Advance Design of RC Structure 1 - Islamic...
Transcript of Advance Design of RC Structure 1 - Islamic...
Lecture 11 Advance Design of RC Structure
1 Advance Design of RC Structure
Retaining Wall
Lecture 11 Advance Design of RC Structure
2 Retaining Walls
What are retaining walls
Retaining walls are soil-structure systems
intended to support earth backfills.
Type of retaining walls
Gravity retaining wall
gravity walls rely on their own weight to
provide static equilibrium.
typically made of plain (unreinforced)
concrete or stone blocks.
Cantilever retaining walls
cantilever walls derive a portion of their
stabilizing forces and moments from the
backfill soil above the heel.
require the use of steel reinforcement to
resist the large moments and shear stresses.
Lecture 11 Advance Design of RC Structure
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Lecture 11 Advance Design of RC Structure
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Lecture 11 Advance Design of RC Structure
5 Retaining Walls MSE walls
Mechanically Stabilized Earth (MSE) walls derive their stability
from the internal stresses developing at the interface between the
soil and the reinforcement elements.
MSE walls are constructed by compacting the soil in layers
separated by reinforcement strips or sheets. Reinforcement strips are
attached to facing units, and extend far enough into the backfill to
ensure adequate pullout resistance.
Soil-Nailed walls
Lecture 11 Advance Design of RC Structure
6 Retaining Walls Reinforced Earth Walls
Geotextile-Reinforced Walls
Cantilever Sheet Piles
Reinforced Earth Walls
Lecture 11 Advance Design of RC Structure
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Cantilever Sheet Piles
Lecture 11 Advance Design of RC Structure
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Lecture 11 Advance Design of RC Structure
9 Cantilever Retaining Walls
Basic Principles
Cantilever walls are made of reinforced concrete, & come in different
geometries.
Rely on their self-weight to resist sliding & overturning, but derive part
of their stability from the weight of the backfill above the heel of the
wall.
Lecture 11 Advance Design of RC Structure
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Lecture 11 Advance Design of RC Structure
11 Cantilever Retaining Walls
Typical Dimensions of retaining walls
Lecture 11 Advance Design of RC Structure
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Lecture 11 Advance Design of RC Structure
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Lecture 11 Advance Design of RC Structure
14 Cantilever Retaining Walls
Basic Design Principles
In addition to the external stability, cantilever walls must also satisfy
internal structural.
The wall section should be able to withstand the shear stresses and
bending moments resulting from the lateral earth pressure as well as the
difference in pressure between the top and bottom faces of the base.
Lecture 11 Advance Design of RC Structure
15 Cantilever Retaining Walls
External stability
In analyzing or designing for external stability, all the forces acting on
the structure are considered. These forces include lateral earth
pressures, the self-weight of the structure, & the reaction from the
foundation soil.
The stability of the wall is then evaluated by considering the relevant
forces for each potential failure mechanism.
The wall has to be stable against:
Sliding
Overturning
Bearing capacity
max
1allBC
qFS
q
Lecture 11 Advance Design of RC Structure
16 Cantilever Retaining Walls
Design Example
Given data
As shown in the figure
Design the retaining wall
' 25cf MPa
420yf MPa2150 /allq kN m
Lecture 11 Advance Design of RC Structure
17 Design Example Step 1: Check for overturning
Calculate the weight per unit width (Wi)
(per meter) 1 23.5 0.5 0.7 8.23W kN
2 23.5 5 0.5 58.75W kN
3 23.5 0.5 1.4 16.45W kN
4 (17 2.5 19 0.2)1.4 112.7W kN
Moment arm (xi)
1 0.35x m
2 0.95x m
3 1.9x m
4 1.9x m
Lecture 11 Advance Design of RC Structure
18 Design Example Calculate the active earth pressure & the water pressure
1' 17 2.5 0.271 11.52h kPa
2' (17 2.5 (19 9.8) 2.5) 0.271 17.75h kPa
9.8 2.5 24.5u kPa
4 (17 2.5 19 0.2)1.4 112.7W kN
The active forces P1 to P4 per unit width
1 0.5 11.52 2.5 14.4P kN
2 17.75 2.5 44.38P kN
3 0.5 (17.75 11.52) 2.5 7.79P kN
4 0.5 24.5 2.5 30.63P kN
Moment arm (yi)
1 2.5 2.5 / 3 3.33y m
2 2.5 / 2 1.25y m
3 2.5 / 3 0.83y m
4 0.83y m
1 sin350.27
1 sin35aK
Lecture 11 Advance Design of RC Structure
19 Design Example Calculate the active earth pressure & the water pressure
i iRoverturning
O i i
W xMFS
M P y
8.23 0.35 58.75 0.95 16.45 1.9 112.7 1.9
14.4 3.33 44.38 1.25 7.79 0.83 30.63 0.83
Step 2: Check for bearing capacity
The eccentricity on the wall base
0.5 ( ) /R Oe B M M W
OK304.1
2.2 1.5135.3
0.5(2.6) (304.1 135.3) /196.1
0.42 / 6 0.43e m B OK
The maximum & minimum soil pressures at the toe & heel of the base are
2
max 2
196.1 196.1 0.42 6148.5 /
2.6 2.6
xtoe
x
F Mq q y kN m
A I
2
min 2
196.1 196.1 0.42 62.3 /
2.6 2.6heelq q kN m
Lecture 11 Advance Design of RC Structure
20 Design Example
max
1501.01 1
148.5
allBC
qFS
q
Step 3: Check for shear strength at critical section
The ultimate shear on the base at a distance d from the face of the wall is
0.5 .075 0.02 0.405d m
OK
2(148.5 2.3) 2.2952.3 131.3 /
2.6dq kN m
2
max 148.5 /q kN m
Effective depth of base
1.6 (0.7 )uV qb d
148.5 131.3
1.6 1 0.7 0.405 662
kN
Pressure at distance d from the face of the wall
00.17 'cV fc b d
0.17 0.85 30 1 0.405 293 ukN V OK
At the TOE
Lecture 11 Advance Design of RC Structure
21 Design Example
2(148.5 2.3) 0.9952.3 58.2 /
2.6dq kN m
2
min 2.3 /q kN m
1.6 (1.4 )uV qb d
58.2 2.3
1.6 1 1.4 0.405 502
kN
Pressure at distance d from the face of the wall
00.17 'cV fc b d
0.17 0.85 30 1 0.405 293 ukN V OK
At the HEEL
Step 3: Flexural reinforcement
At the HEEL
2 21.4 1.4
1.6 1.6 2.3 81 2.32 6
u heelM M
44.8 .uM kN m
Case I
Lecture 11 Advance Design of RC Structure
22 Design Example 3
2
0.85 ' 2.61 101 1
'
c u
y c
f M
f bd f
3
min2
0.85 25 2.61 10 (44.8)1 1 0.0007 0.0018
420 1(0.405) 25
20.0018(100)(40.5) 7.3sA cm
Use 12mm @ 15cm
W3 + W4
1.6 1.6 16.45 112.7 0.7 144.6u heelM M kN
Case II
3
2
0.85 25 2.61 10 (144.6)1 1 0.0024
420 1(0.405) 25
20.0024(100)(40.5) 9.7sA cm
Use 14mm @ 15cm
Lecture 11 Advance Design of RC Structure
23 Design Example At the TOE
2 20.7 0.7
1.6 1.6 109.1 148.5 109.12 3
u toeM M
53.1 .uM kN m
3
min2
0.85 25 2.61 10 (53.1)1 1 0.0009 0.0018
420 1(0.405) 25
20.0018(100)(40.5) 7.3sA cm
Use 12mm @ 15cm
At the STEM
1.6 1.6 86.7 138.7 .u stemM M kN m
3
2
0.85 25 2.61 10 (148.7)1 1 0.0023
420 1(0.405) 25
14.4 2.83 44.38 0.75 7.79 0.33 30.63 0.33stemM
86.7 .stemM kN m
Lecture 11 Advance Design of RC Structure
24 Design Example 20.0023(100)(40.5) 9.3sA cm
Use 14mm @ 15cm
Step 4: Shrinkage reinforcement
20.0018(100)(40.5) 7.3sA cm
Use 12mm @ 15cm
Lecture 11 Advance Design of RC Structure
25 Design Example
14mm @ 15cm
14mm @ 15cm
12mm @ 15cm
12mm @ 15cm
12mm @ 15cm
Flexural reinforcement
Shrinkage reinforcement
12mm @ 15cm
12mm @ 15cm