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9. Calculating Tractive Effort
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Today, we will start by discussing what required power is in the context of earthmoving operations. Required power is essentially the amount of power needed by a machine to overcome the various resistive forces at a project site.
What kind of resistive forces are we talking about, specifically?
Great question! The primary resistive forces include rolling resistance and grade resistance. Rolling resistance occurs when the wheels or tracks of the equipment move over a surface. Can anyone tell me an example of how surface type impacts this?
I think a concrete surface would have less rolling resistance compared to a muddy or soft earth surface.
Exactly! Remember, for hard surfaces like concrete, the rolling resistance is lower than for softer surfaces. The key takeaway is that higher resistance means you need more required power.
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Now that we've discussed required power, let’s delve deeper into rolling resistance. Rolling resistance can be broken down into surface resistance and penetration resistance. Who can explain what surface resistance is?
Surface resistance is the resistance a wheel encounters when it rolls over a surface, like asphalt or dirt.
Correct! The type of surface and its condition will heavily influence this resistance. Can anyone give me an example of how maintaining a surface can reduce this resistance?
If an earthen road is well compacted and dry, it would be easier for a vehicle to roll over it compared to a poorly maintained, muddy road.
Exactly. Maintaining the surface can significantly lower the rolling resistance and required power, leading to more economical operations.
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Let’s put what we’ve learned into practice. If we have equipment with a gross weight of 20 tons and the rolling resistance is 70 kg per ton, how can we calculate the total tractive effort needed?
We can multiply the gross weight by the rolling resistance value, right?
Correct! In this case, it’s 20 tons times 70 kg per ton, which equals 1400 kg of tractive effort required.
What if the tires sink into the ground? Would that affect our calculation?
Absolutely! That's where penetration resistance comes into play. Each centimeter of penetration adds to the rolling resistance. This is why understanding all components is so crucial.
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Now let's connect our understanding of tractive effort to equipment selection. Why is it important to consider rolling and grade resistance when choosing equipment?
Because the equipment needs to have enough power to overcome those resistances to work efficiently.
Exactly! Additionally, selecting the right type based on project requirements like haul distance and material type is crucial. Any thoughts on what specific factors to consider?
The type of material being moved affects what equipment I'll choose, right? Like using a bulldozer versus a backhoe based on whether it's earth or rock.
Exactly right! Knowing the properties of your project site helps in selecting the most effective equipment.
Overview
Short Summary
This section delves into the fundamentals of calculating tractive effort in earthmoving operations, including key terms and factors influencing equipment performance.
Medium Summary
In this section, we explore the concept of tractive effort in earthmoving operations and how it is calculated. The discussion covers required power, rolling resistance, and grade resistance, alongside the factors like surface and penetration resistance that influence machine performance. Understanding these components is vital for effective equipment selection and project execution.
Detailed Summary
Detailed Summary of Calculating Tractive Effort
In earthmoving operations, calculating tractive effort is crucial for determining how much power equipment requires to function effectively. The primary focus of this section is on the concept of required power, which is the power needed to overcome resisting forces at a construction site. These forces can include rolling resistance and grade resistance.
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Required Power: The power necessary for the machine to operate against various resistive forces on the project site, ensuring that it can maintain movement.
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Rolling Resistance: This is defined as the resistance experienced by the equipment's wheels or tracks as they move over different surfaces. Factors such as the type of surface, wheel size, and inflation pressure significantly affect the amount of rolling resistance encountered. Rolling resistance can be expressed in kilograms of tractive effort needed to move a ton of the vehicle weight over level surfaces.
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Grade Resistance: Refers specifically to the additional effort required to move equipment uphill or downhill on a slope, which is considered separately from rolling resistance.
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Surface Resistance and Penetration Resistance: Rolling resistance can be divided into these two components. Surface resistance refers to the force against the motion of the equipment that’s moving over a surface, while penetration resistance is related to how deeply a tire sinks into a surface, requiring additional force to keep moving.
Overall, a proper understanding of these parameters enables the effective selection and operation of earthmoving equipment within projects, ensuring that it meets the necessary performance while maximizing efficiency.
Audio Book
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Create a free accountSo, what is this required power? So, generally, what is the power needed by the machine to overcome the resisting forces in the project site and keep the machine moving, that is what is a required power. So, you know that every project site is unique, the underfoot conditions of the project site differs from site to site. So, the equipment which are going to use in a particular construction project site has to overcome all the resisting forces in the particular project site. And then it should keep the machine moving.
Detailed Explanation
Required power is the amount of power necessary for a machine to counteract the resistance it faces while operating in the unique conditions of a project site. Every construction site has different types of surfaces and materials that create resistance, such as unstable ground or obstacles. For a machine to function efficiently, it must have enough power to overcome these resistances and continue moving forward.
Examples & Analogies
Think of riding a bicycle through different terrains. When riding on a smooth road, you require less effort to pedal compared to when you're cycling over loose gravel or uphill. Similarly, a construction machine needs different amounts of power depending on the surface it's working on.
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Create a free accountThe first thing we will discuss about the rolling resistance. Rolling resistance is nothing but what is the resistance offered by the hauled route to the wheel which is rolling over the particular surface. So, what is the resistance offered by the hauled route to the wheel which is rolling over the particular surface, so that is what is your rolling resistance. So, resistance to the motion of equipment on a level surface is called as rolling resistance.
Detailed Explanation
Rolling resistance refers to the force that opposes the motion of a wheel rolling over a surface. This resistance varies with different types of surfaces—hard surfaces like concrete present less rolling resistance compared to soft surfaces like gravel or earth. Maintaining the hauled route can help reduce this rolling resistance, ultimately requiring less power from the machine to maintain movement.
Examples & Analogies
Imagine pushing a heavy box across a floor. It slides easily on a wooden floor but becomes harder to push if it's on carpet. The difference in resistance you feel is similar to rolling resistance encountered by different surfaces!
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Create a free accountSo, basically, your rolling resistance is going to depend upon so many factors; one is on your mounting. If it is going to be a wheel mounting, it depends upon the dimension of your tread, it depends upon inflation pressure in your tyre. Apart from that, it also depends upon your condition of the surface on which the wheel is moving.
Detailed Explanation
Several factors influence rolling resistance, including the type and size of the tires and the condition of the surface being traveled over. For instance, wheel-mounted machinery may perform differently depending on the tire's tread and how inflated they are. Wider tires or lower inflation pressures can help distribute weight better on softer surfaces, affecting rolling resistance positively.
Examples & Analogies
Consider a car's tires. A flat tire (low pressure) increases the effort needed to move the car, while a properly inflated tire makes it easier. The size and type of tire tread also change how easily the car drives on different surfaces, just like construction equipment on various grounds.
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Create a free accountFor this particular road, the rolling resistance is given as 70 kg per ton. That means, to move a unique kind of machine on the particular surface, I need 70 kg of force. Now you know what is the gross weight of your machine? What is the gross weight of your machine? It is nothing but 20 tons. Now we can calculate what is the tractive effort needed to overcome this rolling resistance and keep the machine moving.
Detailed Explanation
To calculate the total tractive effort needed to keep a machine moving on a surface, you multiply the weight of the machine by the rolling resistance per ton. If a machine weighs 20 tons and the resistance is 70 kg per ton, the total tractive effort would be 20 tons multiplied by 70 kg, equating to 1400 kg needed to overcome rolling resistance.
Examples & Analogies
Imagine if you're carrying a heavy backpack while walking. If the ground is rough, you exert more effort to move forward. Similarly, if you weigh more (like our machine weight), the amount of effort to keep moving increases according to the roughness of the terrain, precisely like calculating tractive effort.
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Key concepts
Core takeaways and short definitions to help you quickly recall the key ideas from this section.
- Tractive Effort:
The force needed to overcome resistance and move equipment.
- Required Power:
The power necessary to keep the equipment operational against resistive forces.
- Rolling Resistance:
The resistance caused by the surface over which machinery operates.
- Grade Resistance:
Resistance faced when machinery operates on slopes.
- Surface vs. Penetration Resistance:
Distinction between resistance faced on surfaces and that when tires sink into surfaces.
Examples
Step-by-step examples to apply the section's ideas and test your understanding.
If a bulldozer with a gross weight of 30 tons has a rolling resistance of 50 kg per ton, the total tractive effort required would be 30 tons x 50 kg/ton = 1500 kg.
In a case where a truck grossing at 25 tons moves over a gravel road with a rolling resistance of 80 kg per ton, the effort necessary would be calculated similarly.
Memory aids
Imagine a bulldozer sinking into mud during a rainy day. The deeper it sinks, the harder it fights to keep moving. Remembering this scene helps us recall how penetration resistance adds to rolling resistance.
RPG for remembering resistances: R for Rolling resistance and P for Penetration resistance and G for Grade resistance.
Flash Cards
Glossary
Tractive Effort
The usable force required to move a vehicle or equipment at the point of contact with the ground.
Required Power
The amount of power needed by a machine to overcome resisting forces in order to keep moving.
Rolling Resistance
The resistance encountered by wheels or tracks as they move over a surface.
Grade Resistance
The additional effort required for a machine to move uphill or downhill on a slope.
Surface Resistance
Resistance encountered at the surface when equipment rolls over it.
Penetration Resistance
Resistance faced when a tire sinks into the surface, increasing the effort needed to continue moving.