walls exhibited superior performance than that observed for the wall with welded wire reinforcement in the web. Furthermore, SFRC walls containing 0.75% or 1% fiber volume content exhibited a response that was as good as that observed for the wall reinforced with deformed bars as web reinforcement in terms of lateral strength and drift capacity.

This paper investigates the single-sided wind driven natural ventilation with two apertures on the rear wall, regarding different horizontal aperture separations, magnitudes of incoming wind speed and various side ratios (L/D, length/width). In the present work, CFD simulations are performed with Reynolds-Averaged Navier-Stokes (RANS) approach, and pressure correction linked equation is adopted to provide closure. The simulation results indicate that wind flow behind the rear wall is essentially driven by the pumping mechanism due to vortex shedding, in which wind flow direction alternates at a mean rate. The frequency of the "pumping" flow increases dramatically with the wind flow velocity at a wide range of Reynolds numbers. The decrease of free aperture separation reduces the enclosure flow rate whilst the frequency of the wind flow almost maintains at a constant value. The increase of sidewall length has similar impacts on the ventilation frequency and the dimensionless ventilation flow rate. Numerical investigations further demonstrate that non-dimensional ventilation rate can be promoted by increasing incoming wind velocities when the wind speed is less than 5 m/s. This promotion will be restrained when the wind speed is further increased. The simulation results of built enclosure flow rate, frequency of enclosure flow can be applied to improve the ventilation performance of buildings merely with rear wall openings.

This paper presents the results of a set of wind tunnel tests carried out to examine wind-induced overall structural loads on rectangular medium-rise buildings. Emphasis was directed towards torsion and its correlation with peak shear forces in transverse and longitudinal directions. Two building models with the same horizontal dimensions but different gabled-roof angles (0o and 45o) were tested at different full-scale equivalent eave heights (20, 30, 40, 50, and 60 m) in open terrain exposure for all wind directions (every 15o). Wind-induced pressures were integrated over building surfaces and results were obtained for along-wind force, across-wind force, and torsional moment. Maximum wind force component was given along with the other simultaneously-observed wind force components normalized by the overall peak. The study found that for flat-roofed buildings maximum torsion for winds in transverse direction is associated with 80% of the overall shear force perpendicular to the long...

Thin ferrocement walls are the structural elements that comprise the earthquake resistant system of housing built with this material. This article presents the results drawn from an experimental campaign carried out over full-scale precast ferrocement thin walls, which were assessed under cyclic loading conditions. The tests assessed the strength of the walls, their hysteretic behavior, ductility, energy dissipation, equivalent damping, their coefficient of energy dissipation and their characteristic failure mode when subjected to cyclic loading conditions. Finally, an analytical model that modeled the nonlinear dynamic behavior exhibited by ferrocement walls was implemented; its feasibility and potential use in earthquake resistant design of ferrocement walls was evaluated.

En la década del 80, los paneles fotovoltaicos eran muy caros y en Cuba sólo se utilizaban para casos excepcionales donde se hacía imposible llegar con líneas de trasmisión eléctricas. En los últimos años se ha producido una disminución gradual de los precios de los paneles lo cual ha propiciado el desarrollo de una política para incrementar el número de parques fotovoltaicos a lo largo de todo el país en el periodo comprendido entre 2011 y 2022. Es una tendencia internacional la colocación de paneles solares sobre edificaciones (naves industriales, edificios, viviendas) debido a los altos costos que tiene el suelo en la actualidad, lo que atenta contra la utilización de esta fuente de energía. En Cuba, esta forma de colocación de los paneles no se encuentra bien aprovechada. La incorporación de la energía solar como fuente alternativa en las residencias y otros centros grandes consumidores de las ciudades cubanas es uno de los retos del Ministerio de Energía y Minas (MINEN). En este contexto, el espacio para ubicar los paneles tiene un papel decisivo y el empleo de las cubiertas de las edificaciones adquiere especial significación. Este trabajo tiene como objetivo ofrecer recomendaciones en cuanto a las características ideales que deben tener las cubiertas de edificaciones bajas para la colocación de estas estructuras teniendo en cuenta el efecto de la carga de viento. Se ejemplifican esas recomendaciones a través de un caso de estudio.

The stiffness of structural walls is a key parameter for seismic design because the distribution of shear forces depends on the relative stiffness of each wall of the structural system. The study of stiffness degradation of lowrise reinforced concrete walls has been focused on the description of the deterioration of such structural property. This study aims at proposing a semi-empirical model for assessing the lateral stiffness degradation in terms of drift ratio of thin and lightly reinforced concrete walls for low-rise and low-cost housing subjected to seismic demands. The variables of the study are the height-to-length ratio of walls (0.5, 1 and 2), type of concrete (normal-weight, lightweight and self-compacting), steel ratio of web shear reinforcement (0.125% and 0.25%), and the type of web shear reinforcement (deformed bars and welded-wire meshes). The experimental program comprises 23 walls tested under quasi-static reversed-cyclic loading. Lateral stiffness computed using measured response of walls are compared with stiffness computed using recommendations prescribed by codes or reported in a literature review. The effect of geometrical and mechanical properties of walls on stiffness is also assessed in the paper. In addition, the study proposes limit values of stiffness degradation for different limit states and performance levels.

Wind flow over low-rise buildings in the atmospheric boundary layer (ABL) is accompanied by some complex flow physics such as flow separation and generation of vortices in the shear layer. The uncertainties associated with such complex flow mechanisms make the case-by-case experimental or numerical investigation of buildings’ aerodynamic behavior fundamental. Engineers have aspired to replicate the full-scale real wind behavior in wind-tunnels to create more resilient infrastructures. Traditional wind-tunnel experiments struggle to accurately predict surface pressures despite being widely embraced by the structural engineering community. This limitation is attributed to the lack of large-scale turbulence and low Reynolds numbers in wind-tunnels. Such drawbacks prompted the consideration of aerodynamic testing by the open-jet concept. Open-jet experiments of building models with higher Reynolds numbers reveal the generation of higher mean and peak pressure coefficients, compared to t...

Buildings are bluff bodies, compared to streamline objects, such as airfoil. Wind flow over buildings leads to separation and hence a complex spatial and temporal mechanism that governs the nature and intensity of aerodynamic forces. This complexity mainly comes from the transient nature of incident turbulent winds and the fluctuating flow pattern in the separation bubble. The study of building aerodynamics is vital for the evaluation of cladding pressures, drag, shear, and uplift forces that are essential for safe and economic design. Flow separation makes it challenging to estimate loads without referring to direct physical and/or computational simulation. For several decades, aerodynamic testing has been employed for the estimation of wind pressures and forces on buildings. However, for residential homes and low-rise buildings, it has been always a challenge to predict full-scale pressures by traditional wind tunnel testing, as per the lack of large turbulence and Reynolds number...

Most Malaysian rural houses are categorized as non-engineered buildings and vulnerable to damage during events such as windstorms due to the fact that these houses lack engineering considerations. These houses are characterized by having an attached kitchen house, and many of these houses were previously damaged by thunderstorms. The current research investigated the air flow characteristics changes surrounding these houses as a result of the presence of the kitchen. The roof pitch, position, gap height, and overhang were investigated using computational fluid dynamics (CFD) simulations. The results showed that the kitchen position at the center resulted in a slight increase in the suction on the ridge of the roof; however, it significantly altered the flow pattern in the windward and leeward directions. The results also showed that the roof overhang, roof pitch, and kitchen position contributed severely to the damage of the rural house. Moreover, the highest suction occurred at the...

A strong wind would cause roof openings on a low-rise building and bring further structural damage. Previous related studies focused on different shapes of openings on flat roofs. Little study has been done on the sloped roofs with openings in vulnerable roof areas. In this study, wind tunnel tests were carried out to investigate the steady-state and transient internal pressure characteristics due to opening at the vulnerable roof areas of a low-rise building. The tests considered both steady-state and transient openings of roof. The experimental results indicated that the steady-state internal pressure distribution tends to be uniform and that the internal pressure induced by leeward roof ridge opening is obviously lower than that induced by the windward one. The fluctuation effect around the orifice area is apparent with the skewed wind direction and the combined effect of internal and external pressures on the unopened roof side is significantly smaller than that on the opened si...

Wind hazards are one of the most disastrous events that frequently occur in the United States. Hurricane Irma, which hit the southeast coast in 2017, left a majority of damage concentrated on low-rise buildings and wooden construction in its wake. As revealed by recent hurricane damage reconnaissance, hardware-type roof-to-wall connections are especially vulnerable to high wind suction. There is only limited research on the assessment of wind loads on these roof-to-wall connections, which are important components of the wind load path. Hence, it is essential to have realistic estimates of wind effects on these connections to ensure a safe design. To fill this fundamental knowledge gap, an extensive large-scale aerodynamic testing study has been recently conducted at the NSF-Natural Hazard Engineering Research Infrastructure (NHERI) Wall of Wind (WOW) Experimental Facility (EF) to investigate wind actions resulting from simulated hurricane force winds. A wooden gable roof building of a large length scale of 1:4 was adopted for this study. Seven trusses were used to construct the roof and were connected to the top plate of the side walls. Load cells were mounted at the roof-to-wall connection (RTWC) level to measure the effective net wind-induced forces. The model was tested under different wind directions varying from 0 to 360 • with an increment of 5 • under varying wind speeds. In addition, three different configurations, i.e., one enclosed and two partially enclosed, were considered to assess different internal pressure scenarios that affect the net loading on the roof-to-wall connections and the overall roof system. The RTWC force coefficients distribution along the entire roof was obtained. The results were compared to force coefficients recommended by ASCE 7-16 version for the cases of Main Wind-Force Resisting System (MWFRS) and Component and Cladding (C&C). The experimental results were in between MWFRS and C&C values based on the ASCE provisions in general. However, for partially enclosed case, some values slightly exceeded those based on the ASCE C&C provisions. Also, the overall uplift on the roof was found to be dependent on the location of the opening (i.e., opening on long side vs. short side of the building).

This paper presents the results of a set of wind tunnel tests carried out to examine wind-induced overall structural loads on rectangular medium-rise buildings. Emphasis was directed towards torsion and its correlation with peak shear forces in transverse and longitudinal directions. Two building models with the same horizontal dimensions but different gabled-roof angles (0o and 45o) were tested at different full-scale equivalent eave heights (20, 30, 40, 50, and 60 m) in open terrain exposure for all wind directions (every 15o). Wind-induced pressures were integrated over building surfaces and results were obtained for along-wind force, across-wind force, and torsional moment. Maximum wind force component was given along with the other simultaneously-observed wind force components normalized by the overall peak. The study found that for flat-roofed buildings maximum torsion for winds in transverse direction is associated with 80% of the overall shear force perpendicular to the long...

Florida suffers annually from landfalling hurricanes that impose multi-hazards on coastal communities and particularly residential structures that are damaged through flooding, storm surge, and strong winds. Thus, to mitigate flooding and storm surge hazards, the Federal Emergency Management Agency (FEMA) recommends elevating coastal structures to a safe level above the ground level [1]. According to FEMA, houses that were elevated 12 ft above ground were reported safe after the passage of Hurricane Katrina in 2005 [2]. This also agrees with Hurricane Ike damage survey findings [3]. While the safe elevation height is a function of storm surge risks, many areas in Florida houses may be elevated to as high as 17 ft to avoid storm surge damage. There are two considerations of this:

Wind hazards are one of the most disastrous events that frequently occur in the United States. Hurricane Irma, which hit the southeast coast in 2017, left a majority of damage concentrated on low-rise buildings and wooden construction in its wake. As revealed by recent hurricane damage reconnaissance, hardware-type roof-to-wall connections are especially vulnerable to high wind suction. There is only limited research on the assessment of wind loads on these roof-to-wall connections, which are important components of the wind load path. Hence, it is essential to have realistic estimates of wind effects on these connections to ensure a safe design. To fill this fundamental knowledge gap, an extensive large-scale aerodynamic testing study has been recently conducted at the NSF-Natural Hazard Engineering Research Infrastructure (NHERI) Wall of Wind (WOW) Experimental Facility (EF) to investigate wind actions resulting from simulated hurricane force winds. A wooden gable roof building of a large length scale of 1:4 was adopted for this study. Seven trusses were used to construct the roof and were connected to the top plate of the side walls. Load cells were mounted at the roof-to-wall connection (RTWC) level to measure the effective net wind-induced forces. The model was tested under different wind directions varying from 0 to 360 • with an increment of 5 • under varying wind speeds. In addition, three different configurations, i.e., one enclosed and two partially enclosed, were considered to assess different internal pressure scenarios that affect the net loading on the roof-to-wall connections and the overall roof system. The RTWC force coefficients distribution along the entire roof was obtained. The results were compared to force coefficients recommended by ASCE 7-16 version for the cases of Main Wind-Force Resisting System (MWFRS) and Component and Cladding (C&C). The experimental results were in between MWFRS and C&C values based on the ASCE provisions in general. However, for partially enclosed case, some values slightly exceeded those based on the ASCE C&C provisions. Also, the overall uplift on the roof was found to be dependent on the location of the opening (i.e., opening on long side vs. short side of the building).

During strong wind events such as hurricanes and thunderstorms, building roofs are subjected to high wind uplift forces (suctions), which often lead to severe roofing component damage and possibly, water intrusion. It is therefore crucial to accurately estimate peak suctions (negative pressures) on roofs for design purposes and to develop mitigation devices to reduce wind uplift and possible damage. Past research suggests that mitigation devices, in various forms and configurations, can significantly reduce wind effects on buildings' roofs. Perforated parapets have been shown by many researchers to be one of the most effective and low-cost mitigation devices for reducing roof suction. However, such devices contain perforations of critical functionality that may be Reynolds number Re dependent. Therefore, it is essential to study their functionality and possible Re dependency in wind tunnel testing. This paper focuses on investigation of Reynolds number Re similitude aspects of porous devices and large-scale model testing of discontinuous porous parapets to estimate their roof uplift reduction efficacy that would be representative of the prototype (full-scale) conditions. Large scale (1:8) experiments were implemented at the 12-Fan Wall of Wind Experimental Facility (WOW) at Florida International University (FIU) to achieve adequate local Reynolds number Re to ensure realistic results. In this study, a relatively smaller ratio of parapet height to roof height has been considered as compared to previous studies. The paper delineates the step-by-step design of the parapets based on kinematic similitude requirements cited in the literature. The goal was to achieve a discontinuous porous parapet design that provides similar uplift reduction efficacy as compared to those reported in the literature, but with lower height and smaller length to ensure cost-effectiveness, ease of installation, and architectural aesthetics of the retrofitted building. The effects of perforated parapets on both individual tap and area-averaged pressure coefficients were explored. The results indicated a maximum of 45% reduction in individual tap peak pressure coefficients at the corner roof and a 40% reduction in area-averaged peak pressure coefficients. The study showed that low-height ratio perforated parapets could be as effective as those reported in the literature with higher height ratios.

The walls of modern low-rise economic housing in several Latin American countries are typically thin and have a low concrete strength, web steel ratios that are smaller than the minimum prescribed by current codes, and web shear reinforcement made of welded-wire mesh. In light of these particular wall characteristics, research was aimed at developing a performance-based backbone model capable of predicting the seismic behavior of reinforced concrete (RC) walls for one- and two-story housing. The selected tri-linear model is associated with three limit states: diagonal cracking, peak shear strength, and ultimate deformation capacity. The model was developed on the basis of the observed response of 39 quasi-static and shake table experiments. Iterative nonlinear regression analyses were performed for deriving the semi-empirical equations in this study. The paper also discusses the adequacy of some existing models to predict the seismic behavior of RC walls and the limitations of the p...

9 Wind tunnel testing represents an established technique for the assessment of wind-induced pressure on cladding systems. Nonetheless, some physical events, such as the pressure peaks that occur on a building’s lateral facades, are not fully understood. To enable detailed analysis of the nature of these pressure peaks, we performed high-resolution pressure measurements on a high-rise building in two different wind tunnels: the closed-circuit wind tunnel of Politecnico di Milano, and the open-circuit Wall of Wind facility at Florida International University. The objective of the paper is to present the experimental set-up and the highresolution pressure data, and to investigate the characteristics of the extreme suction events at individual pressure taps and their relevance for cladding design. We first compare the two atmospheric boundary layers, and subsequently present the pressure coefficients statistics. Then, we present probability density functions of the local and area-avera...

It is well established by different seismic damage surveys conducted all over the world that the asymmetric structures are more susceptible to seismic damage than their symmetric counterparts. Moreover, it is also pointed out by a number of previous research effort that such damage in asymmetric structures is more aggravated in R/C structures due to progressive strength and stiffness degradation of R/C structural elements. Community structures like auditoriums generally have load resisting elements distributed only near the boundary region of the structures leaving a large empty space at the central region. Seismic behaviour of such type of R/C asymmetric systems are investigated in a limited form (Dutta, 2001) considering only spectrum consistent far field ground excitations. However, study of such systems under near-fault ground excitations are also of great importance as there may be a huge gathering of people inside an auditoriums and amount of energy input to the structural sys...

The pressure within a building, produced by wind action, is dependent on the magnitude of external surface pressure, the size and position of all openings connecting exterior to interior of the building and the effective enclosed volume. Internal pressure fluctuations within a sealed building are generally small in magnitude and intensity in comparison with its external pressures. But when there are dominant openings (operable façades) or sudden failures across the exterior façade, the building interiors can experience wind pressures of similar magnitude to that of the exterior. Therefore, in such cases, it becomes essential to determine the realistic values of wind pressures to be used for the design of inter-tenancy walls. This paper outlines a methodology using wind tunnel pressure measurements to calculate the wind loads on the inter-tenancy walls of tall buildings (i.e. walls separating individual apartments and do not include the walls within the same apartment).

The European program HORIZON2020 aims to have 20% of electricity produced by renewable sources. The building sector represents 40% of the European Union energy consumption. Reducing energy consumption in buildings is therefore a priority for energy efficiency. The present investigation explores the most adequate roof shapes compatible with the placement of different types of small wind energy generators on high-rise buildings for urban wind energy exploitation. The wind flow around traditional state-of-the-art roof shapes is considered. In addition, the influence of the roof edge on the wind flow on high-rise buildings is analyzed. These geometries are investigated, both qualitatively and quantitatively, and the turbulence intensity threshold for horizontal axis wind turbines is considered. The most adequate shapes for wind energy exploitation are identified, studying vertical profiles of velocity, turbulent kinetic energy and turbulence intensity. Curved shapes are the most interesting building roof shapes from the wind energy exploitation point of view, leading to the highest speed-up and the lowest turbulence intensity.

This paper presents the results of a set of wind tunnel tests carried out to examine wind-induced overall structural loads on rectangular medium-rise buildings. Emphasis was directed towards torsion and its correlation with peak shear forces in transverse and longitudinal directions. Two building models with the same horizontal dimensions but different gabled-roof angles (0o and 45o) were tested at different full-scale equivalent eave heights (20, 30, 40, 50, and 60 m) in open terrain exposure for all wind directions (every 15o). Wind-induced pressures were integrated over building surfaces and results were obtained for along-wind force, across-wind force, and torsional moment. Maximum wind force component was given along with the other simultaneously-observed wind force components normalized by the overall peak. The study found that for flat-roofed buildings maximum torsion for winds in transverse direction is associated with 80% of the overall shear force perpendicular to the long...

In recent years, high-strength, lightweight materials have been widely used in the construction of high-rise buildings. Such structures generally have flexible, low-damping characteristics. Consequently, wind-induced oscillation greatly affects the structural safety and the comfort of the building's occupants. In this research, wind tunnel experiments were carried out to study the wind-induced vibration of a building with a tuned liquid column damper (TLCD). Then, a model for predicting the aerodynamic response in the across-wind direction was generated. Finally, a computing procedure was developed for the analytical modeling of the structural oscillation in a building with a TLCD under the wind load. The model agrees substantially with the experimental results. Therefore, it may be used to accurately calculate the structural response. Results from this investigation show that the TLCD is more advantageous for reducing the across-wind vibration than the along-wind oscillation. When the across-wind aerodynamic effects are considered, the TLCD more effectively controls the aerodynamic response. Moreover, it is also more useful in suppressing the acceleration than the displacement in biaxial directions. As s result, TLCDs are effective devices for reducing the wind-induced vibration in buildings. Parametric studies have also been conducted to evaluate the effectiveness of the TLCD in suppressing the structural oscillation. This study may help engineers to more correctly predict the aerodynamic response of high-rise buildings as well as select the most appropriate TLCDs for reducing the structural vibration under the wind load. It may also improve the understanding of wind-structure interactions and wind resistant designs for high-rise buildings.

The internal forces and stresses were analyzed and utilization of the design resistance in selected members of the roof structure with local and global geometrical imperfections was evaluated. Values of these imperfections were based on the information given in the standards EN 1090-2 and EN 1993-1-1. Besides the basic reference model with imperfections, models without imperfections, with different equivalent load arrangements by the authors’ own concept and comparatively according to the standard EN 1993-1-1 were analyzed. The calculations were made using the 1st and the 2nd order analysis. Conclusion concerning accuracy of the internal forces estimation and limit states check by use the equivalent load system proposed in the standard EN 1993-1-1 are presented. Deficiencies in the provisions of this standard in terms of adopting equivalent loads in roof structures with imperfections, resulting in underestimation of the stresses in the bottom chords of the roof trusses, has been dem...

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The pressure within a building, produced by wind action, is dependent on the magnitude of external surface pressure, the size and position of all openings connecting exterior to interior of the building and the effective enclosed volume. Internal pressure fluctuations within a sealed building are generally small in magnitude and intensity in comparison with its external pressures. But when there are dominant openings (operable façades) or sudden failures across the exterior façade, the building interiors can experience wind pressures of similar magnitude to that of the exterior. Therefore, in such cases, it becomes essential to determine the realistic values of wind pressures to be used for the design of inter-tenancy walls. This paper outlines a methodology using wind tunnel pressure measurements to calculate the wind loads on the inter-tenancy walls of tall buildings (i.e. walls separating individual apartments and do not include the walls within the same apartment).

Wind flow over low-rise buildings in the atmospheric boundary layer (ABL) is accompanied by some complex flow physics such as flow separation and generation of vortices in the shear layer. The uncertainties associated with such complex flow mechanisms make the case-by-case experimental or numerical investigation of buildings’ aerodynamic behavior fundamental. Engineers have aspired to replicate the full-scale real wind behavior in wind-tunnels to create more resilient infrastructures. Traditional wind-tunnel experiments struggle to accurately predict surface pressures despite being widely embraced by the structural engineering community. This limitation is attributed to the lack of large-scale turbulence and low Reynolds numbers in wind-tunnels. Such drawbacks prompted the consideration of aerodynamic testing by the open-jet concept. Open-jet experiments of building models with higher Reynolds numbers reveal the generation of higher mean and peak pressure coefficients, compared to t...

The nonlinear behavior of existing low rise reinforced concrete buildings with structural deficiencies was examined in this study. A set of push over analyses has been done for hypothetically defined four representative different types of widely used frames with four, five and six stories. The structural deficiencies such as the low compressive strength of concrete in existing buildings, low percentage of reinforcement in column sections, lack of proper lap splicing in critical regions of columns and beams in existing buildings are all grouped and have been taken into consideration in push over analyses. Also, possible structural changes such as alterations in the orientations of columns, having additional stories on top of the existing building and changing the demand of live loads on the existing structure are idealized for representative frames to obtain load-top deflection curves. All graphs achieved can be utilized in quick assessment work to evaluate earthquake load resisting capacities of the huge amount of existing low rise similar reinforced concrete structures constructed in earthquake prone areas.

The "Dimitrios Vikelas" athletic center in Ermoupolis of Syros, Greece, consists of two buildings. Building B has a steel superstructure that was constructed approximately 35 years ago. It was initially used as a boat shelter and no design calculations were made. It contains steel columns with varying cross section heights. The spans are bridged via trusses and I-beams. Significant geometrical inconsistencies are noted among the existing steel connections and failures have been recorded as a result of buckling in several beams and bracings during the service life of the athletic center. The current study presents an investigation performed in order to diagnose building structural problems and propose strengthening and intervention measures. The goal of this study was to improve the load-carrying capacity of the structure in order to comply with the current design codes. Moreover, enhancement of the dynamic properties of the strengthened structure was demonstrated using modal analyses. The structural behavior was determined in a more precise manner via non-linear wind time-history and incremental static analyses. The analytical results explain the development of failures in the existing structure.

The consistency of measurements in various wind tunnels is of concern to designers and code writers. This study attempts to quantify the variability of wind effects estimates based on tests conducted at six wind tunnel laboratories. Pressure tap measurements were made on wind tunnel models of four buildings. Comparisons were made between estimated 50th percenttiles of ͑1͒ peak positive moments in a frame section near the knee joint and ͑2͒ peak pressure coefficients of a roof tap nearest a building corner. Modeling of suburban terrain contributes significantly to the variability. Other factors are eave height, wind direction, and frame location within the building. Coefficients of variation were about 10-40%. A subsequent phase of this research entails a detailed analysis of the reasons for the variabilities. The results could help future improvement of wind load factors that account for all relevant uncertainties in the estimation of wind effects and efforts to improve and standardize wind tunnel simulations.

Wind loads on low-rise buildings in general and residential homes in particular can differ significantly depending upon the laboratory in which they were measured. The differences are due in large part to inadequate simulations of the low-frequency content of atmospheric velocity fluctuations in the laboratory and to the small scale of the models used for the measurements. The imperfect spatial coherence of the low frequency velocity fluctuations results in reductions of the overall wind effects with respect to the case of perfectly coherent flows. For large buildings those reductions are significant. However, for buildings with sufficiently small dimensions (e.g., residential homes) the reductions are relatively small. A technique is proposed for simulating the effect of low-frequency flow fluctuations on such buildings more effectively from the point of view of testing accuracy and repeatability than is currently the case. Experimental results are presented that validate the proposed technique. The technique eliminates a major cause of discrepancies among measurements conducted in different laboratories. In addition, the technique allows the use of considerably larger model scales than are possible in conventional testing. This makes it possible to model architectural details, and improves Reynolds number similarity. The technique is applicable to wind tunnels and large scale open jet facilities, and can help to standardize flow simulations for testing residential homes as well as significantly improving testing accuracy and repeatability. The work reported in this paper is a first step in developing the proposed technique. Additional tests are planned to further refine the technique and test the range of its applicability.

As a part of the ongoing National Institute of Standards and Technology research on the development of a new generation of standard provisions for wind loads, we present results of a pilot project on the estimation of wind effects in low-rise building frames. We use records of wind pressure time histories measured at a large number of taps on the building surface in the boundary layer wind tunnel of the University of Western Ontario. Time histories of bending moments in a frame are obtained by adding pressures at all taps tributary to that frame multiplied by the respective tributary areas and influence coefficients. The latter were obtained from the frame designs provided by CECO Building Systems. We compare results obtained by using the pressure time history records with results based on ASCE 7 standard provisions. The comparison suggests that provisions which use aerodynamic databases containing the type of data described in this work can result in designs that are significantly more risk-consistent as well as both safer and more economical than designs based on conventional standard provisions. We outline future research on improved design methodologies made possible by the proposed approach to the estimation of wind effects. We note that the use of the proposed methodologies is fully consistent with the ASCE 7 Standards insofar as these allow the use of wind-tunnel data for estimating wind load effects. Finally, We note that the proposed methodologies may be used for damage assessment for insurance purposes.

ABSTRACT: We descn"be the database-assisted design approach for wind loading, and its application for estimating limit states -including ultimate limit states --for low-rise buildings and taIl buildings experiencing along-wind, across-wind, and torsional dynamic effects. Database-assisted designs account for the temporal and spatial variation of wind effects and can result in far more risk-consistent, safe, and economical structures than those based on conventional stanllard provisions. Structural reliability methods,are currently applied to da- tabase-assisted designs with a view to developing improved,estimates of probabilities of failure under wind loads. INTRODUCnON,of the type used in U.S.

This paper presents the details and results of pseudo-elastic lateral testing of a full-scale one-story L-shaped house. The nature and extent of tests are designed to generate data needed to develop and validate a whole building structural model of a light-frame structure. This particular test house is unique in that it is fully supported at its base by load cells, which measure loads in three principal directions. Under an applied load, we are able to see for the first time how the loads are distributed and shared through the walls. Results to date show that even at very low levels of loading (i.e. displacement within ±1.0mm or load of about ±10.0 kN), there is significant load sharing in the system. Both roof system and transverse end walls participate in distributing the loads. In the next phase of testing, the house will be tested to destruction.