§1The permanent fastener
A solid rivet is a headed pin passed through the assembled plates and closed by forming a second head on the plain end — after which the joint can only be undone by destroying the rivet.
That permanence is the defining trade. A bolted joint can be serviced; a riveted joint cannot, and in exchange it cannot loosen either — there is no thread to back off, no preload to relax past a nut, and the driven rivet fills its hole, so the joint carries load in bearing and shear without the slip a clearance-bolted joint allows. How the rivet is driven matters. Hot riveting — the boiler and bridge practice — closes a red-hot rivet whose shank swells to fill the hole, and as it cools it contracts axially and clamps the plates, adding a friction grip on top of the shear connection: the thermal-contraction arithmetic of the materials pages, put to work. Cold riveting suits smaller sizes and softer alloys, filling the hole by plastic flow alone. Riveting built the structural world — boilers, ships, bridges, and every aircraft skin still — before welding displaced it from heavy structure; it survives where welding cannot go: dissimilar or heat-sensitive materials, thin sheet, and field joints made with no power but a gun and a bar.
Contents§2Proportioning the joint
Before any strength check, the joint’s three dimensions — rivet diameter, length and pitch — are set from the plate by simple proportioning rules.
Diameter. Unwin’s empirical rule ties the rivet to the plate: d = 6√t = 6√10 = 19.0 mm, rounded to the stock 20 mm. The rule’s logic is balance — a rivet much thinner than this shears before the plate is working; much fatter and the holes waste the plate (§5). Length. The blank must fill the grip and leave enough shank to form the closing head: about 1.5 d of allowance for a snap (round) head, so for two 10 mm plates, L = 20 + 1.5 × 20 = 50 mm. Too short and the head forms starved and loose; too long and the excess buckles sideways in the hole. Pitch. The spacing along the seam is chosen around 3 d — here 60 mm — close enough that the plate between holes is not the obvious weak link, open enough to leave net section; §4 and §5 test exactly that choice. And the edge distance from rivet centre to plate edge is kept at least 1.5 d, which is what removes the fourth failure mode from the arithmetic (§3).
§3Four ways to fail
A loaded riveted joint is a chain of four links — the rivet in shear, the plate in bearing, the plate in tension, and the plate edge — and the joint’s strength is whichever link gives first.
The hero draws them. Rivet shear: the rivet cross-section is cut across at the plate interface — once in a lap joint (single shear), at two planes in a butt joint with cover plates (double shear, twice the area). Bearing: the rivet crushes the hole it bears on, elongating it; the check is the projected area d × t against a bearing allowable, which is set well above the tensile allowable because bearing is a contained, local crush. Tearing: the plate parts in tension across its net section — the pitch minus the hole, (p − d) t — between holes; every hole punched in the seam is strength given away, and this mode is where it is paid for. Edge shear-out: a rivet too near the edge tears the tongue of plate in front of it out through the edge — and this one is not calculated but designed out, by the 1.5 d edge-distance rule of §2, after which it never governs. The method that follows is pure minimum-of-a-set thinking: compute the first three per pitch length of seam, and the smallest is the joint.
Contents§4Working a lap joint
Run the three checks for the §2 joint — Ø20 rivets, 10 mm plate, 60 mm pitch — and the lap joint’s weakness shows immediately: the single-sheared rivet governs, far below what the plate could give.
| Check | Formula | Capacity |
|---|---|---|
| Rivet shear — single (lap) | τ · πd²/4 | 31.4 kN |
| Rivet shear — double (butt) | 2 · τ · πd²/4 | 62.8 kN |
| Bearing on plate | σb · d · t | 60.0 kN |
| Tearing between holes | σt · (p − d) · t | 60.0 kN |
| Solid plate (reference) | σt · p · t | 90.0 kN |
| For the lap joint the governing minimum is the single-sheared rivet at 31.4 kN — barely half what either plate mode could carry, and only 34.9% of the 90.0 kN the unpunched plate would take. The lesson is structural: a lap joint wastes its plate, because one shear plane per rivet caps the chain well below the plate’s links. It is also eccentric — the two plates’ pulls are offset by one plate thickness, so the joint bends as it loads — which is the second reason serious seams are butt joints (§5). | ||
§5The butt joint and efficiency
Put the same rivets in double shear with cover plates and the governing mode changes, the capacity nearly doubles — and the joint lands exactly on the ceiling that the holes themselves impose.
A butt joint sets the two plates end to end and straps them with cover plates, so every rivet is cut at two planes: shear capacity doubles to 62.8 kN, and the pulls are in line, removing the lap joint’s bending. Now the chain’s weakest links are the plate modes, bearing and tearing, tied at 60.0 kN — the joint is balanced, with rivet and plate running out together, which is precisely what the §2 proportioning rules aim at. Efficiency: 60.0 ÷ 90.0 = 66.7%. And that number is no accident — tearing can never exceed (p − d)/p of the solid plate, which for a 20 mm hole at 60 mm pitch is exactly 66.7%: this joint has reached the ceiling its own holes impose. The only way higher is to change the geometry of the ceiling — wider pitch with the rivets in multiple rows, so fewer holes cross any one section — which is how boiler seams of the riveted era were driven into the 80s of per cent. Efficiency is therefore the honest single number for a riveted seam: it states, directly, what fraction of the plate you paid for is still working.
§6Blind rivets
The blind rivet solved the one problem the solid rivet never could — a joint reachable from one side only — by putting the closing tool inside the rivet.
A blind (“pop”) rivet is a hollow sleeve on a headed mandrel. The tool grips the mandrel and pulls; the mandrel’s head bulbs the far end of the sleeve against the blind side of the work, and at a set force the mandrel snaps at its designed break point — the click of every hand riveter — leaving the formed joint behind. No access, no bucking bar, no second operator: which is why blind rivets own sheet-metal assembly, enclosures, ducting and repair work. Their limits follow from the construction: a hollow sleeve carries less shear than a solid shank, the retained mandrel stub can rattle or fall out, and standard types are not sealed — so the family has grown specialised members: sealed types with a closed end for weather-tight work, grooved and peel types for soft or brittle parents, and structural blind rivets that lock the mandrel permanently in the sleeve, approaching solid-rivet strength and rated accordingly. At the other end of the craft, the aircraft solid rivet driven with a gun and bucking bar remains the benchmark the blind rivet is measured against — and the reason it exists.
Contents§7Quick reference
The working core of the page on one card rack.
Proportions
d = 6√t → 19.0 → 20 mm
L = grip + 1.5d = 50 mm
Four modes
shear · bearing · tearing
edge: designed out at 1.5d
Lap joint
single shear governs: 31.4 kN
efficiency 34.9%
Butt joint
double shear 62.8 kN
balanced at 60.0 kN → 66.7%
Ceiling
η ≤ (p − d)/p
more rows raise the ceiling