2017 CRW: Breakout Session 2: Unbreakable Laws: Physics of a Move

Don Mahnke P.EngPresidentHydra-Slide Ltd.

1975-1991

1991-2005

and

ETARCO-MAMMOET

1991-2005

and

ETARCO-MAMMOET

2011-present

DESIGN – MANUFACTURING - SALES• Heavy Track Skidding Systems• Low Profile Skidding Systems• Synchronous Power Units• Hydraulic Turntables• Ekki Jacking Timbers• Alignment Shoes• Climbing Jacks

Why do we care about Physics?

• We generally think only of weight and size.What happens when we start to move things?



• Forensic Engineers use the Laws of Physics to look at the underlying causes of accidents




• Laws of Physics can be used to predict what will happen in order to prevent occurrences




• Laws of Physics can be used to predict what will happen in order to prevent occurrences

• Let’s look at what happens when you try to break laws of physics


What We’ll Cover• Newton’s Laws of Motion

What We’ll Cover• Newton’s Laws of Motion• Types of Forces• Weight (gravity)• Inertia/Momentum (Kinetic Energy)• Centrifugal Force• Impact Force• Wind Force


• Stability• Airplanes/Barges/Railcars/Trucks/Cranes



• Force – Work – Power



• Force – Work – Power• Choosing the right equipment



• Force – Work – Power• Choosing the right equipment• First Hydra-Slide Skid System

LAWS OF PHYSICS (Newton’s Laws of Motion)

Sir Isaac Newton1643 - 1727

First law:

?

Second law:

?

Third law:

?


First law:

An object will remain at rest or move at a constant velocity, unless acted upon by an external force.

Second law:

?

Third law:

?


First law:


Second law:

?

Third law:

?


First law:


Second law:

Acceleration and force are vectors; an object will accelerate in the same direction as the direction of the net force applied. (F = ma).

Third law:

?

A Force acts on an object


First law:


Second law:


Third law:

?

The Force has both Magnitudeand Direction


First law:


Second law:


Third law:

?

The object moves in the direction of the Force


First law:


Second law:


Third law:

?

The Force can be broken down intoIts Horizontal and Vertical components


First law:


Second law:


Third law:

For every action there is an equal and opposite reaction.


First law:


Second law:


Third law:

For every action there is an equal and opposite reaction.

Force as a Vector

Example: • Spreader Bars

Estimate Sling Forces

Force as a Vector


Typical Spreader Bar

Force as a Vector


Measure Bar Length and Sling length.Draw to scale

Force as a Vector


Draw load weight vectorsTo scale

50,000 lbs 50,000 lbs

x

Force as a Vector


Vertical component in topSlings must be same asload weight vectors.(Equilibrium)

x

x

Force as a Vector


Force in sling is along sling axis

Force as a Vector


Measure length of sling Force(using same scale)

50,000 lbs 50,000 lbs

57,350 lbs

Weight

• Weight is a Force that is a result of Gravity acting on a Mass.

Weight


• It never changes unless the Mass changes

Weight



• The Force can be considered acting at itsCenter of Gravity (or Center of Mass)

Weight



• The Force can be considered acting at itsCenter of Gravity (or Center of Mass)

• It always acts straight down

Inertia and Momentum

• Inertia is a tendency to do nothing or to remain unchanged.



• Momentum is the quantity of motion of a moving body, measured as a product of its mass and velocity.

p = m v



• Momentum is the quantity of motion of a moving body, measured as a product of its mass and velocity.

p = m v

• Kinetic Energy is the energy that a body possesses by virtue of being in motion.

KE = ½mv2

Centrifugal Force

• Centrifugal Force is known as a “fictitious” force

Centrifugal Force


• It is a reaction to the pull towards the center of the curve (Newton’s Third Law)

Centrifugal Force


• It is a reaction to the pull towards the center of the curve (Newton’s Third Law)

• The object wants to continue moving in a straight line (Newton’s First Law) but is being pulled towards the center of the curve. It is being accelerated towards the center. a = v2

r

Centrifugal Force

Example:80,000 lb. truck going around a 100’ radius curve at 30 mph (44 ft/sec)

Centrifugal Force

Example:80,000 lb. truck going around a 100’ radius curve at 30 mph (44 ft/sec)

F = m x a

Force = Wt x v2= 80,000 x (44)2

g r 32.2 100

= 48,000 lbs

When stationary, the total force in the sling is equal to the weight of the object.

But what if the load falls? The impact force generated when the load is stopped depends on three factors:

• The load’s weight• The distance of the fall (which determines

time and velocity)• The stopping distance

Impact Forces

Example: A one-ton load falls for one foot and when it’s caught, the sling stretches by one inch while arresting the load.

Impact Forces


______t = √2h/g where g = 32.2 ft/s2

= 0.25 s_____

V = √2gh = 8.1 ft/s

Impact Forces


______t = √2h/g where g = 32.2 ft/s2

= 0.25 s_____

V = √2gh = 8.1 ft/s

The load takes a quarter of a second to travel one foot, and is moving at 8.1 ft/s. (about 5.5 mph)

Impact Forces

The load’s kinetic energy is:

KE = 1/2mv2

= 65600 lb∙ft2/s2

and all this energy is absorbed by the slings in one inch:

F = KE = 65600 lb∙ft2/s2

d 0.083 ft

F = 790500 lb∙ft/s2

The equivalent of 24500 lbsabout 12 times the weight of the load.

Impact Forces

12 ton

WindForces

WindForces

Fw = .0035(v)2

Fw (lbs/ft2)V (mph)

WindForces

Example: Wind Force on a 15’ x 20’ panel

Gentle Breeze 10 mph Force = 105 lbs

Strong Breeze 30 mph Force = 945 lbs

Storm 70 mph Force = 5,145 lbs

Wind Forces

How much wind would be needed to blow over this truck?

Wind Forces


Wind Forces


Truck Righting Moment = 15,000 x 4’-0” = 60,000 ft-lbs

Wind Force must be more than this Wind x 8’6” > 60,000 Wind Force > 7,058 lbs

If projected area is about 53’ x 8’-6” = 450 ft2

Wind Pressure = 7058/450 = 15.7 psf (more than 67 mph)

STABILITY

• All forces are in Equilibrium

STABILITY


• Righting moment exceeds the overturning moment

STABILITY


• Righting moment exceeds the overturning moment

• Lift is within capacity

STABILITY

Unstable• Overturning moment

exceeds the righting moment

• Over Capacity

Aircraft Stability(Roll Stability)

Why are the wings angled up?Dihedral Angle




Inherent Stability


In some Cargo and Military Aircraft,stability comes from a low center of gravity.

Barge Stability

Roll-On

Barge Stability

A barge floats becauseof buoyancy.

The buoyancy forceIs equal to the weightof water displaced.

Barge Stability

When a load is applied to the barge, it is pushed down into the water

Barge Stability


and the buoyancy increases

Barge Stability


and the buoyancy increases

Barge Stability

If the weight is movedoff center, the bargetilts.

The buoyancy forcemoves to balance theoff center weight.

Inherent Stability

Barge Stability Ballasting to maintainStability during roll-on.


Pre-ballastWater is added into thebarge equivalent to theweight coming on



Water is added to the wing tanks to be used for leveling barge



Water is added to the wing tanks to be used for leveling barge

Additional water can be added to bring the barge level to the dock

Barge Stability Roll-on

Place Ro-Ro ramps


Water is moved from one side tank to the other to keep barge level

Water is pumped out of center tank to offset the weight coming on


Water is moved from one side tank to the other to keep barge level

Water is pumped out of center tank to offset the weight coming on

Barge Stability

With weight fully on bargeand moving towards centerwater is pumped back to first wing tank to keepbarge level

Barge Stability

With weight fully on bargeand moving towards centerwater is pumped back to first wing tank to keepbarge level

Barge Stability

With load centeredon barge, all wateris pumped out of barge

Barge Stability

With load centeredon barge, all wateris pumped out of barge

Barge Stability

A potentially dangerouscondition if water is left in barge during transit

The ballast water can slosh from side to sidecausing decreasedstability

Barge Stability

Railcar Stability

Railcar Stability

Railways move a lot of high volume cargo and their track systemsare designed for high speed movement

Movement of large and heavy objects often presents particular problems for the Railways

Railcar Stability

Inside of Curve

Superelevation

Normal maximumCCG is 98” ATRwithout special handing

Schnabel Railcarswith Side Shift

Transporter Stability


ESTA Recommendationson 3 or 4 Point suspension groupings



• Load weight not exceed 75% of rated capacity



• Load weight not exceed 75% of rated capacity• Tipping angle not exceed 9° (7 ° + 2 °)


3 Point suspension groupings

CCG






• Statically Determinant


3 Point suspension groupings – 75% capacity





• Statically Indeterminant







Crane Stability

Demag AC-700

Crane Stability

Demag AC-700

Crane Stability

Force from Loadis applied at boompoint

Crane Stability


Crane Stability


Crane Stability

“Effective”Combined Center of Gravity

Crane Stability

Effect of Levelness

Crane Stability

Effect of Levelness

140’ Boom

Crane Swinging a Load

Use Laws of Physics to predict path of Load



Crane starts to swing but load lags behind due to Inertia.(Newton’s first Law)



Crane continues to swing And load starts to move.As it picks up speedCentrifugal Force causes itto move outward



Crane continues to swing. Load moves in a circular pathbut at a larger radius



Crane stops swinging. Load continues to movein a circular path at a larger radius.



Load continues to movein a pendulum motioncausing various side loadson crane.



Load lags behind crane andThen swings at a wider radius.

Thanks to NCSG for Simulator Video



Load lags behind crane causing sideload on boom




Load lags behind crane causing sideload on boom




Load swings at a wider radiusCausing potential overload




Load swings at a wider radiusCausing potential overload


CentrifugalForces

Centrifugal Force can increase effective lift radius and cause side-loading on boom.

WindForces

A Wind Force away from Crane can increaseeffective lift radius.

A Wind Force from the side can cause side loading on boom.

Crane – Barge Combination




FORCE – WORK - POWERForce - a Force is defined as any external effort that can cause an object with mass to change its velocity. Force can also be described as a push or a pull that has both magnitude and direction, making it a vector quantity.

The man in the picture below is applying a push Force on the car in a forward direction.

FORCE – WORK - POWERWork - a force is said to do Work when it acts on a body, and causes a displacement in the direction of the force.

If, as a result of his pushing Force, the car moved forward a certain distance, he has done Work.

FORCE – WORK - POWERPower - Power is the rate of doing work. It is equivalent to an amount of energy consumed per unit time.

If you consider the time it took to move the car a certain distance, you can calculate the Power.

FORCE – WORK - POWER

Application in hydraulics:If you want to raise an object to a height

• The Force required will be equal to its weight

• The Work required will be equal to its weight times the height of the lift. (For any given situation these quantities will be fixed)

• The Power required to do it can vary and will depend solely on how fast you want to do it.

FORCE – WORK - POWER

Example:• If you want to lift a 100,000 lb. load up 1 foot

the Work required will be 1 x 100,000 = 100,000 ft-lbf

• If it is done in 2 seconds, the Power required will be 100,000/2 = 50000 ft-lbsf/sec (or about 100 HP)

• If the same lift is done over 30 seconds, the Power required will be 100,000/30 = 3330 ft-lbsf/sec (or about 6 HP)

In Hydraulics, it is possible to produce very high Forces and do a large amount of Work with relatively low Power (but taking a longer time)

Cranes are one of the most common and useful pieces of equipment on a construction site but may not always be the best choice for moving loads horizontally.

Choosing the right equipment for the jobOften more than one “right” choice


• Technical Constraints

• Crane availability

• Limits on crane setup space

• Limits on pick and set area

• Overhead clearances and obstructions








• Safety & Risk Assessment








• Safety & Risk Assessment

• Financial

• Crane costs vs. benefits


A 145 ton transformer needs to be placed on the pad in the foreground.

What is the best way to do it?.......Is this a job for a crane?


Consider• Suitability and capacity of

available equipment

• Work space availability

• Safety considerations

• Schedule constraints

• Crew expertise

Transformer 290,000 lbs

Block/Rigging 10,000 lbs

Total Lift 300,000 lbs

• Let’s look at the information for an 800 ton Demag mobile crane to see if it can do the job.

• Find the operating range in the load chart for placing the 145 ton transformer.

Choosing the right equipment for the job













• In this case it is determined that the crane has sufficient capacity to lift and place the transformer and there was sufficient access.

• However, the crane was not chosen…..Why?

• Other considerations:

• The crane was not available at the required time

• The crane would be very expensive to mobilize

• When the Power Station is complete there will not be overhead clearances for the crane, so it could not be used for a change-out.

• The contractor had just purchased a skid system

• Skidding was considered less disruptive to other operations at the construction site.


How did they do it?

How did they do it?

A hydraulic skidding system, sometimes referred to as a Jack and Slide System

It is a horizontal load handling method that involves hydraulic cylinders pushing (or pulling) shoes that carry a load over a controlled friction surface on a guided track.

The force is applied directly to the skid shoe and is completely contained within the system.

A Case for Skidding Systems

• The ability to move extremely heavy loads.• The load sits on skid shoes which are

pushed by hydraulic cylinders.• The load is never freely suspended • High friction reduces risk of uncontrolled

movement• No "external forces" and no holdbacks are

required.• Simple setup.• Low height for optimum stability


• Newton’s First Law• Load moves slowly so no appreciable Momentum or Kinetic

Energy. Run away is restricted by friction force.




• Newton’s Second Law• Forces are inline with direction of move and load moves in

same direction. No centrifugal forces.




• Newton’s Second Law• Forces are inline with direction of move and load moves in

same direction. No centrifugal forces.

• Newton’s Third Law• Reaction to pushing force is contained within track and no

external forces.


First “Hydra-Slide” skid system

Don Mahnke P.EngPresidentHydra-Slide Ltd.

Date post:	21-Jan-2018
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2017 CRW: Breakout Session 2: Unbreakable Laws: Physics of a Move

Education