APPLICATION AND EXTENSION OF THE IFC STANDARD IN CONSTRUCTION COST ESTIMATING FOR TENDERING IN CHINA Ma Zhiliang1, Wei Zhenhua1, Song Wu2 and Lou Zhe1 1 Department of Civil Engineering, Tsinghua University, Beijing, China. Email:
[email protected] 2 School of the Built Environment, University of Salford, United Kingdom.
ABSTRACT The purpose of this paper is to investigate the possibilities and methods of applying the IFC (Industry Foundation Classes) standard, i.e. the mainstream standard of BIM (Building Information Modeling) data to the construction cost estimating for tendering in China. Through analyzing the existing standards and the IFC standard, the problems of using the IFC standard are identified and the solutions are explored. An information requirement model for construction cost estimating for tendering in China was established, which includes seven aspects of information entities. Then each aspect of the information was expressed by using the IFC standard to verify the completeness of the IFC standard and to establish the IFC based information model. As a conclusion, the IFC standard can be used to express the information for the construction cost estimating for tendering in China as a whole, but some extensions in the form of proxy elements and property sets are needed. The established information model can be applied to the development of construction cost estimating software. KEYWORDS Cost estimating, Building information model, Cost information model, The IFC standard. INTRODUCTION BIM (Building Information Modeling) technology has attracted more and more attention in AEC/FM (Architecture, Engineering and Construction/ Facility Management) field because it introduces a revolutionary technology comparable to CAD that emerged about two decades ago. BIM is designed to facilitate the information sharing among the stakeholders in different phases for better decision (NIBS 2009). As a major data standard for BIM, the IFC (Industry Foundation Classes) standard published by the IAI (International Alliance for Interoperability) plays a very important role in the process, since it is a standard for sharing data throughout the project lifecycle, globally, across disciplines and across technical applications in the AEC/FM industry (BuildingSMART 2009). The IFC standard is a complex data standard covering currently nine domains such as architecture, structure, HVAC, electric etc. It specifies the data structure based on 3D geometric model and object-oriented representation. More than 20 vendors of application software are supporting the IFC standard so far so that the data exchange among their relevant products can be realized automatically (IAI 2009). However, in spite of its complexity, the IFC standard can support only a limited number of use cases in AEC/FM industry and more developments are required when it is used for more use cases (Weise 2008). With regard to construction cost estimating, which is one of the critical activities for any construction project, the IFC standard has been applied in various use cases. Faraj et al. developed an IFC Web-based collaborative construction computer environment called WISPER (Web-based IFC Shared Project Environment), which built an IFC-based object-oriented database to help users realize the network integration and sharing of the design, budget, schedule and other information in construction projects (Faraj 2002). Fu et al. applied the IFC standard in the life-cycle cost assessment. The prototyping system could automatically extract cost estimating data from the design results of IFC files, and then transfers the data to a pre-existing component of life-cycle cost assessment (Fu 2004). Sheryl et al. developed an IFC-based cost estimating system. By using the design results of IFC files as input, the system could automatically apply corresponding quota to accomplish cost estimating according to the component geometries and properties (Sheryl 2003). Tanyer et al. developed a tool for 4D-
model schedule simulation. The tool allowed users to build a 4D-model of the project and provides cost estimating function by using the design results of IFC files as input (Tanyer 2005). Yabuki et al. applied the IFC standard in the cost estimating of earthwork and accomplished the cost estimating function according to the 4D model (Nobuyoshi 2005). However, those research works have not addressed the application of the IFC standard in the construction cost estimating for tendering subject to a certain local standard, as well as the extension of the IFC standard upon needs. The insufficiency of the IFC standard for representing information may not cause major problems in the application areas that are not strongly associated with standards, but it may do for those that have a close link with local standards, because many standards, such as the cost estimating for tendering, are different from country to country and the IFC standard is still not adequate enough to cover all countries. Under such circumstances, one may extract the applicable data from the IFC file and supplement the additional data in the application software as in the existing research works reviewed above. A better approach is to extend the IFC standard to accommodate the standards of each country so that all the relevant local information can be shared efficiently by different application software through an IFC file. This paper explores the application and extension of the IFC standard in construction cost estimating for tendering for Chinese standards. The information required by the Chinese standards for construction cost estimating for tendering is analyzed to establish an information requirement model. Then the information model is described by using the entities in the IFC standard, in which the extension of the IFC standard is proposed in order to represent all the information in the information requirement model. It not only lays a sound foundation for developing the BIM-based application software for construction cost estimating for tendering subject to Chinese standards, but also demonstrates a feasible approach to extending the IFC standard to satisfy the requirements for different countries. INFORMATION REQUIREMENT MODEL In China, mainly two methods are being used for construction cost estimating for tendering. One is called the quota method and the other is called the Bill-of-Quantity method (the BQ method for short hereafter). The quota method was established for the planned economy by learning from the former Soviet Union, and the cost of project obtained based on this method is actually the cost decided by the government. With the development of the market economy, the BQ method was established and it allows the cost of the project to be determined according to the technical level of enterprise and the market price. Now both methods are used in the practice in China, although only one method can be adopted in a project and the latter method is becoming more popular. When the quota method is used, the tender and bidder have to do the following works. First, divide the project into cost-items based on the division-items information provided by the national or local quota as specified in the related standards (for the national quota refer to (MOHURD 1995); for the local quota refer to (BMCC 2001) as an example). Second, calculate the quantity of each cost-item based on the calculation rules and unit as specified in the related standards. Third, calculate the consumption of the construction resource of each cost-item based on the national or local quota. Fourth, according to the prices of the labor, material, equipment from the quota and the calculation rules, calculate the cost value of each cost-item. Then, all the cost-items are summarized to obtain the total cost of the project. It is worth emphasizing that the whole process based on the quota method has to be gone through by both of the tender and the bidder and the cost of project provided by the tender and the bidder is based on the same standards and quota. In case of the BQ method, the tender firstly divides the project into BQ-items, which can also be called costitems based on the BQ standard (MOHURD 2008). Second, the tender calculates the quantity of the cost-items. Third, the bidder calculates the consumption of the construction resources for each cost-item based on the national, local quota or its own internal quota. Fourth, based on the prices of labor, material, equipment in the market and the calculation rules of the overheads in the standard, calculate the cost value of each cost-item. Then, all the cost-items are summarized to obtain the total cost of the project. Thus, it is clear that both methods follow the same principle: First, divide the project into cost-items. Second, calculate the quantity of the cost-items based on the calculation rules. Third, calculate the consumption of the construction resources according to the quota. Finally, calculate the cost value of each cost-item and then summarize them to determine the total construction cost. In addition, the quantity of the cost-items for the BQ method can be computed from that for the quota method, because the latter method is the base and it is more detailed. The major differences between the two methods include the fineness of the cost-items division, and the calculation rules for computing the total construction cost, which are specified in the related standard.
Based on the two methods, the information requirement model for the construction cost estimating for tendering in China is established as shown in Figure 1. As it is shown in the figure, seven aspects of information entities are included in the model, i.e. product information, division-items project information, quantity information, resource information, price information, schedule information and cost-items information, where the schedule information is included to facilitate the cost information for tendering to be used in project management of later stage. Among them, the product information represents the result of design, which contains building and surroundings components; the division-items project information represents the categories that the components belong to according to the standards; the quantity information is obtained by calculating based on the product information and the calculation rules; the resource information, i.e. the information for the consumption of labor, materials and machines in construction projects, is obtained by using quantity information and the quota in the standards; and the price information usually comes from the market or the local quota; the schedule information is established by the contractor and is used to obtain the construction cost estimating with time; and the costitems information corresponds to the various costs including the cost of the components, and constitutes the total cost of the project. As a part of the information requirement model, standards include the division-items standard (the quota standard or the BQ standard) and calculation rules. The division-items standard is used to determine the divisionitems project information of the project and the calculation rules is used to calculate the quantity of the cost-item and the unit. Quota indicates the amount of construction resources that are consumed by each unit cost-item and is used to calculate the consumption of the construction resources. Through the above explanation, it is clear that the information requirement model applies to both methods for construction cost estimating in China. Schedule information
Product information
Logical relationship Project Division - items project division information
Cost-items information
Mathematical relationship
Standards Calculate Quantity
Apply quota
Quota
Market
Quantity information
Resource information Price information Summarize cost
Legend Data reference flow Relation Selected relationship
Figure 1 Information requirement model for construction cost estimating for tendering THE IFC STANDARD AT A GLANCE Currently, the official version of the IFC standard is IFC2x3 final version, which covers nine domains in building construction, including HVAC, electrical, architecture, construction management, facility management, structure component, structure analysis, tube & fireproofing and construction controlling (BuildingSMART 2007). In this paper, the discussion on the IFC standard will be based on this version. The IFC standard owns a hierarchical and modular framework, which is divided into four bottom-up layers, i.e. resource layer, core layer, interoperability layer and domain layer, and each layer consists of a number of modules which further contains various entities, types, enumerations, rules and functions. Among them, the entity represents the abstraction of objects which have the same properties, and is the information agent to describe the information of building and surroundings components when the IFC standard is used. Since the types, enumeration, rule and function are defined to express the properties of entities and to provide additional constraints and methods for the properties, an entity is on a higher level than them.
There are totally 653 entities in the IFC2x3 final version. It is obviously a difficult work to make full use of them when developing BIM-based application software, so it is necessary to establish an information model based on the entities to facilitate the information sharing among the related application software at first. It deserves to add that the IFC standard represents the entities by using an object-oriented approach. Thus the entities correspond to the objects, and the inheritance among entities applies as well. It must be pointed out that utilizing the inheritance can reduce the work of redefining the content inherited from the super entity. Correspondingly, description of both the entities and their inheritance relationship are required in the information model to give a full picture of the use of the related entities. In the following discussion, the EXPRESS-G will be used to describe the information model, as many authors do in their relevant papers. Three mechanisms are provided to extend the IFC standard, i.e. defining new entities or types, using proxy elements, and using the property sets or types (Weise 2008). Among them, defining new entities or types is the best way to extend IFC standard among the three alternatives, because the new entities and types can then be used in the same way as the existing ones, while in the case of the other two alternatives, additional implementation agreements about the definition of the property sets and proxy elements are required if they are used to share data with other application software. However, it normally takes at least two years to define new entities by the IAI (Weise 2008), and the other two alternatives may be more practical to meet specific local requirements, for example, the Chinese requirement for construction cost estimating for tendering. EXPRESSION OF BUILDING PRODUCTS BY USING THE IFC STANDARD As stated above, the quota method is the traditional method of construction cost estimating for tendering in China, while the BQ method has been adopted only in recent years. In fact, the BQ method still follows the divisional structure of the building and surroundings components as adopted in the quota method, but only at the higher level. It means that as long as the information required by the quota method is available, the information for the BQ method can be generated automatically. Therefore, the following discussion on product information will be based on the information required by the quota method. According to the quota method, building products are divided into four groups in the research, i.e. the design products, the temporary products, the decoration/accessory products and other products as shown in Table 1, in order to establish the relationship with the IFC standard.
No.
Group
1
Design products
2
Temporary products Decoration/accessory products Other products
3 4
Table 1 Division of building products Building products contained Pile, wall, column, foundation, beam, slab, steel bar, stair, railing, handrail, roof truss, door, window, steel part (grid, bracket, truss, etc.), miniature Earthwork, rockwork, scaffold, framework Cushion layer, leveling layer, surface layer, roof, waterproof layer, anticorrosion layer, heat preservation and insulation layer, plaster, paint, coating Chimney, water tower, masonry stove, ditch, pool groove, reservoir, silo
In the IFC standard, building products are defined by using the entity IfcProduct which represents an object with description of geometric representation and local placement. Obviously, the entity IfcBuildingElement that inherits from IfcProduct can be used to describe the components in the group of design products and that in the group of decoration/accessory products. Since IfcBuildingElement is an abstract entity, its derived entities are actually used to describe various kinds of specific building and surroundings components. As a result of our research, a correspondence between components in the group of design products and that in the group of decoration/accessory products and the entities in the IFC standard (called IFC entities for short) is established, as shown in Table 2. Detailed analysis reveals that each component in the group of design products and that in the group of decoration/accessory products can be exactly described with the corresponding entity in the IFC standard.
No. 1 2 3 4 5 6 7
Table 2 Correspondence between building products and IFC entities (to be continued) IFC entity Building products components IfcBeam Beam IfcColumn Column IfcWall Wall IfcPile Pile IfcRailing Railing, handrail IfcRamp Ramp IfcStair Stair
No. 8 9 10 11 12 13 14 15 16 17 18
Table 2 Correspondence between building products and IFC entities (to continue) IFC entity Building products components IfcFooting Foundation IfcMember Roof truss, steel part IfcSlab Slab IfcWindow Window IfcDoor Door IfcReinforcingElement Steel bar IfcPlate Steel platform IfcRampFlight Ramp flight IfcStairFlight Stair flight IfcBuildingElementProxy Coping, eaves, keel, etc. IfcCovering Cushion layer, leveling layer, etc.
The components contained in the group of design products are physical building components which the components in the group of decoration/accessory attach to and they may also have openings as well in some cases. In order to express their relationship, for example, the relationship between a wall and its decoration or accessory such as the protective layer, some relationship entities in the IFC standard are necessary. As an example, Figure 2 shows the information model which describes the relationship between the physical wall and its decoration, accessory and openings by using IFC entities. In the IFC standard, the entity IfcCovering is used to describe the decoration or accessory products, and the entity IfcRelCoversBldgElements is used to describe the attachment relationship between IfcCovering and physical building components (here it is a wall). Meanwhile, the entity IfcOpeningElement is used to describe the openings, and the entity IfcRelVoidsElement is used to describe the relationship between openings and physical building components, while the entity IfcRelFillsElement is used to describe the relationship between filling elements and openings. IfcRelVoidsElement
(ABS) IfcProduct
IfcRelCoversBldgElements RelatingBuildingElement (INV) HasCoverings S[0:?] RelatedCoverings S[1:?] (INV) HasCoverings S[0:1] IfcCovering
1 (ABS) *IfcElement 1
(ABS) IfcBuildingElement 1 *IfcWall
RelatingBuildingElement (INV) HasOpenings S[0:?]
RelatedOpeningElement (INV) VoidsElements
(ABS) IfcFeatureElementSubtraction 1 IfcOpeningElement RelatingOpeningElement (INV) HasFillings S[0:?] IfcRelFillsElement RelatedBuildingElement (INV) FillsVoids S[0:1]
Legend Name
IFC entity
Type
Basic data type
Type
Defined data type
Enum Select
Enum type Select type Common relationship Optional relationship Inheritence
IfcDoor
Figure 2 Information model for the relationship between the physical wall and its decoration, accessory and openings For the temporary products and other products, since no specific IFC entity is available to describe them, the entity IfcProxy can be used. Due to the limit of space, it is not included in this paper. EXPRESSION AND EXTENSION OF THE DIVISION-ITEMS PROJECT INFORMATION BY USING THE IFC STANDARD According to the standards for construction cost estimating for tendering in China, estimators need to divide the project into cost-items firstly based on the division-items project information, i.e. the properties of different kinds of components, such as construction method, construction technology, geometric feature, material, equipment, job category and so on. Take wall for example, it can be classified into an in-situ concrete wall, a brick wall or a stone wall according to its material and construction technology. Furthermore, the in-situ concrete wall may be classified into straight wall, curved wall or other kinds of walls according to its cross section and construction method. In the IFC standard, the entity IfcBulidingElementType and its subtypes are used to describe the type of components. However, the pre-defined type classification in the IFC entities is too simple to cover the divisionitems project information which has been listed in Chinese standard for construction cost estimating for tendering. Therefore, it is necessary to use the entity IfcPropertySet, which is a container class that holds
dynamically extensible properties as a property set. The contained properties in the property set are described by using the entity IfcProperty which is the abstract supertype of the entities IfcSimpleProperty and IfcComplexProperty. IfcSimpleProperty is used to define a single property object and its subtypes can be used to define various properties. IfcComplexProperty is used to define complex properties that may logically contain other properties, and its logical relationship with the contained properties is described by using the entity IfcPropertyDependencyRelationship, as shown in Figure 3. (ABS) IfcSimpleProperty
(ABS) IfcPropertySetDefinition 1 1
IfcPropertySingleValue
1
*IfcPropertyEnumeratedValue
HasProperties S[1:?] (INV) PartOfComplex S[0:1]
HasProperties S[1:?] (ABS) IfcProperty
*IfcPropertySet
Name STRING
Description STRING
*IfcPropertyBoundedValue
UsageName
1 *IfcComplexProperty
DependingProperty (INV) PropertyForDependance S[0:?]
STRING
DependantProperty (INV) PropertyDependsOn S[0:?]
IfcPropertyDependencyRelationship
*IfcPropertyTableValue IfcPropertyReferenceValue *IfcPropertyListValue
Figure 3 Information model for expressing dynamically extensible properties Based on the above discussion, the property sets are established in this research corresponding to the standard National Unified Basic Quota of Construction Works (MOHURD 1995), which is the basic standard of cost estimating for the quota method in China, because the local standards are supposed to be in consistent with the standard. The standard includes the rules for quantity calculation, the division-items, the units of measurement in the cost estimating, and the basis of preparing local valuation table of construction works (civil works) to estimate the construction cost. Totally, 104 property sets, were established in the research to cover the needs for representing information that is included in the standard. Considering that the standard has been used in China for more than five decades, the property sets that were established in this research could satisfy the information needs of various standards for construction cost estimating for tendering in China in most cases. As an example of a property set, Table 3 demonstrates the property set definition of the in-situ concrete wall. Table 4 demonstrates the contained properties and the valuation rules of the property set of the in-situ concrete wall.
Property set Name Applicable Entities Applicable Type Value Definition
Name
Wall type
Concrete type Concrete grade
Table 3 A typical property set definition Pset_in-situ concrete wall IfcWall, IfcStandardWall In-situ concrete wall Definition from the cost estimating standard in China: Property set to capture the division-items project information of the wall which is in-situ concrete wall. The specific value of its property can decide a cost-item. Only all the property value in the property set can be used to divide the wall to the same cost-item. Table 4 Property definition for a typical property set Property Type Data Type PEnum_WallType: Straight wall, elevator shaft IfcPropertyEnumeratedValue straight wall, curved wall, large steel framework wall, sliding framework wall PEnum_ConcreteType: IfcPropertyEnumeratedValue Rubble concrete, concrete IfcPropertyEnumeratedValue
PEnum_ConcreteGrade: C10, C15, C20, etc.
Definition Specify the type of wall. Specify the type of concrete. Specify the type of concrete grade.
PEnum_FrameWorkType: Combined steel framework, Framework Specify the type IfcPropertyEnumeratedValue composite wood framework, type of framework. Framework wood framework, large steel framework, sliding framework Bracing PEnum_FrameWorkType: Specify the type IfcPropertyEnumeratedValue type Steel bracing, wood bracing of bracing. Note. The Framework is a complex property composited by two simple properties which are framework type and bracing type.
It must be pointed out that the definition of the established property sets is not supported by current version of the IFC standard. As a result, the information corresponding to the established property sets can only be read but its semantics cannot be automatically recognized in the current IFC-supported application software. In fact, this problem also exists when the entity IfcProxy is used to express the components of the temporary products and other products. To solve this problem, a proposal for adding these property sets into the IFC standard needs to be submitted to the IAI and the procedures for extending the IFC standard needs to be gone through. This paper is just the first step of the effort. It is expected to establish a standard for property sets for the construction phase in China. It is hoped that the IAI will notice the practice for China through this paper and extend the IFC standard in the aspect of construction cost estimating by considering the requirement in major countries, which can be realized by following the approach of this paper. EXPRESSION OF THE SCHEDULE INFORMATION BY USING THE IFC STANDARD In the IFC standard, the entity IfcProcess (an abstract IFC entity), its subtypes and corresponding relational IFC entities are used to describe the schedule of projects. Take the in-situ concrete wall for example, the specific construction tasks may include the transportation of steel bar, the assembling and installation of steel bar, the manufacture and transportation of framework, the installation and removing of framework, the transportation of concrete, the casting and curing of concrete etc. The entity IfcTask, which is a subtype of IfcProcess, is used to describe these tasks, while the entity IfcRelSequence is used to describe the sequence of these tasks. The entity IfcWorkSchedule which is used in the schedule control, establishes a one-to-many relationship with IfcTask by IfcRelAssignsTasks. Figure 4 shows the schedule information model. RelatingProcess (INV) IsPredecessorTo S[0:?] (ABS) *IfcControl
TaskId
IfcWorkSchedule
Status STRING
RelatedProcess (INV) IsSuccessorFrom S[0:?]
1
STRING
(ABS) IfcProcess
*IfcRelSequence
1
WorkMethod STRING
RelatedObjects (INV) HasAssignments S[1:?]
RelatingControl (INV) Controls S[0:?]
*IfcRelAssignsTasks
IsMilestone
*IfcTask
BOOLEAN Priority
TimeForTask
INTEGER IfcScheduleTimeControl
Figure 4 Schedule information model EXPRESSION OF THE OTHER INFORMATION BY USING THE IFC STANDARD As discussed above, the quantity information, the cost-items information, the resource information and the price information are directly used in the cost estimating. Especially, the price information, which comes from the market or has been included in some local quota standards, has no need for establishing an information model. In the IFC standard, the entity IfcElementQuantity can be used to describe the quantity information of the physical building components which will be used as the quantity of cost-items, including the description of various parameters and all metrics of the items in National Unified Basic Quota of Construction Works. Figure 5 shows the quantity information model. IfcQuantityLength
MethodOfMeasurement
STRING
(ABS) IfcPhysicalSimpleQuantity
IfcElementQuantity
STRING
Quantities S[1:?] Name (ABS) IfcPhysicalQuantity Description
HasQuantities (INV) PartOfComplex S[0:1]
IfcQuantityArea Unit
1
IfcNamedUnit
1 Quality
IfcQuantityVolume
IfcQuantityCount
Discrimination
IfcPhysicalComplexQuantity
1
STRING
IfcQuantityWeight
Usage IfcQuantityTime
Figure 5 Quantity information model As shown in Figure 6, the entity IfcCostItem is used to describe the cost-items in the IFC standard, while the entity IfcRelNests is used to describe the logical self-contained relationship which expresses the relationship that
a cost-item contains other cost-items. It must be pointed out that the relationship entities in the IFC standard could be used to describe any kind of logical relationship. The entity IfcRelAssociatesAppliedValue is used to describe the association between the cost-items and resource with the cost values, while the entity IfcAppliedValueRelationship is used to describe the algorithmic association between the cost values, such as the direct construction cost equals the sum of the labor cost, the material cost and the mechanic cost. Therefore, by providing the method of describing the algorithmic association, any mathematical model between the cost-items which could satisfy various valuation methods can be established. Similarly, the entity IfcCostSchedule is used to describe the one-to-many relationship between the schedule and the cost-items which is used in the cost control through the entity IfcRelSchedulesCostItems. IfcRelSchedulesCostItems
RelatingControl (INV) Controls S[0:?] SubmittedBy IfcCostSchedule
RelatedObjects S[1:?] (INV) HasAssignments S[0:?]
PreparedBy
IfcRelNests RelatingObject (INV) IsDecomposedBy S[0:?]
IfcCostItem Status
TargetUsers S[1:?]
RelatedObjects S[1:?] (INV) HasAssociations S[0:?]
IfcActorSelect
RelatingAppliedValue (ABS) IfcAppliedValue
IfcRelAssociatesAppliedValue SubmittedOn ComponentOfTotal (INV) ValueOfComponents S[0:?]
UpdateDate ID
IfcDateTimeSelect PredefinedType IfcCostScheduleTypeEnum
RelatedObjects S[1:?] (INV) Decomposes S[0:1]
IfcAppliedValueRelationship STRING
1 IfcCostValue
Components S[1:?] (INV) IsComponentIn S[0:?]
Figure 6 Cost-items information model In the IFC standard, the entity IfcResource and its subtype IfcConstructionResource is used to describe the resource information, which includes the equipments resource, the labor resource, the personal resource, the subcontractors resource, the products resource and the material resource, as shown in Figure 7. When the schedule information is considered, the component should have a one-to-many relationship with the resources. Otherwise, the resource information should have a certain relationship with the schedule information in order to clearly describe the usage of the resource in the construction progress. (ABS) IfcResource
IfcSubContractResource IfcConstructionProductResource IfcConstructionMaterialResource
1
1 (ABS) IfcConstructionResource
IfcConstructionEquipmentResource 1
IfcLaborResource IfcCrewResource
Figure 7 The information model for the composition of the resource THE INFORMATION MODEL FOR COST ESTIMATING FOR TENDERING BY USING THE IFC STANDARD According to the above content, the information model for construction cost estimating for tendering based on the IFC standard is established as shown in Figure 8. In the model, the one-to-many relationship between IfcProcess and IfcProduct is established through the entity IfcRelAssignsToProcess in order to describe the relationship between the construction tasks and products so to ; the entity IfcRelAssignsToControl is used to associate IfcResource with IfcCostItem in order to describe the resource consumption; the entity IfcRelDefinesByProperties is used to associate the entity IfcPropertySet with building products and the property set of the division-items project information is used to describe the properties of specific type product described by the content ObjectType in IfcObject in order to describe the division-items project information; the entity IfcRelDefinesByProperties is also used to associate IfcElementQuantity with costitems in order to describe the quantity information; the entity IfcRelAssociatesAppliedValue is used to associate IfcApplivedValue with resource and cost-items in order to describe the price information; the entity IfcRelAssignsToControl is used to associate IfcCostItem with IfcProduct in order to describe the relationship between building products and the cost-items, and then a whole description of the project is given. Furthermore, the entity IfcRelAssingsTasks is used to associate IfcWorkSchedule with IfcTask in order to describe the cost
distribution of the project and the entity IfcRelSchedulesCostItems is used to associate IfcCostSchedule with IfcCostItem in order to realize the cost control and management. The information model can be used for developing the application software for construction cost estimating in two folds. One is to be referred to organize the data structure for the application software, the other is to be referred when inputting the data from design result and outputting the result of cost estimating to the IFC file. Detailed description of the methods for these is out of the scope of the paper. Resource information
RelatingAppliedValue (INV)ValuesReferenced
RelatedObjects S[1:?] (INV)HasAssignments S[1:?]
(ABS) IfcResource
Price information
IfcRelAssociatesAppliedValue
IfcAppliedValue 1
RelatedObjects S[1:?] (INV)HasAssignments S[1:?] RelatedObjects S[1:?] (INV)HasAssignments S[1:?]
RelatingControls (INV)Controls S[0:?]
*IfcRelAssignsToControl
Cost-items information RelatedObjects S[1:?] (INV) HasAssignments S[0:?]
IfcRelSchedulesCostItems
IfcCostItem
Schedule information
RelatingControl (INV) Controls S[0:?]
RelatingControl (INV) Controls S[0:?]
RelatedObjects (INV) HasAssignments S[1:?]
*IfcRelAssignsToProcess
IfcCostValue
IfcRelAssignsToControl
RelatedObjects S[1:?] (INV) IsDefinedBy S[0:?]
IfcCostSchedule
RelatedObjects (INV) HasAssignments S[1:?] RelatingProcess (INV) OperatesOn S[0:?]
(ABS) IfcProcess 1
*IfcTask RelatedObjects (INV) HasAssignments S[1:?]
*IfcRelAssignsTasks RelatingControl (INV) Controls S[0:?]
IfcWorkSchedule
Product informaion (ABS) IfcProduct 1
(ABS) *IfcElement
IfcRelDefinesByProperties
(ABS) IfcPropertySetDefinition
1
1 1
(ABS) IfcBuildingElement 1 。。。
RelatingPropertyDefinition (INV) PropertyDefinitionOf S[0:1]
RelatedObjects S[1:?] (INV) IsDefinedBy S[0:?]
Division-items information *IfcPropertySet
1
Quantity information IfcElementQuantity
Figure 8 Information model for construction cost estimating for tendering Currently, a BIM-based application software is being developed by the authors and the feasibility of the information model has been verified. CONCLUSION This paper has developed the information requirement model for construction cost estimating for tendering in China, and discussed the application and extension of the IFC standard for representing the model, and finally the information model for cost estimating for tendering is established. The findings of this study are concluded as follows: (1) The information requirement for the construction cost estimating for tendering in China can be summarized into seven aspects: the building products information, the division-items project information, the cost-items information, the schedule information, the quantity information, the resource information and the price information. (2) The IFC standard can be used to describe the above seven aspects of information as a whole. However, the current version of the IFC standard could not yet directly support the expression of the construction temporary products, other products and the division-items project information which is required in the standards of the cost estimating in China, and therefore, it needs to be extended in order to support the direct data exchange with relevant application software when used in China. (3) The information model for cost estimating established in this paper is based on the IFC standard. It realized the logical association among products, schedule, resource, cost-items and property sets. It also provided the division-item property sets, associations, with cost-items and the mathematical relationship. Therefore, this information model can be applied in various methods of the construction cost estimating for tendering in China.
(4) The research not only lays a sound foundation for developing the BIM-based application software for construction cost estimating for tendering for Chinese standards, but also shows a feasible approach to extending the IFC standard to satisfy the requirements for different countries. ACKNOWLEDGEMENT This study is supported by the National Technological Support Program for the 11th-Five-Year Plan of China (No. 2007BAF23B02). REFERENCES Beijing Municipal Commission of Housing and Urban-rural Development (BMCC). (2001). Valuation Quota of Construction Works in Beijing (in Chinese). BuildingSMART. (2007). IFC2x Edition 3 TC1, (Apr. 7, 2010). BuildingSMART. (2009). Model - Industry Foundation Classes, (Apr. 7, 2010). Faraj I, Alshawi M, Aouad G, et al. (2002). “An industry foundation classes Web-based collaborative construction computer environment: WISPER”, Automation in Construction, 10(1), 79-99. Fu C., Ghassan A., Amanda M.P., et al. (2004). “IFC implementation in lifecycle costing”, Journal of Harbin Institute of Technology, 11(4), 437-441. Institute of Building Sciences (NIBS). (2009). National BIM Standard Version 1 - Part 1: Overview, Principles, and Methodologies, (Apr. 7, 2010). International Alliance for Interoperability (IAI). (2009). Industry Foundation Classes, (Apr. 7, 2010). National Ministry of Housing and Urban-Rural Development of China (MOHURD). (1995). National Unified Basic Quota of Construction Works (GJD-101-95, in Chinese). National Ministry of Housing and Urban-Rural Development of China (MOHURD). (2008). Code of Valuation With Bill Quantity of Construction Works (GB50500-2008, in Chinese). Nobuyoshi Y., Tomoaki S.. (2005). “A Management System for cut and fill earthworks based on 4D CAD and EVMS”, Proceedings of the 2005 ASCE International Conference on Computing in Civil Engineering, Cancun, Mexico, July, 1619-1626. Sheryl S.F., Martin F., John K., et al. (2003). “A generic feature-driven activity-based cost estimation process”, Advanced Engineering Informatics, 17(1), 23-39. Tanyer A.M., Aouad G.. (2005). “Moving beyond the fourth dimension with an IFC-based single project database”, Automation in Construction, 14(1), 15-32. Weise M, Liebich T, Wix J. (2008). “Integrating use case definitions for IFC developments”, Proceedings of 7th European Conference on Product and Process Modeling, Zarli A, Scherer R, ed., Sophia Antipolis, France, September, 637-645.
