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Rigid Airfield Pavement Research at Rowan

Rigid Airfield Pavement Research at Rowan . Presented by: Yusuf Mehta, Ph.D., P.E. Wednesday April 25 th 2012. ACKNOWLEDGEMENTS. Rowan University Co-PI : Douglas Cleary, Ph.D., P.E. Graduate students : Akshay Joshi, Charles Cunliffe

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Rigid Airfield Pavement Research at Rowan

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  1. Rigid Airfield Pavement Research at Rowan Presented by: Yusuf Mehta, Ph.D., P.E. Wednesday April 25th 2012

  2. ACKNOWLEDGEMENTS • Rowan University • Co-PI: Douglas Cleary, Ph.D., P.E. • Graduate students: Akshay Joshi, Charles Cunliffe • Undergraduate students: Samuel Henry, Charles Calimer, William McNally. Victor Smith, Nicole Giannelli • Federal Aviation Administration • Dr. David Brill, Dr. Gordon Hayhoe • Dr. SatishAgarwal • SRA • Dr. Edward Guo • Dr. QiangWang

  3. Outline • Part 1: Effect of LTE(S) on design thickness and effect of temperature curling on LTE(S) of airfield pavement • Part 2: Impact of Pavement Damping and Aircraft Speed on Stress-based LTE using 3D Finite Element Analysis • Part 3: A Study to Determine the Impact of Cracking on Load Transfer Efficiency of Rigid Airfield Pavements

  4. Effect of LTE(S) on design thickness and effect of temperature curling on LTE(S) of airfield pavements

  5. PROBLEM STATEMENT • The impact of LTE(S) on design PCC thickness is unknown • Variations in temperature / moisture → volume changes • Slab warping may affect LTE • Impact of temperature gradient on critical edge stresses needs to be determined • The sensitivity of LTE(S) to temperature gradient is unknown www.cement.org

  6. OBJECTIVES • Determine the impact of LTE (S) and loading intensity on design PCC thickness • Determine the effect of temperature gradient on critical stresses at the joint • Study the effect of temperature curling on LTE of the joint under varying sub-structure conditions Load transfer using steel dowel bars

  7. MODELING CC2 SECTION USING FAARFIELD AND FEAFAA Structural design data for CC2 test item (Brillet. al. 2009) • Airplane SWL-50 (Single Wheel Load) single gear aircraft is used • Gross weight is varied from 35,000 lbs (156 kN) to 62,500 lbs (278 kN)

  8. IMPACT OF LTE ON DESIGN THICKNESS • FAARFIELD special version allow to vary LTE(S) • FAARFIELD model • Gross airplane weight is varied from 35 kips to 62.5 kips • 100,000 annual departures • 0% annual growth • LTE(S) → 0.25 to 0.50 • Airplane SWL-50

  9. IMPACT OF LTE ON DESIGN THICKNESS (MRG) • Design thickness reduces by 1.87 in. as load decreases from 50 kips to 40 kips • At 50 kips, PCC thickness drops by 3.53 in. with increase in LTE(S) from 0.25 to 0.5

  10. STATISTICAL ANALYSIS • A statistical model was developed to determine the sensitivity of thickness to LTE(S) • LTE(S), modulus of sub-grade reaction, load intensity and number of total departures are the Dependent variables

  11. NON-LINEAR REGRESSION ANALYSIS • The non-linear regression analysis yields the following equation: • R squared = 0.995 • For an increase in LTE (S) by a value of 0.10, the • design thickness reduces by approximately • 1.3 inches (33 mm).

  12. IMPACT OF TEMPERATURE GRADIENT ON STRESSES • A 2-slab FEAFAA model is used • Slab thickness for MRG, MRC and MRS = 12 in. • Airplane SWL-50 with gross weight = 50 kips is used • Joint stiffness = 131 ksi • Temperature at the top of slab: 0 oF • bottom temperature is varied from 12 oF to -12 oF Slab curling due to temperature gradient

  13. IMPACT OF TEMPERATURE GRADIENT ON STRESSES • At 50 kips load, for an increase in temp. gradient from -1oF/in. to 1oF/in.: • Joint stresses for MRG and MRC reduce by 15% • Joint stress for MRS reduce by 17%

  14. IMPACT OF TEMPERATURE GRADIENT ON LTE(S) • LTE(S) increases with decrease in temperature gradient • At 0oF/in., the LTE(S) of the pavement sections is about 0.34 • LTE(S) increases by ≈ 0.04 for all sections for every 1oF/in. drop in temperature gradient

  15. CONCLUSIONS • LTE(S) affects the design PCC thickness considerably • (+) temperature gradients yield lower joint stresses & lower LTE(S) than (-) temperature gradients • Stiffer sub-structure causes lower joint stresses than a weaker sub-structure at a given temperature gradient • LTE(S) is insensitive to the sub-structure stiffness at a given temperature gradient

  16. Impact of Pavement Damping and Aircraft Speed on Stress-based LTE using 3D Finite Element Analysis Presented by: Akshay Joshi Rowan University November 8th, 2011

  17. BACKGROUND • MRC section of CC2 test pavement is used for analysis • MRC section is loaded using NAPTV (2004) NAPTF wheel configuration Structural design data for MRC

  18. Wheel Path (North Carriage) Wheel Path (South Carriage) BACKGROUND • Field data used for analysis: • Strain profile from sensor CSG-7 • HWD test data Location of concrete strain gages in MRC section

  19. PROBLEM STATEMENT • Research conducted on pavement responses under moving loads is limited • The ratio of dynamic LTE(S) to static LTE(S) varies in the range 1 to 2 depending on speed and pavement damping ‘Cs’ (Yu et. al. (2010) • The impact of aircraft speed on critical tensile stresses and dynamic LTE(S) needs to be determined • The effect of pavement damping on dynamic LTE(S) is unknown • Aircraft wheel configuration and loading intensity may affect the dynamic LTE(S) at the joint

  20. OBJECTIVES • Calibrate the 3D FE model for MRC using HWD data • Validate the model using strain values measured under NAPTV loading • Determine the effect of aircraft speed on tensile strain values at the bottom of PCC at the joint (εcritical) • Determine the effect of aircraft speed, wheel configuration and pavement damping values on dynamic LTE(S)

  21. 3D FE MODEL USING ABAQUS • 4-slab MRC section is modeled using ABAQUS 6.10 • Dowel joints are simulated using springs • Rayleigh damping is used to simulate pavement damping • The dynamic LTE(S) is not sensitive to foundation reaction modulus ‘k’ and foundation damping ‘Ck’ (Yu et. al. (2010)) • Joint spring constant (ks) and damping constant (β) values for MRC section are unknown

  22. Simulated impulse P (lbf) Actual HWD impulse 0 30 Time, ms 3D FE MODEL USING ABAQUS Model properties used for MRC section HWD loading impulse

  23. CALIBRATION OF kS AND β VALUES Location of loading wheel & geophones for HWD • Spring constant (ks) is adjusted to match field LTE(δ) of 0.81 • ks = 210 million lbf/ft gives the desired LTE(δ) • β value is adjusted to match actual field deflections • β varies with load; β = 0.30s to 0.35s gives the desired deflections

  24. CALIBRATION OF kS AND β VALUES Comparison of FEM deflection with field data

  25. VALIDATION OF MRC MODEL • Strain profile from CSG-7 is compared with predicted strain profile • Calibrated values of ks and β are used • A time lag is observed in the FEM strain predictions due to pavement inertia and damping

  26. SENSITIVITY ANALYSIS • A range of damping values is used (β = 0.20 s to 0.60 s) • Aircraft speed is varied from 3.67 fps to 20 fps • Dynamic LTE(S) is calculated as follows:

  27. EFFECT OF AIRCRAFT SPEED ON CRITICAL TENSILE STRAINS ks = 21 million lbf/ft. • A 4-slab model is used with loading configuration similar to NAPTV • εcritical values drop by 37%, 50% and 56% for β value of 0.2 s, 0.4 s and 0.6 s respectively as the speed increases from 3.67 fps to 20 fps

  28. EFFECT OF AIRCRAFT SPEED ON LTE(S) • Dynamic LTE(S) increases with aircraft speed & damping value • For β = 0.2s, the LTE(S) value increases by 0.09 as the speed of the aircraft increases from 3.66 fps to 20 fps ks = 21 million lbf/ft.

  29. EFFECT OF PAVEMENT DAMPING ON LTE(S) • A 4-slab model is used with SW loading configuration and speed=20 fps • Pavement damping and joint stiffness value is varied • LTE(S) values are closer to 0.5 for higher pavement damping values • The increase in β from 0 to 0.2s causes an increase in LTE (S) by 0.10

  30. EFFECT OF AIRCRAFT LOAD AND WHEEL CONFIGURATION ON LTE(S) • β = 0.4s; ks = 2.1x107 lbf/ft; aircraft speed = 20 fps is used • LTE(S) increases by 10% as wheel configuration changes from single wheel to duel wheel from duel wheel to duel tandem wheel configuration

  31. CONCLUSIONS • The critical tensile strain (εcritical) values at the joint reduce significantly with increase in the aircraft speed • LTE(S) increases with aircraft speed and pavement damping value. • LTE(S) is more sensitive to pavement damping at lower aircraft speeds. • LTE(S) is insensitive to aircraft load but sensitive to wheel configuration.

  32. A STUDY TO DETERMINE THE IMPACT OF CRACKING ON LOAD TRANSFER EFFICIENCY OF RIGID AIRFIELD PAVEMENTS

  33. Outline • Introduction • Background • Effect of localized cracking on LTE (S) • Findings & Conclusions

  34. Objectives • Determine the behavior of LTE (S) as trafficking progresses • Determine the effect that cracking has on the behavior of LTE (S)

  35. Research Approach • Task I: Determining when localized cracking was visually observed on Slabs S7 and S8 • Task II: Gathering strain gage data for concrete strain gages (CSG’s). • Task III: Synchronizing strain gage data and determine LTE (S) • Task IV: Determining change in LTE (S) with trafficking

  36. Background: Full Scale Testing at NAPTF • Construction Cycle 2 (CC2)

  37. Background: Test Vehicle CC2 (MRC) • Dual tandem gear type • nominal load for all tests the same • Traffic on test item MRC began on • April 27 and ended on June 24, 2004

  38. Effect of Localized Cracking on LTE (S) • Visual analysis of crack maps • CSG-5 & CSG-7 on Slabs S7 & S8 • Loading began May 5th • First crack appeared on S7 June 1 • Cracking continued and became more localized by June 4th • Last day of valid data June 22nd

  39. Determination of Onset of Invalid Data June 23rd June 1st

  40. LTE (S) at Position 1 in the Go Direction First visible cracks on slab S7 Cracks form close to CSG-5 & 7 Begin of last day of valid data

  41. LTE (S) at Position 4 in the Go Direction First visible cracks on slab S7 Cracks form close to CSG-5 & 7 Begin of last day of valid data

  42. Summary of Findings for LTE (S) • LTE (S) on first day of testing maintained values between 0.4 and 0.5 for all cases. • LTE (S) maintained values roughly above 0.40 until May27th. • LTE (S) is declining but not continuous day to day. • LTE (S) did not drop below 0.25 in any case.

  43. Future Work • To study the impact of temperature curling on critical edge stresses and LTE (S) for CC6 test pavement sections under varying • PCC modulus • Base layer modulus • loading intensity • To model CC6 test sections for analysis of pavement responses under dynamic conditions using ABAQUS • To analyze NAPTF data to compare performance of different types of pavement joints in CC6

  44. Thank You!!

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