Title:
Creating Custom 2D Dynamic Blocks for Pipe Structures in Civil 3D
Issue:
Civil 3D comes with a library of standard structure styles, but many firms require custom 2D plan symbols for pipe structures that reflect:
Different structure types (MH, CB, DI, vaults)
Custom frame sizes
Flow direction indicators
Contractor-friendly annotations
Agency-specific symbols
Scaled representation at various viewport scales
Civil 3D structure styles alone cannot produce complex 2D symbols in plan view.
As a result, designers often rely on:
Static blocks that don’t rotate with the pipe
Manually drawn symbols for each structure
Drafting “exploded” blocks that break annotation intelligence
Symbols that don’t resize or align automatically
This leads to inconsistencies, wasted time, and increased QA/QC effort.
Solution:
Use AutoCAD Dynamic Blocks to build intelligent, customizable 2D symbols for pipe structures—blocks that stretch, flip, rotate, display different sizes, and automatically align to pipe direction.
Once built, these dynamic blocks can be assigned to Civil 3D structure styles to fully automate plan view symbology.
Step 1 — Start with a Clean Base Block
Open a blank DWG.
Draw your basic 2D pipe structure symbol:
Circle (structure wall)
Rectangular frame or grate outline
Flow direction arrows (optional)
Hatch (optional)
Use real dimensions (e.g., 48", 60", etc.) or design them graphically.
Convert the geometry into a Block:
BMAKE > Name: STR_MH_2D_BASE
Step 2 — Add Dynamic Behavior Using the Block Editor
Right-click the block → Block Editor
This is where the intelligence is added.
Step 3 — Add Parameters + Actions
Here are the most useful parameters for pipe structure blocks:
1. Rotation Parameter (aligns with pipe direction)
Add a Rotation Parameter at the block’s center
Add a Rotate Action and assign it to all visible geometry
This makes the structure rotate automatically when placed on a pipe network.
2. Flip (Mirror) Parameter for Symmetry
Useful if the symbol needs to flip across a centerline (e.g., directional arrows or offset frames).
Steps:
Add Flip Parameter > Vertical/Horizontal
Add Flip Action > Select all geometry
3. Visibility Parameter (supports multiple symbol types in ONE block)
This is one of the most powerful tools.
Example visibility states:
Manhole
Curb Inlet
Grated Inlet
Junction Box
Vault
Cleanout
Steps:
Add Visibility Parameter
Create new states
Turn geometry on/off per state
Now your block becomes a multi-symbol library in a single object.
4. Stretch Parameter (structure diameter or frame length)
If you want adjustable sizes:
Add a Linear Parameter
Add a Stretch Action
Select the circle or frame edges
This allows the designer to stretch a 24", 36", 48", 60" manhole without swapping blocks.
5. Lookup Table (predefined structure sizes)
Instead of free stretching, use a Lookup Parameter:
Example table:
Structure Size Diameter Frame Length
24" MH 2.0 ft 2.0 ft
48" MH 4.0 ft 4.0 ft
60" MH 5.0 ft 5.0 ft
72" MH 6.0 ft 6.0 ft
Assign the Lookup Parameter to geometry and visibility states.
This guarantees standardized, approved sizes.
Step 4 — Add Attribute Definitions (for automatic labeling)
Use ATTDEF to create text attributes like:
Structure Number
Rim Elevation
Invert Elevation(s)
Type
Station / Offset
Size
Set them as annotative if you want scale awareness.
Step 5 — Save and Test the Dynamic Block
In the block editor:
Use Test Block
Try rotating
Flip in both directions
Switch visibility states
Stretch or change size
Apply lookup values
Fix anything that behaves incorrectly.
Step 6 — Assign Dynamic Block to Civil 3D Structure Styles
Go to Toolspace > Settings > Pipe Network > Structure Styles
Choose a Plan View style
Under display components, set:
Plan View Symbol > Use Block > Select your custom block
Map the block’s insertion point to the structure location.
Now every time Civil 3D inserts a structure, your custom dynamic block displays automatically.
