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Getting The Numbers Right With BIM

 

Quantity surveying (QS) is an essential part of the construction process – from project concept to building handover. It is a profession that requires skilful deployment of in-depth knowledge, accurate interpretation of designs and numerical representation of component quantities.

Traditionally, this is a manual process and as such is time consuming and prone to errors. To produce a bill of quantities (BOQ) report using traditional methods of quantity surveying, QS engineers have to:
• Open a new template report to record the particular type of QS data;
• Open the drawing file containing the items to be quantified;
• Record the relevant information into the appropriate report header;
• Then for each and every element of this type, they must: locate the element, ensure it is unique, determine and record the elements axi, and measure and record the element’s dimensions and characteristics

While this produces a BOQ report, it covers only this part of the work and this type of element. To produce a BOQ report for the building, the process must be repeated for each element type, each floor, and every drawing. It is easy to see why this process is so time consuming. In such a convoluted manual process, mistakes will occur – not just the obvious errors associated with moving data between files but the risk of double counting and missed elements as projects consist of multiple plans and elevations which can represent the same elements in several drawing files. Multiple 2D drawings themselves are likely to contain many errors further compounding the problem.


Integrating BIM and QS

Building Information Models (BIM) can be integrated with common software to reduce the time and errors associated with traditional quantity surveying processes. The time issues can be addressed and errors eradicated by automating the process. There are two steps required to achieve this – the first being the production of a properly configured BIM.

‘Properly configured’ is very important phrase to understand. It is a common misconception to think that a BIM is simply a 3D representation of 2D plans and elevations used to visualise a design and locate overlapping or clashing components. Whilst both of these outputs are of great value to the construction process, they are only two of the myriad benefits that can be derived from such a model.

When produced correctly, a BIM assigns construction data to each element modelled. This means that those elements can be interrogated to provide details such as dimensions, locations and material composition.

Put simply, the model’s in-built intelligence knows what each building element is, where it is located, what it is made of and how much there is of it. In other words, the model can automatically create a BOQ.

Yet, to derive a meaningful BOQ, the model has to be created in such a way as to deliver a BOQ that is configured to construction methodology. It is not enough to just ‘count’ the building elements, because in reality the construction process groups the activities and the model must take this account.

It is, therefore, necessary to have a framework in place to define the design protocols for the model – such a framework is commonly described as a work breakdown structure (WBS) or standard method of measurement
(SMM). Once this has been defined, the model can instantly create a BOQ that is 100 per cent accurate and moreover, every time a design change is made in the model, the BOQ is updated.

The second step in the process is use the BOQ to produce reports in the required format. This can be done at any stage of the QS remit.

• For estimating, there are a number of software that integrate directly with BIM technology to produce seamless interoperability between the two platforms. It is usually only necessary to ensure that the BOQ is produced using the same WBS or SMM as the estimating tool.

• For tendering, it is normally sufficient to provide a detailed BOQ to enable creation and submission of bids. As most BIM tools can produce BOQs in standard formats (Excel, 123 etc), there is little work required other than formatting.

• For construction control, it is necessary to develop a workflow based on the prevailing QS system in use, in order to match the required process for issue, approval and revision of drawings. As the resulting periodic reports are usually created using standard platforms (MS, Lotus etc), it is reasonably simple for an experienced programmer to create the required utilities to drive the process automatically

Although work is required initially to develop the skills and processes needed to integrate BIM and QS processes, the resulting benefits undoubtedly justify the investment. Once the skills and processes are in place, ongoing benefits increase with every project.

Tahir Sharif Biography

Tahir has been influential in encouraging the adoption of BIM with Governments, Developers, Consultants, Contractors, Service providers, Vendors and System Integrators. He has advised on BIM usage and Integrated Project Delivery implementation for Iconic Projects throughout the Middle East, Asia and Europe. Tahir is a senior BIM advisor on leading projects where the use of the BIM models are being used for preventative measures to reduce costs, allow better planning, and improve quality and asset management throughout the lifecycle of the project.

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