Questions within the Calc.Tasks Flashcards
What are the shortcomings of the so far analyzed guts velocity profile when it comes to a real design task? What additional information/ analyses should be used/ applied?
- Reduced data availability
- No information about direction dependency
- No defailed roughness parameters (sector-wise)
- No information about neighbour buildings
Given:
Cross-section of an enclosed pedestrian footbridge (as a connection between two buildings).
Do you expect force components in y direction? Justify your reply
Yes, forces in y-direction will occur because the gust turbulence have sigma_y components as well. Additionally, the pressure fluctuations on the surface are stochastic
Given:
Cross-section of an enclosed pedestrian footbridge (as a connection between two buildings).
Given the fact that the structure is a pedestrian bridge. Which dynamic wind effects could rise?
GIV an ViV dependent on dynamic properties.
SIV only for very long constructions (seems not likely)
GIV = Gust Induced Vibrations
VIV = Vortex Induced Vibration
What profile for qp(z) would you recommend for a compact building (height equal to depth and width)?
In case of a compact building, the velocity pressure qp (z=H_Top) has to be applied over the total height (blockage effect)
Please explain the term “return period”. How would you determine a wind velocity with a return period of 20 years?
The return period refers to the level of statistical safety. For a wind speed with a yearly probability of 2% (p=0,02) the retun period deives to R = 1/0,02 = 50 years. For R = 20 years, p equals to p=0,05. THe corresponding value can be found at y=-ln(-ln(1-0,05))= 2,97
What is a stagnation point?
The stagnation point is the windward location at which alpha = 0, cp= +1
Given is a meterological Station in Cuxhaven and a Construction Site in Hamburg.
Please comment the general suitability of the station Cuxhaven for Hamburg.
Due to the distance of ~100 km the usability of the station for Hamburg ist limited.
The wind zone map shows different wind zones for both locations, hence there is a overregional influence
Given is a meterological Station in Cuxhaven and a Construction Site in Hamburg.
Which steps would be necessary for a complete directional analysis of the main structure?
1) Sectorewise determination of the roughness cat. around the weather station and the site
2) Sectorwiese determination of yearly extreme wind speeds
3) Sectorwise determination of v_b (using the Gumbelmethode)
4) Calculation of sectorwise qp for the site taking into accounnt both roughness catergories
5) Combination with sectorwise aerodynamic coefficients
Explain the definition of a mean pressure coefficient cp
The pressure coefficient is defined base on the difference between the flour speed at a reference location and a surface location. The equation is based on the general Bernoulli Equation
Could the surface loading be estimated according to Eurocode 1-4 in a conservative way as well?
The Eurocode load assuptions do not take into account the influence of neighbored buildings. Hence, in areas with channeling effects, the pressure coefficiente of EC1-4 might not be safe!
How can vortex induced vibration (generally) be suppressed or rather avoided? Please describe 3 possible methodes
1) Installation of fluid tuned mass dampers or tune mass damper
2) increase of stiffness (additional fixation)
3) Modification of aerodynamic shape
At which point it´s necessary to determine the factor cscd?
As the Eigenfrequency is above 5 Hz, gust induced vibration are not expected.
cscd = 1,0
At which point could you expect vortex induced vibrations?
vcrit < 1,25 * vm
