Structural steel symbols: how to read steel on drawings

A reviewer-grade reference for structural steel symbols on framing plans, connection details, and shop drawings: shape designations, weld symbols, bolt symbols, line weights, and the abbreviations that appear next to them.

Structural steel drawings use a layered symbol language: shape symbols identify what the member is, connection symbols specify how it joins the rest of the frame, line weights show where it sits in 3D space, and abbreviations communicate elevation, orientation, and bolt grades. Reviewers who only know the shape symbols miss most of the constructability issues; the highest-leverage symbols on a real drawing set are the connection and weld symbols, because that is where fabricators and erectors run into trouble.

Source-of-truth rule

When a symbol on the framing plan disagrees with the typical details sheet, the typical details sheet wins. When the typical details sheet disagrees with the project specifications (Division 05 12 00 Structural Steel Framing), the specifications win.

Steel Shape Symbols

Shape symbols identify the cross-section of a structural steel member. The same shape appears in three places on a drawing set: as a label on the framing plan, as a row in the column or beam schedule, and as a profile drawn at scale in the typical details.

Wide Flange (W) Beam/Column

W12×26, W14×90

I-shaped section with parallel flanges. The first number is nominal depth in inches, the second is weight in pounds per foot. Drawn on plan as a rectangle aligned with member axis; on details as an actual I-section profile.

Where you see it: Framing plans, column schedules, beam schedules, connection details. Most common symbol on commercial structural drawings.

Hollow Structural Section, Rectangular (HSS)

HSS8×4×3/8

Rectangular tube with rounded corners. Dimensions are outside-to-outside, last number is wall thickness in inches. Drawn as a rectangle on plan; details show the hollow interior.

Where you see it: Brace frames, exposed columns, secondary framing, canopies, sign supports.

Hollow Structural Section, Round (HSS)

HSS6.625×0.280

Round tube. First number is outside diameter, second is wall thickness. Drawn as a circle on plan or a circle-with-center-line on details.

Where you see it: Architecturally exposed columns, pipe braces, handrails on structural framing plans, truss webs.

Channel (C and MC)

C12×20.7

U-shaped section with flanges on one side. First number is depth, second is weight per foot. MC denotes a miscellaneous channel with non-standard flange proportions.

Where you see it: Stair stringers, light framing, edge angles, built-up sections.

Angle (L)

L4×3×3/8

L-shaped section with two perpendicular legs. Dimensions are long leg × short leg × thickness, in inches.

Where you see it: Lintels, bracing, shelf angles, connection elements, gusset reinforcement.

Plate (PL)

PL 3/4×12

Flat steel. First dimension is thickness, second is width. Often called out with length when discrete (e.g., PL 3/4×12×0'-6”).

Where you see it: Base plates, stiffeners, gusset plates, splice plates, cap plates.

Structural Tee (WT, MT, ST)

WT6×13

Half of a wide flange cut along the web. WT cut from W, MT from M, ST from S. Used for truss chords and hanger connections.

Where you see it: Roof truss details, hanger and rod connections, miscellaneous steel.

For the full dimensional table of every rolled shape and grade, see our Structural Steel Shapes Reference.

Connection Symbols

Connection symbols are where most coordination issues live. Bolt symbols, weld symbols, and connection-type call-outs determine fabricator effort, erection sequence, and field tolerance. Mis-reading a moment connection symbol as a shear connection is one of the most expensive structural review misses.

Bolted Connection

Ø¾ A325 SC, 4 BOLTS

Shown as filled circles for bolt locations. The annotation specifies bolt diameter, ASTM grade (A325/F3125 Gr A325 or A490/F3125 Gr A490), and joint type (Bearing or Slip-Critical SC).

Where you see it: Beam-to-column shear tabs, splice plates, base plate anchor patterns, brace gusset connections.

Field Weld

▶ with weld symbol below the reference line

Triangular flag on the leader line indicates a field weld. AWS A2.4 weld symbols specify fillet, groove, plug, slot, with size and length. A circle at the flag means weld-all-around.

Where you see it: Moment connections, base plate to embed plate, miscellaneous steel field assembly.

Shop Weld

No flag — weld symbol only

AWS A2.4 weld symbol with no flag indicates a shop weld. Common notations: 1/4\\ \ fillet 1/4”, > > > > continuous.

Where you see it: Fabricated assemblies, built-up members, shop-welded connections shown on the detail sheet rather than the framing plan.

Anchor Bolt

Ø¾ A.B. with embed length

Plan symbol is an open or filled circle with a centered cross. Detail shows projection above grout, embedment, and any plate washer. Material is typically ASTM F1554 Gr 36, 55, or 105.

Where you see it: Column base plates, equipment pads, hold-down details at shear walls, embed plates.

Moment Connection

MC or filled triangle at beam end

A solid triangle, filled square, or “MC” label at the end of a beam indicates a moment connection (typically a fully welded or bolted flange detail).

Where you see it: Special Moment Frames (SMF), Intermediate Moment Frames (IMF), Ordinary Moment Frames (OMF) on framing plans.

Pinned Connection

Small circle at beam end

A small open circle at a beam end indicates a shear-only (pinned) connection. Typically a shear tab, double angle, or single-plate connection.

Where you see it: Most simple-span beam-to-column and beam-to-girder connections in gravity framing.

Weld symbol gotcha

Symbols below the reference line apply to the arrow side of the joint. Symbols above the line apply to the other side. Reviewers who flip these on a moment connection detail send the fabricator weld it on the wrong face, a common shop-drawing RFI.

Line Weights and What They Mean

Line weight is how a 2D framing plan communicates 3D. The same shape designation can appear as a heavy continuous line and a medium dashed line on the same plan, meaning two members of the same size at different elevations.

Heavy continuous line

Member at the level being drawn (the top-of-steel level of the framing plan)

Medium dashed line

Member above the framing plan level (overhead beam, lintel, or future framing)

Heavy dashed line

Member below the framing plan level (often used in detail keying)

Hatched rectangle

Concrete or grout fill (e.g., column base plate grout, embed plate fill)

Center line with double-dash break

Column line designator (grid line) — letters in one direction, numbers in the other per AISC convention

Common Steel Abbreviations

Steel framing plans rely on abbreviations to keep call-outs short enough to fit alongside members. Memorizing this list separates fluent reviewers from beginners.

BOSBottom of steel — elevation of beam bottom flange or column base

TOSTop of steel — elevation of beam top flange or column cap

T.O.C.Top of concrete — reference for embed plates and anchor projections

EOSEdge of slab

S.O.G.Slab on grade

TYP.Typical — detail applies to all similar conditions

OPP.Opposite — detail is mirrored at the other side

SIM.Similar — detail applies with noted differences

UONUnless otherwise noted

GR.Grade — as in A992 Gr 50 or F1554 Gr 55

FFFar face — reinforcing or bolts on the far side of a member

NFNear face — reinforcing or bolts on the near side of a member

L.L.H.Long leg horizontal (angle orientation)

L.L.V.Long leg vertical (angle orientation)

B.P.L.Base plate

C.P.L.Cap plate

STIFF.Stiffener plate

C.J.P.Complete joint penetration (groove weld)

P.J.P.Partial joint penetration (groove weld)

F.S.Far side

N.S.Near side

S.C.Slip-critical (bolted connection)

S.N.Snug-tight (bolted connection)

P.T.Pretensioned (bolted connection)

Looking for the complete structural abbreviation set? See our Structural Abbreviations guide.

Sources

AWS A2.4, Standard Symbols for Welding, Brazing, and Nondestructive Examination

AISC 360-22, Specification for Structural Steel Buildings

AISC 303-22, Code of Standard Practice for Steel Buildings and Bridges

ASTM F3125, Standard Specification for High Strength Structural Bolts

ASTM F1554, Standard Specification for Anchor Bolts

Practitioner insight

“Eighty percent of the structural RFIs I generate as a shop drawing reviewer come down to a weld symbol the EOR drew on the wrong side of the reference line, or a bolt grade that does not match the project specs. The shape symbol is almost never the problem.”

— Source: Conversations with structural shop drawing reviewers at AISC-certified steel fabricators serving the Southeast US, synthesized from Helonic’s submittal review interviews, Q1–Q2 2026.

Structural Steel Symbols FAQ

What are the most common structural steel symbols on framing plans?

On a typical commercial framing plan you will see (1) shape designations like W14×22, HSS8×4×3/8, and L4×3×3/8 labeling each member, (2) connection symbols — filled circles for bolts, weld symbols for welds, and small open circles or filled triangles indicating pinned versus moment connections, (3) elevation call-outs like TOS, BOS, and T.O.C. tying members to a benchmark, and (4) line weights indicating whether a member is at, above, or below the plan level. The structural cover sheet should define every symbol used.

How do I read a steel weld symbol?

AWS A2.4 weld symbols follow a horizontal reference line. The weld symbol below the line means the weld is on the arrow side; above the line means the other side. A flag at the bend indicates a field weld (not shop), and a circle at the flag means weld-all-around. The number to the left of the weld symbol is the leg size (for fillets) or depth (for grooves), and the number to the right is the length. For example, “1/4 \\ 4-12” under the line means a 1/4-inch fillet weld, 4 inches long, repeated every 12 inches on center.

What is the difference between a moment connection symbol and a shear connection symbol?

Moment connections are typically shown as a filled triangle, filled square, or “MC” label at the beam end — they transfer both shear and bending moment from beam to column. Shear (pinned) connections are typically shown as a small open circle or with no special symbol at the beam end. Looking at the connection schedule or typical details sheet will confirm — most projects designate moment frames on a separate framing key plan in addition to the symbol.

What does HSS mean on structural drawings?

HSS stands for Hollow Structural Section — a steel tube that can be rectangular, square, or round. The designation HSS8×4×3/8 means a rectangular tube with outside dimensions 8” by 4” and a 3/8” wall thickness. HSS6.625×0.280 is a round tube with a 6.625” outside diameter and 0.280” wall thickness. HSS is governed by ASTM A500 (most common) or A1085 for premium dimensional tolerances.

What is the difference between A325 and A490 bolts on a structural drawing?

Both are high-strength structural bolts, now both grouped under ASTM F3125 (A325 became F3125 Grade A325, A490 became F3125 Grade A490). A325 (now A325) has 120 ksi minimum tensile strength; A490 has 150 ksi. A490 is used where higher capacity per bolt is needed but cannot be galvanized (risk of hydrogen embrittlement). The drawing call-out typically specifies the grade, joint type (SC for slip-critical, N or X for bearing), and pretensioning method.

Why do framing plans use different line weights for the same member?

Line weight indicates whether the member is at the level shown, above it, or below it. A heavy continuous line is a member at the framing plan elevation (e.g., top of steel for that floor). A medium dashed line is a member overhead — typically an overhead beam, lintel, or future framing that sits above the plan level. A heavy dashed line is below the plan level. This is the only way a 2D plan can communicate 3D framing relationships without separate sections.

Where is the structural steel symbol legend in a drawing set?

On a typical commercial set, structural symbols and abbreviations are on the S0.0 series sheets (general notes and legends), usually S0.1 or S0.2. Connection-specific symbols (welds, bolts, typical connection types) are often on a separate “typical details” sheet (S5.0 or S6.0 series). If a symbol is not defined on the legend, that is a coordination gap worth flagging — the steel fabricator may interpret it differently than the engineer intended.

Manas Gandhi

Co-founder & CTO, Helonic

Manas is the co-founder and CTO of Helonic, where he leads engineering and AI research for construction drawing analysis. He works directly with structural, MEP, civil, and fire protection engineers to translate the way they review drawings into AI systems that flag the issues that actually matter in the field. Before Helonic, he built machine learning pipelines for technical document understanding and has spent the last several years interviewing licensed design engineers and discipline leads to ground product decisions in real practice rather than industry assumptions.

Areas of focus

AI for technical document understanding
Cross-discipline coordination workflows
Code compliance automation (IBC, NEC, NFPA, IPC, IMC, ASCE)
Structural and MEP drawing review systems

How this page was researched: Symbol set assembled from AWS A2.4 (Standard Symbols for Welding, Brazing, and Nondestructive Examination), AISC 360-22 (Specification for Structural Steel Buildings), AISC 303-22 (Code of Standard Practice), and the structural general notes sheets from a sample of commercial drawing sets reviewed inside Helonic. FAQ topics drawn from common shop drawing review questions raised by steel fabricators and structural reviewers on those projects.

Last reviewed by Manas Gandhi · May 2026

Keep exploring

Related references for structural steel drawing review.

Structural Steel Shapes Reference

Full dimensional table for W, HSS, L, C, MC, WT, and plate sections.

Structural Abbreviations

Full list of abbreviations used on structural drawings.

Steel Connection Types

Bolted, welded, and hybrid connections with typical details.

How to Read Structural Drawings

Reading framing plans, sections, schedules, and details.

See Helonic on your drawings

Helonic's AI verifies that member designations are consistent between framing plans and column/beam schedules, flags missing connection symbols, and cross-checks bolt and weld call-outs against the project structural specifications.