Retaining Counterfort Wall Design

Document No.ISBT_MAIN_01 RCC DESIGN OF RETAINING WALL (-4.8M) FOR TERMINAL BUILDING OF MAIN ISBT Rev. No. 0 Project Title INTERSTATE BUS TERMINAL, SARAI KALE KHAN, NEW DELHI Institute For Steel Development & Growth Client COMMISSIONER (TRANSPORT), GOVERNMENT OF DELHI ISPAT NIKETAN', 1st. Floor 52 / 1A Ballygunge Circular Road Name of Unit MAIN TERMINAL BUILDING FOR ISBT Kolkata - 700019 Drawing Ref. Designed by: G.C. Checked by: G.C. Approved by: Date: 30.11.06 CALCULATIONS Reference

A) Design of Peripheral Retaining Wall at basement level for Bus Parking Area at -4.8 M level: 0.30 Lateral Pressure on Wall due to Surcharge Load(k 0 x q )

Formed Ground Level (EL. +205.50M)

0.60

0.30

High Flood Level (HFL) (EL. +205.14M)

H1 = 0.36 M Retaining Wall

Counterfort Beam

0.45

5.10

H2 = 4.44 M

Lateral Pressure on Wall due to Submerged Soil (k 0 x γsub x H2) Lateral Pressure on Wall due to Water ( γw x H2)

EL. +200.70M

1.0

0.42

Lateral Pressure on Wall due to Saturated Soil (k 0 x γsat x H1)

2.0

Fig. 1:

Basement Slab

Section showing Counterfort retaining Wall for Bus Parking Area at -4.8M Level

DESIGN PARAMETERS FOR RCC RETAINING WALL: Formed Ground Level High Flood Level (HFL) Top of Slab at Basement Level Formed Ground Level at 205.5M corresponds to High Flood Level (HFL) at 205.14M corresponds to Height of Retaining Wall below Formed Ground Level Height of Retaining Wall above Formed Ground Level Height of Retaining Wall for saturated soil pressure, H1 Height of Retaining Wall for submerged soil pressure, H2 Overall Height of Retaining Wall Centre - to - centre distance of Counterfort (Span of Wall) Overall Clear Depth of Counterforts at bottom Overall Depth of Counterforts at bottom Overall Depth of Counterforts at top Variation of Depth of Counterforts from -4.8 M starts at Overall Depth of Horizontal beam at top of Wall Overall Width of Horizontal beam at top of Wall Thickness of Counterfort assumed Overall Thk. of Wall spanning between Counterforts Overall Thk. of Base Slab spanning between Counterforts Coefficient of Earth Pressure at Rest, k0

= = = = = = = = = = = = = = = = = = = =

205.50 205.14 200.70 0.00 -0.36 4.80 0.30 0.36 4.44 5.10 4.00 2.00 2.45 0.60 1.00 0.60 0.30 0.75 0.45 0.42

M M M M M M M M M M M M M M M M M M M M

Surcharge Load at Formed Ground Level on soil, q

= =

0.50 2 2.00 T/M

Unit weight of Saturated Soil, γsat (Max.)

=

3 1.94 T/M

Unit weight of Water, γw

=

3 1.00 T/M

Unit weight of Saturated Soil, γsub (Max.) Grade of Concrete considered Clear cover to reinforcement provided

= = =

3 0.94 T/M M30 5.00 Cm.

Page 1 of 7


Peripheral Retaining Wall at basement level for Bus Parking Area at -4.8 M level: i) Design of Wall Slab (Uncracked Design): Since, the major portion of the wall will be in contact with water, the same has been designed based on the principles of uncracked design as per working stress method Load Cases: i)

Lateral Pressure on Wall for Saturated Soil

=k0γsatH1=

ii)

Lateral Pressure on Wall for Submerged Soil

=k0γsubH2=

iii)

Lateral Pressure on Wall for Surcharge

=k0q

=

iv)

Lateral Pressure on Wall for Water

=γwH2

=

2 0.35 T/M (Triangular) 2 2.09 T/M (Triangular) 2 1.00 T/M (Uniform) 2 4.44 T/M (Triangular)

Now for all practical purposes, there will be two types of combined load cases as follows: 2 Load Case I, Uniform Lateral Pressure due to Surcharge = 1.00 T/M = f1 2 Load Case II, Linearly varying Lateral Pressure for Soil & Water = 6.88 T/M = f2 Analysis for Uniform Pressure Loading: Here, Shorter Span, lx = Longer Span, ly =

4.00 M 5.16 M

∴ly/lx =

1.29 i.e. 1.3

5.16/4 =

Which gives from IS: 456 - 2000, α x (+ve) =

0.036

α y (+ve) =

0.024

α x (-ve) =

0.047

α y (-ve) =

0.032

Mx (+ve) =

Positive BM for Horizontal Span =

α x (+ve) x f1 x lx2 =

0.58 T-m/m

Mx (-ve) =

Negative BM for Horizontal Span =

α x (-ve) x f1 x lx2 =

0.75 T-m/m

My (+ve) =

Positive BM for Vertical Span =

α y (+ve) x f1 x lx2 =

0.38 T-m/m

My (-ve) =

Negative BM for Vertical Span =

α y (-ve) x f1 x lx2 =

0.51 T-m/m

Analysis for Triangular Pressure Loading: Here, Horizontal Span, lx = Vertical Span, lz =

4.00 M 5.16 M

∴lx/lz =

0.78

4/5.16=

Considering total length of wall to be divided equally @ 4.0 M c./c. between Counterforts and a Longitudinal Beam running throughout at the top of wall, the wall panel closely follow case 2 (figure 2) of Chart 53 of page 185 of Reynold's Handbook, freely supported at top edge and fixed at other three sides (Refer "Reinforced Concrete Designer's Handbook", Tenth Edition, Charles E. Reynold & James C. Steedman)

For which,

λ1 =

Coeff. for Maximum -ve Vertical BM at base i.e.at junction of base slab =

Page 2 of 7

0.027


Design of Peripheral Retaining Wall basement for Bus Area at -4.8 λ Coeff. for Maximum +veatVertical BMlevel at around 0.4Parking x Vertical Span = M level: 2=

0.0095

λ3 =

Coeff. for Maximum -ve Horizontal BM at supports for Horizontal Span =

0.033

λ4 =

Coeff. for Maximum +ve Horizontal BM at center of Horizontal Span =

0.015

(Considering no -ve BM at top of Vertical Span allowing top edge beam to rotate) Mx (+ve) =


λ4 x f2 x lx2 =

1.65 T-m/m

Mx (-ve) =

Negative BM for Horizontal Span =

λ3 x f2 x lx2 =

3.63 T-m/m

My (+ve) =

Positive BM for Vertical Span =

λ2 x f2 x lz2 =

1.74 T-m/m

My (-ve) =

Negative BM for Vertical Span =

λ1 x f2 x lz2 =

4.94 T-m/m

Now, considering the bending moments arising due to uniform and triangular laoding are additive irrespective of their position of occurrence, the values of Maximum Bending Moments are: Mx (+ve) =

Positive Maximum BM for Hor. Span =

0.58

+

1.65

=

2.23 T-m/m

Mx (-ve) =

Negative Maximum BM for Hor. Span =

0.75

+

3.63

=

4.38 T-m/m

My (+ve) =

Positive Maximum BM for Ver. Span =

0.38

+

1.74

=

2.12 T-m/m

My (-ve) =

Negative Maximum BM for Ver. Span =

0.51

+

4.94

=

5.46 T-m/m

Now, using Tor steel rebar and considering Asc = As i.e. cross-sectional area of compression rebar is equal to the cross-sectional area of tension rebar and k = d1/d = 0.39/0.45 = 0.87 say

0.85

Where, d1 = effective depth and d = overall depth of wall Now, considering uncracked section for M30 grade of concrete & k = 0.85, the value of M/bd12 = (Refer Table 2.6 (page 15) of "Handbook of Tor Steel Research Foundation" - Design of Water Retaining Structure with Torsteel)

Hence, Effective depth, d1 required per meter length of wall, d1 = deff. =

√(5.46 x 105) / (3.57 x 100) =

39.090 Cm.

Hence, overall depth d, required = 39.09 + 0.8 + 5 = 44.89 Cm. (Considering Maximum dia of reinforcement used as 16 mm and Clear cover of 50 mm) Overall depth provided = 45 Cm., Hence OK, Now, percentage of reinforcement required to be provided = Area of reinforcement required =

100 P

=

0.3

2 11.81 Cm per m

Provide 16 Tor reinforcement @ 160 c/c on both faces of wall vertically at junction of base slab At junction of counterfort and wall, effective depth required = Area of reinforcement required =

√(4.38 x 105) / (3.57 x 100) = 35.037

2 10.58 Cm per m

Provide 16 Tor reinforcement @ 160 c/c on both faces of wall horizontally at junction of counterfort & wall

Page 3 of 7

3.57


Peripheral Retaining Wall at basement level for Bus Parking Area at -4.8 M level: ii) Design of Counterfort (Uncraked Design): Since, the major portion of the counterfort will be in contact with water, the same has been designed based on the principles of uncracked design as per working stress method Considering the total horizontal load on a wall panel to be carried by each counterforts for an effective command area of 4.8 M x 4.0 M, 0.30 Formed Ground Level (EL. +205.50M)

Lateral Pressure on Wall due to Surcharge Load 2 = 1.0 T/m

0.60

0.30

High Flood Level (HFL) (EL. +205.14M)

H1 = 0.36 M Retaining Wall Counterfort Beam

0.45

5.10

H2 = 4.44 M

Β

Β EL. +200.70M

1.0

Fig. 2:

Α 0.42

Α

Lateral Pressure on Wall due to Soil & Water = 6.88 T/m 2

2.0

Basement Slab

Section showing Pressure Diagram for Retaining Wall of Bus Parking Area at -4.8M Level

Maximum Cantilever Moment at Section A - A, = 0.5 x 6.88 x 4.0 x 4.8 x 4.8 / 3 + 1 x 4.0 x 4.8 x 4.8 / 2 =

151.70 T-m/m

Hence, Effective depth, d1 required for Counterfort at Section A - A, d1 = deff. =

√(151.70 x 105) / (3.57 x 75) =

238.024 Cm.

Overall Depth required = 238.024 + 1.25 + 5.0 =

244.3 Cm.

Overall Depth provided =

245.0 Cm.,

2.45 M =

Hence OK

Now, Various pressures at Section B - B, i.e. for H3 = H2 - 1.0 M = = Height of Pressure Diagram below Formed Ground Level

3.44 M 3.80 M

i)

Lateral Pressure on Wall for Saturated Soil

=k0γsatH1=

ii)

Lateral Pressure on Wall for Submerged Soil

=k0γsubH3=

iii)

Lateral Pressure on Wall for Surcharge

=k0q

=

iv)

Lateral Pressure on Wall for Water

=γwH3

=


Now for all practical purposes, there will be two types of combined load cases as follows: 2 Load Case I, Uniform Lateral Pressure due to Surcharge = 1.00 T/M = f1' 2 Load Case II, Linearly varying Lateral Pressure for Soil & Water = 5.41 T/M = f2' Hence, Maximum Cantilever Moment at Section B - B, = 0.5 x 5.41 x 4.0 x 3.8 x 3.8 / 3 + 1 x 4.0 x 3.8 x 3.8 / 2 = Hence, Effective depth, d1 required for Counterfort at Section B - B, d1 = deff. =

√(80.92 x 105) / (3.57 x 75) =

173.85 Cm.

Page 4 of 7

80.92 T-m/m

Document No.ISBT_MAIN_01 RCC DESIGN OF RETAINING WALL (-4.8M) FOR TERMINAL BUILDING OF MAIN ISBT Rev. No. 0 Project Title INTERSTATE BUS TERMINAL, SARAI KALE KHAN, NEW DELHI Institute For Steel Development & Growth Client COMMISSIONER (TRANSPORT), GOVERNMENT OF DELHI ISPAT NIKETAN', 1st. Floor 52 / 1A Ballygunge Circular Road Name of Unit MAIN TERMINAL BUILDING FOR ISBT Kolkata - 700019 Drawing Ref. Designed by: G.C. Checked by: G.C. Approved by: Date: 30.11.06 CALCULATIONS Reference Overall required = 238.024 + 1.0 + 5.0 = level for Bus 179.8 Cm. Area at -4.8 M level: Design Depth of Peripheral Retaining Wall at basement Parking Overall Depth provided =

2.45 M =

245.0 Cm.,

Now, Maximum Shear at Section A - A, VAA = 0.5 x 6.88 x 4.0 x 4.8 + 1.0 x 4.0 x 4.8 =

85.21 T

Maximum Shear at Section B - B, VBB = 0.5 x 5.41 x 4.0 x 3.8 + 1.0 x 4.0 x 3.8 =

56.29 T

Hence OK

Now, reinforcement required for Maximum Bending Moment at Section A - A, Ast. reqd. =

Asc. reqd. = (0.302 x 238.024 x 75)/100

2 53.91 Cm

= 2 4.91 Cm

For 25 dia. Tor reinforcement bar, Area available =

Using 25 dia. Tor reinforcement bar, Numbers required on both faces =

11

and reinforcement required for Maximum Bending Moment at Section B - B, Ast. reqd. =

Asc. reqd. = (0.302 x 173.85 x 75)/100

2 39.38 Cm

=

Using 25 dia. Tor reinforcement bar, Numbers required on both faces =

8

Now, for maximum shear force, VAA at section A - A, 100Ast/bd1 = (100 x 11 x 4.91) / (75 x 238.024) = For which, τc =

0.30255 %

2.46 Kg/Cm2

∴ VCAA = 2.46 x 75 x 238.024 = Hence, VSAA = VAA - VCAA =

43915.5 Kg =

43.92 T

41.29 T =

41289.6 Kg


2 0.79 Cm

∴ Spacing of 10 dia. Tor rebar = (2 x 0.79 x 1500 x 238.024) / 41290 =

13.662

L

Provide 2 , 10 Tor reinforcement bar @ 125 c/c. upto 1.0M height from -4.8M level

Now, for maximum shear force, VBB at section B - B, 100Ast/bd1 = (100 x 8 x 4.91) / (75 x 238.024) = For which, τc =

0.22003 %

2.20 Kg/Cm2

∴ VCBB = 2.20 x 75 x 238.024 =

39274 Kg =

39.27 T

Hence, VSBB = VBB - VCBB =

17.02 T =

17015.6 Kg


2 0.79 Cm

∴ Spacing of 10 dia. Tor rebar = (2 x 0.79 x 1500 x 238.024) / 17016 =

33.153

Provide 2 L , 10 Tor reinforcement bar @ 250 c/c. from -3.8M level to top of counterfort Provide 10 Tor reinforcement bar @ 250 c/c. from -4.8M level as side face reinforcement on both sides

Page 5 of 7


Design of Peripheral Retaining Wall at basement level for Bus Parking Area at -4.8 M level: iii) Design of Horizontal Beam at Top (Cracked Design): Considering the total horizontal freely supported moments are to be effective on each top edge beams, the moment coefficients are as follows: O/A Depth of Beam =

0.5 M,

Width of Beam =

Clear cover to main rebar =

5.0 Cm.,

0.4 M,

Modular Ratio, m =

13.04

λ5 =

Coeff. for Maximum Freely supported vertical Bending Moment =

0.0205

λ6 =

Coeff. for Maximum Freely supported horizontal Bending Moment =

0.0290

Bending Moment due to combined triangular loading: Mx (+ve) =


λ6 x f2 x lx2 =

3.19 T-m/m

α x (+ve) x f1 x lx2 =

0.58 T-m/m

Bending Moment due to uniform loading: Mx (+ve) =


Total +ve Horizontal Bending Moment =

3.77 T-m/m

Now, for maximum vertical Bending Moment which will impart Torsion in the edge beam: Torsional Moment due to combined triangular loading: My (-ve) =

Torsional Moment for Vertical Span =

λ5 x f2 x lz2 =

3.75 T-m/m

α y (-ve) x f1 x lx2 =

0.51 T-m/m

Torsional Moment due to uniform loading: My (-ve) =

Torsional Moment for Vertical Span =

Total Torsional Moment =

4.27 T-m/m

Equivalent Bending Moment = [T x (1 + D/b)]/1.7 = Total Effective Design Bending Moment = Now, effective depth required, d1 reqd. =

5.64 T-m/m

9.41 T-m/m √(9.41 x 105) / (13.04 x 40) =

42.48 Cm.

Considering clear cover of 50 mm and maximum dia of main reinforcemnt as 20 mm and link dia as 6 mm, Overall Depth reqd. = 42.48 + 5.0 + 1.0 + 0.6 = 49.1 Cm. < 50.0 Cm. Hence OK Ast reqd. =

(9.41 x 105) / (2300 x 0.9 x 43.4) =

2 10.48 Cm.

Using 4 Nos. 20 Tor reinforcement bar, total area provided =

2 12.56 Cm.

>

2 10.48 Cm.

Hence OK Since the edge beam is freely supported, Provide nominal Shear Reinforcement, 8 dia. Tor @ 200 c/c. Minimum spacing of shear reinforcement to be provided = (Asv x 0.87 x fy) / (0.4 x b) = Hence OK

Page 6 of 7

22.566 Cm.


Design of Peripheral Retaining Wall at basement level for Bus Parking Area at -4.8 M level: iv) Check for Overturning & Load on piles: Considering overall depth of Pile Cap = For Maximum Overturning Moment at -

1.00 M 5.8 M level,

i)

Lateral Pressure on Wall for Saturated Soil =

k0γsatH1=

ii)

Lateral Pressure on Wall for Submerged Soil =

k0γsub(H2+1)=

iii)

Lateral Pressure on Wall for Surcharge =

k0q

iv)

Lateral Pressure on Wall for Water =

γw(H2+1)

= =


Now for all practical purposes, there will be two types of combined load cases as follows: 2 Load Case I, Uniform Lateral Pressure due to Surcharge = 1.00 T/M = f1'' 2 Load Case II, Linearly varying Lateral Pressure for Soil & Water = 8.35 T/M = f2'' Considering length of Pile Cap = Dia of Pile Cap =

3.20 M, and width of Pile Cap =

0.90 M

600 mm, and Clear edge distance from pile cap =

150 mm

Maximum Overturning Bending Moment: = 0.5 x 8.35 x 4.0 x 5.8 x 5.8 / 3 + 1 x 4.0 x 5.8 x 5.8 / 2 =

254.45 T-m

Balancing Moment, =2x4x4.8x2x2.2 + 0.45x4x5.1x2.5x(0.225+0.75) + 4x2x0.42x2.5x2.2 + 1x3.2x0.9x2.5x1.6 = (Weight of Soil) (Weight of Wall) (Weight of Base Slab) (Weight of Pile Cap) Additional Bending Moment (Couple) to be taken by Piles = Using 2 nos 600 dia piles, lever arm available = Load on each pile= 135.62/2.3 =

+

221.34 T-m

134.90 T-m 2.3 M

58.65 T

Total vertical Load on pile cap, = 2x4x4.8x2 + 0.45x4x5.1x2.5 + 4x2x0.42x2.5 + 1x3.2x0.9x2.5 = Vertical laod on each pile = Maximum Compressive load on pile = Maximum Tensile load on pile =

115.35

57.68 T 116.33 T -0.98 T

(Using 600 dia pile, capacity = 128.5 T) (For 600 dia pile, Tension Capacity = 64.25 T) Hence OK

Page 7 of 7

Retaining Counterfort Wall Design

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