4D helps ‘see’ risks in projects
Integrating 4D into the entire planning process helps visualise the risks associated with projects especially those involving a large amount of data, says buildingSmart ME president TAHIR SHARIF.
01 March 2011
HAVING a comprehensive understanding of risks is critically important in construction projects.
However, traditional methods of assessing the risks do not enable them to be visualised. Project managers traditionally detail risk in reports, supported by inventories, sketches and (usually) Gantt Charts. With incomplete information, decision making is compromised.
The arrival of 4D models, to some extent addresses, the problem. However, evidence suggests that the potential of 4D is not being fully utilised.
In creating construction schedules, a planner follows a basic three-stage process:
• Design interpretation: the planner uses the design information to illustrate and visualise the work. Traditionally, this is based on 2D drawings supplemented by sketches and the process produces a list of the activities required to construct the project (sometimes referred to as work breakdown structure, WBS);
• Resource allocation: the next stage is to define the resources required to achieve the defined tasks in terms of manpower, machinery and materials and based on those resources, allocate durations to the key activities; and
• Scheduling: the final stage is to determine the dependency between activities and arrange them in a logical way to optimise the construction sequence.
The common output of the above process is a critical path method (CPM), applied to calculate the longest path of planned activities over the project duration, which in turn determines the earliest/latest each activity can start/finish. In simple terms, this process identifies which activities make up the ‘longest path’ (also known as critical path) and those which can be delayed without extending the project duration (also known as ‘total float’).
To assist the planners, software tools are available based on two primary methodologies: Gantt Chart, where activities are illustrated by horizontal lines representing tasks over a specified duration, and Line of Balance, where specific activities are represented as lines, the slope of which represents the rate at which the task can be executed.
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The Trump Tower ... earlier proposed for Dubai. |
Gantt Charts are very useful to represent the high-level principal activities of a complex project, but can be very difficult to understand when applied to visualise large numbers of tasks or even smaller numbers with a high number of dependencies.
Line of Balance, which includes the concept of location as well as time, is an excellent method of visualising the flow of project activity. While Line of Balance has many advantages over Gantt planning at a detailed level, it is a less understood methodology and software tools are not yet commonplace.
Common 4D applications
4D combines a 3D model with the construction schedule, producing a dynamic representation of key stages in the construction process in both time and space. This enables the construction sequence to be more easily communicated than by the simple use of charts and sketches.
The use of 4D has grown rapidly in recent years as 3D models become more widely available. It is therefore not surprising that 4D CAD is increasingly being used to support construction planning. Adding ‘time’ facilitates the natural progression from 3D to 4D.
It is already well understood that linking elements from a 3D model to activities in planning tools can create a space and time (4D) model. This helps the planner visually link task to workplace thereby facilitating the creation of a logical construction sequence.
However, this process is only using the 3D geometric model to review the planners programme rather than assist with the process from the beginning.
Most projects involve fragmented practices. Each contractor/subcontractor develops its own discipline specific programmes, which are not easily co-ordinated hence giving rise to potential conflicts (logistics and space), during construction.
On a complex project, many planners (incorporating multiple disciplines) can be involved in the process. Being able to work in a collaborative environment from the early project phases is the only real solution.
This concept is less widely understood and yet brings with it the real power of 4D – the ability to integrate 4D into the entire planning process.
A summary of the current 4D model approaches and their limitations will provide a better understanding of this concept.
Current 4D planning methods
A 4D model is developed by linking 3D model elements (product breakdown structure – PBS) to construction activities (WBS), which are created using the manual or the semi-automated approach.
In the manual process, the 3D model and programme are developed independently and then the PBS and WBS are manually linked via a 4D tool (although some CAD systems offer this tool as an integral element of their software). This provides a ‘review only’ facility and although useful, it has limited value generally and none at all in the collaborative planning environment.
In the semi-automated process, the PBS and WBS are linked within a database (usually to some pre-defined classification system). To produce the simulation, it is still necessary to have a 3D model and a pre-defined programme, but the link creation is automated. While this is an improvement compared to manual linking, the same limitations apply.
Clearly, to move to a true 4D construction planning environment another solution is required.
Collaborative 4D planning
If the multidisciplinary planners can work in a shared environment, then it is possible to plan collaboratively – that is, work not only on their own programmes but also interactively in relative real time. In this environment, it is possible to co-ordinate programmes much as the designers would co-ordinate trades in a combined 3D model.
The critical factor is the 3D model itself, because if all planners use this as the starting point, then all planning considerations will originate from a common data environment.
As the 3D model is the source of PBS, having the correct file format and information is critical – these can be provided by a building information model (BIM).
Given a 3D model created in the BIM environment, PBS information of a building such as doors, windows, beams and columns, can be generated easily from its internal data specifications. Furthermore, the planner can interrogate the BIM and its elements to obtain additional information such as materials, dimensions, compositions and zoned data to facilitate the creation of the WBS.
Another factor is that if BIM has been co-ordinated, then spatial conflict and collisions have already been identified and rectified, enabling the planners to concentrate fully on coordinating their sequence.
In this shared environment, planners can work collaboratively at three levels:
• High: social interaction is facilitated amongst the planners by an improved communication network;
• Mid: system interaction allows planners to interact with the BIM to analyse the PBS and interrogate elements to facilitate WBS definition; and
• Low: system broadcasting/access to updated simulations to planners and other stakeholders to help eliminate conflicts and communicate construction process.
Benefits
The creation and application of 4D process and technology is not being fully realised in many applications. As a result, most applications simply use the process to produce visualisations and review programmes.
However, using BIM as the starting point, 4D can be used as an integral part of the planning process. By incorporating multiple trades, benefits that traditional approaches miss, will be realised. These benefits include: project visualisation – as an aid to communication at all project phases; schedule verification – single and multiple trades; planned Vs actual simulations (requires updating of model during construction); elimination of conflicts; ‘What if’ scenario planning; temporary works – analysis of workflow; site logistics and layout; and training tool for planners.
Case study
Although internationally, there are many projects completed where the 4D process and technology has been used, in the Middle East they are fewer in number and are in varying stages of completion.
The 4D process was used in the early phase of the now stalled Trump Tower in Dubai, UAE to visualise and communicate construction sequence.
The Trump International Hotel and Tower site is located at the centre of The Palm Jumeirah, a man-made island off the west coast of Dubai. The building was expected to straddle a monorail line that links The Palm to the mainland. This constraint was a primary factor in the project’s design – in particular the curvilinear asymmetric shape of the two towers merging at 150 m above ground.
The structural framing for the building essentially consists of two reinforced concrete towers linked at the 40th floor level by a steel structure. This structure comprises a pair of 10-storey-high coupling trusses, working in unison with the concrete core walls, to maximise structural efficiency. This hybrid entity creates a structural spine upon which other large secondary trusses would be built to form the transfer deck, from which an array of steel elements spring to carry 22 floors up to the summit of the pinnacle.
The main contractor, Al Habtoor/Murray & Roberts, created a 3D model to both supplement its estimating capabilities and to act as a co-ordination tool. The 3D model was linked to the programme schedule to create a 4D model.
The 4D BIM capabilities proved very useful in planning the construction sequence of the more complex elements of the project. The link between the concrete cores in each tower consists of some 5,000 tonnes of steelwork that has a high degree of geometrical complexity, which cannot be easily communicated using 2D tools alone. The sequence of construction of all major components was modelled with the time element clarifying the exact sequence of erection. These major elements were easily broken down into further sub-assemblies, which benefited all parties to the project – design, planning, fabrication and construction.
“4D BIM technology is a very useful tool especially for projects where geometrical complexities are evident. It is the best available platform to convey large amounts of data and is very effective in assisting the designer to consider fabrication and construction issues at an earlier stage,” said Matthew Esther, senior structural engineer and associate from WS Atkins ME.
“It is hoped that seamless forward and backward integration of 4D BIM with a wide range of design and analysis tools will ensure that such facilities become the industry standard,” he added.
The project was halted in late 2008, by which time the design was complete and the foundations were installed.
