The Seventh Asia-Pacific Conference on Wind Engineering, November 8-12, 29, Taipei, Taiwan PRESSURE FLUCTUATIONS ACTING ON A TAPERED TALL BUILDING Young-Moon Kim 1, Ki-Pyo You 1, Jang-Youl You 2 and Chang-Hyun Song 2 1 Professor, Division of Architecture and urban Engineering, Chonbuk National University Duckjin-dong Duckjin-gu Jeonju, 561-756, Korea, kym@chonbuk.ac.kr 2 Researcher, Boundary Layer Wind Tunnel Laboratory, Chonbuk National University Duckjin-dong Duckjin-gu Jeonju, 561-756, Korea, wmjlove1877@chonbuk.ac.kr ABSTRACT In this research to investigate the variations of across-wind pressure fluctuations acting on a tapered tall building, pressure tests were carried out using four types of pressure building models which have different taper ratio of 5%, 1%, 15% and one basic model of a square cross-section were made and tested under the two typical boundary layer representing suburban (BL1, α =.15) and urban(bl2, α =.33) flow with the wind direction of degree condition. KEYWORDS: TAPERED TALL BUILDING, ACROSS-WIND, PRESSURE FLUCTUATINGS Introduction Most modern tall buildings with efficient structural systems use high-strength materials to reduce their weight, and to be more slender and flexible they have lower damping values, which makes them more susceptible to wind-induced excitations that have the potential to reduce their structural safety and cause discomfort to the occupants of the building(kareem,1983). The fluctuating pressure on the side face of a square building model was measured under the condition of open and urban flow environments and the data of pressure coefficients, power spectra, autocorrelation, co-spectra, cross-correlations and etc. were computed and compared the experimental results with each other.(kareem,1984) Many investigations have therefore been conducted to reduce such excitations to an allowable level and to improve the performance of tall buildings. Most of these investigations concentrate on aerodynamics modifications of the cross-sectional shapes of the buildings, such as using slotted and chamfered corners, fins, setbacks, buttresses, horizontal throughbuilding openings and variations of the cross-section with height, that is, tapering. Davenport (1988) has suggested that tall buildings whose cross-sectional shape is tapered along their height might spread the vortex-shedding over a broad range of frequencies, thus reducing the cross-wind responses. Tanagi et al. (1999) investigated the taper effect for reducing acrosswind excitations comparing it with the along-wind excitation based on the aeroelastic model tests using a tapered model with and without chamfered corners. Y.M Kim et al. to investigate the effect of tapering on reducing the rms across-wind displacement responses of a tall building, an experiment using an aeroelastic tapered model of a tall buildings with taper ratios of 5%, 1% and 15%, and one basic model of a square crosssection without a taper was conducted in a wind tunnel which simulated the suburban environment and shows that the increase in tapering might have an adverse effect, increasing the rms across-wind displacement responses when the structural damping ratio is very low.
The Seventh Asia-Pacific Conference on Wind Engineering, November 8-12, 29, Taipei, Taiwan In this research to investigate the variations of across-wind pressure fluctuations acting on a tapered tall building, pressure tests were carried out using four types of pressure building models which have different taper ratio of 5%, 1%, 15% and one basic model of a square cross-section were made and tested under the two typical boundary layer representing suburban(bl1, α =.15) and urban(bl2, α =.3) flow with the wind direction of degree condition. Dimension of each model are shown in Fig. 1. Figure1. Dimension of each models Wind-tunnel Experiment A wind-tunnel experiment using pressure model was conducted in a boundary layer wind-tunnel at the Department of Architectural Engineering, CNU. The incident flows representing open and urban flow environments as BL1 and BL2 were simulated. The vertical distribution of the mean wind velocity and turbulence intensities are shown in Fig. 2. The direction of wind is a degree angle of attack. Diameter of a pressure tap was 1 mm and flexible tube of short length of was used. The sampling rate was 1Hz and 128 channel pressure transducer was used to acquire 2 channel pressure data simultaneously. A typical tap location are shown in Fig.3, where C indicate the column line and L the level of the side face. The tap location of ith level of jth column is represented as (i, j) and etc. 1. HEIGHT(z/H).6.2.. 2. 4. 6. 8. 1. 12. VELOCITY (m/s) 1 2 3 Turblence Intensity(%) 4 Figure2. Profile of the mean longitudinal wind Velocities and turbulence intensities
The Seventh Asia-Pacific Conference on Wind Engineering, November 8-12, 29, Taipei, Taiwan Figure3. Pressure tap locations on side face Results of Experiments Figure 4 show the normalized co-spectra associated with the reduced frequency of between spanwise locations of Model 1 for the BL1. They show that the magnitude of the cospectra is decreased as exponentially decaying function as the separated distance between tap locations is far away from the leading edge region and the reduced frequency is increased particularly at the leading edge region., but not sure at the trailing edge region as shown in Fig. 5. A high- amplitude peak around a reduced frequency of.1, which is known as the Strouhal frequency, is also appeared at the leading edge region than that of the trailing edge. This explain that the spectral energy from vortex-shedding is more distinct at the leading edge region than that of trailing edge. M1C1 7m/s -.15 - model 1 M1C2 7m/s -.15 - Model 1 M1C3 7m/s -.15 - Model 1 (1,2)-(2,2) (1,2)-(3,2) (1,2)-(4,2) (1,3)-(2,3) (1,3)-(3,3) (1,3)-(4,3) - - - - - -.2.6.2.6.2.6 Figure. 4 Spanwise normalized co-spectra for Model 1, C1~C3
The Seventh Asia-Pacific Conference on Wind Engineering, November 8-12, 29, Taipei, Taiwan M1C4 7m/s -.15 - model 1 M1C5 7m/s -.15 - model 1 (1,4)-(2,4) (1,4)-(3,4) (1,4)-(4,4) (1,5)-(2,5) (1,5)-(3,5) (1,5)-(4,5) - - - -.2.6.2.6 Figure. 5 Spanwise normalized co-spectra for Model 1, C4~C5 Figure 6 present co-spectra at the leading edge region(c1) of a tapered Model 2-4. A similar trend of Model 1 is appeared except for Model 4, which is not present the spectral peak around a reduced frequency of.1 and the magnitude of spectral amplitude is lower than any other Model, particularly for that amplitude around a reduced frequency of o.1. And that spectral peak occurs around a reduced frequency.13 for Model 3. M2C1 7m/s -.15 - model 2 M3C1 7m/s -.15 - Model 3 M4C1 7m/s -.15 - Model 4 - - - - - -.2.6.2.6.2.6 Figure. 6 Spanwise normalized co-spectra for Model 2-4, C1 Figure 7 present co-spectra around the leading edge region(c2) of a tapered Model 2-4. It also show similar trend of C1. M2C2 7m/s -.15 - model 2 M3C2 7m/s -.15 - Model 3 M4C2 7m/s -.15 - Model 4 (1,2)-(2,2) (1,2)-(3,2) (1,2)-(4,2) (1,2)-(2,2) (1,2)-(3,2) (1,2)-(4,2) (1,2)-(2,2) (1,2)-(3,2) (1,2)-(4,2) - - - - - -.2.6.2.6.2.6 Figure. 7 Spanwise normalized co-spectra for Model 2-4, C2 Figure 8 present co-spectra of middle edge region(c3) of a tapered Model 2-4. A similar trend of Model 1 and Model 2 appears and Model 3 and Model 4, and spectral peak occurs around a reduced frequency of.15.
The Seventh Asia-Pacific Conference on Wind Engineering, November 8-12, 29, Taipei, Taiwan M2C3 7m/s -.15 - model 2 M3C3 7m/s -.15 - Model 3 M4C3 7m/s -.15 - Model 4 (1,3)-(2,3) (1,3)-(3,3) (1,3)-(4,3) (1,3)-(2,3) (1,3)-(3,3) (1,3)-(4,3) (1,3)-(2,3) (1,3)-(3,3) (1,3)-(4,3) - - - - - -.2.6.2.6.2.6 Figure. 8 Spanwise normalized co-spectra for Model 2-4, C3 Figure 9 present co-spectra around the trailing edge region(c4) of same tapered Models. A similar trend appears for Model 2-4. However the reduce frequency associate with spectral peak for Model 4 is around.15, which is higher than that of.12 for Model 3. M2C4 7m/s -.15 - model 2 M3C4 7m/s -.15 - Model 3 M4C4 7m/s -.15 - Model 4 (1,4)-(2,4) (1,4)-(3,4) (1,4)-(4,4) (1,4)-(2,4) (1,4)-(3,4) (1,4)-(4,4) (1,4)-(2,4) (1,4)-(3,4) (1,4)-(4,4) - - - - - -.2.6.2.6.2.6 Figure. 9 Spanwise normalized co-spectra for Model 2-4, C4 Figure 1 show co-spectra at the trailing edge region (C5) of same tapered Models. A similar trend as in C4 appears as shown in Fig. 9. M2C5 7m/s -.15 - model 2 M3C5 7m/s -.15 - Model 3 M4C5 7m/s -.15 - Model 4 (1,5)-(2,5) (1,5)-(3,5) (1,5)-(4,5) (1,5)-(2,5) (1,5)-(3,5) (1,5)-(4,5) (1,5)-(2,5) (1,5)-(3,5) (1,5)-(4,5) - - - - - -.2.6.2.6.2.6 Figure. 1 Spanwise normalized co-spectra for Model 2-4, C5 The normalized co-spectra of chordwise direction at levels 1, 2 and 3 for Model 1, which is not tapered, are presented in Fig. 11. The spectral peak amplitude at the leading edge region around a reduced frequency of.1 is higher than that of trailing edge region. And the magnitude of peak amplitude reduced sharply as the trailing edge region is reached than that of leading edge region, so spectral
The Seventh Asia-Pacific Conference on Wind Engineering, November 8-12, 29, Taipei, Taiwan peaks are narrower and distinct. This trend is appear at all levels. However, at the leading edge region of level 3, the spectral amplitude is not reduced in all reduced frequency range as presented in Level 3 of Fig. 11. M1L1 7m/s -.15 - Model 1 M1L2 7m/s -.15 - Model 1 M1L3 7m/s -.15 - Model 1 (2,1)-(2,2) (2,1)-(2,3) (2,1)-(2,4) (2,1)-(2,5) (3,1)-(3,2) (3,1)-(3,3) (3,1)-(3,4) (3,1)-(3,5) - - - - - -.2.6.2.6.2.6 Figure. 11 Chordwise normalized co-spectra for Model 1, L1-L3 Figure 12 present co-spectra of chordwise direction at the level 1(L1). Spectral peak around a reduced frequency of.1 appear distinctly for Model 1, which is not tapered, as shown in Level 1 of Fig. 11. The reduced frequency range associate with spectral peak for tapered model is moved to the rightside of.1 reached to around the reduced frequency range of.2 as a taper ratio is increased, which is shown in Fig.12. M2L1 7m/s -.15 - Model 2 M3L1 7m/s -.15 - Model 3 M4L1 7m/s -.15 - Model 4 - - - - - -.2.6.2.6.2.6 Figure. 12 Chordwise normalized co-spectra for Model 2-4, L1 At level 2, a variation of co-spectra of tapered model is present in Fig. 13. It show similar trend appears for Model 1-3 excepting Strouhal frequency for Model 3 is around.13. There is no spectral peak in all frequency range. M2L2 7m/s -.15 - Model 2 M3L2 7m/s -.15 - Model 3 M4L2 7m/s -.15 - Model 4 (2,1)-(2,2) (2,1)-(2,3) (2,1)-(2,4) (2,1)-(2,5) (2,1)-(2,2) (2,1)-(2,3) (2,1)-(2,4) (2,1)-(2,5) (2,1)-(2,2) (2,1)-(2,3) (2,1)-(2,4) (2,1)-(2,5) - - - - - -.2.6.2.6.2.6 Figure. 13 Chordwise normalized co-spectra for Model 2-4, L2
The Seventh Asia-Pacific Conference on Wind Engineering, November 8-12, 29, Taipei, Taiwan Figure 14 present co-spectra at level 3 for tapered models. A similar trend for Model 2-4 is presented. Strouhal frequency of Model 3-4 are.13, which is different from that of.1 for Model 1and 2. And the co-spectra at the leading edge region of Model 1 is not present spectral peak around the reduced frequency range of o.1 and continued without reduction in all frequency range. M2L3 7m/s -.15 - Model 2 M3L3 7m/s -.15 - Model 3 M4L3 7m/s -.15 - Model 4 (3,1)-(3,2) (3,1)-(3,3) (3,1)-(3,4) (3,1)-(3,5) (3,1)-(3,2) (3,1)-(3,3) (3,1)-(3,4) (3,1)-(3,5) (3,1)-(3,2) (3,1)-(3,3) (3,1)-(3,4) (3,1)-(3,5) - - - - - -.2.6.2.6.2.6 Figure. 14 Chordwise normalized co-spectra for Model 2-4, L3 Figure 15 present normalized co-spectra for BL2(.33), with which incident turbulence flow is increased than that of BL1. Comparing it with BL1's, a similar trend is present between each of them. However, the magnitude of spectral peaks for BL2's are decreased in all of the reduced frequency range, and the spectral peaks around the Strouhal frequency are wider than that of BL1's. M1C1 7m/s -.33 - Model 1 M1L1 7m/s -.33 - Model 1 M2C1 7m/s -.33 - Model 2 M2L1 7m/s -.33 - Model 2 - - - - - - - -.2.6.2.6.2.6.2.6 M3C1 7m/s -.33 - Model 3 M3L1 7m/s -.33 - Model 3 M4C1 7m/s -.33 - Model 4 M4L1 7m/s -.33 - Model 4 - - - - - - - - -.2.6.2.6.2.6.2.6 Figure. 15 Spanwise and Chordwise normalized co-spectra for BL2 (Model 1-4;C1,L1)
The Seventh Asia-Pacific Conference on Wind Engineering, November 8-12, 29, Taipei, Taiwan Conclusions Spectral characteristic of pressure fluctuation on a side face of a square and tapered building model is reported herein based on wind pressure experiment. The spectral peak of the pressure fluctuation around the Strouhal frequency is decreased and the Strrouhal frequency is moved to the rightside of that value of square model as taper ratio is increase and the separated distance of tap locations between spanwise and chordwise direction is far from the leading edge region. And the effect of increasing turbulence of incident flow is appeared as the spectral peaks around the Strouhal frequency is wider and the magnitude are decreased. Acknowledgements Financial support for this work was by Korea Science & Engineering Foundation through the National Research Laboratory Program (M158-51-81) References Kareem A (1983), Mitigation of wind induced motion of tall buildings Journal of wing Engineering Industrial Aerodynamic. Vol.11, pp273-284 Kareem A, Cermark J.E., (1984), Pressure fluctuations on a square building model in boundary-layer flows Journal of wing Engineering Industrial Aerodynamic. Vol.96, pp17-41 Davenport A.G.(1988), The response of super tall buildings to wind second century of the skyscraper council on Tall Buildings and Urban Habitat, pp75-725 A.A Fediw, M. Nakayama, K. R. Cooper, Y. Sasaki, S. Resende-lde, S. J. Zan(1995), "Wind tunnel study of an oscillating tall building", Journal of wind Engineering Industrial Aeridynamic, No 57, pp249-26 K.R.Cooper, M. Nakayama, Y. sasaki, A. A. Fediw, S. Resen-ide, S. J. Zan(1999), "Unstready aerodynamic force measurements on a super tall building with a tapered corner section", Journal of wing Engineering Industrial Aerodynamic, NO72, pp199-212 Tnnagi Y, Nakaayama M, Yamamoto K(1999), Experimental study on wind response of tapered tall buildings Part1, Force Measurement Proceedings of AIJ, pp33-34 Young-Moon Kim, Ki-Pyo, Nag-Ho Ko(28) Across-wind response of an aeroelastic tapered tall building Journal of wind engineering and industrial Aerodynamic, vol 96, issues 8-9.