Bearing Replacement on Eleven Heavy Haul Rail Bridges for Roy Hill

LEC have been a key technical advisor to Roy Hill throughout their ongoing heavy haul rail bridge bearing replacement program, from feasibility desktop studies through to advanced finite element analysis and bearing replacement.

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DESKTOP STUDY OF HEAVY HAUL RAIL BRIDGES

FOCUSING QUESTION

Would it be feasible for the existing rail bridges to withstand an increased axle load and thus enable Roy Hill to increase their rail haulage capacity whilst utilising their existing infrastructure?

THE SOLUTION

LEC undertook a desktop study of three selected bridge spans to determine the maximum load carrying capacity of the existing waterway and overpass steel girder rail bridges along Roy Hill’s mine-to-port rail corridor.  Design checks of the main bridge components were carried out for strength (i.e. bending & shear) and serviceability.

THE LEC ADVANTAGE

Based on the outcome of the desktop study, LEC were able to advise Roy Hill of several opportunities that could be explored to increase the axle load on the bridges, such as detailed assessment using finite element analysis (FEA), site deflection & strain gauge measurements to determine the actual Dynamic Load Allowance (DLA), and de-rating of the bridge design load factors.

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DETAILED ANALYSIS OF HEAVY HAUL RAIL BRIDGES

FOCUSING QUESTION

Determination of the actual Dynamic Load Allowance (DLA) for selected heavy haul rail bridges.

THE SOLUTION

Detailed finite element analysis (FEA) was undertaken by LEC to obtain analytical stress results, which were then compared with on-site strain gauge measurements obtained by Roy Hill’s sub-contractor.  This enabled LEC to determine an actual DLA for these bridges.

THE LEC ADVANTAGE

A detailed three-dimensional finite element model of the rail bridges was created by LEC in MSC.FEA using predominantly QUAD4 plate elements (four noded quadrilateral isoparametric element) and HEXA elements (eight-noded brick elements) were used to model the concrete deck. MSC.FEA is a state-of-the-art finite element analysis software package which is well-suited to this type of application.

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VISUAL INSPECTION OF HEAVY HAUL RAIL BRIDGE BEARINGS

FOCUSING QUESTION

Roy Hill’s rail line has 11 steel girder rail bridges that form part of the vital link between their mine operations and port export facility, and their safe operation is reliant on the condition of the bridge bearings.

THE SOLUTION

Periodic visual inspections of the bridge bearings were undertaken by LEC to monitor the deterioration rate of the bearing by means of measuring the vertical gap between the upper and lower half of the bearing.

THE LEC ADVANTAGE

The team at LEC were able to provide recommendations based on the periodic measurement data.  This allowed Roy Hill to prioritise the bearing replacement programme accordingly.

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BRIDGE BEARING DESIGN REVIEW

FOCUSING QUESTION

Roy Hill are replacing the existing elastomeric pot bearings with spherical bearings and the technical aspects of this change need to be fully understood to ensure safe & reliable operation.

THE SOLUTION

LEC carried out a technical review of the new spherical bearing design, including reviewing the design criteria, design loads & parameters and undertaking structural design checks (such as bolt shear capacity & weld design calculations).

THE LEC ADVANTAGE

During the design review, LEC identified some anomalies in the design loads which were able to be resolved with the original bridge designer and the new bearing supplier. LEC’s dimensional reviews, based on both documentation and site measurements, ensured the new spherical bearings will fit the existing bolt arrangements.

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TECHNICAL ASSISTANCE DURING BEARING CHANGEOUT

FOCUSING QUESTION

To minimise disruption to heavy haul rail operations, the bearing changeouts were scheduled during tight shutdown windows.

THE SOLUTION

LEC provided on-site technical support for the bearing changeouts to enable quick resolution of any technical queries.

THE LEC ADVANTAGE

By collaborating with Roy Hill and their sub-contractors, LEC were able to ensure the bearing changeouts occurred on schedule and in accordance with the design intent.

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SUMMARY OF SERVICES PROVIDED BY LEC TO ROY HILL

• Structural Integrity Assessment

• Advanced Finite Element Analysis

• Site Inspections of Existing Bearings and Dimensional Measurements

• Independent Review of the New Bearing Design

• Technical Assistance during the Installation of the New Bearings

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Fatigue Cracking of Rail Wagons

Consistent fatigue cracks were observed in a number of coal wagons, which had resulted in loss of revenue for the rail operator. Structural modification of the wagon body structure was required to prevent the crack from re-appearing. The main challenge on this project was to develop an effective solution while minimising the increase in wagon tare mass. Any increase in the ore wagon weight would reduce their payload and the associated revenue.

As part of the design process, a finite element model of the wagon was created. The model incorporated sufficient details to reasonably predict the location and magnitude of stress concentrations and hence locations where fatigue cracking may initiate. Fatigue analysis was carried out in accordance with the recommendations given by the Association of American Railroads (AAR), Fatigue Design of New Freight Cars. The results from this analysis were in close agreement with the locations of the existing cracks.

Based on this assessment, a local structural strengthening solution was developed to effectively reduce the fatigue stress. The geometry of the local strengthening was optimised to minimise the weight and for ease of installation. The proposed structural modifications (<1% of the wagon tare mass) have since been successfully implemented and have extended the service life of the wagons by at least 15 years.

Service Life Extension for a Bucketwheel Reclaimer

A bucketwheel reclaimer had been decommissioned after 25 years due to extensive structural defects, including cracking in the luffing pivot rocker region.

For these defects to be repaired, the traditional approach would be to fully dismantle the reclaimer in the reverse order to which it had been constructed, however this would require an extensive laydown area, high capacity cranage and months of construction work with the associated high risk. Another alternative would be the complete replacement with a new reclaimer, which would require a significant cost and timeframe for the procurement and commissioning of the new machine.

Instead, an in-situ structural remediation solution was undertaken which enabled the client to resume operations in 12 months, sooner than a traditional refurbishment and at a cost saving of several million Australian dollars.

The major remediation works included:

• Repair of structural cracking in the rocker arm assembly.

• Hydraulic luffing cylinders were removed, refurbished and re-installed.

• Slew bearing replacement.

• Bucketwheel replacement, including shaft and drive assembly.

• Replacement of heavily corroded structural members on bucketwheel boom.

The superstructure of the reclaimer was lifted in-situ with the boom and counterweight still assembled, which allowed the change out of the slew bearing and the repair of the rocker assembly.

This implementation required purpose-built temporary luffing cylinders, temporary support frames, and the installation of safety features such as strain gauges to monitor the loads and stability throughout the construction process.

Repair & Prevention of Cracking in an Existing Tippler

Photograph of tippler during installation

Cracks in the Cage Structure

A number of cracks were identified in the cage structure of an existing rotary tippler, during routine site inspection, after approximately 10 years in operation. These cracks were immediately addressed using temporary repair procedures by the port operator.

While the temporary repair prevented immediate disruptions to the port operation, a long-term structural solution to the tippler cage structure was required in order to prevent similar cracks from reappearing. A conceptual structural modification was developed with the aid of Finite Element Analysis (FEA). A three-dimensional FEA model of the tippler cage structure was created and analysed to determine the extent of the highly stressed regions. This allowed the structural modification to be designed effectively and efficiently, as well as minimising the tonnage of the structural remediation work.

Comparative analysis with the existing (unmodified) tippler structure was carried out to verify the effectiveness of the structural modification. The final design solution was proposed to the port operator and the Original Equipment Manufacturer (OEM) for their acceptance and approval. The proposed structural modification has since been approved by the OEM and successfully implemented on site.

LEC’s Finite Element Analysis (FEA) Capabilities

Why use FEA ?

Structures in the resource and heavy industrial sectors are often geometrically complex and cannot be readily simplified to a traditional beam/frame structural analysis approach. Advanced Finite Element Analysis (FEA) techniques facilitate a more accurate representation of plated structures and thick casting / forging components using 2-D and 3-D elements, respectively.

What FEA software does LEC use ?

LEC use MSC.FEA finite element software, which is a combination of MSC.Patran (finite element modeling pre- and post-processing software) and MSC.Nastran (finite element analysis solver). Nastran is a finite element analysis program that was originally developed for NASA, in the late 1960’s, in the United States. LEC personnel have been using MSC.Nastran software since 1992.

What FEA is not

FEA is not a silver bullet for complex structural problems. The old adage of “garbage in garbage out” is very applicable to FEA computer analyses. Proper selection of solution parameters, element types, mesh density, load & boundary constraints are essential in order to produce a reliable finite element analysis model. One also cannot underestimate the importance of the interpretation of the finite element analysis results. This interpretation skill will allow the analyst to make sound engineering decisions based on the analysis results. That is why all LEC’s advanced structural analyses using finite element modeling, analysis and design checks are carried out in-house by highly experienced and dedicated LEC specialist engineers and technologists.

Typical FEA workflow

LEC retain MSC.FEA licenses for the following advanced structural analysis:

Solution Type	Typical Application on LEC’s Projects
Linear static analysis / linear buckling analysis	Independent design review and development of design solution for a variety of structures in the resource and heavy industrial sectors.
Natural frequency / modal analyses	Dynamic sensitive structures (e.g., stacks/chimneys), preliminary analysis for structures subjected to vibrating loads (e.g., crushers).
Transient dynamic analysis (frequency/time domain)	Detailed dynamic analysis for structures subjected to vibrating loads
Geometric and material non-linear analysis	Structural forensic investigation.

LEC’s typical finite element analysis workflow is shown in the diagram below:

Click here to explore some of the projects completed by LEC personnel using finite element analysis.