Loads on structures Flashcards
In coastal engineering numerous structures with different functions are used:
- Breakwater (rubble mound and monolithic)
- Dikes
- Seawalls
- Revetments
- Storm surge barriers
-and more
Breakwaters have the following tasks:
- Protection of pier and harbor facilities and other civil structures against wave impact
- Reduction of dredging in harbor entrances
- Function as landing pier
- Channeling and management of currents
- Protection of specific coastal areas against reinforced wave impacts or
morphological changes
functional constraints (wave transmission / overtopping) of Outer breakwaters
Large overtopping may be acceptable, limited by tolerable wave transmission
functional constraints (wave transmission / overtopping) of breakwaters protecting basins with moorings
relatively large overtopping may be acceptable, moderate transmission may be tolerated.
functional constraints (wave transmission / overtopping) of breakwaters with moorings
Only limited overtopping will be acceptable.
functional constraints (wave transmission / overtopping) of breakwaters protecting sheds, parking and storage areas
Very limited overtopping will be acceptable.
Components of wave energy E,i=?
reflected energy (E,r), dissipated energy (E,d), and transmitted energy (E,t)
Formula for hydraulic gradient I
I=au+bu^2
a,b = Forchheimer coefficient
u= flow velocity in porous media
Formula for Hydraulic efficiency R
R= K,r^2+K,d^2 = (1-K,t^2)
Reflecting energy percentages of natural or constructional barriers
Natural sandy beach: 0.3 – 4
Underwater breakwater: 10 – 35
Rubble-mound breakwater: 10 – 50
Perforated Caisson breakwater: 4 – 35
Vertical Caisson breakwater: 50 – 90
On which parameters does the wave reflection on breakwaters depend on?
-geometry of the structure
-permeability characteristics of the structure
-steepness (s = HS / L0) of the incoming waves
Formula of the breaker parameter xi
xi=tan(alpha)/sqrt(H,s/L,0)
What are advantages and disadvantages of flexible floating breakwaters?
Advantages:
- Cost-effective, flexible and transportable construction
- Fast installation
- Independent of the building ground
- Possibility to use legacy issues (e.g. car tires)
Disadvantages:
- Effectiveness only against short waves
- Use only in moderate sea conditions up to H = 2.0 m
- Anchoring required
What are advantages and disadvantages of rigid floating breakwaters?
Advantages:
- Simple moving to other locations
- Needs less space
- Use as a berth
Disadvantages:
- Ineffectiveness at longer wave lengths
- Use only in moderate sea state (H < 2.0m)
- Anchoring required
- Resonance problems
- Sensitivity when exceeding the design sea state
What are advantages and disadvantages of Caisson breakwaters?
Advantage:
- Clear, simple geometry
- Low consumption of material
- Possible use as a pier
Disadvantage:
- Sensitive construction in settlements of the ground
- Sensitive construction if design sea state is exceeded
- Sudden failure by breaking waves
- Strong waves reflection on constructions without permeable front
