Comprehensive Study on Wind-induced Pressures, Forces and Vibrations of Supertall Buildings Based on Field Measurements and Wind Tunnel Tests

基於現場實測和風洞試驗的超高層建築風壓、風力及振動綜合研究

Student thesis: Doctoral Thesis

View graph of relations

Author(s)

Detail(s)

Awarding Institution
Supervisors/Advisors
Award date15 Sept 2023

Abstract

The rapid developments in building materials and construction technologies have given rise to a significant increase in the number of supertall buildings (i.e., buildings with heights >300 m) over the last few decades. Due to their relatively low natural frequencies and damping ratios, supertall buildings with increasing heights become more sensitive to wind excitations than those in the past. Since wind loads generally dominate structural design of supertall buildings, evaluation of wind pressures, wind loads, and wind-induced responses for supertall buildings is a crucial issue in their structural design. To this end, this thesis presents a comprehensive study on the wind-induced pressures, forces, and vibrations of supertall buildings by means of field measurements under typhoon condition and wind tunnel tests.

First, this thesis presents a field measurement study of the wind pressures on a 600-m-high supertall building during Super Typhoon Mangkhut. A synchronous monitoring system including 48 pressure transducers was implemented to measure the wind pressures on the cladding of the supertall building during the super typhoon event. It is noted that this was the first study that the wind pressures were measured on a skyscraper under extreme wind condition based on a larger number of pressure transducers than previous studies. From the field measurements, the mean, root-mean-square fluctuating, and peak (maximum and minimum) pressure coefficients are analyzed and discussed. Then the mean and peak pressure coefficients are used to validate the design values stipulated in structural design codes of China, America, and Japan. The comparative study reveals that the design values of the peak pressure coefficients on the windward and leeward faces of the supertall building are conservative, while those on the side faces are nonconservative. As for the mean pressure coefficients, the design values are conservative for all faces. Moreover, the non-Gaussian characteristics, power spectral densities, coherences, and correlations of the measured wind pressures are analyzed to explore the mechanisms of pressure fluctuations on the four sides of the supertall building.

Second, simultaneous wind pressure measurements on a 1:500 scale model of the supertall building were conducted in wind tunnel test. The field measurements of wind pressures are further analyzed to investigate the wind pressure characteristics on the supertall building under extreme wind condition and utilized to validate the wind tunnel test results. The full-scale and model-scale wind pressure coefficients (mean, root-mean-square fluctuating, maximum and minimum) are compared and analyzed in detail. Moreover, to explore the deviations between the full-scale and model-scale results, the Reynolds number effect (5.5 × 104 to 1.8 × 108) on the wind pressure coefficients as well as their probability distributions, power spectral densities, spatial correlations and coherences are investigated. The comparative study shows that the wind tunnel test can reproduce the wind pressures on the windward face. Nevertheless, for the other faces, wind pressures from the wind tunnel test generally deviate from the field measurements. The reasons for the discrepancies, especially the Reynolds number effect, are discussed.

Third, the aerodynamic forces on the supertall building are investigated based on the field measurements and wind tunnel test. The local wind force coefficients (drag and lift) and their power spectral densities obtained by the full-scale measurements and the model experiment are compared and discussed. The comparative study shows that the wind tunnel test generates conservative mean local drag coefficients and RMS local lift coefficients, while the model experiment provides smaller predictions of the RMS local drag coefficients at high levels than those from the on-site measurements. The Reynolds number effects on the local wind forces and the Strouhal number are investigated as well. It is found that the Reynolds number has evident effects on the local wind force coefficients, while its influence on the Strouhal number is negligible.

Subsequently, this study evaluates the time-variant modal parameters of the supertall building based on the building accelerations measured during Super Typhoon Mangkhut. Then, the identified time-variant modal parameters are combined with the wind loads estimated from the wind tunnel test to reproduce the typhoon-induced building accelerations. The results show that the reproduced accelerations based on the time-variant modal parameters agree well with the field-measured ones. Moreover, a comparative study between adoption of the time-variant modal parameters and time-invariant modal parameters is conducted, which shows that the former case provides more accurate estimation of the building dynamic responses during the extreme typhoon event.

Furthermore, to investigate the mechanism of the wind-induced responses of supertall buildings, a series of wind tunnel tests on a 3D aeroelastic square cylinder with an aspect ratio of 10 is conducted. The along-wind and across-wind displacement responses are measured under smooth flow and four turbulent flow fields with different turbulence intensities and integral length scales. The vortex-induced vibration and galloping of the cylinder are experimentally studied through the aeroelastic model experiment. Moreover, the effect of free-stream turbulence with a higher-level turbulence intensity than previous studies is investigated.

To sum up, this thesis comprehensively investigates the wind-induced pressures, forces, and vibrations of supertall buildings by means of the full-scale measurements during Super Typhoon Mangkhut and wind tunnel tests. The objective of this study is to enrich the knowledge and further the understanding of wind-induced pressure, forces and vibrations of supertall buildings, and the outcomes are expected to provide useful information for the wind-resistant design of supertall buildings.