McKinney and Fischer. 4D Analysis of Temporary Support Kathleen McKinney 1 and Martin Fischer 2 ABSTRACT

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1 4D Analysis of Temporary Support Kathleen McKinney 1 and Martin Fischer 2 ABSTRACT 4D s (3D-CAD + time) are currently used as a communication tool to visualize the construction process. This virtual construction provides construction planners with the opportunity to assess the constructability of a proposed design and construction plan. With a 4D, planners can identify possible temporary support problems which may exist due to improper construction sequencing of building components. Such problems may cause construction delays, re-design, or damage to the existing structure. This paper discusses how 4D s can be used to ensure temporary support of building components during installation. We describe an information that provides the reasoning mechanisms to support 4D analysis of temporary support. 1. Introduction Construction managers rely on experience and extensive planning to prevent costly field errors. Managers must conceptually visualize how the construction process will unfold. 4D-CAD is a useful tool to help visualize the construction process and prevent potential problems in the field [Collier and Fischer 1995]. Visualization, however, does not provide project managers with information to compute cost, predict productivity, identify damage or temporary support problems issues critical to evaluate the constructability of a proposed construction. For example, during the construction of a roof on a local Bay Area building (Fig. 1-A), workers discovered the could not be installed since the design did not specify a connection detail. No support for the was available. The roof and sheet-metal subcontractors were forced to stop construction and propose a solution to resume roof construction based on the following issues: what kind of connection detail had to be added a single c-channel to support and roof tiles or a two piece c-channel who would install the connection detail roofer or sheet-metal contractor when would the new connection detail be installed before or after the roof tiles or after the roof tiles This paper describes a 4D information supporting computer-based 4D analysis to evaluate the availability and adequacy of support for problems such as these. In other words, when used in conjunction with a 4D tool, this information supports analysis of a proposed 4D and, e.g., allows comparisons between two construction sequences. The 4D information will help determine which offers better constructability with respect to temporary support needed during installation. We begin by describing 4D concepts relevant to this constructability analysis. We discuss ing issues, reasoning mechanisms, and future research related to the creation and use of 4D information s. 1 Graduate Research Assistant, Department of Civil Engineering, Stanford University, Stanford, CA Assistant Professor, Department of Civil Engineering, Stanford University, Stanford, CA Page 1

2 3D building B 4D GRAPHIC CONTENT input to 4D for scenario 1 3D 3D graphic entity A elaborates into non-explicit associations construction abstraction of 3D building information insulation water shield tile activity generation of zone components ROOF ZONE A C zone components ROOF ZONE B ROOF ZONE C transforms into 4D SYMBOLIC CONTENT project: scenario 1 'part-of' related to 4D product component 4D process component building components wall activities roof activities 4D Process Model walls roofs 4D Product Model install install install soft insulation install hard insulation install install tiles soft insulation hard insulation tile zone A zone B tiles zone A tiles zone B install metal deck zone A install metal deck zone B install tiles zone A install tiles zone B zones wall zones roof zones zone roof A zone roof B zone roof C Figure 1: Parts of a 4D Model: Graphic and Symbolic Content 2. What is 4D Analysis? 4D analysis requires reasoning about the symbolic 4D content(fig. 1) of a 4D. A 4D contains associations between a graphic view of a building and the view of the construction of that building [McKinney et al. 1996]. 4D content refers to the semantic description of a 4D s parts: 3D-CAD, construction, and time-space associations. There are two kinds of 4D content: 4D product components and 4D process components (Fig. 1). The 4D product components represent graphic entities and components of a 3D- CAD building and the relationships between those components and other 4D components. 4D process components represent information for a construction Page 2

3 project and the relationships between those components and other 4D components. For a 4D analysis, 4D component definition involves identifying and describing the form and function of 4D content necessary to perform a specific analysis. 3. Modeling Issues There are three inputs to a 4D analysis: 1) 3D-CAD 2) and 3) 4D component library (Fig. 5). The 4D analysis requires the 3D to be transformed into a 4D product and the into a 4D process. The scope of our ing efforts does not include these transformations. We describe, however, the requirements for these transformations: 3.1 3D-CAD Model 4D Product Model A 3D-CAD typically consists of a set of graphic entities related to one another through an XYZ coordinate system. A 4D product contains the semantic relationship and semantic grouping of the CAD entities as necessary to relate to the construction. For example, the 3D consists of 3D surfaces and 3D solids defined by the XYZ location of the vertex points. A 4D product component is formed by assigning or deriving a semantic description to a graphic entity or entities, such as roof and wall. Additionally, definition of the 4D product component in terms of geometric and relational attributes is necessary for performing a 4D analysis. The relational attributes include traditional relationships between 3D product components, such as supported-by [Darwiche et al. 1989] and connected-to. In addition, these attributes describe how building components relate to the construction, e.g., relating zones [Winstanley and Hoshi 1992] to 3D entities. The assignment or derivation of semantic descriptions and relationships is possible, yet not easily achievable. We have identified the following potential problems: 1) Inference of Part-Of Relationships Part-of ( decomposes-into ) [Nederveen and Tolman 1992] relationships describe parentchild component relations necessary for 4D analysis. For example, and tile components are part-of the roof (Fig. 1). Inferring this relationship, however, is not easy with current CAD tools. 2) Generation of Zone Components One current limitation to representation of 4D graphic content is the level of granularity of 3D-CAD entities. For example, the roof section circled in Fig. 1-A is one graphic entity. To realistically represent the construction process, the roof should be represented by several graphic entities. This would require building a very detailed 3D-CAD. However, if construction planners could identify zones representative of how the roof construction is planned, the roof graphic entity could automatically be split into those respective zones (Fig. 1-C) without requiring extensive 3D-CAD re-ing. 3) Extraction of Geometric Entity Information Access to 3D-CAD geometry is critical for defining the form (geometric attributes) of a 4D product component. Extraction of coordinates of the roof section and surface boundary information is possible, but mapping this information to a meaningful measure, e.g. length of or angle of roof is still difficult. 4) Capture of Functional and Associative Relationships Although it is possible to derive supported-by functional relationships through geometric algorithms, the mechanism to capture a variety of functional and/or associative relationships from 3D-CAD s do not exist. To capture the associative relationship between a CAD entity and a activity essential to establishing the time-space link, extensive add-on Page 3

4 features to most CAD systems are required. Similarly, to derive adjacent-to or connectedto relationships, sophisticated algorithms or manual entry are required. 4D process 'activity' component 'activity' attribute early_start late_start early_finish late_finish duration lag list_of_predecessors list_of_successors related_graphic_component source of value CPM calculation/user input late_start? early_finish? CPM calculation user input lag? user input/4d input related_graphic? 3.2 Schedule Information Process Model 4D process components are represented by two types of components: and activity. The component contains a list of all the activities in the process. The also keeps track of information during the 4D simulation. The updates a list of completed activities, activities in progress, and the current simulation time. zone_activity related_zones? 4D activity components contain information for a late_finish CPM calculation Figure 2: 4D Process Activity Component Definition construction activity. This information can be acquired in several ways. For our 4D analysis we require the information as shown in Figure 2. Most of this information is contained in standard CPM s. The attribute related_graphic_component refers to the 3D-CAD component representing the building feature associated with the construction activity. For example, the install tiles zone A activity is associated with the 3D-CAD tiles zone A component in Figure 1. libray of 4D components user input/4d input standard library parts userdefined parts soft insulation hard insulation tile singe c-channel A. component definition for 'tile' component in library component_type types_of_suport_required component_support edge_support continuous_support structural_support supported_by adjacent_to tile_angle tile_thickness fastening_type fastening_method 'tile' check_edge_support? check_continuous_support? check_structural_support? check_component_support? edge_support_for? continuous_support_for? structural_support_for? find_supported_by? find_adjacent_to? find_angle? find_thickness 'nail' check_fastening_method? two part c-channel lower edge c-channel upper edge c-channel Figure 3: 4D Component Library and Example Component Definition The zone_activity attribute is valid for activities which are broken down into zone segments. For example, the install tiles activity is broken down into install tiles - zone A, install tiles - zone B, etc. This breakdown is generated when the construction zones are created. 3.3 Representing Building Components as 4D Component Library The 4D analysis is dependent upon a 4D component library. The library contains the template component definitions from which the 3D-CAD components inherit their definitions. For example, the library for our example contains a set of standard component types:, tile,, etc. (Fig. 3). Each component type is defined with a set of attributes or methods necessary to provide the information for the 4D analysis (Fig. 3-A). Page 4

5 In the context of this paper we are particularly interested in the support requirements of these components. 4. Types of Support Analyzed Using the case study we identified five kinds of support conditions that affect constructability. We describe each of these conditions and the information necessary to perform the specific support analysis. 1. structural support condition where a building component must have adequate structural support to carry its own dead weight. For example, the roof tiles are supported-by the and steel beams and so on. These components must provide adequate structural support. 2. continuous support condition where certain building components such as roof tiles or insulation requires continuous-support-for for its entire bottom surface 3. edge support condition where a building component requires support for a specific surface. For example, roof tiles may require edge-support-for its bottom edge if the roof is pitched steeply. 4. connection support condition where building components must be connected to another building component with a particular fastening method. The must be connected-to another building component with nails, bolts, etc. 5. adherence support condition where building component requires adherence-to another building component. For example, requires adherence-to a wall surface with a specific adherence method. For support analysis, every component must satisfy at least one or more of these support conditions. For example, insulation requires continuous support and connection support. It is not necessary to check insulation for structural or edge support. The types of support required attribute contains this knowledge for each component (Fig. 3-A). 5. Reasoning Mechanism for 4D Support Analysis Given the inputs as described in Section 3 and the requirements for checking support, we now describe the reasoning mechanisms that allow computer-based 4D support analysis of the roof construction (Fig. 4). The reasoning is invoked by the method Check_Project_Support? This method starts the clock for a 4D simulation of the construction for a project. The component tracks the time and waits for the completion of a 4D product component. For example, when the check_project_ support? is invoked for the roof construction, the first completed component is metal_deck_zone_a. The 4D support analysis then begins with the method check_component_support? performed on the metal_deck_zone_a component. This method looks at the attribute types_of_support_required to determine which support conditions will be checked. For the, the check_supported_by? and check_fastening_method? methods check_project_support? start_simulation? wait for 4D product component attribute construction_complete = 'complete' check_component_support? invokes method for each types_of_support_required potential types of support methods 1) check_structural_support 2) check_continuous_support 3) check_adherance_support 4) check_edge_support 5) check_connection_support 'yes' if support is satisfied Figure 4: Reasoning Mechanism 'no' and explanation if support is not satisfied Page 5

6 are performed. If these methods return a yes value then the component passes the support check. If either method returns a no value, then a message is returned explaining the failed support condition. However, the 4D simulation continues until the value of the construction_complete attribute is yes for all building components. 6. Test Case Example of 4D Support Analysis 3D-CAD scenario 2 & 3 A single c- channel insulation information scenario 2 B water shield insulation tiles water shield information scenario 3 C input single c-channel tiles control task mechanism single c-channel output component libraries planner build 4D CAD-based 4D tool support knowledge evaluate temporary support 4D support reasoning mechanism D. 'tile zone A' component definition (Scenario 2) component_type types_of_suport_requir ed component_support edge_support continuous_support structural_support supported_by adjacent_to tile_angle tile_thickness fastening_type fastening_method construction_complete 'tile' check_edge_support? check_continuous_support? check_structural_support? component_type types_of_suport_requir ed beam 11, beam component_support 13 tile zone connection_support B, tile zone C 33.5 supported_by.5 connected_to 'nail' scenario 1 (See Figure 1 for Input) fails connection support tile fails edge support scenario 2 fails connection support tiles fail edge support scenario 3 support satisfied E. ' zone A' component definition (Scenario 1) fastening_type fastening_method construction_complete '' check_connection_support??? 'nail' Figure 5: Input and Output for Three Test Case Scenarios Figure 5 shows the predicted output of a 4D analysis support for three different construction sequence scenarios and the resulting 4D product component definition for a tile and 4D product component. In scenario 2 the check_component_support? method returns values indicating temporary support failure for edge support. The check_edge_support? method first checks to see if the 4D product component, in this case tile requires edge support. Edge support is required for roof tiles when the pitch of the roof exceeds a certain value. If edge support is required then the check_edge_ support? method checks for other 4D product components which are related to this component with the edge-support-for relationship. In this scenario, the edge support condition is not satisfied. In scenario 1, temporary support for the fails since there is no component with the relation connected-to. However, in Scenario 3, this support condition is satisfied with the c-channel. In Scenario 2, even though the attribute connected-to contains the c-channel, the check_connected_to? method fails, because the c-channel is not yet installed. Page 6

7 7. Future Research We have defined requirements for the representation and reasoning of 4D content for 4D support analysis. Other research efforts at CIFE include 4D cost, productivity, and damage analysis. We are consolidating these s to support combined reasoning about 4D s from these and possibly other perspectives. As we build information s to support these analyses we will begin to address the ing issues presented in Section 3. One challenge lies with building an integrated system linking a 3D-CAD ing tool, a scheduling tool, and a knowledge-based reasoning tool. A second challenge is to provide an intuitive interface to build and interact with graphic and symbolic 4D s and their analysis results. We are most interested in research that addresses the generation of 4D content. Our next task is to determine the best methods and techniques for generating that information. This includes mechanisms to: generate part-of and other relationships that arise due to elaboration of construction s and collaboration between contractors, generate and adjust zones as required to display and reason about a construction in a way that reflects practice, and represent and capture associative relationships between 4D product components, such as connected-to, supported-by, and adjacent-to within a CAD-based 4D environment 8. Acknowledgments The authors gratefully acknowledge the support of the Center for Integrated Facility Engineering (CIFE) at Stanford University and its member companies. We would also like to acknowledge Burcu Akinci, Jennifer Kim, Sheryl Staub, Atul Khanzode and John Kunz who contributed to the development of the 4D information. 9. References Collier, Eric, and Fischer, Martin (1996). "Visual-Based Scheduling: 4D Modeling on the San Mateo County Health Center." Proceedings of the Third Congress on Computing in Civil Engineering, Jorge Vanegas and Paul Chinowsky (Eds.), ASCE, Anaheim, CA, June 17-19, 1996, Darwiche, A., Levitt, R. E., and Hayes-Roth, B. (1989). OARPLAN: Generating Project Plans by Reasoning about Objects, Actions and Resources. Artificial Intelligence for Engineering Design, Analysis and Manufacturing 2(3): p ) McKinney, Kathleen, Kim, Jennifer, Fischer, Martin, Howard, Craig (1996). "Interactive 4D-CAD." Proceedings of the Third Congress on Computing in Civil Engineering, Jorge Vanegas and Paul Chinowsky (Eds.), ASCE, Anaheim, CA, June 17-19, 1996, Nederveen, G. A. v. and F. P. Tolman (1992). Modelling multiple views on buildings. Automation in Construction 1(3): Winstanley, G. and K. Hoshi (1992). Model-Based Planning Utilizing Activity Aggregation Based on Zones. CIFE Technical Report No. 69, Stanford University, Stanford, CA Page 7

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