Brent Cross Shopping Centre – Counting the cost benefits of BIM

  • Client: Hammerson and Standard Life Investments
  • Lead Contractor: Alinea
  • BIM Tools: Autodesk Revit

Alinea successfully used BIM for costing and material take-off on the Brent Cross Shopping Centre redevelopment and refurbishment. The project was a winner in the recent BIM4SME awards. Here is an extract of its published case study.

The £1.4bn project involves a significant extension of the existing shopping centre, including new retail and restaurant units, associated mall areas, multi-storey car parks, cinema, along with the refurbishment of the existing centre and associated external works – as a phase within a larger regeneration and infrastructure project.

BIM methodology was used to design the entire project. Alinea collaborated with the design team to produce some 40+ ever-evolving models in various software platforms.

Developing its previous working knowledge of BIM projects, the sheer number of buildings and scale of the project was a challenging, yet valuable and rewarding experience. Alinea used the models extensively for quantity extraction to enhance accuracy and efficiency throughout the cost planning process.

The BIM principles, in the context of agreeing rules of measurement and extracting for measurement purposes were:

  • To be hands-on and have open and honest dialogues with the project team about what they intend to do with the model and how they use it from a cost perspective;
  • To work collaboratively in all aspects (not only between BIM specialists and surveyors internally but also with the external BIM enabled design team);
  • To issue models to Alinea with an information only status, to support the 2D information (which is derived from the model). With designer approval, it is then Alinea’s decision whether to use model-derived quantities for cost planning. If so, rather than simply using the raw outputs, they carry out extensive processes in order to review, validate and understand them, as ultimately they take full responsibility for their use.

What the initiative was and how it worked

Following commencement on the project, after the rest of the design team but still within Stage 0, Alinea’s first priority was to agree and align a suitable Work Breakdown Structure (WBS) within the BIM Execution Plan between models and client requirements for cost reporting.

It is always critical to establish and agree this format with all parties immediately, but it was even more pertinent on this project due to the number of consultants and buildings. The project’s initial single model evolved into 40+ models between all disciplines.

The next priority, from a measurement perspective, was to agree, still within Stage 0, both current and future design stage needs from a quantification perspective including aligning to appropriate LoD (Level of Detail) and LoI (Level of Information) references. This included the identification of key drivers such as areas, basic object definitions (eg wall types) and phasing (eg existing or new). Alinea’s early cost advice was based upon limited design information with many costs generated on an area driven basis.

This meant that their next focus was to work with the lead architect to define a room and area naming strategy that would work for the duration of the project and to embed this vital data within the models. This is turn allowed Alinea to create a comprehensive area schedule which was used extensively for cost planning purposes.

After a full and robust validation process, this allowed them to achieve full area generation on individual buildings as well as the full, federated scheme for the +1,200 rooms and spaces.

Working together, physically, with the architect to embed this data in the live models required a joint agreement on GEAs, GIAs and NIAs as the scheme and the models evolved – preventing a separate process following each model update of resolving area discrepancies.

The largest challenge within this process was identifying appropriate naming terminology as a result of two disciplines’ differing opinions when undertaking a joint task – which was resolved by mutual agreement with the client.

Wall Type referencing is a key area of object definition

The project was generally split by buildings between two architects – Callison RTKL and ChapmanTaylor – which created a further challenge for Alinea from a measurement rule, object naming and functionality perspective.

Not only did the models need to be physically coordinated from a design perspective between the architects, but the vast quantities of data held therein needed to follow the same pre-agreed rules, in order for the federated data to work together.

Each architect clearly had their own previously established in-house ways of working from previous projects which they intended to adopt at the outset on this project.

Initially, neither had fully comprehended the further requirement of two practices creating one data driven project together. In many instances there were differing opinions on specifying and the approach to setting up an object’s data and parametric functionality.

By way of example, modelling internal doors (and door openings) was approached in different ways by each architect which would have led to specification divergences. One practice had a multiple defined object approach and the other was more option driven within fewer objects.

Alinea requested resolution from a measurement perspective to avoid inefficiencies when cost planning and reduce wasted capital cost. A joint Revit family naming convention was established by review, which Alinea requested and mediated.

This was well received and adopted immediately by all parties – and mitigated extensive remodelling and possible programme delays, had it been considered later.

How it was implemented and what the benefits are

As part of Alinea’s design team liaison, it had to ensure constant communication to establish what could be used at any point in time given the “Work in Progress” nature of the models.

An example was on the structural steelwork harvesting whereby the structural engineer advised Alinea, only following interrogation, that they could not use a particular zone of object data for cost planning, on the basis they did not have sufficient time to size the weights correctly within their 3D design.

The structural engineer therefore inserted a “placeholder” as the object data within the model and advised that Alinea was to refer to their 2D information for cost planning purposes.

Steel model for one building prior to Alinea’s apportionment exercise

Had this not been communicated, then there could have been a risk of using an incorrect quantity leading to incorrect cost advice. In terms of progression from this position, Alinea ensured that it met with the engineer after subsequent model releases in order for them to advise Alinea on what zones were not usable.

Despite having numerous models, it was a necessary part of Alinea’s cost planning on the project to break down the individual models further, in even more detail beyond the level within the WBS.

These focused on individual aspects such as car park spiral ramp options and structural frame apportionment between usages (eg retail units, cinema, back of house areas) in one building – for the reasons of cost option studies and/or client reporting requirements.

It is unacceptable to expect the engineer to build in this level of breakdown within their models as it is of no benefit to them. Alinea’s method for achieving apportionment of models has progressed on this project due to the number of these examples, which Alinea has undertaken within Revit.

A client challenge to their cost apportionment exercise was being able to visually demonstrate and prove such apportionment within a 3D image. To progress this, Alinea established a method of applying colour filters to the validated dataset, which was well received.

This new concept on visual demonstration proved to be useful and they have thus adopted it on other projects to benefit other clients.

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