Bridge Component Fabrication Marginal Unit Cost Calculation
Marginal unit cost in bridge fabrication equals direct plate, consumable, labor, and testing costs plus step-fixed capacity adjustments.
Fillet Weld
Meaning
Structural joint geometries join two metal surfaces at right angles or near-right angles without complete plate edge beveling. Designers specify a fillet weld to connect lap, tee, or corner joints across structural frameworks, machinery bases, and stiffened plate structures. The classification boundary excludes groove joints where plate edges are chamfered for full penetration, applying solely to triangular cross-section deposits placed in internal corners.
Throat Dimension
Effective distance from the root to the face determines mechanical load carrying capacity in angle joints. Inspection protocols require measuring fillet weld leg length and actual throat thickness to verify compliance with structural drawings. Undersized throat dimensions create weak shear planes, while excessive weld sizing increases heat input and plate distortion.
Automated gauges measure profile convexity to ensure smooth stress transitions.
Stress Concentration
Abrupt directional changes at the weld toe create local stress rises under cyclic loading conditions. A poorly contoured fillet weld acts as a notch, accelerating fatigue crack initiation along structural stiffeners. Grinding toe radii or applying post-weld peening redistributes local stresses, extending service life in dynamic load environments.
Process selection influences bead profile smoothness and root penetration quality.
Load Capacity
Shear stresses govern failure mechanisms in corner joints subjected to tensile or bending loads. Assuming full strength from a small fillet weld during pilot testing leads to structural failure under full production operational stresses.