The engineering budget primarily consists of two key elements: the measurement of engineering quantities and engineering valuation.
At the core of construction cost control lies the construction drawing budget, which itself is based on the calculation of drawing quantities. Traditionally, calculating engineering quantities accounts for over 80% of the total workload for budget personnel. This process is complex and detailed. Additionally, varying quantity calculation rules across different regions further complicate achieving accurate measurements. With ongoing technological advancements, the construction industry continuously evolves, designing increasingly diverse and complex building structures, which adds further challenges to quantity calculation.
The BIM budget management solution is implemented in four stages: establishing a BIM parametric model, creating a BIM quantity model, performing BIM quantity classification and summarization, and finally, establishing a BIM cost information model.
1. Establishing a BIM Parametric Model. The software comes pre-configured with national engineering quantity pricing standards and regional quota pricing standards. It also allows customization of component deduction relationships and calculation rules to align with local regulations across provinces and regions. Using three-dimensional modeling and entity deduction relationships, the software automatically summarizes and calculates quantities, ensuring high accuracy. Corresponding pricing quotas are extracted for each engineering quantity, forming the basis of the engineering budget.
A BIM model digitally represents building facilities with rich data and object-oriented features, incorporating intelligent and parameterized characteristics. Component information within BIM is computable, enabling automatic identification and calculation of component quantities based on geometric and physical information embedded in the model. The resulting engineering quantity statistics integrate seamlessly with budgeting software, and analysis results are stored within the BIM model for future updates and applications. These features make BIM-based quantity calculations more accurate, faster, and scalable.
2. Creating a BIM Quantity Model. Currently, the practical application of BIM in China mainly focuses on design and construction simulation stages. However, extracting engineering quantities directly from BIM models provided by design teams remains challenging due to three main reasons:
- Differences between design BIM models and the data required for quantity calculation, such as scaffolding designs for interior and exterior walls, which are often not fully reflected.
- Complexity in designing detailed decorative works, like intricate practice index tables.
- Inconsistencies between built-in quantity calculation rules and actual cost requirements for fasteners and other elements.
To address these issues, software developers typically use two approaches: one involves cost personnel recreating models based on drawings to calculate quantities. While this method supports importing 2D AutoCAD drawings, recognition accuracy is often low, especially for steel reinforcement and fine decorations. The other approach exports a BIM model compliant with IFC standards from the design BIM model, which can then be imported into the BIM quantity model. Pricing information is added, and quantity deduction relationships are adjusted according to specifications to form the BIM quantity model.
3. BIM Quantity Classification and Summarization. Summarizing and compiling information on components of the same type is a repetitive and tedious task. BIM’s automatic summary and calculation functions simplify this process, making it more accurate and transparent.
A BIM model integrates various parameter information and applies constraint parameters such as component specifications, sizes, models, and materials. Each component’s unique number and precise three-dimensional position are recorded, enabling spatial filtering, classification, and calculation. Classification labels are assigned based on component attributes, and statistics are compiled according to different calculation rules. This significantly improves the speed and accuracy of quantity summarization.
4. Establishing a BIM Cost Information Model. Cost information is linked to the BIM model to create a measurement and pricing file, establishing what is called a Cost BIM (CBIM) model. Project feature information is matched with BIM attributes to determine corresponding quota sub-items based on the project’s characteristics. Consumption rates and base material prices from the quota library are then applied to generate the initial project quantity list.
This integration of design and cost information allows modifications in the BIM design model to automatically update cost estimates. However, challenges remain because engineering measurement relies on design components in BIM models, while pricing depends on list items and quota sub-items, an issue not yet fully resolved.
Typically, the design component information is exported from the BIM model into an engineering quantity interaction file via IFC files, then imported into Cost BIM. By matching component attributes with project characteristics, pricing list items are automatically linked with quota sub-items or historical comprehensive unit prices from similar projects.
This process enhances cost preparation efficiency, ensures accuracy, consistency, and standardization in information description, and lays the groundwork for accumulating and applying cost index data based on building element classification standards and list items.
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