56-61_as432411995 standardseptoct12

7/27/2019 56-61_AS432411995 standardSeptOct12

1/656 Australian Bulk Handling Review: September/October 2012

IntroductionAS4324.1 Mobile equipment for continu-

ous handling of bulk materials Part 1-

General requirements for the design of

steel structureswas introduced in 1995.

The Standard had a long gestation period

[5], with work commencing in 1978. Its

release in 1995 was timely in response

to a number of failures of bulk materials

handling machines in Australia in the ear-

ly 1990s. This Standard applies to mobile

equipment for continuous handling of

bulk materials, e.g. excavators, stackers,

reclaimers, shiploaders, and ship unload-ers. It was intended that AS4324: Part 1,

which deals with steel structures, would

be followed by other parts addressing

mechanical, electrical and other aspects.

However this has not occurred.

The International Organization forStandardization (ISO) has published a de-

sign standard for bulk materials handl ing

machines, ISO5049.1 [3] which has been

widely used internationally and was used

in Austral ia prior to 1995. There are signif-

icant differences between AS4324.1 and

ISO5049.1; generally speaking, machines

designed according to AS4324.1 are heav-

ier than similar machines designed to

ISO5409.1. German Standard DIN 2226

[2] has been written specifically for ma-

chines working in large brown coal open

cut mines, including bucket wheel ex-cavators. AS4324.1 has adopted material

from DIN 22261 and its predecessors in

addition to material from ISO5049.1.

Protective or load limiting devices in

the electrical, control, mechanical and

hydraulic systems are very importantin determining the load imposed on a

machine. This is an area which requires

close attention both in the design phase

and on site to ensure that the installed

devices perform the correct function.

AS4324.1 adopts a philosophy of not

overly relying on electrical protection

devices for structural integrity.

Application of AS4324.1 totypes of machinesAS4324.1 is intended to apply to both

rail-mounted yard machines and contin-uous mining machines which are usually

mounted on crawlers. Appendix E in the

Standard gives illustrations of the types

of machines for which the Standard is in-

tended to apply. A description of some

AS4324.1-1995 standard for design of bulk

materials handling machines

The increasing level of mineral exports from Australia has resulted in the need for expansions to existing

facilities and new export facilities. Rail-mounted materials handling machines such as shiploaders,

stackers and reclaimers are significant investment items for the ports and mines involved in the supply

chain for export of these commodities. Australia is one of the few countries to have its own standard for

such equipment: AS4324.1.

Figure 1 - Stacker Reclaimer

By Richard Morgan, Aspec Engineering

ENGINEERING SERVICES


2/657Australian Bulk Handling Review: September/October 2012

of the more common types of rail-mounted machines follows

below.

Stacker reclaimersFigure 1 shows the components on an older style of stacker

reclaimer. The machine has a long travel motion along tracks

propelled by driven wheels on the bogie system. In the stack-

ing mode, bulk material is fed onto the machine from the yardbelt via a tripper which discharges onto the elevator. Material

travels on a conveyor up the elevator and discharges through a

chute onto the boom conveyor. The bulk material discharges

onto the stockpile from the end of the boom.

In reclaiming mode the boom conveyor reverses direction.

Bulk material is reclaimed from the stockpile by the bucket

wheel which rotates via a driven shaft. The buckets dig ma-

terial from the stockpile and discharge them onto the boom

conveyor. The boom conveyor discharges material through a

central chute onto the yard conveyor.

The boom can pivot in a vertical plane about a central bear-

ing to follow the stockpile terrain. This motion is driven by hy-

draulic cylinders and is termed luffing. The boom can also

rotate in the horizontal plane about a circular bear ing. This mo-tion is dr iven by a gear system and is termed slewing.

Machines of this type are sensitive to changes in balance

about the luffing pivot. Changes in weight and weight distribu-

tion need to be carefully monitored and controlled. The repeti-

tive loading due to the bucket wheel motion requires considera -

tion for metal fatigue of the structure and slew bearing. Other

machine configurations are used, e.g. a C frame configuration

can slew to both sides of the rail tracks without the need to ex-

tend the elevator away from the machine with the tow bridge.

StackersStackers predominately long travel with limited slewing mo-

tions in order to lay the stockpiles for subsequent reclaiming bya slewing or bridge type reclaimers. On modern designs luffing

is carried out by means of hydraulic cylinders. Stackers with

longer spans are often articulated to provide less variation in

load during the luffing motion.

ReclaimersBucket wheel boom type reclaimers are similar to a bucket

wheel stacker reclaimer (see Figure 1) but without the stacking

function, so they do not include a tripper and elevator. Bridge

reclaimers of the bucket wheel type are often used for reclaim-

ing on the face of a blended stockpile. Such machines have

rakes which are used to loosen material on the active face.

ShiploadersLong travelling shiploaders with a wheelbase up to approxi-

mately 20 metres commonly have a portal structure spanning

the rails and a fixed boom gantry set at 90 degrees to the rail

track. The boom conveyor and shiploading chute shuttle in and

out to load the hatches and due to geometry, there are limita-

tions on the length of in-board travel of the shuttle. The shuttle

mechanism may vary the length of the boom or the boom may

be of fixed length with the shuttle within the boom. Another

configuration is the bridge type which has a large travelling

bridge spanning from the seaward rail to a second rail or pivot

point some distance behind the berth. A shuttling trolley sys-

tem, which supports the boom, tower, and luffing winch sys-

tem, travels along the bridge.The portal slewing type shiploader is suitable for ships with-

out masts and cargo gear. Trimming of hatches is accomplished

by a combination of slewing and long travel motions. The portal

slewing and shuttling type shiploader allows for greater flexibil-

ity in loading di fferent ship types than the portal slewing type.




LoadsThe following section describes some

of the important load conditions which

have been expanded or covered in more

detail in AS4324.1 than in the ISO or DIN

Standards.

Digging Resistance U and AbnormalDigging Resistance UUThe calculation procedure for digging

resistance requires this load to be based

on drive motor torque. In the authors

experience site measurements generally

show that machines are driven to the

limits of the drive system.

Lateral Digging Resistance Sand Abnormal Lateral DiggingResistance SSAS4324.1 requires lateral digging resist-

ance to be based on available slew or

long travel drive capacity. Site measure-ments generally support this approach,

even for bucket wheel reclaimers or oth-

er yard machines.

Permanent Dynamics DThe treatment of permanent dynamics

uses dynamic effects factors which mul-

tiply the appropriate dead and live loads.

The factors used in AS4324.1 include

additional values to cover rail-mounted

machines as well as crawler mounted

equipment.

Wind Loads Operating W and WindWhile Idle WWWind loads, either for operating condi-

tions or for extreme winds with the

machine out of operation, are referred

to the Australian Standard AS1170.2. Ad-

ditional requirements are included for

gust effects on the superstructure and

for wind at a 45 degree angle to the main

structure axes.

Travel Skew Forces LSFor rail-mounted machines, AS4324.1

nominates a calculation procedure fortravel skew forces which is similar to

that in the Crane Standard AS1418. This

includes consideration of asymmetrical

traction forces on each rail, commonly

encountered on bridge-type shiploaders.

Travel Device Obstructed LLIn AS4324.1, the approach adopted is to

assume that these loads are generated

where one side of a travel ling machine

is suddenly obstructed and brought to

rest in 300 mm. Consideration of the dy-

namics of the event, including inertialeffects, is required.

Boom Collision Loads FS, FTAS4324.1 considers the combined effect

of both inertia and drive torques for a

stopping distance of 300 mm. AS4324.1

includes load cases to address such acci-

dents for both slewing and non-slewing

machines. In the latter case, the limiting

long travel drive force rather than slew

torque will determine impact loads.

AS4324.1 includes a longitudinal boom

impact case, representing the situationfor a slewable boom machine, where the

impact might occur while the boom is

facing forward at a shallow angle to the

long travel direction.

Buffer Loads OOThe principle adopted is that rail-mount-

ed machines should be equipped with

buffers, and that the machine structure

should be capable of surviving a buffer

impact situation where the machine

is driven into the buffers at full long

travel speed. With this impact case as

well, both iner tia and drive forces arerequired to be considered concurrently.

Bucket Wheel Loss BLAS4324.1 a lso includes a requirement to

design bucket wheel machines for the

situation following loss of the bucket

wheel, shaft and associated gearbox

from the boom, as a result of a bucket

wheel shaft failure or similar accident.

Inclusion of this load case was a result of

several failures of this type.

Non-Permanent Dynamic Effects DDThis applies to inertia forces due to dy-namic load effects, such as abnormal ac-

celeration and braking of moving parts

occurring less than 20,000 times during

the life of the machine (e.g. emergency

braking). Allowance needs to be made

during the design phase for these ef-

fects. During the commissioning phase,

care needs to be taken in testing the

emergency stops on the machine. When

emergency stopping is via the braking

system, rather than via controlled elec-

trical stopping, severe forces can be im-

parted into the structure if the brakes orrail clamps are not adjusted correctly and

are applied too quickly following power

deactivation of the electrical system.

Burying (ZZ)This load case is for where collapse

of a stockpile or slippage of the bank

could cause the reclaiming or excavat-

ing component of an operating machine

to become partially or fully buried. The

Standard allows for the need for any such

appropriate loading to be addressed in

the procurement specification and g ivessuggestions on how this may be covered.

Load combinationsAS4324.1 shows how dif ferent load

components should be considered in

combination. These are summarised

in Table 3.7 of AS4324.1, together with

safety factors and stability margins.

Loads are grouped according to their fre-

quency of occurrence, i.e. main loads,

additional loads and special loads. The

frequency of occurrence of these load

groups are similar to those stated in thecrane standard, AS1418.1 [8].

Stability against overturningIn order to check safety against over-

turning, AS43241.1 requires the stabil-

ity ratio, (Ms/M

o) to be calculated for the

prescribed load case combinations. Ms

is the minimum stabilising moment due

to the total permanent load referred to

a possible axis of tipping and Mo is the

maximum overturning moment due to

the prescribed load case combination of

vertical and horizontal non-permanent

overturning forces referred to the sameaxis of tipping.

The Standard nominates minimum

stability ratios against overturning to be

applied to load case combinations vary-

ing between 1.5 and 1.1, being higher

(1.5) for more frequent operational load-

ing conditions, lower (1.33) for less fre-

quent operational loading conditions,

and lower again (1.2 or 1.1) for much less

frequent abnormal loading conditions.

Fatigue

AS4324.1 refers to AS4100 [7] for fatiguedesign. AS4100 reflects current practice

for the design of welded steel structures

subject to fatigue loads. There are im-

portant differences between AS4324.1

and ISO5049.1. AS4324.1 is prescriptive

and gives detailed guidance on how to

calculate the load cases and which load

combinations to consider. ISO5049.1 uses

an outdated mean stress approach to

fatigue design which is not adapted to

modern standards. It should also be noted

that structures affected by fatigue must

be regularly inspected for fatigue damage

for design code rules such as AS4100 toapply.

For combining the effects of cyclical

load components, the AS4324.1 approach

is to consider the fatigue damage result-

ing from the cyclical stresses produced by

each component of the loading spectrum

and carrying out a cumulative damage

assessment by miners rule summation.

AS4100 requires a capacity factor of 0.7 to

be applied for non-redundant load paths

and inaccessible areas for inspection.

Strength assessmentAS4324.1 allows for the use of either thepermissible stress method (also termed

working stress) to AS3990 [9] or limit

states method to AS4100 to be used for

strength design.



4/6

Buckling assessmentAS4324.1 permits buckl ing assessment, either to the limit state

procedures of AS4100 or to the permissible stress procedures

of AS3990. This is directly applicable to design of beams and

columns. Design of plate work structures for the base and oth-

er major components to resist buckling and to accommodate

shear lag effects is not well covered in the steel design stand-

ards AS4100 or AS3990. AS4324.1 covers this to some extent insection 5.4 and Appendix J.

Machine procurement specificationThe standard method for procuring bulk materials handling

machines is a design and construct contract with the contrac-

tor having responsibility for design, manufacture, supply and

instal lation. The procurement specification needs to be written

to ensure that the configuration and performance parameters

upon which the requirements for the machine were determined

can be met realistically in practice. Appendix B in AS4324.1

gives guidance on issues which should be covered specifically

in the purchase specification.

Design auditAppendix K in AS4324.1 gives guidance for design auditing and

certification by an independent third party engineering con-

sultant. This may be by means of independent calculations or

by checking and reviewing the original design calculations and

by computer analysis.

WeighingAS4324.1 requires that after a machine has been constructed,

the mass and centre of gravity of the machine as built should

be accurately determined. The final weight of a machine is of-

ten greater than that advised at the time of tender even when

the supplier has carried out an upfront concept design phase.

AS4324.1 stipulates that if the construction mass exceeds themass used in the calculation of static loads by more than five

percent, the stresses in the machine should be re-checked.

Experience with AS4324.1 and suggestedchangesThe following section covers some of the areas where the

authors organisation has found issues in the application of

AS4324.1 that required resolution. Areas that may need to be

addressed in revisions to AS4324.1 are also identif ied.

Fatigue Non-Redundant Load PathsThe requirement in AS4100 to allow for a capacity factor of

0.7 for non-redundant load paths or for areas which cannot be

readily inspected has caused difficulties and can be subject toquite different interpretation by different parties. Procurement

specifications should be specific in this respect to avoid differ-

ing interpretations.

Treatment of Burying Load CaseThe burying load case is applicable to reclaimers and particular-

ly covers the situation where material from the bank or stock-

pile slumps onto the end of the boom. One way of handling

this, as suggested in AS4324.1, is to assume that the boom can

support the full weight of this material. Another way this has

been handled is to allow the luffing hydraulic system to relieve

and the boom to be partially supported by the stockpile. Pro-

curement specifications should be specific in this respect.

Blocked Chute Flooded BeltThe case of blocked chutes and conveyor-flooded belts happen-

ing concurrently can be onerous and there is a temptation by

designers to try to relax requirements to design for a flooded


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belt by measures such as installing a

profile plate in the feed chute. This ap-

proach should be treated with caution

as the machine can easily be modified in

service to remove the profile plate with-

out reference to the designer. Similarly,

designers may tend to rely on blocked

chute cut-off switches to limit the loadfrom material overflowing from the top

of a clogged chute. In practice, these

cut-offs are not instantaneous or may

malfunction, causing greater loadings

than assumed.

Design AuditQualifications of the design audit engi-

neer and the need to audit mechanical

and electrical items are not covered in

AS4324.1. Where the audit engineers

function is provided as part of the con-

tract for the machine, the purchase spec-

ifications should be specific in this re-spect to avoid differing interpretations.

Boom Collision on Non-SlewingMachinesOn non-slewing machines such as ship-

loaders and stackers where the boom is

fixed at right angles to the long travel

tracks, it is usually not practical to de-

sign for the boom collision load case

and it may be necessary to rely on anti-

collision systems. It is suggested that

further guidance be given in revisions to

AS4324.1.

Travel Device Obstructed On BridgeMachinesOn long span bridge machines such as

shiploaders and reclaimers it is usually

not practical to design for the travel de-

vice-obstructed load case and it is nec-

essary to rely on anti-collision and skew

control systems. It is suggested that fur-

ther guidance be given in revisions to

AS4324.1.

Digging Cut-Off Settings and

Protection SystemsTypically, bucket wheel drives are sized

to provide sufficient power to dig and

lift the stockpile material. The drive is

sized to operate at about 100% of motor-

rated torque for the majority of its op-

erating time. During operation the dig-

ging torque will vary based on a number

of factors, such as the type of material

being reclaimed and stockpile slumps.

The primary and secondary protection

settings are provided so that the load on

the machine is not excessive and the ma-

chine can continue to operate withouttoo many overload stoppages. The nor-

mal digging resistance (U) is calculated

based on 1.1 times the first protection

setting but not less than 1.1 times the mo-

tor-rated torque. The abnormal digging

resistance (UU) is calculated based on

1.1 times the greatest protection setting

but not less than 1.5 times the motor-rate

torque. Diversity for protection systems

is particularly beneficial. For example,

a protection system implemented using

one mechanical protective device and

one electrical protective device has ahigh diversity component.

Fluid couplings of any type on the

bucket wheel drive train are not general-

ly suitable as a torque limiting device for

normal digging or associated lateral dig-

ging and it is suggested that the Standard

be revised so as not to refer to f luid cou-

plings as a load limiting device.

Permanent Dynamics DIn general more guidance on the ap-

plication of permanent dynamic ef-

fects would be a useful addition to the

standard.For stability calculations, a uni-

form dynamic multiplier as adopted in

AS4324.1 can produce non-conservative

results. A triangular-distributed accel-

eration as shown in Figure 2 is more

appropriate.

Redundancy of Stays, Ropes andHydraulic CylindersIn cases where an operators cab is lo-

cated on a boom, there is a requirement

for the boom support to be redundant,

with two total ly independent support

systems. The design of ropes or stays is

required to consider the dynamic load-

ing which would occur following failureof one of the support systems. The mag-

nitude of the dynamic load multiplier

and the need to have this on top of the

safety factors is an area which can be

subject to quite different interpretation

by different parties. It is suggested that

further guidance be given in revisions to

AS4324.1.

Loss of Bucket WheelThis load case was introduced primarily

for situations where the bucket wheel is

on a cantilevered section of shaft. Wherethe bucket wheel is not cantilevered

but held captive by the boom support

structure and the discharge/circular

chute in case of shaft failure, this load

event may not be applicable. It would be

appropriate to revise the Standard to re-

flect this.

Wind LoadsThe Standard is written with reference

to the 1989 edition of AS1170.2 and uses

wind forces for permissible stress de-

sign, Vp rather than wind forces for ul-timate design Vu. Subsequent editions of

the wind load standard, AS1170.2 pub-

lished in 2002 and 2011 only include Vu

and do not include Vp. specifically. This

is an area where revision would be ap-

propriate. It may be necessary to define

an intermediate wind speed for reloca-

tion to the storm park position and for

parking with rail clamps. Care needs to

be taken in cyclonic areas where wind is

a controlling load case, as use of permis-

sible stress design wind speed may be

non-conservative.

Plate BucklingThe AS4324.1 assessment method for

plate bucking can be difficult to apply.

In practice, plate bucking is generally

handled by finite element analysis and

alternative design standards such as

BS5400 [1] or the Merrison Committee

recommendations [4] are used. It is sug-

gested that revisions to AS4324.1 should

address this.

Limit States Code Calibration

Table 3.7 of AS4324.1 gives load multi-plying factors to be used with the limit

states method to AS4100. Normally, the

limit states design method uses partial

load factors vP, which differ for each

type of load and range generally between

1.2 and 1.5 depending on the statistical

variabil ity of the load type. However, for

AS4324.1 this factor is taken as the same

for all load components. In AS1418.1 for

cranes, the standard notes that where

the limit states design method is used,

care needs to be taken so that the design

gives a degree of safety not less than that

for the permissible stress design methodto AS3990. Such a cautionary note could

be included in a revision to AS4324.1 in

the short term. Ultimately a full code

calibration of the load multipliers should

be carried out in a similar manner to that

carried out by Warren et al [11] for crane

girders.

ConclusionsAS4324.1 has been in use for over 16 years

and major machine suppliers and design

audit engineers operating in Australia

are now familiar with the document.Since the introduction of AS4324.1, the

majority of new machines in Australia

have been subject to a third party de-

sign audit. Its application in the procure-

ment of bulk handling equipment for

Figure 2 - Triangular Distribution of Acceleration.



6/6

Australian ports and mines has genera lly resulted in robust and

reliable machines which are expected to offer long-term ben-

efits. Some areas in the Standard have caused issues and pend-

ing revisions to the Standard, this has generally been covered

in purchase specifications. Now that most industry participants

are famil iar with the Standard, revisions would be appropriate as

part of continuous improvement in the industry.

References1. British Standards Institute (1982). BS5400: Steel, Concrete

and Composite Bridges.

2. German Institute for Standardization (2006), DIN 22261-2

Excavators, Stackers and Ancil lary Equipment in Brown Coal

Open Cut Mines Part 2 Calculation Principals

3. International Organization for Standardization (1994).

ISO5049.1: Mobile Equipment for the Continuous Handling of

Bulk Materials Par t 1 Rules for the Design of Steel Structures.

4. Merrison, A. W., Flint, A. R., Harper, W. J., Horne, M. R. and

Scruby, G. F. B. (1973). HMSO Merrison Committee Report

on the Design and Erection of Steel Box Girder Bridges, Par t

1 to Part 4.

5. Morgan, R. C. (2011) Design of Materials Handling Machinesto AS4324.1-1995, Australasian Structural Engineering Con-

ference, Perth, 12 July 2012

6. Morrison, W. R. B. et al. (1996). A New Australian Standard

for Continuous Bulk Materials Handling Machines, National

Conference on Bulk Materials Handling 30 September - 2 Oc-

tober 1996, Melbourne.

7. Standards Australia (2008). AS4100: Steel Structures.

8. Standards Austra lia (2002). AS1418.1: Cranes, hoists and

winches - General requi rements.

9. Standards Australia (1993). AS3990: Mechanical Equipment

Steelwork.

10. Standards Australia (1995). AS4324.1: Mobile equipment for

continuous handling of bulk materials Part 1 - General re-quirements for the design of steel structures.

11. Warren, J. S. et al. (2005). Reliability models of overhead

traveling crane loading for code calibration, ICOSSAR, Mill-

press, Rotterdam.

Every effort has been made to ensure that the information contained in this

article is correct. However, Aspec Engineering Pty Ltd or its employees take no

responsibility for any errors, omissions or inaccuracies.

SGS expands Australianminerals processing facilities

SGS has expanded its Australian mineral processing test-work facilities, including a new mineral processing labora-tory complex adjacent to its existing Perth operation.

SGS says the expansion, now completed, will allow it to

increase its focus from hydrometallurgical testing to include

services for comminution, flotation, magnetic and gravity sep-

aration, filtration, thickening and iron ore characterisation.

The expansion involved:

A continuous three stage crushing plant with a capacity of

approximately 3tph.

A 20m fully instrumented iron ore drop-tower.

A continuous pilot comminution and flotation plant includ-

ing conventional, f lash and column f lotation.

Pilot hi-rate and paste thickening. Pilot fi ltration equipment. Pilot wet magnetic separation equipment (LIMS, REMS,

WHIMS and Slon).

Contact: Richard Morgan, [email protected]

Contact: www.sgs.com


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