# A Web-Based BIM-AR Quality Management System for Structural Elements
## 3 Quality Control System Development  
The proposed workflow needs a suitable system for it to be realized. Such a system has been developed based on a stepwise procedure. Ideally, the starting point is the 3D BIM model of the structure in industry foundation class (IFC) format. IFC is one of the open standards in the buildingSMART portfolio; it is a neutral data format to describe, exchange, and share all building information including geometry, spatial relationships, attributes, and quantity [36]. With such a format, the model can be then imported in suitable software to prepare the time schedule of the project, define the actors involved, and assign the physical elements to the work schedule, obtaining the 4D BIM model. The developed QC system synchronizes the 4D model and the quality information, generating a web-based checklist, storing all the inspection results and generating the link in the 4D IFC model to the AR application. By importing the synchronized 4D IFC model into the AR application, it is possible to visualize the BIM model on site, while the checklist is also accessible and can be updated. The QC system was developed using the asp.net framework based on C# programming language to synchronize all information needed. Since the system is platform-independent and it can be accessed through any type of web browser, it can be accessed through either desktop or mobile devices and there are no requirements on the type of operating system. The input/output scheme of the system is represented in Figure 5.  
Figure 4: Quality control phases for a concrete structure execution. Figure 3: Example of generic physical object elements. The main packages/modules used to generate the quality system are the xBIM Toolkit which is a NET open-source software development BIM toolkit that supports IFC: it allows reading, creating, and viewing BIM Models in the IFC format. Two core libraries of the xBIM toolkit are xBIM Essentials and xBIM Geometry which are written in C# and C++. To allow addition of the BIM model to the checklist, WeXplorer was used; it is the visualization part of xBIM toolkit and uses WebGL technology giving 3D viewing control. There are no specific entities for quality information in the IFC standard, therefore new entities describing the quality management process and their relationships with other information have been created [37]. The entity IfCQuality has been defined as an entity connected to other different entities describing the quality of an element. One of them is IfCInspectionLot and its subset IfcQualityParameters. The latter is categorized with respect to the epoch (IfcQualityPhase) and the type (IfcQualityCategory) of the control. IfcQualityAcceptance and its subset IfcQualityDoc describe the information regarding the inspection results and the related uploaded documentation. IfcInspectionPlan describes the assignments of activities and their schedule information in the framework of QC. These new entities are related to other entities already defined in the IFC standard Version 4 such as IfcProduct and its inherited entities describing the designed products, or IfcWorkSchedule describing the timing of the activities. Figure 6 shows the IFC-based process model and the relevant entities. As an example, in the case of a wall that should be under inspection after concreting, the geometrical data and its properties are represented by IfcWall as a type of IfcProduct and it has one assigned IfcQuality entity. This entity is defined by three IfcInspectionLot, specifically cross-sectional geometry, surface control, and hardened concrete quality. Regarding the cross-sectional geometry of IfcInspectionLot, three parameters (dimensions, skewness, orthogonality) are related to geometry (IfcQualityCategory) and execution phase (IfcQualityPhase) with their own upper and lower deviation limits.