II – REVISION BIBLIOGRÁFICA
4 – CONSTRUCCIÓN DE MODELOS
The benefits of the BIM technologies span the entire building/construction lifecycle starting from the conceptual design/feasibility stage to handover and facility maintenance stage or even up to the decommissioning or demolition of the building. The following section summarises the most common benefits of BIM at various stages of the construction project (Eastman et al., 2011).
4.4.1 Pre-‐construction/Feasibility Study
At this stage the main goal is to understand whether the desired functions from a building or a structure can be realised within the available budget and time. BIM
provides a platform to visually appraise the spatial requirements and rapidly quantify the cost and time aspects of the project by linking it with the cost data in a parametric way. Specifically the following benefits are realised:
4.4.1.1 Improving programme certainty through spatial analysis
There are tools available to automatically check models against spatial requirements, for example minimum size of a particular type of room, minimum height of a door or distance between the wall an opening (such as a window). By automating such tasks, the quality and speed of design improves greatly.
4.4.1.2 Rapidly consider and explore design alternatives
By linking the parametric BIM model to cost estimating and energy analysis systems, it is possible to rapidly evaluate design alternatives to analyse the performance of the facility from cost, time and performance perspective.
4.4.1.3 Receive early feedback from downstream players through programme simulation
By linking a high level project plan even during the feasibility study/concept development stage and developing a 4D model, a significant amount of variability can be reduced by carrying out a constructability review. Having a 4D simulation done early on a project where new construction or refurbishment is taking place side-‐by-‐side an operational building can also help identify the impact of construction activities on building operation.
4.4.2 Design and Detail
4.4.2.1 More accurate early visualisation of design
With earlier 3D (non BIM) technologies where geometric models were created with non-‐parametric technologies, significant time and effort was required to generate such visualisations and on many occasions they were not accurate. However, with the advent of BIM technologies, it is now possible to visualise design at any stage with accurately reflects what has been designed. This is significant especially at early stages to capture the design intent from client and to communicate to key stakeholders.
4.4.2.2 Automatic propagation of design changes
Design is an iterative process and changes are made constantly, especially when design from various sources have to be synchronised (i.e. structural, architectural, MEP). With BIM, it is now possible to control and link the object properties in a parametric way, and hence changes made to one object/element ensures that all connected objects change their properties in a parametric way.
4.4.2.3 Generating accurate drawings automatically
Even with BIM, it is necessary to generate and distribute 2D drawings at certain stages. However, drawing generation from majority of BIM system is an automatic process and drawings always correspond to the current model ensuring accuracy. 4.4.2.4 Better collaboration between designers
Synchronising design early ensures minimal rework and improved accuracy and quality of design. With BIM it is possible to regularly synchronise design and perform tasks such as clash detection. This ensures that design is error free and any constructability or performance issues are identified early.
4.4.2.5 Linking design to cost estimates
Many design decisions are linked to the cost, and the possibility to generate automatic cost estimates based on the BIM model at any stage during design enables to client to make better informed decision. It can also help during the bidding/tendering stage to provide an accurate bill of quantities to all bidders. 4.4.2.6 Improving Performance of the Facility
BIM enables carrying out sophisticated simulation such as acoustics, energy and lighting during the design stage. Again, this enables the client to make informed decisions and makes sure the facility performs to the requirements. With government imposing stringent guidelines with carbon emissions, it helps achieve those targets and improves sustainability.
4.4.3 Construction
4.4.3.1 Performing clash detection
With BIM it is possible to synchronise design models from all disciplines before construction begins (and also during construction when design is going on in
parallel) to identify any hard (physical) or soft (tolerance) clashes between elements. This ensures that these issues do not delay the construction process and also minimises rework if the clashes are found after construction has taken place. 4.4.3.2 Using 4D/5D for production planning
When a project plan is linked to a BIM model, the combined model is called 4D. When cost and quantity information is linked to such a model the model is called a 5D model. Such 4D and 5D models can help contractors understand how a construction project will look like at any given point in time. This functionality greatly depends on the level of detail the model is based upon and may vary if the temporary structures are not included and if the plan is only at a high level (i.e. a master plan).
4.4.3.3 Prefabrication with BIM
With BIM the geometric data is accurately represented and this enables building components to be sent directly for automated fabrication using numerically controlled machines. Steel fabricated components, precast concrete elements, fenestration and glass fabrication are already manufactured on construction projects using this method. Offsite construction is proven to improve construction quality and is promoted in the UK by the Government.
4.4.3.4 Integrating supporting systems with BIM
Construction is a complex process and many information systems related to supporting activities such as safety, quality, procurement and logistics are used on a typical construction process. All of these systems share a common data model – that of the construction facility. BIM can provide a common platform to facilitate efficient functioning of these systems.
4.4.4 Fit-‐out and Handover
4.4.4.1 Visual feedback during fit-‐out operations
During the fit-‐out operations, a significant number of parallel activities are going on. The fit-‐out process can become quite complex especially for projects such as hospital buildings where specialist machines have to be installed, linked and tested before handing over the facility to the owner. In such situations, visually keeping a
track of the progress can be quite useful to ensure efficient operation. BIM can be used to provide a visual workflow for tasks such as – arrival, testing, installation and sign-‐off of equipment and systems for construction projects. Tasks at a different stage in the workflow can be coloured differently in BIM to visually provide a feedback to the project manager.
4.4.4.2 Digital handover with accurate as-‐built model
With BIM it is possible to use technologies such as laser scanning to first compare the actual construction with design model and then to provide an accurate as-‐built model of the facility. Laser scanners provide a “point cloud” of the 3D geometry, which can be imported in many popular BIM systems to then develop a surface model that can be overlapped on top of the design model to make comparisons. Also, during the handover stage it is also possible for the contractor and subcontractors to capture accurate information about the building from operational perspective. For example, information regarding important assets such as manufacturing data, operational and performance data and service related information could be captured for a digital hand-‐over to the client.
4.4.5 Operation and Maintenance
An accurate as-‐built model that carries up-‐to-‐date information about a facility’s assets and its operational data can be extremely useful to the FM team. This has been demonstrated by the Maryland General Hospital case study (Eastman et al., 2011). When the Facilities Management system is integrated with the Building Information Model, the operatives can refer to hidden objects (behind the structure) and bring up relevant information to reduce time taken to respond to a call.
4.4.6 Summary
BIM can be seen not only as a technology or a set of technological tools, but as a process change that supports the entire lifecycle of the construction project. It provides the basis for new design and construction capabilities and changes in the roles and relationships among a project team. When adopted well, BIM facilitates a more integrated design and construction process that results in better quality buildings at lower cost and reduced project duration. (Eastman et al., 2011).