1 / 18

PCN and CDF Overload Methods

PCN and CDF Overload Methods. ICAO ACN Overload Criteria. Chapter 2 of the ICAO Pavement Design Manual Guidance on Overload Operations For those operations in which magnitude of overload and/or the frequency of use do not justify a detailed analysis the following criteria are suggested:.

latoya
Download Presentation

PCN and CDF Overload Methods

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. PCN and CDF Overload Methods

  2. ICAO ACN Overload Criteria Chapter 2 of the ICAO Pavement Design Manual Guidance on Overload Operations For those operations in which magnitude of overload and/or the frequency of use do not justify a detailed analysis the following criteria are suggested: • For flexible pavements occasional movements by aircraft with ACN not exceeding 10 per cent above the reported PCN should not adversely affect the pavement. • For rigid pavements, in which a rigid pavement layer provides a primary element of the structure, occasional movements by aircraft with ACN not exceeding 5 per cent above the reported PCN should not adversely affect the pavement. • If the pavement structure is unknown the 5 per cent limitation should apply; and • The annual number of overload movements should not exceed approximately 5 per cent of the total annual aircraft movements.

  3. Relative ACN Values

  4. Relative ACN Values

  5. Exact and Approximate Rigid ACN Figure 1-4 from ICAO Pavement Design Manual, k units are MN/m3

  6. ACN Computation • Pavement thickness for the overload aircraft is not the same as for the design aircraft (used to compute pavement PCN). • ACN Traffic for the overload aircraft is the same as for the design aircraft (10,000 coverages). • But by definition the traffic for the overload aircraft is much less than for the design aircraft.

  7. Using Cumulative Damage Factor (CDF) for Overload

  8. Computational Procedure 1. Compute CDF for current airplane mix 2. Check structural condition for current mix, 3. Compute CDF for overload aircraft 4. Compare CDF with and without overload aircraft 5. Evaluate increase in theoretical damage (CDF) from overload operations

  9. How to Determine CDF Limiting Criteria? • ACNR is the ratio of ACNs for the overload aircraft to the design aircraft. • St is the sensitivity of change in pavement life to change in pavement thickness. • See the paper for details

  10. Numerical Example - 1 • Run COMFAA in Flexible ACN Mode. • 737-500 at 134,000 lbs, B subgrade, ACN = 37.4 (t1 = 27.84). • Adjust load until ACN = 1.1 x 37.4 (ACN = 0.1). • 737-500 at 144,500 lbs, ACN = 41.1, (t2= 29.19). Represents an overload aircraft at the ACN limit.

  11. Numerical Example - 2 • Run FAARFIELD with: • 4-in P-401 • 8-in P-109 • Balance P-154 • 737-500 at 134,000 lbs and 1,200 annual departures • Run Design on the subbase: • 10.9-in P-154 • CDF = 1.0

  12. Numerical Example - 3 • Increase the load to 144,500 lbs at the same traffic and run Life • CDF = 2.14 over 20 years • Total departures to CDF of 1.0 = 11,208 in 9.3 years • CDF corresponding toACN = 0.1 is CDF = 1.14 • Increasing annual departures by 1,368 also gives CDF = 1.14

  13. Numerical Example - 4 • Therefore a CDF can represent either an increase in load or an increase in traffic, or a combination of the two. • But a ACN is affected only by an increase in load. Traffic is fixed and the structure is a dependent variable.

  14. Numerical Example - 5 • Add a true overload aircraft to the 737-500 at 134,000 lbs. • 787 at 486,000 lbs at 12 annual departures • Run Life: • CDF = 1.05 • CDF = 0.05 • CDF for the 737 = 1.0 • CDF for the 787 = 0.65

  15. Numerical Example - 6

  16. Numerical Example - 7

  17. Numerical Example - 8 • 737 ACN = 37.4. • 787 ACN = 80.1, does not meet the ACN criterion. • Probably need to apply a minimum total number of departures for overload aircraft with CDF >= 1.0, at least 240, maybe as many as 1,000. • Also remember tire pressure.

  18. ACN-PCN versus CDF • Is it possible to compare the ACN-PCN procedure with the CDF procedure and to derive compatible overload criteria? • Is the equation derived in the paper valid?

More Related