Eurocodes made more viable and affordable

Background

Reid Steel is a world renowned specialist in the design, engineering, fabrication and erection of pre-engineered steel frame buildings and structures. Headquartered in Christchurch, on the South coast of England, the company employs some 130 direct staff, with a design engineering team of 7 members. With an annual turnover target of £30+ million, Reid Steel is active in the UK, European and world-wide markets. To date the company has exported to over 140 countries across the world.

Though much of its work in steel structures is comprehensively covered by BS5950 and BS5400, the withdrawal of the relevant British Standards meant that the company needed to design its bridge projects using Eurocodes sometime before the Shanklin Lift Bridge project was awarded.

However, the complexity of navigating the relevant standards unaided made their use daunting and there was a real need to find a method to make the use of Eurocodes more practical. In this case the situation threatened to compromise the design of the bridge itself.

"Eurocodes Plus already delivers Eurocodes  accessibility, cost savings and a freeing-up of resources. As our Eurocodes journey continues we may well uncover other advantages."

The customer need

The original cliff face passenger lift at Shanklin was built around 1891. Having been rebuilt in 1958 following wartime bombing, the lift comprises a tower descending from cliff top level to beach, with a connecting bridge enabling passengers to walk in either direction between the top of the lift tower and the cliff top. When, in 2016, a major electrical fault brought forward a planned large-scale overhaul of the lift, Reid Steel was appointed by MCM Construction to design and install a new bridge between lift shaft and cliff top.

‘Because Eurocodes pay greater attention to a number of important facets of bridge design, such as global buckling and harmonic response, and because the Highways Agency is no longer keen to adopt bridges built to British Standards, we had already taken the decision to build all our UK bridges to Eurocodes’, John Harrison explains. ‘On the Shanklin Lift project, we also had an additional driver. The technical requirements for constructing and installing the 16.5-metre bridge on an eroding cliff top had limited our total bridge weight to 12.6 tonnes. This included the steel frame, the floor, the roof membrane and the glass walling. To install the large panes of glass, our design preference was for a Vierendeel truss structure, in which the structural members form rectangular, rather than triangular, openings and the frame has fixed joints that are capable of transferring and resisting bending moments’.

Vierendeel truss bridges of this kind are flexible structures. As a result, the bridge assumes a resonant frequency within the range of users’ footsteps, which can cause a disturbing degree of movement. Eurocodes enables a detailed harmonics response analysis to be carried out, to prove that a proposed structure will provide the rigidity required for user comfort.

For Reid, the challenge lays in locating and navigating the relevant codes across at least four standards. ‘Because of the complexity of Eurocodes’, John Harrison explains, ‘We would quite literally have had a 3-inch deep layer of Eurocodes documents covering every inch of our meeting room table. That’s not the most practical resource with which to work’.

The solution

Having taken the operating decision to use Eurocodes on all bridge contracts, Reid Steel had initially attempted a number of projects using the physical Eurocodes documentation. A subscription to BSI’s Eurocodes PLUS had then been purchased a year or so before the Shanklin Lift Bridge project came about. By then, the suite had proved itself to Reid’s engineers as being capable of marshalling the extensive and challenging Eurocodes into a viable resource for undertaking the required calculations.

‘Because Eurocodes PLUS hyperlinks between the various code documents so comprehensively, it was possible to handle our calculations without needing a vast array of physical documents open at once’, John Harrison explains. ‘This reduces down the complexity significantly’.

This had a fundamental bearing on the design solution of the Shanklin Lift Bridge.

‘Without Eurocodes PLUS, I’d guess that the time needed to do a bridge of this kind using Eurocodes might be 250% greater than the time required using BS 5950’, Mr Harrison continues. ‘On the Shanklin Lift Bridge, with severe constraints on the total materials weight for the bridge, and other considerations such as the difficulty of glazing the bridge walkway over the cliff edge, our favoured design solution featured the Vierendeel truss structure. Because of the complexity of the harmonics response analysis that this requires, without Eurocodes PLUS on hand we may well have been forced to consider another, less desirable design solution’.

Customer benefits

For Reid Steel, Eurocodes PLUS delivers a number of key benefits.

Eurocodes offers far more support than does BS 5950 for the bridge structures that comprise an important part of the company’s order book. It is only the comprehensive hyperlinking of Eurocodes PLUS that makes it practical for Reid to navigate the codes required.

Purchasing the four core Eurocodes (1, 2, 3 and 8) mainly applicable to its work, plus the various adjuncts and National Annexes, would cost Reid Steel well in excess of £10K a year. It is likely that the saving to Reid is in excess of 70%, even before the savings on human resource are considered.

The web-based, continuously updated Eurocodes PLUS platform has obviated the need for Reid to maintain a large portion of its own standards library, producing a measurable saving in staffing resource.

‘Eurocodes are due for a full revision in 2020’, says Reid’s John Harrison. ‘They would certainly benefit from some streamlining. But Eurocodes does hold the promise of a universal and complete standard, with the myriad advantages this might bring to the industry’. For Reid Steel, as well as for a wealth of other UK engineering firms, Eurocodes PLUS would be the key to enjoying those benefits.

John Harrison, Structural Engineer, REIDsteel