Please comment the general suitability of the station Cuxhaven for Hamburg.
distance ~100km - usability of this station is limited
windzone map shows different wind zones for the locations
overregional influence
Which steps would be necessary for a complete directional analysis of the main structure?
sectorwise detemination of the roughness cat. around the wheater station
sectorwise detemination of yearly extreme wind speed
calculation sectorwise of q p
combination of sectorwise aerodyn. coefficients c p
Explain (generally) the definition of a mean pressure coefficient cp.
The pressure coefficient is defined base on the difference between the floor 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 EC load assumptions don’t take into account the influence of neighbored buildings. in areas with channeling effects, the pressure coefficients of EC 1-4 might not be safe!
Assume a structural factor of cscd = 1.22 has been derived by appropriate calculations. What are the consequences with respect to the structural design due to that result?
As the factor is higher than 1.1, the static load has to be increase by this factor. Furthermore, a fatigue verification should be perfomed.
How can vortex induced vibrations (generally) be suppressed or rather avoided? Please describe 3 possible methods.
installation of fluid taned mass dampers or tune mass dampers
modification of aerodynamic shape
increase of stiffness (additional fixation)
compact building
In case of a compact building the velocity pressure q_p has to be applied over the total hight (blockage effect)
Explain “return period” and determine a wind velocity with a return period of 20 years
Return periods refers to the level of statistical safety. For a wind speed with a yearly probability of 2% (p=0,02) the return period derives to R=1/0,02 = 50 years. Hence 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 the stagnation point?
The stagnation point is the windward location at which u_s = 0; cp,s = +1
Why are those values potential outliers?
The two lowest values are treated as outliers as they dont follow the Gumble distribution.
basic velocity for place b if a is already calculated
The basic velocity is equal to c) as it does not depend on the roughness conditions on site
How could the basic velocity recommendation for the construction site be enhanced for the present project?
The analysis should be performed direction-dependend. Therefore, all sectors at Tempelhof need to be classified to a suitable roughness category.
In which regions do you expect the highest underpressure and why?
Highest underpressure: windward edge and due to neighbouring increased flow speed (channel-effect)
What is the Bernouli Equation.
Relation between pressure and velocity
Reason for underpressure on a surface of an object in wind flow
compressed streamlines, increased flow velocity
Main difference comparing sharpedged and rounded objects with respect to their aerodynamic behaviour:
The flow separation of sharpedged crosssections is predefined and
independent on scale.
Drag force of different crosssections (lowest to highest)
Triangular (tip windward), square, triangular (edge windward)
Comparing the overall resulting force of a slender and a compact building with same height. What ratio of total force F to the bui
lding width b is higher and why?
The slender one has a lower ratio of F:b, due to the applicable height
profile of the velocity pressure
Do you think it’s necessary to determine the factor cscd for the given structure? Eigenfrequenz > 5Hz
As long as the Eigenfrequenz is above 5 Hz, gust induced vibrations are not expected for the present structure -> c_s, c_d = 1,0
What are the reasons for the definition of a ”basic velocity vb” according to the definition given in Eurocode?
vb can be defined in a larger scale, independent on local development and vegetation
Using vb ensures a unique statistical base
vb can be expressed independent on the roughness category.
What is expressed with the integral length scale of turbulence Lux?
The correlation of flow velocities in space.
Why are there different kinds of aerodynamic effects (pressure, force, moment, etc.)?
As wind effects are dependent on time and space on the surface.
Based on which theoretical assumption are streamlimes used for the pressure analysis?
Bernoulli equation and continuity equation, assuming a steady flow.
What means mechanical admittance?
The relation between harmonic force and structural response.
The dependency between deflection and aerodynamic force.
What influences the structural damping?
Material
Type of construction, connections
What is the reason for self-induced vibrations?
Modification of the aerodynamic properties dependent on structural deflection.
What are the shortcomings of the so far analyzed gust velocity profile when it comes to a real design task? What additional information/analyses should used/applied?
Reduced data availability
No information about direction dependency
No detailed roughness parameters
No information about neightbours buildings
Do you also expect force components in vertical direction by horizontal windflow?
Forces in vertical direction will occur because the gust turbulence have vertical components as well. Additionally, the pressure fluctinations on the surface are stochastic.
Given the fact that the structure is a pedestrian bridge. Which dynamic wind effects could arise?
GIV and VIV dependent on dynamic properties SIV only for very long constructions.
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