I 002 - Lifting - Cranes - Safety In Design

Design Guides

I 002 Cranes
Rev 03 [Jan 09]

Provisions for the Safe Use of Cranes on construction sites

INTRODUCTION

1. Cranes are designed to lift freely suspended loads in a vertical plane

2. Lifting operations in construction are commonly carried out using cranes and they should be covered in the Health and Safety Plan. When constructing the plan consideration would need to be given to the ways in which the cranes are intended to be used, ie, by the manufacturer and hirer, and any limitations that would affect safety in the conditions expected on site. Consequently, information would need to be provided by various parties so that factors influencing crane safety can be assessed at a sufficiently early stage.

3. The purpose of this Guidance is to provide designers with basic information on crane types and the factors they should consider when designing a structure whose components will be delivered by cranes. It includes typical site and environmental constraints to be taken into account at the design stage of a project that are important for the safe use of cranes.

4. The information in this note will help designers to fulfil their responsibilities. They should study it and apply the information with the assistance of expert advice [as necessary] to their designs and modify them, to create safe conditions for lifting operations.

LIFTING ON SITES

5. Any plan should include information to everyone involved in the specification, installation or use of cranes to be made aware of the fundamental criteria and planning issues needed to ensure that lifting operations are initiated and proceed in a logical and safe manner.

6. While contractors have a duty to operate cranes safely, these duties can be made extremely difficult by thoughtless design, which puts pressure on them to use cranes at their operating limits and beyond.

7. Information relating to the site is an important contribution to a safe system of work particularly with regard to planning the lifting operation and selection of the correct crane and associated equipment.

TYPES OF CRANES

8. There are many types of crane and a detailed classification is given in ISO 4306. However, the vast majority of cranes used for construction work in the UK can be classed as:

a) Lorry Loaders, which are suitable for delivery purposes and routine lifting operations associated with the vehicle on which they are fitted.
b) Truck Mounted/Mobile Cranes, which are suitable for short duration operations where mobility around site is important.
c) Crawler Cranes, which are suitable for longer duration operations and ‘pick and carry duties’ and for use on some types of terrain where a wheel mounted crane would not be appropriate.
d) Tower Cranes are suitable for semi-permanent installation for covering large areas whilst taking up relatively little room at ground level.

9. Within each class of the above classes there is a wide variation of types and lifting capacities. Descriptions of the various types and details of requirements for their safe use are given in the respective parts of BS 7121.

SELECTION OF CRANES

10. While economic factors may influence the choice of a crane, it is essential that the crane selected is capable of lifting ALL loads that it would be expected to handle, within its capacity and stability limits. Manufacturers supply duty charts, which show the SWLs for specific duties. These would give designers useful information about the size of crane required and, consequently, the space and loading requirements on the site.

FACTORS AFFECTING SAFETY WITH CRANES

11. Some of the important factors affecting safety with cranes are explained below.

The characteristics of the load to be lifted

12. For a safe lifting operation, it is necessary to know the weight, dimensions and position of the Centre of Gravity [CoG] of the load. Therefore, the information provided should, at least, include:

a) The maximum weight to be lifted;
b) Any non-routine handling instructions that are necessary for a safe lift;
c) The position of the CoG of asymmetric loads or loads of non-uniform mass [preferably marked].

13. Special lifting accessories may have to be designed for lifting asymmetric loads or loads of non-uniform mass. Lifting is made safer when designated lifting points are either provided or marked on the load.

14. deleted

15. . The weight and dimensions of lifting accessories add to the weight to be lifted.

The crane position

16. Where the load is to be lifted from, the route it will take during the lift and where it will be landed should be taken into account. Therefore potential obstructions, either permanent or temporary, should be taken into account. Obstacles include: buildings and other structures, trees, overhead power lines, etc;

17. If the crane is to be positioned on or next to an existing structure it may overload such a structure - a design calculation check may be required to establish whether temporary strengthening or propping is needed.

18. The radius over which a crane has to lift will have a significant effect on the loads that can be lifted and to what height they can be lifted. Table 1, below, for a particular type of crane, illustrates this point:

Tabel 1: Illustrating the relationship between lifting capacity and lifting radius

Radius [m]	Capacity [t]	Max height [m]
3	30	50
10	7.3	47
20	2.2	44
30	0.5	35

Clearances

19. Safe distances of the crane from the structure under construction, adjacent buildings, roads and pedestrian accesses must be maintained.

20. Mobile cranes need adequate space for the correct deployment of outriggers. In addition, they should be able to slew and manoeuvre the load with adequate clearance from obstructions. A minimum clearance of 600mm should be allowed for.

21. Other, equally important, considerations include:

a) Clearance to overhead electric cables: Cranes must never be positioned in the exclusion zone around overhead electricity cables. Lifting operations close to electricity cables or pylons may have to be scheduled during power off conditions.
b) Clearance to railway tracks, overhead catenaries and public highways: If a crane is to be positioned adjacent to a railway, canal or public highway an independent design check may be required, proving that the scheme has been planned and engineered such that no damage will occur to existing structures, property or to the public.
c) Clearance for aircraft near airfields: cranes operating within 6km can be a hazard to air traffic, especially if their height exceeds 10m, or when the top of the crane is higher than the surrounding structures or trees. [Notify the Airfield Manager]

Erection and dismantling constraints

22. Cranes have to be erected and dismantled. Normally more space will be needed for these operations.

Ground conditions and foundations

23. In order to operate safely, cranes need adequate foundations or support. Therefore, the ground conditions on a site are important. Crane operators need to know about:

a) Character of the ground including water conditions;
b) Engineering properties of strata relevant to the support of the crane or design of the foundations;
c) Location of any underground hazards eg open or back-filled excavations, services, drainage pipes, tunnels, trenches and basements.

24. Some of these factors may govern the design; many of them can be removed or made easier to control by considering them during the design.

Site weather conditions

25. Prevailing weather conditions and exposure of the site can affect a lifting operation. Wind, in particular, can affect how a load behaves when it is lifted. Structural items, which offer a large effective area to the wind can be difficult to control, even in very moderate winds, eg, shutters for concrete.

26. Manufacturers will specify maximum wind speeds for erection, lifting, out of service and dismantling operations. In very exposed areas (eg.cliff tops) or areas subject to wind turbulence (eg. built-up areas), these speeds may have to be reduced.

TOWER CRANES FOUNDATIONS

27. The design of tower crane foundations requires close consultation between a number of parties such as the Crane Manufacturer, Temporary Works Designer, Permanent Works Designer and Structural Engineer.

28. Sometimes, due to limitations of the tower crane or its foundation it is necessary to tie the crane tower to another structure to achieve sufficient height to complete the project under construction. Most tower sections can only be connected to a tie at certain points and the designer will need to consult the Crane Manufacturer for the maximum allowable shear forces on the tower.

ROUTES TO AND ACCESS ONTO THE SITE

29. Cranes need access routes and space for erecting and extending them and vehicles delivering the loads. Special access may be required for both the crane and high capacity trailers often used for deliveries such as counter-weights and jib sections.

30. When working in city centres, getting the crane on and off the site will require advance planning often in conjunction with police and local authorities and will possibly require facilities for overnight working.

USEFUL REFERENCES

ISO 4306-1:1990 Cranes- Vocabulary Part 1: General

ISO 4306-2:1994 Lifting Appliances- Vocabulary Part 2: Mobile Cranes

BS 7121:Part 1:1989 Code of practice for the safe use of cranes – General requirements.

BS 7121:Part 3:2000 Code of practice for the safe use of cranes – Mobile Cranes.

BS 7121:Part 4:1997: Code of practice for the safe use of cranes – Lorry Loaders

BS 7121:Part 5:1997 Code of practice for the safe use of cranes – Tower Cranes

BS 1377: Methods of test for soil for civil engineering purposes

BS 5930: Code of Practice for Site Investigations