Structural Engineering & Statics
where the load goes
Concept

Bracket — where it appears

A plate or short member standing out from a column's face to carry a load at a distance from it, fixed back to the column by bolts or welds. The distance loads the fixings two ways at once, twisting them in the plate's plane and pulling them off the column, so every bolt carries shear and tension together.

Named by 2 essays across one field — each of them below, with the objects they name alongside it.

Capacity against load direction, layout by layout. The same capacities as a function of direction on straight axes, for a load through (150, 150) mm. Three rows of two is weakest at 138°, 135.8 kN. Two rows of three is weakest at 312°, 135.8 kN. A ring of six, r = 70.4 mm is weakest at 132°, 150.3 kN. The curves cross: no layout is strongest in every direction, and the one to choose is the one whose lowest point is highest.

The bracket pushed from the wrong side

A six-bolt bracket checked for a load straight down carries 198.5 kN. Push the same load through the same point at 138 degrees and it carries 135.8 — the direction changes the torque as well as the shear, and the worst direction is one no drawing shows. The capacity of a group whose load can turn is a closed curve, the bolt that governs it changes as the load turns, and what the curve rewards is not a larger polar moment but a smaller distance to the furthest bolt.

connections · Bolt group The bolt that governs is worst at only one thing. The plate of a bracket of six M20 grade 8.8 bolts in three rows of two at 75 mm, loaded 150 mm to the side of the group and 150 mm in front of the column face, with the load at 60° from straight down, drawn at the group's capacity on the elliptical interaction, 227 kN. Each bolt's arrow is its shear in the plane of the plate and its disc grows with its tension, which comes from the load's distance in front of the column: bottom left 9 kN and 67 kN; middle left 33 kN and 76 kN; top left 74 kN and 84 kN; bottom right 40 kN and 35 kN; middle right 51 kN and 43 kN; top right 84 kN and 51 kN. The most shear is on the top right bolt and the most tension on the top left; the one that reaches its interaction first is the top left, and the next, the top right, is at 0.97 of its own.

The bracket with no worst bolt

A bracket that stands out from its column is pulled off the column by the same load that twists it in its plane, so every bolt carries shear and tension at once. Straight down, one corner bolt is worst at both and the check is that bolt's. Tilt the load and the most sheared bolt and the most pulled bolt come apart; the one that fails is whichever of them its interaction reaches first, and at the angle where they swap the group has two worst bolts and no single one.

connections · Bolt group

Named alongside it

The objects these essays reach for when they reach for this one.

Bolt groupEccentricityElastic methodLoad directionPolar momentBolt bearingBolt tensionInteractionTorsion

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