What is the difference between simple shear and moment connections?

Simple shear connections transfer vertical shear only while allowing end rotation — the beam is modeled as a pin in structural analysis. Moment connections transfer both shear and bending moment while restraining rotation — the beam is modeled as fixed (fully or partially). Simple shear connections are the default for gravity framing (90%+ of beam connections in a typical steel building). They use shear tabs, double angles, or end plates with bolts near the beam web centerline, allowing the beam end to rotate under load and relieving the connection of moment demand. Moment connections are required where the frame resists lateral loads through bending of the beams and columns. They connect the beam flanges (which carry the moment couple) to the column via CJP welds, bolted flange plates, or extended end plates with bolts outside the flanges. The cost difference is substantial: a typical shear tab connection costs $50-150 per beam end (shop weld plate to column, field bolt beam web), while a fully welded moment connection costs $300-800 per beam end (field weld top/bottom flanges, field bolt web, backing bars, inspection). For a 10-story building, using moment frames only where needed for lateral resistance (typically 2-3 bays per direction) and shear connections everywhere else saves 15-25% on steel connection costs compared to an all-moment-frame design.

What are the 8 limit states checked in shear tab design?

AISC Manual Part 10 requires checking 8 limit states for single-plate shear tab connections: (1) Bolt shear — single shear for the bolts connecting the beam web to the plate, φrn = φ × Fnv × Ab per bolt. For 3/4" A325-N bolts in single shear: φrn = 0.75 × 54 × 0.442 = 17.9 kips/bolt. (2) Bolt bearing and tearout on the plate — φrn = φ × 2.4 × d × t × Fu (bearing) or φ × 1.2 × Lc × t × Fu (tearout), whichever is smaller per bolt. (3) Plate shear yielding — φVn = φ × 0.6 × Fy × Agv where Agv = plate depth × plate thickness. (4) Plate shear rupture — φVn = φ × 0.6 × Fu × Anv where Anv = (plate depth − n × dh) × plate thickness. (5) Block shear rupture — combination of shear yielding/rupture on the vertical plane and tension rupture on the horizontal plane per AISC Eq. J4-5, often the governing limit state for thin plates with small edge distances. (6) Weld shear — fillet weld connecting the plate to the supporting member, φRweld = φ × 0.6 × FEXX × 0.707 × weld size × (2 sides × plate depth). For E70XX electrodes: 1.392 kips per inch per 1/16" of weld size per side. (7) Plate flexure — the eccentricity e = a/2 (half the distance from weld line to bolt line) creates a moment M = V × e that the plate must resist; φMn = φ × Fy × Zplate (plastic section modulus of plate). (8) Beam web — bearing/tearout on the beam web (similar to limit state 2 but with beam web thickness), and beam web block shear. All 8 must be checked; the lowest φRn governs.

When should extended end plate moment connections be used?

Extended end plate (EEP) moment connections are the most common field-bolted moment connection. A plate is shop-welded to the beam end and field-bolted to the column flange with bolts positioned both inside the beam flanges (tension bolts) and outside the flanges (additional tension bolts extending beyond the beam depth). EEP connections are prequalified per AISC 358-22 for SMF and IMF applications up to W36 beam sizes when designed per the prescribed procedure. Advantages over field-welded flange connections: no field welding (bolts only), eliminating the welder qualification, UT inspection, and weather sensitivity of CJP field welds; faster erection (bolting vs welding saves 20-40 minutes per connection); prequalified design procedure eliminates the need for connection-specific testing. The design procedure per AISC 358 Chapter 6 checks: bolt tension rupture (the two rows of bolts outside the tension flange resist the flange force), bolt shear combined with tension, end plate flexural yielding (yield line analysis of the plate, with thickness typically 3/4" to 2" depending on beam size), beam flange to end plate weld (CJP or fillet), column flange flexure (must be thick enough to prevent bending that would reduce bolt pretension), and panel zone shear. EEP connections are heavier than welded flange connections (the plate alone can be 40-150 lb) and require precise shop fabrication (plate flatness, hole alignment). Cost comparison: EEP is typically 10-20% cheaper than field-welded flange when field welding costs are high, but 5-10% more expensive when shop welded flange plates with field bolted web is an option.

How are column splices designed and what are the key limit states?

Column splices join column sections at erection joints, typically located 4-6 ft above the floor level (top of steel) for erection access. For W-shape columns, splices transfer axial compression, any tension from uplift/cantilever, and shear from lateral drift. Partial-joint-penetration (PJP) groove welds are standard for compression splices — the column ends are prepared and welded directly (no splice plates) where both column sections are the same depth. For columns of different depths, filler plates and flange/ web splice plates are required. Key limit states: (1) Compression bearing — AISC J1.4 requires that the compression splice transfer the full column axial load by bearing of finished column ends (milled to a smooth surface), with the weld providing only nominal connection (typically 50% of the flange area in PJP). For columns with finished ends: the bearing stress Fp = 0.9Fy on the contact area; for an 8" flange × 0.5" thick × 2 flanges: contact area = 8 in², bearing capacity = 0.9 × 50 × 8 = 360 kips in bearing alone. (2) Tension splice — if net tension exists, flange splice plates with CJP or fillet welds must develop the full tension force, checked for plate yielding, plate rupture, and weld capacity. (3) Shear transfer — erection loads and lateral drift produce shear across the splice, typically resisted by a web splice plate or the web portion of the column welds. (4) Alignment — AISC 303 erection tolerances require ±1/16" column alignment at splices, so the splice detail must accommodate small misalignment.

What makes braced frame connections different from other connection types?

Braced frame connections (gusset plate connections) transfer large axial forces from the brace into the beam-column joint. Unlike shear connections (shear only) or moment connections (shear + moment), brace connections primarily transfer axial tension and compression, with the force often exceeding 200-500 kips in a typical mid-rise SCBF. Design uses the Uniform Force Method (AISC Manual Part 13): the gusset-to-beam and gusset-to-column interfaces are sized so the resultant of the interface forces passes through the brace work point (intersection of beam, column, and brace centerlines), eliminating moment on the connection interfaces. Key limit states: (1) Whitmore section — the effective width of gusset plate resisting the brace force, defined by spreading the force at 30° from the first row of bolts to the last row, checked for tension yielding and compression buckling. (2) Gusset plate buckling — the unbraced length of the gusset free edge is checked against a plate buckling criterion; for SCBF, a 2t linear clearance for the buckling hinge is required. (3) Interface weld — the weld between gusset and beam/column must transfer the full interface force. (4) Beam and column local checks — the beam web and column web/flange must resist the concentrated gusset force without local yielding, web crippling, or sidesway buckling. For SCBF connections per AISC 341, demand-critical welds at the gusset-to-beam interface require notch-toughness qualifications (CVN ≥ 20 ft-lb at 0°F). Gusset plates are typically 3/8" to 1" thick A572 Gr. 50 plate.

Steel Connection Types — Explained with Examples

Steel connections transfer forces between members. The type of connection determines whether it carries shear, moment, axial force, or a combination. AISC 360 Chapter J governs connection design. This page explains every major connection type, when to use each, and what limit states to check.

Connection Classification

Connections are classified by the forces they transfer and their rotational stiffness:

Category	Transfers	Rotational Stiffness	Example
Simple (shear)	Shear only	Flexible (pinned)	Single-plate shear tab
Moment (rigid)	Shear + Moment	Rigid	Fully welded flanges
Partially restrained	Shear + partial moment	Semi-rigid	Extended end plate
Axial (tension/compression)	Axial force	Varies	Gusset plate brace
Base	All forces to foundation	Rigid/fixed	Column base plate

AISC defines three frame types based on connection behavior:

Frame Type	AISC Designation	Connection Type	Analysis Method
Simple framing	Type PR (flex)	Shear only	Gravity beams pinned
Moment framing	Type FR (fixed)	Rigid moment connection	Lateral frame analysis
Partially restrained	Type PR	Semi-rigid	Requires moment-rotation data

Simple Shear Connections

Simple shear connections are the most common connection in steel buildings. They transfer vertical shear from beams to columns or girders while allowing rotation (treating the beam end as a pin).

Types of Simple Shear Connections

Type	Description	Typical Capacity	Advantages
Single-plate (shear tab)	Single vertical plate welded to support	10-200 kips	Simple, shop welded
Double-angle	Two angles bolted to beam, bolted/welded to support	10-300 kips	Very common, forgiving
Single-angle	One angle bolted to beam web	5-50 kips	Economy, light beams
Tee (WT cut)	WT section bolted to beam web	10-150 kips	Good eccentricity control
End plate	Plate welded to beam end, bolted to support	10-200 kips	Shop welded, clean look
Seated connection	Angle seat supporting beam from below	5-80 kips	Simple, beam sits on seat

Single-Plate Shear Tab Design Checklist

Bolt shear (single or double shear)
Bolt bearing and tearout on plate
Plate shear yielding (Agv × Fy)
Plate shear rupture (0.6 × Anv × Fu)
Block shear (combination yielding + rupture)
Weld shear (plate to support)
Plate flexure (due to eccentricity)
Beam web checking (bearing, tearout, block shear)

AISC Manual Tables for Simple Connections

Connection Type	AISC Manual Table
Single plate	Table 10-10, 10-11
Double angle	Table 10-1 through 10-4
Single angle	Table 10-12
End plate	Table 10-5, 10-6
Seated	Table 10-7, 10-8

Moment Connections

Moment connections transfer both shear and bending moment. They are required in moment frames to provide lateral resistance against wind and seismic forces.

Types of Moment Connections

Type	Description	Stiffness	Application
Fully welded flanges	Beam flanges groove-welded, web bolted	Rigid	Heavy moment frames
Flange plates (bolted)	Top and bottom plates bolted to flanges	Rigid	Field bolting
Extended end plate	End plate with bolts outside flanges	Rigid	Clean, prequalified
Bolted flange plates	Angles or tees on flanges	Rigid	Retrofit
Reduced beam section (RBS)	Flanges cut back near connection	Rigid	Seismic (AISC 358)
Free flange	Web detached near connection	Rigid	Seismic

Prequalified Moment Connections (AISC 358)

For seismic applications (AISC 341), only prequalified connections may be used without testing:

Connection	Prequalification	Max Beam Depth	Typical Use
Reduced Beam Section (RBS)	AISC 358	W36	Most popular seismic
Bolted Unstiffened End Plate (BUEP)	AISC 358	W24	Moderate seismic
Bolted Stiffened End Plate (BSEP)	AISC 358	W36	Heavy seismic
Welded Flange (WUF)	AISC 358	W36	Welded construction
Kaiser Bolted Bracket	AISC 358	W24	Bolted alternative
SidePlate	AISC 358	W36	Proprietary
SlottedWeb	AISC 358	W24	Moderate seismic

Moment Connection Design Checklist

Flange force: Ff = M / (d - tf)
Flange weld capacity (CJP or fillet)
Flange plate tension/compression yielding
Flange plate rupture (net section)
Flange plate bolt shear
Flange plate block shear
Panel zone shear (column web)
Column flange bending (prying action)
Continuity plate requirements
Web bolt group (shear transfer)
Column strong-axis/weak-axis checks (unbalanced moments)

Braced Frame Connections

Braced frame connections transfer axial forces through gusset plates. The connection must accommodate the brace force and the geometry of the brace-to-frame intersection.

Gusset Plate Connection Types

Type	Force Transfer	Design Approach
Uniform force	Balanced axial + shear on plate	Thornton method (AISC)
Concentric	Force through work point	Ideal, not always possible
Eccentric	Force offset from work point	Include moment in design
End gusset	Brace connects to beam or column end	Shorter gusset
Mid-span gusset	Brace connects at beam mid-span	Vertical brace to beam

Gusset Plate Limit States

Brace tension yielding (Ag × Fy)
Brace tension rupture (Ae × Fu)
Gusset shear yielding
Gusset shear rupture
Gusset block shear
Bolt shear and bearing
Weld shear (brace to gusset)
Whitmore section (effective width at gusset)
Gusset buckling (compression brace)
Interface forces (beam-to-gusset, column-to-gusset)

Base Plate Connections

Base plates transfer column forces (axial, shear, moment) to the concrete foundation. Design per AISC 360 Chapter J and ACI 318 Appendix D.

Base Plate Type	Forces	Design Method
Axial only (gravity)	Compression only	AISC Table method
Moment base	Compression + tension	Strut-and-tie method
Anchored base	Uplift + shear	ACI 318 Appendix D
Embed	Shear + moment	Steel embed design

Key limit states for base plates:

Bearing on concrete (φPp = φ × 0.85 × f'c × A1)
Base plate bending (cantilever from column)
Anchor bolt tension (uplift or moment)
Anchor bolt shear
Concrete breakout (tension and shear cones)
Anchor pullout
Concrete side-face blowout (shallow embedment near edge)

Splice Connections

Splices join two members end-to-end. Required when member length exceeds mill or transport limits (typically 60-70 ft for columns, 50-60 ft for beams).

Splice Type	Members	Location	Notes
Column splice (pl)	Columns	4 ft above floor	Full-penetration or bolted
Beam splice (pl)	Beams/girders	Per engineering	Flange + web plates
HSS splice	HSS columns	Mid-height or at floor	Butt plate or direct weld
Brace splice	Bracing	Per engineering	Gusset or butt splice

Column splices per AISC are typically designed for a minimum of 50% of the smaller member capacity, or the actual forces from analysis, whichever governs.

Connection Selection Guide

Situation	Recommended Connection	Why
Gravity beam to column	Single-plate shear tab	Simplest, most economical
Gravity beam to beam	Double-angle or single-angle	Field bolted, forgiving
Moment frame (non-seismic)	Flange plate moment	Field bolted, no special testing
Moment frame (seismic)	RBS per AISC 358	Prequalified, ductile
Chevron brace to beam	Gusset plate (balanced)	Handles reversal, compact
X-brace	Gusset plate with slit	Allows crossing braces
Column base (gravity)	Grouted base plate	Simple bearing design
Column base (moment frame)	Anchored base plate	Resist moment, tension anchors
Truss chord splice	Bolted flange + web plates	Full capacity splice

Frequently Asked Questions

What is the most common steel connection? The single-plate shear tab (shear connection) is the most common connection in steel buildings. It consists of a single plate shop-welded to the supporting member and field-bolted to the beam web. AISC Manual Tables 10-10 and 10-11 provide precalculated capacities.

What is the difference between simple and moment connections? Simple connections transfer shear only and allow beam end rotation (pinned). Moment connections transfer both shear and bending moment, providing rotational stiffness. Moment connections are required for moment-resisting frames that resist lateral loads.

When do I need a moment connection? Moment connections are needed when: (1) the building uses a moment frame for lateral resistance, (2) the beam has a cantilever overhang, (3) frame stability requires fixity, or (4) seismic design requires ductile moment connections per AISC 341.

What is a gusset plate? A gusset plate is a flat steel plate that connects a diagonal brace to the beams and columns of a braced frame. It transfers the brace axial force into the frame through welds and bolts. The plate is typically designed using the uniform force method (Thornton method) from the AISC Steel Manual.

How do I choose between welding and bolting? Shop connections are typically welded (controlled environment, no weather). Field connections are typically bolted (faster, no inspection delays, reversible). Critical moment connections may use field welding (CJP welds) with required testing. The AISC preference is to minimize field welding.

Bolted Connections — Bolt capacity calculator
Welded Connections — Weld capacity calculator
Base Plate Design — Base plate calculator
Weld Symbols — Reading weld symbols
Beam Connection Design — Connection design guide

Disclaimer

This is a calculation tool, not a substitute for professional engineering certification. All results must be independently verified by a licensed Professional Engineer (PE) or Structural Engineer (SE) before use in construction, fabrication, or permit documents. The user is responsible for the accuracy of all inputs and the verification of all outputs.