Bridge Structural Failure: A Case Study by CEAI

CEAI

Bridge Structural Failure: A Case Study by CEAI

 

Structural engineering, in its most literal sense, is the engineering that underpins the structural integrity and strength of a building or structure. Structural engineering is critical in the construction of major structures such as skyscrapers, bridge, and dams.

Unfortunately, we have seen some heinous structural failures in the past, resulting in mass damage of property and human lives. One of the deadliest man-made disasters in human history is bridge structural failure. Today, we take a look at the recent collapse of the Morandi Bridge in Genoa, Italy. The bridge structural failure, which occurred in August 2018, resulted in 43 human fatalities as well as significant economic losses for the country.

Several case studies have been conducted on this specific incident, with several consulting engineers from around the world debating the causes of the disaster and how it all could have happened. The bridge was designed by Riccardo Morandi, a well-known Italian civil engineer. He was regarded as one of Italy’s most innovative civil engineers.

Prof. (Dr.) G. Michele Calvi explained the process of building the Morandi bridge in a recent webinar attended by members of the Consulting Engineers Association of India (CEAI). Morandi used traditional construction methods such as stay-cables and prestressed concrete, according to his studies.

However, he also explained how the construction process was not as precise as it should have been. The methods used to construct the antennae and piers left room for corrosion and water penetration inside the bridge. Furthermore, the number of steel cables used in the process was a whopping 50 percent greater than that used today. This also left a significant amount of space to inject between the cables and the duct.

CEAI is the member organization of FIDIC and has done a case study on Aftermath of Collapse for Bridge Structural Failures

Collapse Assessment

The consulting engineers’ forum then discussed the various collapse mechanisms that could have been activated in the case of the Morandi bridge disaster. Prof. (Dr.) G. Michele Calvi went on to demonstrate the various options.

First, the disaster could have been caused by excessive corrosion of the steel and other materials used in the bridge. However, a resultant of approximately 50-60% corrosion also causes a significant displacement. In such a case, the assessment authorities could have been notified and taken action. However, this was not the case. As a result, the calculations could not be reconciled, and Prof. Calvi concluded that corrosion could not have been the primary cause of the Morandi bridge structural failure.

Second, impulsive load has the potential to be disastrous. Prof. Calvi, on the other hand, presented calculations indicating that impulsive load would cause horizontal oscillations in the bridge until it returned to a stationary position. The damage and collapse of the supporting span would result, but not a global collapse.

A third possibility that was discussed was a) a failure in the stays and antennae and b) a sudden loss of connection between the stay and the main deck.

CEAI is the member organization of FIDIC and has done a case study on Aftermath of Collapse for Bridge Structural Failures and shares the Probable causes of Collapse

Major Causes of Collapse

Prof. Calvi elaborated on several factors that could have combined to cause the Morandi bridge structure to fail in his closing remarks. Among these factors were:

  1. Extremely high quality of cinematic reproduction
  2. Cinematics compatible with coil fall
  3. Construction flaws
  4. Absence of cable ducts
  5. Presence of large voids in the bridge structure
  6. Abnormal corrosion progression fundamental to bridge structure failure.

Inferences of Bridge Structural Failure at Morandi

One could draw many conclusions as to why the Morandi bridge collapsed, but the study mentioned above suggests that it was a combination of failures at various levels of the construction. The construction of Morandi bridge was  done in a way to withstand the the variables of today’s seismic events as discussed in the study.

However, despite minor flaws in the bridge’s construction, it was a series of malfunctions on August 14, 2018 that resulted in the collapse of one of the structure’s main spans, turning it into one of the most egregious modern-day disasters.

Since the year 2000, there have been 115 major bridge collapses around the world, which is both interesting and unfortunate. And more than 22 of them have occurred in the last three years alone. The Morandi bridge in Genoa was made up of 11 spans ranging in length from 65 to 210 metres, as well as 12 pylons on which they rested. The collapse of one of its main spans was unexpected given that the structure was designed to last at least a century, beginning in 1967.

As a result of the incident, many people were killed and property was severely damaged, and the incident caught the eye of many top consulting engineers, including those at CEAI, as an unfortunate example.

If you found this information useful, you might be interested in reading some more insightful articles on CEAI’s official website.

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