Design Solutions for Widening the A1-A9-A14 Italian Highways

In Italy the major part of the national highway system is entrusted to the Autostrade Company which has to manage about 3400 km of highways, comprising a total of about 3000 bridges. Since the first highways were built in the sixties, many of them are no longer adequate to meet the current functional and safety standards. In order to answer the continuously increasing demands due to the high volume of traffic flow, and to comply with the new national regulations, the company and its design company, are widely involved in planning the widening and strengthening of a great part of the highway network. In this complex context, they chose to define a unitary approach as regards the most appropriate criteria for widening and rehabilitating interventions, aimed to represent an important reference for all the designers involved in the design activities. Basically, the widening intervention consists of an enlargement of both superstructure and supports in continuity with the existing parts. The widening portion is rigidly connected to the existing one in order to ensure a strong cooperation in resisting external forces. In particular, the design of the widening portion is addressed by the concept that this kind of intervention is a part of the strengthening strategy. In fact, by accurately designing the structural members of the widening portion with the objective of uniform distribution of all design forces, the overall performance of the construction can be improved. When the old structure did not present any severe deficiency, the beneficial effects of the widening intervention can be shown to be enough for ensuring the satisfaction of safety requirements in both static and seismic conditions. More frequently, however, a more stringent upgrading of the structural performance is needed by focussing the attention on the deficiencies emerging during seismic events. In this paper, after a brief overview on the basic widening criteria, many representative case studies are presented by describing the adopted widening intervention as well as the additional strengthening interventions.