WESLEA Help File

WESLEA Help file Reformatted from the original HELP file by Luis R. Vásquez-Varela, PhD (c). Universidad Nacional de Colombia Sede Manizales, 2016.

1 WESLEA for Windows-General Procedure WESLEA for Windows is a mechanistic pavement analysis program that can calculate pavement response to applied tire loads. Pavement response is defined in terms of stress, strain, and displacement. The pavement response may then be used to predict the pavement life with respect to fatigue or rutting rutting.. The following following outline outline describes the general procedure for using the program. First select a system of units to work in. WESLEA for Windows always begins in English units, but the user may select SI (Metric) from the Units menu. There are three main types of inputs that must be entered by the user. Structure Load Conditions Evaluation The drop-down main menu gives access to each of the input screens, as shown below.

After entering the inputs, select View Output from the Output drop down menu. If a standard load configuration was selected, t he pavement life has all ready been determined. If a non-standard load configuration (Other Other)) was chosen, the pavement pavement life must be determined manually. Find the maximum tensile strain at the bottom of the first layer and enter this into the fatigue performance equation. equation.

Find the maximum vertical compressive strain at the top of the subgrade and enter this into the rutting performance equation.

2 Changes from Version 2.0 Two primary changes have been made since V ersion 2.0. Change 1: In the output dialog box, there is now a button (shown below) to directly view the transfer functions.

Change 2: The exported data file now contains the fatigue and rutting life calculations in addition to the transfer

functions used in the calculation.

3 Structure 3.1

Pavement Structure Inputs

This dialog box defines the pavement structure to be analyzed. The particular inputs are outlined below. Select the number of layers.

For each pavement layer, specify Material Type Modulus Poisson’s Ratio

Thickness Slip Condition

3.1.1

Material Type

Select the type of material to be used in each layer. Each material has an associated range of  modulus and Poisson’s ratio. Abbreviation AC PCC G.B. Soil Rock Other

3.1.2

Name Asphalt Concrete Portland Cement Concrete Granular Base Soil Rock Other

Modulus

The modulus represents the stiffness of the material expressed in psi. When a material is selected, a range of moduli and an optimum value are chosen by the program. Any value within the range may be used for the modulus. Material AC PCC G.B.

Minimum Modulus, psi 80,000 2,000,000 5,000

Default Modulus, psi 500,000 4,000,000 20,000

Maximum Modulus, psi 2,000,000 7,000,000 50,000

Material Soil Rock Other

Minimum Modulus, psi 3,000 500,000 500

Default Modulus, psi 12,000 4,000,000 1,000,000

Maximum Modulus, psi 30,000 1,000,000 10,000,000

Material AC PCC G.B. Soil Rock Other

Minimum Modulus, MPa 552 13,790 35 21 3,447 3

Default Modulus, MPa 3,447 27,579 138 83 6,845 6,895

Maximum Modulus, MPa 13,790 48,263 345 207 27,579 68,948

3.1.3

Poisson’s Ratio

Poisson’s ratio is a material property that describes how it deforms. By definition, Poisson’s ratio is:

        When a material is selected, a range and default values are chosen. Any value within the range for the material may be used. Material AC PCC G.B. Soil Rock Other

3.1.4

Minimum Poisson 0.15 0.14 0.35 0.20 0.10 0.10

Default Poisson 0.35 0.18 0.4 0.45 0.15 0.35

Maximum Poisson 0.40 0.25 0.45 0.50 0.25 0.50

Thickness

The thickness of each layer must be specified in terms of inches. By default, layers not used in the problem will have a thickness of 999 inches (2,537 cm) to simulate and infinite amount of material. When choosing number of layers greater than the previous number, be sure to change the heights of the new layers from 999 (2,537) in.

3.1.5

Slip Condition

This parameter describes the interface between two layers. Slip = 1 Full Adhesion (No slip). Slip = 0 No Adhesion (Full Slip) .

4 Loads The wheel loads applied to the pavement are expressed in terms of a particular wheel configuration. Due to the symmetry of most axles, only half the axle nee ds to be modeled as shown below.

There are four standard load configurations. The fifth configuration (Other) must be entered manually. Choosing a standard configuration will automatically define the number of tires in the configuration and their spacing.

Single

Tandem

Tridem

Steer

Other

The total number of load applications should be entered.

Each tire requires a load magnitude, tire pressure, x location, and y-location. Checking the UNIFORM boxes will apply the load or pressure shown to all tires in the configuration. Deselecting the UNIFORM boxes allows for different loads and pressures to be ente red.

The load identifier, shown below, indicates which tire in the configuration the load magnitude, tire pressure, and x, y locations are referencing.

Use the Next or Previous load buttons to view each load in the configuration.

4.1 4.1.1

Load types Single Axle with Dual Tires

Tire Spacing and Critical Locations in Plan View.

4.1.2

Tandem Axle with Dual Tires

Tire Spacing and Critical Locations in Plan View.

4.1.3

Tridem Axle with Dual Tires

Tire Spacing and Critical Locations in Plan View.

4.1.4

Steer Axle with Single Tires

Tire Spacing and Critical Locations in Plan View.

4.1.5

Other

This selection requires the load information to be manually entered. The steps below outline the process and provide some guidance in constructing a configuration. It may be helpful to first draw a sketch of the proposed configuration prior to entering the information into WESLEA for W indows. Step 1. Enter the number of tires in the configuration(maximum of 20).

Step 2.  Enter the total number of load applications.

Step 3. Enter the following for each tire.

X-location Y-location Load magnitude Tire pressure

Step 4. Click on to verify input. Step 5.  Choose Evaluation from the Input menu and enter the critical locations for the specified wheel

configuration. Step 6. Choose View Output from the Output menu.

4.2

Total Number of Load Applications

This value refers to the total number of repeated applications of the specified wheel configuration that the pavement will experience. This value is used in Miner’s Hypothesis to estimate damage.

For example, say that 2 million tandem axles are expected to be applied during the life of the pavement during the summer condition. A value of 2 million should then be entered as shown below.

4.3

Load Magnitude

The load magnitude represents the weight on each tire, expressed in pounds of force. For example, an 18,000 lb. (80 kN) single axle with 4 tires would have 4,500 lb. (20 kN) per w heel.

4.4

Tire Pressure

Tire pressure is usually assumed to be the tire inflation pressure. A current (1997) typical value for truck tires is 100 psi (690 kPa). Tire pressure is used within WESLEA for Windows to calculate the contact area between the tire and road. The area is assumed to be circular and is found by:

      4.5

Coordinate System in WESLEA for Windows

X and Y define the horizontal plane. Z defines the vertical position in the pavement. Positive Z is downward. X is defined transversely across the pavement (perpendicular to traffic). Y is defined longitudinally across the pavement (parallel to traffic). The origin is placed directly beneath the first wheel load in the configuration.

5 Critical Locations This dialog box specifies the critical locations in the pavement. Stress, strain, and deflection will be determined at these locations for the given set of loading and structural conditions. In general, the vertical locations of interest are at the bottom of the first layer and the top of the subgrade. The figure below illustrates these locations. The horizontal tensile strain at the bottom of layer 1 is used to predict fatigue. The vertical compressive strain at the top of the subgrade is used to predict rutting.

The x, y locations are usually specified directly beneath tires and at the midpoint between tires. These locations will generally yield the greatest strain and experience the most damage. If a standard load configuration was selected (single, tandem, tridem, steer), the evaluation locations are all ready given by default. If a non-standard configuration was entered (Other), the critical locations must be spec ified. Entering Critical Locations

5.1

Fatigue

Fatigue cracks form as a result of repeated tensile stresses and strains at the bottom of the first pavement layer. The fatigue life may be used in Miner’s Hypothesis to estimate fatigue damage. An equation developed at the University of Illinois was modified using Mn/ROAD fatigue crack data to predict number of repeated loads until fatigue failure. The equation is:

 .4  −6   2.83 × 10 (  ) Mn/ROAD Fatigue Equation Where: Nf   =

number of repeated loads under current structural conditions before a fatigue crack will form.

εt =

maximum horizontal tensile strain at bottom of first layer caused by one pass of current wheel configuration, expressed in microstrain.

5.2

Rutting

In WESLEA for Windows, rutting is attributed to stresses applied to the subgrade. The rutting life may be used in Miner’s Hypothesis to estimate rutting damage. An equation was developed using Mn/ROAD pavement performance data that predicts rutting of 20 mm (0.5 inch):

 .7  6   1.0 × 10 (  ) Mn/ROAD Rutting Equation Where: Nf   =

number of repeated loads under current structural conditions before rutting failure will occur.

εv =

maximum vertical compressive strain at the top of the subgrade caused by one pass of current wheel configuration, expressed in microstrain.

5.3

Miner’s Hypothesis

Miner’s Hypothesis is used   to estimate accumulated pavement damage. As shown below, it is simply the

summation of the applied number of loads over the allowable number of loads.



  ∑  =

Where: D=

accumulated damage.

ni =

number of repeated load applications in condition i.

Nfi =

number of allowable repetitions in condition i calculated from fatigue or rutting performance equations.

M=

number of groups of different loads.

D should be calculated in terms of fatigue and rutting for each set of structural and tire load configuration conditions. Failure in a particular mode occurs when D = 1. In other words, failure is defined as the number of applied loads exceeding the number of allowable loads.

5.4

Entering Critical Locations

To enter locations manually, deselect the Standard Locations box as shown below.

Enter the number of locations to evaluate. A maximum of 50 locations is permitted. This group also indicates which location is currently shown.

Each location requires a layer number and an x, y, z coordinate.

Use the Next and Previous buttons to view each location’s data.

5.5

Strain Sign Convention

The sign convention for strain in WESLEA for Windows is: - microstrain = tension. + microstrain = compression. Maximum Horizontal Tensile Strain

Therefore, the maximum horizontal tensile strain at the bottom of the first layer is the most negative strain value in the x or y direction. This value would be entered as a POSITIVE number into the fatigue performance equation. Maximum Vertical Compressive Strain

The maximum compressive vertical strain at the top of the subgrade is the most positive strain value in the z direction. This value would be entered as a POSITIVE number into the rutting performance equation.

6 Output This dialog box contains the output of the WESLEA mechanistic analysis. The Location Identifier group specifies how many total critical locations were input and indicates which location is currently displayed.

The Location Data group indicates the layer and x, y, z coordinate of the current location.

The Location Control buttons may be used to view each location specified.

The Model Output group contains the pavement response data for the curre nt location.

The Pavement Life group indicates the number of applied loads, the number of allowable loads by fatigue or rutting, and the relative damage (Miner’s Hypothesis).

The Export Data button allows the data to be exported in a tab-delimited format.

6.1

Model Output

Normal Stress

Pavement stress due to the applied loading condition (psi or kPa). Sign Convention

Normal MicroStrain

Pavement strain due to the applied loading condition. Sign Convention Displacement

Pavement displacement due to the applied loading condition (milli-in. or micrometer). Sign Convention Shear Stress

Pavement shear stress due to the applied loading condition (psi or kPa). Sign Convention

6.1.1

Stress Sign Convention

The sign convention for normal stress in WESLEA for W indows is: - stress = tension. + stress = compression. The figure below illustrates the positive stress condition on an e lement in addition to positive displacements:

6.1.2

Displacement Sign Convention

Displacements are positive along their respective axes as shown in the figure:

6.2

Export Data

Enter the path filename in the edit control box. The browse button may be used to easily select the desired drive and filename. Providing the extension “.xls” will allow the file to be opened in Excel. However, the file is just

tab-delimited and can be opened in any type of spreadsheet or text editor. Note that WESLEA for Windows will not open Excel automatically, the user needs to do this and then open the exported data file.