[1] This was very technically demanding: the river was fast-flowing, its depth could be as much as 20 m (66 ft) during times of flooding, and the riverbed was made up of a deep layer of gravel.

The methods of calculation known up until now can only be applied in practise with the aid of hypotheses which depart from established fact to a greater or lesser extent, and thus render the projected results uncertain.

In his account of the bridge that accompanied the 1:50 scale model exhibited at the 1878 World's Fair, Eiffel credited Seyrig and Henry de Dion with work on the calculations and drawings.

[1][3] Between 1897 and 1898 there was some concern by technicians about the integrity of the bridge; its 3.1 metres (10 ft) width, the interruption of principal beams, its lightweight structure, and its elastic nature.

[3] As a consequence, restrictions were placed on transit over the structure between 1900 and 1906: axle load was limited to 14 tons and velocity to 10 kilometres (6.2 mi) per hour.

[3] Consulting with a specialist in metallic structures, French engineer Manet Rabut, in 1907, the Oficina concluded that the arch and the works performed on the bridge were sufficient to allow circulation.

[3] In 1916, a commission was created to study the possibility of a secondary transit between Vila Nova de Gaia and Porto.

[3] The analysis of the stability of the bridge, handled by the Laboratório Nacional de Engenharia Civil (LNEC), resulted in the injection of cement and repair of the masonry joints and pillars that connected with metallic structures.

[3] Another analytic study in 1966 began to analyze upgrading service to electrical locomotives (Bò-Bó), leading to the conclusion of the electrification of the Linha Norte.

In 1991, rail service over the bridge ended because the single track and speed restrictions limited transit to 20 kilometres (12 mi) per hour.