Assessment

Question 1

What value for wind is used in UK criteria?

Answer 1

-mean wind values for high winds however it would be gust that affects the stability of pedestrians

Question 2

What are the steps in a wind comfort assessment?

Answer 2

1) look at met data and determine average wind speeds in areas
2) wind rose - tells you direction and probability of the wind

3) correction met data for site:
- season
- surface roughness
- altitude
- direction
- height of building

4) wind tunnel or CFD test
5) ratio used to calculate full scale. Get reference of mean wind to reference and scale up.
6) check against criteria

Question 3

What techniques can be used for wind tunnel or CFD tests?

Answer 3

1) Irwin - vertical pitots which are cheap and a large number of probes can be deployed. Can measure both mean and gust
2) Sand scour - sand is spread in a thin layers on wind tunnel floor and the wind speed turned on at a low value. The speed is gradually increased in small steps and the patterns are photographed. The nature of the wind speed that is measured is not all that clear

3) computational
- large scale prediction (using met data)
- CFD (RANS) - steady, only mean wind speeds and used fr comfort
- Unsteady - used for distress
- LES - large scale, not accurate

Question 4

What is the Lawson criteria?

Answer 4

-windiness is subjective and depends on a number of factors:

1) long term sitting - eating lunch, drinking
2) standing or short term - bus stop
3) pedestrian walking - general walking areas
4) business walking - local areas around tall buildings

Question 5

What are the different types of real measurements

Answer 5

1) Anemometer
- Cup: cheap, only measure horizontal
- Sonic: wind speed, direction, temperature
* 100’s of samples per second so issue with data storage
* relatively cheap

2) LDAR
- uses laser
- one direction
- low resolution (bad accuracy)
- good for high altitude
- laser scattered by particles in atmosphere

3) Pressure Transducer
- have diaphragm and strange gauge
- small and cheap
- multi-holed are used in wind tunnel tests

4) rain gauge
5) pollution gauge

Question 6

Outline the methods engineering designers use to calculate the displacements and accelerations of high-rise structures in cross winds or for turbulent flows.

Answer 6

• cross wind oscillations of dynamic structures occur due to vortex shedding
• force spectrum is defined by experimental data rather than obtaining the wind fluctuations and aerodynamic admittance
• this shows a peak at the frequency of vortex shedding

1) guest speed density - met data (graph of velocity and time) - work of frequency of gust wind speeds
2) high frequency oscillations have lower turbulence so won’t effect building need to correct data (take out of graph) to only have what will effect oscillations so apply aerodynamic admittance filter
3) then get displacement spectrum from force spectrum which has different modes and the is where you add dampers if there are close to resonance of building

Question 7

How do you determine the wind load on a building?

Answer 7

1) determine structural type
2) calculate wind speed characteristics
(use met data and find probability)
3) Calculate loading coefficients
(use wind tunnel of CfD)
4) calculate overall loads and responses

Question 8

What study is needed for snow loads?

Answer 8

1) get met data
2) apply correction factors
- amplitude
- thermal gradient of roof
- wind exposure
- shape factor
3) grumbeil distribution

Question 9

What studies are needed for renewables?

Answer 9

• wind turbine same a maths

- solar look at geography, time of year and direction and angle