Model advantage

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Multidisciplinary consultancy Stopford Projects uses 100-year-old drawings to help create an intelligent 3D model of structural inspection survey results.

Built in 1873, the Winnington Works at Northwich, Cheshire, was acquired in 2006 by Tata Chemicals, the second largest producer of soda ash in the world. Tata Chemicals asked Stopford Projects to perform a full structural survey of the 6,000 m sq wet-side soda ash plant as part of an ongoing asset management and maintenance strategy. Stopford delivered an intelligent 3D model created in Bentley’s ProSteel to map corroded components throughout the plant.

1. Redundant pipework was colour-coded in the model and helped reduce the overall load on the building

The $1.5 million Tata Chemicals project launched in April 2011. Stopford had completed the survey by September 2011, and was awarded follow-on remediation works.

Bentley’s structural steel detailing and fabrication software ProSteel was critical to success because Stopford based its winning bid on fast completion. Although Tata Chemicals did not initially specify an intelligent 3D model as the required deliverable, Stopford persuaded the client to reconsider by demonstrating ProSteel’s features — including model production speed, automatic updating, and model exporting to AutoCAD.

Component survey

The survey team had to start from scratch at Winnington Works. The wet-side soda ash plant is a 10-storey steel-framed building on a T-shaped area with overall dimensions of 90 x 75 m. The structure is a mix of 19th-century timber, early 20th-century columns, beams, and bracing, and 1950s-era steelwork. The supporting structure is now a structural steel shell clad in corrugated steel panels. Structural connections are mainly riveting, with sections riveted to form composite members. The building has remained virtually unchanged since its last major expansion in 1950. Over time, the constant wet, alkaline atmosphere has degraded the materials.

Stopford did the structural inspection and reviewed the major equipment and pipework that impinged on the structure. The survey team inspected 5,750 individual structural elements and prepared documentation, with every element photographed, assessed, numbered, and recorded on drawings. All secondary steelwork was inspected, including platforms, walkways, concrete floors, and other load-bearing elements.

The results of the survey were evaluated for corrosion levels on individual components, so that Tata Chemicals could plan remediation work.


3D model

Stopford began building a basic model based on 671 archived drawings, including as-builts dating back to 1908. The earliest drawings reflected the British Standards of 1906. These original plans yielded enough data for 95 percent of the 3D model. The few 2D drawings of subsequent plant modifications comprised the remaining 5 percent. Also, a fairly recent model of a large vessel was used.

2. Model geometry was directly exported to STAAD and SFRAME for structural analysis

The first step was to create a custom library of obsolete steel and wood member sections in ProSteel, as well as a catalog of obsolete iron pipe standards in AutoPlant Piping, Bentley’s piping design and modelling software. Structural elements were produced using the ProSteel shape files. Custom pipe specifications were produced using modified ductile iron catalogs. General arrangement drawings were generated directly from the model, using ProSteel workframes clipping planes to produce plans and elevations. Column and beam annotations are read directly from the model database.

Colour coding

The general arrangement drawings had numerous sectional views of each floor, and each structural element was given a unique tag number. The 3D model included 13 primary structural steel models, 15 secondary structure models, 13 piping and equipment models, and all 102 staircases in the complex. In total, more than 10,000 structural elements were modelled in ProSteel, and 2,500 metric tons of iron pipe were modelled in AutoPlant Piping.

Stopford took the general arrangement drawings to the site and used the tag numbers on the reports and photographs to inspect the as-built structure. Degraded sections were mapped to create a visual representation to develop maintenance plans. An up-to-date, colour-coded inspection model was produced, and 3D PDFs were generated for client review. Various colours indicated areas with no defects, minor defects, major defects, and severe defects.

Inspection results

During the on-site inspection, ProSteel made it easy to keep the 3D model up to date. A change in the size of a structural section, for example, automatically adjusted all the connecting elements to the modified size, and the respective general arrangement drawings were simultaneously updated.

At the weekly progress meetings, Stopford used Bentley Navigator, Bentley i-models, and progressive PDF views for dynamic project review and analysis. Being able to easily view the 3D model helped the client monitor progress, as well as visualise how the model would aid in maintenance planning. At the conclusion of the project, Stopford delivered a 12-volume survey report, the 3D model in AutoCAD, general arrangement drawings, and as-builts.

3. During weekly client meetings, progress was monitored by reviewing the latest model using Bentley Navigator, an i-model, and progressive PDF views

When remediation commenced, the 3D model was modified to reflect current as-built conditions. Colour-coding facilitated prioritisation of projects, with safety issues highlighted such as spurious loads, restricted access areas, and unsafe stairways.

Maintenance and safety

Stopford produced an adaptable tool for Tata Chemicals to use in maintenance planning and personnel training. The model revealed places that were not readily visible in photographs or drawings, such as areas encased in scaffolding. Plant safety was improved through an awareness of escape routes. All stairways were brought up to modern standards as a result of the inspections.

Tata Chemicals can maintain the 3D model in ProSteel or convert it to AutoCAD solids and/or ACIS bodies. In addition, the ability to interface with other software such as Staad.Pro and Bentley AutoPipe will help to jumpstart future projects that require data for structural analysis, isometric generation, and other functions. Estimating the cost to duplicate or expand facilities is made easier with access to an intelligent 3D model. For example, the 3D model of the Winnington Works wet-side soda ash plant could be used to estimate the cost of future steelwork by extracting the data for the steel components and calculating the total weight.

Counting the cost

Using Bentley software allowed the project team to achieve their schedule for modelling the plant. The firm had priced the job at one-third less than some of the other bidders based on the anticipated ease and speed to model. This was the main reason Stopford was awarded the project, according to David Coupe, piping department manager.

Subsequent to the successful survey project, Stopford was awarded five follow-on projects in the wet-side building and used the intelligent 3D model extensively. These projects included a lateral load study associated with re-cladding the building, stairway replacements to bring stairs up to current standards, removal of a concrete floor and replacement with steelwork, and inspection of the utilities building.


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