Wind Effects on Building Components and Cladding
1. In the spreadsheet "lecture 2 velocity fluctuations.xlsx" there are three sheets labelled as "flat", "open" and "suburban". These sheets contain measured velocity data in one of the boundary layer wind tunnels at Western. The streamwise velocity component is labelled U, V is the lateral component, and W is the vertical component. Find:
(a) u* and Zo values for each profile using the log law, and
(b) the power law coefficients, α, for the mean profiles.
(c) Plot the turbulence intensity profiles for the 3 velocity components. Compare these with the profiles determined using the log law on slide 24 from lecture 2, using the log law coefficients determined in part (a). Discuss how you might change Zo based on these models if you were more concerned with the turbulence levels than the mean speeds.
(d) Assuming a peak factor of 3.0, plot the peak velocity profiles using the experimental data. Determine the power law coefficients, α, associated with these peak speeds. Compare these with the values in ASCE 7 (slide 30 in Lecture 2) and discuss what types of terrain these wind tunnel profiles may represent.
(e) If it can be assumed that these profiles represent model-scale analogues of the atmospheric boundary layer, discuss what the length scale may be considering the mean velocity, turbulence intensity and peak wind speed profiles. Note that the length scale, λL, is defined as the ratio of the height in the wind tunnel (model-scale) to the equivalent height in the atmosphere, i.e., λL = Zms/Zfs. Make sure to discuss your assumptions.
(f) Find the exposure factors for the three terrains at z = 0.1016 m, 0.2032 m, and 0.3048 m if the "open" profile is assumed to be the basic terrain, converting these to full--scale heights using your model scale determined in (e). Use the z = 0.1016 m height (converted to full--scale) as the relevant reference height for the basic wind speed. Calculate the ASCE 7 exposure factors, Kh (or Kz), and compare these values to the wind tunnel data. Discuss the assumptions you have made.
2. For the buildings shown in the figure below (dimensions given in m), (a) determine the size of roof and wall zones using ASCE 7. Sketch these zones. (b) For each house and zone, determine the GCp values for a sheet of plywood (1.2m x 2.4m) - if the plywood is larger than the zone size, discuss your choice for determining the pressure coefficient. Please put these in tabular form. (c) If the houses are located in suburban terrain and the basic wind speed, V, is 95 mph, determine the wind load for these sheathing panels assuming that the internal pressure coefficient is 0 and that the internal pressure is for a partially--enclosed building (i.e., one with a large opening in one wall).
3. In the spreadsheet "wind speed data.xlsx", there is a time series of wind tunnel velocity data obtained in a wind tunnel. Determine:
(a) the mean velocity, and
(b) the turbulence intensity.
(c) Create a "Durst curve".
(d) Compare the results from (c) with the actual Durst curve assuming the mean speed is like an hourly speed. To make these match (to the extent that they can), the model--scale time has to be converted to full--scale time using the relation for time scale as λt = tms/tfs, where t is time. Determine the best time--scale, discussing your assumptions and why differences between the curves may exist, noting that the data may not be from an "open" terrain.