The moving wind towards the building turns aside making an overpressure on the exposed façade. The deviated flow separates at the corner from the building creating a turbulent boundary layer.
Vortex shedding appear as oscillating flow from opposite sides of a structure and engender fluctuating load perpendicular to the wind direction. Structural vibrations may occur due to resonance effect when the frequency of vortex shedding matches the natural frequency of the structure.
Therefore, the Eurocode 1991-1-4 should not be used for buildings taller than 200m and very slender or unusual structures because it does not provide regulation on the following aspects:
wind actions on lattice towers with non-parallel chords;
wind actions on guyed masts and guyed chimneys;
torsional vibrations, for example high buildings with central core;
vibration of bridge decks due to the transverse wind turbulence;
Vibration when more than the fundamental mode must be taken into consideration.
Objective of the thesis
The aim of this research is to find a methodology for the design of exceptional structures which achieve an adequate and homogeneous level of reliability in a cost efficient manner. Structures will have to resist during a lifetime of 25 to 100 years to the effects of various actions with proper safety coefficients adapted to the selected probabilistic format.
This methodology also has to convince the insurance company to cover the widespread exposures of economic and financial loss or gain, physical damage or injury, or delay of construction projects while they are under construction and during maintenance period.
Fazlur Khan, a structural engineer or the father of tubular designs initiated in 1969 the structural systems for skyscrapers by a classification of the height corresponding to each form for steel and concrete structures as in Figure 3. (Khan, 1969)
A new classification that covers most tall buildings today divide them in two sections: interior structures and exterior structures. A structure is called interior when the important part of the lateral load resisting system is placed inside the building. Similarly, if the significant part of the lateral load resisting set is situated at the building border then the system is called exterior structure. (Ali & Moon, 2007)
Because of the limitation of this paper, the details of this approach will not be discussed. Otherwise, the guideline to the applications of this concept is shown if Figure4.
Some new studies suggest a percentage increase in the design parameters depending on the load situation with or without follow up consequences and fire loading. The mentioned probabilistic approach in the previous paragraph for the Eurocode as well as for other codes prescribes design equations to verify the ability of different structural elements to resist to diverse modes of failure. The usual equation includes partial safety factors...