water tank lecture

January 24, 2013 [DESIGN & CONSTRUCTION CONSIDERATIONS OF RC STRUCTURES FOR WATERUTILITIES]

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DESIGN & CONSTRUCTION

CONSIDERATIONS OF

REINFORCED CONCRETE

STRUCTURES FOR WATER

UTILITIES

Prepared byADNAN NAJEM LAZEM

M.Sc. in Structural Engineering

CONTENTS

1. Introduction2. Examples of reinforced concrete structures for water utilities3. Advantages of reinforced concrete structures4. Disadvantages of reinforced concrete structures5. Design considerations6. Construction considerations7. Summary


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INTRODUCTIONIn 1907, Leonard Metcalf, a Boston civil engineer 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 and create an environmental engineering firm calledMetcalf & Eddy.

Wilmington, Delaware 10 million gallon covered water storage tank construction completed at December 2007


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IRAQ, BAGHDAD• Complex of Twin Apartment water storage tanks• Construction completed at march 2010• 375,000 cubic meters storage capacity


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Pile foundation of the RC water tank “Reservoir”

Final Stages of the RC Tank Construct


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ADVANTAGES

1. Easily adaptable to a myriad of different shapes & architectural treatments

2. Many contractors have the capability to place reinforced concrete

3. Reinforced concrete contractor will likely already be on site

4. Durability, Proven track record of over 100 years

DISADVANTAGES

1. Owner preferences may dictate against using reinforced concrete

2. Cost considerations due to quantity of materials required

3. Construction nuances

4. Cracking & durability

DESIGN CONSIDERATIONS

1. Seismic loads

2. Floatation

3. Abnormal pressure loads

4. Retaining elements

5. Influence of adjacent / superimposed structures

6. Integration into existing facilities

7. Security

8. Details, Details, Details!

9. Liner systems

SEISMIC LOADS

According to ACI 350 in chapter four Art (4.1), for Earthquake pressures above base,

the walls of liquid-containing structures shall be designed for the following dynamic forces in

addition to the static pressures:

a. inertia forces Pw and Pr ;

b. hydrodynamic impulsive pressure Pi from the contained liquid;

c. hydrodynamic convective pressure Pc from the contained liquid;

d. dynamic earth pressure from saturated and unsaturated soils against the

buried portion of the wall;

e. the effects of vertical acceleration.


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BUOYANCY

A reinforced concrete reservoir – or any tank – is a boat. A boat floats if designed

Right. Therefore a design checks is required:

1. Buoyant force (uplift) on bottom slab

2. Buoyant force causing tank to float

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

SECURITY

Any reservoir requires security considerations.

1. How will the reservoir be inspected?

2. How will venting be accomplished?

3. Will public access be required of the top slab?

DETAILS

1. Minimum Concrete Strength

2. Minimum Reinforcing Steel

3. Expansion and Construction Joints

4. Waterstops

MINIMUM “ACI.350 CODE” REQUIREMENT:

1. Min. Concrete Strength=4000 psiat 28 days

2. Air Entrainment=5%±1%

3. Maximum Water-cement Ratio=.45

4. Maximum Slump=4 inches

5. Aggregates per ASTM C33, max. aggregate size=1 inch

6. No admixtures containing calcium chloride

EXPANSION JOINTS:


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Expansion joints, main location.


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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

CONSTRUCTION CONSIDERATIONS

Proper adherence to specifications

1. Water proofing process

2. Mix design

3. Placement

4. Curing

5. Deflection of structural members during pouring and vibrating of fresh concrete

6. Details, Details, Details

7. Integration into existing Facilities


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Step 1, Water proofing process

Step 2, Water proofing process


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Placement of fresh concrete

MIX DESIGN

Adding 1 gallon of water to 1 yd3 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 concrete


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Deflection of structural members during construction:

CURING

According to ACI 350-01 “Environmental Structures” Code Requirements:

“Minimum permeability of the concrete will be obtained by using water-cementitious

materials ratios as low as possible, consistent with satisfactory workability and

consolidation. Impermeability increases with the age of the concrete and is improved by

extended periods of moist curing.”

Plastic membrane and water retaining agent were used for curing process


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MINIMUM CONCRETE COVER OF STEEL REINFORCEMENT:

Checking of Minimum Concrete Cover according to ACI 350.1:

1. Concrete Base=3 inches (4” COE)

2. Concrete Walls=2 inches (3” COE)

3. Stilling Basin=6” (COE)

Checking first carried out before Pouring of fresh concrete

LEAK TESTINGAccording to ACI 350-01 “Environmental Structures” Code Requirements:

1.1.3—Each cell of multi-cell tanks shall be considered a single tank and testedindividually unless otherwise directed by the engineer.

1.2.3—Unless specifically allowed by the engineer, the tank shall not be tested before allof the structure is complete and the tank’s concrete has attained its specifiedcompressive strength.

2.3.5—The water shall be kept at the test level of unlined concrete tanks for at least threedays prior to the actual test.

2.3.6—The exterior surfaces of the tank shall be inspected during the period of filling thetank. If any flow of water is observed from the tank exterior surfaces, includingjoints or cracks, the defect causing the leakage shall be repaired.


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BACKFILLINGBackfill and compaction continues as dump trucks haul dirt in and a skid steer and

dozer spread the backfill into eight-inch lifts for compaction.

SUMMARY

1. Engineer helps the owner determine best structural system for the facility.

2. Proper engineer detailing is a major contributor to the long-term success of the

project.

3. Proper concrete mix design, placement, and curing practices is the single most

important factor toward the long-term durability of the structure.

4. Reinforced concrete is not a “forever” material. It requires on-going care and

maintenance. A well-defined asset management program will contribute to the

long-term operation of the structure.

REFRENCE:

1. Maine Water Utilities Association April 12, 2007. Michael E. Malenfant, P.E. Metcalf &

Eddy

2. ACI 350-01 “Environmental Structures” Code Requirements.

3. University of technology, engineering consulting office. Baghdad, Iraq.

water tank lecture

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construction nuances4

design considerations6

design checks

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