What is Connection Detailing Guide used for in structural engineering?

Connection Detailing Guide provides values required for steel design calculations including capacity checks, connection design, and detailing. It is referenced in structural design codes and used by practicing engineers during the design of buildings, bridges, and industrial structures.

Can I use these reference values directly in my design?

Yes, provided the values match your governing code edition and project specifications. Always cross-reference against the primary source (code document, manufacturer data, or published standard). The information on this page is for educational use — final verification by a licensed engineer is required.

How often are these reference values updated?

Reference content is maintained to align with current code editions. When a new edition of AISC 360, AS 4100, EN 1993, or CSA S16 is published, values are reviewed and updated. Check the last-modified date at the bottom of the page and verify against the current edition for your jurisdiction.

Steel Connection Detailing Guide — AISC DG21 & DG22

Complete steel connection detailing reference covering typical shear and moment connection details per AISC Design Guide 21 (Welded Connections) and Design Guide 22 (Façade Attachments), plus the AISC Detailing for Steel Construction manual. Covers bolt spacing and edge distance requirements, clearance and access provisions for erection, shop versus field connection designation, cope dimensions, welding symbols, and drawing documentation standards.

PRELIMINARY — NOT FOR CONSTRUCTION. All results are for educational and reference use only. Must be independently verified by a licensed Professional Engineer (PE) or Structural Engineer (SE) before use in any project.

Overview of Steel Connection Detailing

Connection detailing translates structural design calculations into fabrication and erection instructions. A well-detailed connection drawing eliminates ambiguity, reduces Requests for Information (RFIs), prevents fit-up problems in the field, and ensures that the fabricator produces a connection that meets the design intent. The AISC Detailing for Steel Construction manual (commonly called "DG21" for welded connection detailing) and the AISC Design Guide 22 (façade attachments to steel framing) are the primary North American references for structural steel connection detailing.

The connection detailer must understand both the structural requirements (limit states, load paths, code compliance) and the practical requirements (constructability, access for tools, erection sequence, shop versus field logistics). A detail that is structurally adequate but impossible to erect is a failed design.

Typical Shear Connection Details

Simple shear connections are the most common connection type in steel buildings. They are designed to transfer shear only, with minimal moment resistance to permit end rotation of the beam. The following are the five standard AISC shear connection types:

Shear Tab (Single Plate): A single plate shop-welded to the supporting member and field-bolted to the beam web. This is the most economical shear connection for one-sided beam framing. The plate is typically 1/4 to 1/2 inch thick, with 2 to 5 bolts in a single vertical row. Key detail requirements: (a) the plate must extend past the bolt group to develop the weld; (b) the weld is typically sized for the full shear demand; (c) standard holes in the plate and short-slotted holes in the beam web provide erection tolerance; (d) the beam must be coped if framing into a column web.

Double Angle: Two angles shop-bolted or shop-welded to the beam web, field-bolted to the supporting member. Used for heavier shear loads or where a single plate is insufficient. The outstanding legs of the angles are field-bolted or field-welded to the support. Key details: (a) angle thickness typically 1/4 to 1/2 inch; (b) bolt gage on outstanding legs must provide wrench clearance; (c) for welded outstanding legs, specify end returns at the angle toes.

End Plate: A plate shop-welded to the beam end with field bolts to the supporting member. Common for simple beam-to-column flange connections. Key details: (a) plate width approximately equal to the beam flange width; (b) bolt rows typically 2 to 4, with gage matching the beam flange geometry; (c) the weld between the plate and beam web must be checked for combined shear and moment from the eccentricity between the bolt line and the weld line.

Seated Connection (Unstiffened): An angle shop-welded or bolted to the support with the beam resting on the outstanding leg. Provides erection stability before bolting. The seated angle must transfer the full beam reaction through bending of the angle leg and local web yielding of the beam. Top angle is provided for lateral restraint.

Seated Connection (Stiffened): Same as unstiffened but with stiffener plates welded between the seated angle legs for higher reactions. Used when the unstiffened angle bending capacity is insufficient.

Typical Moment Connection Details

Moment connections transfer both shear and moment between members and require significantly more detailing than shear connections. The following are standard moment connection types per AISC Design Guide 4 (Extended End-Plate) and AISC 358 (Prequalified Connections):

Flush End Plate: A plate welded to the beam end, flush with the beam flanges, field-bolted to the column flange. Used for moderate moment demands. Requires consideration of prying action on the tension bolts. The plate thickness must resist bending at the bolt lines.

Extended End Plate: Similar to flush end plate but with the plate extending above and below the beam flanges, providing additional bolt rows outside the flange. Provides higher moment capacity through larger lever arms. Per AISC DG4, the plate thickness and bolt diameter are selected based on the required moment capacity, with the yield line mechanism governing the plate thickness.

Flange Plate (Bolted Flange Plate): Separate plates bolted to the beam flanges and field-welded to the column. The web connection is typically a single shear plate. This detail separates the flange force transfer (plates) from shear transfer (web plate), simplifying the load path but requiring more field welding.

Directly Welded Flange (WUF-W): The beam flanges are field-welded to the column using CJP groove welds. The web is field-bolted through a single shear plate. This is the most common prequalified moment connection for seismic applications per AISC 358. Key details include: (a) weld access hole geometry per AISC 360 Figure J2.6-1; (b) backing bar removal from the bottom flange weld (seismic); (c) continuity plates at the column opposite the beam flanges; (d) doubler plates if the column web panel zone is overstressed.

Bolt Spacing and Edge Distance Requirements

The AISC 360 Table J3.4 establishes minimum edge distance requirements based on bolt diameter. For standard 3/4-inch bolts, the minimum edge distance is 1-1/4 inches for sheared edges and 1 inch for rolled, gas-cut, or saw-cut edges. The preferred edge distance for detailing is 1-1/2 inches to provide tolerance for fabrication and mill tolerances.

Minimum center-to-center bolt spacing is 2-2/3 times the bolt diameter (2 inches for 3/4-inch bolts). The preferred spacing is 3 times the bolt diameter (2-1/4 inches for 3/4-inch bolts). This provides adequate clearance for bolt installation tools and ensures the connected plies remain in contact through the full length.

Maximum edge distance is 12 times the plate thickness, not to exceed 6 inches. Maximum spacing for bolts connecting parts in compression is the lesser of 24 times the thickness of the thinner part or 12 inches, intended to prevent local buckling of the connected ply between fasteners.

For slotted holes: the long dimension of a short-slot (SSL) is d + 3/16 plus 1/4 inch for each 1/2 inch of bolt diameter above 3/4 inch. Long-slot (LSL) holes have a length of 2.5d. Oversize holes (OVS) are d + 1/8 inch for bolts 7/8 inch and smaller, or d + 3/16 inch for larger bolts.

Cope Dimensions and Clearances

Coped beam connections require notching the beam flanges to clear the supporting member. Standard cope dimensions per AISC Manual Part 9:

Cope depth (dc): Typically dc = k + 1/2 inch for a top cope, where k is the fillet dimension from the top of the beam to the web toe. The extra 1/2 inch provides erection clearance.
Cope length (lc): Must be sufficient to clear the supporting member plus any bolt head projection.
Cope radius: The inside corner of the cope must have a minimum radius of 1/2 inch to reduce stress concentration. AISC 360 Section J4.1 requires a minimum cope radius.
Double copes: When both top and bottom flanges are coped (e.g., beam framing into a girder web where the top and bottom are at similar elevations), the remaining web depth must be adequate for shear transfer and stability during erection.

For erection clearances, allow at least 1/2-inch clearance between the coped surface and the face of the supporting member. For beam ends with end plates or shear tabs, allow at least 1/4-inch clearance between the end plate edge and any obstruction.

Wrench Clearance and Tool Access

Proper wrench clearance is a common oversight in connection detailing. Standard impact wrenches require a minimum of 2 to 3 inches of clear radial space around the bolt. For structural bolts with a heavy hex head (1-1/4 inches across flats for 3/4-inch bolts), the entering clearance must accommodate the socket diameter plus any extension. Specific requirements per RCSC Specification and AISC Detailing for Steel Construction:

For bolt diameters up to 1 inch: 1-3/4-inch minimum clear distance from bolt centerline to any obstruction for standard sockets.
For skewed connections where the bolt axis is not perpendicular to the erection access plane, additional clearance is required.
Tension control (twist-off) bolts require clearance for the sheared spline end to eject without obstruction.
For shop connections, larger clearances are preferred since multi-spindle drilling machines and automatic welding equipment require access.

Welding Symbols per AWS A2.4

Welding symbols are the standard language of connection detailing, communicating all weld requirements on the drawing without ambiguity. The AWS A2.4 system uses a horizontal reference line with an arrow pointing to the joint:

Arrow side: The side of the joint that the arrow touches. Weld symbols placed below the reference line denote an arrow-side weld.
Other side: The opposite side of the joint. Weld symbols placed above the reference line denote an other-side weld.
Both sides: Weld symbols both above and below the reference line.
Field weld flag: A black flag at the junction of the arrow and reference line. Field welds are made at the construction site rather than the fabrication shop.
Weld-all-around circle: A circle at the junction of the arrow and reference line. Used when the same weld is applied continuously around the perimeter of a joint.
Tail: The forked end of the reference line, used for supplementary notes such as welding process (SMAW, FCAW-G), electrode specification, or WPS reference number.

A typical fillet weld callout reads: 1/4 (leg size) to the left of the fillet symbol, length (6) and pitch (12) to the right for intermittent welds, with the symbol on the arrow side or other side position.

Shop Versus Field Connection Designation

Per AISC Code of Standard Practice Section 3.1.2, the Engineer of Record must clearly designate which connections are shop connections and which are field connections. This distinction affects the connection type selection, the welding versus bolting decisions, and the overall erection sequence.

Shop connections are preferred for: (a) all welding where possible — shop welding is more economical, has better quality control, and allows flat-position welding; (b) connections that require CJP groove welds with UT inspection; (c) connections requiring heat straightening or cambering; (d) connections to column flanges where the column is shipped as a single piece.

Field connections are preferred for: (a) beam-to-beam connections where one or both members arrive at the site separately; (b) column splices (typically bolted with flange plates or end plates); (c) diagonal bracing connections where the brace is the last piece erected; (d) connections with large erection tolerances where field fit-up is necessary.

The general rule: fabricate as much as possible in the shop, bolt in the field. Field welding should be minimized and carefully specified with inspection requirements.

Drawing Documentation Standards

A complete structural steel connection drawing set includes:

General Notes: Material specifications (ASTM grades), bolt specifications (ASTM F3125), welding code (AWS D1.1), and inspection requirements.
Typical Connection Details: Standard details repeated across the project, including shear tabs, double angles, end plates, and moment connections.
Specific Connection Schedules: Tables listing each connection with the beam size, support size, connection type, number of bolts, plate thickness, weld size, and any special requirements.
Cope and Blocking Details: Dimensions for all beam copes, stiffener plates, continuity plates, and doubler plates.
Erection Plan: Sequence of erection, temporary bracing requirements, and any limitations on back-span loading before connections are complete.

All connection design loads (shear, axial, moment) for which the connection was designed must be shown on the design drawings per AISC Code of Standard Practice. This allows the EOR to verify that the fabricator's connection design meets the assumed demands.

Worked Example: Shear Tab Detailing

Problem Statement: Detail a shear tab for a W16×26 beam (d = 15.7 in, tw = 0.250 in) framing into a W14×90 column flange. Factored shear Vu = 35 kips. Use 3/4-inch A325-N bolts and A36 plate.

Step 1 — Select plate width and bolt layout: Use PL 1/4 × 4-1/2. Three bolts in a single column at 3-inch spacing. Edge distance = 1-1/4 in min, use 1-1/2 in for tolerance. Plate height = 1.5 + 3 + 3 + 1.5 = 9 inches.

Step 2 — Weld design to column flange: Fillet weld each side of plate. Minimum weld size for 1/4-inch plate per Table J2.4 = 1/8 inch. Weld metal strength per inch per side φRn = 0.75 × 0.60 × 70 × 0.707 × w = 22.27w kips/in. For w = 3/16 in: φRn = 4.18 kips/in per side. Weld length = plate height minus top and bottom clearance = 9 - 0.5 - 0.5 = 8 inches per side. Total capacity = 4.18 × 8 × 2 = 66.9 kips > 35 kips.

Step 3 — Check bolt shear and bearing on beam web: Bolt single shear capacity φrn = 17.9 kips (threads included). Three bolts = 53.7 kips > 35 kips. Bearing on beam web: φrn = 0.75 × 2.4 × 0.750 × 0.250 × 65 = 21.9 kips/bolt. Total = 65.7 kips > 35 kips.

Step 4 — Check block shear on beam web: Shear plane = 1.5 + 3 + 3 = 7.5 in to bolt centerline. Tension plane = 1.5 in. Block shear φRn = 51.8 kips > 35 kips (per Chapter J4.3 calculation).

Step 5 — Drawing callouts:

PL 1/4 × 4-1/2 × 0'-9" (A36)
(3) 3/4" φ A325-N bolts in STD holes at 3" c/c
3/16 fillet weld each side × 8" (E70XX)
1/2" end return at top
PL shop-welded to column, field-bolted to beam web
Short-slotted holes (SSL) in beam web for erection tolerance

Engineering Best Practices

Standardize connection details across a project. Using 3 or 4 standard shear connections significantly reduces fabrication costs compared to custom details for every beam.
Design shear tabs with standard bolt gages that match common drill spacing on automated beam lines (typically 3-inch increments).
For skewed connections, avoid bolt spacings below 3 inches to accommodate skewed nut seating.
Specify erection clearances of 1/4 to 1/2 inch at all interfaces. Tight fits invite field modifications and delays.
For coped beams, provide block shear capacity calculations on the shop drawings. Coped beam block shear is a frequently litigated failure mode.
Include a note on the drawings: "Contractor shall verify all existing conditions and dimensions prior to fabrication."

References

AISC Design Guide 21 — Welded Connections — A Primer for Engineers
AISC Design Guide 22 — Façade Attachments to Steel-Framed Buildings
AISC Detailing for Steel Construction, 3rd Edition
AWS A2.4 — Standard Symbols for Welding, Brazing, and Nondestructive Examination
AISC Code of Standard Practice for Steel Buildings and Bridges

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