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14th International Conference on Wind Engineering – Porto Alegre, Brazil – June 21-26, 2015

The Wind Engineering of the CTF Tianjin Finance Centre

Stefano Cammelli1, Leighton Aurelius

1, William Baker

2, Ronald Johnson

2, David Ho Wing Ip

3 and Derry Yu De Ming

3

1BMT Fluid Mechanics Ltd., Teddington, UK

2Skidmore, Owings & Merrill LLP, Chicago, U.S.A.

3New World Development Company Ltd., Hong Kong, China

email: scammelli@bmtfm.com, laurelius@bmtfm.com, William.Baker@som.com, Ronald.Johnson@som.com,

davidho@nwd.com.hk and derryyu@nwd.com.hk

ABSTRACT: The CTF Tianjin Finance Centre, currently under construction in Tianjin, will be 530 m tall when completed,

making it one of the tallest buildings in the People's Republic of China. For a building of this height, wind forces and resulting

motion in the upper levels can become dominant factors in the structural design of its foundations and lateral-stability system.

This technical paper will describe how an initial wind loading workshop has allowed the design team to develop a finely tuned

architectural form capable of minimizing the detrimental effects of vortex shedding; this process, approximately 10 hours of

wind tunnel time, was able to deliver in real time a number of key design information for a total of 17 different aerodynamic

variations of the tower form: a result which before would only have been possible through an extensive and time consuming

campaign of wind tunnel tests. The way the wind loading has then been refined, making use of simultaneous pressure integration

and aeroelastic techniques will also be described. Details about other wind engineering studies, aimed at investigating the

pedestrian level wind microclimate, the façade wind pressure as well as the stack effect, will also be given.

KEY WORDS: Vortex shedding; High Frequency Force Balance; Simultaneous Pressure Integration; Aeroelastic Testing;

Dynamic Response; Wind-induced Acceleration; Aerodynamic Optimization.

1 INTRODUCTION

The CTF Tianjin Finance Centre (CTFTJ), currently being developed by a subsidiary company of Chow Tai Fook Enterprises

Ltd. (CTF) and project managed by New World Development Company Ltd. (NWD), is located within the Tianjin Economic-

Technological Development Area (TEDA) of the Tanggu district of Tianjin (People's Republic of China), approximately 2 km

away from the Bohai Sea.. It will consist of a mixed-use 530 m super-tall tower (structural roof height 443 m) and a large retail

podium. The 97-storey skyscraper will comprise Grade-A Offices for world class and domestic companies, high-end Serviced

Apartments and a super Luxury Hotel (see Figure 1).

As the authors of this technical paper were fully aware of the fact that the commercial and financial success of a modern

super-tall structure like the CTFTJ is highly dependent on the mature integration between different disciplines such as

architecture, structural engineering and applied aerodynamics, one of the primary goals in developing both the architectural form

and the structural system was to minimize the wind loads on the tower as much as possible. The intent was to reduce the wind

loads to a level where they did not govern the design, which meant that the structure could be primarily designed for just gravity

and seismic loads. This approach not only simplified the design but also resulted in significant material savings. Another goal

was to reduce wind-induced accelerations to the lowest level possible to enhance the comfort levels for the hotel and residence

areas and also to eliminate the need for a tuned mass damper and its associated costs and maintenance requirements.

In order to achieve this, an initial aerodynamic optimization workshop was held in the 4.8 m x 2.4 m boundary layer wind

tunnel of BMT Fluid Mechanics Ltd. (BMT) during the early stages of the design: the aim of this session was not to check a

series of predetermined architectural shapes, but to development directly in the wind tunnel a series of bespoke and wind climate

specific optimized aerodynamic solutions.

By integrating the architectural, structural and wind performance design, the structure was able to have accelerations and wind

loads well below the code requirement while also saving significant material cost relative to a more traditional design approach.

Once the project was de-risked from a strength and serviceability design point of view, the attention of the wind engineering

work moved to the assessment of the façade design wind pressures, the assessment and mitigation of the pedestrian level wind

microclimate and the development of a strategy aimed at preventing stack effect to occur.

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14th International Conference on Wind Engineering – Porto Alegre, Brazil – June 21-26, 2015

Figure 1. Architectural render of the Tianjin CTF Finance Centre (courtesy of Skidmore, Owings & Merrill LLP).

2 PROJECT DESCRIPTION

The L-shaped site plan of the CTFTJ is 185 m long in the north-south direction and 171 m in the west-east direction. The total

architectural area of the project, which has been designed to LEED® Gold standards, is around 390,000 m

2.

The Office spaces occupy 36 floors in the lower portion of the tower; the spans between the central square core and the

exterior of the building are ranging between 13 m to 15 m and the plans, featuring rounded corners, are typically in the range of

3,500 m² to 3,800 m².

The Serviced Apartments are located in the middle portion of the tower; the core-wall spans are in the range of 12 m to 13 m,

with floor plates of approximately 2,000 m² with softly rounded corners. These apartments, accessible from a sky lobby via a

number of private elevators, feature ample spaces with well-balanced perimeter-to-floor space ratio for generous room layouts.

The Luxury Hotel has 364 rooms and a Presidential Suite which can all be accessed from a sky lobby; located in the upper

portion of the tower, these spaces feature smaller floor plates (1,800 m²) with eased corners to maximize panoramic views.

The 4-storey podium has a roof height of 32 m and 4 levels of basement (24 m deep) and it is connected to the west side of the

tower.

3 STRUCTURAL CONSIDERATIONS

With the architectural team, a variable tapered form was developed that reflected the differing floor size requirements between

residential floors and the office floors. The office floor plate size was set at the maximum allowed by code which both

maximized the architectural functional efficiency but also increased the stiffness of the tower.

The core was developed as a reinforced concrete tube-in-tube system with lifts for the office zones in the outer tube and the

lifts for the residential zones in the inner tube. This minimized the size of the core which increased the overall efficiency of the

system and eliminated the need for any core wall transfers. This also resulted in the core to perimeter stiffness ratio being

relatively constant over the height of the building which enhanced the efficiency of the load sharing between the core and the

perimeter.

The perimeter structure is a system of 8 mega-columns at the corners of the tower which are linked by a perimeter moment

frame and a system of sloping columns which are expressed by the “crease” lines in the architectural façade. The sloping

column / frame system is configured to provide high stiffness under wind loads while also allowing high energy absorption

under seismic loads. The very shallow angle from vertical at the residential levels allows high energy absorption (increased

‘frame action in the upper residential zone) whereas the larger angle at the office levels provides higher stiffness where it is

more required in order to maintain stiffness compatibility between the perimeter frame system and the stiff central core. The

sloping columns are separated by a framed bay at the center of structure and between the mega-columns which enhances the

energy absorption of the core / perimeter system. The sloping columns follow curved lines in order to both reduce force

concentrations and to simplify connections and hence construction cost (see Figure 2).

The structural frequencies of the fundamental modes of vibration numerically calculated by Skidmore, Owings & Merrill LLP

(SOM) were: 0.125 Hz (translation), 0.129 Hz (translation) and 0.309 Hz (torsion); the ones associated with second order

modes: 0.373 Hz (translation), 0.386 Hz (translation) and 0.725 Hz (torsion); and the ones associated with third order modes:

0.800 Hz (translation), 0.840 Hz (translation) and 1.220 Hz (torsion).

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14th International Conference on Wind Engineering – Porto Alegre, Brazil – June 21-26, 2015

Figure 2. Elevation and perspective view of the SOM’s Finite Element (FE) model of the tower.

4 WIND ENGINEERING

4.1 Wind climate

It is widely known that the estimation of wind-induced structural responses is highly dependent on the level of accuracy

associated with the first link of the Davenport wind loading chain [1]: the wind climate, including strength and direction.

A detailed wind climate analysis was therefore carried out to determine the wind properties at the project site. This considered

both the wind model described within GB50009-2001 [2], along with the widely accepted Deaves and Harris log law wind

model of the atmospheric boundary layer, as defined in the Engineering Sciences Data Unit (ESDU) Item 01008 [3], an

approach that is considered best industry practice in today’s modern wind engineering. From these two, representative wind

profiles for the different types of terrain characterising the site of the proposed development – generally consisting of

urban / suburban developments in all directions, giving way to open terrain to the northern, western and southern sectors and to

the sea to the east – were derived. Figure 3 shows the comparison of the z parameter, representing the variation of wind

pressure with height (as defined in GB50009-2001 [2]), between the ESDU [3] and the Chines wind code [2] model.

0

50

100

150

200

250

300

350

400

450

500

550

0 0.5 1 1.5 2 2.5 3 3.5 4

He

igh

t [m

]

mu_z [-]

GB50009-2001, Exp C

GB50009-2001, Exp D

ESDU, 25deg

ESDU, 115deg

ESDU, 205deg

ESDU, 295deg

Figure 3. Comparison of wind profiles (z parameter).

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14th International Conference on Wind Engineering – Porto Alegre, Brazil – June 21-26, 2015

An important feature of the local wind climate within the Tianjin region is of course the prevalence of certain wind directions

over others (being the result of variations in macro-scale / global weather patterns). To investigate this, a detailed extreme value

analysis was conducted using wind climate data sourced from the weather station at Binhai International Airport (station

identification 545723, located to the south-west of runway 34L) and at Tianjin Xiqing weather station (station identification

545270). In addition, a sensitivity analysis was conducted based on the data acquired from the Binhai International Airport as to

the impact of the number of years examined (namely from 1981-2010 and from 1990-2010) to better understand the influence of

the most recent urban developments on the actual wind records. The outcome of extreme value analyses conducted on the above

wind records is graphically presented in Figure 4 (please note that the Binhai and the Xiqing data closely overlap).

0

10

20

30

40

1 10 100

Win

d S

pe

ed

, 10

min

me

an, E

xpo

sure

B [

m/s

]

Return Period [Years]

Binhai, 1981-2010

Binhai, 1990-2010

Xiquing, 1992-2010

GB 50009-2001

For use with wind loading estimation

Figure 4. Variation of estimated and prescribed basic wind speeds (referenced as a 10-minute mean, 10 m height over

Category B terrain).

For strength design, the design wind loads for the 100-year return period have been code-matched to correspond to the

stipulated 10 m height 10-minute mean design pressure of 0.6 kPa for the Tanggu district of Tianjin. A similar procedure has

been adopted for the 50-year return period design wind loads (0.55 kPa) used for drift checking. For building acceleration and

rotational velocity predictions, site-specific design wind speeds for the 1- and 10-year return periods were derived from an

analysis of long-term wind records, an approach considered best practice in wind engineering. The derived 10 m height

10-minute mean design pressures for the 1- and 10-year return periods were approximately 0.2 and 0.3 kPa respectively.

4.2 Aerodynamic optimization of the building envelope

The wind tunnel technique employed during the course of the wind tunnel aerodynamic shape optimization workshop was the

high frequency force balance (HFFB, [4], [5], [6], [7] and [8]). The HFFB technique is particularly beneficial in this instance as

it allows changes to the outer shape of the wind tunnel model to take place in a relatively short period of time.

The 1:500 scale HFFB wind tunnel model was designed for stiffness and lightness: a ultra-high modulus carbon fibre internal

“sting” together with light-weight foam material were used to achieve this. The compound frequency of the ‘balance + carbon

fibre spine + foam component’ system was ~80 Hz.

Tests were conducted at a Reynolds number of approximately 1.5∙105 (referenced to top of the building speed and average

width of the tower), which satisfies the experimental requirements of the American Society of Civil Engineers (ASCE) Manual

of Practice [9]. The blockage ratio of the wind tunnel was quantitatively assessed for the worst case wind direction to be ~6%, a

figure which again meets the requirements of [9].

For the first test, a basic form / design of the tower (denoted as the “Baseline”) was tested over a full range of wind directions

to identify the critical aerodynamic responses that would govern the design. A key range of wind angles was then selected, and

wind tunnel tests were repeated with varying design changes developed during the course of the interactive workshop session.

Over the course of the ~10 hours interactive workshop day, a total of 17 different and bespoke aerodynamic solutions were

developed, wind tunnel tested and analyzed in real time such that – as work was conducted on each design iteration, other

architectural forms could be developed and tested in a continuous and efficient manner. Some of the design changes developed

included: the introduction of either a porous or solid “crown” structure over the upper portion of the tower with and without

MEP equipment / water tanks fitted at roof level; the opening of some of the mechanical levels (single or double height); the

introduction of perforated façade at some of the mechanical levels (single or double height); changes to the corner radii; and of

course various combinations of all of the above (see Figure 5).

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14th International Conference on Wind Engineering – Porto Alegre, Brazil – June 21-26, 2015

Figure 5. Some of the architectural variations developed during the one-day interactive wind tunnel session.

The aerodynamic performance of the various adjustments made to the architectural form of the building was directly

monitored during the course of the wind loading workshop session making use of spectral analysis conveniently plotted against

reduced frequency (see Figure 6).

Figure 6. Across wind base overturning moment spectra.

In order to summarize the outcome of the workshop, a series of bar charts were produced for a number of specific load effects

agreed with the design team (see an example in Figure 7).

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14th International Conference on Wind Engineering – Porto Alegre, Brazil – June 21-26, 2015

Figure 7. Example of results summary.

The best performing configuration, from both a serviceability and strength design point of view, featured: the introduction of a

porous crown and louvered ‘wind slots’ introduced at key mechanicals levels. The porous crown enhanced the

three-dimensionality of the flow over the top portion of the tower and, together with the ‘wind slots’, helped the after-body wake

to be re-energized. These design modifications resulted in: ~10% reduction in along-wind response (base moments), ~35%

reduction in cross-wind response (base moment) and ~25% reduction in wind-induced peak accelerations (for the 10-year return

period wind events).

The design at this point evolved taking the lessons learnt in the wind tunnel into consideration.

4.3 Works in preparation of the Expert Panel Review meeting

Whilst preparing for the Expert Panel Review (EPR) meeting, a series of wind tunnel tests, now conducted on the new fully

developed architectural form, were conducted: the main aim of these tests was to gain deeper knowledge on the behavior of the

super-tall building under wind loading excitation. Two were in fact the main aspects which the wind engineers felt important

investigating: the role of the higher modes of vibration of the structure in the prediction of foundation loads, sectional moments

and wind-induced accelerations; and the role of fluid-structure interaction, especially with regard to aerodynamic damping at

reduced frequencies approaching the Strouhal condition.

As the Expert Panel Review (EPR) meeting was anticipated to take place in Spring 2012, the wind engineering for the Project

was undertaken fulfilling the requirements of GB50009-2001 [2], as opposed to the 2012 version of the code which at the time

of the studies was only at draft stage and therefore not mandatory.

Wind tunnel studies were therefore carried out in BMT’s boundary layer wind tunnel at a scale of 1:500 using a number of

different wind tunnel techniques, such as: HFFB, simultaneous pressure integration (SPI) and aeroelastic. The exact same 3D

geometry was used in the design and manufacture of these three wind tunnel models and the exact same set of structural

properties was utilized for the post-processing of HFFB and SPI wind tunnel data and for the design and manufacture of the

complex internal spine of the wind tunnel aeroelastic model.

The HFFB wind tunnel model was designed and constructed following the same procedure described in 4.2 (see Figure 8a).

The wind tunnel pressure model was constructed using Selective Laser Sintering (SLS), a rapid-prototyping technique capable

to achieve a high degree of accuracy (±0.1 mm), and it was equipped with a total number of 1050 pressure sensors (see Figure

8b).

The wind tunnel aeroelastic model was constructed in two stages, namely the internal supporting structure (a tapered lattice

brass spine, needed to replicate the balance between flexural and shear deformation of the real structure, see Figure 8c) and the

external shell sections (manufactured using the SLS technique, see Figure 8d). The base of the model was connected to a HFFB

and the model itself equipped with a number of low-range high-resolution accelerometers as well as strain gauges (see Figure

8e).

Furthermore, due to the size and importance of the building, a parallel wind tunnel test was conducted by Professor Xie

Zhuangning of the South China University of Technology (SCUT) solely based on the HFFB technique. It should be noted that

the tests conducted at SCUT made use of the exact same physical wind tunnel model utilized by BMT.

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14th International Conference on Wind Engineering – Porto Alegre, Brazil – June 21-26, 2015

Figure 8. a. HFFB model; b. pressure model; c. aeroelastic model (internal spine); d. aeroelastic model (under construction);

e. aeroelastic model (fully assembled).

An examination of the results obtained (HFFB, SPI and aeroelastic) indicated that – in terms of structural wind loads – the

proposed tower exhibits a relatively benign dynamic response, particularly in relation to cross-wind excitation driven by vortex

shedding, an obvious benefit of the initial interactive workshop session. The level of 100-year peak wind pressures (damping

level of 2.0% of critical) along the height of the tower was found to be at worst in the range of 2.5 kPa. The results of the wind

tunnel tests are showing, in the along-wind direction, reductions against the GB50009-2001 [2] predictions of the order of 18%.

With regard to the higher order modes, the second order modes are shown to increase the dynamic response on the overall wind

loads by approximately ~2%, whilst the addition to the dynamic response of the third order modes is numerically close to zero.

With respect to serviceability design, the wind-induced peak accelerations at ‘Level 93’ (approximately 440 m above street

level) of the tower (damping level of 1.5% of critical) were sitting at ~5 milli-g and ~9.5 milli-g (1- and 10-year return period

events respectively), meeting both the requirements of ISO [10] (~10 milli-g) and the ones stipulated by the Ministry of

Construction of China [11] (15 milli-g), with the higher order modes contributing ~27%. The authors of this technical paper

would like to emphasize that the level of wind-induced peak acceleration at ‘Level 93’ – much lower than the prescribed

occupant comfort criteria – was obtained without the introduction of any auxiliary damping system.

It should be noted that differences in terms of peak dynamic wind base loads and wind-induced peak accelerations between

BMT and SCUT were respectively of the order of 5% and 10%.

Based on the strength of the findings above, the wind engineering work for the tower was officially approved in Tianjin on the

12th

April 2012 by the Expert Panel chaired by Professor Xinyang Jin from China Academy of Building Research (CABR).

4.4 Value engineering

Upon completion of the EPR process, NWD expressed an interest for value engineering some of the aerodynamic features of

the tower, specifically: the air gaps at the base of the crown and the wind slots at the mechanical levels (between ‘Level 19’ and

‘Level 21’; between ‘Level 44’ and ‘Level 46’; and between ‘Level 71’ and ‘Level 73’). This idea was of course supported by

what was learned during the initial wind loading workshop session, i.e. the major contributor to the reduction of the vortex

shedding excitation was the introduction of a porous crown.

A number of HFFB wind tunnel investigations were therefore undertaken with the aim of quantifying the impact of the above

mentioned potential modifications. Four options were explored: air gaps at the base of the crown fully open + wind slots

between ‘Level 71’ and ‘Level 73’ covered with 50% perforated cladding (Option A); air gaps at the base of the crown fully

open + wind slots between ‘Level 71’ and ‘Level 73’ fully sealed (Option B); air gaps at the base of the crown clad with panels

of gradient porosity + wind slots between ‘Level 71’ and ‘Level 73’ covered with 50% perforated cladding (Option C); and air

gaps at the base of the crown fully clad over the lower 13.5 m portion and featuring a porous screen with gradient porosity of

20% to 70% (open) over the upper portion + wind slots between ‘Level 71’ and ‘Level 73’ covered with 50% perforated

cladding (Option D). In all four options the wind slots between ‘Level 19’ and ‘Level 21’ and between ‘Level 44’ and ‘Level

46’ were completely sealed. The outcome of the wind tunnel testing is summarized in Table 1.

a b c d e

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14th International Conference on Wind Engineering – Porto Alegre, Brazil – June 21-26, 2015

Table 1. Comparison of peak dynamic wind-induced base overturning moments and wind-induced peak accelerations.

Baseline Option A Option B Option C Option D

Mx 100% 98% 98% 101% 104%

My 100% 98% 100% 100% 102%

ä1-yerr 100% 89% 89% 100% 103%

ä10-yerr 100% 91% 94% 104% 107%

In terms of peak dynamic wind base loads the increase in wind loading acting on the super-tall tower was found to be at worst

~4%. In terms of wind-induced peak accelerations the increase in the response of the super-tall tower was at worst ~3% and

~7% for the 1- and 10-year return period wind events respectively.

The configuration the senior management team of NWD in the end decided to adopt for the super-tall tower was ‘Option D’

with slots between ‘Level 71’ and ‘Level 73’ fully sealed: for this specific and untested configuration, BMT estimated – relative

to what was approved for design by the Expert Panel – an increase in the peak dynamic wind base loads of ~4.5% and an

increase in the wind-induced peak accelerations of ~3.5% and ~7.5% for the 1- and 10-year return period wind events

respectively.

It should be noted that the overturning moment due to the frequent seismic event is 21% larger than the overturning moment

determined from the wind tunnel study. It is likely that the CTFTJ super-tall tower is the only building in the world over 500

meters that is governed by seismic forces rather than wind forces (see Figure 9).

Figure 9. Seismic forces vs. wind forces acting on the CTFTJ super-tall tower.

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14th International Conference on Wind Engineering – Porto Alegre, Brazil – June 21-26, 2015

4.5 Other wind engineering studies

Following on from the aerodynamic optimization studies and the subsequent more detailed wind loading work, a number of

other wind engineering studies have been carried out, examining: the façade wind pressures; the wind microclimate at pedestrian

level; and the stack effect.

4.5.1 Façade wind pressures

The wind tunnel pressure model utilized in preparation of the EPR meeting enabled the BMT to derive peak design wind

pressures for the envelope of the tower and associated podium, taking also into account the effect of accidental openings.

Although the changes to the wind slots at the mechanical floors have not been directly wind tunnel tested, design pressures for

these areas have been derived based off experience and engineering judgment.

Cladding pressures were evaluated making use of standard analysis procedures. The predicted 50-year peak net suctions were

on average in the range of 2.5 kPa, with localised peaks near discontinuities in the surface geometry up to 5.0 kPa. Peak net

positive pressures were on average in the range of 1.5 kPa with localised areas going up to 2.5 kPa.

4.5.2 Pedestrian level wind microclimate

The comfort of pedestrians at ground level and on the terrace at ‘Level 5’ of the podium, which feature a number of outdoor

seating areas, was evaluated by combining wind speed measurements taken in the wind tunnel at 75 locations with local wind

statistics for the site. It should be noted that the pedestrian comfort was only assessed with regard to the effect of the mechanical

force of the wind.

Figure 10 illustrates the wind mitigation scheme finally developed to ensure that the wind conditions are suitable for their

intended use in terms of both safety and wind comfort throughout a typical year.

Figure 10. Wind mitigation scheme (ground level).

4.5.3 Stack effect

The outcome of the cladding pressure test, aside from supporting the façade design, was also used as boundary condition for a

detailed bulk-flow model aimed at examining the stack effect within the building.

The multi-zone airflow and contaminant transport analysis software CONTAM [12], developed by the US National Institute

of Standards and Technology (NIST), was used.

This study enabled the buoyancy-driven movement of air within the primary usable spaces of the tower to be thoroughly

quantified for a range of external weather conditions and operational scenarios. These studies also highlighted areas of the

building where pressure differentials across key air-flow paths (such lift doors, wing doors, etc.) would be too high to ensure

smooth operational conditions at all times.

The results of these numerical simulations were presented in terms of:

i. Air infiltration / exfiltration rate through the building envelope;

ii. Flow rate through major air flow paths;

iii. Pressure difference across the building envelope;

iv. Total pressure difference between the main elevator shafts and the exterior environment;

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14th International Conference on Wind Engineering – Porto Alegre, Brazil – June 21-26, 2015

During the course of these studies BMT was able to offer mitigation solutions to the design team, from holistic solutions such

as “tightening” the façade to reduce air-leakage, to more localised measures such as the introduction of air-lock doors,

mechanically-assisted doors and vestibules at key locations.

5 CONCLUSIONS

This technical paper presented the wind engineering ‘journey’ the CTF Tianjin Finance Centre has gone through between

2011 and 2012.

SOM has estimated that the aerodynamic shape optimization work conducted during the very early days of the project saved,

material wise only, best part of 15 million USD. This work, and its success, has only been possible thank to the collaborative

efforts of the organizations behind the authors of this article.

In closing, it is believed that the super-tall building part of the CTF Tianjin Finance Centre project – currently under

construction (see Figure 10) – will almost certainly be one of the world’s most optimized structures from a wind engineering

point of view.

Figure 10. The CTF Tianjin Finance Centre construction site on 24

th February 2015.

REFERENCES

[1] http://www.iawe.org/about/Wind_Loading_Chain.pdf.

[2] Load Code for the Design of Building Structures, GB 50009-2001. [3] Computer program for wind speeds and turbulence properties: flat or hilly sites in terrain with roughness changes, ESDU Item 01008, Engineering

Sciences Data Unit, 2010.

[4] Tschanz T., and Davenport A. G., “The base balance technique for the determination of dynamic wind loads”, Journal of Wind Engineering & Industrial Aerodynamics, Vol. 13, 1983, pp. 429-439.

[5] Kareem A., ”Lateral-torsional motion of tall buildings”, Journal of Structural Engineering, 111(11), 1985, pp. 2479-2496.

[6] Vickery B. J., et al., “The effect of mode shape on the wind induced response of tall buildings”, Proceedings of the 5th United States National Conference on Wind Engineering, Texas Tech University, Lubbock, TX, 1985, 1B-41 – 1B-48.

[7] Flay R. G. J., et al., “Wind induced dynamic response of tall buildings with coupled 3D modes of vibration”, Proceedings of the 10th International

Conference on Wind Engineering, Copenhagen, Denmark, 1999, pp. 645-652. [8] Holmes J. D., et al., “High frequency base balance methodologies for tall buildings with torsional and coupled resonant modes”, Proceedings of the 11th

International Conference on Wind Engineering, Texas Tech University, Lubbock, TX, 2003, pp. 2381-2388.

[9] Manual of Practice No.67 for Wind Tunnel Studies, American Society of Civil Engineers (ASCE), 1999. [10] Bases for design of structures - Serviceability of buildings and walkways against vibrations, ISO 10137-2007.

[11] Technical Specification For Concrete Structures Of Tall Building, JGJ 3-2002 - J 186-2002.

[12] http://www.bfrl.nist.gov/IAQanalysis.