How to Use Family Formulas to Calculate Template Engineering Quantities in Revit
BIM models contain a wealth of information and can be used to calculate various engineering quantities, serving as valuable references for design, construction, and cost estimation. Using beams as an example, this article explains how to apply family formulas to calculate the formwork area.
First, add relevant parameters and formulas to the beam family type parameters, as demonstrated in the image below:
Once loaded into the project, the situation appears as shown in the following figure:
For a beam sized 250×700 with a plate thickness of 180 and length of 6075, the calculated formwork area is 7.837 square meters. The formula used is:
0.25 × 6.075 + (0.7 – 0.18) × 6.075 × 2 = 7.837
The formwork area displayed in the project matches this calculated value.
However, after tallying the entire project, the total beam formwork area was found to be larger than the manually calculated amount. Investigating further in the project, it was discovered that the “Length” value in the beam instance properties is often greater than the actual length.
This occurs because the “Length” property in the beam instance refers to the distance between the endpoints of the frame components, which often extend to the center of walls and columns. As a result, this “Length” value cannot be reliably used in the beam formwork area formula.
So how should this length issue be addressed?
Upon closer examination, within the beam instance properties under the “Structure” subsection, there is a parameter called “Cut Length.” This value represents the actual length between walls and columns, as shown below:
To accurately calculate formwork using the beam family formulas, you can either add a “Cut Length” parameter to the beam family and load it into the project for processing, or alternatively, handle this adjustment directly within the project environment.
Here is the approach using Dynamo for processing:
First, add an “Actual Length” parameter within the beam family, as shown in the figure below:
Load the family into the project to verify the parameter:
You will notice that the “Actual Length” parameter initially has a value of 0. To populate it correctly, the “Cut Length” value needs to be transferred to the “Actual Length” parameter. This can be automated using Dynamo.
Using Dynamo, you can retrieve all structural beams within the project, extract their “Cut Length” values, and use the Element.SetParameterByName node to assign these values to the “Actual Length” parameter. This process achieves the desired result efficiently. The Dynamo nodes involved are straightforward, as illustrated below:
【Related Skills: How to Use a Detailed Table to Calculate Weight in Revit】
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