Simple Connection Philosophy — AS 4100 Clause 9.1.4

AS 4100 categorises connections as either simple (pinned), semi-rigid, or rigid. Simple shear connections are designed to:

  1. Transfer the full design shear force V* from the supported beam to the supporting member
  2. Accommodate beam end rotation (typically 0.02-0.03 radians at ultimate) without brittle failure
  3. Resist a nominal tying force for structural integrity (75 kN minimum per AS 4100 Clause 4.3.5)
  4. Provide adequate robustness against accidental load removal (progressive collapse)

Simple connections must NOT develop significant moment. AS 4100 Clause 9.1.4 requires that the connection rotation capacity is demonstrated by limiting the connection moment resistance to less than 20% of the connected beam's plastic moment capacity.

Web Side Plate (WSP) Connection — Design Steps

The WSP is the most common Australian shear connection. A plate (typically 8-12 mm thick) is shop-welded to the supporting member and site-bolted to the beam web.

Step 1 — Bolt Group Shear Capacity

For n bolts in a vertical line, the shear capacity per bolt is:

phi_Vf = phi x 0.62 x f_uf x (n_n x A_c + n_x x A_o)

Where:

For a single-shear WSP connection (threads normally in the shear plane): phi_Vf = 0.80 x 0.62 x 830 x A_o = 411.7 x A_o (MPa x mm^2)

For M20 8.8/S (A_o = 245 mm^2): phi_Vf = 100.9 kN per bolt.

Step 2 — Ply Bearing Capacity — Clause 9.3.2.4

The bearing capacity of the connected ply (beam web or WSP plate) at each bolt:

phi_Vb = phi x 3.2 x d_f x t_p x f_up / gamma

Where:

For a 10 mm Grade 300 WSP plate with M20 bolt, edge condition (gamma = 1.0): phi_Vb = 0.90 x 3.2 x 20 x 10 x 440 / 1000 = 253 kN

Interior bolts (gamma = 1.25): phi_Vb = 203 kN.

Step 3 — Tear-Out (End Distance) Check — Clause 9.3.2.5

Tear-out governs when the bolt is close to the plate edge:

phi_Vt = phi x a_e x t_p x f_up / gamma

Where a_e = minimum edge distance from bolt centre to plate edge in the direction of force, measured parallel to the force.

For a_e = 35 mm, t_p = 10 mm, f_up = 440 MPa: phi_Vt = 0.90 x 35 x 10 x 440 / 1000 = 139 kN

For bolts near plate edges, tear-out typically governs over bearing. Provide a_e >= 1.5 x d_f = 30 mm for M20. Standard practice uses 35 mm edge distance for M20 bolts.

Step 4 — Block Shear Failure — Clause 9.1.10

Block shear is a combined shear rupture (along bolt line) and tension rupture (across the transverse edge) failure:

phi_Rbs = phi x [ 0.6 x f_up x A_nv + f_up x A_nt ]

Where:

For the beam web coped at the top flange, the block shear path runs from the top of the coped web vertically down past all bolts, then horizontally to the beam end. This failure mode is often governing for deep coped beams.

Flexible End Plate (FEP) Connection

The FEP is welded to the beam end in the fabrication shop and bolted to the supporting member on site. It is standard for beam-to-column-flange connections.

Plate Flexibility Requirement — AS 4100 Commentary

For the connection to behave as pinned, the end plate must be sufficiently flexible. The plate thickness t_p should satisfy:

t_p <= d_w / 15 (for 250 Grade plate) t_p <= d_w / 18 (for 300 Grade plate)

Where d_w is the distance from the weld face to the bolt line (typically 50-65 mm).

For a standard FEP with d_w = 55 mm, Grade 300 plate: t_p_max = 55 / 18 = 3.1 mm — this is impractically thin for structural bolting.

In practice, Australian standard FEP connections use 8 mm plates but accept the reduced rotational capacity, which is adequate for beams with span/depth ratios exceeding 18. For shallower beams (span/depth < 15), a WSP connection or seated connection should be used to ensure adequate rotation capacity.

FEP Weld Design

The plate-to-beam weld must transfer V* from the beam web into the end plate. A double-sided fillet weld is standard:

phi_Vw = phi x 0.60 x f_uw x t_t x L_w

Where:

For 6 mm fillet welds (t_t = 4.24 mm) on both sides of the web for 200 mm length: phi_Vw = 0.80 x 0.60 x 480 x 4.24 x 200 x 2 / 1000 = 391 kN per weld line (both sides).

Worked Example — Web Side Plate Connection

Problem: A 410UB53.7 beam (simply supported, 9.0 m span) frames into the web of a 310UC158 column. Design shear force V* = 180 kN. Design a web side plate connection using M20 8.8/S bolts in a 10 mm Grade 300 plate.

Step 1 — Number of bolts: Required bolts based on bolt shear (threads in shear plane): n = V* / phi_Vf = 180 / 100.9 = 1.8 -> minimum 2 bolts

Use 4 bolts in a 2 x 2 grid (2 columns, 2 rows) for robustness. Bolt spacing: 70 mm vertical pitch, 60 mm gauge.

Step 2 — Bolt group capacity (4 bolts): Elevation check — each bolt carries V*/n = 180/4 = 45 kN < 100.9 kN. OK.

Step 3 — Plate bearing check: For the WSP plate (10 mm Grade 300, edge bolts): phi_Vb = 253 kN > 45 kN per bolt. OK.

Step 4 — Tear-out check: Edge distance a_e = 35 mm: phi_Vt = 139 kN > 45 kN per bolt. OK.

Step 5 — Beam web bearing check: 410UB53.7 web: t_w = 7.6 mm, Grade 300. Edge distance to beam end a_e = 35 mm. phi_Vb = 0.90 x 3.2 x 20 x 7.6 x 440 / 1000 = 192 kN > 45 kN per bolt. OK. Beam web tear-out: phi_Vt = 0.90 x 35 x 7.6 x 440 / 1000 = 105 kN > 45 kN. OK.

Step 6 — Weld design (plate to column web): The WSP plate is fillet-welded to the column web on both sides. Plate width = 120 mm, weld length L_w = 120 mm each side.

Weld force per unit length: v* = V* / (2 x L_w) = 180,000 / (2 x 120) = 750 N/mm

Required throat t_t = v* / (phi x 0.60 x f_uw) = 750 / (0.80 x 0.60 x 480) = 3.26 mm

Required leg size: 3.26 / 0.707 = 4.62 mm. Specify 6 mm E48XX fillet weld both sides.

Step 7 — Block shear of beam web: Shear plane: 2 x 70 mm hole pitch + 35 mm end distance, net = 175 - 1.5 x 22 = 142 mm (deducting 1.5 holes for staggered path). Tension plane: 60 mm gauge, net = 60 - 0.5 x 22 = 49 mm.

phi_Rbs = 0.75 x [0.60 x 440 x 142 x 7.6 + 440 x 49 x 7.6] / 1000 phi_Rbs = 0.75 x [284.5 + 163.9] / 1000 phi_Rbs = 0.75 x 448.4 / 1000 x 1000 = 336 kN > 180 kN. OK.

Result: 4 x M20 8.8/S bolts in a 10 mm Grade 300 web side plate, 6 mm E48XX fillet welds. All checks pass.

Angle Cleat Connections

Bolted angle cleats (typically 100 x 100 x 8 EA or 125 x 75 x 10 EA) are used when both the supported beam and supporting member are to remain undrilled in the shop. The angle is bolted to the beam web and to the supporting member.

Key design checks for double-angle cleats:

  1. Bolt shear in beam web leg: As for WSP (threads in shear plane)
  2. Bearing on angle leg: The angle leg is typically 8-10 mm thick — bearing may govern over bolt shear
  3. Angle leg bending: The outstanding leg acts as a cantilever from the bolt line. For large gauge distances (> 50 mm), prying action must be considered per AS 4100 Clause 9.3.6.
  4. Block shear of beam web: As for WSP connections

For double-angle cleats with 4 x M20 8.8/S bolts and 100 x 100 x 8 EA Grade 300 angles, the typical factored shear capacity is approximately 350-400 kN, controlled by bolt bearing on the 8 mm angle leg.

Frequently Asked Questions

What governs web side plate connection capacity in Australian design — bolts or plate?

For AS 4100 web side plate connections, bolt shear capacity typically governs for bolt groups with 3 or fewer bolts in a vertical line. The plate bearing and tear-out at the bolt holes govern for thin plates (typically t < 8 mm). Block shear of the supported beam web governs when the bolt group is near the beam end with a short coped section. For standard M20 8.8/S bolts in a 10 mm plate, bolt shear (100.9 kN/bolt) typically exceeds plate bearing (253 kN/bolt at 35 mm edge distance).

What is the difference between a web side plate and a flexible end plate connection in AS 4100?

A web side plate (WSP) connects the beam web to the supporting member via a plate bolted to the web. It has high shear capacity but negligible moment capacity, providing a true pinned connection. A flexible end plate (FEP) welds a thin plate (8-10 mm) to the beam end and bolts it to the supporting member. The FEP is simpler to fabricate but has limited rotational capacity — AS 4100 requires the plate thickness to be <= d_w/15 for flexibility. For Australian practice, WSP is standard for beam-to-column-web and beam-to-beam connections; FEP is standard for beam-to-column-flange connections.

What tying force should a shear connection resist per AS 4100?

Per AS 4100 Clause 4.3.5, all beam-to-column connections must resist a minimum tying force of 75 kN for structural integrity (robustness against progressive collapse). For beams with tributary areas exceeding 30 m^2, the tying force increases proportionally. The tying force check uses a reduced phi factor of 0.90 for bolts in tension (rather than the shear phi of 0.80), and the connection plate and weld checks use standard phi factors.

How is the rotational capacity of a shear connection verified to AS 4100?

AS 4100 assumes a simple shear connection has adequate rotational capacity if: (a) the connection is of a standard type (WSP, angle cleat, or FEP with t_p <= d_w/15); (b) the distance from the bolt line to the weld face provides adequate deformation length; and (c) the beam is not coped deeper than 0.25 x beam depth for a top cope only, or 0.20 x beam depth for both top and bottom copes. For non-standard connections, explicit rotational analysis per the ASI Connection Design Guide is required.

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This page is for educational reference only. Shear connection design per AS 4100:2020 Clause 9 and ASI Design Guide 4. All designs must be independently verified and certified by a licensed Professional Engineer. Results are PRELIMINARY — NOT FOR CONSTRUCTION.

Disclaimer: This content is for educational purposes only. Results must be verified by a licensed professional engineer. Steel Calculator provides preliminary design tools — NOT a substitute for professional engineering judgment.