300 George Street, Brisbane Pedestrian Level Winds -Wind ... · Bao Jia Development Pty Ltd 300 George Street, Brisbane Pedestrian Level Winds -Wind Tunnel Test 21Oct 2013 70Q-13-0325-TRP-339502-1

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Vipac Engineers & Scientists Ltd.

Level 2, 146 Leichhardt Street, Spring Hill, QLD 4000

PO Box 436, Toowong, QLD 4066

t. +61 7 3377 0400 | f. +61 7 3377 0499 | e. [email protected]

w. www.vipac.com.au | A.B.N. 33 005 453 627 | A.C.N. 005 453 627

300 George Street, Brisbane

Pedestrian Level Winds - Wind Tunnel Test

for

Bao Jia Development Pty Ltd

70Q-13-0325-TRP-339502-1

21 Oct 2013




21 Oct 2013

70Q-13-0325-TRP-339502-1 Commercial-In-Confidence Page 2 of 50



DOCUMENT NO: 70Q-13-0325-TRP-339502-1

REPORT CODE: TRP

PREPARED FOR: PREPARED BY:

Bao Jia Development Pty LtdLevel 16, 97 Creek St.

Vipac Engineers & Scientists Ltd.

Brisbane, QLd, 4000 Level 2, 146 Leichhardt Street, Spring Hill, QLD 4000

PO Box 436, Toowong, QLD 4066

CONTACT: Yee Jien

Tel: +61 7 3123 2880 Tel: +61 7 3377 0400

Fax: +61 7 3123 2881 Fax: +61 7 3377 0499

PREPARED BY:

Author: Sophie Lamande Date: 21 October 2013

REVIEWED BY:

Reviewer: Zhuyun Xu Date: 21 October 2013

AUTHORISED BY:

Martin Wilson Date: 21 October 2013

REVISION HISTORY

Revision No. Date Issued Reason/Comments

1 0

21 October 201310 October 2013

revised itemsInitial Issue

DISTRIBUTION

Copy No.__1____ Location client

KEYWORDS: 300 George Street, Brisbane, Wind Effects

NOTE: This document contains commercial, conceptual and engineering information that is proprietary to Vipac Engineers & Scientists Ltd. We specifically state that inclusion of this information does not grant the Client any license to use the information without Vipac’s written permission. We further require that the information not be divulged to a third party without our written consent.




21 Oct 2013


EXECUTIVE SUMMARY

Vipac Engineers & Scientists Ltd (VIPAC) has been commissioned by Bao Jia Development Pty Ltd to carry out a wind tunnel test to determine the likely pedestrian level wind conditions of the proposed development at 300 George St, Brisbane.

A model was constructed according to drawings supplied by Zenx Architects. The proposed development and surrounding buildings covering a circular area of approximately 500 m radius were included in the model at a 1:400 scale. The approaching mean and turbulent flows of the Terrain Category 3 Atmospheric Boundary Layers (for all directions) was modelled based on Australia Standard AS 1170.2-2011.

Wind tunnel testing was carried out in the Boundary Layer Wind Tunnel Facility at Vipacs Melbourne laboratories during October 2013.

The findings of the current study are summarised as follows:

With the proposed design,

The development will satisfy the criterion for safety at all locations;

With the recommended landscaping, wind conditions will satisfy criterion for walking comfort in adjacent ground level footpath areas on Adelaide St, Ann St, North Quay and George St;

With the recommended landscaping, wind conditions will satisfy criterion for standing comfort at the building entrance areas, and;

With the recommended windscreens/landscaping, wind conditions will satisfy the criterion for walking on the podium rooftop terraces.




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TABLE OF CONTENTS

INTRODUCTION .....................................................................................................................51

1.1 Site of the Proposed Development ............................................................................................... 5

1.2 Environmental Wind Effects........................................................................................................ 11

REGIONAL WIND CLIMATE .............................................................................................. 122

ASSESSMENT CRITERIA .................................................................................................... 133

3.1 Applicable Criteria....................................................................................................................... 15

WIND TUNNEL SIMULATION............................................................................................. 164

4.1 Similarity Requirements.............................................................................................................. 16

4.2 Approach Wind Simulation ......................................................................................................... 16

TEST PROCEDURE .............................................................................................................. 185

5.1 Omni Directional Pressure Sensor Test ..................................................................................... 18

WIND TUNNEL TEST RESULTS.......................................................................................... 216

6.1 Safety.......................................................................................................................................... 21

6.2 Comfort ....................................................................................................................................... 22

RECOMMENDATIONS......................................................................................................... 237

CONCLUSIONS ..................................................................................................................... 258

REFERENCES ....................................................................................................................... 269

OMNI-DIRECTIONAL SENSOR POLAR PLOTS ......................................................... 27APPENDIX A:

TEST PHOTOS ............................................................................................................... 48APPENDIX B:

DRAWING LIST............................................................................................................. 50APPENDIX C:




21 Oct 2013


INTRODUCTION1

Vipac Engineers & Scientists Ltd was commissioned by Bao Jia Development Pty Ltd to carry out a wind tunnel test of the likely pedestrian level wind conditions of the proposed development at 300 George St, Brisbane.

1.1 Site of the Proposed Development

The proposed development is a mixed use building with three towers on a common podium. The Residential tower is 260m above street level; the Office tower is 132 m above street level and the Hotel tower is 110 m above street level. The site is bounded by Ann Street, George Street, Adelaide St and North Quay. There are a number of high rise buildings in the immediately surrounding areas as shown in Figure 1. A satellite view of the proposed development with the surroundings of an approximately 3 km radius is shown in Figure 2. The ground level plan of the development is shown in Figure 3, and building sections are shown in Figure 4 and Figure 5.

Figure 1: Satellite image of the site of the proposed development at 300 George St, Brisbane

North

Proposed Development Site




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This report details the pedestrian level wind assessment results of the tests carried out on a 1:400 scale model of the proposed development in Vipac’s Boundary Layer Wind Tunnel in Melbourne. The results show the wind effects in ground level public areas adjacent to the development as proposed. The wind effects on the outdoor podium rooftop areas on are also detailed. All tests were conducted in Vipac’s Boundary Layer Wind Tunnel Laboratory in Melbourne during October 2013.

The pedestrian wind environment study of the development was conducted using omni-directional pressure sensor techniques to predict wind velocities.

The study investigated safety and comfort in ground level pedestrian access-ways nearby the project, as well as the outdoor terrace areas of the podium rooftop. These areas were assessed against the recommended walking criterion. The building entrances were also tested and assessed against the recommended standing criterion.

The buildings model was constructed based on drawings supplied by Zenx Architects. Figure 6 and Figure 7 show the 1:400 scaled buildings of the proposed development as well as the surrounding developments in the wind tunnel. A complete list of the drawings used to construct the model is provided in Appendix C. Vipac understands that the Office tower has increased by approximately 8.5 m since the design on which the wind tunnel model is based. However, this will not have a bearing on the outcomes of the wind tunnel study.

Figure 2: Assumed terrain roughness for wind speed estimation

Proposed Site

North

Terrain Category 3




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Figure 3: Ground floor plan of the proposed development at 300 George St, Brisbane

North




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Figure 4: Section of the Residential and Office towers




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Figure 5: Section of the Hotel Tower

110 m




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Figure 6: Overall view from the north of the 1:400 scale model of the proposed development and surrounding buildings in the wind tunnel

Figure 7: Close up view from the northeast of the 1:400 scale model of the proposed development in the wind tunnel




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1.2 Environmental Wind Effects

Atmospheric Boundary Layer

As wind flows over the earth it encounters various roughness elements and terrain such as water, forests, houses and buildings. To varying degrees, these elements reduce the mean wind speed at low elevations and increase air turbulence. The wind above these obstructions travels with un attenuated velocity, driven by atmospheric pressure gradients. The resultant increase in wind speed with height above ground is known as a wind velocity profile. When this wind profile encounters a tall building, some of the fast moving wind at upper elevations is diverted down to ground level resulting in local adverse wind effects.

The terminology used to describe the wind flow patterns around the proposed development is based on the aerodynamic mechanism, direction and nature of the wind flow.

Downwash – refers to a flow of air down the exposed face of a tower. A tall tower can deflect a fast moving wind at higher elevations downwards.

Corner Accelerations – when wind flows around the corner of a building it tends to accelerate in a similar manner to airflow over the top of an aeroplane wing.

Flow separation – when wind flowing along a surface suddenly detaches from that surface and the resultant energy dissipation produces increased turbulence in the flow. Flow separation at a building corner or at a solid screen can result in gusty conditions.

Flow channelling – the well-known “street canyon” effect occurs when a large volume of air is funnelled through a constricted pathway. To maintain flow continuity the wind must speed up as it passes through the constriction. Examples of this might occur between two towers, in a narrowing street or under a bridge.

Direct Exposure – a location with little upstream shielding for a wind direction of interest. The location will be exposed to the unabated mean wind and gust velocity. Piers and open water frontage may have such exposure.




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REGIONAL WIND CLIMATE2

The mean and gust wind speeds have been recorded in the Brisbane area for over 30 years. These data have been analysed and the directional probability distribution of wind speeds have been determined. The directional distribution of hourly mean wind speed at the gradient height, with a probability of occurring once per year (i.e. 1 year return period) is shown in Figure 8. The wind data at this free stream height are common to all Brisbane city sites and may be used as a reference to assess ground level wind conditions at the proposed site.

The figure shows that the winds from the SE sector are the prevailing winds for Brisbane.

Figure 8: Directional Distribution Hourly Mean Wind Velocities (ms-1) at 250m Height for Brisbane




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ASSESSMENT CRITERIA3

Vipac's assessment criteria for pedestrian wind comfort are based on some consensus of international opinion. A set of annual maximum peak 3-second gust velocities is derived from meteorological data for the geographical location under consideration, for each wind direction to be assessed. For all of these possible wind directions and speeds, the regions where each of the wind speed criteria may be exceeded are then considered.

Most people will consider a site unacceptable for a given activity if the mean and/or gust velocities in that area during the annual maximum wind event exceed the annual maximum wind speed criterion for that activity. The site would also be likely to be considered excessively windy for that activity during more moderate winds.

The threshold gust velocity criteria are:

Table 1: Recommended Wind Comfort and Safety Gust Criteria

Annual Maximum Gust Speed

Result on Perceived Pedestrian Comfort

>23m/s Unsafe (frail pedestrians knocked over)

<16m/s Acceptable for walking (steady steps for most pedestrians)

<13m/s Acceptable for standing (window shopping, vehicle drop off, queuing)

<11m/s Acceptable for sitting (outdoor cafés, gardens, park benches)

In a similar manner, a set of hourly mean velocity criteria with a 0.1% probability of occurrence are also applicable to ground level areas in and adjacent to the proposed development. An area should be within both the relevant mean and gust limits in order to satisfy the particular human comfort and safety criteria in question.

The threshold mean velocity criteria are:

Table 2: Recommended Wind Comfort and Safety Mean Criteria

Mean wind speed exceeded 0.1% of the time

Result on Perceived Pedestrian Comfort

>15m/s Unsafe (frail pedestrians knocked over)

<10m/s Acceptable for walking (steady steps for most pedestrians)

<7m/sAcceptable for standing (window shopping, vehicle drop off, queuing)

<5m/s Acceptable for sitting (outdoor cafés, gardens, park benches)

The Beaufort Scale is an empirical measure that related the wind speed to observed conditions on the land and sea. Table 3 describes the categories of the Beaufort Scale. The comparison between these observed conditions and the comfort criteria described above can be found in Table 4.




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Table 3: Beaufort Scale - empirical measure relating wind speed to observed conditions on land

Beaufort Number

Descriptive Term

Wind Speed at 1.75 m height (m/s)

Specification for Estimating Speed

0 Calm 0-0.1

1 Light Air 0.1-1.0 No noticeable wind

2 Light Breeze

1.1-2.3 Wind felt on face

3 Gentle Breeze

2.4-3.8 Hair disturbed, clothing flaps, newspapers difficult to read

4 Moderate Breeze

3.9-5.5 Raises dust and loose paper; hair disarranged

5 Fresh Breeze

5.6-7.5 Force of wind felt on body, danger of stumbling when entering a windy zone

6 Strong Breeze

7.6-9.7 Umbrellas used with difficulty, hair blown straight, difficult to walk steadily, sideways wind force about equal to forwards wind force, wind noise on ears unpleasant

7 Near Gale 9.8-12.0 Inconvenience felt when walking

8 Gale 12.1-14.5 Generally impedes progress, great difficulty with balance in gusts

9 Strong Gale

14.6-17.1 People blown over

Table 4: Comparison between Mean comfort criteria and the observed conditions

Comfort Criteria Beaufort Scale Equivalent

Safety >9 – Strong Gale

Walking 5 – Fresh Breeze

Standing 4-5 – Moderate to Fresh Breeze

Sitting <4 – Moderate Breeze




21 Oct 2013


3.1 Applicable Criteria

The following table lists the specific areas adjacent to the proposed development and the corresponding recommended criteria. All areas adjacent to the development should be considered without landscaping when designing for safety. This is because the permanence of vegetation is not guarunteed and foliage is likely to be stripped during high wind events. However, when designing for comfort, trees and other landscaping features can be considered in the analysis of the wind environment.

Table 5: Recommended application of criteria

Area Specific location Recommended Criteria

Public Footpaths Around the proposed development on George St, Ann St, Adelaide St, North Quay

Walking

Building entrances Main building entrances are proposed in the inner areas arcade areas of the ground floor

Standing

Communal Terrace Areas

Podium rooftop Walking

Figure 9: Schematic plan view of the proposed development with the recommended wind comfort criteria overlaid at the ground level

North




21 Oct 2013


WIND TUNNEL SIMULATION4

4.1 Similarity Requirements

The validity of wind tunnel testing relies on the similarity between model and full-scale parameters. This requires undistorted length scaling (ie. geometric similarity), similarity of flow parameters (ie. kinematic similarity) and finally similarity of pressures and forces.

Complete similarity is usually impossible to obtain because of the competing requirements of the various non-dimensional parameters, (eg. Reynolds Number, Rosby Number and Richardson Number). Some requirements (i.e. Reynolds Number equality) can be waived for sharp edged structures immersed in a neutrally stable atmospheric boundary layer and geometric and kinematic similarity suffice. These are the requirements specified in Section C1.4, AS/NZS 1170.2 Supplement 1: 2011 [4] and are employed in this study.

4.2 Approach Wind Simulation

The wind effects tests were carried out in the 3m wide 2m tall 16m long Boundary Layer Wind Tunnel at Vipac Engineers and Scientists Ltd in Melbourne. The Boundary Layer Wind Tunnel is designed to simulate the flow incident on a proposed development by modelling the upstream terrain characteristic roughness. To this end, an estimate of the upstream terrain properties for the development has been made and reproduced in the wind tunnel.

The approaching mean and turbulent flows of the Terrain Category 3 Atmospheric Boundary Layer (for all directions) was modelled based on Australia Standard AS 1170.2-2011 (Figure 2). The wind tunnel calibration velocity and turbulence intensity profiles for Terrain Category 3 are shown in

Figure 10. These represent the wind velocity and turbulence intensity profiles approaching the model of the development. Closer to the ground the wind moves more slowly but with increased turbulence. The simulated approach is indicative of full-scale planetary boundary layer velocity and turbulence intensity profiles.




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Figure 10: Mean Velocity and Turbulence Intensity Profiles for Terrain Category 3 (1:250 scale)




21 Oct 2013


TEST PROCEDURE5

The pedestrian wind environment in the footpath area (on Adelaide St, Ann St, North Quay and George St) and the podium rooftop terrace areas were assessed using the Omni directional pressure sensor test (point method) [4].

5.1 Omni Directional Pressure Sensor Test

Velocity measurements were made using Irwin sensors (Omni directional pressure sensors) installed at several locations on the ground level footpath areas, entrances of the proposed development.

The distribution of Irwin sensors has allowed the determination of the variation in velocity sufficient to capture the changes in velocity distribution that can typically occur over such areas. The resolution of measurement locations is in accordance with that prescribed in the Wind Tunnel Testing Quality Assurance Manual of the Australasian Wind Engineering Society.

PVC tubes with 1.5 mm internal diameter linked the Irwin sensors to pressure transducer device using a tuned arrangement to prevent harmonic fluctuations.

Velocity measurements were obtained at 10 wind azimuth increments starting from 0 (north) for a full

360 circle. The sampling time is determined based on the similarity criteria and corresponds to a total time of one hour in full scale. Statistical analysis was carried out on the signals for the mean and standard deviation. All velocity coefficients derived from the wind tunnel were converted to velocities by integrating the data with the Brisbane wind climate and corresponding to a 1-year return period design wind speeds.

A total of 41 sensors were used in order to provide a quantitative measure of the ground level wind speeds at various locations around the proposed development. The sensor locations are shown in Figure 11 and Figure 12.




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Figure 11: Sensor Locations and Numbers – ground floor of the development

North




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Figure 12: Sensor Locations and Numbers – podium rooftop

North




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WIND TUNNEL TEST RESULTS6

The aerodynamic interactions around the proposed development do not show an influence on ground level wind conditions in the adjacent areas.

There are a number of design features that act to mitigate adverse wind conditions in and adjacent to the proposed development. These include the curved envelope of the Residential Tower and podium, the setback design of the entrances and the setback of the towers from the podium edge.

The pedestrian wind environment in the footpaths, main entrances and podium rooftop outdoor terrace areas were assessed using Omni directional pressure sensor tests. These results are presented as polar plots for the gust wind speeds and are shown in Appendix C of this report. Figure 13 shows an example of these plots. In the figure, the colour circles represent the velocities for the different criteria and the dark blue and maroon data points represent the test predicted gust velocity for the 36 directions. The graph shows a comparison between the wind effects with and without the street trees on Adelaide St.

Figure 13: Polar plot showing the wind gust compared with safety and other comfort criteria

6.1 Safety

This test was conducted without landscaping as discussed in Section 3.

Testing indicated that with the proposed design, all ground level pedestrian areas adjacent to the proposed development and the terraces on the podium rooftop will meet the safety criterion.




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6.2 Comfort

Testing indicated that if the existing street trees are not considered, some ground level pedestrian areas adjacent to the development exceed the walking comfort criterion. However, with the existing street trees on the opposite side of Adelaide Street, and the street tree placement adjacent to the development as described in Section 7, all ground level pedestrian areas adjacent to the proposed development will meet the walking criterion.

Testing indicated that if the existing street trees are not considered, some entrance areas adjacent to the development exceed the standing comfort criterion. However, with the existing street trees on the opposite side of Adelaide Street, and the street tree placement adjacent to the development as described in Section 7, the main entrance areas of the proposed development will meet the standing criterion. Additionally, main building entrances have rotating doors that will reduce wind infiltrating into the lobbies and reduce other adverse effects associated with high winds at building entrances.

Testing indicated that in the absence of landscaping on the podium rooftop, some ground areas exceed the recommended walking comfort criterion. If landscaping is introduced as per the recommendations in Section 7 then the terraces on the podium rooftop will meet the walking comfort criterion. If the recommendations are not implemented the area will still meet the walking safety criterion.




21 Oct 2013


RECOMMENDATIONS7

The wind tunnel tests revealed that all areas surrounding the development comply with the safety criterion. Therefore, Vipac makes no recommendations in this regard.

Considering comfort, the wind tunnel tests revealed that at almost all locations, the wind conditions are predicted to be within the recommended criteria. Without landscaping, there are some areas on Adelaide St that exceeded the walking comfort criterion. To ameliorate these wind conditions, trees in the locations shown in Figure 14 can be planted on Adelaide St.

Without landscaping, there are some areas on the podium rooftop terrace that exceeded the walking comfort criterion areas where landscaping can be used to shield the terraces from the incoming winds have been identified, and are depicted in Figure 15.

Figure 14: Trees on the ground level recommended to achieve walking comfort criterion on the ground level




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Figure 15: Recommended wind control measures to reduce all areas to within the recommended criteria

Porous windscreen; planters or trees – 1.8 m high

Porous windscreen; planters or trees – 1.8 m high




21 Oct 2013


CONCLUSIONS8

Vipac has carried out the wind tunnel testing for pedestrian level wind effects of the proposed development at 300 George St, Brisbane.

Wind conditions were assessed based on internationally accepted comfort and safety criteria. Based on the test results, the following conclusions are drawn:

With the proposed design,

The development will satisfy the criterion for safety at all locations;

With the recommended landscaping, wind conditions will satisfy criterion for walking comfort in adjacent ground level footpath areas on Adelaide St, Ann St, North Quay and George St;

With the recommended landscaping, wind conditions will satisfy criterion for standing comfort at the building entrance areas, and;

With recommended windscreens/landscaping, wind conditions will satisfy the criterion for walking comfort on the podium rooftop terraces. If the recommendations are not implemented, the podium rooftop terraces will still meet the walking safety criteria.

This Report has been Prepared

For


By

VIPAC ENGINEERS & SCIENTISTS PTY LTD.




21 Oct 2013


REFERENCES9

1. Australian/New Zealand Standard 1170.2:2002, Wind actions

2. Melbourne, W. H., “Criteria for Environmental Wind Conditions”, Jour. Industrial Aerodynamics, Vol. 3, 241-249,1978

3. Simiu E, Scanlan R, “Wind Effects on Structures”. Wiley-Interscience

4. Aynsley R., Melbourne W., Vickery B., Architectural Aerodynamics Applied Science Publishers




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OMNI-DIRECTIONAL SENSOR POLAR PLOTSAppendix A:




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TEST PHOTOSAppendix B:

Existing and recommended street trees on Adelaide St

Residential Outdoor Terrace




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Connection Hotel/Serviced Apartments

Hotel Podium Outdoor Terrace




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DRAWING LISTAppendix C:

Podium

Hotel Tower

Office Tower

Residential Tower

Documents

300 George Street, Brisbane Pedestrian Level Winds -Wind ... · Bao Jia Development Pty Ltd 300 George Street, Brisbane Pedestrian Level Winds -Wind Tunnel Test 21Oct 2013 70Q-13-0325-TRP-339502-1