Bolted Steel Connections

Bolted Steel Connections

Check both sides of the hole: A bolt can have adequate shear and tension strength while the connected plate fails in bearing, tearout, net-section rupture, or block shear. A slip requirement is another distinct check.

Bearing-Type and Slip-Critical Behavior

In a bearing-type connection, load transfer at ultimate strength can involve bolt shear and contact between bolt shank and hole. Connected material must resist bearing deformation and tearout. The connection may experience some slip before bearing develops, subject to the actual hole and fabrication conditions.

A slip-critical connection uses pretensioned bolts and friction across prepared faying surfaces to resist slip at the required limit state. Slip resistance depends on pretension, number of slip planes, surface condition, hole type, fillers, and applicable factors. Passing slip does not waive bolt shear/tension or connected-material strength checks required for the connection. Conversely, passing bearing strength does not satisfy a project requirement that slip be prevented.

Use AISC Steel Construction Manual, 15th edition, for a 2026 exam. Do not use later bolt tables or provisions.

Bolt Shear, Tension, and Interaction

Determine whether each bolt is in single or double shear and whether threads are included in a shear plane. Divide concentric load only when bolt stiffness and geometry justify equal force. For tension connections, include direct tension and any prying action created by flexible end plates, tees, or angles. When shear and tension occur together, apply the AISC interaction rule rather than checking each at 100% independently.

The number of bolts times one-bolt resistance is valid only when all bolts participate as assumed and spacing, deformation, long-joint, grip, and related provisions are satisfied. Connection deformation and fit-up can affect distribution.

Worked Four-Bolt Connection

A four-bolt bearing-type connection carries factored shear V_u = 240 kips. The problem supplies design bolt shear resistance 70 kips/bolt, design connected-plate bearing/tearout resistance 65 kips/bolt, and—if slip-critical behavior is required—design slip resistance 45 kips/bolt.

Bolt shear design resistance is

4(70) = 280 kips,

so the bolt-shear ratio is 240/280 = 0.857 and this check passes.

Plate bearing/tearout resistance is

4(65) = 260 kips,

so its ratio is 240/260 = 0.923 and this stated check passes.

Now check block shear of the plate. Let problem-given properties be F_y = 50 ksi, F_u = 65 ksi, gross shear area A_gv = 6.0 in², net shear area A_nv = 4.8 in², net tension area A_nt = 1.5 in², and U_bs = 1.0. The AISC nominal block-shear expression is the lesser of

0.6F_uA_nv + U_bsF_uA_nt

and

0.6F_yA_gv + U_bsF_uA_nt.

The two values are

0.6(65)(4.8) + 1.0(65)(1.5) = 284.7 kips

and

0.6(50)(6.0) + 1.0(65)(1.5) = 277.5 kips.

Thus R_n = 277.5 kips. With problem-given φ = 0.75, design block-shear strength is

φR_n = 0.75(277.5) = 208.1 kips < 240 kips.

Block shear governs and the strength design fails even though bolt shear and hole bearing pass. If slip-critical behavior is required, 4(45) = 180 kips < 240 kips, so the stated slip check also fails. Do not add the 208.1-kip block-shear resistance to the 280-kip bolt resistance; they are alternative links in one series load path.

Connected-Material Limit States

Trace possible failure paths on a sketch. Check gross-section yielding away from holes, net-section rupture through holes with the applicable effective-net-area treatment, bearing and tearout at each hole, and block shear around the group. Hole size deductions, stagger, edge distance, pitch, plate thickness, and load direction alter the paths. Gusset yielding/buckling, local connection eccentricity, and the supported member's own limit states may also govern.

A larger or stronger bolt can worsen plate bearing demand concentration unless plate geometry changes. Adding bolts can create a longer joint, smaller edge distance, or a new weak block path. Recalculate rather than assuming bolt count alone improves every limit state.

Eccentric Bolt Groups

A load whose line of action misses the bolt-group centroid creates direct force plus moment M = Pe. Under an elastic group method, direct shear is distributed to bolts and the torsional component is proportional to bolt distance from the group centroid, with direction tangent to that radius. Vectorially add direct and torsional components at each bolt; the farthest bolt is not automatically critical when directions cancel at one side and reinforce at another.

A reliable workflow is:

1. Locate the bolt-group centroid from actual bolt coordinates.
2. Resolve applied load and compute eccentric moment about that centroid.
3. Distribute direct force under the selected method.
4. Calculate moment-induced forces using the applicable elastic or instantaneous-center method.
5. Vector-sum force at every bolt and check shear/tension interaction.
6. Use resulting hole forces for connected-material and slip checks.

Detailing and Final Audit

Confirm bolt grade/diameter, hole type, installation and pretension requirements, faying-surface condition, washers, access, edge distances, spacing, and corrosion/fire environment. Then check the load path into both connected members.

Before selecting an answer, list four separate capacities: bolt, slip if required, hole bearing/tearout, and plate paths. The smallest compatible resistance governs; success of one list item says nothing automatic about the others.