INFLUENCE OF WIND ON LIFTING OPERATIONS

Influence of Wind on

Lifting Operations

Presenter : Sreenath Pokkadavath 13/10/2016 1

Lifting Operations - Safety

PDO LIA QUATERLY MEETING September 2016

Objective

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Influence of Wind on Lifting Operations

Every lift carries a set of risks that needs to be managed in order

to prevent an accident from occurring.

Often wind speed is being considered with least importance or

“under estimated” as a hazard that could cause crane accidents.

In the event of many recent catastrophic crane accidents in Gulf

region as well as around the world, happened to due to wind; Its

important for professionals like us to consider wind as

considerably important factor while preparing for any lift, whether

as a part of thorough examination or a regular operation.

Statistics

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In 2009 and 2010, from the total tower crane accidents

reported, the following statistics has been made.

Accidents

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Few crane accidents in last 33 months due to wind

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Sr.

No. Date

Typ of Crane/s

involved Accident - details Location Fatality Injury

1 26-Jan-14

Tower Crane

tower crane jib collapsed on IYLO building in Croydon,

London during a storm. Croydon, London NIL NIL

2 27-Jan-14

2 x Tower Crane

A heavy storm in northern Belgium on took down two tower

cranes at the site of a new hospital in Oekene, Roselare. Roselare, Belgium NIL NIL

3 14-Jan-15

Crawler Crane

A crawler crane overturned on a wind farm in Janneby,

Germany, Flensburg, Germany NIL NIL

4 2-Feb-15

Crawler Crane

A large crawler crane working on the new Timsah Arena

Stadium, in Bursa, Turkey Bursa, Turkey 1 1

5 18-May-15 Tower Crane A tower crane came down across the airport road Doha, Qatar 1 3

6 18-Jun-15

Tower Crane

A tower crane collapsed spectacularly in the Guangxi Zhuang

Autonomous Region of southern China after extreme winds Guangxi Zhuang, China NIL NIL

7 5-Feb-16

Crawler Crane

Crawler Crane with luffing jib collapsed as it was lowering

due to wind alert, on to busy street Manhattan, USA 1 3

8 12-Aug-16

Tower Crane

A heavy gust of wind sent the headache ball of a crane into

the window of Three World Trade Center New York, USA NIL NIL

9 26-Oct-15

Tower Crane

The luffing jib of an out of service tower crane blew over the

back of the superstructure in strong winds Tel Aviv, Israel NIL NIL

10 28-Mar-16

Tower Crane

A crane has been bent over double in the high winds amid

Storm Katie in Greenwich, east London. Greenwich, UK NIL NIL

11

8-Aug-14

Mobile Crane

crane overturned and his cab was damaged in Grand Meadow,

Minnesota. The crane looks to have been well set up and it is

assumed that the wind took the load out of radius, creating an

overload and causing it to swing into the cab Minnesota, USA NIL 1

12 11-Sep-15

Crawler Crane

a crawler crane toppled over onto the Masjid al-Haram, the

Grand Mosque in Mecca Mecca, KSA 111 394

Wind Basics

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Wind speed is critical for safe crane operations. Wind is moving air. Wind is caused by differences in the atmospheric pressure. When a difference in atmospheric pressure exists, air moves from the higher to the lower pressure area, resulting in winds of various speeds. Often wind and occurring gusts of wind are an under estimation factor in accidents with mobile and/or crawler cranes.

Gusts

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The speed of a gust is the average value of the wind speed measured for duration of 3 Seconds. The gust speed is higher than the average wind speed, which is measured over a period of 10 minutes. (definition based on EN 13000) Gusts at the ground are caused by either turbulence due to friction, wind shear or by solar heating of the ground. These three mechanisms can force the wind to quickly change speed as well as direction. In the case of friction, gusts are generated when wind blows around buildings, trees or other obstacles. This type of gustiness is generally largest near tall buildings and valley ways and least over large water bodies. The duration of a gust is usually less than 20 seconds.

Wind gust accident

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Gusted around 80–105 km/h

Gusts

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In the cities with high buildings the roughness lays highest. This creates impression that the wind is not so strong there. However in large cities with high buildings there are also large urban canyons present. The air is compressed on the wind sides of the houses and its speed raise considerably whilst it blows though the urban canyons. This phenomenon is known as “Nozzle effect”. If the normal wind speed in open terrain is 6 m/s for example, then in an urban canyon it can certainly reach 9 m/s.

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Influence of Wind on Lifting Operations Wind Load

The generic formula for wind load is F = A x P x Cw where F is the force or wind load, A is the projected area of the object, P is the wind pressure, and Cd is the drag factor. wind pressure, P = ½ x (density of air) x (wind speed)2

The density of air is about 1.25 kg/m3. The wind speed must be expressed in m/s. The drag factor depends on the shape of the body

If the wind speed doubles, the wind pressure increases by a factor of four times and so with the Wind Load. This means that a small increase of wind speed can have a significant effect on the safe operation of the mobile crane.

Wind force on crane

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The wind forces exerted on both a mobile crane and the load suspended from it,

may well be quite large and affect both the strength and stability of the crane, and

safe handling of the load.

Effect when wind from front

The wind from the front does not reduce the

loading of the hook, hoisting cable, hoisting

cable rollers and hoisting winch because the

load continues to work with its gravitational

force. With wind from the front these

assemblies can be overloaded if continues to

lift until the LMI shut-off! The load reduction

caused by the wind from the front can overload

the complete crane with the booming guying, if

it has been loaded up to the point of LMB shut-

off beforehand!

The crane driver must therefore know the

weight of the load and must not exceed the

max load capacity!

Wind force on crane

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Effect when wind from rear

The wind from the rear may induce additional loading on the crane

and the LMI may shutoff before the actual load lifted being reached

due to enhanced load reading.

Also the load from rear may push the boom to deflect and may also

push the load ahead and thus lead to increase in radius than the

operator derricked the boom.

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Effect when wind from sides

The wind from the side is particularly dangerous for the crane boom and the

load. This is not determined by the LMI. This can result in the crane being

overloaded. Crane being designed to lift load vertically, it wont withstand much

of the side loading.

warning from an operator warning label on

Manitowoc crawler crane:

“The effect of wind can severely shock and side

load the boom and jib, possibly causing tip over

or damage. As a general rule, if the wind

causes the centerline of the freely suspended

load to move out past the hinge pin on either

side of the book or jib, the load should

immediately be lowered to the ground.

Operations should not resume until the wind

has subsided. For specific wind conditions and

rules for your crane, refer to operator’s manual

or contact manufacturer.”

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Wind from the front Wind from the rare Wind from the side

Boom With wind from the

front the boom system

is relieved of load. The

load indication is too

low. The LMI shut-off

actuates only with the

load that is greater

than the maximum

permissible load

capacity.

With wind from the rare the

boom system is additionally

loaded. The load indication is

too high. The LMI shut-off

actuates at a load that is less

than the maximum

permissible load capacity

according to the load chart.

With wind from the side the

boom system is side-loaded.

The load indication is similar

to the display when

operating without wind. The

LMI does not take side winds

into account.

Load The form and the deadweight of the load play’s a large role with the influence of the

wind. The wind caused the load to swing and this in turn causes the crane boom to

swing. This swinging (Dynamic) of the boom causes the crane’s loading to increase. In

the limit range the LMI shut-off could be switching in and out constantly. With special

load such as with a rotor for example, the wind can have the effect of reducing the

load due to the shape of the rotor.

Overview of wind hazards

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Wind force acted on suspended load

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A calculated maximum permissible wind speed is given for every crane load chart in the load chart book. How ever this dependent on the length of the boom (even percentage of extension) and the crane configuration. The sail area is considered to 1.2 sq.m/ton weight of load as reference from EN 13000 for these calculations. These standard sail area values are based on wind resistance factor (Cw) or drag factor and projected surface area of load. Sail area Aw = Projected surface x Drag factor If sail area is greater than 1.2 m² / ton weight of load; and then the maximum permissible wind speed mentioned in the crane load chart is no longer valid.

Drag Factor reference chart

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Permissible wind speed as per load chart

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There are 2 methods to find the actual permissible wind speed; those are Method 1 : by using a wind force diagram specific to the load chart’s permissible wind speed like given below.

Method 2: by using formula Vmax = Vmax load chart x √[(1.2m²/t X m)/(Ap x Cw)]

• The mass of the working load (m) • The maximum projected surface area (AP) of the load (see below) • The drag factor (cw)

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Measuring Wind speed

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The best method to measure the wind speed to rely on the anemometers provided on the crane’s boom tip by manufacturer. These should have their indicators located in clear view of operator In the absence of a wind measuring device on the crane, the appointed person must arrange to obtain wind speed data at frequent intervals. This may be by means of a hand held anemometer, data from the anemometer fitted to a tower crane on the site or a local weather forecast. Hand held anemometers can be depend upon only when there no anemometer available on boom tip or some option on height. Because hand held anemometers would give reading only for ground level wind, but wind speed increases as height increases.

Height dependent wind speed

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Height above the ground in meters 10 20 30 40 50 60

Wind speed multiplier 1 1.1 1.17 1.22 1.26 1.29

Wind speed reading in portable anemometer (in kmph) Actual wind speed at boom tip (in kmph)

15 15 16.5 17.55 18.3 18.9 19.35

16 16 17.6 18.72 19.52 20.16 20.64

17 17 18.7 19.89 20.74 21.42 21.93

18 18 19.8 21.06 21.96 22.68 23.22

19 19 20.9 22.23 23.18 23.94 24.51

20 20 22 23.4 24.4 25.2 25.8

21 21 23.1 24.57 25.62 26.46 27.09

22 22 24.2 25.74 26.84 27.72 28.38

23 23 25.3 26.91 28.06 28.98 29.67

24 24 26.4 28.08 29.28 30.24 30.96

25 25 27.5 29.25 30.5 31.5 32.25

26 26 28.6 30.42 31.72 32.76 33.54

27 27 29.7 31.59 32.94 34.02 34.83

28 28 30.8 32.76 34.16 35.28 36.12

29 29 31.9 33.93 35.38 36.54 37.41

30 30 33 35.1 36.6 37.8 38.7

31 31 34.1 36.27 37.82 39.06 39.99

32 32 35.2 37.44 39.04 40.32 41.28

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LTM 11200 9.1; ROTOR LIFTING, 1 FATALITY GUST 25/07/2011

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Documents

INFLUENCE OF WIND ON LIFTING OPERATIONS