LOAD CAPACITY OF LISTER RIG MATS SUPPORTED ON … · LOAD CAPACITY OF LISTER RIG MATS SUPPORTED ON...

LOAD CAPACITY OF LISTER RIG MATS

SUPPORTED ON GRADE

REPORT SUMMARY PREPARED BY

ACIUS ENGINEERING LTD. OCTOBER 16, 2012

LOAD CAPACITY OF TYPICAL LISTER INDUSTRIES RIG MATS

INTRODUCTION

This report summary outlines the results of finite element computer models that were

created in order to determine the loading capacity of typical Lister Industries’ rig mats. A

pair of line loads was used for the analysis to determine maximum load capacity of the

mats.

ANALYSIS METHODS FOR LISTER RIG MATS ON VARIOUS SOILS

Line loads were increased on each model until the first evidence of failure occurred. This

was repeated for each model with varying soil spring constants to allow for changing soil

conditions.

Once the maximum stresses were reached for the wood and steel, the maximum deflection

of these elements in the model was also noted.

RESULTS AND CONCLUSIONS

The conclusions of the finite element modeling of the Lister Industries’ mats show that there

are two modes of failure in determining the load capacity. The first mode occurs when the

timber infill begins to reach its ultimate bending stresses. A failure in the timber may result

if a heavier point load from a wheel was to overstress the timber locally, without failing the

steel beams. Rigs with tracks may allow the rig to spread its weight out over the timber

infill and directly transfer load to the steel beams. A much higher loading capacity can be

reached for the rig mats under this condition because the steel will fail at a higher load.

The maximum loading results are summarized in the charts and graph below. The results

from the analysis show a maximum loading capacity in kips for only one of the line loads

though two line loads were used in the analyses. The maximum deflection in the mats at the

failure loads are listed above each bar graph.

8' x 40' Rig Mat 3 Beams

Modeling

Results

Loose Sand k = 15 pci

Load Capacity Bending Stress in Wood Moment in Steel Beam Deflection

(kips) (psi) (ft-kips) (inches)

192.4 1667.9 1.24 (Wood)

267 38.65 1.73 (Beam)

Medium Sand k = 45 pci



242.6 1638.9 0.54 (Wood)

368 40.11 0.84 (Beam)

Sand/ Silt Mix k = 90 pci



284.4 1667.9 0.371 (Wood)

418.3 38.87 0.546 (Beam)

Compacted Gravel k = 250 pci



376 1697 0.228 (Wood)

552 38.43 0.335 (Beam)

Fig. 1 Load Capacity with various soil conditions for 8’ x 40’ Mats

10' x 40' Rig Mat 4 Beams

Modeling

Results

Loose Sand k = 15 pci



200.8 1682.4 1.307 (Wood)

292.8 41.16 1.772 (Beam)

Medium Sand k = 45 pci



259.3 1692.6 0.595 (Wood)

393.2 41.6 0.902 (Beam)

Sand/ Silt Mix k = 90 pci



301.2 1701.3 0.394 (Wood)

460.1 41.53 0.603 (Beam)

Compacted Gravel k = 250 pci



393 1711.5 0.239 (Wood)

569 38.65 0.346 (Beam)

Fig. 2 Load capacity with various soil conditions for 10’ x 40’ Mats

Capacity of Lister Industries Rig Mats in Various Soil Conditions

192.4

1.24"

242.6

0.54"

284.4

0.37"

376

0.23"

393

0.24"

200.8

1.31"

259.3

0.6"

301.2

0.39"

368

0.84"

267

1.73"

418.3

0.55"

552

0.34"

569

0.35"

460.1

0.6"

393.2

0.90"

292.8

1.77"

0

100

200

300

400

500

600

Loose Sand k = 15

pci

Medium Sand k = 45

pci

Sand/ Silt Mix k = 90

pci

Compacted Gravel k

= 250 pci

Soil Type

Note - deflections listed below the max load capacity for each case

Load Capacity in Kips (1000 lbs) for Single Track Load

8' x 40' Rig Mat 3 Beams Ultimate bendingstresses in wood reached

10' x 40' Rig Mat 4 Beams Ultimate bendingstresses in wood reached

8' x 40' Rig Mat 3 Beams Ultimate bendingstresses in steel reached

10' x 40' Rig Mat 4 Beams Ultimate bendingstresses in steel reached

Fig. 3 Summary of load capacities of Lister Industries’ mats for various sub-grade soil

conditions

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