Advanced and Robust Analysis of Wind Effects
Advanced and Robust Analysis of Wind Effects
Creating outdoor spaces that are comfortable and fit for purpose is more important now than it has ever been. For us this means finding wind mitigation strategies that fit with the aesthetics and intent of a development and this can be one of the most critical aspects of the studies we undertake.
For this reason, we felt it would be useful to highlight some of the options for wind mitigation and perhaps in the process give you some ideas for your next project.
We often employ a combination of the following strategies to reduce the impact of wind effects and if you’d like to get our take on your project, we’d welcome you to reach out – we’re always happy to assist.
Natural Landscaping
As well as often being aesthetically pleasing, hedges and trees can mitigate horizontal wind acceleration at ground and elevated levels. It is also possible to mitigate downdraught from facades as well as wind acceleration around building corners.
Trees along the boundary of a space are good for mitigating direct exposure to wind as well as wind funnelling between buildings. They are unlikely to be suitable for downdraught from buildings.
A combination of large planters that break up wind flow at ground level with dense planting may be enough to reduce wind speeds for a given activity. This approach can be effective to reduce the impact of funnelling, for which a combination of shrubs and small trees should be used.
Trees and hedges do not always have to go in straight lines. Here is an example of a green tunnel, which could make for an extremely effective mitigation strategy for combatting downwash. Pergolas or green canopies could be equally effective, although care should be taken to make sure that foliage is dense and effective during the right season.
Balconies and Raised Terraces
Commonly found on balconies, but also outdoor terraces, balustrades are most effective for direct exposure to winds. For larger outdoor terraces such as this one, a combination of a balustrade and natural landscaping can be effective as balustrades are not suitable for reducing downwash.
Balcony edge screens can be used when an elevated terrace is relatively deep and subjected to strong wind being upwashed from the façade below. This does not work if the wind conditions are generated by the tower above the terrace.
End screens or architectural features such as this one can be incorporated to negate the impact of wind acceleration around the corner of a building. If done correctly it can create an interesting feature too.
Excellent for creating, sheltered, usable spaces inset balconies are often the most effective method for ensuring private balconies meet comfort criteria. By combining screens such as that shown in the image below with an inset balcony a space is created that is versatile and protected all year round.
Screening can be positioned between different apartment blocks to reduce the impact of side-streaming at elevated levels as well as reduce the impact of direct exposure to the wind. Positioning these midway screens correctly is key to ensuring the most comfortable space.
This treatment is very effective for situations where there is a venturi effect between two tall buildings or a street canyon effect. This idea can also be used to design an airlock for the main entrance to a building.
For balconies that are north facing and exposed, it is often worth considering where winter gardens or a combination of winter gardens and balconies might be a preferred alternative to standalone balconies.
Where screening might be unsightly and natural landscaping impossible due to other restraints, it might be worth considering a piece of artwork or sculpture. By picking something that has a porosity appropriate for wind mitigation, you could have a beautiful addition to your space that is functional too! This might be used to reduce wind funnelling between buildings.
Perhaps the most famous canopy in London is The Leadenhall Building. Canopies such as this may be required when flat facades create downdraughts that impact at ground level.
The location and size of the building will have a significant impact on the size and position of the canopy required. They are usually not suitable for direct exposure to wind, wind funnelling between buildings or wind acceleration around building corners.
Similar to canopies, but on a much smaller, more localised scale, overhang shading is often porous and has the combined benefit of sun shading. Useful for mitigating downdraught from building façades, it is less suitable for direct exposure.
This is a great solution for open spaces where seating is required, but the opportunity for natural landscaping is limited.
Screens such as this can mitigate direct exposure to wind and wind funnelling between buildings but are not suitable for downdraught from buildings.
Porous screening is good for mitigating direct exposure to wind and wind funnelling between buildings. By making the screens porous, it has been proven that the distance for which shelter is provided is increased (when compared to solid screens). However, screening is unlikely to be suitable for downdraught from buildings.
Building Shaping and Building Form
Getting the overall building massing right at an early stage can save significant headache later in design.
As a rule of thumb, a cluster of buildings can offer shelter to one another and push the windy areas to the edge of the cluster. Also, orienting the narrower side of a tall building to the prevailing wind direction helps to reduce downdraught forming.
Masterplan Studies using Computational Fluid Dynamics (CFD) are particularly effective at informing early stage design as it is relatively easy to move buildings around in the simulation and re-test.
Podiums are often effective at mitigating downdraught off a building façade. However, if the podium itself is then designated as a usable space, such as a garden or a seating area, care must be taken to ensure that this meets comfort criteria. Podiums are not suitable for reducing the impact of direct exposure or wind funnelling between buildings.
By recessing the corner of a building, it is possible to reduce the wind acceleration around the corner. This mitigation strategy is not suitable for direct exposure to wind, wind funnelling between buildings or downdraught.
Sharp corners create more acceleration than rounded ones. By rounding off corners, it may be possible to bring comfort levels within comfort criteria if corner acceleration is leading to exceedances.
CTBUH Best Tall Building in Asia and Australasia Award CTBUH Urban Habitat Award
Tony Rofail presents at the 10th International Urban Design Conference
Advanced Modelling for Comfort to Enhance the Experience of Shopping Centre Customers
Pedestrian Microclimate Testing in London
Wind Environment Effects Case Study
Construction is now underway for the soon to be tallest office tower in Sydney.Designed by Foster + Partners, the 263m tall tower has been named ‘Salesforce Tower, Sydney’, with the US software giant Salesforce as the anchor tenant. The building has obtained Sydney’s first Platinum pre-certification for ‘WELL core and shell’ and aims to achieve a 6 Star ‘Green Star Design and As-Built’ rating when the construction completes in mid-2022. The 53-storey tower is being developed by Lendlease, in partnership with China’s Ping An Real Estate and Japan’s Mitsubishi Estate Asia.
Windtech worked closely with Lendlease as the wind engineering consultant for this ground-breaking project from concept design through to the detailed design development phases.
Windtech undertook a comprehensive pedestrian wind comfort study using a scaled wind tunnel model consisting of the subject tower and the neighbouring buildings. Accurate local wind speed measurements were made in Windtech’s state-of-the-art boundary layer wind tunnel using hot-wire anemometry and effective mitigation strategies were formulated within tight design constraints imposed by the local planning authority, the architect and the client. Windtech’s scope included the testing of the wind mitigation measures to ensure that the critical outdoor pedestrian areas at ground level and the various elevated terraces with the subject tower development meet the relevant wind comfort and safety criteria when built. Windtech also assessed the solar glare impact of the façade materials pertaining to the overall development on driver visibility via a detailed solar light reflectivity study.
Windtech also undertook a wind tunnel study of the design wind loads on the façade cladding and façade fins,as well as the ultimate design loads on the tower structure. Wind tunnel measurements required for these studies were obtained using more than 500 individual pressure sensors instrumented on the scaled study model of the development. The simultaneously acquired measurements were analysed using Windtech’s advanced multi-sector analysis technique, which provides an order of magnitude improvement in the accuracy of the load predictions compared to wind tunnel analysis techniques used by the majority of other wind engineering consultants. This assisted structural engineers Robert Bird Group in their quest to provide a robust and yet efficient design of the tower structure. Prior to the commencement of construction, a detailed wind tunnel investigation was also carried out to quantify the effect of wind-driven rain onto the various entrances to the building.
As construction works progressed into this year, Windtech also undertook a wind noise and vibration assessment on the exterior skin of the development.This study provided preventative measures to mitigate the potential for the generation of wind-induced noise and vibration from the various architectural features proposed for the façade of the development.
Windtech is partnering with the Jakarta government to deliver a brand-new, multi-function stadium named Jakarta International Stadium that can host around 82,000 spectators. The stadium will be incredibly luxurious, with facilities comparable to those at Manchester United’s Old Trafford stadium and Real Madrid’s Santiago Bernabeu stadium. Features include perforated external panels and two moving panels on the roof which can be open or closed to suit the different events.
Prior to wind tunnel testing, a detailed wind tunnel model was carefully replicated at 1:300 scale using the latest 3D printing technology to ensure accurate modelling of the small gaps between the wall cladding and to properly model the flow regime around the curved façade.
The model was carefully instrumented with to enable testing for both the ‘open-roof’ and the ‘closed-roof’ configurations. The testing was then carried out in one of Windtech’s three state-of-the-art wind tunnels to estimate the design wind pressures distributed across the light-weight structure elements.
Windtechalso undertook a full pedestrian wind comfort study, assessing the microclimate for the important outdoor areas such as the playing field and the seating bowl. In this study, hot wire anemometry, which is proven to be the most accurate method for data collection, will first be used to collect data on the local wind speeds at various locations in and around the stadium. These wind speeds will then be compared against Lawson’s comfort criteria to provide information on the suitability of each area for its chosen use or activity.
Subsequently, this wind speed data was used to calibrate the computational fluid dynamics simulation and combined with a seasonal analysis of the local climate including temperature to provide the project team with a more complete understanding of the spectators’ overall comfort. This hybrid approach of combining CFD with results from wind tunnel testing not only offers a robust analysis of thermal comfort, wind comfort, natural ventilation performance as well as suitability of wind conditions for the hybrid turf proposed for the arena, the first of its kind in Indonesia.
We are pleased to announce that the 2019 edition of the Quality Assurance Manual for Wind Engineering Studies of Buildings has recently been released by the Australasian Wind Engineering Society (AWES-QAM-1-2019). Tony Rofail, who is a Director of Windtech Consultants, has been instrumental in developing this recent edition. This is the first update to the 2001 edition, in which Tony was also a major contributor. The 2001 edition has been widely referenced around the world.
This document is unique in that it covers minimum standards for broad range of wind engineering studies relating to buildings, including important details such as minimum wind tunnel data sampling parameters and instrument specifications. The AWES-QAM-1-2019 provides an outline of the minimum standards for wind tunnel testing with emphasis on the preparation of wind tunnel models and appropriate procedures for conducting a number of studies including façade pressure studies, pedestrian wind environment studies and the study of structural response of a tall building. This edition also covers minimum standards for reporting, data retention/storage, prototype tests, section model tests, air quality studies, wind shear and turbulence impacts near airports and computational fluid dynamics (CFD) modelling.
This recent update was commissioned by the Australasian Wind Engineering Society, who have kindly agreed to make this edition available at no charge. A copy of this document can be downloaded by clicking on the link below:
Download a PDF copy of AWES-QAM-1-2019
View Windtech Consultants’ Contributions to other Technical Papers
Windtech is pleased to announce a partnership with a global fabricator to provide a turnkey solution for its high performance, low cost innovative damper solution as well as for tuned liquid damper solutions. Dampers are often the most cost effective way to mitigate the physiological and other effects of excessive movement at the top of a tall building on occupant comfort. Windtech models these effects in their wind tunnels using the most rigorous techniques and can also peer review wind tunnel results that recommend the installation of a damper. Windtech can also assist in providing design and performance specifications for other types of tall building motion dampers such as tuned mass dampers and viscou dampers.
Windtech has recently developed and implemented an innovative high performance, low cost damper solution that can often be integrated within a proposed fire hydrant tank, effectively eliminating the loss of space and minimising the cost. This unique design can be tailored to suit your particular building and can work within strict dimensional constraints.
Our services include design, testing of prototypes, on-site measurement of the building’s dynamic properties prior to installation as well as tuning, commissioning and post installation performance monitoring of the dampers. Windtech has a team of expert engineers that can manage turnkey damper solutions around the world with the option of installing long term monitoring systems to monitor the performance of the dampers and to detect any changes to the building’s dynamic properties over time.
Below are sample case studies where Windtech has been involved in the installation of various types of dampers.
The Independent, Austin, Texas
This project met the acceleration criteria for a residential tower. However the client requested that the fire hydrant tanks at the top of the building be used for the dual purpose of the fire sprinkler system and to reduce the acceleration response of the tower.
Windtech utilised its innovative high performance, low cost damper system for this project, which has the added advantage of its performance being able to be tuned within the strict dimension constraints of the fire hydrant tank.
The result was a semi-tuned liquid damper that, when tuned, can provide up to 2% additional damping to the structure but can still provide 0.9% damping at a tuning ratio of 0.8.
By covering a broad range of frequencies, on-going maintenance costs are significantly decreased for the damper. By also incorporating the damper technology into the fire hydrant tank the damper as a ratio of total construction cost is under 0.15%.
88 Queens Bridge Street, Southbank, Australia
This project involved the determination of the necessary size, mass and location of tanks required for an effective Tuned-Liquid Damper (TLD) system for the tower located at 88 Queens Bridge Street, Southbank.
The initial wind tunnel study undertaken by Windtech indicated that the building accelerations at the top of the tower will exceed the relevant criteria of occupant comfort.
A TLD system was designed to control the excessive motion to meet the criteria.
