Connection Design 101 for Detailers Who Didn't Go to Engineering School

Most detailers learn connection design by looking at what other detailers drew before them. That's how the trade works. You look at a clip angle connection on the last project, check the bolt spacing, match the pattern, and move on. Eventually, though — when an EOR sends back a submittal with comments, or a PM asks why you detailed a shear tab instead of a clip angle — you need to understand what's actually happening at the connection: what forces are moving through it, why one configuration works and another doesn't, and where the line falls between a detailer judgment call and a decision that needs an engineer's stamp. This post is not an engineering course. It won't teach you to design a moment connection from scratch. What it will give you is the conceptual foundation that makes you a better detailer — one who can read a connection detail, understand why it's built the way it is, and know when something doesn't look right.

Why Connection Design Knowledge Makes You a Better Detailer

Your job isn't to stamp connections. That's the EOR's responsibility. But detailers make dozens of micro-decisions on every project — bolt gauge lines, cope dimensions, weld access holes, plate thickness — and those decisions interact with the connection's structural behavior in ways that matter. A cope that's too deep weakens the web. A weld access hole in the wrong place creates a stress concentration on a seismic moment connection. A shear tab detailed without accounting for the beam's end rotation creates binding on the shop floor.

Understanding steel connection design basics for detailing means you catch these issues before the submittal goes out. It means you can have a real conversation with the EOR when something on the design drawings doesn't make sense. And it means fewer RFI cycles, which matters to every fabricator trying to hold a schedule.

The Three Forces a Connection Must Transfer

Every connection in a steel structure is doing one or more of three jobs: transferring shear, transferring moment, or transferring axial load.

Shear is the vertical force — the beam's reaction load trying to slide down past the supporting member. Most beam-to-column and beam-to-girder connections are primarily shear connections. The load goes: beam web, into the connection element, into the support.

Moment is rotational force — a couple that tries to pull one flange in tension and push the other into compression simultaneously. Moment connections are used where the frame needs to resist lateral loads (wind, seismic) or where continuous beam behavior is required. They're more complex to detail and more sensitive to geometry.

Axial load is tension or compression along the member's length. Bracing connections and chord splices carry significant axial. Hangers and tension rods are pure axial. Some connections carry all three simultaneously.

When you're reading structural connection design fundamentals on a set of drawings, the first question is always: what forces is this connection carrying? The answer drives every decision that follows.

Simple Shear Connections

Simple shear connections assume the beam end is free to rotate — they transfer vertical load without restraining the beam's natural tendency to deflect and rotate at the support. The three workhorses are clip angles, shear tabs, and end plates.

Clip angles are attached to the beam web with bolts or welds, then bolted or welded to the supporting member. Double-angle connections (one angle on each side of the web) are among the most flexible and forgiving configurations in the AISC manual. They accommodate end rotation well and are easy to adjust in the field.

Single plates (shear tabs) are a shop-welded plate on the support with field-bolted connection to the beam web. They're cleaner to fabricate and faster to erect than clip angles, which is why fabricators often prefer them. But they're less forgiving of misalignment and the plate thickness, weld size, and bolt count all matter in ways the detailer needs to respect.

End plates are less common for simple shear but appear on beam-to-beam framing where access for clip angles is limited. They're shop-welded to the beam end and field-bolted to the web of the supporting girder.

AISC Table 10-1 through 10-12 (Part 10 of the Steel Construction Manual) provides standard configurations for all of these. More on that below.

Moment Connections

Where simple shear connections let the beam end rotate freely, moment connections lock that rotation — they transfer both vertical shear and the beam's end moment into the column. That changes everything about how the connection is detailed.

Extended end plates are the most common moment connection in commercial construction. A plate is shop-welded to the beam end with fillet welds to the flanges and web, then field-bolted to the column flange with high-strength bolts. The bolt pattern — typically four or eight bolts in a stiffened configuration — must align with the column flange and accommodate the prying forces that develop under load.

Welded flange connections are used on high-seismic projects (SDC D and above) where the connection must meet Special Moment Frame (SMF) or Intermediate Moment Frame (IMF) requirements under AISC 358. The beam flanges are CJP-welded directly to the column flange. Prequalified connections like the WUF-W and Kaiser Bolted Bracket have specific dimensional and weld requirements that are not detailer discretion — they come from the engineer's connection design and the prequalification documents.

Moment connections are demanding to detail because tolerances are tighter, weld quality requirements are stricter (often requiring UT), and the geometry between bolt lines, column face, and beam depth is interdependent.

Bracing Connections and Work Point Geometry

Bracing connections — gusset plates connecting diagonal braces to beams and columns — are where detailers most often run into geometric problems. The work point (where the centerlines of the brace, beam, and column all intersect) drives the geometry of the entire connection. Move the work point, and you change the eccentricity, which changes the forces in the welds and the plate.

On a Uniform Force Method (UFM) connection designed per AISC Chapter 13, the gusset plate dimensions, weld lengths, and bolt patterns are all tied to the work point location. If the detailer adjusts the gusset to clear a conflicting member without notifying the EOR, the connection may no longer work. This is a hard stop — get the engineer involved before you move a work point.

Bolt Basics: Grade, Pretension, and Installation Method

A325 and A490 are the two high-strength bolt grades you'll see on most structural steel connection design drawings. A490s are stronger but more expensive and less forgiving of overtightening. Most commercial projects use A325 (now F3125 Grade A325 under the unified ASTM standard).

The installation method matters more than most detailers realize. Bearing bolts (snug-tight) transfer load through bearing on the bolt shank and are sufficient for most simple shear connections. Pretensioned bolts have a specified minimum pretension and require turn-of-nut, DTI washers, or tension-control (TC) bolts to verify. Slip-critical connections require pretension plus a clean faying surface — they're used where slip would be unacceptable (long-slotted holes, seismic connections, connections subject to load reversal).

The connection drawing or general notes will specify. Don't default to snug-tight if the drawings call for pretensioned.

Weld Basics: Fillet, CJP, and PJP

Fillet welds are the default. They're placed in the corner between two pieces and sized by the detailer (or by the engineer — read the notes). Most shear tab welds, clip angle welds, and gusset welds are fillets.

CJP (Complete Joint Penetration) groove welds fuse through the full thickness of the base metal. They're required on seismic moment connections, tension splices, and connections where the full section capacity needs to be developed. CJPs require weld access holes and backing bars in most configurations, and typically require UT inspection on primary members.

PJP (Partial Joint Penetration) groove welds penetrate only partway through. They appear on column splices, heavy baseplate connections, and built-up member assembly. They're stronger than fillets for the same weld volume but have limitations in tension applications — the EOR specifies where they're permitted.

The project's general weld notes (GN) and AWS D1.1 compliance requirements will define minimum preheat, inspection class, and electrode specification. Read them before you start detailing.

Reading AISC Table 10 as a Detailer

Part 10 of the AISC Steel Construction Manual is your primary reference for standard simple shear connections. The tables give you bolt capacity, weld capacity, and maximum/minimum connection depths for clip angles, shear tabs, and other configurations across a range of beam sizes and reaction loads.

As a detailer using Tekla Structures or SDS/2, you'll often be working from connections that reference these tables. When an EOR says "W16x36, 30-kip reaction, shear tab" — Table 10-10a will tell you whether a 3-bolt or 4-bolt configuration works for that load. If you're in a shop that details standard connections without engineer-designed connection data for every joint, knowing how to read these tables keeps you from detailing something that doesn't work.

AISC makes the manual available to members, and the connection design chapters are worth reading slowly, with a pencil.

The Line Between Detailer and Engineer

Know where your authority ends. Standard connections within AISC table limits, copying geometry from engineer-provided connection data, maintaining specified bolt patterns and weld sizes — that's detailer territory. Modifying a connection because it conflicts with another member, changing a weld size because it "looks small," adjusting a moment connection bolt pattern because the column flange is narrow — those require engineer involvement.

When something doesn't look right, the right move is always to document the issue, send an RFI, and wait for direction. A connection that goes to the shop floor wrong costs more to fix than any RFI delay.

The structural steel connection design fundamentals covered here aren't a license to start stamping connections. They're a framework for understanding what you're looking at — so you can detail it correctly and know when to stop and ask.

NRSteel works exclusively with fabricators on commercial and institutional structural steel projects. If you're evaluating detailing partners who understand the fabricator's side of the business — schedules, submittals, shop floor efficiency — get in touch to discuss your next job.