Effect of Transient Dynamic Loading on Flexible Pavement Response

Transcription

1 Effect of Transient Dynamic Loading on Flexible Pavement Response Imad L. Al-Qadi Founder Professor of Engineering Pyeong Jun Yoo Graduate Research Assistant Illinois Center for Transportation University of Illinois at Urbana-Champaign Transportation Research Board, 86th Annual Meeting January 21-25, 27 Washington, D.C.

2 Outline Background 3-Dimensional Finite Element Model Dynamic Wheel Load Model Pavement Response Analysis Summary and Future Research 2

3 Overall Research Approach Instrumentation Field Test 3-D Finite Element Modeling 3

4 Tire Loading and Pavement Response Tire Loading Pavement Responses 4

5 Drawbacks of Current Analysis Vehicular Loading: Stationary Circular Pressure Distribution: Uniform Vertical Contact Stress No Surface Tangential Contact Stress Effect of Vehicle Speed & Dynamic Loading: Loading Time-Dependent Pavement Responses Transient Local Dynamic Loading 5

6 Finite Element Approaches Axisymmetric 2D-Plane Strain 3D FE Loading Static Static Static/Dynamic Loading Area Circular Single Line Load Versatile Computation Time and memory Lowest Middle Highest Intensity Interface Modeling No Partial Yes Discontinuity Modeling No Partial Yes Major Disadvantage 6

7 Analytical Approaches System Equation Loading Time Stiffness Computing Steps Computing Intensity Residual Error Static FE Static Equilibrium Independent Tangent Stiffness Low Low High Dynamic FE Equation of Motion Dependent Effective Stiffness High High Low Major Differences 7

8 Al-Qadi et al. (24) Heavily Instrumented Virginia Smart Road Comparison between Dual and Widebase Tires 445/5R22.5, 455/55R22.5 Test parameters: speed, axle load, tire pressure Pavement Damage Evaluation: Linear Viscoelastic Material properties Usefulness of 3D FE Simulation Quasi-Static Repeated Moving Wheel Load Analysis Steering wheel is the most Detrimental Pavement Damage Analysis 8

9 Importance of Loading Dynamics Cebon (1986) Dynamic Component of Wheel Load Reduction in pavement Service Life Four times Increase in Fatigue Damage under Dynamic Loading 4 % Reduction in Rutting Damage Even for a Smooth Pavement: 1~15% increase in pavement response Shen (1996) Dynamic Displacement 18% Higher than the Static One 9

10 Why Dynamic Analysis Is Needed? Quasi-static visco analysis: Does not consider mass inertia and damping forces Dynamic analysis: Considers mass inertia and damping forces effect on pavement responses Various contact areas of tire imprint can affect the inertia forces Pavement response is affected by loading amplitude Successfully coupled with linear viscoelastic material property as a strain energy dissipation source 1

11 3D FE Model Pavement Design In-Plane Dimension (mm) Infinite Domain 11

12 Boundary Effect Check for Dynamic Analysis The Location of Infinite Element: at least 6 Times of Tire Loading Radius in Horizontal and Longitudinal Direction. Roller Roller Roller Roller 12

13 Loading Amplitudes Traditional Method Triangular, Trapezoidal, Rectangular Amplitude Impulsive loading (hammering) Include loading and unloading steps All the tire imprint elements have same loading history Continuous Loading: Newly Developed Method Loading amplitudes are linearly varied Variation in loading history at entrance and exit part of tire imprint 13

14 1.2 Trapezoidal Loading (Traditional) All tire imprints have the same loading amplitude Loading Amplitude Time (sec) 14

15 Continuous Loading (Entrance/ Exit Part) Contact Pressure (MPa) A5 A6 A7 A8 Time step Contact Pressure (MPa) A1 A2 A3 A4 15 Time Step

16 Difference in Loading Amplitude Longitudinal Strain (µ) Strain-oscillation at the bottom of HMA Time (sec) Rib 1 Rib 2 Rib 3 Rib 4 Rib 5 Longitudinal Strain (µ) No oscillation at the bottom of HMA: Properly Damped Rib 1 Rib 2 Rib 3 Rib 4 Rib Time (sec)

17 3 Dimensional Surface Contact Stresses 7 Compressive Stresses 6 Contact Stresses (kpa) Tire Rib Width (mm) 17 Horizontal Stresses Longitudinal Stresses Center of Tire Rib

18 Pavement Response Validation Bottom of the Wearing Surface (38.1mm) Longitudinal Strain (µ) Measured Calculated.1.2 Time (sec) Longitudinal Strain (µ) Bottom of the HMA (188 mm) Measured Calculated Time (sec)

19 Tensile strain (µ) Quasi-Static vs. Dynamic Analysis High Initial Strain Peak Strain about 26 µ T1 T2 T3 T4 T5 T6 T7 T8 T Time(sec) 35 T1 T2 T3 T4 T5 Implicit Dynamic: Tensile Strain at the Bottom of HMA Tensile strain (µ) T6 T7 T8 T9 Smaller initial Strain Quasi-Static: Tensile Strain at the Bottom of HMA Higher Peak Strain: 35 µ Time(sec)

20 Quasi-Static vs. Dynamic Analysis Tensile Strain (µ) Surface.5in 4 Quasi-Static Analysis Dynamic Analysis Depth(mm) 8 3in 12 6in 16 2

21 Dynamic Excitation Dominancy at 5 ºC Strain (µ) mph 65mph Low Temperature (5 C) Higher Dynamic Excitation at High Speed: Higher Dynamic Impact Viscoelasticity Dominancy at 25ºC Tensile Strain Longitudinal Strain Compressive Strain -1 Intermediate Temp. (25 C) -8 Lower Dynamic Excitation at High Speed: Viscous Dissipation Strain ( ) mph 65mph 21 Tensile Strain Longitudinal Strain Compressive Strain

22 Shear Strain Concentration at HMA In-Depth Distribution within a HMA Layer Dual-tire Loading: Four Critical Straining Points Wide-base tire Loading: Two Critical Straining Points Depth (mm) Compressive Shear Strain (µ) Widebase Tire Loading Dual-tire Loading Higher Shear Strains are exerted by the Dual Tire Loading 22

23 Critical Shear Strain vs. Tensile Strain (5mph) 5 4 5mph/ 3in Shear Strain Tensile Strain Shear Strain: Critical Value inside the HMA Maximum Tensile Strain at the Bottom of HMA Strain (µ) Shear Strain Tensile Strain 1 3in of HMA 3 5mph/ 12in 4 8 kips 1 kips 12 kips Shear Strain Tensile Strain 5mph/ 6in Strain (µ) 2 1 Strain (µ) in of HMA 8 kips 1 kips 12 kips 1 6in of HMA 8 kips 1 kips 12 kips 23

24 3D Dynamic Analysis: Transient Dynamic Loading 24

25 3D Dynamic Analysis: Stress Distribution Inside a Pavement 25

26 Summary Pavement Actually Subjected to Dynamic Wheel Load Simulation of Moving Wheel Load Continuous Loading Amplitude Transient Dynamic Wheel Load Subroutine 3D FE Model Various Pavement Response Analysis Successfully coupled with Dynamic Loading Model Implicit Dynamic Analysis Results in Greater Values than Quasi-Static Analysis 39% in Tensile Strain at the Bottom of HMA 25% in Compressive Stress on top of Subgrade 1% in Longitudinal Strain 26

27 Future Research Differential Pressure Distribution Feasibility Study on Asymmetry Tire Pressure Effect on Pavement Responses Brake-Maneuvering Effect Study on High Inertia Force Effect on Pavement Responses Development of Real Tire Model Two Solid (Tire and Pavement) Model Deformable + Deformable 27

28 Acknowledgement The National Center for Supercomputing Applications (NCSA) at UIUC Michelin America Research and Development 28

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