An Improved Subgrade   Model for the CrashAnalysis of Guardrail Posts                  Abdelmonaam SASSI, Ph.D.           ...
Introduction: Regulations       NCHRP 350 (1993)                 MASH (2009)   Recommended Procedures                     ...
I- Full scale guardrail model                     L= 53.3 m                     D = 1950 mm                     N = 30 pos...
TYPICAL FULL SCALE GUARDRAIL TEST
II- Component testing of the guardrail                                           post                                     ...
III-1 Soil ModelingSubgrade Method               Continuum Method         -Fast                          -Accurate     -Wi...
III-2 Soil simulation with combining the twIo                    methods Kennedy et al. (2004)    Continuum Method        ...
III-3 Typical Results of the FE Study of the      dynamic testing of the guardrail post                                  P...
IV Proposed modelImpactor             Post                     Lumped                    soil mass                        ...
III-1 Stiffness Calculation (k)        Method of Habibaghi and Langer (1984).                      (Based on the bearing c...
III-2 Lumped Mass calculationIso-displacement contour from Continuum model                    Iso-displacement defined con...
III-3 Damper calculation                                         Parametric Study Results      mx     cx     kx     f    Z...
IV Results of the simulation             Maximum Deflection    Average Force     Peak Force                   (mm)        ...
V- Results of the simulation           Modeled improved by defining space between the                     post and the lum...
CAE Results
IV-3-1 Full Scale guardrail test simulation
IV-3-2 Vehicle response                   Roll AngleVehicle Speed
IV-3-2 Sequential of impact event of dynamic test        Frontal View           Overhead View
V- ConclusionsMethod developed for cohesionless and couldbe extended to cohesive soilMethod accounts for the inertia effec...
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An Improved Subgrade Model for Crash Analysis of Guardrail Posts - University of Windsor

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In this study, a computer simulation model of a rigid impactor loading laterally a roadside W152x13.4 post has been developed. The interaction of cohesionless soil with a post was studied and compared to an existing dynamic test results from a published literature. Two approaches to simulate the soil have been studied: the continuum method where the soil is modeled as a solid element with Drucker and Prager material law, and the subgrade method where the soil reaction is simulated by a series of nonlinear springs. An improved method of the subgrade approach has been developed where the soil is modeled as a system of parallel springs and dampers with a lumped mass attached to the post. A simple procedure to calculate the lumped soil mass and the damping coefficient is presented.

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An Improved Subgrade Model for Crash Analysis of Guardrail Posts - University of Windsor

  1. 1. An Improved Subgrade Model for the CrashAnalysis of Guardrail Posts Abdelmonaam SASSI, Ph.D. May 17, 2012Dept. of Civil and Environmental Engineering, University of Windsor
  2. 2. Introduction: Regulations NCHRP 350 (1993) MASH (2009) Recommended Procedures Manual for Assessing for the Safety Performance Evaluation of Highway Safety Hardware Features TL3-11 TL3-10 TL3-11 TL3-10 2000 kg light 820 kg Sedan 2270 kg light 1100 kg Sedan truck truck V = 100kph V = 100kph V = 100 kph V = 100 kph Angle : 250 Angle : 200 Angle : 250 Angle : 250Pickup truck impacting the guardrail, with 100 km/hspeed at 25 deg impact angle, should not penetrate, under-ride or override the installation.
  3. 3. I- Full scale guardrail model L= 53.3 m D = 1950 mm N = 30 posts V = 100 km/h Angle = 25 deg Depth = 1100 mm
  4. 4. TYPICAL FULL SCALE GUARDRAIL TEST
  5. 5. II- Component testing of the guardrail post Post Impactor 550 mm 1830 mm 1100 mm Dynamic testing Set-upDynamic testing Set-up used by Coon et al (1999) Soil Density Moisture Impact Speed Max Deflection Soil Density 2011 Slide #5 Sassi Moisture Test Kg/m3 Content m/s3 mm Kg/m3 Content Test #1 1980 Dry 4.6 234 42.8 42.8 Test #2 2110 Dry 5.4 314 43.9 43.9 Test #3 2240 Dry 5.9 348 47.3 47.3 Test #4 --- Dry 8.9 Override NA NA
  6. 6. III-1 Soil ModelingSubgrade Method Continuum Method -Fast -Accurate -Widely used -Does account for-Accurate after the peak the inertial effect -Does not account for -Computationally very costly the inertial effect -Soil parameters not available
  7. 7. III-2 Soil simulation with combining the twIo methods Kennedy et al. (2004) Continuum Method Subgrade Method Combined of two methods: -Subgrade method in all the guardrail post -Add continuum method in -Does account for the inertial the impact zone with no little effect or no stiffness and right -Computationally relatively density. costly
  8. 8. III-3 Typical Results of the FE Study of the dynamic testing of the guardrail post Plaxico (2002)Traditional subgrade modeling only with springs missed the inertia effect.
  9. 9. IV Proposed modelImpactor Post Lumped soil mass Soil modeled as: Spring stiffness ( k ) Damper (c ) Lumped mass (m) C, k & m are not constant along the pile embedment
  10. 10. III-1 Stiffness Calculation (k) Method of Habibaghi and Langer (1984). (Based on the bearing capacity approach) kh Nq Nq is the bearing capacity factor y z Nq A B 0.1245yA 15.276 14.09 e Z is the depth B is the width of the post y is post deflection σ’ overburden pressure
  11. 11. III-2 Lumped Mass calculationIso-displacement contour from Continuum model Iso-displacement defined cone centered around the rotation centre of the guardrail post . Lumped soil mass function of z M1 M2 M3 Parametric Study to determine the damping factor ξ
  12. 12. III-3 Damper calculation Parametric Study Results mx cx kx f Z Mass K Cc 5% Cc 20% Cc 12% Mm kg kN/mm N/s cc 2 mk 100 34.08 1.49 18.05 1.81 2.71 2.26 c 200 25.61 2.39 15.65 1.56 2.35 1.96 300 18.35 4.95 19.06 1.91 2.86 2.38 cc 400 12.30 7.62 19.36 1.94 2.90 2.42 500 7.46 10.37 17.59 1.76 2.64 2.20 600 3.83 13.13 14.19 1.42 2.13 1.77 700 1.41 16.09 9.53 0.95 1.43 1.19 800 0.20 19.04 3.92 0.39 0.59 0.49Parametric Study to determine the damping factor ξ 900 0.65 22.12 9.38 0.76 1.13 0.95
  13. 13. IV Results of the simulation Maximum Deflection Average Force Peak Force (mm) (kN) (kN) Test Model Test Model Test Model Test #1 234 233 42.8 43.0 64.0 53.1 Test #2 314 296 43.9 45.9 66.9 57.8 Test #3 348 338 47.3 47.9 67.0 64.3 Test #4* Override Override NA 56.3 104.7 97.2Good correlation between the 4 dynamic tests and the model results
  14. 14. V- Results of the simulation Modeled improved by defining space between the post and the lumped mass Model Continuum Method Spring model Spring/DamperSimulation time (S) 0.180 0.180 0.180 Run time 8.49T T 1.06T T = 40 minutes
  15. 15. CAE Results
  16. 16. IV-3-1 Full Scale guardrail test simulation
  17. 17. IV-3-2 Vehicle response Roll AngleVehicle Speed
  18. 18. IV-3-2 Sequential of impact event of dynamic test Frontal View Overhead View
  19. 19. V- ConclusionsMethod developed for cohesionless and couldbe extended to cohesive soilMethod accounts for the inertia effectMethod accounts for the damping effectMethod accurate and tunableMethod computer time consumption efficient

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