*3.2. 4D BIM Tools and Methods Used in France*

A questionnaire survey was conducted in order to understand 4D BIM practices in France. The questionnaire was first designed then shared online on professional platforms, such as LinkedIn, to allow construction companies to complete it and share their experience and practices. It consisted of three main items: (i) the 4D planning tools used by the company and why (advantages and disadvantages), (ii) the strategy and methods used to implement these tools, and (iii) the different use cases and applications for which these tools were used. The survey was conducted remotely from February to April 2020. Fifty-one participants, including BIM managers and experts from different French construction companies with different backgrounds and specialisations, such as architecture, civil engineering, construction informatics, and project management, received and completed the survey.

As shown in Figure 2, Navisworks and Synchro Pro are the most widely-used BIMbased 4D planning softwares in France with 55% and 25%, respectively. Other 4D planning tools, such as Vico Control (6%), XD Builder (4%) and others (e.g., ITwo 4.0) are used by some French construction companies as well. However, not all the respondents had experienced the use of 4D BIM planning (6%), which demonstrates that the 4D BIM tool is not yet fully implemented and adopted within the French construction ecosystem.

**Figure 2.** Most used 4D BIM tools in France.

The most used 4D tool in France is Navisworks. It is easy to use and enables the linking of activities on a bar chart to corresponding 3D elements in the BIM model. Navisworks can be used for operation control, conflict analysis, construction sequences, and coordination between disciplines. However, this tool requires many manipulations of the BIM model and planning to integrate changes. In addition, to ensure consistency between these two entities (i.e., BIM and planning), it necessitates the adoption of a relevant LoD. The second most popular 4D tool in France, according to the survey, is Synchro Pro. It integrates some planning functionalities and so enables an integrated planning process performed in the same interface as the 4D simulation. However, this tool is still difficult to learn and therefore to implement on construction projects. Compared to Navisworks, it requires more time and practice before project managers can handle it correctly. Indeed, the planning method used by Synchro Pro seems to make the study of spatial constraints more difficult. The activities are defined with respect to their locations, which generates a huge number to manipulate and deal with, in addition to their logical and resource links.

The survey showed that two strategies exist for setting up the 4D planning use case. The first is a real implementation which consists of identifying the needs in terms of 4D planning, selecting the most suitable software by acquiring a license, and finally, developing a training plan to master the corresponding tools and methods. The second strategy to implement 4D planning on a construction project is to outsource this use case by subcontracting it to another engineering company that will use its own solution and methods. This article takes part in the first strategy by proposing a method that allows construction companies to initiate and internally implement 4D planning works for any projects.

However, the results revealed that the use of 4D planning is still limited and mainly restricted to creating and simulating 4D project videos to communicate internally within the same company and/or with the client. These video animations are usually non-interactive and disconnected from the progress of actual onsite works. However, some big contractors, such as Vinci Construction France or Bouygues Construction, have good expertise in 4D planning, and they use it for advanced applications, such as project progress monitoring and control, and employ digital tools that allow site workers to provide daily information on the quantity of tasks performed. The use of these data enables project managers to evaluate onsite production, monitor and control progress, and make the appropriate adjustments to the 4D planning if necessary [16].

Furthermore, the survey highlighted two methods used by the French companies to implement 4D BIM. The first method is based on the 'Hardin and McCool method'. This method [96] is the most commonly used because it applies the basic 4D principle of linking a schedule to a digital model. Indeed, it proposes a solution based around the Navisworks software and its TimeLiner module. By importing a Gantt schedule and a digital model of a project, it is possible to link the corresponding digital objects to each of the project tasks. This link can be performed manually or automatically if the 4D parameters of the digital model have been correctly created and entered. The second method is developed by the iBIM teams at the Vinci Construction France company. This method is based on the use of Synchro Pro software. It consists of remodelling and restructuring the BIM model into elementary objects, creating a task for each item in the schedule, and then linking each elementary object to its corresponding task. This results in a 4D schedule with a very high granularity, since the BIM objects in the original BIM model will be split into many new elementary BIM objects according to their actual onsite construction schedule. For example, an existing slab object (or any other element, such as a floor or wall) within the original BIM model could be split into more than one elementary slab in the new restructured BIM model to be suitable for the 4D planning method. Although this solution allows for the precise planning of the schedule, its main drawbacks come from its highly detailed breakdown. The implementation of this method represents a manual, laborious, and time-consuming process of restructuring and reorganising all the BIM model elements of the built asset. For instance, according to an iBIM's BIM manager, a structural BIM model for a medium-sized project (~10M €) includes more than a thousand elementary building components. Therefore, even if the laborious data restructuring work of the BIM model has been carried out in advance, it is relatively complicated for onsite teams to quickly identify the work in progress and indicate the level of progress.

#### *3.3. Summary of the Identified Problems*

The difficulties encountered by survey respondents corresponded closely with the observations noted in the literature, summarised in Section 2.3, above. This suggests that current methods of creating 4D tools from 3D BIM models are either (i) relatively easy but not suitable for the full range of construction site planning functions (as in the case of the Hardin and McCool approach); or (ii) reasonably suitable for such purposes in terms of their granularity but involve a laborious and time-consuming manual conversion process.

The requirement for the CESI BIM team to undertake the implementation of 4D BIM planning on the Nanterre 2 project presented an opportunity to develop a workflow that addressed these concerns. The aim was to produce an approach to 4D BIM implementation that could produce a construction schedule of maximum functionality with minimum extra effort expended in data exchange. The results, which are presented in the following section, could help project participants more fully exploit the potential of 4D BIM.

Furthermore, to address the problem of how 4D BIM can best be coupled and used with AI technologies to exploit the massive and increasing amount of construction data and enable 4D BIM automation, Section 6 proposes an ontology and demonstrates its application by developing an automated 4D BIM process for application within the context of the RINNO research project.

#### **4. A New Proposed Methodology for 4D BIM Planning: The CESI Process**

The previous sections and literature reviews on construction project planning generally and 4D BIM methods in particular were used as a starting point for understanding the construction industry's needs and then developing the CESI planning process. The purpose of this method is to identify and develop all the steps to be followed to guarantee the achievement of the MOA objectives concerning 4D planning. Following a four-phase process (Figure 3), the CESI method details how this BIM use case should be required and specified by the client until the production and delivery of related deliverables. This solution is intended to be simple and pragmatic. The following subsections detail the different phases of the CESI method.

**Figure 3.** The CESI 4DBIM approach.

#### *4.1. Phase 1: To Express the 4D Objectives in an Initial BIM Specification Document*

The first actor in the project that allows the implementation of BIM is the client. Their role is to express needs which can be explicit, implicit, precise, or vague, depending on their familiarity with construction techniques and rules. However, the client can be supported by an assistant project manager (in French the assistant à maîtrise d'ouvrage, or AMO) who will help to precisely define the client's needs and achieve their strategic objectives. The method proposed recommends the use of SMART objectives (Specific, Measurable, Achievable, Realistic and Time-bound) for each of the BIM use cases desired by the client. For the 4D BIM use case, several SMART objectives can be expressed by the client. For the 4D BIM use case, examples of such SMART objectives are:

• The contractor's response to the invitation to tender must include 4D planning of construction methods for the works in a visual form that demonstrates its feasibility.


This formulation of 4D planning objectives makes it possible to explicitly identify the client's expectations. In this case, the BIM manager will be able to propose detailed solutions to organise the production of BIM models that enable this use case implementation.
