Why use BIM?

There are 10 key ways in which BIM facilitates coherent output in a way that is much more difficult to implement through multiple separate CAD files. They can be divided into two categories: those automated by the computer and those assisted by the computer. The latter require additional visual scrutiny.

Computer automated coordination

Figure 5.1 Concurrent updates to the Central Model in BIM

1. Model updates concurrently: Multiple users work concurrently, changing the geometry, position and parameters of elements. When synchronised, these changes automatically update the elements and associated annotations for every other user. This is much faster than sequentially updating and coordinating individual drawings.
2. Element and view re-use: By linking models, every aspect of the appearance of views and elements in models of one discipline can be re-used as an automatic background by other disciplines. This is an immediate time-saver.
3. Consistency across drawing scales: Orthographic large-scale views (1:500 and 1:200) of 3D elements are consistent with those in the smaller-scale views (e.g. 1:50 and 1:20 detail views) derived from them.

   

   Figure 5.2 Views and elements from structural model re-used in architectural GAs²
   

   

   Figure 5.3 1:50 view (right) is derived from 1:100 section (left)²
   

4. Project-wide datums: Reference datums (like grids and levels) and model elements are presented consistently in multiple view types (e.g. plans, RCPs, section, elevation, details) and linked models. Therefore, they can be re-used without re-drawing, thereby ensuring consistent positioning throughout the entire project.
5. Drawing zone consistency: Several BIM software features will save views representing consistent overlapping areas on each level for general arrangement drawing production. For example, Autodesk Revit has the rectangular scope box that controls the view boundary on multiple levels. For those using Bentley Aecosim, there are saved views boundaries, while Graphisoft ArchiCAD provides Model View Options. These features enable the preparation of drawings that can be read coherently.
6. View templates: In one model file, view and sheet templates can be applied to multiple views in order to maintain consistent presentation standards across the entire drawing set.

   

   Figure 5.4 Project-wide grid lines are consistent for all floor levels²
   

   

   Figure 5.5 Revit scope box used to control grid line offsets²
   

7. Drawing cross-reference automation: When sections, elevations and other details are placed on sheets, the corresponding drawing symbols are automatically cross-referenced with the correct numbers for view and sheet.

   Computer-assisted coordination

   

   Figure 5.6 View template applies consistent properties to multiple drawing views²
   

   

   Figure 5.7 Section label automatically references the associated sheet²
   

8. Resolving complex interferences and construction sequences: As they increase in detail and complexity, multi-disciplinary interface provisions, clearances and construction sequences become easier to understand and resolve in an integrated 3D environment than on multiple separate 2D plans, sections and elevations. While the computer can identify clashes and clearances between elements, some of these may arise from differences in the level of detail. The roof might still be modelled monolithically, and therefore overlap elements from the structural model. For computer-assisted co-ordination, visual scrutiny will work, establishing that structural cross-bracing is in the wrong position because it is positioned in front of a window.

   

   Figure 5.8 Structural model (green) must be coordinated with architecture²
   

   

   Figure 5.9 Door schedule that automatically updates with changes to the model²
   

9. Schedules: Items of furniture, fittings and equipment (FF&E) can be scheduled by room. MEP schedules will automatically reveal items which do not belong to a defined building system. The continuity of design performance requirements (e.g. fire and acoustic rating) can be automatically distinguished by colour coding. Technical coordinators can quickly locate all unconnected equipment and ensure that it is adequately supported and connected to the correct services.

   Again, despite these benefits, there remains a need to scrutinise the schedules to identify extraneous and uncoordinated items.

10. Material quantity schedules: These will facilitate early quantities for off-site construction and preliminary estimates. Again, the computer will extract quantities from monolithic elements, but will not automatically divide up these quantities into the categories of an industry-standard work breakdown structure, such as the New Rules of Measurement 2.

What can Go wrong?

Implementing BIM poorly can lead to difficulties in coordination. Some examples of common mistakes are listed below.

1. Lack of execution on BIM project execution plans: BIM project execution plans define the output standards, the deliverables that will be required from the model and the approach that will be used to produce them to those standards. Failure to implement the plan will lead to incoherent drawing sets caused by inconsistencies in the content of similar drawing types, misunderstandings about how many of each type of drawing is required and the amount of detail to be specified in each. The result is an inconsistently presented and poorly annotated design.
2. Lack of user control when inserting elements: Inexperienced users may insert elements in their correct plan location, but without adequately checking on their 3D coordination in elevation. This is especially true for FF&E, stepped paving and stairs. While this control is not needed when producing a 2D plan drawing by itself, it is essential for working in the 3D environment. Ensuring continuous spatial coordination may require the use of an additional graphics monitor that enables the model to be clearly depicted across two screens showing its orthographic and 3D views simultaneously.

   

   Figure 5.10 Plan of floor slab mistakenly inserted on level 1 in level 2 view²
   

3. Collaborating firms underuse the linking of each other’s models: Firms that lack a process for regularly integrating each other’s model changes will end up working with outdated information and laboriously re-creating (instead of re-using) each other’s model elements and views. The point of collaboration is for firms to build on each other’s efforts; the re-creation of elements that have already been modelled elsewhere wastes time and resources.
4. Underuse of project-wide reference coordinates: Each discipline works to its own reference levels, grids and geometry, instead of sharing the same datums and coordinates. In many cases, as the result of several changes to each discipline’s levels, these coordinates no longer match up.
5. Neglect of 3D model review: Preference for 2D drawing reviews alone (as was customary before BIM) and aversion to the 3D environment can hinder the BIM benefits of making detailed and complex interfaces between elements more easily understood. Often, this preference is expressed by reviewers constantly asking for other staff to print out drawings on their behalf. It is wasteful for those involved in design to be tasked with printing drawings on behalf of other staff who could learn to do it for themselves. This is no more acceptable than a member of staff expecting a colleague to print out emails on his or her behalf. Everyone in the design process should be trained and capable of viewing and printing a drawing sheet that has been set up in the organisation’s default BIM design application.
6. Neglect of schedules: BIM schedules provide a helpful checklist of items, especially those needing complementary structural and MEP systems, interface provisions and clearances. Without using schedules extensively, technical coordinators rely upon visual scrutiny alone, which is more time-consuming and risk-prone.
7. Insufficient model element detail: Simplified elements, such as those comprising a wall-floor junction modelled at early design stages, must be increased in detail for construction purposes. If these 3D elements remain under-developed, every single small-scale drawing will need to be updated with time-consuming overlays of 2D drafting.
8. Over-detailed 3D elements: Rather than creating 3D elements (especially furniture) from scratch, it is often easier to download these elements from the web and insert them as placeholders into a model. The level of detail in these is often more appropriate to later design stages; using them too early in the project can lead to a bloated model. The latter results in slow access and printing, and unresponsive model navigation. Downloaded 3D content should be vetted before use in the model, especially in terms of file size. Unnecessary detail should be stripped out. (In major BIM packages, there are software controls for these elements that can vary what is visible at coarse, medium and fine levels of detail.)
9. Users neglect visibility ‘power tools’, such as view templates: Drafting standards can be embedded in view templates that can, in turn, be applied to multiple views of the same scale and type. The neglect of these tools results in inefficient control of the many views that are used to produce multiple project drawings and schedules. As a result, users spend too much time amending each view in order to maintain visual consistency between several sheets in a drawing set.

Coordination Roles

The PAS-1192-2 documentation provides guidance and illustrations to explain how spatial coordination should be conducted in BIM. Key to this is the role of the task team, which PAS-1192-2 describes in this way:

‘Task Teams are any team assembled to complete a TASK.’

‘Examples: Architectural Task Team; Structural Task Team or multi-disciplinary Task Team to design a specialist part of the project, say a bespoke curtain wall. This may also include the specialist and professional design teams collaborating to complete that task.’

It goes on to state that meetings for spatial coordination utilising BIM will bring together three distinct roles (Chapter 6, Table 6.1):

• Technical coordinators (for each discipline and specialty): In PAS-1192, these are termed task team interface managers.
• Lead Designer’s Project Architect/Engineer: These may be called upon to arbitrate otherwise unresolved design issues.
• BIM Coordinators: Responsible for preparing the models for spatial coordination meetings.

While project architects, engineers and technical co-ordinators are familiar participants in coordination meetings, the use of the model will be facilitated by the BIM Coordinator. Typically, the BIM Coordinator would be a senior technician on the project, well versed in the key coordination issues and capable of setting up and navigating through the model.

Preparation for the Model Coordination Process

There are a number of key steps involved in preparing for the organised exchange of models for coordination:

1. Sub-divide the overall project into several models distinguished by volume and discipline, or specialty. Tabulate development responsibility for each model over the course of the project (see Chapter 2, Table 2.4). The decision about what type of file to share is based on the permitted purpose agreed in the BIM protocol. For spatial coordination, all that is required is to provide each model in a format that can be opened by the application defined in the Post-Contract BIM Execution Plan for accomplishing that purpose (see Chapter 2, Table 2.1).
2. Establish a Common Data Environment, i.e. a secure, managed and mutually accessible project repository capable of storing and sharing all models and issuing update notifications about them to project participants.
3. Establish a file naming protocol to easily distinguish each model contribution, including its revision status. (see ‘Using a data storage naming protocol’ in Chapter 3). Define status codes that communicate its suitability for a given purpose, such as review or coordination see Chapter 8, section entitled Assigning and notifying of model status.
4. At agreed regular intervals, and on request, each discipline’s project lead (known as the task team leader) should approve one or more work-in-progress models for sharing with others, but only after reviewing and approving the derived output.
5. These models are then uploaded to the Common Data Environment in compliance with the agreed timing, standards and naming convention specified in the Post-Contract BIM Project Execution Plan. An update notification should be automatically issued to other project participants.

Clash Avoidance, Detection and Resolution

Preventing clashes is a far better strategy than fixing those that could have been avoided in the first place. The project team’s approach to coordination should prioritise clash avoidance.

1. Typically, clashes can be avoided by pre-assigning the locations and routes of each discipline’s work to particular building zones and levels. Major runs of primary ductwork should be assigned to specific riser locations, while secondary distribution should be assigned to specific levels in the ceiling. On this basis, clashes should only occur at points of exit from and access to service risers. For BIM Level 2, a proprietary application – such as Bentley Navigator^®, Autodesk Navisworks^®, Tekla BIMsight^® and Solibri Model Checker^® – should be used to provide a unified view of the combined multi-disciplinary (i.e. federated) model. A key feature of such applications is the ability to identify interferences between components – i.e. clash detection. In testing for these, selection criteria are applied to reveal specific types of clashes, such as occur between structure, partitions and pipework, or between ceilings and ductwork.
2. Spatial coordination meetings should be scheduled and chaired by the technical coordinator for the Lead Designer. In PAS-1192-2, technical coordinators are described as ‘task team interface managers’. On behalf of their respective teams, their role is to meet regularly and ensure that all disciplines have made adequate complementary provisions for each other and clearances for safety, accessibility, operations and maintenance.

   For spatial coordination, technical coordinators should visually inspect both combined multi-disciplinary models and the drawings that have been derived from them. Assistance in touring the 3D environment should be provided by role of BIM coordinator. As outlined earlier, this is not necessarily a dedicated BIM Manager, but instead a technician on the project who has demonstrated a high aptitude, after initial training, for producing design deliverables and for touring and setting up views in the 3D model.

   When conflicts or the lack of complementary provisions are detected, the technical coordinators’ role is to decide and record the design changes that will be required to resolve these clashes. If they reach an impasse, the lead designer’s project architect or engineer is responsible for arbitrating these design decisions.

3. Once the design changes that are needed to resolve a clash have been agreed and approved, the technical coordinators should implement them through their respective design teams. The work-in-progress models will be updated and the resulting revisions shared with notifications of changes through the Common Data Environment.
4. After downloading the revised models and in conjunction with the BIM coordinator, each technical coordinator should conduct a final check to ensure that the agreed design changes are reflected in each model.

Construction Coordination in BIM: 4D

The coordination of construction processes can be improved by using BIM software to link elements in the model to tasks created in a project management application. This creates a time-lapse animation of the building sequence in which elements will become visible in the same relative order as their respective tasks are organised in the construction sequence. The time dimension is added to the 3D model and explains why this is called 4D.

What Data is Required for 4D?

The development of a 4D simulation requires the integration of two key software resources:

1. 3D model of the project, divided into constructional detail.
2. Project management application file containing a schedule of tasks, abridged to correlate to the level of detail in the associated model.

Early on in the project lifecycle, the model will only contain elements that convey the architectural and engineering intentions of the design suppliers. This design intent model might be useful for creating an indicative animation sequence, but it will not contain elements representative of each task in the construction programme.

In contrast, the virtual construction model replaces the design intent model being developed in further detail by the main contractor working in conjunction with its supply chain. Elements, previously modelled monolithically, must be sub-divided by storey height and movement joints, and into assembly and pre-cast components. Element sub-division would be implemented either through a function of the native application, or in the BIM coordination application itself.

Figure 5.11 and 5.12 a view of the model showing the construction sequence on KAUST and an actual photo of the construction site³

There will also be a requirement to model additional site elements, including:

• Existing buildings and other site topography (if not modelled already)
• Temporary buildings and erected site machinery
• Scaffolding and falsework.

As PAS-1192-2 explains, ‘the Project Information Model is developed firstly as a design intent model, showing the architectural and engineering intentions of the design.’suppliers. Then the PIM is developed into a virtual construction model containing all the objects to be manufactured, installed or constructed.’

Challenges of 5D BIM

There are six main challenges involved in deriving ‘real world’ benefits from 5D BIM:

• The grouping and breakdown of model components into their respective cost analysis elements depends on the level of definition (see Chapter 9). The process of extracting quantities can be hampered by a lack of sufficient detail. Also, the design team is not focused on developing the model in a way that ensures that its constituents will always be assigned to the correct cost categories.
• In the Standard Form of Cost Analysis, there are inclusions and exclusions for each element definition. For instance, as a part of substructure, the lowest floor construction (section 1.1.3) does not include basement walls. The latter should be categorised with external walls (section 2.5). Equally, raised access flooring is grouped with Floor finishes (section 3.2), instead of Floors (section 2.2.1).
• Dimensional parameters of model elements do not automatically yield the required measurement data. For example, for cost analysis, the elemental quantity for slabs is gross internal floor area (to the inner face of the external wall); by contrast, the larger area derived from the model is measured to the slab perimeter. Again, downstand and upstand floor beams are not grouped with the Frame (section 2.1), but with the Upper Floors (section 2.2).
• There is a need to provide specification and design criteria to indicate the required performance of each element. This data will inform the unit cost calculation.
• It may be difficult to divide the finishes of continuous walls and floors extending beyond individual rooms. Some finishes might not even be modelled, but instead be added into the specification.
• Construction classification systems need to be rationalised to allow models to interoperate between them. Uniclass 2 is currently the definitive system for the construction specification in the UK, whereas the New Rules of Measurement 2, used for cost classification, is structured differently.

In order to address these challenges, the BIM Manager must make a strategic reckoning to identify where exactly the effort required to break down and re-group 3D model elements represents a significant improvement on traditional methods of measurement that use 2D drawings. This would be where BIM processes impart either greater speed or accuracy than would be achievable by the latter.

In many cases, it is preferable to employ a hybrid approach that integrates the benefits of 5D BIM with traditional costing techniques. 5D is best used for approximations that help decision-makers compare the cost impact of various design and construction alternatives and to quantify FF&E accurately.