When King Harald V opened the Skarnsund Bridge on 19 December 1991, its 530 m main span was the longest of any cable-stayed bridge in the world. It held that title for about two years, until the Yangpu Bridge in Shanghai opened in 1993. It still shares the record for the longest cable-stayed main span with a concrete deck: the Atlantic Bridge over the Panama Canal, opened in 2019, also has a 530 m concrete main span.

The bridge crosses the Skarnsundet strait in Inderøy, Trøndelag, and is the only road crossing of the Trondheimsfjord. It replaced the Vangshylla–Kjerringvik ferry. Johs. Holt was the structural consultant and Aker the main contractor. Johs. Holt dates the start of works to the winter of 1989, while some contemporary news reports place it in 1988. The record was set by the finished structure. The constraints that shaped it were set by the site, and they were all paid for during construction.

530 m
Main span
1,010 m
Total length
152 m
Tower height
2.15 m
Deck depth
208
Locked-coil stay cables
Constraint 1 — The strait
Foundations dug inside tidal windows
Skarnsundet carries strong tidal currents between the outer Trondheimsfjord and the Beitstadfjord. According to ENR's December 1991 report, the current left only a couple of two-hour periods a day in which the tower foundations could be excavated. The time available on the water, not the crews' productivity, governed the pace of the foundation works.
Constraint 2 — The towers
Conical slipforming to 152 m
The two A-shaped towers rise 152 m above the water. They were built by conical slipforming between 1989 and 1990, with Gleitbau of Salzburg as slipform specialist. In this variant of slipforming, the climbing form follows walls that incline and taper, which is what the legs of an A-frame do as they converge towards the top.
Constraint 3 — The banks
Short anchor spans, balanced with ballast
The steep sides of the fjord limited the anchor spans to about 190 m, against 265 m for each half of the main span. With less length on the landward side to counter the pull of the main-span stays, concrete ballast was placed in the anchor spans to balance the cable loads. The geometry of the banks decided part of the dead load of the structure.
Constraint 4 — The deck
A 2.15 m triangular box over 530 m
The deck is a triangular box section 13 m wide and 2.15 m deep, a span-to-depth ratio of about 1:246 across the main span. It is carried by 208 locked-coil stay cables. That slenderness prompted extensive wind tunnel testing, which raised the design wind speed by 10% and introduced more unfavourable wind spectra.
Four-panel schematic of the Skarnsund Bridge: tower foundations excavated in two-hour tidal windows, A-shaped towers built by conical slipforming to 152 m, short anchor spans of about 190 m balanced with concrete ballast, and a 2.15 m deep, 13 m wide box deck giving a span-to-depth ratio of about 1:246
The four site constraints behind the record span. Schematic, not to scale except where marked; the orientation of the triangular deck section and the deck casting sequence are not shown.
Sources: ENR (December 1991); Gleitbau; Structurae; Johs. Holt. Diagram: EE&HL Network, 2026.

Every metre of slenderness that made Skarnsund a record holder was a metre the construction stage had to carry before the record meant anything.

ENR's December 1991 report on the bridge ran under the headline “Bridge breaks record and builder”. The findings of the wind tunnel programme and other design modifications added about $2.2 million to the price. Together with the tidal limits on the foundation works, these problems put the contractor's finances under enough strain to lead to its takeover, even as the bridge was reported to be finishing on schedule.

That is the commercial pattern worth noting. The features that made Skarnsund a record, a slender concrete deck, short anchor spans on steep banks and a tidal strait with no room for propping, were fixed in the design. Their cost arrived on the contractor's side of the contract, during construction, in the form of lost working hours, extra testing and redesign. A record set by the finished structure does not say who carried the construction-stage risk of achieving it.

For how construction-stage conditions govern outcomes more generally, see Erection Sequence Risk and Temporary Works & Erection Strategy. For the wider sector context, see Erection Engineering in Bridge Construction.

Related case studies: Akashi Kaikyō Bridge · Pelješac Bridge · Millau Viaduct · Chenab Bridge · Sidu River Bridge

Core concepts: What is erection engineering? · What is heavy lift engineering?

The Skarnsund cable-stayed bridge spanning a wide fjord strait between two tall concrete towers, with forested shores under a blue sky
The Skarnsund Bridge across the Skarnsundet strait, Trøndelag, August 2016. Resized from the original for web display.
Photo: Henny Stokseth, via Wikimedia Commons, CC BY-SA 4.0.

Sources: ENR — “Bridge breaks record and builder,” vol. 227, no. 25, December 1991 (tidal windows, anchor spans and ballast, triangular box deck, locked-coil cables, wind tunnel findings, cost increase, contractor takeover); Structurae — structural data; Gleitbau — conical slipforming of the towers, 1989–1990; Johs. Holt — structural consultant's project record and construction start; Riksantikvaren — heritage protection; Wikipedia — timeline of cable-stayed span records; VINCI — Atlantic Bridge, 530 m concrete main span (press release, August 2019). The deck construction sequence is described in C. Hansvold, “Skarnsundet Bridge (Norway),” IABSE-FIP Conference, Deauville, 1994; segment lengths and casting method are not stated here because they could not be verified against that paper.

Frequently Asked Questions

It shares that record. Its 530 m main span was the longest cable-stayed span of any kind when it opened in December 1991, and it held that overall record until the Yangpu Bridge in Shanghai opened in 1993. The Atlantic Bridge over the Panama Canal, opened in 2019, also has a 530 m concrete main span, which its builders describe as a world record, so the two bridges share the distinction.

Skarnsundet is a narrow strait with strong tidal currents between the Trondheimsfjord and the Beitstadfjord. ENR reported in December 1991 that the currents left only a couple of two-hour periods each day in which the tower foundations could be excavated. On a marine foundation, a constraint like that sets the pace of the critical path rather than the productivity of the crews.

The steep banks of the fjord limited the anchor spans to about 190 m, against 265 m for each half of the main span. With a shorter lever arm on the landward side, the back stays cannot balance the main-span stays by span length alone, so concrete ballast was added to the anchor spans to balance the cable loads.

The two A-shaped towers, 152 m tall above the water, were built by conical slipforming between 1989 and 1990. The slipform specialist on the towers was Gleitbau of Salzburg. Conical slipforming lets the climbing form follow walls that incline and taper, as the legs of an A-frame tower do while they converge towards the top.