Design of Edge Beams

Abstract: The purpose of the edge beam is to support the railing and the pavement, function as part of the drainage system and in the case it is integrated into the bridge deck it can serve to distribute concentrated loads. It is located in road environment and therefore exposed to water and salt with chlorides as well as subject to impacts during accidents. It deteriorates in a greater pace than the rest of the bridge and therefore has a shorter lifespan than the bridge in full. A deteriorated edge beam put the safety of the bridge users in jeopardize and increases the need of maintenance, repair and replacement work. These activities affect the surrounding traffic flow due to reduced speed limits as well as closure of traffic lanes. A literature study has been performed to get an understanding of how edge beams are designed and constructed. A great part of this was done by examining codes and regulations. By meeting engineers from different building companies it has been possible to obtain a picture of how it is done in real life and how the path to the final design looks like. Building site visits were carried out to see the process from design to construction i.e. how it is applied in real life. A design study was performed, including a check of crack width in an integrated edge beam over a support, height of bridge deck when a pre-fabricated (brokappa) is used and a comparison in the magnitude of the clamping moment in a steel-concrete bridge with and without an edge beam. All proposals are presented by the Edge Beam Group (EBG, in Swedish, Kantbalksgruppen), which is composed of experienced engineers that works within the frame of the project social optimal edge beam systems governed by the Swedish Transport Administration. The literature research showed that even if the edge bean is prone to deteriorate its lifespan does not have to be governed by its condition. Planned expansion of bridge width and maintenance strategies including the replacement of waterproofing layer could also be a reason for replacement in some cases. A significant increase of reinforcement in the edge beam and top part of the bridge deck over support is needed to obtain an acceptable crack width of 0.15mm. This would however aggravate the casting phase. The use of a pre-fabricated edge beam result in an increase of the bridge deck height. A solution could be to strengthen the anchoring capacity but this could in turn give an over reinforced structure. When it comes to the clamping moment in a steelconcrete composite bridge the integrated edge beam leads to a better distribution of the traffic load. On the other hand, due to the higher dead weight, a bridge deck without an edge beam would result in a lower total moment in the cantilever.