Editorial Type:
Article Category: Other
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Online Publication Date: 01 Dec 2012

Toward Using Tire-Road Contact Stresses in Pavement Design and Analysis

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Page Range: 246 – 271
DOI: 10.2346/tire.12.400403
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ABSTRACT:

Optimization of road pavement design, especially close to the surface of the pavement, requires a more rational approach, which will inevitably include modeling of truck tire-road contact stresses. Various road-surfacing failures have been recorded as evidence that the traditional road pavement engineering tire model idealized by a single uniformly distributed vertical contact stress of circular shape may be inadequate to properly explain and assist in the design against road surface failures. This article therefore discusses the direct measurement of three-dimensional (3D) tire pavement contact stresses using a flatbed sensor system referred to as the “Stress-In-Motion” (SIM) system. The SIM system (or device) consists of multiple conically shaped steel pins, as well as an array of instrumented sensors based on strain gauge technology. The test surface is textured with skid resistance approaching that of a dry asphalt layer. Full-scale truck tires have been tested since the mid-1990s, and results show that 3D tire contact stresses are nonuniform and that the footprint is often not of circular shape. It was found that especially the vertical shape of contact stress distribution changes, mainly as a function of tire loading and associated tire inflation pressures. In overloaded/underinflated cases, vertical contact stresses are the highest toward the edges of the tire contact patch. Higher inflation pressures at lower loads, on the other hand, result in maximum vertical stresses toward the center portion of the tire contact patch. These differences in shape and magnitude need to be incorporated into modern mechanistic-empirical road pavement design tools. Four different idealized tire models were used to represent a single tire type to demonstrate effects of tire modeling on the road pavement response of a typical South African pavement structure incorporating a relatively thin asphalt surfacing. Only applied vertical stress was used for the analyses. It was found that the fatigue life of the road surface layer can be reduced by as much as 94% and strain energy of distortion be increased by a factor of 2.8, depending on the characteristics of the tire model input selected for road pavement design and analysis.

Keywords: tire ; contact ; tire-road ; stress ; force ; measurement ; load ; patch ; pavement ; design ; strain energy of distortion (SED)
FIG. 1
FIG. 1

Distribution of tire inflation pressure of heavy vehicles in South Africa since 1974. (For details in legend, see [35].)

FIG. 2
FIG. 2

Tire inflation pressure differences between the steering and trailing tires of a selected group of heavy vehicles in South Africa in 2003 (from [25]).

FIG. 3
FIG. 3

Flat bed SIM device with Society of Automotive Engineering coordinate system used in this study from the measurements of 3D tire contact force (or stress) conditions inside the tire contact patch of a slow-rolling pneumatic tire (fitted on the HVS).

FIG. 4
FIG. 4

Dual SIM device under dual tire loading using the HVS.

FIG. 5
FIG. 5

Typical vertical (Z) contact stress pattern of a 11×R22.5 dual tire configuration with total tire load of 40 kN, and 520 kPa inflation pressure. Note that a maximum vertical contact stress of approximately 840 kPa was measured on the edge rib of the left tire in this illustration, reported in the text above the main image.

FIG. 6
FIG. 6

Typical lateral (+/−Y) contact stress pattern of a 11×R22.5 dual tire configuration with total tire load of 40 kN and 520 kPa inflation pressure. Note that a maximum contact stress of approximately 187 kPa was measured on the edge of the left tire in this illustration, reported in the text above the main image.

FIG. 7
FIG. 7

Typical longitudinal (+/− X) contact stress pattern of a 11×R22.5 dual tire configuration with total tire load of 40 kN, and 520 kPa inflation pressure. Note that a maximum contact stress of approximately 129 kPa was measured on the fore end of the left tire in this illustration, reported in the text above the main image.

FIG. 8
FIG. 8

(a) HVS tire loading of 20 kN and inflation pressure of 800 kPa (with typical n-shape measured vertical stress distribution), resulting in (b) typical n-shape plastic deformation (rutting) in the thin asphalt surfacing layer [33].

FIG. 9
FIG. 9

(a) HVS dual tire (over)loading of 35 kN (inflation pressure of 420 kPa with typical m-shape measured vertical stress distribution, resulting in (b) typical m-shape plastic deformation (rutting) in the asphalt surfacing layer [33].

FIG. 10
FIG. 10

Typical tire fingerprint of the vertical contact stress variation with tire loading (vertical scale from 15 to 50 kN) and with variation in tire inflation pressure (horizontal axis from 520 kPa to 800 kPa). Tire type 11×R22.5 with tread.

FIG. 11
FIG. 11

Typical field configuration during a special test series with a quad SIM system conducted in 2003 in South Africa at the Heidelberg Traffic Control Center.

FIG. 12
FIG. 12

Typical vertical contact stress footprint of a seven-axle heavy vehicle (22 tires) captured with the SIM system in 2003. Note the poor vehicle maintenance visible from the tire footprints.

FIG. 13
FIG. 13

Quasi-static rolling resistance force data on a textured measuring surface (SIM) for three tire inflation pressure cases of a 315/80 R22.5 tire at different vertical tire loading (Fz) levels.

FIG. 14
FIG. 14

Typical schematic of a multilayer road pavement structural design problem with (real) 3D tire loading. Note: hi = layer thickness; Ei = elastic modulus; vi = Poisson's ratio—for layer i, where i = 1,2,3…, and P = tire load, σ = stress.

FIG. 15
FIG. 15

SIM measured vertical (Z) contact stress for tire 12×R22.5 at load of 20 kN and inflation pressure of 520 kPa.

FIG. 16
FIG. 16

Tire model 1: traditional method: tire loading of 20 kN and assumed uniformly distributed vertical contact stress of 520 kPa of circular shape (i.e., single-disk) with diameter of the disk = 221 mm.

FIG. 17
FIG. 17

Tire model 2: tire loading of 20 kN and average measured vertical contact stress of 612 kPa, assumed to be of circular shape with restriction on the diameter of the single disk = 204 mm (not exceeding the tire width, i.e., fixed width).

FIG. 18
FIG. 18

Tire model 3: total tire loading of 20 kN distributed over four circular disks staggered in two layers. Maximum disk diameter = 204 mm. Maximum Z-stress = 842 kPa.

FIG. 19
FIG. 19

Tire model 4: total tire loading of 20 kN distributed over 206 smaller circular disks with a radius of 4.85 mm each. Maximum Z-stress – 2675 kPa @ x = −7.3612 mm and y = 76.5 mm.

FIG. 20
FIG. 20

Definition of the five-layer road pavement structure used for the various analyses. Materials according to [37] and screen clip from mePADS software [34].

FIG. 21
FIG. 21

Two-dimensional representation of measured vertical stress for tire model 4 (206 circular disks of radius 4.85 mm each), with analyses positions 1 and 2 indicated inside the tire contact patch.

Contributor Notes

2 Presenter/Corresponding author. Email: mbeer@csir.co.za
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