PRECON

Prestressed Water & Wastewater Tanks
info@precontanks.com (352) 332-1200
PRECON Corporation Contact
(352) 332-1200 info@precontanks.com
Prestressed Concrete Tank Engineering

Design and Details

The basis for the success of prestressed tanks is in two areas. The first is the steel shell diaphragm that is the heart of the wall and which makes the wall impermeable. The second is the bonded prestress wire which is applied under full load giving a uniform, measurable prestress force around the full circumference of the tank. Shotcrete, fully encasing the prestress wire, bonds it to the wall and prevents corrosion.

Tank Construction

Sectional Information

The tanks can be divided into the following sections. Each section below provides a description of that part of the tank.

PRECON prestressed concrete tank construction sectional diagram
Current PRECON Construction Diagram Image will be reworked during final design production
Foundation and Base

Floor

Our standard floor is a 4-inch-thick reinforced concrete slab designed to act as a flexible membrane slab in accordance with AWWA D-110.

The floor is vibratory screeded to consolidate concrete and obtain encasement of floor reinforcing steel. After applying a light broom finish, the floor is water-cured until tank construction is complete.

A highly reinforced 4-inch membrane slab is able to withstand a maximum differential settlement between the center of the tank.

We design and build structural floors for many applications including piles, vibral compaction, rock anchors, tension piles due to high water table, and ballast slabs, also due to water table.

Piles Vibral Compaction Rock Anchors Tension Piles High Water Tables Ballast Slabs
Prestressed Wall Assembly

Wall

Wall Construction

Core Wall

The core wall is constructed of shotcrete, encasing a continuous steel shell diaphragm. The thickness of the core wall is designed to accept the initial compressive forces applied by prestressing, backfill, and other applicable loads with a minimum thickness of 3 1/2 inches.

The wall typically tapers uniformly on the outside face from top to bottom as required by design computations. The steel diaphragm shall have a minimum of 1 inch shotcrete cover.

Interior and exterior surfaces of the core wall shall be water-cured.

Impermeable Barrier

Diaphragm

A 26-gauge steel diaphragm is embedded in the prestressed wall and epoxy bonded to a PVC waterstop embedded in the floor to form a watertight wall extending the full height and circumference of the tank wall.

The diaphragm is composed of vertical panels fabricated with re-entrant ribs that form a mechanical interlock between the inside and outside layers of concrete.

All vertical laps and joints between the diaphragm sheets are sealed with an epoxy sealant.

Final Protection

Covercoat

The final layer of prestressing wires is encased and protected by the covercoat, a minimum of 1 inch of shotcrete applied in a uniform manner and finished to provide a smooth, beautiful, and long-lasting light broom finish.

Circumferential Compression

Prestressing

Prestressing is the process of wrapping the tank wall with a continuous steel strand under high tension to keep the tank walls in constant compression even when the tank is filled with water.

The placement of the prestressing wire forms a continuous uniform helix of such pitch as to achieve the unit compressive stress required to maintain residual compression of the core wall when the tank is full of water.

Extra prestressing in the dome band serves to counteract the radial thrust of the dome weight pushing the top of the wall outward. This allows the dome to remain free-standing with no interior supports.

Completed PRECON prestressed concrete tank with concrete dome
Free-Span Roof System

Dome

After shooting the wall, we construct a falsework of shoring, ribs, and plywood decking and pour a reinforced concrete roof in a thin-shell spherical shape with a rise of one-tenth of the tank diameter.

The dome will be a free-span, self-supporting system with no interior columns or supports after the prestressing process is complete.

Access, Safety and Functionality

Accessories

The following tank accessories provide accessibility, safety, and overall functionality for our tanks.

Fiberglass Inside Ladder with a stainless steel T-S Rail safety device Aluminum Exterior Ladder with a cage, T-S Rails, security gate, or some combination Fiberglass Access Hatch Cover Aluminum Handrail around the hatch or the whole dome Stainless Steel Wall Manhole Precast Concrete Dome Overflows Fiberglass Center Vent Fiberglass Liquid Level Indicator Dome Penetrations for Instrumentation Elevated Concrete Walkways Aluminum Stairs, Platforms and Catwalks Vortex Breakers over the outlet pipe Tank Baffling, either polypropylene curtain or CMU wall Any other specialty item the design engineer may wish to include
Final Appearance

Exterior Finishes

Special exterior finishes may include architectural finishes, special painting formats, or unpainted tanks.

Technical Resources

Typical Tank Drawings

The linked details are in PDF format and show features of a typical reservoir tank.

Additional detail drawings are available in PDF and electronic formats. These can cover any of the tanks shown on the website. Additional drawings can give greater description information than those shown here.

PDF Drawing 3 Pages
Plan and Section

Tank Plan and Section Views

Open PDF Drawing
PDF Drawing 3 Pages
Pipe Details

Tank Inlet, Outlet and Drain Pipe Details

Open PDF Drawing
PDF Drawing 6 Pages
Accessory Details

Tank Accessory Details

Open PDF Drawing
Technical Specifications

Typical Tank Specifications

The typical specification covers tank design, submittals, construction, testing, floor, wall, prestressing, shotcrete covercoat, accessories, coatings, and the free-span concrete dome roof.

View Typical Tank Specifications
Tank Design AWWA D-110 and ACI 372
Core Wall Steel Shell Diaphragm
Prestressing Bonded High-Tensile Wire
Tank Floor Reinforced Concrete
Tank Roof Free-Span Concrete Dome
Tank Components

Tank Accessories

The following tank accessories provide accessibility, safety, and overall functionality for our tanks.

Fiberglass inside ladder with a stainless steel T-S Rail safety device
Aluminum exterior ladder with a cage, T-S Rails, security gate, or some combination
Fiberglass access hatch cover
Aluminum handrail around the hatch or the whole dome
Stainless steel wall manhole
Precast concrete dome overflows
Fiberglass center vent
Fiberglass liquid level indicator
Dome penetrations for instrumentation
Elevated concrete walkways
Aluminum stairs, platforms, and catwalks
Vortex breakers over the outlet pipe
Tank baffling, either polypropylene curtain or CMU wall
Any other specialty item the design engineer may wish to include
Protective Finishes

Tank Coatings

Interior Coatings

Epoxies and Polyurethanes

PRECON has experience in applying protective interior coatings using a variety of epoxies and polyurethanes. These coatings can be used to protect the interior of the tank from conditions associated with water and wastewater treatment processes.

Exterior Coatings

Acrylic and Acrylate Coatings

PRECON has experience applying acrylic and acrylate exterior coatings for aesthetic purposes.