water tank-lecture
TRANSCRIPT
January 24, 2013[
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DESIGN & CONSTRUCTIONCONSIDERATIONS OF
REINFORCED CONCRETESTRUCTURES 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. Shortly thereafter, they decided to join forces and create an environmental engineering firm called Metcalf & 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”
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Final Stages of the RC Tank Construct
ADVANTAGES1. Easily adaptable to a myriad of different shapes & architectural treatments 2. Many contractors have the capability to place reinforced concrete3. Reinforced concrete contractor will likely already be on site4. Durability, Proven track record of over 100 years
DISADVANTAGES1. Owner preferences may dictate against using reinforced concrete2. Cost considerations due to quantity of materials required3. Construction nuances4. Cracking & durability
DESIGN CONSIDERATIONS1. Seismic loads2. Floatation3. Abnormal pressure loads4. Retaining elements5. Influence of adjacent / superimposed structures6. Integration into existing facilities7. Security8. Details, Details, Details!9. Liner systems
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SEISMIC LOADSAccording 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.
BUOYANCYA 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 slab2. Buoyant force causing tank to float3. Reduced base slab friction if tank sliding (uneven backfill) is a design consideration
SECURITYAny 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?
DETAILS1. Minimum Concrete Strength2. Minimum Reinforcing Steel3. Expansion and Construction Joints4. Waterstops
MINIMUM “ACI.350 CODE” REQUIREMENT:1. Min. Concrete Strength=4000 psiat 28 days
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2. Air Entrainment=5%±1%3. Maximum Water-cement Ratio=.454. Maximum Slump=4 inches5. Aggregates per ASTM C33, max. aggregate size=1 inch6. No admixtures containing calcium chloride
EXPANSION JOINTS:
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Expansion joints, main location.
WATERSTOP DETAILBase slab to wall interface is most critical and most difficult to construct of all
construction joints:1. Raised starter wall2. Bend top steel down at wall
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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 CONSIDERATIONSProper adherence to specifications1. Water proofing process2. Mix design3. Placement4. Curing5. Deflection of structural members during pouring and vibrating of fresh concrete6. Details, Details, Details7. Integration into existing Facilities
Step 1, Water proofing process
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Step 2, Water proofing process
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Placement of fresh concrete
MIX DESIGNAdding 1 gallon of water to 1 yd3 of concrete will:
1. Increase slump about 1 inch2. Increase air content about 1%3. Increase shrinkage about 10% and increase cracking4. Reduce compressive strength about 200 psi5. Waste about 25 lbs of cement per cubic yard6. Increase shrinkage about 10% and increase cracking7. Decrease freeze-thaw durability about 20%8. Decrease wear resistance to traffic9. Increase dusting and other surface defects10. Increase time needed to finish the concrete
Deflection of structural members during construction:
CURINGAccording to ACI 350-01 “Environmental Structures” Code Requirements:
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“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
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)
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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 tested individually unless otherwise directed by the engineer.
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.
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.
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.
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SUMMARY1. 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.
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