How Marks Are Assigned in Tekla
Tekla Structures assigns piece marks automatically based on geometry — two members with identical geometry, material grade, and attached components receive the same mark. A mark suffix (A, B, C) distinguishes members that differ only in minor ways (a bent member vs. its mirror). Manual mark assignment overrides the automatic system and should be used carefully — manually assigned marks can create duplicates that Tekla's auto-checking won't catch.
The Duplicate Mark Check
Before any drawing is released, run a duplicate piece mark check — verifying that no two different members share the same piece mark. In Tekla, this is the 'Check Model' function. A duplicate mark means one member is mislabeled, and when both members are fabricated, two identical marks will exist in the yard — one of which will go to the wrong location during erection. The erection delay to find and sort the mislabeled members can cost a half-day of crane time.
Confirming Marks Against the Erection Drawing
The final mark verification check compares the piece marks shown on the erection drawing against the marks in the BOM and on the shop drawings. Every mark on the erection drawing must have a corresponding shop drawing; every mark in the BOM must appear at least once on an erection drawing. Marks that appear in the BOM but not on the erection drawing represent members that may not be installed — or that are installed with no location reference for the erection crew.
How Mark Numbering Conventions Work
Most shops and detailing firms use a prefix-based piece mark convention that groups members by type: columns starting with 'C' or 'CL,' beams with 'B,' girders with 'G,' braces with 'BR,' miscellaneous steel with 'M' or 'MIS,' plates with 'PL.' Within each prefix group, marks are assigned sequentially (C1, C2, C3) with letter suffixes for minor variants (C3A, C3B for left-hand and right-hand mirrors). This convention is not universal — different detailing firms and different fabrication shops use different systems. The convention should be agreed at project kickoff and documented in the project-specific detailing standards.
- Column base plates — 'BP' prefix, numbered with their associated column
- Splice plates — 'SP' prefix or suffix on the column mark (C3-SP)
- Gusset plates — 'GP' prefix with brace mark reference
- Embed plates — 'EP' prefix, often numbered with the concrete element they embed in
- Standard hardware (anchor rods, leveling nuts) — listed in BOM by specification item, not individual mark
Mark Verification During Shop Inspection
The physical piece mark on the fabricated member — stamped, painted, or tagged — must be legible and must match the shop drawing before the member leaves the shop. AISC Code of Standard Practice Section 6.4.2 requires that piece marks be applied to each member in a manner that remains legible during handling, shipping, and erection. Inspectors checking members before shipment should verify the piece mark against the drawing and BOM, not just read the mark on the member. Marks that are illegible, transposed, or missing are non-conformances that must be corrected before shipment — not in the field during erection.
Dealing with Mark Conflicts from Multiple Detailing Releases
On phased projects where multiple drawing packages are released at different times, piece mark conflicts can arise if sequential numbering is not maintained across releases. If Package 1 ends at B-245 and Package 2 begins at B-001 — because a second modeler started a new sequence — the fabrication yard will have two members called B-001 from two different packages. This is the piece mark conflict most likely to go undetected until erection. The solution is a project-wide piece mark register maintained in real time, with each release package reserving a specific mark number range before modeling begins.