SkyCiv Bolted Connection Design

How a structure is joined decides how it behaves. Bolting competes with welding, riveting and pinning, and it stays the common choice across steel frames, bridges and heavy machinery because the joint can be assembled on site and taken apart again.

Designing one means checking every way it can fail: the bolts in shear and tension, and the connected plates in bearing, tear-out and block shear. This page covers those checks and the tool runs them.

A bolted connection is a mechanical assembly joining two or more structural elements with a threaded bolt, a matching nut and usually one or more washers.

Welding makes a permanent joint. Bolting can be either, which is the practical difference: the same detail can be specified for a joint that will be dismantled during maintenance, or one that never will.

Connections are classified by how load crosses the joint:

• Bearing-type: the plates are allowed to slip slightly until the bolt shank bears against the side of the hole. Load then transfers through direct shear on the bolt body and bearing pressure on the connected material.
• Slip-critical (friction-type): high-strength bolts are tensioned so the plates are pinched together, and friction between the faying surfaces carries the load with no slip at all. This is the choice under fatigue, dynamic load reversal or severe vibration.

The distinction drives the design. A bearing-type joint is checked against bolt and plate strength; a slip-critical joint is checked against the clamping force holding the faying surfaces together.

1. Bolt shear: the applied force exceeds the shear strength of the bolt shank across the shear planes.
2. Bolt tension: axial tension pulls the bolt apart, usually at the threaded region where the cross-section is reduced.
3. Plate bearing: the bolt crushes the hole wall or the edge of the connected plate.
4. Tear-out: a bolt placed too close to the plate edge tears the material away.
5. Block shear: a block of material at the end of the connection tears out, shearing along one plane while pulling apart along an intersecting one.

All five have to be checked. The bolts are rarely the weakest part; bearing, tear-out and block shear in the connected material govern often enough that skipping them is how a connection gets under-designed.

Working the five failure modes by hand against AISC 360-16 or AS 4100:2020 is slow, and slow checking is where arithmetic errors come from. Automating it moves the effort to deciding what to check rather than doing the sums.

• Model 3D connection geometry in a web browser, from a library of over 80 pre-configured AISC connection types.
• Run automated capacity checks for shear, tension, bearing and block shear to AISC 360-16 and AS 4100:2020.
• See stress distribution, force transfer and likely failure points.
• Produce calculation reports for client submission and authority approval, with the clause behind each check cited.
• Issue CloudCAD detail drawings with bolt schedules and dimensions, and export the geometry to IFC for BIM coordination.

• Speed of erection: bolting on site needs less specialised labour than field welding, so the steel goes up faster.
• Quality control: high-strength bolts are made to standard in a factory, so their properties are known before they arrive.
• Inspection: torque, tension and alignment can all be checked without damaging the joint.
• Adaptability: a bolted member can be removed, replaced or reinforced without disturbing much around it.

Two things decide whether that holds up in service. High-strength bolts need a defined tensioning method to reach their specified preload, whether that is turn-of-nut, a calibrated wrench or direct tension indicators. And the assembly needs corrosion protection suited to the environment, through galvanizing, weathering steel or a protective coating.

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