Tanks

The Most Versatile & Durable Concrete Tank Available

DuraStor™ Tanks (AWWA D115 Tendon Prestressed Concrete Tanks) offer the benefits of prestressed concrete and the geometric flexibility of conventionally reinforced concrete.

Unlimited Applications –
Any Shape, Any Size

Whether driven by process or space considerations, DuraStor™ Tanks may be engineered and built into any shape or size, similar to conventionally reinforced tanks.

Durable & Watertight

STRUCTURAL TECHNOLOGIES’ DuraStor™ Tanks are ideal for use in water storage and treatment structures – high strength steel tendons apply compression to the tank floor, walls, and roof to counteract the applied forces and provide residual compression. This method actively reinforces the structure providing crack free concrete, joint free slabs, and no measurable leakage.

Economical – up to 25% Cost Savings

STRUCTURAL TECHNOLOGIES’ DuraStor™ Tanks are ideal for use in water storage and treatment structures – high strength steel tendons apply compression to the tank floor, walls, and roof to counteract the applied forces and provide residual compression. This method actively reinforces the structure providing crack free concrete, joint free slabs, and no measurable leakage.

Featuring VSL Post-Tensioning

DuraStor™ Tanks are reinforced with VSL systems – which have been used as the industry standard for post-tensioning throughout the world.

VSL® is the registered trademark of VSL International Ltd.

Products and Systems

DuraStor™ Tanks are prestressed concrete storage tanks reinforced with post-tensioning tendons (governed by ACI 350 and AWWA D115). This method actively reinforces the structure and significantly enhances its watertightness and long-term durability. DuraStor™ Tanks can be constructed in many shapes to suit project needs – there are no practical limitations. Tanks have been constructed with capacities up to 30,000,000 gallons. Experience the benefits of prestressed concrete with the geometric flexibility of conventionally reinforced concrete.

Tank Roof Options
Flat Roof Option

Similar to the floor, the roof slab is cast in a single placement with no construction joints.

This method results in a watertight slab that eliminates the possibility of substances entering the tank and contaminating the contents. The roof slab is column-supported with typical spans in the 30-foot range each way. Slab thickness is approximately 8 inches. Roof shoring is placed immediately following the column and column footing placement to minimize construction time. Post-tensioning tendons are placed orthogonally as in a typical two-way suspended slab and are “stage stressed” in the same manner as the floor slab tendons. After the tendons are stressed, the shoring is removed through access hatches. Dome roof prestressed concrete tank.

Dome Roof Option

Column-supported flat roofs are often chosen for buried tanks or where a less visible tank is desired. A cast-in-place concrete dome is an efficient option for circular tanks where a flat roof is not required

Roof Slab: AWWA D110-04 Code Wrapped Prestressed Tank AWWA D115-06 Code Tendon Prestressed Tank
Concrete placement multiple placements – shrinkage cracking and joints with horizontal waterstops that are a potential for contamination and maintenance single placement is standard practice, no joints
Method of reinforcement mild steel only 3.8.1 prestressed with 150 psi minimum residual precompression in each direction
Membrane required to prevent leakage into tank? possibly – depending on roof slope and if leakage needs to be prevented 3.8.4 no, concrete surface is crack-free and sloped 1% minimum for drainage
Tank Walls

The wall is composed of full-height segments frequently 12-inches thick. They’re cast in lengths of approximately 75 feet with no horizontal construction joints. Post-tensioning tendons placed horizontally may be tensioned at pilasters or pilasters may be eliminated depending on the project requirements. Tendons are also placed vertically to provide compression to the concrete and accommodate vertical bending moments and thermal stresses.

On large tanks it is possible to place as many as four wall segments per week. Column footings and columns are cast concurrently with the wall to minimize the duration of construction. If required, walls may have any architectural finish, form liner or coating to meet the project’s aesthetic requirements.

Wall AWWA D110-04 Code Wrapped Prestressed Tank AWWA D115-06 Code Tendon Prestressed Tank
Minimum Thickness 3.5.4 as low as 3.5″ – depending on wall type I, II, III or IV 3.7.3 9″, however 11″ -12″ is most common
Required minimum horizontal residual compression from prestressing 3.4.2.2 200 psi for wall above grade, 50 psi for wall below grade – only concrete core wall within the wrapping is prestressed – shotcrete coatings on prestressing steel has no residual compression and is usually in tension 3.7.4.1 200 psi for wall above grade, 100 psi for wall below grade – entire wall thickness is prestressed with minimum residual compression
Required minimum vertical residual compression from prestressing 3.5.3 200 psi only on concrete core wall within the wrapping is prestressed – shotcrete coatings on prestressing steel has no residual compression 3.7.5 200 psi for above grade, 125 psi for below grade – entire wall thickness is prestressed with minimum residual compression
Sheet steel diaphragms provide watertightness? 3.5.6 yes – if wall type II, III or IV. If not vertically post-tensioned wall must have a steel diaphragm. Vertical rebar may be eliminated depending on design. steel diaphragms not used or required as quality concrete is impermeable
Steel sheet diaphragms provide flexural reinforcement? 2.5.1.3, 2.9.1 26 gauge steel sheets relied on for watertightness and vertical flexural reinforcement – field joints require field-applied sealants, type IV walls require field-applied sealants at form tie holes steel diaphragms not used or required as quality concrete is impermeable
Inside face concrete cover on vertical mild reinforcement 3.5.4.2, 3.5.6.2 1″ on steel sheet diaphragm and rebar 3.11 1.5″ on rebar if not two-way prestressed, 1″ on rebar if two-way prestressed
Precast panel misalignment? 5.2.7 up to 3/8″ misalignment allowed for precast wall segments, wall segments are cast-in-place, no misalignment possible
Vertical mild reinforcement ratio 3.5.6 0.0025 each face (steel diaphragm is included in ratio for type II, III and IV walls) no minimum may be required if prestressed and depending on concrete stresses
Vertical prestressing protection “unbonded grouted” system – grade 150 bar in a PVC duct with epoxy grout, vertical prestressing only used on type I tanks 1.3 5″ minimum cover of bi-axially precompressed concrete, HDPE duct and coating in accordance with PTI and ACI standards
Horizontal prestressing protection 5.3.3.3.4 Sacrificial galvanizing on wire with one inch of non-prestressed shotcrete cover. Shotcrete cover goes into tension as it shrinks and when tank is filled, cover can delaminate, leakage source difficult to locate – water migrates beneath the shotcrete. 1.3 3″ minimum cover of bi-axially precompressed concrete, HDPP duct, high-performance grouting in accordance with PTI and ACI standards
Wall construction methods 1.1.1 four different wall types that can result in sole sourcing of a particular type cast-in-place construction is non-proprietary
Shotcete cover on metal diaphragms  3.5.4.2, 3.5.6.2 for diaphragms, 1″ inside face cover and 0.5″ cover on outside prior to wrapping
Tank Floor Slabs

STRUCTURAL TECHNOLOGIES’ DuraStor™ Tanks are ideal for use in water storage and treatment structures – high strength steel tendons apply compression to the tank floor, walls, and roof to counteract the applied forces and provide residual compression. This method actively reinforces the structure providing crack free concrete, joint free slabs, and no measurable leakage.

Floor Slab AWWA D110-04 Code Wrapped Prestressed Tank AWWA D115-06 Code Tendon Prestressed Tank
Minimum Thickness 3.8.2 four inch for non-prestressed, no prestressed option – ACI 350 allows three inch thickness if reinforced with WWF 3.6 5″ if prestressed, 6″ if non-prestressed
Concrete Placement 3.8.2 multiple placements – shrinkage cracking and joints that are a potential for leakage and maintenance single placement is standard practice – no joints or penetrations
Reinforcement mild steel only 3.6 prestressed with 200 psi residual each direction
Minimum Reinforcement Ratio 0.005 – mild reinforced only – # 5 at 15.5″ maximum 3.6 .0015 in addition to prestressing
Concrete Cover on Reinforcement 3.8 none specified – ACI 350 H.4 allows 1.5″ top and 1.5″ bottom – less for 3″ slabs 3.11 1.5″ top, 2″ bottom

Product Design & Engineering Support

Solutions For:

• Change in Code
Seismic Upgrade
• Increased Loads
• Missing or Misplaced Reinforcement
• Deterioration
• Low Concrete Strength
• New Penetrations & Openings
Force Protection
Pipe Rehabilitation

Prestressed Concrete Tank Team Leader

Read more about our products and applications on our  pipeline rehabilitation solution builder page

Design-Assist & Engineered Product Support

• Investigation Support
• Solution Development
• Budget Development
• Specification Assistance
• Constructability Consulting
• Application Engineering
• Quality Control Programs
• Project-Specific Design-Assist

Featured Prestressed Concrete Tank Case Studies

Frequently Asked Questions

What is prestressed concrete?

Prestressing is the introduction of stresses to a structural member, usually with high-strength steel 7-wire strands, that counteract the internal stresses resulting from the member’s self-weight and superimposed loadings.

Pre-tensioning is the method of prestressing associated with production of structural components at a pre-cast concrete facility. Post-tensioning is the method of prestressing associated with concrete members cast-in-place at the project site.

What are the benefits of a post-tensioned tank?

Concrete is a material with high compressive strength but relatively low tensile strength. Through the principles of structural design, the level of post-tensioning applied to a structural component can reduce or eliminate the tensile stresses in the concrete depending on code requirements and the desires of the structural design engineer.

Post-tensioning allows for large concrete placements without construction, expansion, or control joints. The floor and roofs slabs are each cast in single placements eliminating the maintenance and leakage associated with construction joints. Wall segments are cast full-height in lengths of approximately 80 ft. with no horizontal construction joints.

The ultimate stress of the prestressing strands is 270 ksi compared to 60 ksi yield stress for mild reinforcement allowing for greatly reduced reinforcement ratios. Reinforcement congestion is eliminated simplifying concrete consolidation.

Post-tensioning allows for thinner members resulting in reduced materials, placement labor, construction schedule, and costs compared with conventionally reinforced tanks.

Post-tensioned concrete is an inherently water tight material. Expensive coatings and liners, that require ongoing maintenance, are not required.

The post-tensioning tendons, which are the primary structural reinforcement, have multiple layers of corrosion protection including the highly pre-compressed concrete cover, thick polyethylene ducts filled with high-performance grout or corrosion-inhibiting coating, encapsulated anchorages, and watertight duct connections.

The construction sequencing of a post-tensioned concrete tank allows for multiple tasks to be accomplished simultaneously. For example, wall construction proceeds in parallel with column and roof shoring placement. The resulting construction schedule is highly efficient in comparison to other methods of tank construction.

Is the post-tensioning method of prestressing new technology?

Post-tensioning technology has been accepted widely in the United States since the 1950’s. The range of structural applications includes office and residential buildings, parking structures, bridges, foundations, ground anchors, containment structures, and structural strengthening – thousands of structures are constructed annually with post-tensioning as the primary reinforcement. It is a favored method of construction for its construction speed, economy, and durability.

Hundreds of post-tensioned concrete tanks have been built in the United States with the earliest being in service for over forty years; hundreds more have been constructed world-wide.

What codes and standards govern the design and construction of Concrete Tanks?

The design and construction of post-tensioned tendon-prestressed concrete water tanks is governed by the following building codes and standards:

  • American Concrete Institute ACI 350-06 Code Requirements for Environmental Engineering Concrete Structures and Commentary
  • American Water Works Association ANSI / AWWA D115-06 Tendon – Prestressed Concrete Water Tanks
  • American Concrete Institute ACI 373R-97 (Report Recommendations) Design and Construction of Circular Prestressed Concrete Structures with Circumferential Tendons

The Post-Tensioning Institute provides the following technical reports and specifications:

  • Design of Post-Tensioned Slabs Using Unbonded Tendons
  • Acceptance Standards for Post-Tensioning Systems
  • Design and Construction of Post-Tensioned Slabs-On-Ground
  • Field Procedures Manual for Unbonded Single Strand Tendons
  • Specifications for Unbonded Single Strand Tendons
  • Recommendations for Prestressed Rock and Soil Anchors
  • Specification for Grouting of Post-Tensioned Structures
  • Anchorage Zone Design
Is this method of construction limited by freezing weather conditions? TOP

Construction can proceed in freezing temperature conditions as the concrete members are protected from the elements with insulating blankets and heat is applied to the curing concrete as required

What shapes and capacities are available?

STRUCTURAL TECHNOLOGIES can provide many shapes to suit the project needs including circular, rectangular, rectangular with rounded corners, egg-shaped digesters, irregular-shaped polygons, oval, – there are no practical limitations with this method of construction. Economical capacities have been constructed ranging from 250,000 gallons to above 30,000,000 gallons.

Are Tanks applicable to various site and seismic conditions?

Site conditions may require a fully-buried, partially-backfilled, above-grade, sloped backfill or conditions where ground water is above the tank floor – a DuraStor™ Prestressed Concrete Tank is adaptable to any of these conditions.

The design methodology and structural detailing of prestressed concrete tanks is well-developed. Concrete structures, and particularly prestressed concrete tanks, have the proven ability to withstand severe earthquakes.

Does this type of tank construction involve proprietary reinforcement systems, construction methods, or construction equipment?

Similar to a building or bridge, tendon-prestressed concrete tanks are generic structures with no proprietary reinforcement systems, construction methods, construction equipment, tendon tensioning and grouting equipment, etc. The potential for project delays due to unavailable proprietary equipment is not an issue. The projects are usually designed by consulting engineers and competitively bid by general contractors local to the project.

My existing circular tanks are above grade with dome roofs, can a Prestressed Concrete Tank be built to match them?

The wall can have any architectural finish, form liner, or coating to match existing structures if required. Additionally, stressing buttresses for tensioning circular tank horizontal wall tendons are easily eliminated. Flat concrete roofs, aluminum domes, or concrete domes are available to suit the customer’s needs.

Are Prestressed Concrete Tanks suitable for storage of liquids other than potable water?

They are appropriate for all types of liquid containment including chilled water, storm water retention, sludge, wastewater, digesters, ethanol, petroleum products, and liquefied natural gas. Additionally, they are used in the storage of materials such as coal, grains, ash, cement, clinker, and nuclear containment – the design and construction of structures for the storage of granular materials is governed by other codes.

What are the project delivery choices available to an owner who wants a Prestressed Concrete Tank?

STRUCTURAL TECHNOLOGIES may provide a performance specification with owner-defined design requirements. In this case the tank will be on a design-build basis.

STRUCTURAL TECHNOLOGIES may assist the owner’s structural engineer in the design of the tank. The tank is then competitively bid by a group of pre-qualified list of general contractors.

The owner’s structural engineer may design the tank which is then competitively bid by a group of pre-qualified general contractors.

What are the access limitations to constructing a Prestressed Concrete Tank?

Construction access can often be limited by adjacent structures or a desire to minimize the excavation. Wrapped-type prestressed concrete tanks require a minimum 10’ wide working area at the entire perimeter of the tank for wrapping and shotcreting operations. A Prestressed Concrete Tank may be constructed from the inside of the tank, therefore there is no access limitation.

Are structural modifications possible with a Prestressed Concrete Tank?

Future wall penetrations such as piping, mechanical systems or access openings may be accommodated with a DuraStor™ Prestressed Concrete Tank. Vertical and horizontal tendon spacings vary from approximately 2’ – 5’ and may be either avoided or if severing tendons is required an engineered external reinforcement system such as carbon fiber reinforced polymer sheet may be applied.