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Pipe Comparisons

Pipe Comparisons. A Look At Rigid & Flexible Pipe Products. Why Are We Here?. To examine the basics that differentiate concrete pipe from flexible alternatives To use those basics to specify the right product for the job. There is NO Perfect Pipe.

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Pipe Comparisons

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  1. Pipe Comparisons A Look At Rigid & Flexible Pipe Products

  2. Why Are We Here? • To examine the basics that differentiate concrete pipe from flexible alternatives • To use those basics to specify the right product for the job

  3. There is NO Perfect Pipe • All pipes bring certain strengths and weaknesses. • Good designers must accommodate for strengths that best benefit the project, while making sure the weaknesses don’t affect the project long term

  4. Corrugated Steel Pipe

  5. HDPE - Plastic Pipe

  6. Reinforced Concrete Pipe

  7. What are the important attributes of a pipe?

  8. The Important Attributes of a Piping System • Strength • Durability-LCA • Hydraulics • Installation • Cost • Low Risk/Maintenance

  9. The Bottom Line : Buried pipe must perform two critical functions Conduit Buried Pipe Structure

  10. Concrete Pipe Strength Delivered on the Truck Rigid pipe The majority of the structural strength of this pipe system has been designed, built into,and tested in the pipe. It is not built in the field.

  11. Strength of Flexible Pipe has to be Built in the Trench • Flexible pipe • The majority of the structural strength of this type of pipeline system is not built in nor delivered on the truck. • Strength of all plastic pipe systems depends on the quality and placement of the backfill materials by the contractor.

  12. Pipe Strength vs Stiffness PRECAST RCP • f’c = 4000 psi - 6000 psi min (ASTM) • Steel = 65,000 psi • RCP is a structure. • Many Class (strength) choices per load condition to choose from. • Strength increases with age.

  13. HDPE - Pipe Stiffness • Is a measure of the inherent strength of the pipe as a function of applied load and the resulting deflection. • By the parallel plate method.

  14. Flexible Pipe Stiffness Comparison Diameter HDPE CMP 18” 40 psi 465 psi 24” 34 psi 200 psi 30” 28 psi 103 psi 36” 22 psi 60 psi 42” 19 psi 38 psi 48” 17 psi 25 psi

  15. Factors Effecting Pipe Stiffness • Temperature-plastic • Time • Resin Quality • Wall profile/thickness • Soils- In poorer soils, higher pipe stiffness is required.

  16. Reduced Pipe Stiffness Results In • Increased deflections • Reduced hydraulic capacity • Inability to obtain proper compaction • Increased reliance on soil to carry load • Increased stress & strain • Decreased buckling resistance • Ground surface settlement • Joint leaks

  17. The absence of structure often results in an ineffective conduit!

  18. Adding Stiffness After the Fact HDPE

  19. Too Light A Gage - CMP

  20. CMP Strength?

  21. No Wall Strength to Resist Loads HDPE

  22. Wall Buckling - After 45 Days HDPE states:" haunch compaction is critical and should be placed by hand" HDPE

  23. As Good as Concrete?

  24. Wall Buckling - The Finale HDPE states: "the strength of plastic pipe is built into the trench" HDPE

  25. Deflection, Buckling & Cracking 30% Deflection HDPE says-"control of deflections and localized deformation are very important in design & construction" HDPE

  26. HDPE says: "it's more durable"

  27. Recap - Structural • Concrete pipe is a structure. The strength is delivered on the truck. • Flexible pipe is not. Low Bidder must engineer the system with his installation of quality backfill. • Risk & Liability-Advantage Concrete Pipe!

  28. The Important Attributes of a Piping System • Strength • Durability • Hydraulics • Installation • Cost • Low Risk/Maintenance

  29. U.S. Army Corps of EngineersEM 1110-2-2902Conduits, Culverts and Pipes (1) Concrete. Most studies estimated product service life for concrete pipe to be between 70 and 100 years. Of nine state highway departments, three listed the life as 100 years, five states stated between 70 and 100 years, and one state gave 50 years. (2) Steel. Corrugated steel pipe usually fails due to corrosion of the invert or the exterior of the pipe.Properly applied coatings can extend the product life to at least 50 years for most environments. (3) Aluminum. Aluminum pipe is usually affected more by soil-side corrosion than by corrosion of the invert. Long-term performance is difficult to predict because of a relatively short history of use, but the designer should not expect a product service life of greater than 50 years. (4) Plastic. Many different materials fall under the general category of plastic. Each of these materials may have some unique applications where it is suitable or unsuitable. Performance history of plastic pipe is limited. A designer should not expect a product service life of greater than 50 years. Excerpt from Para. 1-4 Life Cycle Design

  30. 1999 TDOT Service Life • RCP - is only pipe used in 100 year road designs • CMP - Only allowed in roadways with design life up to 50 years. 10/12 gage. (Specify required gage in specifications) • HDPE - Limited usage in roadways with a 25 year maximum design life.

  31. CMP Durability?

  32. Poor Resin - NCHRP Report 429 49% of HDPE fails to meet own spec.

  33. Flotation A durability issue for both pipe and roadway!

  34. At a Theater Near You!

  35. Buoyancy • RCP PIPE • Specific gravity = 2.4 Resist buoyancy forces best of all pipe products. • HDPE PIPE Specific gravity = .95 (less than water) tendency to float.

  36. HDPE

  37. Recap - Durability • Concrete pipe 100+ year life • HDPE is 25 year maximum design life • Risk and liability – What is the Project Design Life and LCA?

  38. The Important Attributes of a Piping System • Strength • Durability • Hydraulics • Installation • Cost • Low Risk/Maintenance

  39. Hydraulics - Proper Pipe Size

  40. What Factors Determine Hydraulic Capacity • Pipe Diameter • Slope • Roughness (friction factor)

  41. Downsizing RCP when CMP is Specified The roughness coefficients or Manning’s “n” differences of RCP (.012) and CMP (.024) Allow for reducing the concrete pipe diameters at least one pipe diameter smaller when outlet control governs. CMP RCP

  42. We should do same for - smoothed line N-12 HDPE?

  43. Manning’s ‘n’ Value • CONCRETE PIPE • Laboratory - .010 • Field - .012 • HDPE PIPE • Laboratory - .009-015* • Field - .012-.026 • They promote .010 ! *Tullis Report-Waviness of liner

  44. Corrugation Growth! If this pipe were made of metal, it would have a Manning’s “n” of .024

  45. Manning’s “n” of 0.010???

  46. Recap - Hydraulics • A higher “n” value for HDPE, closer to value of CMP • Risk to Owner/Engineer = undersized pipe

  47. The Important Attributes of a Piping System • Strength • Durability • Hydraulics • Installation • Cost • Low Risk/Maintenance

  48. SIDD - Versatility with RCP • Type 1: Highest Quality installation using select granular soils with high compaction requirements for haunching and bedding.(A-1 & A-2) • Type 2: Allows silty granular soils with less compaction required for haunching and bedding.(A-3) • Type 3: Allows use of soils with less stringent compaction requirements for haunching and bedding. • Type 4: Allows use of onsite native material for haunching and bedding with no compaction required. (6” of Bedding is required if rock foundation)

  49. Using Onsite Material is RCP’s Advantage!

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