Advanced Engineering Informatics 30 (2016) 39–53

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Advanced Engineering Informatics

journal homepage: www.elsevier .com/ locate/ae i

Extending IFC to incorporate information of RFID tags attached tobuilding elements

http://dx.doi.org/10.1016/j.aei.2015.11.0041474-0346/� 2015 Elsevier Ltd. All rights reserved.

⇑ Corresponding author.E-mail addresses: a_mot@encs.concordia.ca (A. Motamedi), mo_solta@encs.

concordia.ca (M.M. Soltani), m_setaye@encs.concordia.ca (S. Setayeshgar), hammad@ciise.concordia.ca (A. Hammad).

Ali Motamedi a, Mohammad Mostafa Soltani b, Shayan Setayeshgar b, Amin Hammad c,⇑a Individualized Program (INDI), Concordia University, 2145 Mackay Street, M 302, Montreal, Quebec H3G 2J2, CanadabBuilding, Civil and Environmental Engineering, Concordia University, 1455 de Maisonneuve Blvd. West, EV-6.139, Montreal, Quebec H3G 1M8, CanadacConcordia Institute for Information Systems Engineering, Concordia University, 1515 Ste-Catherine Street West, EV7.643, Montreal, Quebec H3G 2W1, Canada

a r t i c l e i n f o

Article history:Received 24 April 2014Received in revised form 5 November 2015Accepted 16 November 2015Available online 14 December 2015

Keywords:Building information modelingRadio frequency identificationIndustry foundation classesModeling

a b s t r a c t

Building Information Modeling (BIM) is emerging as a method of creating, sharing, exchanging andmanaging the building information throughout the lifecycle between all stakeholders. Radio FrequencyIdentification (RFID), on the other hand, has emerged as an automatic data collection and informationstorage technology, and has been used in different applications in the AEC/FM (Architecture,Engineering, Construction, and Facilities Management) industry. RFID tags are attached to building assetsthroughout their lifecycle and used to store lifecycle and context aware information taken from a BIM.Consequently, there is a need for a standard and formal definition of RFID technology components inBIM. The goal of this paper is to add the definitions for RFID components to the BIM standard and tomap the data to be stored in RFID memory to the associated entries in a BIM database. The paper definesnew entities, data types, and properties to be added to the BIM. Furthermore, the paper identifies therelationships between RFID tags and building elements. These predefined relationships facilitate the link-age between BIM data and RFID data. Eventually, the data that are required to be saved on RFID tags canbe automatically selected using the defined relationships in a BIM. A real-world case study has beenimplemented to validate the proposed method using available BIM software.

� 2015 Elsevier Ltd. All rights reserved.

1. Introduction Various mechanical/electrical elements have already been

There is an evident need for a standard data model to be used asthe basis for computer-aided design, planning, construction andmaintenance. Building Information Modeling (BIM) is emerging asa method of creating, sharing, exchanging and managing the infor-mation throughout the lifecycle to tackle the problems related tointeroperability and information integration. The Industry Founda-tion Classes (IFC) standard developed by Building SMART Alliance(BSA) (formerly known as International Alliance of Interoperability(IAI)), has matured as a standard BIM in supporting and facilitatinginteroperability across the various phases of a building lifecycle[18]. IFC is an object-oriented, non-proprietary building datamodel. However, modelling all possible objects related to the build-ing industry is extremely complex. Therefore, the BSA introducedan incremental development of the IFC model by providing anextensible architecture for extending IFC in various domains.

added to the current version of the IFC standard (e.g., Sensor, Actu-ator, and Alarm). However, there are other technologies such asRadio Frequency Identification (RFID) that are being used in theAEC/FM (Architecture, Engineering, Construction, and FacilitiesManagement) industry and are not yet defined in the IFC. Similarto barcodes, RFID is a technology for identifying and trackingobjects. The RFID technology introduces several advantages overbarcoding in that its operation does not require line-of-sight orclean environments, and the stored data are dynamic and modifi-able. RFID has been identified as one of the ten greatest contribu-tory technologies of the 21st century. An increasing number ofenterprises are employing RFID to improve their efficiency of oper-ations and to gain a competitive advantage [4]. RFID-based sys-tems have been used in different applications in construction andmaintenance, such as asset tracking and locating, inventory man-agement, equipment monitoring, progress management, facilitiesmanagement, tool tracking, material management, and qualitycontrol (e.g., [19,21,28,43,22,39,30]). Furthermore, RFID is one ofthe main enabling technologies for the Internet-of-Things (IoT)[1]. IoT is emerging and the number of building devices that areequipped with such data storage and communication devices isincreasingly growing.

40 A. Motamedi et al. / Advanced Engineering Informatics 30 (2016) 39–53

Motamedi and Hammad [26] introduced a framework to useRFID memory for facilitating various operations throughout thelifecycle of the building. The framework suggested to permanentlyattach RFID tags to building elements where the memory of thetags is populated with accumulated lifecycle information of theelements taken from a standard BIM database. This informationis used to enhance different processes throughout the lifecycle,such as providing the technicians with the maintenance instruc-tion for assets. Moreover, a facility with RFID-equipped assetscan potentially provide users with assets’ location data [28,35].The motivation behind their research was to make some parts ofBIM data available to building occupants/users when there is nodata access to the BIM database (e.g., emergency, lack of data con-nectivity, lack of access permissions) in order to provide location-based services, and to provide BIM data redundancy.

Based on the assumption that the RFID tags are permanentlyattached to building elements, the tags can be considered as ele-ments of the building. Consequently, there is a need to formallydefine these RFID tags and their associated properties in the build-ing’s data model. The data in the model are essential for trackingand maintaining the RFID components throughout the lifecycle ofthe building. Moreover, due to the fact that RFID memory is popu-lated with BIM data, defining RFID as an object in the model facili-tates the data linkage andmanagement. The data interrelations canbe achieved by defining the RFID system components (e.g., tags andreaders) as objects in a BIM together with their logical and physicalrelationships to other objects. Effort inmodeling sensors resulted innew standards (i.e., SensorML) or new entities in the BIM (i.e.,IfcSensor). However, RFID components cannot be considered assensors due to their different characteristics and functionalities.Many researchers mentioned the need for adding RFID definitionsto the BIM model (e.g., [7,38,37]). However, no extension has yetbeen proposed. This study is motivated by the above-mentionedneeds and aims to provide a solution for current gaps.

The objectives of the present paper are: (1) to perform require-ments’ gathering in order to define RFID system components, theirproperties, and their relationships with other building elements;(2) to integrate the definitions and property sets into the IFC stan-dard by either mapping them into existing IFC definitions or defin-ing new entities; and (3) to validate the proposed approach anddemonstrate its technical feasibility using a case study by usingavailable IFC-compatible software.

2. Review of related research

2.1. Building Information Modeling (BIM) and Industry FoundationClasses (IFC)

According to Associated General Contractors Guide (AGC, 2005),BIM is a data-rich, object-oriented, intelligent and parametric dig-ital representation of facilities. Views and data appropriate to var-ious users’ needs can be extracted and analyzed to generateinformation that can be used to make decisions and improve theprocess of delivering a facility.

The BIM database is mandated to contain data related to allaspects of the facility (e.g. geometry, mechanical systems, con-struction scheduling) that are accumulated throughout the lifecy-cle. Consequently, various types of data that are useful forstakeholders should be defined and added to available standards.

The IFC developed by BSA has matured as a standard of BIM insupporting and facilitating interoperability across the variousphases of the construction lifecycle [18]. It is now supported bymost of the major Computer-Aided Design (CAD) vendors as wellas by many other applications [17,20]. The IFC model representsboth tangible building elements (e.g. walls, doors, beams) andmore abstract concepts (e.g., schedules, activities, spaces,

organization, and construction costs) in the form of entities. Eachentity can have a number of properties such as name, geometry,materials and relationships [45]. IFC supports a limited numberof use cases in the AEC/FM industry and more developments arerequired to extend IFC for new applications [42,24].

2.2. Extending IFC

IFC follows an object-oriented approach by assigning entities toobjects with predefined attributes that can be inherited by allrelated entities. An IFC model can be described using the EXPRESSdata definition language which has the advantage of being com-pact and well suited to include data validation rules within thedata specifications. Additionally, ifcXML is provided as anotherway to describe the model using an XML schema [3].

There are three mechanisms to extend IFC: (1) by defining newentities or types, (2) by using proxy elements, and (3) by using theproperty sets or types [42]. Ma et al. [24] noted that, among thethree alternatives, defining new entities or types is the best wayto extend the IFC standard since the newly defined entities andtypes can then be used in the same way as the existing ones. How-ever, it normally takes at least two years to define new entities bythe BSA [42]. For the other two alternatives, additional implemen-tation agreements about the definition of the property sets andproxy elements are required if they are used to share data withother application software. Hence, the other two alternatives aremore practical to meet specific local requirements.

Several research projects have been conducted to extend the IFCstandard to include new objects, entities, and relationships (e.g.,[9,10,11,23,24]). For example, Weise et al. [40] proposed an exten-sion for the structural engineering domain which was not sup-ported in the IFC standard at the time. The same group furthersuggested an IFC extension for structural analysis [41]. However,there is no research aiming to propose an extension to IFC for RFIDsystems.

2.3. Sensor modeling

Sensor Model Language or SensorML represents a standard sen-sor description language for all aspects of sensor geolocation con-sidering XML format as a description framework. Initially, theSensorML was targeting the geolocation and remote sensinginstruments. However, it became more popular and played a keyrole for describing the capabilities of any sensor. After testing theSensorML through a set of implementation and interoperabilityexperiments, the first technical version of SensorML was approvedby OpenGIS Consortium (OGC) in 2006 [2].

Additionally, the IFC standard has definitions for sensor entities.Based on the definition provided by BSA data model standard, theterm IfcSensor is defined as the following ‘‘A sensor is a device thatmeasures a physical quantity and converts it into a signal whichcan be read by an observer or by an instrument” [17]. Althoughseveral modeling efforts have been done for sensor technology(e.g., SensorML and IfcSensor), RFID devices cannot be representedusing sensor entities. For example, as RFID itself does not measureany physical quantities, IfcSensor cannot represent RFID elementsin the IFC. RFID is a data storage and communication technologyand not a sensing technology. However, RFID can be coupled withsensors (e.g., temperature, GPS, humidity, or vibration sensors). Insuch products, the RFID functionality is used to store the sensor’sreadings and transmit them to the readers.

2.4. Building information management using RFID

Elghamrawy and Boukamp [7] presented a methodology formanaging construction document information using RFID-based

A. Motamedi et al. / Advanced Engineering Informatics 30 (2016) 39–53 41

semantic contexts. In their research, RFID is used for automatedcomponent identification to support information retrieval on siteusing a context ontology. For that purpose, a database is developedto link RFID data to the related context. Their research discussedthe necessity to systematically store relationships between RFIDtags and associated building components. However, BIM is not uti-lized to either store the documents or the relationships.

Amongst several research projects that suggest linking buildingelements to the objects in a virtual model using RFID technology(e.g., [26,8]), Sørensen et al. [38] and Sørensen et al. [37] proposedcreating a link between virtual models (e.g., BIM) and physicalobjects in the construction process using available ontologies. Intheir research, RFID tags are attached to physical objects and theirIDs are added to the model. Their research stated that there is aneed for modifying the IFC for allowing objects’ information retrie-val based on registered RFID tags. They also recommended tomodel RFID tags not only as ID attributes but as an object or aproperty set in the IFC model.

2.5. RFID data structure

Generally, there are three types of data storage approaches forRFID systems: storing in a remote database, storing on the tag,and storing using an integrated approach. Using a remote databaserequires the object ID stored on the RFID tag to have access to therelated information of the tag on the remote database [8]. In thismethod, the tag does not necessarily have large memory capacitysince it only needs to carry the object ID. In addition to the remotedatabase, all the required information is stored in the memory ofthe tag when the ‘‘Data-on-Tag” method is chosen for the RFID sys-tem. Independent data access is the main advantage of this methodand the user only needs to find the tag and read its memory inorder to access any related information. However, this methodmay increase the deployment cost of the RFID system since itneeds tags with a high memory capacity and sometimes it maynot be feasible to store all of information in the tag’s memory.Therefore, the integrated method, which takes the advantages ofthe previous two methods, can be used. In this method, the infor-mation with the higher priority to access is stored in the memoryof the tag while the remaining useful information can be stored inthe remote database and is accessible by providing the object IDstored on the RFID tag.

Guven and Ergen [12] investigated the factors affecting theselection of data storage approach in RFID applications through asurvey research. They concluded their study by introducing theapplication environment, cost efficiency, multiple number of par-ties, need for monitoring up-to-date progress data, collecting envi-ronmental conditions, industry-related specifications, and readingrange requirement as affecting factors. Moreover, they suggestedintegrating BIM and RFID to enable monitoring the usage of thebuildings as future work. Another study done by Motamedi andHammad [26] proposed a Data-on-Tag storage model while parti-tioning the memory space of the tag into: (1) ID, (2) specifications,(3) status, (4) process data, (5) history data, and (6) environmentdata. Furthermore, Saini et al. [33] proposed storing building floorplans using RFID-based distributed storage. In their method, theyassumed that the floor plans are organized in the form of an XMLdocument which can be directly saved in the user memory parti-tion of the RFID tags.

3. Research vision

As explained in Section 1, RFID tags are extensively used insupply chain management and are attached to various buildingelements. Moreover, several industry and research projects

suggested attaching RFID to building elements for lifecycle man-agement and various process improvements, especially duringthe construction and operation phases of the building’s lifecycle.Consequently, RFID equipment will be available in buildings andtags will accompany the elements throughout their lifecycle.

3.1. RFID as a building element

Available RFID systems in the facility may have different types,shapes, sizes and properties. Thus, in order to represent theirshapes and properties, as a new type of building elements, thereis a need for standard and formal definitions for RFID systems ina BIM. Additionally, RFID tags have distinct relationships withother building elements. For example, tags are physically attachedto a certain element or logically assigned to host informationrelated to one or a set of elements. These relationships are consid-ered as the building data and should be kept and maintainedthroughout the lifecycle. Furthermore, the data about the orienta-tion of RFID antennas, their precise location and their usage historyare useful for various operations. Having RFID as a BIM entityprovides a standard method to store the above-mentionedinformation.

Fig. 1 shows a pump with an RFID tag attached to it. The geo-metric representation and the properties of the pump are storedin a virtual model. Our method proposes adding the virtual modelof the tag, its properties and information about the relationshipswith the building elements to the BIM model as explained below.

3.2. RFID memory as BIM data storage

Available RFID tags in a facility are used to store data related tobuilding elements. As explained in the survey by Guven and Ergen[12], many researchers proposed using RFID data as lifecycle datastorage. Based on the framework proposed by Motamedi and Ham-mad [26], explained in Section 1, these data are dynamic and takenfrom a standard BIM file/database. For example, the memory of atag can contain the maintenance information of the asset such asthe condition or the last inspection date. Moreover, the tags memorycan contain data related to several elements or spaces. For exam-ple, the tag can contain the location coordinates of various assetsin a room, or it can have the list of occupants in the room [28].In order to relate the elements’ data stored in a BIM to their asso-ciated tags’ memory, the relationship between the elements andtheir associated tags should be identified and modeled. Havingthese relationships defined in a BIM, the process of selecting datato be stored in tag’s memory can be facilitated.

Most of the research and industry projects, in which RFID tagsare used to store lifecycle data, maintained the relationshipbetween the tags and the components through a separate, compli-mentary data table (e.g., [7]). Additionally, the selection of data tobe stored on the RFID tag has been handled by the developed pro-totype application. There has not been any formal method sug-gested to systematically relate the tags’ data with the entries inthe BIM database.

3.3. Data synchronization

As RFID tags act as a distributed data store for BIM data, there isa need to maintain data consistency by updating and synchroniz-ing the data on these tags. Data synchronization is very importantas the tags are highly distributed and, due to their different read-ability ranges, are mostly updated irregularly. Synchronizationtechniques have been studied by many researchers in the field ofcomputer science and database management (e.g., [36,34,25]).The aim is to increase the concurrency and to reduce the chanceof data rollback. Methods such as using timestamps or version

RFID Tag Shape and proper�es

Inspec�on Data

Pump Shape and proper�es

Logical Assignment

Physical A�achment

BIM(Virtual Model)

Pump(Physical Object)

User or Third party technician (Read access)

Facili�es Management Technician (Read/Write Access)

BIM Subset

RFID Tag

Physical A�achment

PumpData Update

Fig. 1. Conceptual vision of the proposed method and its applications.

42 A. Motamedi et al. / Advanced Engineering Informatics 30 (2016) 39–53

control are common for this purpose. However, for the case ofbuilding information stored on both distributed tags and a centraldatabase, it is desirable to have the most updated version of thedata in a central BIM at all times to be accessed by all stakeholders.Hence, although the data is stored on RFID tags to be used locallyfor context awareness, the data should be copied from a BIM[26]. This suggests that even if the data is acquired in the field,the most updated version is always stored on the BIM databaseand kept synchronized with the tags. This will also allow BIM tokeep the history of data changes in the RFID memory. However,there might be instances when the RFID data is more recent (suchas sensor readings that are automatically saved on the RFID tag). Insuch cases, the RFID data is synchronized with BIM using times-tamps through pre-defined relationships.

Fig. 1 shows an application overview of our approach. It showsthe physical pump with an RFID tag attached to it and the BIMmodel that contains the geometric representation and propertiesof those elements. The BIM contains the data about the physicalattachment relationship as well as the assignment relationshipbetween the two elements. The figure also shows how the subsetof BIM data stored on the tag can be accessed in the field by thetechnician who has the read-only access permission. The data onthe tag are updated and synchronized with BIM by a facility man-agement technician who has the read-write access to the data.

4. Main use cases

Two scenarios that describe the process flow to use the IFCdatabase to update/synchronize RFID data are presented in the fol-lowing subsections. These sample scenarios show how adding thedefinitions of RFID tags together with their relationships withother objects in the BIM will facilitate the process of data manage-ment and synchronization. They also demonstrate the processsteps to use the IFC database for updating the data of tags.

4.1. Scenario 1: Updating asset’s information during inspection

As explained in Section 1, RFID tags can be used to store infor-mation that assists the inspection/maintenance/repair process (e.g.manufacturing date, inspection instruction, inspection dates, andcondition). Having the information available on the tags willprovide technicians with the asset’s information while they are

performing their activities. In order to update the assets data onthe tags, a central IFC database is used. Having RFID tags definitionin the IFC model, together with their relationships to other ele-ments, will facilitate the process of automatically composing thedata file to be saved on tags. Additionally, some information aboutthe field inspection is suggested by many researchers to be savedon the tags (e.g. last inspection date, overall result, and next duedate). The detailed inspection data should be saved in the IFC data-base as the asset’s history to be used by different stakeholders (e.g.,for maintenance planning). The process to construct the subset ofinspection data to be saved on a tag attached to a certain asset isas follows: (1) The user scans the tag and the software reads itsID; (2) The software queries the ID in the IFC database; (3) Usingavailable relationships in the IFC database, the software identifiesthe related asset(s); (4) The software reads the related inspectioninformation of each related asset from the IFC database; (5) Thesoftware builds a file containing the result of the queries; and (6)The file is merged into the data on the tag.

4.2. Scenario 2: Storing the location coordinates of assets on a locationTag

An RFID location tag is a long-range tag whose memory containslocation coordinates of several fixed assets in an area copied from aBIM model [28]. These tags are used to provide the users with thelocation coordinates of assets in an area. Having location coordi-nates of assets on these tags, the user equipped with a handhelddevice can read the tag’s memory and query the coordinates ofthe target asset to be shown on the floor plan. For that purpose,the list of coordinates should be updated on the tags as new assetsare installed or moved in the area. The BIM database contains theaccurate coordinates of fixed assets. Using the relationshipsbetween the assets and the RFID tags, the most updated list ofcoordinates can be built and transferred to the tags. In order toupdate the assets’ coordinates on the tags, the following stepsare followed: (1) The tag is scanned and its ID is read by the soft-ware; (2) The software queries the ID in the IFC database; (3) thesoftware reads the properties of the scanned tag from the IFC data-base and verifies if the detected tag is a location tag; (4) Usingavailable relationships in the IFC database, the software identifiesthe related assets; (5) The software reads the location coordinatesof each related asset from the IFC database; (6) The software builds

A. Motamedi et al. / Advanced Engineering Informatics 30 (2016) 39–53 43

the data file containing the queried data; and (7) The data file ismerged into the data on the tag.

5. Proposed extension for IFC

The definitions and data structure of the latest version of avail-able IFC standard (i.e., IFC4) are used as the basis for our proposedIFC extension for RFID. The aim is to define the minimum numberof objects and relationships. This will avoid the unnecessaryexpansion of the model by reusing available relationships andproperty sets. A detailed example of the information that can bestored on RFID tags will be given in Section 6.

5.1. Requirements gathering for RFID system definitions

In order to add the definitions of RFID system components (i.e.,tags, readers and antennas) to IFC, detailed requirements gatheringis performed using the following steps: (1) Identifying RFID tech-nology components (explained in Section 5.1.1); (2) Identifyingthe properties for each RFID component type including Physicalproperties and specifications such as electrical, radio, enclosure rat-ing and shape; Operation properties such as installation date andthe write cycle count; and Data management properties such asencryption type and markup language (explained in Section 5.1.2);and (3) Identifying the relationships with other elements(explained in Section 5.2).

Various resources are used for the design phase including RFIDmanufacturers’ data sheets and specifications (e.g., [15,44,31]), andscenario/case studies in which RFID technology is utilized for life-cycle management of facilities (e.g., [26,8]). In order to identify therelationships between RFID components and building elements,our proposed framework (explained in Section 1) in which RFIDtags are assigned or attached to building elements is used.

5.1.1. RFID system elementsRFID hardware can be grouped in three major categories; (1)

RFID tag (transponder), (2) RFID reader (Transceiver), and (3)antenna. Each of these entities and their associated attributesshould be defined. An antenna is defined in IFC as an enumerationof IfcCommunicationsApplianceType. Hence, this definition can beused to model the antenna attached to readers and tags.

The RFID components are defined under the IFC ElectricalDomain schema which forms a part of the Domain Layer of theIFC model [17]. A new type (i.e., RFIDSystemType) is proposed tobe defined in IFC with four enumerations: (1) passive tag, (2) activetag, (3) passive reader, and (4) active reader. Fig. 2 shows the hier-archy of entities for the new defined object. Other possible types,such as Semi-Active RFID that inherits properties of both activeand passive tags, can be identified using a combination of proper-ties related to each of the above major types.

Although IfcSensor entity is available in the IFC, it cannot beused to represent data communication and data storage devicessuch as RFID devices. As shown in Fig. 2, RFIDSystem is defined asa subtype of IfcFlowTerminal. Based on the definition provided byBSA data model standard, ‘‘The distribution flow elementIfcFlowTerminal defines the occurrence of a permanently attachedelement that acts as a terminus or beginning of a distribution sys-tem. [. . .] A terminal is typically a point at which a system inter-faces with an external environment”. Entities such as AudioVisual Appliance, Communications Appliance, and Electric Appli-ance, Lamp or Outlet are defined under this supertype. It showsthat elements that generate energy or data flow can be alsoincluded under this supertype. As IfcFlowTerminalType covers bothelectrical and communication elements, it is the most suitablesupertype for the RFID element.

5.1.2. RFID system properties definitionAs explained in Section 5.1, various resources are used to iden-

tify the required property sets of RFID systems’ components. Forexample, data sheets provided by RFID tags manufacturers wereused to identify the required set of electrical and radio propertytypes to be included (e.g., [15,44,31]). A review of available RFIDsystems is conducted to identify various shapes and casing materi-als for RFID tags. Moreover, properties related to the operation ofRFID components during the lifecycle are added such as: installa-tion date, current battery level and the incremental write cyclecount. These data are used to identify the state of RFID usage atany given time. These data can be used to plan for replacementor maintenance of the tags that are reaching their end of lifecycle.The properties related to the data storage of RFID tags should becaptured because the RFID memory is used to store data. For exam-ple, various standard IDentifiers (IDs) that are assigned, the type ofcipher that is used to encrypt the data [27], and the markup lan-guage are required to be defined. It is also suggested to add a localcopy of the memory content of the tags in the BIM database. Hav-ing a local copy of the last updated content of the memory can beused to check for data integrity and synchronization. As explainedin Section 2.5, the method introduced by [33] can be adapted tostore the IFC-XML documents on RFID user memory spaces.

The properties of RFID systems are defined according to prop-erty set assignment concept of the IFC. Available property sets areused, such as Electrical Device Common, Condition, EnvironmentalImpact Indicators, Manufacturer (Type and Occurrence), Service Life,and Warranty. IFC standard [17] can be referred for details onabovementioned sets. Table 1 shows the existing property sets inthe IFC that are reused as shared property sets for the RFID system.

IFCMaterialUse definition is used to define the material used forthe tag and its casing. Identifying the material for casing of the taghas special importance since the radio communication capabilityof a tag is highly influenced by the type of its casing when attachedto metallic objects. Separate property sets are defined to includetype-specific information. For example, the battery life can be onlya property of active tags. Table 3 shows the recommended propertyitems for all RFID system entities. Additionally, the sample data-sheets for example values in the table are referenced. The propertyitems can be grouped into three categories: (1) General specifica-tions including, radio, electrical, physical, safety and memory prop-erties; (2) Operation properties including the data about the usageof RFID, and (3) Data management properties including the IDsand the memory encoding and markup language. These propertyitems are placed in five Property Sets (PSet) that are: RFID CommonPSet (for properties that are shared between all types), Active tagPset, Passive Tag Pset, Active reader Pset, and Passive reader Pset.

5.1.3. Location of the RFID tags and readersThe locations of the RFID system entities are modeled using

available methods in IFC for representing the location, orientationand placement of items as follows:

Absolute or relative placements: The RFID entity placementcan be identified in various methods such as: (1) absolute: byan axis placement, relative to the world coordinate system,(2) relative: by an axis placement, relative to the object place-ment of another product (for example, the element to whichthe tag is attached to), (3) by grid reference: by the virtual inter-section and reference direction given by two axes of a grid. InIFC, this placement can be represented using IfcObjectPlacementand its subtypes IfcLocalPlacement and IfcGridPlacement.IfcLocalPlacement defines the relative placement in relation tothe placement of another product or the absolute placementwithin the geometric representation context of the project.

(ABS) IfcRoot

(ABS) IfcObject

(ABS) IfcElement

(ABS) IfcDistribu�onElement

(ABS) IfcRela�onship(ABS) IfcObjectDefini�on

(ABS) IfcDistribu�onFlowElement

(ABS) IfcFlowTerminal

IfcRfidSystemIfcRfidSystemType

IfcRfidSystemTypeEnum

(ABS) IfcProduct

(ABS) IfcPropertyDefini�on

IfcDistribu�onChamberElement

IfcEnergyConversionDevice

IfcAudioVisualAppliance

IfcCommunica�onsAppliance

IfcElectricAppliance

Fig. 2. IFC hierarchy for RFID system.

Table 1Shared property sets for RFID system [17].

Name of Pset Description

Pset_ElectricalDeviceCommon A collection of properties that arecommonly used by electrical devicetypes

Pset_Condition Determines the state or condition ofan element at a particular point intime

Pset_EnvironmentalImpactIndicators Environmental impact indicators arerelated to a given ‘‘functional unit”(ISO 14040 concept)

Pset_ManufacturerOccurrence Defines properties of individualinstances of manufactured productsgiven by the manufacturer

Pset_ManufacturerTypeInformation Defines characteristics of types(ranges) of manufactured productsgiven by the manufacturer

Pset_PackingInstructions Packing instructions are specificinstructions relating to the packingthat is required for an artifact in theevent of a move

Pset_ServiceLife Captures the period of time that anartifact will last

Pset_Warranty An assurance given by the seller orprovider of an artifact

44 A. Motamedi et al. / Advanced Engineering Informatics 30 (2016) 39–53

Details related to this placement method can be found in IFCdocumentation [17].Containment: The RFID system entity is located in a space thatis part of a building and a floor. The location of the tag can beidentified based on the containment relationship to know thespatial level that the tag is located in. IfcRelContainedInSpatialStructure, is used to assign elements to a certain level of the spa-tial project structure. Predefined spatial structure elements inIFC to which RFID tags can be assigned are: (1) site, (2) building,(3) stories, and (4) space.

Fig. 3 shows how an RFID tag (instance of IfcProduct) canhave containment relationship with certain building story orspace. It shows that in addition to the containment relationship,

the tag has its absolute or relative placement definitions usingIfcLocalPlacement.

5.2. Relationships with other objects

The RFID tag/reader is either attached to an asset/building ele-ment or is part of it (as a subcomponent). These relationships arephysical attachment or decomposition type. Fig. 4 shows how anRFID tag or reader has one-to-one physical relationship with anelement that it is attached to. Although each tag/reader is attachedto only one element, several RFID tags/readers can be physicallyattached to one element. Section 5 provides an example of an envi-ronment in which RFID tags are physically attached to its elements.

The decomposition relationship between an RFID tag and theassociated building element can be defined using existing IFC rela-tionship definitions. For example, the reader can be an internal partof a communication device, such as a handheld computer or cellphone. In this case, a decomposition relationship can be used toidentify such setting. Entities such as IfcRelDecomposes and its sub-type IfcRelAggregates are used to realize this relationship betweentags and their associated elements. As shown in Fig. 5, these rela-tionships are used when the tag is an internal part of an element.

In order to describe the physical connectivity between an RFIDtag/reader and a building element, IfcRelConnectsElements togetherwith IfcConnectionGeometry are used. IfcConnectionGeometry isadded to describe the geometric constraints of the physical con-nection of two objects. The physical connection information isgiven by specifying exactly where at the relating and related ele-ment the connection occurs. Additionally, IFC provides the eccen-tricity subtypes, to describe the connection when there is adistance between the tag and the element. IFC provides the follow-ing connection geometry/topology types: (1) point/vertex point,(2) curve/edge curve, and (3) surface/face surface.

Furthermore, one or many elements or spaces can be logicallyassigned to a tag in order to keep data related to them in its mem-ory. The following are different alternatives for object-to-tagassignments: (1) A single element is assigned to a tag (asset tag):The tag contains data about one element. In this scenario, the tag

Fig. 3. IFC containment relationships (adapted from IFC2x4-RC3 (2011)).

Fig. 4. RFID tag attachment and assignment relationships.

Fig. 5. Decomposition relationship.

Table 2Definitions and properties of ports.

Elementtype

Portname

Flowdirection

Type Description

Antenna Radio SinkSource Signal Electromagnetic wavesSignal SinkSource Signal The modulated analog

signal in a circuit

Activereader

Power Sink Electrical Receives electrical powerNetwork Sink Data A network link to a routed

deviceDevice Sink Signal A device connection such as

USB or serialSignal Source Signal The modulated analog

signal in a circuit

Activetag

Power Sink Electrical Receives electrical powerSignal Source Signal The modulated analog

signal in a circuit

Passivetag

Signal Source Signal The modulated analogsignal in a circuit

Passivereader

Power Sink Electrical Receives electrical powerNetwork Sink Data A network link to a routed

deviceDevice Sink Signal A device connection such as

USB or serialSignal Source Signal The modulated analog

signal in a circuit

A. Motamedi et al. / Advanced Engineering Informatics 30 (2016) 39–53 45

is attached to the same element. (2) A group of elements isassigned to a tag (group asset tag): More than one element isassigned to the tag (for example, the fire extinguisher, fire hoseand the first aid box are assigned to a tag). (3) Several spacesand/or elements are assigned to a tag (location tag): The tag con-tains data about the space (e.g., coordinates, room number andoccupants) and data about selected elements in that space. (4) Aspace is assigned to a tag (area tag): The tag contains data aboutthe space (e.g., floor plan, occupants). (5) A group of spaces isassigned to a tag (zone tag): The tag contains data about a groupof spaces (e.g., contains department name). Fig. 4 conceptuallyshows the relationship of an RFID tag and associated and attachedelements and spaces. All of the above-mentioned logical relation-ships between tags and elements can be described in IFC by usingIfcRelAssignsToProduct entity.

5.2.1. RFID systems connections and portsPorts are defined for different types of RFID System entities such

as tags and readers in order to model the connectivity to/betweenantennas as well as the connection to the power source. IfcRelCon-nectsPortToElement and IfcRelConnectsPorts are used in order torealize these connections. Table 2 shows the defined ports for dif-ferent RFIDSystem types. The table presents the name of the port,its flow direction, its flow type, and a short description. For exam-ple, an active RFID tag receives electrical power from its battery viaPower port. Fig. 6 shows the sample port connectivity diagrambetween an RFID active reader and an active tag. In this connectiv-ity diagram, the active reader is equipped with an external antennawhich is connected to the reader via a cable. It also receives energyfrom the battery through its unidirectional power port that isshown in the figure.

6. Case study

6.1. Description of the case study

In order to validate the proposed method, the mechanical roomof the Genomics Centre at Concordia University is chosen for the

case study. The building is modeled in Autodesk Revit Architecture2012 [32] and the mechanical elements are added to the model.RFID tags are attached to a selected set of elements to host theirrelated BIM information. In order to add RFID components to themodel, active and passive RFID tags are modeled in Revit underthe electrical equipment category and added to the BIM modelof the building. The modeled passive and active tags are attachedto mechanical elements (e.g., pump, chiller) and the walls,respectively.

Passive asset tags are attached to a selection of elements, andlong-range active location tags are attached to walls near some ofthe entrances of the mechanical room to provide the maximumreadability from the corridor. Fig. 7(a) shows the passive tags thatare attached to pumps. The tags are rugged and designed to workwell near metallic objects. Fig. 7(a) also shows the assets’ namesused in the model and the names of their assigned passive tags.Fig. 7(b) shows a long range active tag attached close to theentrance of a room. The active tags host larger amount of data

Table 3Proposed property sets.

Category Property item Description Example ActiveTag

PassiveTag

Reader

General specifications Standardcompliance

Communication, memory, ID type, and data type standards ISO18000-6Cc U U U

Range Operating readability range of tag or reader 50 mb U U U

Frequency Communication frequency range for the tag 920 MHza U U U

Operatingtemperature

Temperature range at which the device operates �20 �C to 55 �Cc U U U

Enclosure rating IP and NEMA Ratings IP68b U U U

Shock Environmental testing standard DIN/IEC68-227a U U U

Vibration Environmental testing standard DIN/IEC68-2-6a U U U

Antenna type Type of internal or attached antenna to the tag 1/4 wave monopole U U U

Total memorysize

Total size of tags memory 32 KBa U U

Transmit power Maximum transmission power 10–33 dBma U U U

Datatransmissionrate

Data communication rate 128 Kbps U U U

Shape type (1) Label, (2) Ticket, (3) Card, (4) Glass bead, (5) Integrated,(6) Wristband, (7) Button

Label U U

Battery type Battery type standard LR AAa U

Max. writecycle

Number of cycles that the tag can be written on 100,000a U U

Encoding Content encoding standard ASCII U U

Storage type Read-write, read-only and WORM (write once, read many) WORMb U U

Reader type Mobile, Fixed Stationary (Fixed)c U

Number ofantennas

Total number of supported or attached antennas 2c U U U

Antennaconnector

The standard for the RF antenna connector RP-TNCc U

Reader buffer Number of tags that can be read 400 U

Operation Properties Installation date Date when the unit is installed 01/01/2012 U U U

Battery level Percentage of available battery 40% U

Write cyclecount

Number of the write cycle 1280 U U

Data Management EPC number Universal identifier as defined in the EPCglobal tag datastandard

urn:epc:id:sgtin:0134000.213254.343f

U U

TID 32-bit transponder identification number 2E8E0D4Cf U U

Encryption Method and possibly keys for encryption of the data AESe U U

Markuplanguage

Data presentation standard/markup language XMLe U U

Memorycontent

Reference for the existing content on the tag’s memory IDd U U

a Identec i-Q350 [15].b OmniId Power 50 [31].c Zebra FX9500 [44].d [26].e [27].f [8].

Fig. 6. RFIDSystem connectivity and ports.

46 A. Motamedi et al. / Advanced Engineering Informatics 30 (2016) 39–53

compared to the passive tags and are readable from longer dis-tances [16].

The model of the mechanical rooms is then exported to the IFCformat and extra codes are added to the EXPRESS file in order todefine new properties and relationships for tags and elementsbased on the IFC 2 � 4 standard. The modified IFC model is thenviewed by a standard IFC viewer [29] to verify the consistency of

the model. The logical relationships are manually added to themodel for six mechanical elements. The names of these elementsare shown in Fig. 8. Fig. 8 also shows two sample rooms (i.e.,Room_1 and Room_2) that are defined in the model using IfcSpacedefinitions. The active tag contains various data types related tothe room and selected elements that are located in the room.Table 4 shows the types of data that are saved on passive and

(a) Passive RFID tags attached to mechanical assets (b) Active location tag attached to the wall

Fig. 7. Attachment of RFID tags to building elements.

.

Pump_1

Pump_2

Pump_3

Room_2

Chiller_1

Motor_1

Room_1

HW_Tank

Active Location Tag (LT1) Passive Asset Tag (AT_CH1)

Fig. 8. Concordia University Genomics Center BIM model view.

A. Motamedi et al. / Advanced Engineering Informatics 30 (2016) 39–53 47

active tags. As shown in Table 4, passive asset tags contain only theID of the tag and the last inspection date of the asset that the tag isattached to, due to the limited memory size of passive tags. Theactive location tag’s memory contains data related to other ele-ments and spaces in addition to its own ID. For example, it storesthe location coordinates of elements in the room. Consequently,the user who is reading the memory of the tag from a distancewould be able to identify the locations of elements as well as theirroom number. The location tag’s memory also contains the infor-mation related to the authorized users who have access to theroom and the hazardous materials that are stored in the room.

These data can be used for procedures related to access security,safety and emergency.

Four main relationship types are defined for active location tags:(1) physical relationship (attachment): which is the relationshipbetween the tag and the object it is attached to (i.e., wall). (2) Spa-tial containment: which is the relationship between the tag and thespace that contains the tag (i.e. corridor). (3) Assignment to spaces:which is the logical relationship of the tag and spaces assigned to it(e.g. rooms assigned to the location tag). Fig. 9 shows the assign-ment of Room_1 and Room_2 to the active tag LT1. (4) Assignmentto elements: which is a logical relationship to show the relation

Table 4Data saved on the tags.

Tag type Data type Example

Passive asset tag ID urn:epc:id:sgtin:0134000.213254.101

Related Asset’s LastInspection Date

12/12/12

Active location tag ID 123Related Spaces Name Room_1Related Space IDs 123Related SpacesAuthorized Users

John Smith

Related Spaces HazardousMaterials

None

Related Assets Name Chiller_1Related Assets ID 321Related AssetsCoordinates

X, Y

48 A. Motamedi et al. / Advanced Engineering Informatics 30 (2016) 39–53

between specific elements and the tag. In our case study, four ele-ments are assigned to the active location tag (as shown in Fig. 9).Similarly, three main relationships are defined for the passive assettags: (1) physical relationship (attachment); (2) Spatial containment;and (3) Assignment to elements.

6.1.1. Adding relationships using EXPRESS languageAfter creating the model objects in Revit, various relationships

should be defined. The current version of Revit supports only thespatial containment relationship (i.e., IfcRelContainedInSpatialStructure) from the required types of relationships. Hence, the modelis exported to IFC format and other relationships are manuallyadded using the EXPRESS language [17]. Fig. 9 shows some of therelationships between various elements including the spaces andassets and their attached tags. As shown in the figure, fourmechanical elements and two rooms are assigned to the locationtag (i.e., LT1). This location tag is attached to Wall_1 and containsthe data types presented in Table 4. The figure also identifies var-ious types of relationships that have been added to the IFC data-base in order to realize the required relationship definitions forthe case study.

Table 5 shows parts of the modified IFC file describing the fol-lowing: (1) the definitions of some elements (i.e., the active locationtag (LT1), a chiller (Chiller_1), a passive asset tag attached to the

Room_1

HW_TANK(Hot Water Tank )

MOTOR_1(Motor)

CHILLER_1(Chiller)

Wall_1

Corridor

AT_HWT(Passive Asset Tag )

AT_M1(Passive Asset Tag )

AT_CH1(Passive Asset Tag )

LT1(Ac�ve Loca

Tag)

SIfcRel

Logical Assignment - IfcRelAssignsToProduct

Elements

Spaces

1

65

4

32

7

Fig. 9. Case study entitie

chiller (AT_CH1), a room (Room_1), and a corridor (Corridor_1);(2) the coordinates of LT1, AT_CH1, and Chiller_1; (3) various rela-tionships including: the physical relationship between the passivetag and the chiller, logical relationships between the passive tagand the chiller, the logical relationships between the active tagand all assigned elements and spaces, a containment relationshipbetween the corridor and all the elements in it, and a containmentrelationship between Room_1 and all the elements in it; and (4) asample property set definition and its values for a sample passivetag (AT_CH1) and a sample asset (Chiller_1). The numbers shownin Fig. 9 correspond to the numbers in the comment column ofTable 5. For example, the assignment of several elements andspaces (including Chiller_1 and Room_1) to the location tag is real-ized with line #373559 in the EXPRESS code.

As explained in Section 4, the recorded data and relationships inthe IFC database are used to automatically construct the data file tobe saved in the tag’s memory. The data types to be saved in tagsmemory are selected based on the process requirements. Two sce-narios explained in Sections 4.1 and 4.2 can be realized in our casestudy. For the first scenario (i.e., to update the asset’s inspectionresults on its RFID tag), the data presented in Table 5 can be used.The table contains the definitions of the passive tag (AT_CH1)(#287118) and the chiller unit (Chiller_1) (#139022), the assign-ment relationship between the chiller and its tag (#373558), con-dition history of the chiller including inspection date and theinspection results (#373561, #373562), and EPC ID of the tag(#373563). For example, in order to store the inspection date (i.e.,AssessmentDate) on the RFID tag attached to Chiller_1, the softwareapplication first queries the ID of the tag and finds the related asset(i.e., Chiller_1) using the assignment relationship (#373558). Itthen updates the chiller’s inspection date (#373561) using a logicalrelationship (#373573) that relates condition property sets(#373571) to the element (i.e., Chiller_1).

Table 5 also includes the sample data to realize the second sce-nario (i.e., to update the location coordinates of elements on a loca-tion tag). It includes the definitions of the active location tag (LT1)(#289712), the definitions of a sample asset (Chiller_1) (#139022)and the room (Room_1) (#384), the coordinates of the chiller(#139014), and the assignment of the chiller to the location tag(#373559). The application that is used to update the tags shouldhave a procedure to lookup the needed entries in the IFC databaseand create a new file to be merged into the memory of scannedRFID tag.

PUMP_2(Pump)

_1

PUMP_3(Pump)

Room_2

�on AT_P1(Passive Asset Tag )

AT_P2(Passive Asset Tag )

AT_P3(Passive Asset Tag )

Physical Connectivity - IfcRelConnectsElements

patial Containment - ContainedInSpatialSpace

PUMP_1(Pump)

s and relationships.

Table 5Part of EXPRESS code for the model.

EXPRESS code Comment

/⁄ Definitions ⁄/#139022=IFCBUILDINGELEMENTPROXY(‘GUID’,#41,’Chiller_1’,$,’148 Tons’,#139021,#139012,’365499’,.

ELEMENT.);Definition of the chiller ‘‘Chiller_1”

#289712=IFCBUILDINGELEMENTPROXY(‘GUID’,#41,’LT1’,$,’RFID Active Tag’,#289711,#289706,’454896’,.ELEMENT.);

Definition of active location tag ‘‘LT1”

#287118=IFCBUILDINGELEMENTPROXY(‘GUID’,#41, ‘AT_CH1’,$,’RFID Passive Tag’,#287117,#287112,’450749’,.ELEMENT.);

Definition of passive tag ‘‘AT_CH1”

#384=IFCSPACE(‘GUID’,#41,’1’,$,$,#348,#382,’Room_1’,.ELEMENT.,.INTERNAL.,$); Definition of ‘‘Room_1”#668=IFCSPACE(‘GUID’,#41,’3’,$,$,#606,#666,’Corridor_1’,.ELEMENT.,.INTERNAL.,$); Definition of ‘‘Corridor_1”

/⁄ Coordinates ⁄/#286239=IFCCARTESIANPOINT((-7797.6,-19299.2,736.4)); Coordinates of passive tag ‘‘AT_CH1”#289285=IFCCARTESIANPOINT((-8462.1,-18433.7,758.9)); Coordinates of active location tag ‘‘LT1”#139014=IFCCARTESIANPOINT((-8176.7,-18055.8,50.9)); Coordinates of the chiller ‘‘Chiller_1”

/⁄ Physical Relationships ⁄/ Attachment of Passive tag ‘‘AT_CH1”to the ‘‘Chiller_1”:Relationship (1)#183985=IFCRELCONNECTSELEMENTS(‘GUID’,#41,$,$,$,#139022,#287118)

/⁄ Logical Relationships ⁄/#373558=IFCRELASSIGNSTOPRODUCT(‘GUID’,# 41,$,$,#139022,#287118) Assigning chiller to the passive tag: Relationship (2)#373559=IFCRELASSIGNSTOPRODUCT(‘GUID’,# 41,$,$,(#139022, #267844,#192183,#226763,#226855,

#238888,#235,# 384),$,#289712)Assigning assets and spaces to the active tag:Relationships (3), (4)

/⁄ Spatial containment Relationships ⁄/#373318=IFCRELCONTAINEDINSPATIALSTRUCTURE(‘GUID’,#41,$,$,(#107262,#109710,#109958,#111027,

#111481,#111564,#111967,#112210,#139022,#159580,#159804,#159940,#160032,#192183,#194222,#244834,#267844,#289240,#291290),#384);

Containment relationship for assets inside ‘‘Room_1”including: Relationships (5), (6)

#373340=IFCRELCONTAINEDINSPATIALSTRUCTURE(‘GUID’,#41,$,$,(#107890,#108403,#108556,#112859,#113354,#113837,#127697,#128030,#128131,#244264,#244345,#244636,#270365,#280369,#282636,#290391),#668);

Containment relationship for assets inside ‘‘Corridor_1”including: Relationship (7)

/⁄ Properties Values ⁄/#373561=IFCPROPERTYSINGLEVALUE(‘AssessmentDate’,$,IFCDATE(‘2014–02-02’),$); Inspection date#373562=IFCPROPERTYSINGLEVALUE(‘AssessmentCondition’,$,IFCLABEL(‘Good-8/10’),$); Inspection results (condition)#373563=IFCPROPERTYSINGLEVALUE(‘EPCNumber’,$,IFCIDENTIFIER(‘urn:epc:id:

sgtin:0134000.213254.101’),$);EPC number

/⁄ Property Sets Definitions ⁄/#373571=IFCPROPERTYSET(‘GUID’,# 41,’Pset_Condition’,$,(#373561, #373562)); Condition property set#373572=IFCPROPERTYSET(‘GUID’,# 41,’Pset_RFIDSystemPassiveTag’,$,(#373563, #373564, #373565)); Passive RFID property set

/⁄ Relating Property sets to elements ⁄/#373573=IFCRELDEFINESBYPROPERTIES(‘GUID’,# 41,$,$,(#139022), #373571); Relating condition property set to ‘‘Chiller_1”#373574=IFCRELDEFINESBYPROPERTIES(‘GUID’,# 41,$,$,(#287118), #373572); Relating RFID property sets to passive tag ‘‘AT_CH1”

Fig. 10. Software application process flow.

A. Motamedi et al. / Advanced Engineering Informatics 30 (2016) 39–53 49

6.2. Prototype system

A prototype system has been developed to validate the applica-bility of the proposed method. The application is designed to facil-itate the inspection process using a portable handheld RFID reader

and active RFID tags. It allows facility management technicians toaccess data both on RFID tags and the IFC file, and to update themwith the latest inspection results. The definitions for RFID system(explained in Section 5.1) and the spatial and logical relationshipsbetween tags and assets (explained in Section 5.2) in a locally

Fig. 11. Prototype software snapshots.

50 A. Motamedi et al. / Advanced Engineering Informatics 30 (2016) 39–53

stored IFC file are used in the developed software application. Theprototype system utilizes a standard BIM database to store andretrieve maintenance/inspection data. Additionally, it synchronizesthe BIM data stored on the RFID tags with the main BIM databasein order to maintain the most updated version of the data to beshared amongst the stakeholders. Fig. 10 shows the process flow-chart for the prototype application. Fig. 11 shows snapshots ofthe prototype system.

(1) The user scans RFID tags (Fig. 11(a)). The power level of thehandheld RFID device can be adjusted to be able to read tags fromlonger distances. (2) The user chooses an RFID tag from a list ofdetected tags in the area. The software shows a short descriptionof tags (e.g. the asset that the tag is physically attached to) as wellas the Received Signal Strength Indicator (RSSI) value for eachdetected tag. Fig. 11(b) shows a snapshot of the interface of theprototype application. At this stage, the user can view and editthe data saved on the selected RFID tag (Fig. 11(c)). As shown inthe software snapshot, data such as Related Space Name and ID,Authorized users, Hazardous Materials, Related Asset ID, Coordi-nates, and Last Inspection Date are stored on the RFID tag. (3)

The application uses IFC relationships to show a list of relatedassets to the chosen RFID tag (Fig. 11(d)). (4) The user selects theasset that the inspection should be performed on (Fig. 11(d)). (5)and (6) The application retrieves and displays the IFC data. Datasuch as Manufacturing Date, Last Inspection Date, Condition, andNext Due Date are retrieved from the IFC file (Fig. 11(e)). Addition-ally, a URL that refers to a webpage containing the inspection pro-cedure is shown. The user can edit the assets data if required. (7)and (8) The user saves the changes to the IFC file and the RFIDtag memory by hitting the Update button (Fig. 11(c) and (e)). Theprototype system first saves the changes to the locally stored IFCfile and then synchronizes the data with the memory of the RFIDtag. The application displays the Update Successful message aftersynchronization is complete (Fig. 11(f)).

In order to validate the prototype system, we evaluated the pro-cess time for the Preventive Maintenance (PM) inspection activitiesdone on a collection of building mechanical assets (e.g., pumps andmotors). The inspection process using the prototype system is com-pared with the IT-assisted inspection. The IT-assisted inspectionscenario utilizes a commercial mobile application (i.e., DataSplice

Work Order

Technician

Download Work Order

Lookup & View History View Instruction Perform Inspection

Record Inspection ResultsExport to BIM

(a) IT -Assisted Inspection Process

Work Order

Technician

Download Work Order

Read Tag Lookup & View History View Instruction

Perform InspectionRecord Inspection Results

(b) Proposed Inspection Process

Fig. 12. Simulation models of IT-assisted and proposed inspection processes.

Table 6Duration range for each activity (min).

Activity IT-assistedmodel

Proposedmodel

Min Max Min Max

Office Receive/download work order 0 0 0 0

Work site Read tag N/A N/A 0.25 0.25Lookup & view history 1 2 0.5 1.5View instruction 1 2 1 2Perform inspection 3 7 3 7Record inspection results 2 4 2 3.5

Back office Export to BIM 1 1.5 N/A N/A

Table 7Simulation results.

Model Time saving (%)

IT-assisted Proposed

Averaged time (min) 13.53 12.27 9Standard deviation (min) 3.74 3.45 8

A. Motamedi et al. / Advanced Engineering Informatics 30 (2016) 39–53 51

[5]) and a Computerized Maintenance Management System(CMMS) (i.e., IBM Maximo [14]) to facilitate the inspection process.It should be mentioned that the IT-assisted inspection processrequires wireless connectivity of the mobile inspection device tothe central BIM database. The inspection process goal is to performthe visual inspection and store the results in a BIM database. In ourtest, the search time to find assets is not considered as it the samefor all scenarios and the average value is building specific. AlthoughRFID-equipped assets have the potential to facilitate their localiza-tion, we have not used such capability in our test.

The main metric for the evaluation is the process time. Fig. 12shows the process diagram of the IT-assisted inspection scenario

using DataSplice and IBM Maximo (Fig. 12(a)), and our prototypesystem (Fig. 12(b)). A discrete event simulation technique (e.g.,[6]) is employed to quantitatively analyze the performance of thescenarios. Two different simulation models were developed forthe abovementioned scenarios. The simulation software is fed withthe time durations of activities gathered from interviews with Con-cordia Facilities Management personnel and initial testing of thedeveloped prototype system. Table 6 shows the time durations ofactivities in each scenario. The prototype system could potentiallyimprove two main processes that are shared among the two sce-narios (i.e., look up and view history and record inspection results).In addition, the process of exporting the data to the BIM in the IT-assisted method is enhanced by direct update of the BIM using theproposed prototype system.

WebCyclone [13] is used to perform the simulation assuminguniform distributions of the time durations of activities and itwas run for 500 cycles to generate the results. Table 7 shows theaverage estimated inspection times of both scenarios and theirstandard deviations as the output of the simulation. The prototypesystem shows 9% decrease in the process time and 8% decrease inprocess time variation.

6.3. Discussion

Although several CMMS applications exist to facilitate theinspection and maintenance of assets, they are not utilizing a cen-tral BIM database to store and retrieve assets’ data. The data is usu-ally stored in a separate database and the relationship between theRFID tags and assets are maintained through a separate data table.However, the developed prototype system uses the BIM databaseas a central data storage. It uses IFC definitions to identify the rela-tionships between assets and RFID tags. It also uses IFC standard tostore data on RFID tags. This would maintain one data storage stan-dard. Additionally, data synchronization is more easily achieved as

52 A. Motamedi et al. / Advanced Engineering Informatics 30 (2016) 39–53

there is only one central database. Based on our proposed method,the subset of IFC data to be stored on the tag is automatically cre-ated from the original IFC file and copied to the tags memory.Hence, the IFC file automatically contains the most recent data tobe accessed by all stakeholders who have access permissions.

The case study and the prototype system demonstrate the pos-sibility of allowing the users to access the RFID tag data related to aspecific asset together with the IFC data of the same asset. Thisinformation helps the users perform inspection and maintenanceactivities more efficiently by having broader range of data in handwhile performing the task. Additionally, the prototype system pro-vides a single data entry stage which reduces the data entry time.The prototype system is evaluated using the metric of the processexecution time by comparing the time spent for IT-assisted inspec-tion with time spent using the prototype system. The simulationresults showed that using the prototype system shortens the pro-cess duration. Yet, the improvement on the data quality is anothermain benefit of the approach that cannot be easily quantified. Theproposed method for defining RFID components as model elementsand defining logical and physical relationships in a BIM willenhance maintenance data management efforts by providing newadded values, such as centralized management, interoperability,access to a wider range of data, visualization, and up-to-date dataaccess. Moreover, having RFID tags as model elements togetherwith the defined relationships in the BIM database can supportnumerous other applications in other areas such as emergencymanagement, location based services, and indoor localization.

7. Conclusions and future work

The paper elaborated on the needs, motivations and benefits ofincluding standard definitions of RFID systems in the BIM. A modelbased on requirements’ gathering is developed in order to identifyand define the entities, property sets, ports, and relationships forRFID system components. New IFC entities, property sets and portsare defined for the RFID system. In the case study, various IFC-compatible tools are utilized to test the proposed extension ofIFC. Furthermore, the modularity and extensibility of the modelare taken into account to accommodate the possible future typesand properties of RFID systems. A prototype application is devel-oped to demonstrate the benefits of the proposed method in facil-itating the inspection and maintenance tasks of assets.

The conclusions of this paper are as follows: (1) The proposedBIM extension provided definitions for new entities, relationships,and property sets for the IFC. (2) Using definitions of RFID tagstogether with their spatial and logical relationships to other ele-ments, the subset of BIM data that is required to be copied on RFIDtags can be easily selected. (3) The proposed RFID extension tookfull advantage of reusing available entities, relationships, and prop-erty sets in IFC. Only the necessary and unavailable entities areproposed to be added. (4) The case study showed that althoughthe current BIM tools have some limitations in utilizing existingIFC entities, the scenarios for interrelating BIM and RFID data canbe done by manually editing the EXPRESS code. (5) The prototypesoftware application demonstrated the potential of the proposedapproach to facilitate data management for inspection and mainte-nance of assets. The future research includes further testing of theproposed method in other practical applications. Moreover, thesame methodology can be used to add the definitions of othertypes of sensors to BIM.

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