GB2326629A - Nuclear Safety Crane with Extendible Boom and Isolation from Seismic Loading - Google Patents

Description

IMPROVEMENTS IN WEAPON HANDLING AND NUCLEAR SAFETY CRANES This invention relates to the field of cranes and lifting equipment, and more specifically but not exclusively to the use of such cranes and handling equipment in dockside weapon, nuclear safety and explosives handling roles.

In applications where the handling of goods such as weapons or explosives is required to be effected by means of a crane or lifting equipment, due to their safety requirements such cranes or lifting equipment require special features and are usually referred to as high integrity cranes (HIC).

Similar integrity is required for cranes undertaking nuclear lifts. The current theory and state of the art surrounding the design of an HIC is based upon making such equipment inherently safe by the use of over-engineered designs to meet reliability targets and to withstand arduous loading cases such as those produced by seismic activity.

The safety features required from HICs lead unavoidably to expensive designs which are costly to design, manufacture, construct, install, test and commission. By their very nature, HICs carry a host of safety features such as failsafe components and dual load path and control assemblies.

The requirement for enhanced safety features can lead to complex designs which although adequately meet the specification required to handle weapons and/or explosive materials or undertake nuclear lifts, are by their very nature difficult and expensive to maintain and are subject to low availability problems due to frequent automatic safety shutdowns. Additional maintenance to meet reliability targets is required.

One particular problem associated with HICs when used in the context of the loading of weapons or explosives or undertaking nuclear lifts in a dockside environment is the requirement for the HIC to be able to withstand seismic activity, whilst holding or moving its load at its worst load case, without the possibility of structural collapse or dropped load. These criteria have resulted in the state of the art dockside weapon handling crane designs being relatively large, inflexible and dedicated to particular tasks. Such state of the art cranes can also require large space envelopes and dockside movement areas in order to be able to perform their task. The supporting structures for these cranes have to meet similar design criteria.

Cranes and lifting equipment currently used in dockside cargo handling applications in almost all cases ultilise a fixed length jib and a method of load and jib counter-balancing using fixed counter-balance weights.

In terms of dockside weapon handling capability, cranes used for the loading and/or unloading of weapons and cargo into boats and submarines are currently required to have high height lift capabilities to perform particular loading or unloading functions, typically such heights being in excess of 30 metres. To manufacture a state of the art HIC to perform a 30 metre plus lifting operation results in a large fixed jib structure which, save for its use in the particular high lifting function, will be operating with a rope or cable length far in excess of that required for the remaining functions.

Our invention provides a crane apparatus which meets all current civilian and military safety requirements relating to weapon and explosives handling and nuclear lifts. Furthermore our invention provides a substantially lighter and smaller design of crane which overcomes all the current problems associated with the design, justification, construction, installation, test, commissioning, operating and maintaining of large HICs. Cranes according to our invention may be provided in either static/fixed or travelling/mobile form.

According to our invention there is provided a crane having an extendible and retractable boom means, said boom means having a counter-balance mass system linked thereto, said crane further comprising means for isolating the crane structure from seismic loading.

A specific embodiment of the invention will now be described by way of example only, with reference to the accompanying drawings: Fig 1 is a diagramatic representation of a mobile crane in accordance with the invention.

Fig 2 shows a plan view of a crane in accordance with the invention in situ on a dockside.

Fig 1 shows a mobile dockside crane 2 having a supporting framework structure 4 and a boom and jib assembly 6. The boom and jib assembly 6 is comprised of a telescopic boom section 8 and a fixed latticework jib section 10, the vertical extension of the entire assembly 6 being controlled by one or more actuators 12. The crane cabling system comprises a single or double reeved lifting cable 14 connected to a machinery house 16 located near the base of the crane structure 4.

The weight of any load carried by the crane 2 at the hook end 17 is counter-balanced using an equilibrium system comprising of a movable counter-balance weight 18 connected to the boom and jib assembly 6 by a mechanical hydraulic linkage 20. This location of machinery house and counter-balancing weight enables the centre of gravity of the whole crane assembly 2 to be kept as low to the ground level as possible, thereby reducing the toppling moment of the crane assembly.

The ground mobility of the crane is effected by a wheel and bogey arrangement 22 which enables the crane assembly 2 to be moved along the dockside. Once the crane 2 is positioned in location for use, a plurality of outrigger feet 24 can be deployed such that substantially all the weight of the crane assembly 2 is taken through said outrigger feet 24.

Fig 2 shows a crane assembly 2 positioned on a dockside 32 and located on a pair of movement rails 34 which allow the entire assembly to move along said dockside. A ship 36 containing goods to be loaded into a vessel 38 is positioned next to the dockside 32 and the crane assembly 2 fully extends its combined boom and jib assembly 6 such that loads may be picked up from the cargo hold 40 of the ship 36 and deposited in the cargo hold 41 of the vessel 38. Where appropriate using the luff, hoist and slew motions a series of four outrigger feet 24 are shown in plan view deployed thereby spreading the load of the crane 2 and its associated carried load over a wider area, thereby providing a more stabilised work platform.

Where a different class of vessel is berthed the power plant of the vessel 38 is shown at location 43, and in a case where a particular vessel is in fact nuclear powered, it can be seen that the movement envelope of the crane assembly 2 as dictated by the arc 42 ensures that should any catastrophic failure of the crane assembly 2 and its retracted boom and jib 10 occur there is no possibility that any falling load or structure will impact on the area of the power plant 43.

Should it be the case that an operation is required whereby the boom and jib assembly 6 needs to be extended to a height in excess of 30 metres then in some configurations it may be possible for the boom and jib 6 to impact upon the area 43 in the event of a catastrophic failure. The impact will be reduced by the jib counter-weight 18 plus the hydraulic rams by using a crane assembly 2 which has a retractable and deployable boom and jib assembly 6 then the probability of catastrophic failure resulting in impact on area 43 of the nuclear vessel is greatly reduced due to the fact that the vast majority of operations performed in the loading of goods will in fact occur with the telescopic element 8 of the boom 6 in its fully retracted position, the length of the jib 10 being sufficient to effect loading.

In order to minimise the weight of the boom and jib assembly 6 the fixed jib 10 can be manufactured as a latticework structure, which is common in crawler crane jib applications, and provides for a stiff, strong and lightweight permanent jib length which can be used for the majority of operations on the dockside. Other designs of jib such as box section jibs and other engineering solutions may also be utilised, but the common factor required for the design of this particular crane is that the assembly be as light as possible.

In the provision of facilities where any form of nuclear fuel or substance is present or service which supports a nuclear facility, one of the fundamental concepts is to avoid the necessity of providing nuclear enhanced crane facilities.

When possible cranes and lifting equipment are located remote from any nuclear related services or reactors to overcome the problem of possible catastrophic failure of the crane resulting in an impact on any nuclear material or nuclear implicated service. When the crane cannot be situated away from any nuclear material or nuclear implicated service the design has to be qualified for what is known as dropped load and uncontrolled lowering, and against failure or collapse under identifiable hazard or seismic loading as defined by the current nuclear safety standards.

Seismic motion can impose significant additional loadings on large structures. The state of the art method of reducing the effect of seismic loading on the crane is by increasing the strength of the structure resulting in a costly and over-designed arrangement. By utilising the outrigger feet 24, normally used solely for stabilising the crane in use, if a material which exhibits seismic isolation properties is selected for the outrigger foot or its bearings and mountings then when a seismic event occurs and the crane is supported on the outrigger feet 24 the crane structure 4 will not see the full seismic motion and the associated loading. Various methods of seismic isolation using this principle may be considered, for example, the actual foot of the outrigger may be made of the "rubberised" seismic isolation material, or indeed the bearing assembly which connects the outrigger support arms 26 may indeed be supported on such an isolating material. Additionally the coupling between the base of the crane unit 30 and the wheel and bogey units 22 may indeed comprise a seismic isolation material 28 thereby isolating the main portion of the crane structure 4 from the vibrations and motion associated with seismic action.

It will be seen that our invention combines in a novel way the benefits of mobile crane technology and the advantages of variable jib extension. Many modifications and improvements to the embodiment described above will now suggest themselves to ones skilled in the art of crane design.

For example the crane may be provided in a static or fixed form rather than the mobile/travelling form shown in the example.

Claims (9)

1. A crane having an extendible and retractable boom means, said boom means having a counter-balance mass system linked thereto, said crane further comprising means for isolating the crane structure from seismic loading.

2. A crane as claimed in claim 1 wherein said extendible and retractible boom means comprises a telescopic structure means and a fixed end jib means, said fixed end jib means remaining extended for use when the telescopic structure means sections of said boom means are fully retracted.

3. A crane as claimed in claim 2 wherein said fixed end jib means comprises a latticework, box or other structures.

4. A crane as claimed in claims 2 or 3 wherein means for isolating the crane structure from seismic loading comprises a plurality of deployable and retractable outrigger means.

5. A crane as claimed in claim 4 wherein seismic isolation of the crane is achieved by means of the foot of said outrigger means comprising a seismic isolation material.

6. A crane as claimed in claim 4 wherein seismic isolation of the crane is achieved by means of the bearing assembly on which the deployable outrigger is mounted comprising a seismic isolation material.

7. A crane as claimed in claims 2 and 3 wherein means for isolating the crane structure from seismic loading comprises the use of seismic isolation bearing materials located between the crane structure and its bogey and wheel assemblies.

located between the crane structure and its bogey and wheel assemblies.

8. A method of loading and unloading waterborne craft using a crane having an extendible and retractable boom means, said boom means having a corresponding equilibrium counter-balance mass system linked thereto, said mobile crane means further comprising means for isolating the crane structure from seismic loading.

9. A method of loading and unloading waterborne craft as claimed in claim 8 wherein said extendible and retractable boom means comprises a telescopic structure means and a fixed end jib means, said fixed jib means remaining extended for use when the telescopic structure means sections of said boom means are fully retracted.