Widening of the hydraulic section of a masonry arch bridge in Sardinia

The following work aims to analyse and work out the issues relating to the widening of the hydraulic section of a two arched bridge in Sardinia. Its small hydraulic section proved to be insufficient and unable to drain an adequate quantity of water with the possible risk of dangerous flooding. In order to avoid the occurrence of such phenomena it is necessary to build a third reinforced concrete arch. Thus, we pulled down the right abutment of the original bridge and consequently we took the necessary safety measures through an innovative confinement system carried out as follows: • Driving in a line of micro-piles by each bridge pier wall and placing two 42 commercial sections at the level of the arch springing line tightly secured to the micro-pile line tied by means of Dywidag threaded bars . Through such device we needn’t use ribs so avoiding all the problems related to building underwater. Besides, building micropiles enabled the conversion of the original abutment of the pier bridge. • Pulling tensile the Dywidag bars by the springing levels of both arches. The main subject of this writing is the determination of the tie beam pre-tension force, having calculated the horizontal reaction to the arch springing