How bolted vs welded connections actually transfer force differently
Bolts and welds both connect two pieces of steel — but they do it through genuinely different physical mechanisms, with different failure modes and different practical trade-offs in fabrication and erection.
A connection's whole job is to reliably transfer force from one member into the next at a joint — but a bolted connection and a welded connection accomplish that through genuinely different physical mechanisms, not just two interchangeable ways of doing the same thing.
A bolted connection transfers force either through the bolts themselves acting in shear (with the surrounding plate material bearing against the bolt shaft), or, in a slip-critical (friction-type) connection, through friction alone — the plies clamped tightly together by pretensioned bolts, transferring load without the bolt shaft itself ever actually bearing against the hole under normal service conditions. Because of this, a bolted connection has more than one potential failure path to check: the bolts failing in shear, the plate material tearing out around a bolt hole (bearing failure), or a whole chunk of the plate tearing out along a path that runs through the bolt group (block shear) — each a genuinely different failure mode with its own check.
Welds: force transfer through direct material continuity
A welded connection works completely differently: the weld metal itself fuses with and becomes part of the connected members, so force transfers through direct continuity of material rather than through a discrete mechanical fastener. A full-penetration weld, done well, can make a joint genuinely as strong as the base material on either side of it. A fillet weld — the more common, less labour-intensive weld shape — instead relies on the shear capacity of the weld metal along its own throat, which is its own distinct check from a full-penetration weld's.
These physical differences carry real practical consequences. Bolted connections are comparatively easy to inspect visually, straightforward to erect and adjust on site, and tolerant of minor field misalignment — which is a large part of why they dominate site connections. Welded connections are typically stiffer and more rigid, but demand a controlled environment and skilled labour to guarantee quality (weld inspection methods like ultrasonic testing exist specifically because a poor weld can be invisible from the outside), which is a large part of why they're more common in shop-fabricated connections than field ones. Connection Design covers exactly this range — bolted shear, bolted moment and welded connections — checking each connection type's own real failure modes rather than treating "connection capacity" as one generic number (see the related tool below).