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Appendix D1: The use of 3D modelling on a project

This case study describes how 3D modelling (in essence building a virtual prototype of the project in a computer) was used on a live project and the significant benefits for all parties, clients, designers and contractors, which were derived from this method of working.

Introduction

In the mid 1990's the British Airports Authority (BAA) commissioned the first of a series of six similar office buildings. Each was to be approximately 70-80,000 sq ft over three or four floors, and was to be let as general office space.

Visualisation showing the form of construction

Because they had similar design criteria, BAA decided to develop all six sequentially so that lessons learned during the design and construction of the first building could be used to revise the design for the second, thereby reducing both direct costs and the construction period. It also enabled BAA to measure the cost of each building, generate an improvement plan and then re-measure on the following building to establish what savings had been made. Part of the strategy for improvement was to maintain the same project team for all six buildings.

During the construction of the second office block at Gatwick, considerable extra costs (£550,000) were incurred which were directly related to the structural frame, the building services and the curtain walling. The causes were identified as:

• Lack of spatial co-ordination;
• Poor appreciation of manufacturing and construction tolerances;
• Poor management of data, drawings and documents;
• Poor management of information flow.

The demonstration project

To overcome these problems, the Construction Managers proposed that 3D CAD modelling should be used on the third project, a four-storey office development of 64,000 sq ft to be built at Stansted in 1998-9. The 3D CAD modelling team was brought into the project team since they had used these techniques previously on the Heathrow Express project, also for BAA.

At the same time, as preparation for the Stansted project was proceeding, Egan 'demonstration projects' were being sought which would demonstrate how improvements in the efficiency of the construction process could be achieved. The Stansted project was put forward and accepted as a suitable 'demonstration project' and the 3D CAD modelling work was funded under the Government's Partners in Innovation Scheme.

The structure is precast reinforced concrete except for the steel frame to the roof plant room. The concrete columns are supported on bored cast insitu piles. The floors are in-situ post-tensioned concrete. The external envelope is a proprietary curtain walling system. The building has a glazed atrium to maximise daylight penetration. It has an environmentally sensitive air conditioning and interior lighting system. The contract sum was £6m.

3D CAD project modelling

For 3D modelling to be effective it is necessary to exercise strict control over data entering the model and data leaving the model. The process involves the following stages, which were followed on the Stansted project.

• Establishing data standards: To enable design team members to exchange data freely and re-use rather than recreate it, it is necessary to establish a set of Standard Methods and Protocols (SMP) for the project. Adherence to such standards also ensures that the data is of a suitable quality and format for inclusion in the 3D model.
• Preparing the 3D model: Spatial co-ordination and dimensional integrity can be achieved by preparing a 3D model from the 2D drawing data provided by the various designers engaged in the project. If these inputs are combined in the model, and components on one 2D drawing are shown to be occupying the space occupied by components on another 2D drawing, then a 'clash' or ambiguity is highlighted and the matter referred back to the relevant designers for amendment. Also, the modelling process can identify errors and omissions in dimensions so that these can be corrected before the relevant work starts on site.
• Managing the distribution of information: Because design is an interactive process, each designer will amend his drawings many times before final approval as production drawings for construction. It is therefore essential that all amendments be communicated to all members of the design team as soon as possible so that everyone is working on up-to-date information. It is therefore important that this process is carefully managed: electronic data transfer systems are excellent for this purpose.

These basic stages are described in greater detail below.

Establishing data standards

The first task was to prepare the SMP for the project, which would enable the design team to exchangeand re-use data. It would also provide the data in a suitably consistent format for 3D modelling.

A detailed IT questionnaire was e-mailed to each member of the project team, requesting information including:

• What word processing package did they use?
• What spreadsheet software?
• What operating systems did they have?
• What CAD package did they use?

Questions regarding CAD layering standards, backing up methods and communications standards were also included.

The 3D modelling team took account of the survey results when writing the project specific SMP, trying to minimise the impact on the design team members. For CAD data the SMP included the following:

• An agreed spatial origin and grid orientation so that all co-ordinates are positive.
• The units of measurement to be used in all drawings.
• Common drawing sheets with attributed title blocks.
• Layering standards based on BS 1192.
• Drawing numbering and revision convention.
• Drawing scales.
• Standard blocks and symbols.
• Text and dimension appearance and presentation.
• Standard use of abbreviations.
• Approval process.
• Mechanisms for sharing data.

With the SMP document agreed the only real changes for the design team members were to do with how their data was structured. Their design processes were not affected at all. Consequently, all the design team continued working in 2D, producing plans, sections, elevations and details. All drawings passed through an approval process before being issued electronically via an ISDN line to Laing Construction, who acted as the Document Manager for the project.

In order to ensure that the design team was complying with the project SMP, the modelling team wrote software to check the structure of the data being received. The software checked the following aspects of the drawings for compliance:

• File names.
• Drawing sheet names.
• Title block attributes.
• Viewport scales (and whether they matched the scales listed in the title block).
• Layer names.
• The presence of graphics on a text layer, and vice versa.
• Text styles fonts, widths and heights.
• Dimensions - and whether the text has been over-ridden.

The result was a report containing all the details of the drawing ('read' from the title block) and listing any failures to comply with the SMP document. Whilst compliance didn't guarantee the quality of the design, it ensured that the data was structured correctly, and helped the design team members to isolate data they wished to reuse. The checking system was later developed as a commercial product and is now sold as 'CAD Checker'.

Once passed through the checking procedure, the electronic drawing files were registered within the Laing Construction drawing management system, DistList. DistList uses a distribution matrix automatically to process the files, create zip files of drawing files and issue sheets, and issue them directly to the relevant companies via ISDN connections. This ensured all project team members could receive the information on the same day it was issued by the originating design office.

The distribution matrix was populated with a Master Document Index produced by each design team member. The MDI was an Excel spreadsheet in which the design office entered drawing names and numbers, planned first issue date, and forecast 'issued for construction' dates. The matrix also included information on who needed to comment on each drawing, and how long the review period was. All document issues were tracked, along with responses received. By tracking this data, reports were generated showing actual drawings received, against the planned dates.

In a parallel process, the electronic drawings were converted from the agreed project format into Drawing Web Format (DWF) to enable them to be viewed via the project extranet. All the information was made available to all members of the project team including the Client and Project Management team. The system was operated in a transparent manner.

Preparing the 3D CAD model

The modelling team included specialist 3D CAD operators who were assigned roles representing each of the main design team members. Consequently there was an architectural modeller, a structural modeller and a services modeller, each taking the 2D CAD data provided by the designers and converting it into 3D.

The building was divided into different models based on discipline, level, area and function; for example, the architectural model had separate sub-models for internal walls, external cladding, cores, floor slabs and ceilings - for each floor.

The services model was broken into different models based on function - plumbing, air conditioning, heating, etc. - again one for each floor. The various systems, such as plumbing, air handling, power and lighting, were modelled separately before being combined to produce an integrated building services model.

All the 3D models were prepared using standard off-the-shelf software packages.

As information evolved through the design process, the modellers continued to update the 3D data to reflect exactly what had been issued for construction.

Because of the use of the SMP, by both modellers and the design team members, all three main discipline models were based on the same co-ordinate system, origin, orientation and units of measurement. This enabled the modellers to combine any or all of the models by using standard x ref and block insertion technology, with full confidence that the resulting data would be true to the designers' intentions.

A fourth 3D modeller analysed the site survey, and modelled the external works, including the access road and car parking. Whilst there was less possibility of co-ordination errors in this area, cut and fill volumetric calculations revealed that a more economic solution was available.

Building the 3D model was intended to serve the following purposes:

• To prove that there was sufficient information to construct the building - the modelling team made no assumptions, and only modelled what had been included on the 2D drawings. Where insufficient or ambiguous data was identified, it was brought to the designers' attention.
• To find conflicting or erroneous design information before it affected the site team.
• To ensure the spatial co-ordination of the data and accuracy and completeness of the dimensions.

The latter two items could be roughly lumped together and termed 'clash detection'.

Further uses were discovered as the project developed, including:

• Construction rehearsal;
• Planning and trade contractor co-ordination;
• Material take-off;
• Visualization.

Each of these is dealt with in more detail over the next few pages.

After each revision to a model, clash detection was carried out. Initially Rebis Explorer was used to execute the clash check, but was replaced by NavisWorks later in the project. All the clashes reported by the software were checked by the modellers to confirm that the 3D data matched the 2D design documents, and then were listed in an Ambiguities List (see below). This identified the drawings involved, and gave a brief description of each 'ambiguity'. The list was issued back to the project team, and published on the extranet, allowing designers to see where there were problems.

KLM STANSTED FOR BAA LYNTON
AMBIGUITY LIST - 5

Compiled list of ambiguities from the 3D Model

Key to ambiguity status:
'A' = Actioned (i.e. ambiguity resolved and revised information issued), 'O' = Ongoing (i.e. ambiguity detected, revised information awaited), 'X' = detected but revised information could not be issued in time. Constructed either as original information, or based upon original information but amended on site.

Extract from IES Ambiguity List

To clash check the entire 3D architectural model against the whole services model took under two minutes on a modern workstation (P4 1.7GHz 2Gb RAM) and returned over 2500 clashes. NavisWorks can zoom to an individual clash, and highlight the objects concerned. It is very doubtful that the clashes highlighted would have been found using the traditional method of overlaying plots on a light-table and it certainly would not be achieved with such rigour and speed.

Managing the distribution of information

The project extranet was the main mechanism for disseminating information after drawings were approved for construction. It was split into 12 areas comprising:

• Design drawings - DWFs of all the current approved for construction drawings.
• 3D architectural model - DWFs of the 3D model with hyperlinks to architectural 2D drawings.
• 3D structural model - DWFs of the 3D model with hyperlinks to structural 2D drawings.
• 3D services model - DWFs of the 3D model with hyperlinks to the services 2D drawings.
• 3D model movies - an internal walkthrough and an external fly-around of the project.
• Architectural images - FIGs and JPGs of the architectural 3D model.
• Product object library - standard CAD blocks and drawings for use on the project.
• Schedules - material schedules extracted from the 3D models.
• Site photographs - progress photographs taken from the site's tower crane.
• Programme - extracts from the project programme.
• Reports - miscellaneous reports.
• Site diary - extracts from the project site diary.

By using Autodesk "Whip!" technology users could view the DWFs, zoom to any area, and print that area to a local laserjet printer.

The DWFs from the 3D models used hyperlinks to connect section markers to the relevant section, and entries in the Ambiguity List to the appropriate area of the DWF. This greatly speeded up the rate at which information could be found.

Site photographs not only provided the ability for off-site staff to see site progress, they were also used to help solve specific issues. Photographs of problem areas were taken and posted on the extranet, allowing office-based staff to see the problem without needing to leave the office. Decisions could be taken far more quickly, and potential delays reduced or avoided.

Benefits

The ability to check the production drawings with such speed and accuracy was of great benefit to both the design and construction teams. The former had a tedious job completed expeditiously and had few queries from site. The latter had a smooth running job without re-working and delays.

The detection of clashes before work was done on site avoided costly re-working and delays. The most significant clashes were valued and an estimated £600,000 (almost 10% of the contract sum) was saved by their avoidance. The investment made in the 3D model to achieve these savings was approximately £85,000, giving a return on investment of 7-1. Software currently available (2002) would reduce the modelling costs by 60%, making the investment even more attractive. It should be borne in mind that the 3D model was based on 2D 'approved for construction' drawings, which already incorporated lessons and improvements derived from the same consultants working on two previous similar projects.

In addition to the two major benefits described above there were a number of secondary spin-off benefits:

• Visualisation: The 3D model permitted the preparation of video images so that a virtual tour of the interior and exterior of the building could be made showing realistic materials and lighting levels
• Material quantities: The use of additional standard software packages enabled quantities of materials to be calculated. This was of benefit in both pricing and planning work.
• 'As built' information: By keeping the 3D model up to date during the course of the site work, the client was provided with a complete 'as built' set of information, which should prove invaluable in operating and maintaining the building.
• Planning, construction rehearsal and specialist contractor co-ordination: The 3D modelling team wrote a piece of software that linked the 3D model to the construction programme. This facilitated planning, construction rehearsal and specialist contractor co-ordination.

Conclusions

This project demonstrates that 3D modelling is an effective and economic method of checking production drawings so that clashes and ambiguities in information are rectified before it is used on site. This results in significant savings.

If the design team were to prepare the 3D model, following the necessary disciplined procedures, co-ordination problems and clashes would be dealt with as part of the design process and the need for the checking process by a separate team would be removed.

3D modelling is not yet widely available in construction, and although its use is likely to increase it will not necessarily be suitable or appropriate for all types of project. Most design offices, however, now use 2D CAD systems and the question arises as to whether these users can benefit in any way from this study. The team responsible for the study has come to the view that, if design teams using 2D CAD systems agree a suitable project SMP, work collaboratively on a single set of project data and manage the flow of data effectively (in much the same way as in 3D modelling), then a significant proportion of the benefits of 3D modelling can be obtained. Authoritative guidance is urgently needed in this area.