Structural Engineering & Statics
where the load goes
Concept

Welding — where it appears

Joining metal parts by melting them together, usually with a filler, so that they solidify as one piece. The heat leaves residual stresses and a zone beside the weld whose strength and toughness can differ from the parent metal's.

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

A I-section at 80% of its plastic moment. The same I-section drawn three ways: the shape, the strain across its depth, and the stress that strain produces in mild steel. The strain diagram is a straight line, because plane sections stay plane whatever the material is doing. The stress diagram is not: 0% of the area has yielded, working inward from both faces, and the neutral axis sits at 70.9 mm against a centroid at 100.0 mm. The compression resultant is 322.5 kN and the tension resultant 322.5 kN, on a lever arm of 180.1 mm, which multiplies back to the 58.1 kNm the section is carrying. A rolled residual stress pattern of ±30% of yield is locked in before any load arrives.

The stress that was there before the load

A rolled steel section leaves the mill carrying eighty N/mm² of stress with nothing applied to it, in a pattern that sums to no force and no moment. It is invisible to every calculation and it is the knee in every column curve.

materials · Residual stress What a 60-degree seam leaves of the wall. The combinations of axial stress σa and hoop stress σh that a tube of 6082-T6 (parent ultimate 310 N/mm², softened zone 185) carries, with its seam at 60° to the axis (solid), inside the parent wall's von Mises ellipse (dashed). Where the solid line falls inside the ellipse the seam's zone fails first. axial tension: 60 per cent of the parent; closed pressure: 78 per cent of the parent; hoop alone: 76 per cent of the parent. The seam is weakest, at 60 per cent, along the loadings whose unstretched line lies on it.

The seam that pressure protects

A soft weld zone pulled at 55 degrees to the load gets no help from the metal around it, because 55 degrees is the line a plate under uniaxial tension does not stretch. A spiral-welded tube winds its seam at about that angle. Pressurise the tube and the line that does not stretch moves to the tube's own axis, so the spiral seam is suddenly well protected and the longitudinal seam is the exposed one. The soft zone's weakness belongs to the loading as much as to the weld: a seam is in danger only where the field around it leaves its line unstretched.

materials · Heat-affected zone

Named alongside it

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

Biaxial stressColumn curveConstraintFirst yieldHeat-affected zoneHoop tensionImperfectionMoment-curvatureNeckingProof stressResidual stressSelf-equilibrating

All concepts