<p>The need for a highway link was highlighted after 12 people died in a ferry accident in 2002 on the Karakaya Dam reservoir near Malatya, Turkey. The closest link to the ferry route is a thirty year old, 2030 meter long single track steel truss railroad bridge. The existing bridge, with 29 identical spans, is supported on massive piers. The existing steel truss superstructure has design-originated seismic deficiencies. This is because the current seismic requirements of the bridge specifications have increased since recent regional analysis has shown demands to increase as compared to past assessments. The main focus of this paper is to demonstrate that the additional highway deck placed on top of the truss not only provides a needed highway link but also helps the bridge structurally to mitigate the seismic deficiencies. As part of this effort, the seismic and structural reliability of the bridge, review of existing design, modifications, material tests and structural monitoring test results are evaluated. The provided solution of the upper highway deck system not only adds mass but also rigidity to the truss bridge, helping to solve some of the inherent design problems associated with the existing structural system.</p>

The existing Komurhan Bridge was built over the dam reservoir prior to water storage. The aging segmental post-tensioned concrete bridge with two lanes had an active sagging problem at its mid-span. As the traffic demand increased over the years, the authorities decided to add two more lanes to have a twin two-lane road for this part of highway network. Therefore, a need was developed to build a new bridge. Unlike the existing one, the suggested crossing needed to pass 300 meters wide water body with a depth of 45 meters to avoid piers at water body. Couple of alternatives was considered to cross the deep water at conceptual design phase. The focus of this study is given to the conceptual design of a cable-stayed bridge with two towers crossing the water at the narrowest location. This option results in a curved back span at one side of the water. A three-dimensional computer model was developed to assess challenges in design. Special care is given to the design details of the cables and the superstructure. Even if one of the back spans is curved, the proposed conceptual cable-stay bridge design is satisfactory under service and earthquake loads.