new challenges for mobile cranes due to increasing hub...

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New challenges for mobile

cranes due to increasing hub

heights in the wind mill

industries

Presented by Hans-Dieter Willim, LIEBHERR Werk Ehingen GmbH

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Why is the hub height continously increasing??

Hans-Dieter Willim 2

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Comparison of a 77 m rotor on 90 m and 125 m hub height


At 90 m hub height the

wind speed is increasing

very much with height.

The lower blade gets less

wind pressure than the

upper blade, this results in

cyclic loading of the rotor

bearing

At 125 m hub height the

increase of wind speed is

moderate

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Increasing hub Height

Source:


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Increasing Hub Heights in Germany

http://windmonitor.iwes.fraunhofer.de/windmonitor_de/3_Onshore/2_technik/4_anlagengroesse/

Average hub

heightAverage rotor

diameter 2015:

125 m


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Example of a new wind mill

Hub height up to 159 m,

required lifting height of

crane: 170 m

Full power output starts at 13 m/s wind speed:

High probability for winds exceeding 13 m/s

during mounting of the wind mill!


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Increasing hub heights for wind

mills with integrated water tank

Gaildorf


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Function

Water tank integrated

in the foundation


200 m

Power station

max.32 MW

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Diameter 2.5 m

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Diameter of

water tank 63 m


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If h = 15 m: 47 000 m³

200 m difference in altitude: 13 000 kWh

each wind mill (estimated efficiency

50%), approx. 4 h with 3 MW

The erecting crane needs

more distance to the

center of the tower

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Increasing

lifting

height by

40 m due

to the

additional

water tank


Hub height: 178 m

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Summary

The hub heights of wind

mills are exceeding 160 m

in Europe

Crane boom lengths are

exceeding 170 m

Extreme long booms will be

used frequently


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What

challenges

are rising up

for the crane

due to the

increasing

lifting

heights?


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Supporting base of the crane


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The

supporting

base of the

crane has not

increased

with the boom

length!!


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Total

center of

gravity

of crane

and

load is

very

high up


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Stability

The Criteria tipping angle

is important on long

booms in all directions

LG 1750,

165 m + 12 m

LR 1750,

165 m + 12 m

Extreme long booms:

According to the very

high center of gravity

and the small supporting

base, a small amount of

energy is required to tilt

the crane


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Very little potential

energy required to

tilt the column

A lot of potential

energy required to

tilt the column

a

a

Tipping angle


Big tipping

angle

Small tipping

angle

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Tipping angle

in EN 13000

Tipping angle calculation

to take accelerations and

decelerations into account

The standard EN 13000

only asks for a tipping

angle in boom direction,

not transversal to the

boom direction

EN 13000 will be

amended accordingly


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Moving with long booms

Due to the high

center of gravity

moving of

erected cranes

with long booms

is very risky!

21Hans-Dieter Willim

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Willim, LIEBHERR Werk Ehingen GmbH

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Climbing on mats

When climbing on mats ground

pressures are increasing

dramatically


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Side loadings on crane booms can increase with

boom length

Mobile crane booms can bear only limited side

forces

Side forces can result from slewing accelerations or

decelerations, wind on crane and load or from an

unlevelled crane

Side forces are bending the boom sidewards, the

vertical force of the load is bending the boom further


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Elastic side deformation of

the crane`s boom

Example:

LR 1600/2 with 156/F12

• 0.3°unlevelled: 5.4 m

• 0.3° + 9 m/s: 7.9 m

• 0.3° + 12.8 m/s: 10,5 m

Crawler base: 8.4 m


load

10.5 m

Therefore we have not increased the

boom length on the LR 1600/2 further

Longer booms: LG/LR 1750 SX

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Side load test with strain gage measuring according to SAE J 987

Side load test

with 2% of load


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Side

deflection

The side

deflection is

increasing with

the boom

length!

The boom is

highly loaded

due to the side

bending


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Long booms

A perfect levelling of a mobile crane

with long boom is essential for safety

If the crane is 0.3° out of level (max.

allowable according to EN 13000, B30.5)

the tip of a 160 m boom will have a side

movement of approx. 1.5 m without

load!

Side inclination and strong side wind

on the load and the boom adds up!

Ground pressures will increase!


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Levelling of the crane

• With increasing boom

length it is very

important that the

crane is accurately

levelled!

• Crawler cranes

equipped with

outriggers or LG

cranes can be levelled

more accurately

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Additional outrigger forces

Depending on boom length and surface area of

the load the additional outrigger forces can

increase up to

35%

due to wind and elasticity of the crane

These additional outrigger forces are not included in

the operation planning systems of the manufacturer


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Challenges: buckling of long booms

If the length of a boom is increasing from 100 m to

150 m without changing the cross section, the

bearable load is decreasing by 56%

Much stronger booms are required


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For extreme

long booms a

stiffer design is

required

The CC8800-1 with the „boom booster“


Stiffer booms

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Stiffer booms

The LG 1750 will be

equipped with additional „X“

sections for higher

capacities on longer booms


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Boom supports required for erection

Boom

support


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Long booms require a lot of empty space for

erection

Source: CC3800

Internet


Long booms

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Erection of wind mills in forests

Limited space for mounting of crane and

rotor

WIND KRAFT Journal, Ausgabe 4/2011, Seite 20


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Erecting on the hill


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Wind and long booms

The wind

speed

increases with

height!

The wind risk

is increasing

with the boom

length!

Heig

ht

ab

ove g

rou

nd

ground

Turbulences close to ground

Wind speed


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Longer booms

For a rotor lift the weather

window will be smaller:

more frequently too high

wind speeds

Downtime of the crane due

to high winds will

increase

It might be cheaper to use

the next size of crane

which allows higher wind

speeds


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Single blade installation: reduced wind risk


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Check future wind speed

Check the wind

speed forecast

constantly

during the time

the boom is

erected


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wind

Wind on long crane booms when moving the crane

While moving the

crane with a long

boom, the ground

pressure under

the crawlers can

increase a lot due

to wind forces on

the boom!


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Moving the crane with a long boom

Q: WIND KRAFT Journal, Ausgabe 1/2011, Seite 26

The danger will increase if

cranes are moved with long

booms under high wind

speed conditions according

to:

the high center of gravity,

The wind area of the boom

The big lever arm of the

wind forces


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Wind on crane boom


Wind on long crane booms increases ground

pressures ! Q: WIND KRAFT Journal, Ausgabe 1/2011, Seite 26


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Wind risk for long booms out of service


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Decision to lower down the boom to the ground

If the wind forecast predicts

strong winds the following

decisions must be taken:

Is the predicted wind speed

higher than the allowable wind

speed to leave the crane

erected?

Yes: lower down the boom

system to the ground before the

wind speed gets higher than the

allowable value for erection/take

down of boom

No: position the

crane booms

according to the

wind chart of the

crane


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Decision: lowering of boom or leave it standing

The decision to lower down the

boom system shall be taken

according to the weather

forecast

Attention: the max.

wind speed for

lowering the boom

system can be less

than the wind speed

for parking the crane

exampel: LR 11350

S 114 D42 W84

S 87°,W 46°

Max. wind speed with

closed slewing gears

Max. wind speed for

slewing against the wind

Max. wind speed for

lowering or erecting of

boom

300 t200 t


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For more information please see

the LIEBHERR leaflet and video

LIEBHERR leaflet and film


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ICSA International Crane Stakeholders Association


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Wind from the back with long booms

Q: Enercon

wind

Due to the wind forces on the

crane boom and the load, the

display of the rated capacity

limiter displays more load

If the crane capacity is at it´s limit, the

rated capacity limiter will cut off

European cranes delivered after may

2010: in overload mode the speed is

reduced to 15 %


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Long booms and tag lines

With increasing hub height the

horizontal component of the

tag line force is reduced


To control the blade

or the rotor by

taglines gets worse

with increasing hub

heights



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0G/2 x µ = 0.45 t

Tag lines

With increasing hub height the angle α

is increasing. Therefore the horizontal

component of the force is very small


On slippery ground (µ = 0.1)

the fork lift cannot hold the

rotor

αG=9t

G/2 G/20.45 t

4.5 t


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Single blade installation

reduces the danger of

high side loads to the

crane´s boom by strong

wind gusts

Guiding of the blades is

required as the center

of gravity and the center

of the wind area is

different

Single blade installation


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LIEBHERR Single Line Guiding System


Option on LG and LR 1750

Ropes to the blade

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Working with long booms at deep

temperatures

Due to ice in the groove of the sheave,

the rope can come out of the sheave!


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Frequent erection of extreme long booms

For erection of these long

booms the highest rope pull

on the erection winches is

required

According to the big lifting

heights the full rope length is

necessary with the max. rope

pull


Wire ropes are getting wear

parts!

The additional costs for

replacement ropes must be

taken into account

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Twist of the hoist ropes on long booms

With increasing boom length the

tendancy of the hoist ropes to twist

around each other is increasing: The

hook block starts to twist


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Hook block for LG and LR 1750 with X boom

• Special anti twist design with a wide distance of sheave blocks

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Inclination display of ballancer


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Thank you for your attention


new challenges for mobile cranes due to increasing hub...

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