Infant Henrique Bridge over the River Douro, Porto

The river Douro at Porto provides the splendid setting for several world renowned bridges. The last one built consists of a shallow and extremely thin arch spanning a distance of 280 m under a stiff box-beam deck. This "Maillart" type of arch bridge sets a world record. The deck is the stabilizing element of the slender arch. The bridge was built by setting up rigid triangular structural systems requiring temporary struts and diagonals to complement those bars provided by the arch and the deck. The equilibrium of the two bridge halves cantilevering over the river at a height of more than 70 m was achieved by cables anchored into the granite slopes, together with reinforced concrete struts built on the ground forming rigid triangular structural systems with the deck and temporary diagonals. The construction of this bridge was foreseen to be extremely difficult. Therefore, state-of-the-art monitoring equipment was installed on the bridge and its foundation elements for on-line follow up of the construction method and the several imposed settlements, upwards and downwards, introduced into the structure. The bridge is affected by the maritime climate of Porto, and thus a variety of environmental monitoring systems were installed on the bridge. The structural behaviour of the bridge is controlled and supervised on-line from the design office. A direct follow up on actual conditions ensures timely structural interventions for the rehabilitation of the bridge, if required.