Wind Loads on Tall Building Structures
Video of an aeroelastic (dynamic) model being tested in one of Windtech’s Wind Tunnels
Structural Wind Loads and Building Acceleration
As populations in cities increase, there is a trend towards tall, slender, flexible and light-weight buildings. As such, key engineering challenges present themselves as buildings become more susceptible to wind induced excitation, which affects not only the strength of the structure, but also the comfort of end users.
Wind loading codes have been made available for building designers as a recipe book on how to design for wind, however they lack the ability to be applicable for all cases. This is because the underlying assumption in all codes is that the building takes the form of a simple rectangular prism shape. As such the institutions that govern the provision of these codes deliberately make them conservative, as they are typically used for buildings of all shapes and sizes, and in some cases for buildings that depart away from the prescribed code envelopes. By conducting wind tunnel testing in lieu of the codes, the building designer often avoids overdesign as they are given the opportunity to optimise the structure though a more accurate and telling set of results. Rare cases where the loads may be in exceedance of the codes are also picked up, eliminating the potential of under design. [Aaron reached this point]
WINDTECH uses two key methods in its analysis of structural loads on tall buildings. The High Frequency Force Balance (HFFB) technique uses a base balance to measure overturning moments in the wind tunnel at a scale of approximately 1:300. The High Frequency Pressure Integration uses a similar model, but instead of using a base balance, uses hundreds of pressure tappings. Both methods are incredibly accurate and have been verified against other leading wind tunnel laboratories.
For buildings with rigidly linked towers it can be useful to consider the load sharing between towers and. WINDTECH have developed a methodology for determining this load share and thus negate the need for over-design. Additionally, for tall and slender buildings (a rule of thumb might be to consider structures with a height to breadth ratio greater than 5) WINDTECH is also experienced in carrying out aeroelastic studies.
Tip deflection is also measured in the wind tunnel, enabling accurate measurement of building accelerations. With a comparison against various occupant comfort criteria, adjustments can subsequently be made to ensure limits are not exceeded. Note that measurements are normally presented for three different levels of damping, but we can of course cater to client requirements in this respect.
