Wind tunnel tests of tall buildings are capable of accurately determining the wind loads on a bui... more Wind tunnel tests of tall buildings are capable of accurately determining the wind loads on a building in its current surroundings, since the surroundings are included in the wind tunnel modelling. The tests may also include some future developments if they are known to be imminent. However, the question of the effects of possible longer term changes in surroundings needs to be considered. In some cases the development of the city may be mature resulting in little likelihood of future changes, but in rapidly developing cities the possible changes may be significant. It is known that buildings very close to the building under test can have significant sheltering effects in some cases and may amplify wind loads in other cases. Cases have been seen where the removal of an important adjacent building more than doubled the wind loads. Wind tunnel testing can readily determine loads in the different scenarios but the question of how to treat the data requires some thought. This paper presents a method called the Combined Risk Method in which the results from the various test scenarios are combined to provide a single risk consistent relationship between load and return period. It does require that the various stakeholders agree on a reasonable probability for each scenario, but once this is done the method makes the path clear to developing appropriate design loads. The paper includes examples of application of the method to several projects.
Wind-induced damage to multi-layer building wall systems, such as systems with vinyl siding, is c... more Wind-induced damage to multi-layer building wall systems, such as systems with vinyl siding, is common, especially in hurricane-prone areas. Wind load distribution through these multi layered walls and the amount of load reduction due to pressure equalization is expressed through pressure equalization factors (PEFs). The ASTM D3679 standard suggests a PEF of 0.36, which means a 64% reduction in the net pressure on the siding. This paper presents results from an experimental study conducted on a low-rise building subjected to realistic wind loading conditions at the wall of wind (WOW) experimental facility at Florida International University. Results from area-averaged mean and peak pressure coefficients indicated that a very small portion of the total wind load is carried by the vinyl siding. However, PEFs were found to be much higher when individual taps were considered. For instance, PEFs ranged from 71 to 106% for the case of pressure coefficients with negative sign (suction) and from 39 to 110% for the case of pressure coefficients with positive sign (pressure). When a combined set of taps was considered, PEFs ranged approximately from 50 to 80% for the case of "suction" and from 15 to 75% for "pressure." Based on the 1 m 2 of tributary area used in ASCE 7-10 Standard, results show that the net load on vinyl wall siding can be obtained by reducing the net design load for the entire wall assembly by 25 and 60% for suctions and pressures, respectively. However, a smaller tributary area (<1 m 2) can experience a local peak load that can induce damage to connections, especially in the case of relatively flexible wall coverings, with no or very little load sharing between connection points. Results indicate that for smaller areas (~0.2 m 2) the allowable percentage reductions should not be more than 15 and 25% for suctions and pressures, respectively. This study shows that the suggested ASTM PEF of 0.36 may lead to the underestimation of loads for the design of details affected by local loads. However, further research is needed to consider more cases when developing adequate design load guidelines for vinyl wall sidings.
This paper describes a combined experimental-numerical investigation into the estimation and pred... more This paper describes a combined experimental-numerical investigation into the estimation and prediction of peak wind pressure loadings on the roofs and roof-top appurtenances of low-rise buildings. Preliminary results for the appurtenance examined here, a rooftop photovoltaic (PV) array, located on the top of the Hogue Technology Center (HTC) at Central Washington University (CWU) in Ellensburg, Washington will be discussed. These include numerical results from finite element models as well as from the pressure sensor, accelerometer, and strain gauge time series data. Designs of physical models of the full-scale and proposed 1:20 and 1:100 scale wind tunnel tests of the array and the building rooftop to be performed at the NSF NHERI Wall of Wind Experimental Facility (WOW EF) at Florida International University (FIU) will be presented.
SUMMARY: This paper describes the application of scale model and computer simulation techniques t... more SUMMARY: This paper describes the application of scale model and computer simulation techniques to the prediction of microclimate variables important to spectator comfort, turf growth and ice surfaces. These techniques have become increasingly powerful and provide valuable information during the design of sports facilities that will enhance their quality and functionality.
Traffic signals are a critical part of the transportation infrastructure and it is important that... more Traffic signals are a critical part of the transportation infrastructure and it is important that they be robust enough to resist extreme wind storms lasting several hours. Failure of the signal systems results in unsafe traffic conditions during and after a storm, and the time taken for repairs delays recovery. A significant fraction of existing signals use span-wire supporting systems. The wire spans can range from 15 m to 60 m, depending on the width of the highway intersection, and exhibit nonlinear characteristics. The typical signal system used in Florida consists of the signal units, a catenary wire, hangers, a tensioned messenger wire, and the end support posts. The hangers are connected to the catenary wire at their upper ends and to the signal units at their lower end. They are also connected to the messenger wire just above the signal units. In light winds the weight of the signals is taken by the catenary wire and swinging of the signals is restrained by the messenger wi...
Coastal areas of the US are affected by extreme wind events, including hurricanes. Roofs are the ... more 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.
Controlling vibrations of structures through the use of damping systems continues to increase as ... more Controlling vibrations of structures through the use of damping systems continues to increase as structures become lighter and more slender. This includes buildings, towers, vehicular bridges and pedestrian bridges. As a result, the tools used for design of these supplemental damping systems need to take into account the nature of the applied loads to get a more accurate determination of the way the structure will behave with the damping system. Wind tunnel testing to determine the wind-induced forces on structures has been common for many years. It is common for significant buildings and towers to have wind tunnel testing performed, beginning with the High-Frequency Force-Balance (HFFB) test and occasionally an aeroelastic wind tunnel test is performed to better determine aeroelastic effects such as aerodynamic damping and vortex-induced phenomena. Detailed knowledge of the nature of the wind-induced forces can be used with advanced analysis techniques to accurately describe the behaviour of a supplemental damping system. In addition to wind-induced forces, it may be necessary to consider seismic forces if the structure is located in a region with seismic activity. To date, damping systems which have been implemented to reduce vibrations of structures have been primarily designed using frequency domain analysis techniques. Beginning with the work of Den-Hartog (1956), many have produced estimates of effective damping of a damped structure and reduction in motion and amplitudes of the damping system. Computing limitations have limited the ability to perform time-domain analysis of the combined structure and damping system. More recently, software commonly available to structural
Journal of Wind Engineering and Industrial Aerodynamics, 2016
Large-scale wind tunnel testing is preferred for small structures and building appurtenances for ... more Large-scale wind tunnel testing is preferred for small structures and building appurtenances for maintaining modeling accuracy and minimizing Reynolds number effects. In these circumstances the ability to obtain a large enough turbulence integral scale is usually compromised by the limited dimensions of the wind tunnel. So, it is not normally possible to fully simulate the low frequency end of the turbulence spectrum. In this paper the approach is taken of dividing the turbulence into two distinct statistical processes, one at high frequencies which can be simulated in the wind tunnel, and one at low frequencies which can be treated in post-test analysis using the assumptions of quasi-steady theory. In this Partial Turbulence Simulation (PTS) method the contribution of both the high and low frequency turbulence on the wind loads on the structures is included by using the probability of load from each of the two processes, with one part coming from the wind tunnel data representing the high frequency component and the remainder from the assumed probability distribution (taken in this paper as Gaussian for generic boundary layer flow) of the missing low frequency component. The two processes are approximated as independent of each other. The efficacy and validity of the method and its various assumptions are assessed by comparing predicted local peak pressure coefficients from tests on large scale models of the Silsoe cube and Texas Tech University (TTU) building in the Wall of Wind facility at Florida International University (FIU) with the corresponding full-scale data. Generally good agreement was found between the model results and full scale, particularly when comparing the highest overall peak pressure coefficients. These results, although limited to peak local pressures on the two test buildings for which good full scale data are available, are encouraging and invite further experiments to explore the range of applicability of the PTS method. This method, although developed in the Wall of Wind facility at FIU, can be equally used in conventional boundary layer wind tunnels and has the potential to enhance the ability of existing boundary layer wind tunnel facilities to predict full scale wind loads.
Journal of Wind Engineering and Industrial Aerodynamics, 2017
Full-scale experiments were conducted to investigate wind loading on roof tiles in hip, ridge, an... more 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.
Wind is often regarded as the foe of tall buildings since it tends to be the governing lateral lo... more Wind is often regarded as the foe of tall buildings since it tends to be the governing lateral load. Careful aerodynamic design of tall buildings through wind tunnel testing can greatly reduce wind loads and their affect on building motions. Various shaping strategies are discussed, aimed particularly at suppression of vortex shedding since it is frequently the cause of crosswind excitation. The use of supplementary damping systems is another approach that takes the energy out of building motions and reduces loads. Different applications of damping systems are described on several buildings. Wind also has some potential beneficial effects particular to tall buildings. One is that, since wind speeds are higher at the heights of tall buildings, the potential for extracting wind energy using wind turbines is significantly improved compared with ground level. The paper explores how much energy might be generated in this way relative to the building's energy usage. Other benefits ar...
Design and use of spires for natural wind simulation
The status of the spire-roughness technique for planetary boundary layer simulation is briefly re... more The status of the spire-roughness technique for planetary boundary layer simulation is briefly reviewed. The last report on the subject was in 1972 and since then the technique has been applied to a wider range of boundary layers and a much greater body of data has been accumulated. A design method is given with particular emphasis on triangular spires which is suggested are as good as those of more complicated geometry. Results of spire drag measurements are described with due attention to blockage and interference effects. Finally, results from a number of spire generated boundary layers are collected together and compared with full scale data.
This Report describes experimental measurements and theoretical analysis of the flow around a win... more This Report describes experimental measurements and theoretical analysis of the flow around a wing with a single slotted flap under twodimensional flow conditions. The particular experimental techniques of testing and measurement are described. The results show that the measured flow is strongly dependent on the inviscid solution for the flow around the wing and the flap, and that near to the optimum flap position there is only weak interference between the wake from the wing and the boundary layer on the flap. The reasons for the occurrence of an optimum flap position are described, and some comments made
Cross-Spectra of Turbulence Velocities in Isotropic Turbulence
Boundary-Layer Meteorology, 1979
A general expression is given for the cross-spectra of the three turbulence velocity components f... more A general expression is given for the cross-spectra of the three turbulence velocity components for spacings in the across wind direction. The expression is derived assuming that the turbulence is homogeneous and isotropic and that von Karman’s spectrum applies. It is found to give a good description of the qualitative behaviour of cross-spectra observed in laboratory-scale nonisotropic turbulence.
A Calculation Method for the Twodimensional Turbulent Flow Over a Slotted Flap
SUMMARY An integral calculation method for the twodimensional turbulent flow over a slotted flap ... more SUMMARY An integral calculation method for the twodimensional turbulent flow over a slotted flap is described. taking into account the interaction of the wake from the main aerofoil with the boundary layer on the flap, and the variation of static pressure normal to the flap surface. The results are compared with experiment, and it is found that the method gives quite good agreement with the measured variation of the integral properties of the wake and boundary layer, and with the measured skin friction. The limitations of the method are discussed briefly in relation to the more complex approach of a differential method.
The current methods for evaluating the adequacy of metal roofs in withstanding wind-induced loads... more The current methods for evaluating the adequacy of metal roofs in withstanding wind-induced loads involve undertaking uniform uplift pressure tests. These methods may not be truly representative of real conditions, and might set higher minimum design requirements than necessary in some cases and in others it could underestimate effects of very localized peak pressures. This research work presents results of a full-scale experimental study conducted under more realistic wind loading with the panels installed as they would be in the American Society for Testing and Materials (ASTM) E1592 test chamber. The research objectives were to (i) measure the uplift roof pressure experience by mono-sloped standing seam metal roofs and compare them with the provisions of the American Society of Civil Engineers (ASCE) 7-10 standard, (ii) evaluate the performance of standing seam roofs under high winds, and (iii) compare the deflections and failure modes observed under more realistic wind loading to uniform loading tests. The research has provided test based data on aerodynamic loading of two types of standing seam metal roofs (i.e. vertical-leg and trapezoidal), as well as their performances under high wind speeds. Significantly higher pressure was recorded on the trapezoidal roof. This showed that roof panel profile and perimeter
Journal of Wind Engineering and Industrial Aerodynamics, 1979
Methods of reducing and correcting for the distortion effects introduced by pressure tubing syste... more Methods of reducing and correcting for the distortion effects introduced by pressure tubing systems in measurements of fluctuating pressures are discussed. A new technique is described, involving a digital correction technique using the known tubing transfer function. It allows considerably longer tubes and higher frequency response to be obtained than with other methods, and furthermore, phase distortion is effectively eliminated. The simpler technique of inserting restrictors in tubing systems is evaluated and found to reduce the distortion to acceptable levels for short tube lengths.
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Papers by Peter Irwin