The Two Phases of Connection Design
Structural steel connections are designed in two distinct phases. The first is the engineer of record's (EOR) conceptual phase: the EOR determines connection types (moment, shear, or combined), assigns design loads, and specifies governing standards (AISC 360, AISC 358 for seismic, etc.). The second is the working-point phase: the detailer — or a delegated design engineer — translates those loads into specific geometry: bolt sizes, weld sizes, plate thicknesses, and stiffener requirements. Shop drawings cannot be produced without both phases complete.
EOR Design vs. Delegated Connection Design
Some EORs fully design every connection and show it on their structural drawings. More commonly, EORs specify connection loads on their drawings and delegate the detailed design to the steel fabricator or their detailer. When connection design is delegated, the fabricator assumes responsibility — and liability — for that engineering work. A licensed engineer must stamp the connection calculations in all U.S. jurisdictions. If your detailer does not have in-house licensed engineers, they cannot perform delegated connection design and you will need a separate connection engineer.
Standard Connection Types
The most common steel connection families and what drives their design:
- Simple Shear (Pinned) Connections — shear tabs, single-plate connections, and seated connections; designed for vertical shear load only
- Moment Connections — end-plate (flush and extended), directly welded flange, or bolted flange plates; designed for moment plus shear
- Braced Frame Connections — gusset plates connecting diagonal bracing to beams and columns; designed for axial load with compression buckling check
- Moment Frame (SMRF/IMRF) Connections — seismic-rated pre-qualified connection types per AISC 358; require special inspection and welder qualification
- Column Base Plates — anchor bolt pattern, plate thickness, and grout design; must coordinate with concrete foundation design
- Embed Plates and Weld Plates — for concrete-to-steel interfaces; often overlooked until the concrete pour is imminent
What Information Your Detailer Needs
To complete connection details without generating a wall of RFIs, your EOR or PM should provide at the start of detailing:
- Structural drawings stamped for construction (not permit set only) with connection loads or 'design by fabricator' callouts
- Geotechnical report or foundation design if base plates or embeds are in scope
- Governing structural specifications (Division 05 or project spec) identifying bolt grades, weld procedures, and inspection requirements
- Seismic design category and R-factor if the project is in a seismic zone — this determines whether AISC 341 and 358 apply
- Architectural and MEP drawings to identify copes, penetrations, and clearance constraints
- Schedule — specifically whether connections should be shear-only first with moment connections held for final engineering
The RFI Cycle and How to Minimize It
Every unanswered connection design question during detailing becomes an RFI. RFIs add one to three weeks per round trip on most projects. The most effective way to minimize the RFI cycle: hold a pre-detailing kickoff call that includes the EOR, PM, and detailing firm. Walk through the connection load table, confirm delegated vs. EOR-designed connections, and flag any non-standard framing conditions before detailing starts. Tectonix project managers run this kickoff call on every project because the information gathered there typically saves three to five RFI cycles.
Connection Design and Fabrication Cost
Connection geometry has a direct impact on fabrication cost. Moment end plates require tighter flatness tolerances and more weld volume than shear tabs. Stiffened connections cost more than unstiffened. SMRF welds require certified welders and special inspection logs. When you receive pricing from your fabricator, the connection design assumed is a key variable — if the EOR later specifies a heavier or more complex connection than what was estimated, expect a change order. Locking in connection design before buyout protects all parties.