Excavator & Truck notes

Prévia do material em texto

University of South Australia School of GMC Engineering 
 
 
Intro to Civil & Mining Engineering ١ BVC/١٤-٠٤-١٠ 
Bulk Material Handling Notes 
Trucks 
CIVIL ENGINEERING PRACTICE ١ 
 
MATERIALS HANDLING 
In the industry there is a huge investment in Plant & Machinery to mine treat & transport aggregates. 
The selection, operation & maintenance of the equipment is the domain of the engineers trained in the 
disciplines of minerals, mechanical, electrical and civil engineering, each having an input to the 
successful outcome of the operations safety, production, planning and profitability 
 
 Excavation tools [refer power point notes on slides] 
 Truck Haulage 
 
١. Truck Haulage 
 
١.١ HISTORICAL 
Since the ١٩٣٠s most of the material moved out of open cut mines/quarries has been hauled by 
motorized trucks. Whereas in underground mines material moved along the haulage drives has been in 
rail mounted trucks pushed or pulled by locomotives, and in recent times motorized truck haulage has 
been introduced underground. 
 
Some primitive methods of transport were/are: 
 
 packing 
material carried out in sacks or baskets on the backs of workers, typical duty cycle, 
٧ people-hrs/t-km 
 
 wheel barrow 
transport only, neglecting loading, duty cycle approx. ٦ people-hrs/t-km 
 
 hand trucking 
pushing a truck on steel rails in good condition(i.e. roller bearings on the truck & level 
grade) requires about ٠.٦ people-hrs/t-km. 
 
 
 
Trucks are classified under a number of headings, taken from the Caterpillar Handbook eg.:- 
 
 CONSTRUCTION & MINING TRUCKS 
 
 ARTICULATED TRUCKS 
 
 MINING AND EARTHMOVING TRUCKS 
“Elphinstone” underground machines 
Articulated Trucks 
Rigid Frame Trucks 
 
University of South Australia School of GMC Engineering 
 
 
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Trucks 
 
 
Some of the current day manufacturers include: 
Komatsu 
Terex 
Unit Rig 
Pay-hauler 
Caterpillar 
Euclid 
Wabco 
Bell 
Liebherr 
Tamrock [Toro] 
Atlas Copco-Wagner 
Elphinstone 
and many others that have developed units for specific markets eg. The “Kiruna” underground electric 
truck 
 
١. Capacity 
Trucks are usually listed by tonnage capacity and sometimes their duty eg. ٣٠٠ tonne Off-
Highway, because they exceed highway traffic regulations as far as weight & width are 
concerned. 
 
٢. Type of body / tray 
Standard unit has vertical sides, flat floor made from steel plate 
Open cut truck body, for handling rocks is of thicker plate construction and from higher tensile 
steel. Flared sides sometimes used to provide a larger target for shovel loading, with wearing 
strips welded on the tray floor. 
The ‘V’ body which has a constant slope down from the rear to the cabin is often used. 
In cold countries and with sticky ore the engine exhaust is directed through the body 
construction ribs to emerge at the truck rear. The heated tray prevents freezing of the load and 
facilitates the dumping of the ore. 
Aluminium alloys have been used for body construction, particularly, in handling less abrasive 
materials than rocks, e.g. coal. 
Bodies are usually shaped to provide a protective lip over the driver’s cabin. 
 
٣. Type of power 
Diesel engines have the monopoly and are coupled with either a mechanical transmission or 
electric drive motors, housed in the wheel hubs, driven by a diesel-electric power unit. 
In deep pits on main exit roads ‘trolley-assist’ is sometimes used with electric powered trucks. 
This method uses power picked up by the truck from an overhead line through retractable 
trolley poles and in the process saves significant amounts of diesel fuel as the overhead line 
instead of the on-board electric generator powers the electric wheels. 
The range of power in trucks is considerable dependant on the capacity. The current maximum 
capacities are around ٣٢٠ tonnes utilising a ٢٢٤٠ kW engine 
 
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٤. Transmission type 
There are various systems available to transmit power to the truck wheels: 
 Manually operated mechanical transmissions; ٢٠ t and less trucks 
 Powershift transmissions, including torque convertors, enables gear shifts to be done 
at full engine power, standard for mechanical drive trucks > ٢٠ t size. 
 Electric power to electric wheels. 
The diesel engine in this case drives an AC alternator the current from which is 
rectified to DC voltage which supplies DC power for individual wheel motors 
(usually, two). Because of the better control of electric power fully automatic 
transmission is not needed and, in some cases, manual control is preferred. The 
electric motor drives the wheel through reduction planetary gearing enclosed in the 
wheel assembly. 
 
Recently AC drive technology, as used in rail diesel locomotives, has been 
transferred to electric wheel trucks. In this case, rugged three phase squirrel cage 
induction motors are used in the wheels, instead of the more complex and expensive 
to maintain DC motors. With this system AC power is generated and rectified to DC 
for the control systems and then converted back to AC by thyristor inverters to 
power the wheel motors. 
 
٥. Tyres 
Probably the most important cost element of a haulage truck is tyre cost. It is therefore 
essential that tyre size, tread design, material, carcass design and tyre material are 
appropriate for the duty. Tyres are rated for, both, carrying capacity and speed of travel. 
Adherence to the ratings avoids heat build-up in the tyre which can cause ply separation 
and tyre failure. Tyre rubber because of its insulating properties retains the heat 
generated in it by the flexing created when it is moving. Heat generation in a specific 
tyre depends upon: 
 The mass the individual tyre is carrying 
 The speed at which the tyre is travelling 
 The ambient temperature of the surrounding air 
Normal tyre life for tyres designed for their duty is about ٥ ٠٠٠ hrs. In underground applications this 
reduces to about ٢ ٠٠٠hrs. 
 
Overload on tyres should also be prevented because; 
 ٣٠% overload reduces life by ٤٠% 
 ٥٠% overload reduces life by ٦٠% 
 Whereas an under-load of the tyre by ٢٠% increases the life by ٦٠% 
(Bridgestone “Off-the-Road Tires”) 
 
The amount of work done under given conditions and within a safe range is shown as “Tonne-Km-Per-
Hour (TKPH)” rating of the tyre, which is calculated by the following formula: 
TKPH = Mean tyre load * Average work day speed 
 
Where mean tyre load is in Metric tonnes 
Average work day speed is in km. / hr. 
 
Mean Tyre load = Tyre load: empty + Tyre load: loaded 
 ٢ 
 
Average work-day speed = Round trip distance (km) * No. of cycles per day 
University of South Australia School of GMC Engineering 
 
 
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Total hours of operation per day 
 
(Many of the handbooks will be in ton-mile-per-hour TMPH = ١.٤٦ TKPH) 
 
Tyre manufacturers need to be consulted for the most suitable tyres for the duty, the following table 
gives an indication of tyre rating: 
 
TKPH rating at ambient temp. oC 
Tyre Size Type ١٦o ٢٧o ٣٨o ٤٩o 
 
١٨.٠٠ – ٢٥ 
Standard 
Extra tread 
Radial 
٢١٩ 
١٧٥ 
٣٠٦ 
٢٠٤ 
١٦١ 
٢٨٥ 
١٨٢ 
١٤٦ 
٢٥٥ 
١٦١ 
١٣١ 
٢٣٣ 
 
١٨.٠٠ - ٣٣ 
Standard 
Extra tread 
Radial 
 
 
٣٦.٠٠ - ٥١ 
 
Radial 
 
٧٣٠ 
 
٦٤٢ 
 
٥٦٩ 
 
٥١١ 
 
Tyre size nomenclature, i.e. ٣٦.٠٠ – ٥١, designates the approximate cross-section width of the tyre in 
inches and it’s rim diameter in inches. 
 
A large Bridgestoneearthmover tyre currently manufactured is ٤٨/٩٥ – R٥٧, has a tyre width of ٤٨", rim 
dia. of ٥٧" and an aspect ratio of ٩٥%, ie side-wall height ٩٥% of its width, it has a rated carrying 
capacity of ٧٣ tonnes @ ٥٠ kph, inflated to ٧٠٠ kPa. approximate cost $٤٠ ٠٠٠/tyre 
 
٦. Tyre Care 
Apart from loading, speed, inflation pressure, it is essential that the tyres run on roads that are well 
designed and maintained. A grader becomes a necessary ancillary tool in the pit/quarry. 
 
٧. TRUCK PERFORMANCE 
Truck performance is determined by the factors; 
Utilisation = % of available time used out of the time available for use & 
Productivity = average payload carried per trip multiplied by the trips per hr. (t/h) 
 
Availability is defined as the % age of time the truck is available for work, ie. It is not being repaired or 
undergoing a maintenance service. Consider the following availability pattern for a truck over it’s ١٠ 
year life. 
 
Year ١ ٢ ٣ ٤ ٥ ٦ ٧ ٨ ٩ ١٠ 
Availability % ٨٥ ٨٥ ٨٣ ٨١ ٧٩ ٧٧ ٧٥ ٧٣ ٧١ ٧٠ 
 
Also Utilisation averages out at ٨٥%, for driver’s personal delays, delays caused by other equipment 
etc. 
 
Now max time available is say ٣٦٥days * ٣ shifts / day * ٨ hours / shift = ٨ ٧٦٠ hrs. 
With meal breaks, shift change-overs average operating time = ٧hrs. over the year this equates to 
 
 ٣٦٥ * ٣ * ٧ = ٧٦٦٥ hrs. 
 
 
University of South Australia School of GMC Engineering 
 
 
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It is this time that now must be adjusted for availability & utilisation 
 ٧٦٦٥ * ٨٥% * ٧٩%(for yr.٥) = ٥١٤٧ hrs. (cf. ٨ ٧٦٠hrs. max) 
 
The productivity can now be applied to the effective operating time to get the performance of the truck 
in yearly terms. 
 
 
The tonnes/hour figure is calculated from; 
 
average payload /trip * trips /hr = t/hr. 
 
Payload = f{body size, matl. density, truck fill factor} 
fill factor may be for struck, heaped or part load 
 
The most accurate way of determining the payload is to weigh the truck empty & full. Modern trucks 
have on-board load measuring instrumentation. Mobile axle scales is another method. 
 
The frequency of loads may be obtained in two ways; 
 directly from time & motion studies (the most accurate) or by 
 estimation factors using manufacturers tables 
 
The latter method endeavours to estimate the vehicle’s speed under given conditions over specified 
distances to obtain the cycle time for the trip 
Truck cycle times and the necessary loading, and dumping part of the cycle have been the subject of 
computer simulation methods using probabilistic approaches. The following time elements need to be 
determined, 
 Loading 
 Travelling loaded to the dump 
 Dumping 
 Return trip empty 
 Spotting the truck for loading 
 Delay times 
 
The loading, dumping, spotting and delay times will be the subject of simulation trials later in the 
course. It is the travel times loaded & empty that will be covered in this section 
 
Manufacturers such as Caterpillar & Leibherr produce tables that give the various performance 
parameters, e.g. speed attainable, gear range, available rimpull, etc., but before these can be used the 
gross vehicle weight (GVW, or GMW) and the total resistance must be known 
 
 GVW is the tare weight of the truck + payload 
 Total resistance is grade resistance + rolling resistance 
 Rimpull is the force (kg) available between the tyre and the ground to move the 
vehicle. It is limited by traction. 
 
University of South Australia School of GMC Engineering 
 
 
Intro to Civil & Mining Engineering ٦ BVC/١٤-٠٤-١٠ 
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Grade Resistance is a measure of the force that must be overcome to move a machine over 
unfavourable grades (uphill). 
Grade assistance is a measure of the force that assists machine movement on favourable grades 
(downhill). 
Grades are generally measured in percent slope, which is the ratio between vertical rise or fall and 
the horizontal distance in which the rise or fall occurs. 
For example, a ١% grade is equivalent to a ١ m rise or fall for every ١٠٠ m of horizontal distance; a rise 
of ٤.٦ m in ٥٠ m equals a ٩.٢% grade. 
 
Rolling Resistance (RR) is a measure of the force that must be overcome to roll or pull a wheel over 
the ground. It is affected by ground conditions and load, the deeper a wheel sinks into the ground, the 
higher the rolling resistance. 
Internal friction and tire flexing also contribute to rolling resistance. 
Experience has shown that minimum resistance is approximately ٢% (١.٥% for radial tyres or dual tyred 
trucks) of the gross machine weight (on tyres). 
 
Resistance due to tire penetration is approximately ٠.٦% for each cm of tire penetration. 
Thus rolling resistance can be calculated using these relationships in the following manner: 
RR = ٢% of GMW + ٠.٦% of GMW per cm tire penetration 
 
Total resistance can also be represented as consisting completely of grade resistance expressed in 
percent grade. In other words, the rolling resistance component is viewed as a corresponding quantity 
of additional adverse grade resistance. 
 
This can be done by converting the contribution of rolling resistance into a corresponding percentage 
of grade resistance. Since ١% of adverse grade offers a resistance of ١٠ kg for each metric ton of 
machine weight, then each ١٠ kg resistance per ton of machine weight can be represented as an 
additional ١% of adverse grade. 
 
Rolling resistance in percent grade and grade resistance in percent grade can then be summed to give 
Total Resistance in percent or Effective Grade. 
 
The following formulas are useful in arriving at Effective Grade. 
 
 Rolling Resistance (%) = ٢% + ٠.٦% per cm tire penetration 
 Grade Resistance (%) = % grade 
 Effective Grade (%) = RR (%) + GR (%) 
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TYPICAL ROLLING RESISTANCE FACTORS 
 
Under-footing 
Rolling Resistance Percent 
Tyres 
Bias Radial 
Track Track + Tyres 
Very hard, smooth roadway, concrete, cold 
asphalt, no penetration or flexing 
 
١.٥% ١.٢% 
 
٠% 
 
١.٠% 
Hard, smooth stabilised surfaced roadway no 
penetration under load, watered, maintained 
 
٢.٠% ١.٧% 
 
٠% 
 
١.٢% 
Dirt roadway, rutted or flexing under load, little 
maintenance, no watering,٢٥mm tyre penetration 
or flexing 
 
٤.٠% ٤.٠% 
 
 
٠% 
 
٢.٤% 
Rutted dirt roadway, soft under travel, no 
maintenance, no stabilization, ١٠٠mm tyre 
penetration or flexing 
 
٨.٠% ٨.٠% 
 
٠% 
 
٤.٨% 
Very soft, muddy, rutted roadway ٣٠٠mm tyre 
penetration, no flexing 
 
٢٠% ٢٠% 
 
٨% 
 
١٥% 
 
Various tyre sizes and inflation pressures will greatly reduce or increase the rolling resistance. The 
values in this table are approximate, particularly for the track and track + tyre machines. These values 
can be used for estimating purposes when specific performance information on particular equipment 
and given soil conditions is not available 
 
RIMPULL 
Rimpull is the force (in kg. or KN) available between the tyre and the ground to propel the machine 
(limited by traction) 
 
Rimpull – Speed – Grade-ability curves 
Maximum speed attainable, gear range and available rimpull can be determined from curves as per the 
sample below and available in manufacturers handbooks when machine weight & and total effective 
grade (or total resistance) are known. 
Weight (GVW/GMW) = Machine + Payload 
 
TRACTION 
Is the driving force developed by a wheel or track as it acts upon a surface. It is expressed as useable 
Drawbar Pullor Rimpull. The weight on the driving wheel or track, gripping action of the wheel or 
track, and ground conditions affect the pull. 
The coefficient of traction for any roadway is the ratio of maximum pull developed by the machine to 
the total weight on the drivers 
 
Coeff. Of traction = Pull 
 Weight on drivers 
 
Therefore useable pull = Coeff. Of traction * weight on drivers 
 
 
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COEFFICIENT OF TRACTION FACTORS 
 
 
 
MATERIAL 
TRACTION FACTORS 
Rubber Tyres Tracks 
Concrete ٠.٩ ٠.٤٥ 
Clay loam, dry ٠.٥٥ ٠.٩ 
Clay loam, wet ٠.٤٥ ٠.٧ 
Rutted dry loam ٠.٤٠ ٠.٧ 
Dry sand ٠.٢٠ ٠.٣ 
Wet sand ٠.٤٠ ٠.٥ 
Quarry pit ٠.٦٥ ٠.٥٥ 
Gravel road 
(loose not hard) 
 
٠.٣٦ 
 
٠.٥ 
Packed snow ٠.٢٠ ٠.٢٧ 
Ice 
Semi-skeleton shoes 
 
٠.١٢ 
 
٠.١٢ 
Firm earth ٠.٥٥ ٠.٩ 
Loose earth ٠.٤٥ ٠.٦ 
Coal, stockpiled ٠.٤٥ ٠.٦ 
 
NOTE: The elevated sprocket design Track-type Tractors [D١١N, D١٠N, D٩N and D٨N] with their 
suspended undercarriages, provide up to ١٥% more efficient tractive effort than rigid tracked Track-
type tractors 
 
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Example:- 
For the ٢٤٠ tonne capacity ٧٩٣C truck with the estimated payload of ٢١٨ tonne, operating up a gradient 
of ١١% on a roadway considered as “dirt roadway, rutted or flexing under load, little maintenance, no 
watering, ٢٥mm tyre penetration or flexing”. Find the available rimpull, maximum speed and the 
traction condition required to achieve the operation? 
 
From the Table “Typical Rolling Resistance” for the roadway select RR = ٤% 
 
Total Effective Resistance = GR + RR = ١١ + ٤ = ١٥% 
 
 Gross Weight; loaded = ٣٧٦ ٤٨٨ kg. 
 “ empty = ١٥٨ ٧٦٠ kg 
 
Rimpull, 
Enter the above curve at the loaded Gross weight of ٣٧٦ ٤٨٨ kg and down the line ‘B’ to the 
intersection of the ‘total resistance ‘ line at ١٥%, then proceed horizontally to the rimpull axis & read 
available rimpull = ٥٠٠Kn in 
 
Note the applicable gear ratio vis. ١st. gear at a maximum speed of ٧ kph 
(Note max. Speed in ٦th. Gear = ٥٥ kph.). 
 
From the weight distribution data per Cat. Performance h/book 
 
loaded = ٦٧% on the drive axle 
 i.e. ٠.٦٧*٣٧٦ ٣٨٨ = ٢٥٣ ١٨٠ kg = ٢٥٣٠Kn 
 
Then the minimum traction coefficient t = Rimpull/axle weight 
t reqd. = ٥٠٠/٢٥٣٠ = ٠.٢ 
 
From the table of ‘Coefficient of Traction Factors’ 
a rutted clay loam has a factor = ٠.٤ > ٠.٢ hence OK 
 
The truck is capable of performing the operation albeit with very slow haulage rate 
 
If the grade resistance could be changed at the design stage to say ٧%, and the roadway condition 
upgraded to provide a rolling resistance of say ٢%. 
The resultant performance would be operation in ٢nd. gear, rimpull of ٣٢٠ Kn and a speed of ٩kph 
ie a ٢٩% improvement 
 
Minimum traction coefficient reqd. = ٣٢٠/٢٥٣٠ = ٠.١٣ < ٠.٤ hence OK. 
 
University of South Australia School of GMC Engineering 
 
 
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Caterpillar ٧٩٣C Ridged Frame Truck “Rimpull – Speed – Gradeability curve” 
 
 
 
 
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BRAKE PERFORMANCE 
The speed that can be maintained (without the use of the service brake) when the machine is 
descending a grade with retarder fully on can be determined from the retarder curve below if the 
machine weight & total effective grade is known. Read from gross weight down to % eff. Grade, from 
this point read horizontally to the curve with the highest speed range, then down to the max. descent 
speed brake scan safely handle without exceeding cooling capacity. 
The retarder curve also shows what speed the truck will travel at with retarder fully on without 
application of the service brakes. 
 
The following curve is for the ٧٩٣C truck of the above example; 
 
 
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For the two gradient conditions in the above example; 
A) B) 
GR = ١١% & RR = ٤% GR = ٧% & RR = ٢% 
TR = ١١ – ٤ = ٧% TR = ٧ – ٢ = ٥% 
 
Machine; loaded = ٣٧٦ ٤٨٨kg, empty = ١٥٨ ٧٦٠kg 
For condition A) 
 
Speed = ٢٠kph in ٣rd. gear, loaded, & ٤٠ kph in ٥th. Gear empty , no service braking reqd. 
 
For condition B) 
 
Speed = ٣٠kph in ٤th.gear, loaded, & ٥٥kph in ٦th.gear empty 
 
In case B downhill, truck is travelling at max speed, the safety of the operation is in jeopardy. Service 
braking will be required, but is within the cooling capacity of the brakes. During braking the engine 
rpm should be maintained as high as possible without over-speeding, 
 
Recommendation based on speed conditions, " change down a gear ". 
 
AUTONOMOUS TRUCKS 
Both Caterpillar & Komatsu have for a number of years been developing their (driverless) autonomous 
truck control system. 
 
The Komatsu system was set up on one of their ٧٧ tonne capacity trucks, the trial showed that it was 
capable of staying on a pre-programmed route while travelling at up to ٣٦kph going forwards and 
١٠kph in reverse. The truck’s position deviated no more than ٢m from the pre-programmed route whilst 
moving and ٠.٥m at any stopping point, giving sufficient accuracy for loading or tipping. 
 
Both machines detect obstacles by radar systems which can slow down or stop the vehicles if 
necessary. 
 
Advantages of autonomous trucks argued by the suppliers are; 
Human truck drivers represent about ٢٠% of the fleet running cost 
Difficult to find skilled drivers particularly in increasingly remote locations 
eg. wilds of Canada with ferocious climatic conditions and cover vast areas. (fly in-out of 
drivers to the machines) 
Mines located in high mountain areas may require firms to fit costly oxygen systems into the 
truck cabs, to allow the drivers to breath!. 
Computer controlled trucks do not suffer production delays due to sickness or tiredness of 
operators, and can continue to operate at optimum levels right through the night. 
 
What is not stated is the technology will always require servicing and the argument then will 
centre around the availability not of truck drivers but of electrical technicians, who ideally 
could be one and the same. 
 
University of South Australia School of GMC Engineering 
 
 
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 The diagram shows some of the key components that control Komatsu’s autonomous truck 
 
 
 
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 Assignment: 
١. In truck haulage applications the parameter known as Rim-pull is determined following the 
estimation/calculation of Total Resistance, made up of grade, rolling and air resistance, and the Gross 
Vehicle Weight, made up of Tare/Empty Weight plus the Payload. Manufacturers prepare performance 
curves for their vehicles to ascertain its ability to haul the payload and determine the speed for the 
given situation. The Rim-pull curve for an Off-Highway Caterpillar truck model ٧٧٣D is shown 
below. 
Given the following road conditions described as " Dirt roadway, rutted or flexing under load, little 
maintenance, no watering, ٢٥mm tyre penetration or flexing". The gradient of the haul road out of the 
pit is ١:١٢.٥. It may be assumedthat the air resistance is negligible. 
From the performance handbook the weight distribution on the front & rear axles when loaded is ٣٣.٣% 
& ٦٦.٧% respectively. 
 
For a given payload of ٤٠ tonnes, determine: 
The Gross Vehicle Weight? 
Total Resistance? 
Rimpull? 
Speed out of the pit? & Gear selection? 
Actual Coefficient of Traction? vs. Coefficient of traction given the road conditions?, 
Will the unit haul the load? 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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٢. Outline some of the advantages & disadvantages of Diesel-Electric haul trucks 
٣. List safety hazards you might identify in a trucking operation 
٤. Given that the expected life of a set of tyres for an Off-Highway truck is ٥ ٠٠٠hrs. and the cost per 
tyre is $٤٠ ٠٠٠, calculate the cost to the owner if the tyres are run at ٣٠% and ٥٠% overload and compare 
the resulting relative unit cost of tyres to the owner 
 
The above assignment is to be handed in by Friday ٢٠th. May ٢٠٠٥