Selection of Tower Crane – Operational characteristics

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The operating characteristics of a Tower Crane are largely determined by its type
of mounting, type of tower and type of jib.

A tower crane with a static base only occupies a limited area but is able to cover, from its fixed position, all points at which loads are to be handled within the maximum slewing radius. They can be set at varying heights up to their maximum free standing height. They can also be extended beyond this limit by tying the crane back to the supporting structure.

Rail-mounted tower cranes have a larger area of coverage as they can travel along their tracks carrying their rated loads. However, the height requirement should not exceed the free standing height as recommended by the manufacturer. On the other hand, the crane service would be disrupted whenever work must be done on or near the track. The advantage of mobile tower cranes lies in great inward reach without the long jib which would normally be required to reach over the top of the structure.

Generally, truck-mounted tower cranes are completely self-contained and can be driven along roads. They are generally capable of comparatively rapid erection and dismantling. They are however generally unable to travel in their fully erected state and cannot handle loads while travelling.

Crawler-mounted tower cranes are required to be transported on a low-loader or towed on special road axles when travelling on public roads. Inside the workplace, some can travel over firm, flat, level ground carrying loads up to a specified proportion of their rated loads. They are also able to travel in a partially erected state but without load over unprepared ground provided it is within certain limits of level and compaction.

With a horizontal trolley jib, the hook is suspended from the trolley and moves in a horizontal direction when the radius is changed. Unless a luffing jib is equipped with a level-luffing device, the hoist motion will have to be simultaneously operated to achieve level travel of the hook when changing radius.

A horizontal trolley jib usually has a smaller minimum operating radius than the equivalent luffing jib and is thus able to handle loads closer to the tower of the crane. For a given height of tower, however, a greater height of lift is available with a luffing jib, and the jib can be raised or lowered to clear obstacles. One advantage of a fixed luff jib is that its extra height at the jib head enables it to clear objects that would obstruct a horizontal trolley jib. The advantage of a rear-pivoted luffing jib is that it has a smaller minimum hook radius than an ordinary luffing jib.

For articulated jibs, some designs are not required to weather vane. In this case, the crane is made to withstand storm winds with the jib drawn into minimum radius; there is then no need for a 360° obstruction-free slewing path. One type of this crane has a hinged jib arranged so that the outer portion remains horizontal. As the jib is folded, the outer portion rises, giving increased height and the ability to pass over obstructions.

The selection of a crane for any job should be made only after a thorough examination of all the factors involved. In general, it is good practice to select a machine which has a working margin in respect of the load capacity and other anticipated requirements.

Selection of Tower Crane – Mounting configurations

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Tower Crane are also characterised according to their mounting configuration. They are available as static bases, rail-mounted units and mobile units.

Static bases -There are three main types of static bases.

In-situ base – The crane is mounted on special corner angles, frames or an expendable tower section, cast into the concrete foundation block.
On own base – The crane is mounted on its own base section or chassis which, without wheels and travelling gear, but with ballast, stands on a concrete base.
Climbing base – The crane is supported by the structure which it is being used to construct, and to which it is attached by climbing frames and wedges. The height of the cranes can be extended as the height of the structure increases by means of climbing supports attached to the frames. Climbing support can be metal ladders, rods or tubes. A climbing crane may be mounted initially on a fixed base and its support be later transferred to climbing frames and supports.

Rail-mounted units – The cranes are mounted on a chassis frame which is supported on rail wheels. The wheels are usually double flanged. When all wheels are removed, some tower cranes can be used as static-based cranes

Mobile units – The mobile mounting configuration consists of truck-
mounted, wheel-mounted or crawler-mounted units.

Truck-mounted tower cranes – Tower cranes mounted on truck or lorry chassis are available. It is essential that this type of crane has its outriggers extended. The outriggers should be securely set up and level on its jacks when handling loads.
Wheel-mounted tower cranes – These are not normally self- propelling and may be moved by towing by a suitable vehicle. They are provided with stabilizers or outriggers and jacks which should be set (and the wheels either removed or raised clear of the supporting surfaces) before commencing erection or lifting operations.
Crawler-mounted tower cranes – There are two principal types of crawler bases used on this type of tower cranes. One is a twin- track type which is mounted on one pair of crawler tracks. The crane requires outriggers to be extended and jacks set when handling loads. The other is the straddle-type which is mounted on four widely spaced crawler tracks, each of which can be adjusted to height. Both types of tower cranes should be set firm and level when handling their rated safe working loads. In general, they do not have the same freedom of mobility as for example crawler-mounted mobile cranes. Reference should be made to the crane specification and to the manufacturer regarding conditions under which these machines may travel in their erected state.

Selection of Tower Crane – Jib configurations

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The main types of jib used on Tower Crane are horizontal trolley jibs, luffing jibs, fixed-radius jibs, rear-pivoted luffing jibs and articulated jibs.

Horizontal trolley jibs (“A” frame type) – They are held in a horizontal or slightly raised position by tie bars or ropes connected to an “A” frame on the top of the tower crane. The hook is suspended from a trolley which moves along the jib to alter the hook radius. A suitable allowance needs to be made for deflection when calculating the clearance between adjacent cranes

Horizontal trolley jibs (flat top type) – They are connected directly to the tower top and do not require tie bars or ropes connected to an “A” frame. This reduces the overall height of the crane. The hook is suspended from a trolley which moves along the jib to alter the working radius. A suitable allowance needs to be made for deflection when calculating the clearance between adjacent cranes

Luffing jibs – They are pivoted at the jib foot and are supported by luffing cables. The hoist rope which supports the load usually passes over a sheave at the jib head, and the hook radius is altered by changing the angle of inclination of the jib

Fixed-luff jibs – They are also mounted on pivots at the jib foot. Unlike the luffing jibs, these are held by jib-ties at a fixed angle of inclination. On some types, the hook is suspended from the jib head and the hook radius cannot be altered, whereas on others the hook is suspended from a saddle or trolley which travels on the jib

Rear-pivoted luffing jibs – The jib pivot of this type of jib is situated at the top and behind the centre line of the tower and the hook is supported by the hoist rope which passes over a sheave at the jib head

Articulated jibs – The jib has a pivot point somewhere in its middle area. Some models are level-luffing; that is, the hook elevation remains constant as radius changes. It is possible to provide either a trolley or a fixed-location hook or even a concrete pump-discharge line. Articulated jibs are mounted on towers identical to those used with horizontal trolley jibs

Types of tower cranes

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Static and mobile Tower Crane are available in a wide variety of types and configurations according to the particular combination of tower, jib and type of base which they employ.

Tower configurations

Tower cranes are available with either fixed or slewing towers. On the fixed tower type the slewing ring is situated at or near the top of the tower and the jib slews about the vertical axle of the stationary tower. The slewing ring on the slewing tower type is situated at the bottom of the tower and the whole of the tower and jib assembly slew relative to the base of the crane. The towers can be further classified as being mono towers, inner and outer towers and telescopic towers.

Mono Towers – The jib is carried by a single tower structure which may be either fixed or slewing. Provision may be made in the design to permit the tower to be extended

Inner and Outer Towers – They are characterised by the jib being carried by a fixed or slewing inner tower which is supported at the top of the fixed outer tower. Provision may be made in the design to permit the outer tower to be extended

Telescopic Towers – The tower structure consists of two or more main sections which nest into each other to enable the height of the crane to be altered without the need for partial dismantling and re-erection. Telescopic towers are usually of slewing type and more common on rail-mounted and mobile tower cranes

Selection of Tower Cranes

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Each class of Tower Crane possesses certain basic characteristics which will usually dictate the one most suited to a particular application. Tower cranes must be selected to suit the job. If the crane’s basic characteristics do not match the job’s requirements, unsafe conditions will be created and accidents are prone to happen.

Reference should therefore be made to the following sub-sections 6.2 and 6.3 below for details of different crane types and their operational characteristics.

The type of tower cranes to be used should be considered against the job requirements for a particular application. Points to be considered in making the selection include:

weights and dimensions of loads;

heights of lift and distances/areas of movement of loads;

number and frequency of lifts;

length of time for which the crane will be required;

workplace conditions, including ground conditions for crane standing, and space available for crane access, erection, operation and dismantling; and
any special operational requirements or limitations imposed including the existence of other cranes in close proximity.

Safe Use of Tower Cranes – Responsibilities and Requirements of Personnel

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Owner responsibilities Tower Crane

It is the responsibility of owner to ensure that the personnel who prepare the equipment, erect/alter/dismantle it, operate it, and work with it are well trained in both safety and operating procedures.

The owner must ensure erection, dismantling and height alteration operations of every tower crane are carried out by competent workmen under supervision of a competent person and monitoring by a supervising engineer as described in section 10 below.

The owner must ensure that all tower cranes are operated by trained, experienced, competent and qualified crane operators.

The owner and personnel working with a tower crane must also ensure that the personnel who direct, rig and handle the loads have received training in the principles of the operation, are able to establish weights and judge distances, heights and clearances, are capable of selecting tackle and lifting gear as well as rigging method suitable for the loads to be lifted, and are capable of directing the movement of the crane and load to ensure the safety of all personnel.

The owner is responsible for conducting risk assessment for all operations of a tower crane and putting together a crane safety programme and method statements, educating all related personnel in safe practices and the assignment of definite, individual safety responsibilities. The owner must plan all phases of the operations involving the crane.

The owner must ensure maintenance of every tower crane is carried out by inspection and maintenance technicians as described in section 13 below.

The owner must ensure all inspections, examinations and tests for the operations of every tower crane described in section 14 below have been carried out accordingly.

Tower crane operator

The tower crane operator should be responsible for the correct operation of the crane in accordance with the manufacturer’s instructions and within the safe system of work. He should at any one time only respond to the signals from one slinger/signaller who should be clearly identified. In particular, the tower crane operator should:

have attained the age of 18 years and hold a valid certificate issued by either

the Construction Industry Training Authority before 1 January 2008 or the Construction Industry Council or by any other person specified by the Commissioner for Labour (Regulation 15A(1) of the LALGR);
have been adequately trained in the operation of the type of crane he is
operating and have sufficient knowledge of the crane and its safety devices;
fully understand the duties of the slinger and be familiar with the signal code shown in Table 1 in order to implement safely the instructions of the slinger or signaller; and
fully understand the radio/tele-communication signals between the parties concerned.

Slinger

The slinger should be responsible for attaching and detaching the load to and from the crane, and for the use of correct lifting gear in accordance with the planning of the operation. In particular, the slinger should:

have attained the age of 18 years;
be fit with particular regard to eyesight, hearing and reflexes;
be agile and have the physique to enable him to handle lifting tackle;
have been trained in the general principles of slinging and be able to establish
weights and judge distances, heights and clearances;
be capable of selecting tackle and lifting gear as well as rigging method suitable for the loads to be lifted;
understand the signal code shown in Table 1 and be able to give clear and precise signals;
be capable of directing the movement of the crane and load in such a manner as to ensure the safety of personnel and plant; and
fully understand the radio/tele-communication signals between the parties concerned.

Signaller

Where the crane operator of the tower crane does not have a clear and unrestricted view of the load carried by the crane or the point of attachment for a load where no load is being carried and such view is necessary for the safe working of the crane, a signaller shall be employed to relay the slinger’s instructions to the crane operator (Regulation 15B(1) of the LALGR).

The signaller should be responsible for relaying the signal from the slinger to the crane operator. He is also responsible for directing the safe movement of the crane. In particular, he should:

have attained the age of 18 years (Regulation 15B(2) of the LALGR);

be fit with particular regard to eyesight, hearing and reflexes;

understand the signal code shown in Table 1 and be able to transmit the instructions of the slinger in a clear and precise manner; and
be easily identifiable to the crane operator (e.g. by wearing ‘high-visibility’
clothing, or other means).

Safe Use of Tower Cranes – Planning of the Lifting Operation

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All lifting operations should be planned to ensure that they are carried out safely and that all foreseeable risks have been taken into account. Tower Crane Planning should be carried out by a competent person appointed for this purpose. In cases of repetitive or routine operations, this planning may only be necessary in the first instance, with periodic reviews to ensure that no factors have changed.

Planning should include the consideration of:

the load such as its characteristics and the method of lifting;

the selection of a suitable crane appropriate to the operation, ensuring that
adequate clearances are maintained between the load and the crane structure;

the selection of lifting gear, the weight of which should be taken into
account when assessing the load on the crane;

the position of the crane and the load before, during and after the operation;

the site of the operation, taking into account proximity hazards, space availability and suitability of the ground or foundation such as the allowable bearing capacity of the ground;
any necessary erection, alteration and dismantling of the crane;

the environmental conditions that exist or may occur at the site of the operation, which may necessitate stopping the operation when conditions are unsuitable; and
the effectiveness of communication among relevant parties, such as that
between the operator and the signaller(s).

Risk assessment

The risk assessment carried out by a competent person as part of the planning process should identify the hazards associated with the proposed lifting operation. The assessment should evaluate the risks involved and the nature and extent of any measures required to mitigate those risks. The competent person should also take into consideration hazards identified by the overall workplace risk assessments.
Generic risk assessments are unlikely to be sufficient since most workplaces have hazards that are unique to that situation and should be taken into account in the separate workplace specific assessment. The results of the risk assessment should be used in the preparation of the method statement for the workplace.
The risk assessment together with the manufacturer’s instructions should then be used to develop a detailed method statement for the lifting operation in the workplace.

Safe Use of Tower Cranes – Management of the Lifting Operation

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Safe system of work Tower Crane

A safe system of work should be established and documented by the owner. Such system should be followed for every lifting operation whether it is an individual lift or a series of repetitive operations. This safe system of work should be prepared and endorsed by the owner, with the advice of the competent person, safety officer and other relevant personnel. The same principle should be applied whether the lifting operations are carried out at a construction site or the crane is a permanent fixture, e.g. in a factory or at a dock. The safe system of work should be effectively communicated to all parties concerned by the owner.

The safe system of work should include but not limited to the following:

planning of the operation;

selection, provision and use of a suitable crane and equipment;

maintenance, examination and testing of the crane and equipment;

the provision of a log-book for the competent examiner/competent person/mechanic to enter the details of testing, examination, inspection, maintenance/repair works which have been carried out for the crane;
the provision of properly trained and competent personnel who have been made aware of their relevant responsibilities under sections 6A and 6B of the FIUO;
adequate supervision by properly trained and competent personnel;

observing for any unsafe conditions such as adverse weather conditions that may arise during operation;
ensuring that all necessary test and examination certificates and other documents are available;
preventing unauthorized movement or use of a crane at all times;

the safety of other persons who may be affected by the lifting operation; and

the contingency plan providing procedures to be followed in case of emergency situation.

The lifting operation should be taken to include any necessary preparation of a
site, and the siting.

Control of the lifting operation

To ensure the implementation of the safe system of work, a responsible person should be appointed to have overall control of the lifting operation. This appointed person should have adequate training and experience to enable these duties to be carried out competently.

Safe Use of Tower Cranes – Definition

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Automatic safe load indicator Tower Crane
It means a device intended to be fitted to a crane that automatically gives an audible and visible warning to the operator thereof that the crane is approaching its safe working load, and that automatically gives a further audible and visible warning when the crane has exceeded its safe working load (Regulation 3(1) of the LALGR).

Certified plan
It includes drawings, details, diagrams, calculations, structural details, structural calculations, geotechnical details and geotechnical calculations which are certified by safety supervision personnel.

Competent examiner
A competent examiner, in relation to the carrying out of any test and examination required by the LALGR, means a person who is –

appointed by the owner required by those regulations to ensure that the test and examination is carried out;
a registered professional engineer registered under the Engineers Registration Ordinance (Cap. 409) within a relevant discipline specified by the Commissioner for Labour; and
by reason of his qualifications, training and experience, competent to carry out the
test and examination (Regulation 3(1) of the LALGR).

As at the date of this Code, Mechanical Engineering and Marine & Naval Architecture are the specified disciplines specified by the Commissioner for Labour.

Competent person
A competent person, in relation to any duty required to be performed by him under the
LALGR, means a person who is -appointed by the owner required by those regulations to ensure that the duty is carried out by a competent person; and
by reason of training and practical experience, competent to perform the duty
(Regulation 3(1) of the LALGR).

Climbing frames
Frames of a climbing crane, which transfer the loadings from the crane on to the structure
that supports it.

Climbing ladders
Vertical structural frameworks by means of which some types of climbing cranes are raised.

Condition of tipping
A condition when a crane is subject to an overturning moment which cannot be increased by even a small amount without causing the crane to fall over.

Free-standing height
The maximum height at which a tower crane can operate without being held by ties or guys.

Gauge
The dimension between the inner faces of the rail heads of the rail track of a crane.

Height alteration
It means climbing of a tower crane or the addition or removal of mast section to or from the main tower.

Overlapping zone
An overlapping zone is the space which may be swept by the load, its attachment or any part of the tower crane, and common to at least two tower cranes.

Owner
In relation to any crane, includes the lessee or hirer thereof, and any overseer, foreman, agent or person in charge or having the control or management of the crane, and the contractor who has control over the way any construction work which involves the use of the crane is carried out and, in the case of a crane situated on or used in connection with work on a construction site, also includes the contractor responsible for the construction site (Regulation 3(1) of the LALGR). A contractor is responsible for a construction site if he is undertaking construction work there or, where there is more than one contractor undertaking construction work at the site, if he is the principal contractor undertaking construction work there (Regulation 3(2) of the LALGR).

Project engineer
Project engineer means the registered structural engineer (RSE) appointed under section
4 of the Buildings Ordinance (Cap. 123) (hereafter referred to as BO); or for project(s) with exemption granted by the Building Authority from the procedures and requirements relating to the appointment of a RSE under section 4 of the BO, a competent person whose appointment is, subject to prior agreement of the Building Authority, to take up the responsibilities and duties of a registered structural engineer; or the supervising officer of similar capacity in project(s) of the Housing Authority; or the engineer(s) as specified in the works contracts appointed to act on behalf of the client organization for the supervision and management of the works project(s) of the government departments of the Hong Kong Special Administrative Region; or any independent checking engineer(s) of similar capacity appointed by the principal contractor at the request of the government departments of the Hong Kong Special Administrative Region, as the case may be.

Rail ties
Ties used to retain rails at the correct distance apart and to withstand the imposed tensile and compressive forces.

Registered professional engineer
Registered professional engineer means a person whose name is on the register of registered professional engineers established and maintained under section 7 of the Engineers Registration Ordinance (Cap 409).

Registered safety officer
Registered safety officer means a person registered under Regulation 7 of the Factories and Industrial Undertakings (Safety Officers and Safety Supervisors) Regulations (Cap
59Z).

Registered structural engineer
Registered structural engineer means a person whose name is for the time being on the structural engineers’ register kept under section 3(3) of the BO.

Safety supervision personnel
For building works and street works, it means the “Technically Competent Person of Grade T5” (TCP T5) who possesses the academic or professional qualifications and experience of building works or street works that satisfy the requirements set out in the Code of Practice for Site Supervision issued by the Buildings Department for a particular type of site supervision or management tasks; or the person responsible for engineering safety supervision as specified in the works project(s) of the government departments of the Hong Kong Special Administrative Region, as the case may be. For other industrial undertakings, it means a registered professional engineer in structural discipline.

Wedges
The means of securing the tower within tie frames or climbing frames of a tower crane.

Working space limiter
A working space limiter is a limiting device to prevent the load, its attachment or any
part of the tower crane from entering an overlapping zone.

Safe Use of Tower Cranes – Scope

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Safe Use of Tower Crane – Scope

This Code provides guidance on the safe use and operation of tower cranes to ensure the safety of personnel working at or nearby those cranes.

This Code covers management and planning of the lifting operation of tower cranes, requirements for operators, slingers and signallers, siting, erection, dismantling, height alteration, maintenance and testing of tower cranes. It also contains guidance pertaining to the selection, safe use and specific precautions when tower cranes are operating within a workplace.

Reference is also made to relevant Hong Kong legislation in particular section 6A and 6B of the FIUO, the provisions in the Factories and Industrial Undertakings Regulations (Cap. 59A) (hereafter referred as the FIUR), the Factories and Industrial Undertakings (Lifting Appliances and Lifting Gear) Regulations (Cap. 59J) (hereafter referred as the LALGR), the Factories and Industrial Undertakings (Guarding and Operation of Machinery) Regulations (Cap. 59Q) (hereafter referred as the GOMR) and the Construction Sites (Safety) Regulations (Cap. 59I) (hereafter referred as the CSSR). Attention is drawn to the requirements and procedures for testing and examination of cranes under the LALGR and the British Standard BS 7121.