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 ▫ Undergraduate students: Samuel Henry, Charles Calimer, William McNally. Victor Smith, Nicole Giannelli Federal Aviation Administration ▫ Dr. David Brill, Dr. Gordon Hayhoe ▫ Dr. Satish Agarwal SRA ▫ Dr. Edward Guo ▫ Dr. Qiang Wang

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

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

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

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

MODELING CC2 SECTION USING FAARFIELD AND FEAFAA  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) Test ItemMRCMRGMRS PCC Surface 30.5 cm (12 in.) PCC (P-501) 30.5 cm (12 in.) PCC (P-501) 30.5 cm (12 in.) PCC (P-501) Sub-base cm (10 in.) aggregate sub-base (P-154) None15.2 cm (6 in.) Econocrete base (P-306) Sub-base 2None 21.9 cm (8.6 in.) Aggregate sub-base (P-154) Sub-gradeClay (CH) Medium Strength Sub-grade (4 ft.) CBR 7 Clay (CH) Medium Strength Sub-grade (4 ft.) CBR 7 Clay (CH) Medium Strength Sub- grade (4 ft.) CBR 7 Structural design data for CC2 test item (Brill et. al. 2009)

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

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

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 FactorsNumber of Levels Values LTE(S)50.25, 0.3, 0.35, 0.40, 0.45, 0.50 Total departures (in millions) , 0.5, 2 Sub-grade reaction (x 1000, kci) and Load (kips)635, 40, 50, 55, 60, 62.5

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

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 o F  bottom temperature is varied from 12 o F to -12 o F Slab curling due to temperature gradient

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

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

 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 CONCLUSIONS

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

BACKGROUND  MRC section of CC2 test pavement is used for analysis  MRC section is loaded using NAPTV (2004) Test SectionMRC PCC Surface 30.5 cm (12 in.) PCC (P-501) Sub-base 25.4 cm (10 in.) aggregate sub- base (P-154) Sub-gradeClay (CH) Medium Strength Sub-grade (4 ft.) CBR 7 NAPTF wheel configurationStructural design data for MRC

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

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 ‘C s ’ (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

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 (ε critical )  Determine the effect of aircraft speed, wheel configuration and pavement damping values on dynamic LTE(S)

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 ‘C k ’ (Yu et. al. (2010))  Joint spring constant (k s ) and damping constant (β) values for MRC section are unknown

3D FE MODEL USING ABAQUS Model properties used for MRC section Concrete and Foundation Model Linear Elastic Elements C3D8I - 8-node linear brick, Incompatible modes Mesh Size 6in. X 6in. (slab); 12 in. X 12in. (foundation) InteractionsSurface to Surface Hard Contact Joint Simulation Spring elements are used and spring constant is defined Pavement dampingStiffness proportional, ‘β’ Foundation damping Neglected LoadingHWD / Dynamic Boundary Conditions Displacements U 1 and U 2 in base layer is constrained in the plane of direction. Sub-grade layer is constrained in all directions at the bottom 0 30 P (lbf) Time, ms Actual HWD impulse Simulated impulse HWD loading impulse

CALIBRATION OF k S AND β VALUES  Spring constant (k s ) is adjusted to match field LTE(δ) of 0.81  k s = 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 Location of loading wheel & geophones for HWD

CALIBRATION OF k S AND β VALUES Comparison of FEM deflection with field data

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

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:

EFFECT OF AIRCRAFT SPEED ON CRITICAL TENSILE STRAINS  A 4-slab model is used with loading configuration similar to NAPTV  ε critical 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 k s = 21 million lbf/ft.

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 k s = 21 million lbf/ft.

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

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

 The critical tensile strain (ε critical ) 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. CONCLUSIONS

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

Outline  Introduction  Background  Effect of localized cracking on LTE (S)  Findings & Conclusions

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

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

Background: Full Scale Testing at NAPTF  Construction Cycle 2 (CC2)

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

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

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

LTE (S) at Position 1 in the Go Direction First visible cracks on slab S7Cracks form close to CSG-5 & 7 Begin of last day of valid data

LTE (S) at Position 4 in the Go Direction First visible cracks on slab S7Cracks form close to CSG-5 & 7 Begin of last day of valid data

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 May27 th. LTE (S) is declining but not continuous day to day. LTE (S) did not drop below 0.25 in any case.

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

Thank You!!