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 Engineering Context

Structural steel frames are assemblies of members joined by connections. The type of connection determines how forces flow through the structure. Choose the wrong type, and the entire structural model is invalidated -- a frame analyzed as "rigid" with connections detailed as "simple" will drift far beyond the analysis prediction and may collapse.

This page catalogs every major steel connection type, the structural role each serves, the typical detailing, and the design standard references. It is a type selection guide for practicing engineers. For the underlying limit state equations (bolt shear, bearing, block shear, weld strength), see the Steel Connection Design Guide. For worked numerical examples, see Connection Design Examples.

Connection Classification by Structural Behavior

AISC 360-22 Section B3.4 classifies connections into three types based on their moment-rotation behavior:

Simple Connections (Type PR, "Pinned")

A simple connection transfers shear and negligible moment. The connection must have sufficient rotation capacity to accommodate the beam end rotation without developing significant moment. AISC 360-22 Commentary Section B3.4 states that connections with moment capacity less than 20% of the connected beam's plastic moment capacity may be considered simple.

Characteristics:

Shear transferred by bolt group or weld group at the beam web
Minimal moment resistance -- the connection rotates under load
Rotation is accommodated by bolt slip, angle leg flexibility, or plate bending
Not suitable for lateral force-resisting systems (moment frames)

Common simple connection types:

Single-plate shear tab (most common in US practice)
Double-angle (clip angles, bolted-bolted or welded-bolted)
Shear end plate (flush or extended, thin plate)
Single-angle (lightly loaded members)
Tee shear connection (WT section welded to support, bolted to beam web)
Seated connection (unstiffened or stiffened seat angle)

Moment Connections (Type FR, "Fully Restrained")

A fully restrained moment connection transfers both shear and moment with negligible rotation. The connection stiffness must be sufficient to develop the beam's plastic moment capacity without excessive deformation. AISC 341 (Seismic Provisions) further requires that moment connections in seismic force-resisting systems accommodate inelastic story drift through controlled yielding of the beam (not the connection).

Characteristics:

Beam flanges connected to column with full-strength welds or high-strength bolts
Shear transferred through the beam web (shear tab or web plate)
Stiffeners in the column web at beam flange locations (continuity plates) to prevent column web crippling
Doubler plates on the column web to resist panel zone shear

Common moment connection types:

Welded flange moment connection (CJP at flanges, bolted shear tab at web)
Extended end plate (4E, 8ES configurations per AISC DG4/16)
Bolted flange plate (flange cover plates + web shear plate)
Reduced beam section (RBS, "dogbone" -- intentional flange reduction to force plastic hinge away from column face)
SidePlate (proprietary, external plates bolted to beam and column)
Field-bolted moment end plate

Partially Restrained Connections (Type PR, "Semi-Rigid")

PR connections fall between simple and fully restrained. They transfer shear and some moment, but with measurable rotation. The moment-rotation curve must be explicitly included in the structural analysis. PR connections are uncommon in US practice (where frames are typically analyzed as either simple or fully restrained) but are more common in European practice (EN 1993-1-8 provides explicit PR joint models).

Common PR connection types:

Top and seat angle (angles bolted to beam flanges and column)
Flush end plate with thin plate
Double-angle with extended legs
Header angle connection (angle welded to column, bolted to beam -- stiffens the joint partially)

Shear Connections -- Detailed Descriptions

Single-Plate Shear Tab

Description: A single rectangular plate shop-welded to the supporting member (column web, column flange, or girder web) and field-bolted to the supported beam web. The plate thickness is typically 3/8 in. to 5/8 in. The bolt holes are standard round or short-slotted (horizontal slots, for erection tolerance).

Key details: Plate setback = a (typically 3 in. for standard conditions). Bolts are placed at 3 in. vertical spacing. Weld is on both vertical edges of the plate only (not across the top). The top of the plate is left unwelded to preserve simple connection behavior.

Advantages:

Simplest and cheapest shear connection to fabricate
Single-sided -- no shop assembly of multiple parts
Standardized -- AISC Manual Tables 10-1 through 10-5 provide full design tables
Beam can be erected between previously placed beams (no "needle" beams required)

Limitations:

Not suitable for axial load in the beam (the plate buckles in compression)
Requires clearance beyond the beam end for bolt installation (3 in. typical)
Single-sided -- less redundant than double-angle connections

Double-Angle Connection (Bolted-Bolted)

Description: Two angles, shop-bolted or shop-welded to the supported beam web, field-bolted to the supporting member. The outstanding legs are bolted. The angles can be shop-attached to the beam (standard) or shipped loose (less common, for field adjustment).

Key details: Angle thickness typically 5/16 in. to 1/2 in. Long leg against the beam web when the beam depth and connection geometry permit. Bolt gage in the outstanding legs: standard gages per AISC Manual Table 1-7A.

Advantages:

Redundant -- two angles provide two independent load paths
Easily modified for skewed connections (rotate angles)
Can accommodate moderate axial load (angles in compression between bolt groups)
Field-bolted to both sides -- erection is two-stage but reliable

Limitations:

More parts than a shear tab (two angles, more bolts)
Shop bolting or welding required on the beam
Clearance issues with column web stiffeners or gusset plates

Shear End Plate

Description: A single plate shop-welded to the beam end and field-bolted to the supporting member face. The plate projects beyond the beam flanges (extended) or remains within the beam depth (flush).

Key details: Plate thickness 3/8 in. to 3/4 in. for shear-only plates. Bolts in a single column at 3 in. spacing. Weld: fillet weld to beam web (both sides) and beam flanges (if extended).

Advantages:

All shop welding, all field bolting -- efficient erection
Beam length is fixed in the shop (cut to exact length + plate thickness)
Flush end plate fits within beam depth for architectural clearance

Limitations:

Beam length tolerance is tight -- end plate is shop-welded, so the beam must be cut precisely
Not easily modified in the field for misfits

Moment Connections -- Detailed Descriptions

Welded Unreinforced Flange (WUF) Moment Connection

The standard pre-Northridge moment connection, now used with modifications. The beam flanges are CJP groove-welded to the column flange. The beam web is bolted to a shear tab shop-welded to the column. After the 1994 Northridge earthquake, this connection was found to fracture at the beam flange-to-column flange weld due to stress concentrations, low-toughness weld metal, and the backup bar creating a notch. Modern WUF connections use notch-tough weld metal (E70T-6 or E71T-8 with Charpy V-notch requirements), removed backup bars with reinforcing fillets, and weld access holes detailed per AISC 358 Section 6.2.

Reduced Beam Section (RBS, "Dogbone")

The most common post-Northridge moment connection for SMF. A radius-cut is made in the beam flanges at a specified distance from the column face, reducing the flange width by approximately 40-50% over a length of 0.5d to 0.85d. This intentionally weakens the beam, forcing the plastic hinge to form in the reduced section (away from the CJP weld). The connection at the column face is designed to remain elastic at the maximum probable moment from the RBS.

Key dimensions (AISC 358 Section 5.3):

Cut start: a = 0.50 to 0.75 bf from column face
Cut length: b = 0.65 to 0.85 d
Cut depth: c = 0.20 to 0.25 bf (radius = (4c^2 + b^2) / (8c))

Extended End Plate (4E, 8ES)

Description: A plate welded to the beam end with bolts above and below the flanges (extended plate). The 4E configuration has 4 bolts total (2 tension, 2 compression). The 8ES configuration has 8 bolts (4 tension, 4 compression) for deeper beams and higher moment. Design per AISC DG4 and DG16 using the yield line bolt force model.

Key details: Plate is typically 1 in. to 2-1/2 in. thick. Bolts are A325 or A490, fully pretensioned. Stiffeners between the end plate and beam flanges are common for 8ES configurations. This is the dominant moment connection in metal building systems (pre-engineered buildings).

Bolted Flange Plate (BFP) Moment Connection

Description: Flange cover plates are bolted to the beam and column flanges, similar to a splice plate but at the connection. The web is connected with a shear tab. This is a fully bolted field connection (no field welding). Common in regions where field welding quality control is difficult or weather-dependent.

Key details: Flange plates are typically the same width as the beam flange, 3/8 in. to 3/4 in. thick. Bolts are in bearing-type or slip-critical, depending on the application. The bolt group at the beam flange is designed for the flange force Pu = Mu / (d - tf) plus the axial force component.

Braced Frame Connections

Gusset Plate Brace Connection

Description: A gusset plate connects the brace (HSS, W-shape, or double-angle) to the beam-column intersection. The brace bolts or welds to the gusset, and the gusset bolts or welds to the beam and column. For concentric braced frames (CBF), the work point (intersection of brace, beam, and column centerlines) should be at the gusset centroid or the brace axis should pass through the work point to minimize eccentricity.

Key limit states:

Gusset plate buckling (compression -- Whitmore section check, AISC DG29)
Block shear at the gusset-to-beam and gusset-to-column bolt groups
Brace net section fracture (at the bolted connection to the gusset)
Gusset weld to beam and column (typically fillet welds)
Beam and column web local yielding at gusset attachment

End Plate Brace Connection

HSS braces can be connected using a slotted end plate -- the HSS wall is slotted, the end plate passes through the slot, and fillet welds connect the HSS wall to the plate inside and outside. The plate is then bolted to the gusset. This creates a compact connection that fits within the HSS profile.

Column Splices

Column splices join two column sections (typically at 2 to 3 story intervals, just above a floor level for erection convenience). Per AISC 360 Section J1.4, compression splices require the column ends to be finished to bear (milled). The splice plates provide continuity for moment, tension (from uplift or lateral load), and erection stability.

Typical splice types:

Flange plate splice: Plates bolted to both flanges of upper and lower columns. Most common for W-shapes.
Web plate splice: Plates bolted to both sides of the web for shear transfer.
Welded splice: CJP groove weld at flanges. Used for heavy columns or seismic applications.
Butt plate splice: Columns bear directly (milled ends), with small side plates for alignment only. Used when moment transfer is negligible.

Base Plate Connections

The column base plate transfers the column forces (axial, shear, moment) into the concrete foundation. Detailed treatment is in the Base Plate Design Reference and Column Base Plate Reference.

Connection types at the base:

Exposed base plate: Plate with anchor rods visible above the concrete. Standard for gravity columns.
Embedded base plate: Plate cast into the concrete pier. Used for high moment resistance or architectural concealment.
Grouted base: Standard 1-2 in. grout pad between the plate and concrete for uniform bearing.

Choosing the Right Connection Type

Condition	Recommended Connection	Why
Simple beam-to-girder shear connection	Shear tab or double angle	Lowest cost, standardized
Simple beam-to-column flange	Shear tab	Single plate, no shop assembly
Beam with axial load (collector, drag strut)	Double angle or extended shear tab	Angles brace the connection in compression
Beam-to-column web	Shear tab or double angle	Column web clearance limits other types
Moment frame -- shop weld, field bolt	Extended end plate (4E)	All field bolting, good for remote sites
Moment frame -- shop and field weld	WUF or RBS	FEMA 350 prequalified, high ductility
Brace connection (HSS to gusset)	Gusset plate with slotted end plate or direct weld	Compact, fits within brace profile
Column splice	Flange plate + web plate (bolted)	Standard, erection-friendly
High shear with low axial	Shear tab	Designed for shear only, most cost-effective

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Disclaimer

This page is for educational and reference use only. It does not constitute professional engineering advice. Connection selection and design must be performed by a licensed Professional Engineer (PE) or Structural Engineer (SE) for the specific project. The site operator disclaims liability for any loss arising from the use of this information.