published_or_final_version / abstract / Civil Engineering / Master / Master of Philosophy

No description available.

In Hong Kong and other Asian metropolitan cites, high-rise residential buildings become very common. They are highly wind-sensitive, subjected to enormous wind loads at high wind speeds and may exhibit aeroelastic behavior at normal wind speeds. Many residential buildings often have an irregular shape with apartments arranged as wing sections extending from a central core so that all apartments on the floor can enjoy views. Between adjacent building wings are deeply recessed cavities. Most wind loading codes and guidelines assume stagnant flow inside the recessed cavities and wind loads are calculated based on the simplified enveloping building shape. This research studies how the static and dynamic wind loads on a tall building are modified by the presence of recessed cavities. The H-section tall building, with square enveloping shape, is selected to represent a building with two recessed cavities. A number of these building models with a systematic variation of breadths and depths of the recessed cavities are tested in the wind tunnel. Fluctuating wind forces and moments on the building models are measured and the dynamic building responses are investigated by the HFFB technique. The results show significant reductions in across-wind load fluctuations on the H-section buildings at wind incidence normal to building face with a cavity. Greater reductions are found on the fluctuation levels and the spectral energies at the vortex excitation frequency when the width/depth of the recessed cavities becomes larger. A resonant across-wind response modification factor (RMF) is adopted to quantify the effect on wind-induced dynamic building responses. For the across-wind response at critical wind incidence, the presence of recessed cavities can lead the value of RMF to as low as 0.67, that is reduction of building responses by 33%. To understand the mechanism of wind load modification caused by the presence of recessed cavities, wind pressure on all faces of the H-section tall buildings including the cavity faces are measured. Correlations of across-wind forces contributed by different building faces are analyzed. A clear quasi-periodic fluctuating component is found on the forces from the two building side faces and they act in phase in the across-wind direction. The across-wind force contributions from side faces of the windward or leeward recessed cavity are generally out-of-phase. As a result, the overall excitation levels of the total across-wind force on the building are reduced due to the presence of recessed cavities. To complement the wind tunnel study, computational fluid dynamics modeling using large-eddy simulation (LES) is carried out to study the unsteady wind flow around and wind loads on the H-section tall building with the widest and deepest recessed cavities. Furthermore, the two-dimensional (2D) case of smooth flow past 2D H-section cylinders is investigated. Both the LES and 2D experimental results give consistent observations and mechanisms of the effects of recessed cavities on the modification of dynamic wind loads on the tall building as the wind tunnel results. The thesis also reports studies on the effects of upstream terrain types, building heights and building shapes on the wind effects of H-section tall buildings. / published_or_final_version / Civil Engineering / Doctoral / Doctor of Philosophy

No description available.

No description available.

published_or_final_version / Civil Engineering / Doctoral / Doctor of Philosophy

No description available.

An aerodynamic investigation of cylindrical and Y-shaped building structures was carried out. Specific emphasis was directed towards determining the pressure distribution over three configurations: a flat top, a single dome and a dome with a counter-dome. The Y-model was tested in all three configurations while the cylindrical model was tested in dome/counter-dome configuration only. Both models were tested at Reynolds number(Re) of 360000 and 720000. Surface flow visualization was carried out to reveal regions of separation, recirculation and reattachment. It was found that a large region of negative pressure can be achieved with the dome counter-dome configuration. The maximum negative Cp for this configuration was about 50% higher than the maximum value observed with the flat top or single dome configuration. When the gap between the dome was decreased the maximum negative Cp increased; the increment being greater at the lower Re. Also, for the same Re and gap, the dome with higher curvature showed higher maximum negative Cp; the difference being more pronounced at the lower Re. The effect on the pressure distribution of an opening in the center of the lower dome and of an air flow through that opening was also investigated. It was observed that for injection rates corresponding to typical design flow rates required for ventilation of tall full scale buildings, the pressure distribution remains essentially unaltered. / Master of Science

Thesis (PhD (Civil Engineering))--University of Stellenbosch, 2011. / ENGLISH ABSTRACT: In South Africa, wind constitutes the most critical environmental loading affecting the design of the built environment. The wind climatic information, which is currently incorporated in structural design standards, is based on the analysis of records from a limited number of wind recording stations, mainly located in large cities, and was done several decades ago. In view of the size and the climatological diversity of South Africa, this information cannot be deemed to be adequate. Therefore, the incorporation of welldistributed and updated information on wind climate is essential. The present study endeavoured to address this issue. A strong wind climatology was developed with the use of observed climate data, with the most significant result that a mixed strong wind climate is prevalent in the greater part of South Africa. Statistical approaches to estimate extreme wind speeds were investigated with applicable wind data, with the optimum approach guided by the unique climatological environment and the statistical properties of the utilised data set: For the wind gust analysis the Peak-Over-Threshold method with the exponential distribution is recommended, while in a mixed strong wind climate the “mixed climate” approach is preferred. For the analysis of the hourly mean wind speeds the choice is between the Gumbel distribution and the mixed climate approach, depending on the strong wind climate. The estimation and incorporation of environmental correction factors to the measured wind speeds were necessary as the surroundings of most weather stations did not correspond to the reference Terrain Category. For some of the weather stations it was impossible to compensate for the inadequate exposure and surrounding complex topography, so that a reduced number of weather stations were available for the strong wind analyses. The values estimated for the design wind speeds, adjusted for the short lengths of data records, as well as techniques developed to guide the spatial interpolation of the quantiles, were utilised to develop updated maps of the regional design wind speeds. A comparative study between the results of this study, and that of the previous study on which the current loading code in South Africa is based, indicates that the present study should produce more reliable quantile estimations. / AFRIKAANSE OPSOMMING: Wind vorm die mees kritieke omgewingslading wat die ontwerp van die beboude omgewing in Suid-Afrika beïnvloed. Die windklimaat-inligting wat tans gebruik word in die ontwerp spesifikasies is gebaseer op die statistiese analiese van veskeie dekades gelede op ‘n beperkte aantal windmeting-stasies, hoofsaaklik gesentreer in groot stede. Indien die grootte sowel as die klimatologiese diversiteit van Suid-Afrika in ag geneem word kan hierdie inligting nie as voldoende gereken word nie. Die gebruik van heelwat beter verspreide en opgedateerde inligting oor die windklimaat is daarom noodsaaklik en die studie poog om hierdie leemte aan te spreek. ‘n Sterk-wind klimatologie van Suid-Afrika is ontwikkel deur die gebruik van waargenome klimaatdata, met die mees betekenisvolle bevinding dat ‘n gemengde sterk-wind klimaat in die grootste gedeelte van Suid-Afrika heers. Statistiese benaderings om ekstreme winde te beraam is ondersoek met die beskikbare winddata, met die optimale benadering wat sal afhang van die klimatologiese omgewing van die weerstasie en die statistiese eienskappe van die betrokke windrekord: Vir die wind-stoot analieses word die “Piek-Oor-Drumpel” metode met die eksponensïele verdeling aanbeveel, behalwe in ‘n gemengde sterkwind klimaat waar die “gemengde klimaat” benadering gebruik word. Vir die analiese van die uurlikse gemiddelde winde is die keuse tussen die Gumbel verdeling en die gemengde klimaat benadering, afhangende van die sterk-wind klimaat. Die skatting en toepassing van omgewingskorreksiefaktore vir die windspoed was nodig, aangesien die omgewings waarin die meeste weerstasies is nie ooreenkom met die verwysings Terrein Kategorie nie. Vir sommige weerstasies was dit onmoontlik om vir die onvoldoende blootstelling te vergoed, met die gevolg dat minder stasies beskikbaar was vir die sterk wind analiese. Die geskatte waardes vir die ontwerp-windsnelhede, asook tegnieke ontwikkel vir ruimtelike interpolasie, is gebruik vir die ontwikkeling van kaarte van die omgewings-ontwerpsnelhede, na verstellings van die waardes om te vergoed vir die kort data rekords wat gebruik is. ‘n Kritiese vergelykingstudie wat gedoen is tussen die resultate van die huidige studie, en die vorige waarop die huidige laskodes vir Suid-Afrika gebaseer is, dui aan dat die huidige studie betroubaarder skattings van die kwantiele behoort op te lewer.

Super-tall buildings located in high velocity wind regions are highly vulnerable to large lateral loads. Designing for these structures must be done with great engineering judgment by structural professionals. Present methods of evaluating these loads are typically by the use of American Society of Civil Engineers 7-10 standard, field measurements or scaled wind tunnel models. With the rise of high performance computing nodes, an emerging method based on the numerical approach of Computational Fluid Dynamics has created an additional layer of analysis and loading prediction alternative to conventional methods. The present document uses turbulence modeling and numerical algorithms by means of Reynolds-averaged Navier-Stokes and Large Eddy Simulation equations applied to a square prismatic prototype structure in which its dynamic properties have also been investigated. With proper modeling of the atmospheric boundary layer flow, these numerical techniques reveal important aerodynamic properties and enhance flow visualization to structural engineers in a virtual environment. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2015. / FAU Electronic Theses and Dissertations Collection