TYPES TOWER CRANES IN MALAYSIA
LOAD CARRIED BY THE JIB (BOOM)
|Nos||Distance from the Mast( in meters)||Load Carrying Capacity ( in Metric Tonnes)|
Tower Cranes at the Site: :
Maximum unsupported height - 141 feet (43 meters)
Maximum reach - 164 feet (50 meters)
Maximum lifting power – 6.61 tons (6 metric tons)
Counterweights – 17.6 tons (16 metric tons)
TOWER CRANES AND THE WIND FACTOR
The wind forces exerted on a tower crane and any load suspended from it, may well be quite large and affect the safe handling of the crane and the load. It is not always appreciated that these forces are due to wind pressure, not wind speed, and that wind pressure varies as the square of the wind speed. Consequently if the wind speed doubles, the wind pressure increases by a factor of four times.
This means that a small increase of wind speed can have a significant effect on the safe operation of the tower crane.
The wind pressure can be approximated by:
-Pressure = ½ x (density of air) x (wind speed)2 x (shape factor)
-The density of air is about 1.25 kg/m3.
-The shape factor (drag coefficient) depends on the shape of the body. It has order of magnitude 1 and is dimension less.
-The wind speed must be expressed in m/s. In that case the pressure has units kg/m/s2, i.e. N/m2.
|Bft||Wind speed (m/s)||Wind pressure(N/m2)|
|Lower limit||Upper limit||Upper limit|
The tower crane’s manual will specify the maximum wind speed at which the tower crane must be taken out of service. This is normally 45 mph (20 m/s, 72kph) and is based on the requirements of the tower crane design standards. It is however, a maximum value and does not take into account the time required to take the crane out of service or the difficulty of lifting large area loads in high winds.
Eg - A review of in-service wind speeds by the CPA Tower Crane Interest Group, involving tower crane suppliers, major contractors and the Health and Safety Executive, the industry recommended maximum wind speed at which tower cranes operating in the UK must be taken out of service is 38 mph (16.5 m/s, 60 kph).
However, the operator may decide to take the crane out of service at a lower speed due to the type of load being lifted or difficulty in controlling the crane. The operator has the primary responsibility for making the decision, in conjunction with the appointed person or crane supervisor. The operator’s decision to take the crane out of service should not be overridden by site management under any circumstances.
Measuring Wind Speed for CRANE APPLICATIONS
It is essential that tower cranes are fitted with anemometers or other wind-speed monitoring devices. These should have their indicators located in clear view of the tower crane operator.
The correct operation of these devices should be determined regularly and they should be maintained in good working order. The sensor of the indicator should be positioned so that it can measure airflow uninterrupted by the tower crane or adjacent structures. Sensors are often positioned on the highest point of the tower crane. In cases where a number of wind-speed monitoring devices are located on a site, the device fitted on a specific crane must be used for assessing the wind effect on that crane. Devices located on other parts of the site will not give an accurate wind-speed for that crane.
The Effect of Wind on Suspended Loads
Strong winds may swing suspended loads (crates, panels, etc) out of balance and radius, making the tower crane unstable. If the operator feels that he cannot maintain full control of the load, it should not be lifted.
For large, light loads such as shutters, this situation may occur some way below the tower crane's design wind speed. For example, with a wind speed of 14 m/s (31 mph) the wind load on an 8' x 4' sheet of ply will be 38 kg. If the wind speed increases to 20 m/s (45 mph) the wind load will rise to 76 kg!
High Wind Conditions and Taking the Tower Crane Out of Service
It is important that the operator monitors the wind speed constantly using the anemometer display in the cab. This will give early warning of rising wind speeds and enable him to take action to take the tower crane out of service and descend down the ladders to ground level before the limiting wind speed is reached.
Putting the crane in the out of service condition generally includes ensuring that the jib is free to “weather vane” when out of service so that the minimum wind area is presented to the prevailing wind. On luffing jib tower cranes it is also important that the jib is left at the correct out of service radius, not the minimum radius, to ensure that there is sufficient wind area to ensure that the crane is able to “ weather-vane”.
Planning of Lifts
It is important that all lifts are planned and that note is taken of anticipated wind speeds from site specific weather forecasts, to ensure that lifts are not started in rising winds. It should be borne in mind that most weather forecast wind speeds are for a height of 10m above ground and should be corrected for greater heights. In open countryside, wind speed increases with height as shown in the table below:
|Height Above Ground (metres)||10||20||30||40||50||60||70||80||90||100||110||120||130||140||150|
|Wind Speed Multiplier||1.00||1.10||1.17||1.22||1.26||1.29||1.32||1.35||1.37||1.39||1.41||1.43||1.44||1.46||1.47|
In city centre locations the gust wind speed at a height of 100m will be approximately twice as strong as the gust wind speed at pedestrian level (excluding effects from nearby buildings). Nearby buildings can have a very significant influence on wind forces. Where surrounding buildings are significantly taller they will often generate increased wind loading on nearby lower cranes.
CRANE ACCIDENTS IN MALAYSIA & SINGAPORE
LORRY DRIVER CRUSHED TO DEATH BY CRANE ARM New Straits Times Online, 25 September 2014
MALACCA: A garbage truck truck driver making his early morning rounds was crushed to death after a crane arm fell on his vehicle, here yesterday. The 5.35am incident took place in Banda Hilir, here, near a shopping complex. The 55-year-old driver with Southern Waste Management (SWM) died on the spot due to serious head injuries. The incident occurred as the victim identified as Anas Tawi was waiting in the vehicle for his colleague who was collecting trash, nearby.
"There was a construction project next to the garbage collection site and the crane was lifting goods, when the the crane's arm suddenly fell on the victim's vehicle,” said Acting Melaka Tengah district police chief, Superintendent Razali Abu Bakar . He said they have classified the case as sudden death.
TWO WORKERS KILLED BY CRANE COLLAPSE The Straits Times, Oct 1, 2013
A tower crane accident left two construction workers dead, Monday 30 September 2013. Bangladeshi Ronju Ahmmed, 28, and an unnamed Thai national lost their lives when the crane crumpled down. It had been lifting an excavator when the accident happened. Concrete blocks making up its counterweight fell onto the worksite. The Straits Times reported (1 October 2013) that one man was killed by the falling counterweights while the other was pinned by the crane’s hook assembly as it swung down. Initial speculation centred on the possibility of the tension cables snapping, since the weight of the excavator was reportedly within the crane’s lifting capacity.
CRANE ACCIDENTS AT LRT SITE The Star Online, 20 August 2014
Recovery exercise: A crane being used to lift the concrete span as workers clear the debris to recover the bodies of the three Bangladesh workers.
Three Bangladeshi workers were killed when a concrete span weighing 650 tonnes at the site collapsed at 8.30pm, pining them underneath. The incident occurred while work to construct the parapet for the guideway, made up of 14 units of segmented box girders, was being carried out.
CRANE ACCIDENTS AT MRT SITE The Star Online, 24 June 2014
A Metal Slab From The Pusat Bandar Damansara MRT Construction Site Fell On To Car On 24 June 2014
CRANE ACCIDENTS AT LRT SITE The Star Online, 28 June 2014
PETALING JAYA: Police have opened up a case against the contractors of the Light Rail Transport (LRT) construction site along Jalan Lapangan Terbang Subang, where a falling beam injured two motorists and damaged their cars on Thursday.
During the 9am incident, a steel beam fell from a crane and crashed on top of the victims travelling in a Honda Civic. The car was then hit by a van from behind amid the chaos.
CRANE ACCIDENTS AT LRT SITE The Star Online Mar 28, 2014
Vijayasingam's Hyundai Sonata was caught in rush hour traffic along Jalan Lapangan Terbang Subang when a 10-tonne construction equipment hoisted by a crane at an LRT extension site nearby fell and crushed his car.
The development executive was killed instantly in the freak accident while another driver, Arifpuddin Mansoruddin, 42, in a Nissan Frontier, was injured.