Distinguishing Between 3 Types of Steel Structure Drawings
1. Design Drawing (IFC — Issued for Construction): Created by the structural design engineer. It shows the overall structure diagram, loads, and cross-sections of the structural elements. This is the original document.
2. Machining drawings (Shop Drawing): Prepared by the structural steel contractor (such as Hai Long) based on the design. It details each component for factory fabrication — including precise dimensions, joints, bolts, and welds. It must be approved by the design engineer before manufacturing.
3. Erection Drawing: Instructions on how to assemble components at the construction site — assembly sequence, crane locations, temporary support measures.
Symbol 1: Section of the Component
On steel structure drawings, you will see symbols such as:
- W18×86 or H500×300×11×18This is a steel section. W18×86 means an 18-inch wide flange (I-beam) weighing 86 pounds/foot according to AISC standards. H500×300×11×18 is an H-beam 500mm high, 300mm wide, with a web thickness of 11mm and a flange thickness of 18mm according to JIS/KS standards.
- □150×150×8Square steel tube, 150mm side length, 8mm thickness.
- L100×100×10Angle steel, 100mm long, 10mm thick.
What the developer needs to check: Compare the cross-sectional symbols on the Shop Drawing with the Design Drawing — they must match. If the contractor proposes changes to the cross-section (usually to reduce costs), approval from the design engineer is required.
Symbol 2: Steel Grade
In addition to the cross-sectional area, the steel grade must be clearly stated:
- SS400 / A36: Ordinary carbon steel, yield strength ~250 MPa. Most common.
- SM490 / A572 Gr.50: High-strength steel, yield strength ~345 MPa. Used when a reduced cross-sectional area is required while maintaining sufficient load-bearing capacity.
- SN400B / SN490B: Seismic steel, with controlled C/S ratio to ensure ductility.
What the developer needs to check: Request the contractor to provide Mill Certificate (Steel Mill Certificate) For each batch of materials, verify that the steel received matches the grade specified in the design.
Symbol 3: Welds — Triangle Symbol and Reference Line
Welding symbols on drawings according to AWS standards are one of the most complex parts, but the client only needs to be aware of them:
The three main types of welds:
- Fillet weld: The symbol is a right-angled triangle. The size is indicated next to it (e.g., 10 = weld root size 10mm).
- Groove Weld (CJP — Complete Joint Penetration): The symbol is a V or U shape with "CJP". This indicates a full-thickness penetration weld — requiring mandatory NDT inspection.
- Plug/Slot Weld: Less common.
Important: CJP welds on main column-beam connections must be UT inspected before painting. If the Shop Drawing indicates CJP but the contractor fails to perform UT inspection, this constitutes a violation requiring immediate corrective action.
Symbol 4: Connecting Bolts — Diameter, Strength Grade, and Position
The bolt connections shown on the drawing are as follows:
- M20-8.8: This is an M20 diameter bolt, strength grade 8.8 (tensile strength 800 MPa, yield strength 640 MPa). It is a high-strength bolt commonly used in industrial structures.
- M24-10.9: These are very high-strength bolts, used for connections subjected to heavy loads.
What the developer needs to check:
- How are bolts tightened: by hand (snug-tight) or by torque (pre-tensioned)?
- Standard FDI factory projects typically require high-strength bolts tightened to the clamping force according to AISC — requiring verification by torque wrench.
Symbol 5: Bill of Materials (BOM)
Each Shop Drawing includes a Bill of Materials (BOM) listing all components, including:
| Column | Meaning |
|---|---|
| Mark | Component code (C1, B1, P1…) |
| Qty | Quantity |
| Profile | Section |
| Length | Length |
| Weight (kg) | Weight of each item and total |
| Grade | Steel Marks |
| Remark | Special Note |
What the developer needs to check: The total volume in the Bill of Materials (BOM) must match the volume in the contract. If the contractor adjusts the cross-section downwards, the actual volume decreases while the contract price remains unchanged — this is a point that needs clarification.
Symbol 6: Erection Tolerance
Assembly drawings usually specify allowable tolerances. Standard tolerances are based on the AISC Code of Standard Practice:
| Category | Permissible tolerance |
|---|---|
| Column verticality | ±1/1000 of column height, maximum ±50mm |
| Column heart position deviation | ±6mm (bottom layer), ±25mm (top layer) |
| Beam top height | ± 3mm |
| Joint gap | According to shop drawing |
What the developer needs to check: Require the contractor to conduct an as-built survey after erection — this is especially important before pouring the foundation concrete and installing production equipment.
Symbol 7: General Notes
The bottom right (or right) corner of the drawing always has "General Notes" — this is where the designer writes the requirements that apply to the entire drawing:
1. All structural steel to be ASTM A36 unless noted.
2. All welding to AWS D1.1 latest edition.
3. All bolts to be ASTM A325N unless noted.
4. All welds to be UT tested after welding — CJP welds only.
5. Surface preparation: Sa 2.5 per ISO 8501-1.
6. Paint system: [Specific name of the paint system].
What the developer needs to check: Read the General Notes and keep them as part of the contract documentation. If the contractor fails to fulfill any point, this serves as legal grounds for requesting corrective action.
Symbol 8: Revision Block
In the bottom right corner of each drawing is a revision table detailing the change history:
| Rev | Date | Description | Approved by |
|---|---|---|---|
| 0 | 01/03/2025 | Issued for Approval | ... |
| A | 15/03/2025 | Revised per comments | ... |
| B | 28/03/2025 | Final IFC | ... |
What the developer needs to check: Always work on the latest revision drawings. Many construction errors occur because workers use older versions. Establish a Document Control process from the beginning of the project.
HAI LONG STEEL STRUCTURES IS A REPUTABLE MANUFACTURER OF STEEL BUILDING STRUCTURES.
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In a market that increasingly demands quality, timeliness, and safety, Hai Long Steel Structure Proud to be the leading brand trusted by many large domestic and foreign investors:
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You are looking for one Prestigious and professional steel structure manufacturing and erection unit?
Contact Hai Long Construction for free consultation and quotation:
- HAI LONG CONSTRUCTION JOINT STOCK COMPANY
- Address: Taiyo Building, 97 Bach Dang, Hong Bang Ward, Hai Phong City, Vietnam.
- Hotline: 084 6625 888
- Email: info@hailongjsc.vn
