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Analysis, Design, and Construction Practices in Environmental Engineering

Concrete Structures, Part 1 of 2

ACI Fall 2010 ConventionOctober 24 - 28, Pittsburgh, PA

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Analysis, Design, and Construction Practices in Environmental Engineering

Concrete Structures, Part 1 of 2

ACI Fall 2010 ConventionOctober 24 - 28, Pittsburgh, PA

ACI Fellow Charles Hanskat is Managing Principal at Concrete Engineering Group, LLC, a firm he founded in 2008 located in Northbrook, Illinois. He is a licensed professional engineer in 22 states. Mr. Hanskat has been involved the design, construction, and evaluation of environ-mental concrete and shotcrete structures for

nearly 35 years. He is an active voting member of many ACI technical and Board committees. He is also a Board member on the American Shotcrete Association (ASA) and chair of the ASA Sustainability Committee. He has served on AWWA technical committees developing standards for prestressed concrete for over 25 years. He holds a Bachelor's and Master's degree in Civil Engineering from the University of Florida.

Charles Hanskat, PrincipalConcrete Engineering Group, LLC

EECS are large structures

Carry very high loads over large areas

Loads are vertical and horizontal

Structures are expected to be liquid‐tight

Contents can be aggressive

Environment can be aggressive

Under all expected environmental exposures and loading conditions the structure will remain essentially liquid‐tight and maintain its full structural integrity for 50 to 100 years.

The structure will do this with minimal maintenance.

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Introduction and General Commentary

Chapter 3 – Materials

Chapter 4 – Durability Requirements

Chapter 7 – Details of Reinforcement

Chapter 9 – Strength and Serviceability

Chapter 10 – Flexure and Axial Loads

Chapter 14 – Walls

Chapter 18 – Prestressed Concrete

The liquid‐tightness of a structure will be reasonably assured when:

The concrete mixture is well proportioned, well consolidated without segregation, and properly cured.

Crack widths and depths are minimized.

Joints are properly spaced, sized, designated, water‐stopped, and constructed.

Adequate reinforcing steel is provided, properly detailed, fabricated, and placed.

Impervious protective coatings or barriers are used where required.

For minimum permeability of concrete use:

Low water‐cementitious materials ratio

Extended periods of moist curing

Smooth forms or troweling

Pozzolans may also reduce permeability

For increased workability and improved consolidation consider using:

Water‐reducing agents

Pozzolans

Air entrainment

Reduces segregation and bleeding

Resistance to the effect of freeze‐thaw cycles

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General standards for materials of construction

Where aggregates are alkali‐reactive, impose restrictions on materials to minimize deterioration

Do not use admixtures containing chlorides

Water‐cementitious materials ratio

Cementitious content

Cement type

Minimum compressive strength

Use of pozzolans

Air entrainment

Chloride ion content

Chemical effects

Erosion

Coatings and liners

Leakage control at joints

Minimum Cementitious Material Content

Nominal Maximum Aggregate Size, in.

Coarse Aggregate (ASTM C 33) Size No.

Minimum Cementitious Materials (lb/yd3)

1‐1/2 467 515

1 57 535

3/4 67 560

1/2 7 580

3/8 8 600

Total Air Content for Frost‐Resistant Concrete

Nominal Maximum Aggregate Size, in.

Air Content, percent

Severe Exposure Moderate Exposure

3/8 7‐1/2 6

1/2 7 5‐1/2

3/4 6 5

1 6 4‐1/2

1‐1/2 5‐1/2 4‐1/2

2 5 4

3 4‐1/2 3‐1/2

Other benefits of air entrainment:

Improves workability and consolidation

Reduces segregation and bleeding

Reduces permeability

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Special Exposure Conditions

Exposure ConditionMax. w/cm

RatioMin. fc’,

psi

Concrete w/ low permeability exposed to water, wastewater, and corrosive gases

0.45 4,000

Concrete exposed to freezing and thawing in a saturated condition or to deicing chemicals

0.42 4,500

Corrosion protection of reinforcement in concrete exposed to chlorides

0.40 5,000

Requirements for Concrete

Exposed to Deicing Chemicals

Cementitious Materials Maximum % of Total Cementitious Materials

Fly ash or other pozzolans conforming to ASTM C 618

25

Slag conforming to ASTM C 989 50

Silica fume conforming to ASTM C 1240 10

Total of fly ash or other pozzolans, slag, and silica fume

50

Total of fly ash or other pozzolans and silica fume 35

Benefits of pozzolans:

Improve workability and consolidation

Reduce permeability

Improve sulfate resistance

Improve resistance to alkali reactivity with aggregates

Concrete Exposed to Sulfate‐Containing Solutions

Sulfate Exposure

Water Soluble Sulfate in soil (%)

Sulfate in water, ppm

Cement Type

Maximum w/cm

Specified Compressive Strength fc’ psi

Negligible 0.00‐0.10 0‐150 ‐ 0.45 ‐

Moderate 0.10‐0.20 150‐1,500

II, IP(MS), IS(MS),

I(PM)(MS), I(SM)(MS)

0.42 4,500

Severe 0.20‐2.00 1,500‐10,000

V 0.40 5,000

Very Severe

Over 2.00 Over 10,000

V plus pozzolan

0.40 5,000

Use ASTM C1012 to test for sulfate resistance of mixtures using SCMs.

Other considerations for sulfate resistance:

Adequate cover of reinforcement

Sufficient moist curing

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Comparison of Durability Requirements

Condition

ACI 318‐08 ACI 350‐06

w/cm f’c w/cm f’c

Low permeability (P1) 0.50 4,000 0.45 4,000

Freeze/thaw in moist condition (F2)

0.45 4,500 0.42 4,500

Moderate sulfate exposure (S1)

0.50 4,000 0.42 4,500

Maximum Chloride Ion Content for

Corrosion Protection of Reinforcement

Type of MemberMaximum Water Soluble Chloride Ion in Concrete,

% by wgt cement

Prestressed concrete 0.06

Reinforced concrete 0.10

Common metals used:

Aluminum

Stainless Steel (Type 316)

Galvanized Steel

Epoxy Coated Steel

Aluminum stair with carbon steel bolts

Steel connection to concrete wall

Cast iron hatch cover

Chemical Exposure Groupings

Group 1

Not considered harmful to concrete

May be desired to prevent the absorption of liquids into the concrete

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Group 2

Will stain concrete

Where appearance is a concern

Group 3

Attack and weaken concrete

Generally require a protective lining

Group 3 ‐ Three subgroups:

Group 3A – Slow Attack of Concrete

Group 3B – Attack of Concrete

Group 3C – Rapid Attack of Concrete

Corrosive Gases:

Hydrogen Sulfide

Chlorine

Ozone

Oxygen

Carbon Dioxide

Methane

Hydrogen sulfide attack at cast iron gate

and manhole rungs

Hydrogen sulfide corrosion at concrete

surfaces

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Corrosion and coating failure at clarifier launders

Minimum f’c = 5,000 psi

Maximum w/cm ratio = 0.40

Maximum air content = 6 percent

Minimum 610 lbs cm/cy of concrete

Hard, dense, clean aggregates

Severe exposure to chemicals or gases

External waterproofing

Crack bridging capability

NSF compliance for potable water

Vapor transmission – breathable vs. vapor barrier

Coatings vs. plastic linings

ACI 515.1R

"Effects of Substances on Concrete Guide to Protective Treatments," Portland Cement Association

"Evaluation of Protective Coatings for Concrete," County Sanitation Districts of Los Angeles County

Coating deterioration

Waterstops

Joint sealants

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Expansion joint with steel rail across joint

Concrete cover requirements – increased relative to ACI 318

Shrinkage reinforcement requirements

Maximum spacing of reinforcement is 12 inches

Exposed rebar –insufficient cover Damage due to

leakage through cracks

Shrinkage cracks

Environmental Durability Factor (EDF), "Sd":

Limits steel stresses at service load levels

Reduces tension cracking

Improves liquid‐tightness

Improves corrosion protection and durability

Normal Environmental Exposure:

pH greater than 5

Sulfate exposure less than 1,000 ppm

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Sd = 1.0 for all prestressed reinforcement

Why don't EDFs apply to prestressing?

Concrete is precompressed

Stress in prestressed reinforcement is not directly related to concrete cracking

A minimum residual compressive stress 125 psi is required for liquid‐containing elements

Corrosion protection for unbonded single‐strand prestressing tendons

Unbonded prestressing steel shall be completely encased with sheathing

Sheathing shall be liquid-tight and continuous over entire length

Sheathing shall meet the hydrostatic pressure testing requirements of ACI 423.6 with a hydrostatic pressure of 10 psi

Tendons shall be protected against corrosion in accordance with ACI 423.6, as required for “aggressive environments”

ACI 350.4R, Guideline for the Design of Environmental Engineering Concrete Structures

Satish Sachdev, Chair of the subcommittee ACI-350A, General and Concrete, retired as President and CEO of Klein and Hoffman, Inc. in January 2006 after serving the firm for 36 years, and is currently working in the firm as a senior consultant. Klein and Hoffman, Inc. is a consulting structural engineering firm head-

quartered in Chicago, IL. One of its main businesses is consulting for water and wastewater projects. Mr. Sachdev was chairman of the committee ACI-350, Environmental Engineering Concrete Structures, for 7 years, an ACI member for more than 30 years,was elected Fellow of the Institute in 2007, and received Delmar L. Bloem Award of the Institute, in 2008. He received his B.Sc. in civil engineering from Panjab University in India, and his M.Sc. in civil engineering from University of Wisconsin at Madison.

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cag107sem1-aci350(Draft 9-final).ppt/61

Design Considerations• Rectangular Tanks• Circular Tanks

By Satish Sachdev, FACI, S.E., P.E.


Rectangular Tank Configurations

• Cantilever Wall• Wall and strut• Covered Tank (with Roof)


Cantilever Wall

4' WIDE CATWALK ALL AROUND

A

A


Cantilever Wall

Section A-A

WALL THICKNESS:

L /10 = 16 /10 = 1.6 ft = 19.2 in

Wall Thickness > 12 in

Select Wall Thickness = 20 in


Wall and Strut

4' WIDE CATWALK ALL AROUND

A Strut

A

B B


Wall and Strut

Section A-A Section B-B

WALL THICKNESS:Wall Thickness = L/24 = 8 in

Wall Thickness > 12 inSelect Wall Thickness = 12 in

Strut depth = L / 18.5 40 / 18.5 = 2.16 ft = 25.94 in.

Select strut depth = 30 in.

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Covered Tank


Covered Tank

S ec tion A -A S ec tio n B -B

Slab Thickness= L / 24 (one-end continuous)25 / 24 = 1.04 ft. = 12.5 in.

Select slab thickness= 12 in. Deflections are not expected to be significant


Analysis: Concerns

• For cantilever wall, the end walls could act as two-way slab

• Near the junction of the two walls, the vertical moments gradually diminish

• For wall and strut, the response could be different at strut locations in comparison with other locations along the wall

• For covered tank, the roof-wall interaction need to be considered

• The finite element method (FEM) is used to consider the above effects


FEM- Cantilever Wall

Expansion Joint


FEM- Wall and Strut

Expansion Joint


FEM- Covered Tank

Expansion Joint

2/4/2011

13


Response

Zone 1 Zone 2 Zone 3 Zone 4 Zone 5

Expansion Joint


Zone 1- Near Expansion Joint

0

4

8

12

16

0.00 0.05 0.10 0.15

Displacement (in)

He

igh

t (f

t)

Cantilever Wall Wall and Strut Covered Tank

0

4

8

12

16

-45 -30 -15 0 15

Bending Moment (kip-ft/ft)

He

igh

t (f

t)



Zone 2- Middle of Long Wall Between Strut Locations

0

4

8

12

16

0.00 0.05 0.10 0.15

Displacement (in)

He

igh

t (f

t)


0

4

8

12

16

-45 -30 -15 0 15


He

igh

t (f

t)



Zone 3- Middle of Long Wall at Strut Locations

0

4

8

12

16

0.00 0.05 0.10 0.15

Displacement (in)

He

igh

t (f

t)


0

4

8

12

16

-45 -30 -15 0 15


He

igh

t (f

t)



Zone 4- Last Strut Location, Near End Wall

0

4

8

12

16

0.00 0.05 0.10 0.15

Displacement (in)

He

igh

t (f

t)


0

4

8

12

16

-45 -30 -15 0 15


He

igh

t (f

t)



Zone 5- Near End Wall

0

4

8

12

16

0.00 0.05 0.10 0.15

Displacement (in)

He

igh

t (f

t)


0

4

8

12

16

-45 -30 -15 0 15


He

igh

t (f

t)


2/4/2011

14


Response

Zone 6 Zone 7

ExpansionJoint


Zone 6 – Middle of End Wall

0

4

8

12

16

0.00 0.05 0.10 0.15

Displacement (in)

He

igh

t (f

t)


0

4

8

12

16

-45 -30 -15 0 15


He

igh

t (f

t)



Zone 7- End Wall - Corner

0

4

8

12

16

0.00 0.05 0.10 0.15

Displacement (in)

He

igh

t (f

t)


0

4

8

12

16

-45 -30 -15 0 15


He

igh

t (f

t)



Summary of Results:Bending Moment

Zone

Cantilever Wall & Strut Covered Tank

-ve +ve -ve +ve -ve +ve

1 43.2 - 15.3 8.1 22.6 17.8

2 42.6 - 15.8 7.2 20.8 13.6

3 42.8 - 15.3 8.1 21 16.5

4 36.3 1.1 15.3 8.1 20 11.3

5 9.1 0.7 6.3 3.4 7.5 3.6

6 23.4 5.2 20.7 6.1 17.2 10.1

7 8.8 2.0 8.0 2.6 7.4 3.6


Beam Analysis

0

4

8

12

16

0.00 0.05 0.10 0.15

Displacement (in)

Hei

gh

t (f

t)

Free End Pinned End Fixed End

0

4

8

12

16

-45 -30 -15 0 15


Hei

gh

t (f

t)

Free End Pinned End Fixed End


Beam Analysis

Maximum Bending Moment (kip-ft/ft)

+ve -ve

Cantilever - 42.6

Fixed-Fixed 0.7 12.7

Fixed-Pinned 5.3 16.9

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Cantilever Wall- Frame vs FEM

Zone 1 Zone 2 Zone 3

ExpansionJoint


Zone 1- End Near Exp. Joint

0

4

8

12

16

0.00 0.05 0.10 0.15

Displacement (in)

He

igh

t (f

t)

Shell Beam

0

4

8

12

16

-45 -30 -15 0 15


He

igh

t (f

t)

Shell Beam


Zone 2 -Middle

0

4

8

12

16

0.00 0.05 0.10 0.15

Displacement (in)

He

igh

t (f

t)

Shell Beam

0

4

8

12

16

-45 -30 -15 0 15


He

igh

t (f

t)

Shell Beam


Zone 3 – Near End Wall

0

4

8

12

16

0.00 0.05 0.10 0.15

Displacement (in)

He

igh

t (f

t)

Shell Beam

0

4

8

12

16

-45 -30 -15 0 15


He

igh

t (f

t)

Shell Beam


Cantilever Wall- Frame vs FEM

Zone 4 Zone 5

ExpansionJoint


Zone 4 – Middle of End Wall

0

4

8

12

16

0.00 0.05 0.10 0.15

Displacement (in)

He

igh

t (f

t)

Shell Beam

0

4

8

12

16

-45 -30 -15 0 15


He

igh

t (f

t)

Shell Beam

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Zone 5 –End Wall Near Middle Wall

0

4

8

12

16

0.00 0.05 0.10 0.15

Displacement (in)

He

igh

t (f

t)

Shell Beam

0

4

8

12

16

-45 -30 -15 0 15


He

igh

t (f

t)

Shell Beam


Zone 1

Wall and Strut- Frame vs FEM

Zone 1


Zone 1 – At Strut Location

0

4

8

12

16

0.00 0.05 0.10 0.15

Displacement (in)

He

igh

t (f

t)

Shell Frame

0

4

8

12

16

-45 -30 -15 0 15


He

igh

t (f

t)

Shell Frame


Notes

• Aspect ratio of the tank wall affects the response

• Two-way reinforcement of the wall end where it frames into another wall is necessary

• For covered tank, frame analysis using a 1 ft strip of the tank is appropriate


Design Parameters

f’c = 4500 psi fy = 60 ksi

b =12 in h =20 in

γ (Load Factor) =1.4

Φ = 0.9 (Flexure) Φ = 0.75 (Shear)

M= 43.2 kip-ft/ft V=6 kip/ft

Assume Normal Exposure

Design of Cantilever Wall


Design of Cantilever Wall: Flexure

• Assume bar spacing = 8 in at wall base and bar diameter = 1 in.

• fsmax = 28.27 ksi for β=1.2

• Sd = 1.36• Mu = 1.4 x 1.36 x 43.2 = 82.2 kip-ft/ft

22max)2/2(4

320

b

sds

f

s

y

d f

fs

2/4/2011

17


• ρ = 0.0055

• ρb = 0.0311 ρ < 0.7 ρb o.k.

• ρmin =0.0033 ρ > ρmin O.K.

• ρtemp = 0.005 (on two faces), ρ > ρtemp o.k.

• As = 1.12 in2/ft

)200

;'3

(maxminyy

c

ff

f

Design of Cantilever Wall: Flexure


• Vu = 1.4 x 6 = 8.4 kip/ft

• Vc = 27.4 kip/ft

• φVn = 0.75 x 27.4 = 20.5 kip/ft

• φVn > Vu O.K.

bdfV cc '2

Design of Cantilever Wall: Shear


Circular Tank


Notation

D = Inside diameter of tank in feet

dw = Effective depth of wall

FEM = Finite element method

HW = Wall height in feet

HL = Liquid height in feet

tW = Wall thickness in inches

TW = Tension in wall in kips per foot of wall height

TF = Tension in footing

VW = Wall base shear in kips per foot of wall length

MIF = Wall moment in vertical direction in interior face


• D = 120 feet

• HL = 12 feet (all cases)

• HW = 12 feet or 15 feet

• tW = 14 inches

• No roof

• Similar to large circular clarifier

• Severe exposure

Tank Parameters


• Fixity of footing usually not known accurately

• Design for worse case of: Pinned base

Fixed base

Wall

Slab

Wall Footing

Base Fixity

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18


• PCA table method Water height must equal wall height

Overly conservative if wall height exceeds water height

Does not consider launder effect

Does not consider openings in wall

Limited parameter range

Easy, fast, and cheap

Task Analysis Methods


• Finite element method Can be used for wide range of parameters

Time consuming and expensive

Water height may be less than wall height

Opening effects can be included in design

Launder effects can be included in design

Task Analysis Methods (cont.)


PCA Table Analysis Method (cont.)


Finite Element Model

FEM Program Used - STAAD PRO 2006

Number of surface elements - 4,914

Number of nodes - 4,536

Mesh size - 1 ft. x 1 ft.


Hydrostatic Load

120’

CASE 1

HW=12’, HL=12’, and tW=14”

Finite Element Model (cont.)


CASE 2

HW=15’, HL=12’, and tW=14”

Hydrostatic Load

120’


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CASE 3HW=15’, HL=12’, tW=14”, and Launder (12” thick)

Hydrostatic Load

120’

Launder 3’

3’

3’


0123456789

10111213141516

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14Unfactored Hoop tension (kips / ft)

Hei

ght (

ft)

PCA Table - Case 1

FEM Method - Case 1

FEM Method - Case 2

FEM Method - Case 3

Hoop Tension – Fixed BaseCASE 1

(HW=HL)

CASE 2

(HW>HL)

CASE 3

(with Launder)

Comparison of Hoop Tension

0123456789

10111213141516

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19Unfactored Hoop Tension (kips / ft)

Hei

ght (

ft)

PCA Table - Case 1

FEM Method - Case 1

FEM Method - Case 2

FEM Method - Case 3

Hoop Tension – Pinned BaseCASE 1

(HW=HL)

CASE 2

(HW>HL)

CASE 3

(with Launder)

Comparison of Hoop Tension (cont.)

Moment – Fixed BaseCASE 1

(HW=HL)

CASE 2

(HW>HL)

CASE 3

(with Launder)

0123456789

10111213141516

-8 -7 -6 -5 -4 -3 -2 -1 0 1 2 3Moment (ft-kips/ft)

Hei

ght (

ft)

PCA Table - Case 1FEM Method - Case 1FEM Method - Case 2FEM Method - Case 3

Comparison of Moment

Moment – Pinned BaseCASE 1

(HW=HL)

CASE 2

(HW>HL)

CASE 3

(with Launder)

0123456789

10111213141516

0 1 2 3 4 5Moment (ft-kips/ft)

Hei

ght (

ft)

PCA Table - Case 1FEM Method - Case 1FEM Method - Case 2FEM Method - Case 3

Comparison of Moment (cont.)

CASE 2

(HW>HL)

0123456789

10111213141516

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14Unfactored Hoop Tension (kips / ft)

Hei

ght (

ft)

Fixed BasePinned Base

Combined Hoop TensionDiagrams Used for Design

2/4/2011

20

Combined MomentDiagrams Used for Design

CASE 2

(HW>HL)

0123456789

10111213141516

-7 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5Unfactored Vertical Moment (ft-kips / ft)

Hei

ght (

ft)

Fixed basePinned Base


CASE 2: Reinforcement –Hoop Tension in Wall

TW = 12.8 kips (from FEM analysis)

Tu = 1.4 TW

Tu = 17.9 kips

In severe environmental exposure areas

fs = 17 ksi

Factored hoop tension in wall

Environmental durability factor

= 0.9 (tension-controlled section)

fy = 60 ksi

= 1.4

fsSd = 2.27

fySd =


CASE 2: Reinforcement –Hoop Tension in Wall (cont.)

TU = Sd Tu

Ultimate hoop tension in wall with environmental durability factor

TU = 40.6 kips

As, min = 0.005 (tw12 in)

As, min = 0.84 in2

Provide #6 @ 12 in EF.

As = 0.88 in2

Minimum horizontal reinforcement


CASE 2: Reinforcement –Hoop Tension in Wall (cont.)

Reinforcement for hoop tensionTU

fyAs = 0.75 in2

Provide #6 @ 12" EF as hoop reinforcement.

As = 0.88 in2

Actual stress in reinforcement due to hoop tension

TW

Asf = 14.5 ksi

= 0.856 (less than 1.0, hence, ok)fs

As =

f =

f

#6 @ 12” EF

=12.8 kips

0.88 in2


CASE 2: Reinforcement –Moment in Wall

MIF = 6.3 ft-kips (from FEM analysis)

Mu = 1.4 MIF

Mu = 8.82 ft-kips

= 1.35 (wall thickness is less than 16 in)

Try #6 reinforcing bar.

db = 0.75 in

s = 12 in (12 in max bar spacing)

Factored moment in wall


Durability factor


fy = 60 ksi

= 1.4 (load factor)

fs = 17 ksi

For severe environmental exposure260

s2 + 4(2 + db/2)2

fs = 14.9 ksi

Need not be less than 17 ksi for one-way and 20 ksi for two-way members. Therefore use fs = 17 ksi.

fs =

CASE 2: Reinforcement –Moment in Wall (cont.)

2/4/2011

21


fy

fsSd = 2.27

Ultimate moment in interior face

MU = Sd Mu

MU = 20.0 ft-kips

Sd =

Reinforcement calculation

tw = 14 in

dw = tw - 3 in

dw = 11 in



Reinforcement calculation

= Asfy (d - )Mu

a = 1.47 As

a

2

= (As) (60 ) (11 - )(20.0)(12)

0.9

1.47 As

2

As = 0.42 in2

Asfy

0.85 ba =

(As) (60)

(0.85) (4) (12)a =

fc



#6 @ 12” EF

Minimum vertical reinforcement for flexural members

As, min 3 fc bwdw

fy 0.42 in2

As, min 200 bwdw

fy 0.44 in2

Use min #6 @ 12 in.#6 @ 12” EF

LapSplice



Resisted byHoop tension reinforcement in footingRadial tension in slab

FormulaReaction at the bottom of wall, VW = 1.7 kips/ft (from FEM analysis)

Diameter of tank, D = 120 ft

TF =2

TF = 2

TF = 102 kips

VW D

(1.7 kips/ft) (120 ft)

Hoop Tension in Wall Footing


Factored tension in footing

TF = 102 kips

Tu = 1.4 TF

Tu = 143 kips

In severe environmental exposure areas

fs = 17 ksi

CASE 2: Reinforcement –Tension in Wall Footing


Durability factor


= 1.4

Sd = fy

fs

Sd = 2.27

Ultimate hoop tension in footing with environmental durability factor

TU = 324 kips

TU = SdTu

CASE 2: Reinforcement –Tension in Wall Footing (cont.)

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Reinforcement for hoop tension

As =TU

fy

As = 6.00 in2

Provide 6 - #7 @ T&B of footing.

As = 7.2 in2

Calculated stress in reinforcementdue to hoop tension

f =Tf

As

f = 14.2 ksi fs

f= 0.833 (less than 1.0; hence, ok)

6 - #7 T&B

CASE 2: Reinforcement –Tension in Wall Footing (cont.)


Hoop Tension Reinforcing Bars Wall

Treble Stagger of Reinforcing Bar Splices

Class "B" Lap Splice

Staggering of Hoop Tension Wall Bars


Add Bars

Wall

Wall Footing

Outlet Opening in Wall


• Thick slab may be required• Slab may crank large moments into wall• Unless slab weight exceeds uplift, must control

slab deflection• Thick slab required to take advantage of soil on

footing extension

Groundwater

Groundwater Uplift


Acknowledgement

The Following Committee Members contributed to the Presentation:

1. M. Reza Kianoush, Ph.D., P.Eng.

2. Carl Gentry, M.Sc., S.E., P.E.

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Commentary 350.4R-04: Design Considerations for Environmental Engineering Concrete

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