Structural steel design under AISC 360 generates some of the most technically dense plan review comments on any project. Unlike concrete or wood, where the construction documents typically show every detail needed for field construction, steel design relies heavily on the relationship between the engineer of record's drawings and the steel fabricator's shop drawings. That split responsibility creates documentation gaps that plan reviewers flag repeatedly.
AISC 360-22 (Specification for Structural Steel Buildings) governs the design, fabrication, and erection of structural steel. It is referenced by the IBC through ASCE 7 and is the primary specification for wide-flange beams, columns, braces, and their connections. The violations below are the ones that cause the most review comments and resubmittals on commercial steel-framed projects.
1. Connection design not shown or deferred without documentation
The most common structural steel review comment, by a wide margin: connections are either not shown on the structural drawings or are labeled "by fabricator" without any design criteria. AISC 360 Section J1 through J10 govern connection design, and the engineer of record is responsible for providing either the full connection design or the forces and moments at each connection so the fabricator's engineer can design them.
Plan reviewers need to verify the load path through every connection. When the drawings show a beam framing into a column with no connection detail and no force table, the reviewer cannot verify anything. The comment will be some variation of "provide connection design forces or typical connection details for all beam-to-column and beam-to-beam connections."
2. Missing or inadequate bracing for lateral stability
Every steel compression member and every beam with a compression flange must be braced against lateral-torsional buckling. AISC 360 Chapter C (Stability) and Appendix 6 define the requirements. The unbraced length of a compression flange directly affects the member's available strength, and if the bracing shown on the drawings doesn't match the unbraced length assumed in the design calculations, the member may be undersized.
The most frequent error: the structural plan shows a long-span beam with no intermediate bracing indicated, but the member size was selected assuming bracing at the third points. The reviewer checks the beam's unbraced length against the Lb limits in Table 3-2 of the AISC Steel Construction Manual. If the actual unbraced length exceeds Lp (the limit for full plastic moment), the available flexural strength drops significantly.
| Unbraced length | Available strength | Design implication |
|---|---|---|
| Lb <= Lp | Full Mp (plastic moment) | Compact section, full strength |
| Lp < Lb <= Lr | Linear interpolation Mp to Mr | Inelastic buckling reduces capacity |
| Lb > Lr | Elastic buckling (Fcr) | Significant strength reduction, often controls design |
3. Bolt specification and spacing errors
Bolted connections require specific callouts for bolt grade (A325 or A490, now designated F3125 Grade A325 or A490), bolt diameter, hole type (standard, oversized, short-slotted, long-slotted), and installation method (snug-tight, pretensioned, or slip-critical). AISC 360 Section J3 defines the requirements for each.
Common errors on structural drawings: no bolt grade specified (the note just says "3/4-inch bolts"), no indication of whether connections are bearing-type or slip-critical, bolt spacing less than the 2-2/3 diameter minimum required by Section J3.3, and edge distances that violate Table J3.4. Reviewers check every bolt pattern on the connection details against these minimums.
4. Weld specification deficiencies
Welded connections require callouts for weld type (fillet, groove, plug), weld size, weld length, electrode classification (E70XX is standard for structural steel), and any special inspection requirements. AISC 360 Section J2 governs welded connections, and AWS D1.1 (Structural Welding Code) provides the detailing requirements.
The most common deficiency is undersized fillet welds. Section J2.2b requires a minimum fillet weld size based on the thinner part joined (Table J2.4). A 3/16-inch fillet weld on a 3/4-inch plate violates the minimum. Reviewers also check that weld symbols on the drawings follow AWS A2.4 conventions. Non-standard or ambiguous weld symbols generate comments because the fabricator cannot interpret the designer's intent.
| Thinner part joined | Minimum fillet weld size |
|---|---|
| Up to 1/4 in. | 1/8 in. |
| Over 1/4 to 1/2 in. | 3/16 in. |
| Over 1/2 to 3/4 in. | 1/4 in. |
| Over 3/4 in. | 5/16 in. |
5. Column base plate and anchor bolt design missing
Column base plates transfer gravity loads, lateral loads, and overturning moments from the steel frame into the concrete foundation. AISC Design Guide 1 provides the standard approach. Plan reviewers expect to see: base plate dimensions and thickness, anchor bolt size, grade, embedment depth, and pattern, and the concrete bearing strength verification.
The most common error is showing a base plate on the foundation plan with anchor bolt locations but no design detail. The structural drawings show "see foundation plan" and the foundation plan shows "see structural." Neither provides the plate thickness, anchor bolt grade, or the forces the base plate was designed to resist. This is a coordination failure between the structural engineer and the foundation designer (who may be the same person), and it always generates comments from both the structural and foundation reviewers.
6. Member designations inconsistent between plans and schedules
Steel framing plans use member marks (B1, B2, C1, C2, etc.) to identify individual beams, columns, and braces. The structural schedule or member table lists each mark with its section size, grade, and any special requirements. Reviewers cross-reference the plan against the schedule.
Inconsistencies are surprisingly common: a beam marked B7 on the framing plan that doesn't appear in the schedule, a column marked C3 on the plan but listed as C3A in the schedule, or a member that appears in the schedule as W14x48 but is called out as W14x43 in a connection detail. These discrepancies may seem minor, but each one requires the reviewer to stop and ask which is correct. On a large project with hundreds of members, even a few inconsistencies can generate a page of comments.
7. Inadequate load path documentation for lateral system
The lateral force resisting system (moment frames, braced frames, or shear walls) must have a clearly documented load path from the roof diaphragm down through each floor to the foundation. AISC 360 Chapter C and ASCE 7 Section 12.1 both require a complete load path.
Reviewers trace the lateral load path on the drawings: horizontal diaphragm to collector beam to braced frame or moment frame to column to base plate to foundation. If any element in the chain is not shown or not designed, the load path is incomplete. The most common gaps: missing collector beams at re-entrant corners, drag struts not shown between diaphragm and lateral frame, braced frame gusset plates shown but not designed, and base plates at lateral frame columns not designed for the overturning forces.
8. Steel material grade not specified
AISC 360 Table 2-4 lists the approved steel grades for various structural shapes. The default assumption for wide-flange shapes is ASTM A992 (Fy = 50 ksi), but plates, angles, channels, and HSS each have different preferred grades. If the drawings don't specify the steel grade, the reviewer cannot verify that the member strength calculations used the correct yield stress.
Common errors: a general note that says "all steel ASTM A36" when the calculations assume A992 for wide-flange members, HSS members specified as A500 Grade B (Fy = 46 ksi) but designed as if they were Grade C (Fy = 50 ksi), and plates specified without a grade at all. A single general note that covers the standard grades for each shape type resolves this, but many drawings omit it.
Why steel review comments cluster around connections
The member sizing on a steel project is usually straightforward to verify: the reviewer checks the section properties against the loading and confirms that the demand-to-capacity ratio is acceptable. This rarely generates comments on commercial projects where the engineer uses standard design software.
The comments cluster around connections because that's where the documentation gaps are. Connection design is often deferred, delegated, or split between parties. Providing complete connection forces on the contract documents, showing typical connection details with bolt and weld specifications, and ensuring consistency between plans and schedules eliminates the majority of structural steel review comments.