arch & buttres dam
DESCRIPTION
For Vth Sem UG StudentArch Dam, Buttres Dam, Type of DamsTRANSCRIPT
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It is defined as a solid wall, curved in plan,standing across the entire width of the rivervalley, in a single span.
Structurally behave:
Partly as a cantilever retaining wall standing upfrom its base, and
Partly, the load will be transferred to the two endsof the arch span by horizontal arch action.
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Transfer a large part of their loading bycantilever action.
Depending upon the shape consideration:
Constant radius arch dams
Variable radius arch dams
Constant angle arch dams
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Constant radius arch damsExtrados and Intrados
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Variable radius arch damsExtrados and Intrados
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Constant angle arch damsExtrados and Intrados
Water Pressure
Uplift Pressure
Pressure due to Earthquake forces
Silt Pressure
Wave Pressure
Ice Pressure
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Thin cylinder theory
Method gives wrong results and can relied onlyupon rough estimation of dimensions of arches.
Theory of Elastic arches
Dam divided into horizontal independent arches.
The Trial Load method
Dam divided into
The horizontal arches
The vertical cantilevers
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Thin cylinder theory
t
rh
t
R w
t
rhf w
c
rhR w Reaction,
Compressive stress,
Allowable compressive stress,
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Central angle for minimum concrete
trV )2(
)2(2
rf
hV
c
w
sin2
Lr
431332 0
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Limitation of Thin cylinder theory
The arch sections are not thin cylinders. They arealso not free at abutments, as assumed in theory.
The theory does not consider shear and bendingstresses in the arch.
Analysis is based only on hydrostatic pressure. Icepressure and temperature stresses, though areimportant, not considered in the theory.
Stressed due to yielding of abutments and thosedue to rib shortening have not been accounted.
Plastic flow of concrete and shrinkage of concretenot accounted for.
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Thin Elastic theory
Temperature stresses, due to temperaturechanges
Shrinkage stresses, due to setting of concrete
Stresses due to yielding of abutments
No abutment is rigid and yields to an extentdepends upon the nature of rock.
Stresses due to rib shortening
Caused due to restriction of change in span.
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General formulas
yHL
xMMMM ABA
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. Deck slab typeMultiple arch type
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Simply SupportedSlab type
Buttress spacing andDeck slope
Most economical spacingof buttresses
minimum thickness ofconcrete is fully utilised.
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Simply Supported Slab type
Buttress spacing and Deck slope
Height, thickness and spacing of buttresses
Height of buttress Slenderness ratio = = 12 – 15
Thickness of buttress
Spacing of buttress Massiveness factor = = 2.5 – 3
Thickness of buttress
Concrete quantity/ mlength of dam
cot
1208.0 2
sc F
HV
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Multiple Arch type
Daniel Jhonson Dam, Quebec, CanadaMultiple arch and buttress dam (Height – 216m)
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Multiple Arch type
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Other types
Multiple Dome type
Coolidge Dam, Arizona,USA Multiple domeand buttress dam(Height – 75.95m)
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Other types
Massive Head type
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Massive Head type Advantages
The construction work is easier.
Since water pressure acts radially in a cylindricaltype, and perpendicular in a diamond type, allpressures are normally compressive.
Since the deck is not to ne reinforced, there is noquestion of failure by rusting of steel.
For smaller heights, they prove to give moreeconomical buttress spacing.
Such a dam body offers more resistance to sliding,because it is considerably heavier.
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Other types
Columnar Buttress type Disadvantages :
Require very strong and stable foundations
More skill is required in constructing the buttresses.
24 Hydraulic Structures