This paper describes a comprehensive structural assessment carried out on heritage riveted steel bridge laying over a navigation lock. This bridge was constructed over 100 years ago and is still in service till now. The bridge was subjected to fatigue due to continuous traffic loads. The challenge was not only to set an intensive rehabilitation program but also to increase its load carrying capacity to accommodate new heavy traffic loads. Site inspections for the original bridge structural components as well as its mechanical parts were conducted. The structural performance was evaluated by means of dynamic and static in-situ tests. Eight accelerometers were mounted and distributed among the bridge area. Formal modal analysis was conducted before and after strengthening. The level of strain was also recorded at the end of the retrofitting process. The concept of strengthening was to create a stiffer structural system capable of decreasing the stress level on the old system. Firm restrictions were adopted during the strengthening program. Additional thermal stress due to welding should be avoided, especially at the main riveted girders. Moreover, the original bracing system was kept without removal of any of its parts. Plane trusses were constructed to carry the bridge along secondary hot rolled beams. The trusses were connected laterally through horizontal and inclined members. The structural rigidity was evaluated after strengthening. The fundamental frequency of the bridge was enhanced by 38%. This research depicts the successful efforts for upgrading a heritage bridge without affecting its original riveted components.