The Morandi Bridge Collapse

On the morning of August 14, 2018, a 210 m (690 ft) section of Ponte Morandi Bridge, officially the Viadotto Polcevera (Polcevera Viaduct) in Genoa, Italy, collapsed during a torrential storm. The collapse resulted in 43 fatalities, numerous injuries, and major disruption to European Route E80 through Genoa, one of Europe's major port cities. So, what did we as an engineering community learn from this tragic disaster? Though very saddening when considering the loss of life, the collapse of Morandi Bridge reinforced the critical importance of sound engineering principles and practices necessary for serving and protecting the public.

Opened in 1967, the 1200 m (3900 ft) long Viadotto Polcevera was unofficially named Ponte Morandi (Morandi Bridge) in honor of its structural designer, the Italian Structural Engineer Riccardo Morandi, famous for many breakthrough designs and at the time considered Italy's greatest structural design engineer. Morandi played a pivotal role in the development of structural engineering designs utilizing prestressed concrete and used prestressed concrete in many of his designs.

It was common practice during the 1950’s through the 1970’s to design bridges with no more than a 50-year design life in mind. Design life notwithstanding, the governing role that durability properties very often play was simply not as well understood as much as it is today and more strongly considered in contemporary infrastructure designs. At the time of its collapse, Ponte Morandi was in its 51st year of service. Obviously, given strength reduction factors inherent to design codes, this is not to say that collapse is imminent with any properly designed, properly constructed, and normally-loaded structure marginally exceeding its design life, but Ponte Morandi had durability-related service issues working against it. Principally, Ponte Morandi was subject to significant active corrosion. The steel in Ponte Morandi was experiencing cross-sectional loss of reinforcing bar and prestressing strand area due to corrosion.

The bridge had light late-morning traffic on it at the time of the collapse. Witnesses reported seeing the bridge struck by lightning at the moment of the collapse, specifically at or near a Pylon 9 stay prior to the pylon's collapse. The collapse of Ponte Morandi represented the worst bridge disaster to occur in Europe in over 100 years, and its occurrence prompted a criminal investigation which is still ongoing.

Unrelated to the collapse, mechanically, Ponte Morandi had been subject to continual restoration work within only a few years of opening due to an incorrect initial estimate of creep, which resulted in undulation and excessive displacement of the deck, affecting both deck levelness and flatness. Creep-related remediation took a full decade to complete.

Ponte Morandi was an innovative and aesthetically appealing landmark cable stayed bridge characterized by prestressed concrete piers, pylons, stays and deck sections. Although structurally sound and code-compliant at the time of its design, Ponte Morandi was an atypical mono design cable stayed bridge. Unlike most modern cable stayed bridges, Ponte Morandi was designed with as few as only two stays per span with up to 52 cables bundled together and encased in a post-tensioned concrete shell, creating massive stays. Doing so made the Ponte Morandi stays very difficult to inspect and the design made it highly susceptible to single-point failure. Single-point failure can cause collapse of an entire structure or major portion of a structural system due to failure occurring at a single point of a system component. Single-point failures often occur at connection points. From an engineering perspective, single-point failure designs are not considered sound in any structural system with a goal of high operational reliability or safety. Regardless of the specific manner in which the cables are oriented, most modern cable stay bridges are designed with many exposed stay cables spread out, which is highly desirable for a number of important reasons, including the creation of redundancy and ease of inspection, maintenance, and cable replacement, if necessary.

Demolition of the remaining portions of Ponte Morandi was completed on June 28, 2019. A replacement bridge is scheduled to be completed later this year.

The collapse of Ponte Morandi served as a very unfortunate reminder of the critical nature of sound engineering principles and practices.