Master of Engineering Science
Civil and Environmental Engineering
Ayman El Ansary
As cities grow, the urban topology changes in density resulting in continuous variations in wind flow. The interaction of flow with this changing surrounding environment drives the aerodynamics to become more complex and varying, subjecting the building to significant changes in wind-induced-loads both on structural and non-structural elements. In this study, a series of boundary layer wind tunnel tests are conducted to investigate the impact of city growth on cladding and structural loading by using a typical tall building adopted from the Commonwealth Advisory Aeronautical Council (CAARC) building model. The city growth is represented by five different generic surrounding configurations, varying in height ratios compared to the study building of height (H). The configuration includes isolated case (0000SH), surrounded with 0.25H height (0025SH), 0.5H height (0050SH), 0.75H height (0075SH) and H height (0100SH) of surrounding buildings, respectively. Based on the study analysis, the city growth has different impact on structural and non-structural elements from wind hazard perspectives. The overall recorded mean wind pressures are reduced while fluctuations within these pressures are increasing as the urban environment becomes denser creating wake induced turbulence. Due to Bernoulli and Venturi effect, local pressure increases are observed for certain cases. The results show 30% increase in the negative peak pressures Čp for case 0050SH at a value of -7 compared to the isolated case scenario 0000SH at AoA=90° which subject the building to higher risk of cladding failure. From the main wind force resisting system, the mean and fluctuating base moments reduced by 20% for case 0050SH and 50% for case 0075SH which consequently decreased the peak base moments and top peak acceleration on the structural system.
Summary for Lay Audience
The limited land in urban areas has pushed people to build tall, flexible, and slender buildings, where wind is the governing design load. Several factors can affect the behavior of the building’s structural and non-structural elements. One of the main factors contributing to the behavior of tall buildings is the surrounding layout. While a typical wind tunnel study can involve the actual representation of existing surrounding buildings, it does not take into consideration the effect of future city growth on the behavior of tall buildings. As cities grow, the surrounding layout change, making the wind phenomenon more complex and the flow of wind alters significantly. This variation in wind flow is due to the interaction of fluid flow with the new built environment. This study presents an experimental investigation on the impact of city growth on the behavior of the structural and non-structural elements of tall buildings. The city growth is represented by five surrounding configurations, varying in height ratios. The configurations are divided into 2 phases: first, experimenting a reference isolated model having a height (H). The second phase is experimenting four different surrounding configurations. This includes 0.25H height (0025SH), 0.5H height (0050SH), 0.75H height (0075SH) and H height (0100SH) of surrounding buildings, respectively in suburban terrain. Results have shown different impacts on structural and non-structural elements of tall buildings. For instance, the mean wind pressures on cladding are reduced with the increase of surrounding ratios. On the other hand, a fluctuation increase within the measured pressures was noticed as the urban environment becomes denser. This increase at certain critical configurations was observed to impact the cladding (non-structural) elements which in return subject the cladding elements to higher wind risks through damage accumulations. On the other hand, the structural assessment has shown an overall decrease in base moments with the increase in surrounding heights which consequently reduces the peak base moments and top accelerations, especially for higher surroundings heights.
Abdallah, Hadil M., "Implication of city growth on wind-induced loads for cladding and structural design" (2021). Electronic Thesis and Dissertation Repository. 7740.
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Available for download on Wednesday, March 01, 2023