Construction Modeling Method
September 17, 2008
3D construction models begin with a set of 2D contract documents. These are the construction documents that represent the scope of the contract requirements provided by the design team. The model is constructed to confirm a bid, during contract negotiations, or in the field just ahead of the actual work.
The idea is to use the 3D modeler as a tool to systematically check the 2D documents, test details and dimensions, and understand the assumptions made by the design team — before the documents are used in the field.
1. Start with a site model: this is a scaled scan of the plat map or survey laid over a geographically accurate model base. Use the site model for site utilization planning (SUP), to simulate the impact of weather and sun on construction activities, and to map the regional context of the jobsite.
2. Excavate the building from a workpoint. Base cuts, grading, and shoring on the referenced elevations and dimensions shown on the survey and plot plans. Use scaled equipment models to test available access routes, stockpiles, and staging.
3. Use the 2D documents to begin the foundations (formwork). Set up the scaffolding, falsework, and equipment that will be needed to complete the foundation. Include reinforcing, connectors, and other specialty items shown on the contract documents. The modeling program automatically surveys quantities and identifies phases, tasks, and errors and omissions.
4. Build the structural frame according to the engineered documents. Include staging and lay down area as well as scaled models of the workers, tools, and equipment necessary to complete the framing. The model is built using the sequence and processes anticipated for the construction. Survey quantities are again automatically generated, means and methods are coordinated with field teams, and the resulting model illustrates areas of concern, RFIs, and conflicts.
5. Building systems are installed per plans and specs. Important is to build these systems in the order of their actual construction using scaled models of the tools and equipment needed by each subcontractor. Sequence modeling highlights conflicts, anticipates coordination problems, and tests design assumptions.
6. Finish work follows the contract details. 3D component models are fitted to roofing, curtain and window walls, siding, finishes, cabinetry and furnishings. The completed model focuses on coordinating processes and sequences necessary to complete the contract obligations.
The result is a construction model that details the means, methods, and processes embedded in the contract documents. Errors and omissions are identified (often output from a poorly constructed BIM model) and schedule concerns, subcontractor challenges, value engineer alternatives, and real-world conflicts are illustrated for all to see in three-dimensions.