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Home \ Reinforcing Steel and Swimming Pool Construction

Reinforcing Steel and Swimming Pool Construction

By: Ron Lacher, P.E.
Pool Engineering, Inc
.



Most Custom Swimming Pools are Constructed of Steel Reinforced Shotcrete Gunite


Why? No other structural materials offer similar:

  • Versatility

  • May be applied to an unlimited number of shapes

  • Forming generally not required

  • Durable

  • Economical

Reinforcing Steel and Concrete Work Well Together Because:

  • They Bond Together Well

  • Concrete Offers the Reinforcement Corrosion Protection

  • Similar Temperature Expansion Characteristics

Steel Reinforced Shotcrete (Gunite) is Analyzed Exactly Like Reinforced Concrete

  • Combines Steel and Concrete

  • Takes advantage of the strength of each material

  • Concrete is strong in Compression but weak in Tension

  • Steel is strong in Tension but weak in Compression

  • Minimizes the weakness of each material

  • We have a cook book that tells us how to design a.k.a. The International Building Code

What are the critical elements of reinforcement installations in swimming pools:

  • Reinforcement must be the bar size & spacing specified on the structural plan (or larger)

  • Reinforcement must be the grade of bar specified on the structural plan (or stronger)

  • Reinforcement must have the protection (coverage) specified in the code or structural plan

What are the critical elements of reinforcement installations in swimming pools:

  • Reinforcement must held in place (tied) to prevent movement & vibration

  • Reinforcement must placed in a manner to enable proper encasement in gunite or shotcrete

  • Reinforcement must be in the location specified on the structural plan

  • Reinforcement must be the bar size specified & spacing on the structural plan (or larger)

  • Reinforcement must be the bar size specified & spacing on the structural plan (or larger)

  • The proper encasement of reinforcement is a critical issue in shotcrete & gunite application

  • Reinforced Concrete - concrete & reinforcement must be bonded to act as a unit

  • When rebar is not properly encasement, the concrete isn’t considered reinforced


Because of this, the Building Code places limitations on the size and spacing of rebar in gunite & shotcrete

  • The maximum size of reinforcement shall be No. 5 bars

  • There shall be a minimum clearance between parallel reinforcement bars of 2 1/2 inches

  • Bars larger then # 5 increase the chances of shadowing (voids behind rebar)

Why do Pools Frequently Crack at the Skimmer?

  • Skimmer is a weak point in the Bond Beam reinforcement

  • Reinforcement must be the grade of bar specified on the structural plan (or stronger)

Grade of Reinforcing Steel

  • A common spec from a typical pool structural plan

  • Grade 40 Deformed Bars Conforming to ASTM A615

  • What exactly does this mean?

Grade of Bars

 Grade of Steel

Yield Strength in psi

Code Allowed Strength

Grade 40
Grade 60
Grade 75

40,000psi
60,000psi
75,000psi

20,000psi
24,000psi
24,000psi



Deformed Bars

Rebar must have protrusions to provide a mechanical bond

ASTM A615

Rebar manufactured from hot rolled new billets

Reinforcement must have the protection (coverage) specified in the code or structural plan

MINIMUM COVER, inches

Concrete cast against and permanently exposed to earth: 3“
Concrete exposed to earth or weather:
        No. 6 through No. 18 bar
        No. 5 bar, W31 or D31 wire, and smaller
 
2”
1½”
Concrete not exposed to weather or in contact with ground:
        Slabs, walls, joists: No. 14 and No. 18 bar
        No. 11 bar and smaller

1½”
¾”

Reinforcement workmanship related cracking

Relective Cracking

  • Rebar not securely tied, permits vibration of steel cage during gunite or shotcrete application

  • Inadequate coverage of gunite or shotcrete over reinforcement

  • Caused by reinforcement not following forms

  • May also be gunite related

What are the critical elements of reinforcement installations in swimming pools:

  • Reinforcement must be the bar size & spacing specified on the structural plan (or larger)

  • Reinforcement must be the grade of bar specified on the structural plan (or stronger)

  • Reinforcement must have the protection (coverage) specified in the code or structural plan


Common Questions Regarding Rebar

Does rust have to be removed from rebar?

The Building Code Requirements for Structural Concrete (ACI 318) states in Section 7.4.2:

ACI 318, Sec. 7.4.2: Reinforcement, except prestressing tendons, with rust, mill scale or a combination of both, shall be considered satisfactory, provided the minimum dimensions (including height of deformations) and weight of a hand-wire-brushed test specimen are not less than applicable ASTM specification...

How About Mud?

The Building Code Requirements for Structural Concrete (ACI 318) states in Section 7.4.1:

ACI 318, Sec. 7.4.1: At the time concrete is placed, reinforcement shall be free from mud, oil or other nonmetallic coatings that decrease bond. Epoxy coating of steel reinforcement in accordance with Standards referenced in [ACI 318 Sections] 3.5.3.7 and 3.5.3.8 shall be permitted.

STRUCTURAL SURCHARGES IN SWIMMING POOL CONSTRUCTION

Some of the Forces that Swimming Pool Structures Experience:

  • Soil Pressure

  • Adjacent Structures (Surcharges)

  • Water Pressure

  • Unsuitable Soil Under the Pool

  • Earthquake

Soil Pressure?

  • The force due to soil pressure is assumed to be like a fluid pressure

  • Swimming pools are designed for inward soil pressure based on a term called

  • Equivalent fluid pressure or EFP

  • The fluid pressure of water is 62.4 lb/sq.ft. per foot of depth or 62.4 PCF

  • Most Standard Pool Structural Plans Based On:

  • Non Expansive soil – 30 PCF EFP

  • Expansive Soil – 45 PCF EFP

  • The More Expansive the Soil, the Higher the EFP

  • Extra Ordinary Expansive Soil

  • How Would You Know?

  • Soils Engineer Would Specify

What is a Surcharge?

Required Extra Strength in the Pool Wall Beyond a Standard Pool Built in a Flat Yard

What Does Extra Strength in the Pool Wall Mean?

  • More Reinforcing Steel

Means Extra Cost!

  • More Gunite

Means Extra Cost!

  • Specialized Engineering

Means Extra Cost!

What are Common Surcharges?

Slopes

  • Ascending Slopes

  • Descending Slopes

  • Anything that bears substantial weight on the ground near the pool

  • Retaining Walls

  • Building Footings

  • Patio Cover or Balcony Footings

  • Rock Water Features

Crucial Information on the Location of the Rebar and Thickness of the Concrete:

  • How you can usually tell if the rebar is correctly placed

  • Importance of concrete thickness between soil & rebar and between rebar & the water side of the pool

  • How the above is affected by freestanding pool walls

  • When rebar double curtains are needed


 Copyright © 2012, Pool Engineering, Inc.


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