Adapting LOD definition to meet BIM uses requirements and data modeling for linear infrastructures projects: using system and requirement engineering
Authors: Tolmer Charles-Edouard , Castaing Christophe , Diab Youssef , Morand Denis 
Published: November 2017

Abstract
Background
Within the current organization of design activities it is difficult to fully realize the potential of BIM (Building Information Modelling). In BIM processes, it is necessary to identify and exchange the specific information that is relevant in the exchange information requirements of each project. The concept of level of detail of the information is a tool for describing and quantifying the information that should be exchanged. But the existing definitions of level of detail of information are not easily usable. Precise definitions of methodology, tools and principles are needed to redefine this concept and to use it in order to define the elements of information that are relevant to be exchanged.

Methods
The authors propose the use of System Engineering and Requirements Engineering to define BIM uses and the relevant level of detail of information and its modelling concerned by each BIM use. The authors first explain why, in this context, the existing definitions of LOD, which can mean level of detail, level of development, level of definition, etc., are not sufficient and not always coherent. They demonstrate through real use cases that System Engineering and Requirement Engineering are a part of this methodology and propose, using formalisms, to describe each BIM use in detail.

Results
The authors apply two different approaches to defining the relevant information to each BIM use. Using a top-down conceptual approach they show that Level Of Detail (LOD) is a crucial element in defining the content of a BIM use. They then verify the practicality of their proposal using a bottom-up approach based on three use cases (acoustic studies, safety audit, sizing drainage system). These cases studies allow the authors to address different kinds of systems and objects within a whole infrastructure project. They represent domain use cases (acoustic and drainage) and coordination use cases (safety audit). This part of the work is based on the L2 project in Marseille, which is a Public Private Partnership for expressways.
As a result, a methodology is proposed both to redefine the level of detail of information concept and to describe how this concept is used to complete the BIM uses definition. The system engineering and requirement engineering methods are partially adapted to infrastructure projects. These elements facilitate the description of BIM uses expected in BIM Execution Plans. It was necessary to change the definitions of LOD in order to make them compatible with the methods of requirement management.

Conclusions
Design activities should be reorganized toward the common goal of meeting project needs and requirements. The authors demonstrate that the best way to meet requirements is to define BIM uses using a new definition of the level of detail of information. It has first to consider requirements that have to be reached through BIM and then define the relevant level of detail of information, using the concept of abstraction of reality. To do it well, applying system engineering and requirement engineering, adapted to infrastructure project, is required. To validate this proposal on an entire project, more use cases will be tested in further work.