A procedure for the design of bridge rail anchorage for the installation on existing structures

According to European standards a bridge rail can be installed on a public road only if it has successfully overcome a full scale crash test. The behavior of the restraint system is strongly affected by the characteristics of the anchoring system which, in the case of bridge rails, is generally realized by connecting the steel posts to the edge beam of the bridge deck by means of a given number of steel anchors. The resistance of the anchoring system, on the other hand, is strongly affected by the bridge deck concrete slab characteristics. Therefore the Italian regulations require the designers to check if the barrier can be installed as it was in the crash test, given the specific concrete slab available on site. If not, the designer is required to modify the anchorage system to allow the connecting system to offer a resistance equal or higher than the one offered in the crash test. This problem becomes extremely important when a new bridge rail is installed on an existing structure, the structural and geometric characteristics of which can differ considerably from the ones of the structure used for the crash test. This paper describes a procedure which has been applied to check the compatibility between the existing supporting structure and the bridge rail anchors, as used in the crash test configuration. A number of different design interventions which can be considered when the support doesn’t allow the installation of the bridge rails as crashed are also described.