The Source of Truth for Material Grades
Material grades are specified in the project's structural drawings and Division 05 specifications. Common AISC-required grades are: W-shapes — ASTM A992 (minimum Fy = 50 ksi); HSS round and rectangular — ASTM A500 Grade C (Fy = 46 ksi minimum for rectangular); angles and channels — A36 or A572-50; plates — A36 or A572-50 as specified. The structural drawings govern; when a drawing note conflicts with the specification, the more restrictive requirement applies and the discrepancy should be RFI'd.
Grade Assignment in the Model
Every member and every plate in the Tekla model should have its material grade assigned as a model attribute — not inferred or left blank. Blank material grade fields produce BOM entries with no grade listed, which forces the purchasing department to guess. The Tekla material library contains all standard ASTM grades; custom grades can be added for project-specific requirements. Run a model report after initial setup to verify all members have grades assigned.
Mill Certificate Requirements
Structural specifications typically require mill test reports (MTRs) certifying the material grade and mechanical properties for each heat of steel. MTRs are linked to members through the material heat number, which is recorded during receiving inspection. When a drawing shows the wrong grade, the wrong material may be ordered and the correct MTR will not exist — creating an inspection failure. Correct grades in the model prevent this chain of errors.
Common Grade Substitution Errors and Their Consequences
Grade substitution errors — using A36 plate in a joint that specified A572-50, or A500 Grade B HSS where Grade C was required — are more common than the industry acknowledges because the physical material looks identical to the wrong grade. The consequences range from reduced connection capacity (the A36 plate has 10 ksi lower yield strength than A572-50) to weld procedure non-compliance (some weld procedures are grade-specific per AWS D1.1 Table 4.5). On seismic projects governed by AISC 341, certain connections require specific grades — A992 for W-shapes in seismic moment frames, A500 Grade C for HSS braces — because the expected yield strength range is part of the ductility design. Using the wrong grade in a seismic application can void the connection's prequalified status.
How to Verify Grades During the Detailing QA Check
The drawing QA check should include a specific step: open the Tekla material report and compare every member's model-assigned grade against the structural drawing material schedule. The material schedule on the structural drawings typically appears in the general notes or as a table — it lists member types and their required grades. A one-to-one comparison between the model report and the structural schedule, performed before any drawing is extracted, catches grade mismatches before they reach the BOM or the mill order.
Weld Procedure Compatibility with Material Grades
Material grades directly affect which welding procedures (WPS) are qualified for use. AWS D1.1 requires that welding procedures be pre-qualified or qualified by test for each combination of base metal category and filler metal. ASTM A572-50 falls in base metal category II; ASTM A992 falls in category I/II; ASTM A514 (high-strength plate) falls in category IV and requires specific preheat and interpass temperature controls. A shop that assigns an incorrect material grade to a plate may inadvertently perform welding with an unqualified procedure — which becomes a non-conformance during special inspection. Correct grade assignment in the model is the upstream prevention that eliminates this downstream risk.
Grade Verification During Receiving Inspection
Even when drawings and BOMs show the correct grade, the material delivered to the yard must be verified on receipt. Receiving inspection confirms that heat numbers on material tags match the MTRs provided by the mill, that section sizes match the purchase order, and that visual markings (color codes or stenciled grade markings per ASTM conventions) are present. Sections stored in the yard without legible heat number tags or grade markings should be quarantined until their identity is confirmed — fabricating untracked material creates a documentation gap that special inspectors will flag during their IBC Chapter 17 inspection visits.