CPD 2012 Module 3: Introduction to BIM

BIM enables the design team to work together to model every detail of a building.

Up until the 1980s, the main purpose of architectural models was as a presentational material, to show clients and stakeholders how a concept would look as a finished building. They were often made to a very high standard, but could be expensive, fragile and cumbersome. Drawing and modelling were also often laborious processes.

If major amendments were needed after technical information and costs had been fed into the detailed specification and tender package, you would literally have to “go back to the drawing board” and start again.

Advances in technology have allowed designers to cut the time they spend on models and drawings, and have also enabled greater accuracy of design. The introduction of more advanced computing into mainstream business during the 1980s saw computer aided design take off across a number of industries. CAD is used extensively to design everything from shampoo bottles to cars, trains and buildings. This has automated much of the redrawing and remodelling process.

The introduction of 3D CAD, which was developed in the 1980s but became more mainstream in the 1990s and 2000s, further increased the quality of design. With 3D CAD there is no need for the designer to imagine how 2D objects fit together, therefore reducing errors.

Advantages of BIM

BIM offers benefits for everyone involved in construction projects, including clients, designers, contractors, suppliers and facilities managers.
The government has recognised this, and adopted a strategy that all projects worth more than £5 million will be managed using BIM by 2016. This is another good reason for companies to adopt BIM.

Early design clarity

Late design changes can result in extra cost and delays to a project. With BIM, architectural models, structural models and MEP models can be brought together to carry out virtual testing and highlight conflicting design decisions.

These errors can then be rectified very early in the process. For example, if an architect specifies a window and a structural engineer specifies a beam that conflict, this will be picked up immediately.

Likewise, if a specification does change, BIM can be used to ensure that no new clashes are introduced. To give an example, if a 20mm hardwood floor covering is specified and the client demands a re-specification to 3mm LVT Designflooring, the BIM software will alert the specifier to the conflict with door frame heights and door sizes.

Virtual testing

BIM allows the creation of a building virtually before it is built, so virtual testing can be done early on in the design process to ensure that standards are met.

Aspects of the design that can be tested include:

• Consumption of energy
• Carbon emission rates
• Airflow
• Daylighting

By visualising daylighting, for example, the project team can ensure that skylights are installed at the correct angle and the right size to let in sufficient light. This avoids the need to replace a non-conforming skylight at the end of a build, saving money and time.

Improved visualisations

Architectural models have come a long way since the pre-CAD era of wood, cardboard and glue.

By using 3D studio maps, details can be highlighted and highly detailed planning undertaken, not just by the project team but by the client and end user. BIM visualisations can be used in a number of ways:

• Simulating pedestrian use

Pedestrian simulations can be included to view the density of use and identify bottlenecks, flow rates, queue sizes, journey times and so on. Such information has been used to alter timetables for schools and determine optimum numbers of students.

• Close design analysis

3D parametric models can be used to identify the specifics of products used, for example, in walls and floors, as BIM objects can include a variety of details.

• Fit-out design

Room loading can also be completed early on to ensure accessibility standards are met with the introduction of furniture, for example under the Disability Discrimination Act.

• Managing time & budget

Time and cost are often referred to as the fourth and fifth dimensions of BIM.

By incorporating all of the elements of a construction project, including the time scale, BIM can establish sequencing early on in a project and flag up whether there are any potential clashes in the programme. This can avert delays and, by consequence, save additional costs. For example, when time is added to the model, detailed visualisations of the following can take place:

• What is being done at any given moment
• Activities on a certain date
• What plant is needed
• What hoardings are needed
• Impact on the local area

At present, the major software packages do not automate this process and major revisions still need reworking, but it is a good start.

Cost information can then be added to form the 5D model, including:

• Quantities
• Labour
• Schedule
• Equipment

Rates can then be added, to better understand the cost of the build at a micro scale.

BIM Academy case study

The BIM Academy cites a real-life example from the US.

The use of BIM on a recent project highlighted a structural beam conflict with a sprinkler pipe, enabling it to be immediately rectified.

If it had not been dealt with at an early stage, the conflict would have become apparent during construction, after all the structural supports had been set. In other words, it would have cost $4,664 per clash, which, as there would have been 10 instances per storey, would have risen to $46,640. And as it was a 15-storey building, the total cost would have been $699,600.

It would have incurred the following costs per clash:

• $3,800 for replacing materials
• $205 for removing the beam with a crane
• $195 for installing the new beam with a crane
• $464 for cutting the hole for the pipe in the beam

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