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Design and Construction Considerations of

Reinforced Concrete Structures for Water

Utilities

April 12, 20

DESIGN & CONSTRUCTION

CONSIDERATIONS OF

REINFORCED CONCRETESTRUCTURES FOR WATER

UTILITIES

Maine Water Utilities Association

Apr il 12, 2007

Michael E. Malenfant, P.E.

Metcalf & Eddy

2

CONTENTS

• Introduction

• Examples of reinforced concrete

structures for water utilities

• Advantages of reinforced concrete

structures

• Disadvantages of reinforced

concrete structures

• Design considerations

• Construction considerations

• Summary

3

INTRODUCTION

• In 1907, Leonard Metcalf, a Boston civilengineer whose specialty was water supply

issues, and Harrison Eddy, superintendent of

the sewer department in Worcester,Massachusetts, were introduced by a

professor at Worcester Polytechnic. Shortlythereafter, they decided to join forces andcreate an environmental engineering firm

called Metcalf & Eddy.





Utilities

April 12, 20

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Wilmington, Delaware

•10 million galloncovered waterstorage tank

•Underconstruction,

completionDecember 2007

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6





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Atlanta, Georgia

•Complex ofthree coveredwater storagetanks

•Age from 10years to 80

years

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Framingham, Massachusetts

•115 million gallon covered water storage tank





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Macon, Georgia

•1.8 million gallonpartially buried

covered water

storage tank

•Constructed in1920





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ADVANTAGES

• Easily adaptable to a myriad of different

shapes & architectural treatments• Many contractors have the capability to place

reinforced concrete

• Reinforced concrete contractor will likelyalready be on site

• Durability

• Proven track record of over 100 years

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DISADVANTAGES

• Owner preferences may dictate against usingreinforced concrete

• Cost considerations due to quantity ofmaterials required

• Construction nuances

• Cracking & durability

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DESIGN CONSIDERATIONS

• Seismic loads

• Floatation

• Abnormal pressure loads

• Retaining elements• Influence of adjacent / superimposed structures

• Integration into existing facilities

• Security

• Details, Details, Details!

• Liner systems





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SEISMIC LOADS

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SEISMIC LOADS

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SEISMIC LOADS





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SEISMIC LOADS

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SEISMIC LOADS

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BUOYANCY

Permission is granted to copy, distribute and/or modify this document under the terms of the GNU FreeDocumentation License, Version 1.2 or any later version published by the Free Software Foundation. Photo by

Sean O'Flaherty





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BUOYANCY

• A reinforced concrete reservoir – or any

tank – is a boat. A boat floats if designedright!

• Design checks required: – Buoyant force (uplift) on bottom slab

– Buoyant force causing tank to float

– Reduced base slab friction if tank sliding(uneven backfill) is a design consideration

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SECURITY

• Any reservoir requires security

considerations.

– How will the reservoir be inspected?

– How will venting be accomplished?

– Will public access be required of the top slab?

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DETAILS

• Minimum Concrete Strength

• Minimum Reinforcing Steel

• Expansion and Construction Joints

• Waterstops





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EXPANSION JOINTS

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EXPANSION JOINTS

GOOD LOCATION

BAD LOCATION

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CONSTRUCTION JOINTS





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WATERSTOP DETAIL

Base slab to wall interface is most critical and most

difficult to construct of all construction joints:

1. Raised starter wall

2. Bend top steel down at wall

3. Drop top steel down below waterstop for

entire slab

Options 2 & 3 easier to construct than option

1 but require relatively more material

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WATERSTOP DETAIL

Option 1

Option 3

Option 2

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WATERSTOP DETAIL





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CONSTRUCTION CONSIDERATIONS

Proper adherence to

specifications

– Mix design

– Placement

– Curing

• Details, Details, Details

• Integration into existing

facilities

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MIX DESIGN Add ing 1 gallon o f water to 1 yd 3 of concrete will:

1. Increase slump about 1 inch

2. Increase air content about 1%

3. Increase shrinkage about 10% and increase cracking

4. Reduce compressive strength about 200 psi

5. Waste about 25 lbs of cement per cubic yard

6. Increase shrinkage about 10% and increase cracking

7. Decrease freeze-thaw durability about 20%

8. Decrease wear resistance to traffic

9. Increase dusting and other surface defects

10.Increase time needed to finish the concreteSource: Dick Martin, Engineering Services Group, Grace Performance

Chemicals.

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CURING

“Minimum permeability of the concrete will be

obtained by using water-cementitious materials

ratios as low as possible, consistent withsatisfactory workability and consolidation.

Impermeability increases with the age of theconcrete and is improved by extended periodsof moist curing.”

Source: ACI 350-01.

Environmental Structures: Code

Requirements





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CURING

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DETAILS

• Waterstops & joint construction

• Rebar cover

• Leak testing

• Backfilling procedure

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WATERSTOPS





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WATERSTOPS

VS.

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REINFORCING STEEL COVER

Source: ACI 350-01.

Environmental Structures:

Code Requirements

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LEAK TESTING

Source: ACI 350.1-01. Tightness Testing o f

Environmental Engineering Concrete Structures

1.2.3 —Unless specifically allowed by the

engineer, the tank shall not be tested

before all of the structure is complete and

the tank’s concrete has attained its

specified compressive strength.

1.1.3 —Each cell of multi-cell tanks shall

be considered a single tank and tested

individually unless otherwise directed by

the engineer.

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LEAK TESTING

Source: ACI 350.1-01. Tightness Testing of

Environmental Engineering Concrete Structures

2.3.5 —The water shall be kept at the test

level of unlined concrete tanks for at least

three days prior to the actual test.

2.3.6 —The exterior surfaces of the tank shall be

inspected during the period of filling the tank. If

any flow of water is observed from the tank

exterior surfaces, including joints or cracks, the

defect causing the leakage shall be repaired.





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BACKFILLING

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SUMMARY

• Engineer helps the ownerdetermine best structuralsystem for the facility.

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SUMMARY

• Proper engineer detailing is a major contributorto the long-term success of the project.





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SUMMARY

• Proper concrete mix

design, placement,and curing practicesis the single mostimportant factor

toward the long-termdurability of thestructure.

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SUMMARY

• Reinforced concrete is not a “forever” material.It requires on-going care and maintenance. Awell-defined asset management program willcontribute to the long-term operation of thestructure.

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SUMMARY

The answer to the question of “What

material best suits my project?” is:

“Please tell me a little more aboutyour project.”

Michael E. Malenfant, P.E.

Metcalf & Eddy

[email protected]

781-224-6277

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