Australian Shear Tab Connection Design — AS 4100 Single Plate Connection

Complete design reference for shear tab (single plate, fin plate) connections in Australian structural steel per AS 4100:2020 Clause 9. The shear tab is the most common simple beam-to-column and beam-to-beam connection in Australian steel construction. It provides reliable shear transfer with minimal fabrication cost and simple erection.

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Shear Tab Configuration and Behaviour

A shear tab consists of a single plate (typically Grade 300, 8-12 mm thick) shop-welded to the supporting member (column flange, column web, or beam web) and field-bolted to the web of the supported beam. The plate is cut to width from standard flat bar or plate stock.

The connection is classified as simple (pinned) per AS 4100 Clause 9.1, meaning it transfers shear and minimal moment. The rotational capacity is provided by:

1. Bolt hole clearance (2 mm for standard holes, M20 typical)
2. Plate bending flexibility (the plate is thin relative to its length)
3. Beam web distortion (minor contribution)

The design philosophy is that the shear tab acts as a stiff vertical cantilever transferring the beam end reaction to the bolts, while the plate and bolted assembly are sufficiently flexible to accommodate the beam end rotation without developing significant moment.

Limit States to Check

The following AS 4100 limit states must be verified for every shear tab connection:

1. Bolt shear (Clause 9.3.2.1): Horizontal shear on the bolt group
2. Bolt bearing on the shear tab (Clause 9.3.2.4): Plate bearing and tearout
3. Bolt bearing on the beam web (Clause 9.3.2.4): Typically less critical as the beam web is often thicker than the shear tab
4. Shear tab gross shear yielding (Clause 5.11): V* <= phi x 0.6 x f_y x A_g of the plate at the bolt line
5. Shear tab net shear fracture (Clause 9.1.1): V* <= phi x 0.6 x f_u x A_n of the plate at the bolt line
6. Block shear of the shear tab (Clause 9.1.4): Combined shear + tension fracture around the bolt group
7. Block shear of the beam web (Clause 9.1.4): At the coped or un-coped beam end
8. Weld connecting shear tab to support (Clause 9.7.3): Fillet weld capacity along the vertical leg of the plate
9. Shear tab flexural yielding (Clause 5.1): Check the plate for combined shear and bending at the bolt line

Eccentricity Effects

The shear tab connection is inherently eccentric: the beam end reaction is applied at the bolt line (at the face of the beam web), while the reaction is transferred through the shear tab plate to the support. This eccentricity produces a moment on the bolt group and on the weld:

• Bolt group eccentricity: e_bolt = distance from the bolt line to the support face (typically 60-80 mm for standard detailing)
• Weld eccentricity: the weld must resist both the direct shear V* and the additional moment from the eccentricity

The bolt group analysis uses the elastic method: the shear force per bolt from direct load is V*/n, and the additional shear from the torsional moment V* x e is proportional to the bolt distance from the bolt group centroid.

Elastic Bolt Group Analysis Formula

For a bolt group with n bolts, bolt i at distance r_i from the centroid (r_i = sqrt(x_i^2 + y_i^2)), subjected to shear V* acting at eccentricity e:

Direct shear per bolt (vertical): F_v = V* / n

Torsional force per bolt: F_ti = (V* x e x r_i) / sum(r_j^2)

The resultant bolt force is the vector sum of F_v and F_ti. The most heavily loaded bolt (typically the top and bottom bolts in a vertical column of bolts) is checked against the bolt shear capacity.

Standard Shear Tab Geometries

For quick selection, the following standard shear tab dimensions are commonly used in Australian fabrication for Grade 300 plate with M20 Grade 8.8 bolts:

Capacities are approximate for Grade 300 plate, M20 Grade 8.8 bolts, SP category welds. Each connection requires verification against the specific design loads and beam geometry.

Coped Beam Web Reinforcement

When the top flange of the supported beam is coped (notched) to clear the supporting member flange, the beam web at the coped region is subjected to combined shear and bending from the coped geometry. The reduced beam section must be checked for:

1. Flexural yielding of the reduced section at the cope
2. Web buckling of the coped region (local plate buckling)
3. Lateral-torsional buckling of the coped beam end (if the cope is deep)

For copes deeper than 0.2 d (beam depth), web stiffeners are recommended per AS 4100 guidance. Australian practice is to limit cope depth to 0.15 d for beams without reinforcement.

Worked Example: Shear Tab Design

Problem: A 310UB40.4 Grade 300 beam frames into the flange of a 250UC89.5 column. The beam end reaction (factored) is V* = 120 kN. Design a shear tab connection using an 8 mm thick Grade 300 plate with M20 Grade 8.8 bolts and 6 mm fillet welds (E48XX, SP category). The beam web thickness is 6.1 mm; the top flange is coped 40 mm to clear the column flange.

Given:

• Factored shear: V* = 120 kN
• Shear tab: 8 mm Grade 300 plate (f_y = 300 MPa, f_u = 440 MPa)
• Bolts: M20 Grade 8.8, standard holes (d_h = 22 mm)
• Weld: 6 mm fillet, E48XX electrode (f_uw = 480 MPa), SP category
• Beam web: t_w = 6.1 mm, Grade 300
• Cope depth: 40 mm at top flange
• Bolt gauge: 60 mm from support face to bolt line
• Eccentricity of bolt group: e = 60 + 6.1/2 + 10/2 ~ 68 mm (to beam web centre)

Solution:

Step 1: Number of bolts

Bolt shear capacity: phi V_f = 0.80 x 0.62 x 830 x 245 x 10^(-3) = 100.8 kN (threads in shear plane)

n_b >= 120 / 100.8 = 1.19. Use 3 bolts (one vertical column for a narrow shear tab).

Step 2: Bolt group elastic analysis

Direct shear per bolt: F_v = 120 / 3 = 40.0 kN (vertical)

Bolt positions (y-coordinates from centroid): bolt 1 at +70 mm (top), bolt 2 at 0 (middle), bolt 3 at -70 mm (bottom) sum(y_i^2) = 70^2 + 0^2 + 70^2 = 9,800 mm^2

Torsional moment on bolt group: M_t = V* x e = 120 x 68 x 10^(-3) = 8.16 kNm

Torsional force on top bolt (horizontal): F_tx = (8.16 x 10^3 x 70) / 9,800 = 58.3 kN

Resultant on top bolt: F_r = sqrt(40.0^2 + 58.3^2) = 70.7 kN

Check: F_r = 70.7 kN < phi V_f = 100.8 kN -- OK. Top bolt at 70% utilisation.

Step 3: Bearing on shear tab (8 mm thick)

phi V_b = 0.90 x 3.2 x 20 x 8 x 440 x 10^(-3) = 202.7 kN per bolt >> 70.7 kN -- OK.

Step 4: Shear tab gross shear yielding

Gross shear area at bolt line: A_g = plate depth x t_p = (2 x 40 edge + 2 x 70 pitch) x 8 = 220 x 8 = 1,760 mm^2

phi V_v = 0.90 x 0.6 x 300 x 1,760 x 10^(-3) = 285.1 kN > 120 kN -- OK.

Step 5: Block shear on shear tab

Tension area (gauge between bolts, only one column so block shear check uses the edge distance as the tension path): A_nt = (40 edge - 0.5 x 22 hole) x 8 = (40 - 11) x 8 = 232 mm^2

Shear area (gross): A_vg = (2 x 40 + 2 x 70) x 8 = 220 x 8 = 1,760 mm^2

phi R_bs = 0.90 x (0.6 x 300 x 1760 + 440 x 232) x 10^(-3) = 0.90 x (316.8 + 102.1) = 377.0 kN > 120 kN -- OK.

Step 6: Weld design

Weld length: approximately equal to plate depth = 220 mm (continuous on both sides of the plate, total 440 mm of weld)

Fillet weld 6 mm capacity: t_t = 6 / sqrt(2) = 4.24 mm

phi V_w_per_mm = 0.80 x 0.6 x 480 x 4.24 x 10^(-3) = 0.977 kN/mm

Total weld capacity (both sides): phi V_w_total = 0.977 x 2 x 220 = 430 kN > 120 kN -- OK.

Weld eccentricity check: the weld group also resists moment from eccentricity. With the weld on two sides of the plate (parallel lines), the torsional resistance is small but acceptable given the large reserve in weld shear capacity.

Result: 8 mm shear tab with 3 M20 Grade 8.8 bolts and 6 mm fillet welds. Bolt group governs at 70% utilisation. Connection adequate.

Frequently Asked Questions

What is a shear tab connection per AS 4100?

A shear tab is a single plate welded to the supporting member and bolted to the web of the supported beam, per AS 4100 Clause 9. It is classified as a simple (pinned) connection because the thin plate and bolt hole clearances provide sufficient rotational capacity to accommodate beam end rotation. The shear tab transfers the vertical beam reaction to the support but is assumed to transfer negligible bending moment. It is the most common beam-to-column connection in Australian steel construction due to its simplicity and economy.

What eccentricity must be considered in shear tab design?

The shear tab connection has inherent eccentricity: the beam reaction is applied at the face of the beam web (at the bolt line), while the centroid of the bolt group is offset from the support face by the plate edge distance plus half the bolt diameter. The eccentricity creates a torsional moment on the bolt group and a bending moment on the weld connecting the plate to the support. Both must be included in the design. For standard detailing, the eccentricity e is typically 60-80 mm from the support face to the bolt line centroid.

When is web coping required for shear tab connections?

Web coping (notching the top flange) is required when the supported beam's top flange would otherwise clash with the supporting member's top flange or when the beam depth exceeds the clear space available between the supporting member flanges. The cope depth should be minimised -- a 40 mm cope is standard for the top flange, sufficient to clear the supporting member flange plus fabrication and erection tolerance. Copes deeper than 0.2 d (beam depth) require web stiffening per AS 4100 recommendations.

How does a shear tab differ from a double-angle or end plate connection?

A shear tab is a single plate on one side of the beam web. A double-angle connection uses two angles (one each side of the beam web) providing symmetric load transfer and eliminating the eccentricity moment relative to the beam web. An end plate connection bolts to the beam end (not the web) and the plate is perpendicular to the beam axis. Shear tabs are simpler and cheaper but introduce eccentricity; double angles are symmetric but require more fabrication; end plates are used when the connection must fit within the beam depth and provide some moment resistance.

What minimum weld size is required for shear tab connections per AS 1554?

Per AS/NZS 1554.1, the minimum fillet weld size for a shear tab is 6 mm for plates up to 10 mm thick and 8 mm for plates 10-20 mm thick. The minimum weld size ensures adequate fusion despite heat sink effects from the connected plates. The weld is typically placed on both sides of the shear tab plate (fillet each side), providing a balanced connection. Single-sided welds are not recommended for shear tabs because the eccentricity of the weld relative to the plate centroid produces a twisting moment on the connection.

Educational reference only. All design values must be verified against the current edition of AS 4100:2020 and the project specification. This information does not constitute professional engineering advice. Always consult a qualified structural engineer for design decisions.