Steel Connections Define How the Structural System Behaves Under Load - Connection Type and Details Must Coordinate with the Structural Engineer
Structural steel buildings are assembled from individual members - columns, beams, and braces - that are connected at their intersections. The behavior of the connection determines the behavior of the structural system: a simple (pinned) connection transfers only shear force, not bending moment, and allows the connected elements to rotate relative to each other; a rigid (moment) connection transfers both shear and moment and restrains rotation, creating the fixed-end conditions required for moment frames. The architect's responsibility in steel construction is not to design connections - that is the structural engineer's responsibility (and often the steel fabricator's engineer) - but to understand connection types, their visual implications for the building, their size and depth requirements, and how they are coordinated in the construction documents. The ARE PDD exam tests this coordination knowledge in the context of steel building documentation.
Bolted Connections
Bolted connections use high-strength structural bolts (typically ASTM A325 or A490) to connect steel plates and members. Types of bolt loading: shear (bolt loaded perpendicular to its axis) and tension or tension-shear combined. Types of bolted connection behavior: slip-critical (bolts pretensioned to prevent slipping of the connected pieces under load) and bearing-type (bolts not pretensioned; connection relies on bearing of bolt shank against bolt hole). Bolted connections are field-installed, which makes them more adaptable to field conditions and allows some adjustment. The visual expression of bolted connections (bolt heads and nuts visible on the steel surface) can be an architectural feature in exposed structural steel conditions.
Welded Connections
Welded connections join steel members through fusion of the base metal using an electric arc or other welding process. Weld types: fillet welds (applied in the corner where two plates meet at approximately right angles) and groove welds (applied in a groove prepared in one or both base metals - can provide full-penetration welds for high-strength applications). Welded connections are typically made in the shop (shop welds) rather than in the field (field welds) because quality control is better in the shop environment. Fully restrained moment connections are typically shop-welded. Field welds are used for connections that cannot be pre-assembled - splice plates and field connections between shipped pieces. Welded moment connections in high seismic zones require prequalified connection types (AISC 358) and fracture-critical inspection.
Shear vs. Moment Connections
Simple shear connections (shear tabs, clip angles, double-angle framing) transfer only vertical shear from beam to column; they allow the beam end to rotate freely. Gravity framing uses simple shear connections. Fully restrained moment connections (WUF-W: Welded Unreinforced Flange-Welded Web; RBS: Reduced Beam Section) transfer both shear and moment; they are the beam-column connections in moment-resisting frames. Moment connections are significantly more expensive and require more demanding fabrication, inspection, and testing - they are used only where the lateral system requires moment frame behavior.
Key Exam Points
- Simple connections: shear only; beam end rotates; gravity framing; shear tabs, clip angles.
- Moment connections: shear + moment; fixed end; lateral frames; more expensive; WUF-W, RBS types.
- Bolted: field-adjustable; visible hardware; bearing or slip-critical behavior.
- Welded: shop welds preferred for quality; field welds at splices; moment connections typically welded.
- Seismic moment connections: AISC 358 prequalified types required; fracture-critical inspection.
AREprep's PDD structural content covers steel connection types, how connections are shown on structural drawings, coordination between architectural and structural documents for exposed steel conditions, and how connection design intent is communicated in specifications - giving ARE PDD candidates the steel construction knowledge the exam tests in building system coordination and construction document questions.
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