Strengthening of Large Storage Tank Foundation Walls in an Aggressive Environment by External Post-tensioning. May 7th 2013: Dominique Deschamps

Transcription

1 Strengthening of Large Storage Tank Foundation Walls in an Aggressive Environment by External Post-tensioning May 7th 2013: Dominique Deschamps

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

3 Presentation of the project Three new Storage Tanks were built in 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

4 Presentation of the project Aerial View 3 concerned tanks

5 Presentation of the Project View of one tank

6 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) deep Outer diameter: (35.28 m) Inner diameter: (34.52 m) Central Diameter: (34.90 m) Outer Long. Rebars: 8 #3 Inner Long. Rebars: 4 #3 Stirrups: 2 center to center

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

8 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/m 3 (125 pcf) Resting pressure: K 0 = 0.5 Oil in tank: 60 deep, density: 10 kn/m 3 (62.4 pcf) Self weight of tank: 5% of oil weight

9 Cause of cracks Total load above ground (oil + tank SW): MPa (27.3 psi). Corresponding earth pressure: MPa (13.65 psi) Pressure due to soil: MPa (1.81 psi) Linear Pressure onto Ring Wall (1270 mm: 50 deep) P r = kn/m (0.728 kips/in)

10 Cause of cracks Tensile Axial Force in Ring Wall: Serviceability F r = P r R = 2234 kn (502 kips) Tensile Axial Force in Ring Wall: Nominal Strength F ru = 1.2 F r = 2680 kn (602 kips) Required Longitudinal Rebars: A s = F ru /(0.9*f y ) = in 2 (72 cm 2 ) Reminder: 12 bars #3 in place: 1.32 in 2 (8.52 cm 2 )

11 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

12 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

13 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 Protection Level three: each sheathed strand is grouted into a HPDE duct Protection Level four: each strand is placed into a HDPE duct Protection Level two: each strand is individually placed into a sheath Wire subject to corrosion Protection Level one: each strand is individually greased into a sheath

14 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

15 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

16 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 F r = P r R = 2234 kn (502 kips) No more tensile stress in service

17 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

18 Field Installation Placing of Tendons Tendons pre-prepared at length Supports uniformly distributed along ring wall for maintaining tendons in place before stressing

19 Field Installation Grouting of Tendons Done before stressing

20 End of Work

21 Conclusion Three Large Storage Tanks repaired in less than 3 weeks, mobilization included. Efficient and low-cost repair technique Sustainable and durable technologies

22 Thank you for your attention! Questions?