Open sandwich bridge deck construction—20 years on

Sandwich construction is a relatively simple structural form which offers a high strength-to-weight ratio, this efficiency being exemplified by its widespread use in the aerospace industry. The concept was utilised by the Wolfson Bridge Unit at the University of Dundee in the 1970s, in conjunction with emerging structural adhesive technology, in the form of steel/concrete open sandwich panels for bridge decks. Potential cost savings of the order of 10% in comparison with conventional reinforced concrete were demonstrated. Short- and medium-term proof of the concept was demonstrated as a result of over ten years of research utilising beams, slabs and model bridge decks subject to static, fatigue and sustained loading regimes together with accelerated durability testing. However, before the industry was prepared to accept structural adhesive connections in prime load-bearing connections in new construction, it was recognised that a long trial in an actual bridge structure was required. To this end, Tayside Regional Council agreed to the construction of the 6 m span Wester Duntanlich Bridge in Perthshire in 1984. This paper summarises the early research into open sandwich construction. It then describes the design, construction and load trials on the completed bridge which demonstrated that the technique can be successfully and practically applied to full-scale bridge deck construction. Moreover, its subsequent satisfactory performance in service for 20 years will boost confidence in the potential durability of steel/concrete elements incorporating structural adhesive connections.