Wind-adaptable Design For Supertall Buildings

With conventional wind-resistant design approaches,if the wind loads considered in the preliminary design were underestimated compared to the results of the subsequent wind tunnel tests,significant design changes may have to conduct to the original design.Underestimation on wind loads can lead to an inadequate design to meet the mandatory requirements for building safety and serviceability.This challenge is often encountered in super-tall building design,in which complicated across-wind responses dominate the design loads that are difficult to predict without wind tunnel tests.On the other hand,however,significant design changes,by either aerodynamic modifications or structural enhancements,such as increasing element size or implementing supplemental damping devices,can result in a considerable increase in project costs,an undesirable appearance of the building,and a loss of building usable spaces.Wind-adaptable design(WAD),discussed in the present thesis,provides a new method for supertall building designs to lessen design conflicts between architectural prerequisites and aerodynamic requirements,and increase the efficiency of the structural systems.The main idea of WAD is to design a smart building that can "adapt" wind loads by adjustable aerodynamic devices and/or by optimized modal properties.The thesis presents the study on the theory of the windadaptable design and its application in practice.The main results are given in the following aspects:1)Commentary on conventional wind-resistant design methods: Review the up-to-date research on wind-resistant design methods and the associated optimization approaches,including architectural modifications and structural solutions.The advantages and disadvantages of these approaches are discussed,based on which the concept of wind-adaptable design is introduced.2)Design process with WAD: The process of the wind-adaptable design is introduced,followed by a discussion on design parameters,which include the extreme wind speed for optimized stage design,the common wind speed for basic stage design,and the trigger wind speed for the operation of flow-control devices.In heavy wind storms,the building’s capacity to wind loads is enhanced by on-demand operable flow control measures/devices to effectively reduce the resulting loads and responses.A case study demonstrates the design process of the wind-adaptable design.3)Effects of porous double skin fa(?)ade(Porous DSF)system on structural wind responses of tall buildings: Porous DSF systems have been widely used in the building industry owing to their outstanding performance in energy efficiency and architectural aesthetics.Given the fact that the porous DSFs can soften the airflow separation around building corners,it is anticipated that the porous DSF systems should have the potential to control wind-induced structural responses.However,this potential benefit has not yet received due attention.Therefore,a wind tunnel study was carried out on a typical square high-rise building equipped with porous DSF to verify the effects of the porous DSF system on the wind-induced structural response,particularly on the reduction of building accelerations and structural wind loads.By examining the influence of the porous DSF with different coverage areas and coverage positions on the wind response,the feasibility of applying the porous DSF system in wind-adaptable design is discussed.4)Effects of porous shroud on structural wind responses of circular structures: By taking tall chimneys and solar towers as typical examples of tall circular structures,the effects of porous shroud on structural wind responses are studied.For the tall circular structures,severe vortex-induced oscillations often occur at relatively low wind speeds due to the high Strouhal number.Therefore,the wind responses,not only at the design wind speed but also at the postcritical speeds,need to be considered in the design.The outperformance of the porous shroud in suppressing vortex-induced oscillations was verified in wind tunnel tests using the high frequency force balance model and the full-aeroelastic model by comparing it with many other aerodynamic schemes,such as helical strikes and slatted shroud,etc.The results provide further confirmation on the feasibility of using porous fa(?)ade in wind-adaptable design.5)Application of modal interference approach on supertall buildings: Inspired by the multi-modal flutter theory of bridges,a new method of structural optimization to reduce acrosswind responses of supertall buildings is proposed and named as modal interference approach(MIA).The method is based on an observation that if there exist multiple excited modes in the vortex-induced oscillations,the modal responses will interfere with each other,resulting in the vibration amplitude of the multi-modal response being smaller than that of the single-mode response.Theoretical analysis and wind tunnel tests were performed to validate the influence of the modal interference effects,followed by application studies using design software modeling.The results indicate that the proposed modal interference approach can be used as an effective supplement to the existing structural optimization methods.6)Engineering application and reliability assessment of wind-adaptable design:Referring to the dynamic curtain walls currently utilized in the building industry,the prospect of using porous facades systems as the flow control measures in the wind adaptable design is further discussed.The relevant reliability of the monitoring system and the operating system in windadaptable design is analyzed.Based on the concept of common cause failure(CCF),a mathematical model to assess the reliability of the wind-adaptable system is proposed,with which the key parameters involved in the wind-adaptable design can be determined.