strengthening of large storage tank foundation walls in an

Strengthening of Large Storage Tank Foundation Walls in an Aggressive Environment by

External Post-tensioningMay 7th 2013: Dominique Deschamps

Strengthening of Large Storage Tank Foundation Walls by External PT

• Scope of the paper• Presentation of the project• Cause of cracks• Selection of Repair Technique• Design of External PT• Field Installation


• Presentation of the project• Three new Storage Tanks were built in 2008-2009 in

order to increase the capacity of the plant and reduce the unused time of tanks in the facility.

• Tanks are built upon an outer reinforced concrete ring wall supported by piles.

• Tanks contain oil, heated 130ºF maximum.• Tanks are located at the Hudson River shore


3 concerned tanks

Presentation of the project – Aerial View


• Presentation of the Project – View of one tank


• Presentation of the Project – Detail of the Reinforced Concrete Ring Wall

Ring wall: rectangular section 1’‐3’’ (381 mm) wide per 4’‐2’’ (1270 mm) deepOuter diameter: 115’‐9’’ (35.28 m)Inner diameter: 113’‐3’’ (34.52 m)Central Diameter: 114’6’’ (34.90 m)Outer Long. Rebars: 8 #3Inner Long. Rebars: 4 #3Stirrups: 2 #5 @18’’ center‐to‐center


• Damage: Multiple Cracks due to excessive tension in the ring wall


• Cause of cracks• Ring Wall is subject to uniform tension due to earth

pressure.• Soil material used to fill the space inside the ring wall

underside the tank: 20 kN/m3 (125 pcf)• Resting pressure: K0 = 0.5• Oil in tank: 60’ deep, density: 10 kN/m3 (62.4 pcf)• Self weight of tank: 5% of oil weight


• Cause of cracks• Total load above ground (oil + tank SW): 0.188 MPa

(27.3 psi).• Corresponding earth pressure: 0.0941 MPa (13.65 psi)• Pressure due to soil: 0.0125 MPa (1.81 psi) • Linear Pressure onto Ring Wall (1270 mm: 50’’ deep)

• Pr = 127.50 kN/m (0.728 kips/in)


• Cause of cracks• Tensile Axial Force in Ring Wall: Serviceability

• Fr = Pr R = 2234 kN (502 kips)• Tensile Axial Force in Ring Wall: Nominal Strength

• Fru = 1.2 Fr = 2680 kN (602 kips)• Required Longitudinal Rebars:

• As = Fru/(0.9*fy) = 11.15 in2 (72 cm2)• Reminder: 12 bars #3 in place: 1.32 in2 (8.52 cm2)


• Selection of Repair Technique• Deficiency is essentially due to insufficient tensile

reinforcement• Reinforced concrete repair not adequate for durability

for structures exposed to waste or contaminated water• CFRP technique not adequate since they require

tension to work and tension means cracks and water going under the tanks


• Selection of the Repair Technique• External Post-Tensioning• Eliminate all possible tensions thanks to compression

brought by external PT• Crack Injection• Patch Repair• Use of PT system with a guaranteed lifetime of 50

years


• Selection of Repair Technique• Use of Greased Sheathed Strands 0.6’’ (15.2 mm)

inside a HDPE duct and inner space filled with grout.• Use of anchors protected against corrosion with a

specific coating resisting 50 years of external aggression

Wire subject to corrosion

Protection Level one: each strand is individually greased into a sheath

Protection Level two: each strand is individually placed into a sheath

Protection Level three: each sheathed strand is grouted into a HPDE duct

Protection Level four: each strand is placed into a HDPE duct


• Design of External PT• Compressive Force brought by PT shall be greater

than Tensile Force brought by Earth Pressure• Losses of PT taken into account• Durability improved by taking envelope between

France and US for computing PT losses: France governs (40% more losses)

• Tendons stressed at 75% of G.U.T.S. value


• Design of External PT• 16 tendons 1 strand 0.60’’ distributed over the depth of

the ring wall are required. Length of tendons is 115 m (377 ft)

• 1 anchorage per tendon: anchorage 1X


• Design of External PT• Maximum Compression Force: 2,882 kN (648 kips)• Maximum compressive stress: 5 MPa (720 psi)• Minimum Compression Force: 2,282 kN (513 kips)• Reminder: Tensile Axial Force in Ring Wall:

Serviceability• Fr = Pr R = 2234 kN (502 kips)

• No more tensile stress in service


• Field Installation – Preliminary work• Crack Injection: all cracks greater than 0.5 mm (0.02’’)

were injected• All unsound concrete was removed and redone with

high strength no-shrinkage mortar• Ground around the ring wall was removed and

stabilized (close to River): prevention of water leakage from River


• Field Installation – Placing of Tendons• Tendons pre-prepared at length• Supports uniformly distributed along ring wall for

maintaining tendons in place before stressing


• Field Installation – Grouting of Tendons• Done before stressing


• End of Work


• Conclusion• Three Large Storage Tanks repaired in less than 3

weeks, mobilization included.• Efficient and low-cost repair technique• Sustainable and durable technologies


• Thank you for your attention!

• Questions?

strengthening of large storage tank foundation walls in an

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