Equivalent Loading Frequencies to Simulate Asphalt Layer Pavement Responses Under Dynamic Traffic Loading

Transcription

1 Equivalent Loading Frequencies to Simulate Asphalt Layer Pavement Responses Under Dynamic Traffic Loading Elie Y. Hajj, Ph.D. Alvaro Ulloa, Ph.D. Candidate Peter E. Sebaaly, Ph.D. Raj V. Siddharthan, Ph.D. University of Nevada Reno Asphalt Mixture & Construction ETG Phoenix, Arizona March 18, 211 Introduction Dynamic response of AC pavements under moving load is a key component for accurate prediction of flexible pavement performance. Reliable determination of pavement responses to moving load is essential for a successful mechanistic design procedure. Time and temperature dependency of asphalt must be considered in the mechanistic analysis response model. 1

2 AASHTO MEPDG Approach Linear Elastic Analysis E* 1 t 1, T 1 Static Tire E* 2 t 2, T 2-4 Tire Foot Print (Dual Spacing)/2 Shift Factor, log(at) E* 3 E* 4 E* 5 E* 6 t 3, T 3 t 4, T 4 t 5, T 5 t 6, T Temperature, F c h -2 Transverse Distance, inch HMA Base Subgrade AASHTO MEPDG Vertical stress distribution used to estimate trafficinduced loading time. Axle load configuration, Vehicle speed & Pavement structure 2

3 Literature Review Dongre, R. N., Myers, L. A., and D Angelo, J. A., Conversion of Testing Frequency to Loading Time: Impact on Performance Predictions Obtained from the Mechanistic Empirical Pavement Design Guide, Presented at 85th Annual Meeting of the Transportation Research Board, Washington, D.C., 26. Al Qadi, I. L., W. ie, and Elseifi, M. A., Frequency Determination from Vehicular Loading Time Pulse to Predict Appropriate Complex Modulus in MEPDG, Journal of the Association of Asphalt Paving Technologists, Vol. 77, 28, pp Katicha, S., Flintsch, G.W., Loulizi, A., and Wang L. Conversion of Testing Frequency to Loading Time Applied dto Mechanistic Empirical i i lpavement tdesign Guide, Transportation Research Record No. 287, TRB, Washington D.C., 28, pp Appropriate Representative Elastic Modulus B. S. Underwood and Y. R. Kim Determination of the Appropriate Representative Elastic Modulus for Asphalt Concrete, IJPE, Vol. 1, Iss. 2, 29, pp Evaluated several approximation methods for calculation of stresses & strains in linear viscoelastic materials. MEPDG method is biased towards overestimating the appropriate stiffness by up to a 31% error. Representative modulus to use for LEA is average of d i d l f l 1/ d dynamic modulus at a frequency equal to 1/t p and relaxation modulus evaluated at a time equal to ½ t p. Proposed Method resulted in 2 6% error 3

4 Research Objective Investigate the existence of one or more predominant frequencies (f p ) associated with the AC layer that controls the dynamic response of pavements. AC Critical Reponses : Longitudinal & transverse tensile strains Vertical compressive strains Viscoelastic vs. Pseudo Analysis Viscoelastic Pseudo dynamic Pseudo static Velocity Velocity HMA E* = f(freq) & = f(freq) HMA E* fp =?, fp =? HMA E* fp =? fp = CAB CAB CAB SG SG SG Pavement responses Pavement responses Pavement responses 4

5 Pavement Analysis 3D-Move Analysis Software Freeware Download at: Pavement Analysis 3D-Move Analysis Software - Validation 1. 3D-Move vs. ViscoRoute (21) ViscoRoute (IFFSTAR LCPC): moving circular loaded areas with uniform contact pressure, viscoelastic material properties Reference: Chabot, A., Chupin, O., Deloffre, L., and Duhamel, D., Viscoroute 2.: a tool for the simulation of moving load effects on asphalt pavement, Road Materials and Pavement Design an International Journal, Volume 11/2, 21, pp Loft A., "Evaluation de Viscoroute-v1 pour l étude de quelques chaussées souples", Msc. Dissertation, Dresden University of Technology speciality Urban and Road construction, 25. A38 Pavement Experimental Program for aircrafts. Comparison between elastic computations, ViscoRoute1. simulations and transversal strain measurements at the bottom of bituminous layers for a 4- wheels moving load 5

6 Pavement Analysis 3D-Move Analysis Software - Validation Transverse strain yy, microns HMA thickness = 3.9" 2ºC 3D-Move 2ºC ViscoRoute 1ºC 3D-Move 1ºC ViscoRoute ºC 3D-Move ºC ViscoRoute -1ºC 3D-Move -1ºC ViscoRoute 3D-Move vs. ViscoRoute Vehicle speed = 6 to 7 mph Pavement temperature = -2ºC to 2ºC Vehicle speed, mph -2ºC 3D-Move -2ºC ViscoRoute ViscoRoute Test Results Refer to: Chabot, A., Chupin, O., Deloffre, L., and Duhamel, D., Viscoroute 2.: a tool for the simulation of moving load effects on asphalt pavement, Road Materials and Pavement Design an International Journal, Volume 11/2, 21, pp rons Transverse strain yy, micr 3 HMA thickness = Vehicle speed, mph 2ºC 3D-Move 2ºC ViscoRoute 1ºC 3D-Move 1ºC ViscoRoute ºC 3D-Move ºC ViscoRoute -1ºC 3D-Move -1ºC ViscoRoute -2ºC 3D-Move -2ºC ViscoRoute Pavement Analysis 3D-Move Analysis Software - Validation 2. SD Heavy Off-Road Vehicle Field Sections (2) 6

7 Pavement Analysis 3D-Move Analysis Software - Validation 3. PennState University Test Track (1999) Pavement Analysis 3D-Move Analysis Software - Validation 4. MnRoad (1997) 7

8 Database of pavement responses Structures 1 & 2 pavement analyses completed Structure 1 Structure 2 Structure 3 Structure 4 Pavement Responses Locations 4 inch HMA layer 8 inch HMA layer A Data analysis completed for responses at center line of the load 8

9 Proposed approach to determine f p Example: Bottom of the 4-inch HMA layer: Normal Strains, microns Compression Tension t =.5 sec t =.3 sec Pavement temperature = 7 F Vehicle speed = 4 mph Time, sec Proposed approach to determine f p FFT amplitudes of the normal strains of the 4-inch HMA FFT ampltitude f p = Hz Pavement temperature = 7 F Vehicle speed = 4 mph f p = Predominant frequency f p = 12.8 Hz Frequency, Hz 9

10 f p for the 4-inch HMA layer Case Study Depth (in) Predominant frequency, (Hz) xx yy zz zz Case 1: 7ºF and 4 mph Case 2: 14ºF and 4 mph Case 3: 7ºF and 6 mph Case 4: 14ºF and 6 mph Case 5: 7ºF and 1 mph Case 6: 14ºF and 1 mph fp fpseudo fp fpseudo fp fpseudo fp fpseudo Case 4 Predominant Frequencies Temp = 14 F, V = 6 mph, Tensile Strain xx Lo ongitudinal Strain, exx microns 6 Compression 4 2 t =.1 sec 2 t =.2 sec top 4 bottom Tension Time, sec 1

11 Case 4 Predominant Frequencies Temp = 14 F, V = 6 mph, Tensile Strain xx 12 1 top FFT amplitude f p = Hz f p = 24 Hz f p = 43.3 Hz bottom Frequency, Hz Pseudo-Dynamic Analysis Viscoelastic Pseudo dynamic Velocity= 6 mph Velocity= 6 mph HMA E* = f(freq) & = f(freq) HMA f p = Hz E* fp, fp f p =43.3 Hz E* fp, fp CAB CAB SG SG Pavement responses Pavement responses 11

12 Case 4 Pseudo-Dynamic Analysis Temp = 14 F, V = 6 mph, Tensile Strain xx Maximum tensile strain, microns D Move Viscoelastic fpseudo = Hz fpseudo = /43.3 Hz % 2% f p for the 8-inch HMA layer Case Study Depth* (in) Predominant frequency, (Hz) xx yy zz zz Case 7: 7ºF and 4 mph Case 8: 14ºF and 4 mph Case 9: 7ºF and 6 mph Case 1: 14ºF and 6 mph Case 11: 7ºF and 1 mph Case 12: 14ºF and 1 mph fp fpseudo fp fpseudo fp fpseudo fp fpseudo

13 Viscoelastic vs. Pseudo-Dynamic analysis 4-inch HMA layer 5 Computed pseudo strains, microns inch HMA layer - 7ºF - 4 mph +1% -1% Computed pseudo strains, microns inch HMA layer - 7ºF - 6 mph +1% -1% Computed pseudo strains, microns 5 4-inch HMA layer - 7ºF - 1 mph % -1% microns5 Computed pseudo str rains, inch HMA layer - 14ºF - 4 mph +1% -1% microns12 Computed pseudo str rains, 1 4-inch HMA layer - 14ºF - 6 mph % 4-1% Computed pseudo str rains, microns 12 4-inch HMA layer - 14ºF - 1 mph % 4-1% Viscoelastic vs. Pseudo-Dynamic analysis 8-inch HMA layer Computed pseudo strains, m microns9 Computed pseudo strains, 8-inch HMA layer - 7ºF - 4 mph microns % 5-1% inch HMA layer - 14ºF - 4 mph % 3-1% Computed pseudo strains, m 8-inch HMA layer - 7ºF - 6 mph microns % 5-1% inch HMA layer - 14ºF - 6 mph 75 6 microns9 Computed pseud o strains, 45 +1% 3-1% Computed pseud do strains, microns Computed pseudo strains, microns 2 8-inch HMA layer - 7ºF - 1 mph % 5-1% inch HMA layer - 14ºF - 1 mph % 3-1%

14 Pseudo-Static Analysis Pseudo-Static: Vehicle speed = Linear Elastic Analysis (LEA) Use f p to select E* fp Damping fp = Also Compare pavement responses following MEPDG approach (f = 1/t) Modified MEPDG (f = 1/(2t)) Ferry (f = 1/(2 t)) Pavement responses comparison Maximum tensile strain, microns Pavement temperature = 7ºF Vehicle speed = 4 mph fpseudo dyn= Hz fpseudo stat= Hz Maximum tensile strain yy, microns Pavement temperature = 7ºF.5 Vehicle speed = 4 mph fpseudo dyn = Hz fpseudo stat = Hz Pavement temperature = 7 F 4 inch HMA layer 4 mph Maximum vertical strain zz, microns Pavement temperature = 7ºF.5 Vehicle speed = 4 mph fpseudo dyn = Hz fpseudo dyn = Hz 14

15 Pavement responses comparison Maximum tensile strain, microns Pavement temperature = 14ºF Vehicle speed = 4 mph fpseudo dyn = /3.4 Hz fpseudo stat = /3.4 Hz Maximum tensile strain yy, microns Pavement temperature = 14ºF.5 Vehicle speed = 4 mph fpseudo dyn = Hz fpseudo stat = Hz Pavement temperature = 14 F 4 inch HMA layer 4 mph Maximum vertical strain zz, microns Pavement temperature = 14F.5 Vehicle speed = 4 mph fpseudo stat= 3.4/ Hz fpseudo stat= 3.4/ Hz Pavement responses comparison Maximum tensile strain, microns Pavement temperature = 7ºF 1. Vehicle speed = 4 mph fpseudo dyn=12.8/3.4 Hz fpseudo st=12.8/3.4 Hz Maximum tensile strain yy, microns Pavement temperature = 7ºF Vehicle speed = 4 mph fpseudo dyn = 12.8 Hz fpseudo st = 12.8 Hz Pavement temperature = 7 F 8 inch HMA layer 4 mph Maximum vertical strain zz, microns Pavement temperature = 7ºF Vehicle speed = 4 mph fpseudo dyn = 3.4/12.8 Hz fpseudo st = 3.4/12.8 Hz 15

16 Pavement responses comparison Maximum tensile strain, microns Pavement temperature = 14ºF Vehicle speed = 4 mph fpseudo dyn=/3.4 Hz fpseudo stat=/3.4 Hz Maximum tensile strain yy, microns Pavement temperature = 14ºF Vehicle speed = 4 mph fpseudo dyn= Hz fpseudo stat= Hz Pavement temperature = 14 F 8 inch HMA layer 4 mph Maximum vertical strain zz, microns Pavement temperature = 14ºF Vehicle speed = 4 mph fpseudo dyn= 3.4/ Hz fpseudo stat= 3.4/ Hz Pavement responses comparison Pavement temperature = 7 F 4 inch HMA layer 16

17 Pavement responses comparison Pavement temperature = 14 F 4 inch HMA layer Pavement responses comparison Pavement temperature = 7 F 8 inch HMA layer 17

18 Pavement responses comparison Pavement temperature = 14 F 8 inch HMA layer Overall Findings Use of one single set of f p cannot be assigned to the AC layer to study all responses. Pavement responses can be successfully predicted (within ±1%) by Pseudo-Dynamic equivalent approach. MEPDG approach derives in comparable pavement responses only when asphalt layer is stiff and there are no multiple f p within the asphalt layer. 18

19 Additional needed work Investigate influence of axle load, response location and axle configuration on f p. Investigate influence of CTB on f p. Evaluate different time-frequency conversions. Other! Feedback Acknowledgment This work is part of the overall effort in the Asphalt Research Consortium (ARC) work element E2d. ( FHWA support gratefully acknowledged. Contents reflect the views of the authors and do not necessarily reflect the official views & policies of FHWA. 19