Distinguishing 3 Types of Steel Structure Drawings
1. Design Drawing (IFC — Issued for Construction): Created by the structural design engineer. Shows the overall structural diagram, loads, and component cross-sections. This is the original document.
2. Shop Drawing: Prepared by the steel structure contractor (such as Hai Long) based on the design. Shows details of each component for factory fabrication — including precise dimensions, connections, bolts, and weld lines. Must be approved by the design engineer before fabrication.
3. Erection Drawing: Instructions on how to assemble components at the construction site — assembly sequence, crane positions, and temporary bracing measures.
Symbol 1: Component Section
On steel structure drawings, you will see symbols such as:
- W18×86 or H500×300×11×18: These are structural steel sections. W18×86 means an I-beam (Wide Flange) 18 inches high, weighing 86 pounds/foot according to AISC standards. H500×300×11×18 is an H-beam 500mm high, 300mm wide, 11mm web thickness, 18mm flange thickness according to JIS/KS standards.
- □150×150×8: Square hollow section, 150mm side, 8mm thick.
- L100×100×10: Angle steel, 100mm sides, 10mm thick.
What investors need to check: Compare the section symbols on the Shop Drawing with the Design Drawing — they must match. If the contractor proposes a change in section (usually to reduce costs), it must have approval from the design engineer.
Symbol 2: Steel Grade
Besides the section, the steel grade must be clearly stated:
- SS400 / A36: Common carbon steel, yield strength ~250 MPa. Most popular.
- SM490 / A572 Gr.50: High-strength steel, yield strength ~345 MPa. Used when it is necessary to reduce the section while maintaining load-bearing capacity.
- SN400B / SN490B: Seismic steel, with controlled C/S ratio to ensure ductility.
What the investor needs to check: Require the contractor to provide a Mill Certificate for each batch of materials, confirming that the steel received matches the designed grade.
Symbol 3: Welds — Triangle Symbol and Reference Line
Weld symbols on drawings according to AWS standards are among the most complex parts, but the investor only needs to recognize:
Three main types of welds:
- Fillet Weld: Right triangle symbol. Dimensions are noted on the side (e.g., 10 = 10mm weld leg size).
- Groove Weld / CJP — Complete Joint Penetration: V or U-shaped symbol with "CJP". This is a full-penetration weld — mandatory NDT inspection required.
- Plug/Slot Weld: Less common.
Important note: CJP welds on column-beam connections must be UT tested before painting. If the Shop Drawing specifies CJP and the contractor does not perform UT, this is a violation that requires immediate correction.
Symbol 4: Connection Bolts — Diameter, Grade, and Position
Bolt connections on drawings indicate:
- M20-8.8: M20 diameter bolt, grade 8.8 (800 MPa ultimate tensile strength, 640 MPa yield strength). This is a high-strength bolt commonly used in industrial steel structures.
- M24-10.9: Very high-strength bolt, used for heavy-load connections.
What the investor needs to check:
- What tightening method is used for the bolts: snug-tight or pre-tensioned?
- Standard FDI factory projects usually require high-strength bolts to be tightened to the clamping force according to AISC — this must be verified using a torque wrench.
Symbol 5: Bill of Materials (BOM)
Every Shop Drawing includes a BOM table listing all components, including:
| Column | Meaning |
|---|---|
| Mark | Component ID (C1, B1, P1…) |
| Qty | Quantity |
| Profile | Section |
| Length | Length |
| Weight (kg) | Unit weight and total weight |
| Grade | Steel grade |
| Remark | Special notes |
What the investor needs to check: The total weight in the BOM must match the weight in the contract. If the contractor reduces the section size, resulting in lower actual weight while the contract price remains unchanged, this is a point that needs clarification.
Symbol 6: Erection Tolerance
Erection drawings clearly state the allowable tolerances. Standard tolerances are according to the AISC Code of Standard Practice:
| Category | Allowable tolerance |
|---|---|
| Column verticality | ±1/1000 of column height, maximum ±50mm |
| Column center position deviation | ±6mm (lower floor), ±25mm (top floor) |
| Beam top elevation | ±3mm |
| Joint gap | Per shop drawing |
What the investor needs to check: Require the contractor to measure and provide an as-built survey after erection — especially critical before pouring the foundation concrete and installing production equipment.
Symbol 7: General Notes Table
The bottom right (or right side) of the drawing always contains "General Notes" — this is where the designer records requirements applicable 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 paint system name].
What the investor needs to check: Read the General Notes and keep them as contract documents. If the contractor does not comply with any point, this is the legal basis to request rectification.
Symbol 8: Revision Block
The bottom right corner of each drawing has a revision table clearly recording 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 investor needs to check: Always work with the latest revision drawing. Many construction errors occur because workers use older versions. Establish a Document Control process from the very beginning of the project.
HAI LONG STEEL STRUCTURE IS A REPUTABLE STEEL STRUCTURE MANUFACTURER
Choosing the right steel structure fabrication partner is the deciding factor for the success of every construction project.
In a market context that increasingly demands high quality, schedule, and safety, Hai Long Steel Structure is proud to be a leading brand trusted by many major domestic and international investors:
- A team of experienced engineers, architects, and experts, knowledgeable in the design and construction of factory buildings and warehouses according to international standards.
- Diverse construction capabilities, meeting all project scales and requirements, from simple to complex factory buildings.
- Owning a steel structure factory with modern machinery and equipment systems, ensuring fast, accurate, and safe construction.
- Professional construction process, strictly managed.
Are you looking for a reputable and professional steel structure manufacturing and erection contractor?
Contact Hai Long Construction for free consultation and quotation:
- HAI LONG CONSTRUCTION JSC
- Address: Taiyo Building, 97 Bach Dang, Hong Bang Ward, Hai Phong City, Vietnam.
- Hotline: 084 6625 888
- Email: info@hailongjsc.vn
