Steel Bridge Girder Fabrication and Erection

The job

Frames from two bridge jobs: a railway bridge deck with rails laid on sleepers between two triangulated truss girders, and a highway overpass girder — black-painted, built-up plate section — being lifted into place by crane with an erection crew on a basket platform below. Both are components fabricated in the shop to the bridge engineer's drawings, shipped match-marked and set by crane.

Why it is demanding

The erection window is short. Road or track closures are measured in hours; the girder has to seat on the first attempt and site connections must finish in the planned order. That puts the burden on shop tolerances and template drilling.

Piece length is limited by transport. Long girders are split into transportable segments joined on site with bolted or welded splices; splice positions are chosen with the design engineer where bending moment is low.

Fatigue and corrosion last the whole service life. Traffic loading is cyclic; weld classes, cross-frame connections and truss nodes are detailed accordingly. Surface preparation and a multi-coat paint system are completed in the shop; the site only touches up the splice zones.

How it was built

• Main girders were fabricated as welded built-up plate sections; flange-to-web welds were full penetration, squareness and camber were checked by measurement.
• On the truss bridge, the triangulated main girders and cross members were joined with gusset plates; sleeper bearing surfaces were aligned to the rail axis.
• Site splices (bolted splice plates, cross-frame connections) were trial-assembled in the shop; holes were template-drilled.
• Blast cleaning and multi-coat painting in the shop; pieces were match-marked in erection order and shipped.
• On site the girder was lifted by crane onto its bearings; cross frames were connected, bolts torqued, and the line or road released within the closure window.

Result

The girders seated within the planned closure window; after the site connections were completed, paint touch-up and deck works continued. Span, tonnage, location and date will be added to this page from the firm's form.