Most bridges collapse due to the simultaneous combination of several factors and during (or after) an extreme natural event. So it was in Portugal on March 4, 2001 and recently in Italy with the Genoa Bridge (2018). The natural event has the peculiarity of exploring hidden structural weak points. At the Hintze-Ribeiro Bridge in Entre-os-Rios, the vulnerability at the foundation level was exposed to the increase in water flow in the Douro River during a flood period. The fall of the deck was due to the collapse of one of the columns as a result of the erosion phenomenon in the alluvial bed, which led to the formation of voids near the foundation of the column. Note that erosion is caused by the presence of obstacles (pillars and encounters) in the river’s water flow.
This tragedy marked a turning point in bridge surveillance policy. Previously there were bridges that did not receive regular inspections. Among those inspected, data was often recorded in certain manuscripts that could easily be lost or damaged. Underwater inspections were not a standard practice. After the collapse, aggregate mining in the Douro River was suspended and, in general, those in charge (infrastructures of Portugal, Brisa, etc.) updated the mechanisms and procedures for monitoring the bridges.
Despite all the measures taken after 20 years of the tragic accident that killed 59 people, is it likely that a similar scenario could repeat itself? In civil engineering there is an axiom that relates well to what has been done: “The risk is minimized, but not eliminated.” On the part of these companies, the risk has been minimized, managed and controlled with the perspective that natural accidents are not avoided but the tragedy is minimized.
Today the main companies have their own teams to conduct inspections, which are carried out by technicians with specific training. Most bridges are inspected regularly, with a frequency of between two and six years. The integrity of the foundations is assessed by means of underwater inspections.
19 years have passed since one of the greatest public works tragedies in Portugal. Almost two decades later, the wounds remain incurable in families who have been unable to grieve for their loved ones. 56 people died, 36 bodies were never found. The accident occurred on March 4, 2001 at 9:15 p.m. (Photo gallery updated March 4, 2020)
Manuel Roberto, Nelson Garrido, Paulo Pimenta and Fernando Veludo
In 2001 not all companies had automatic management systems, which essentially consisted of a computer database and local access. Most companies currently use a second generation management system that allows them to inventory and manage the structural condition and plan maintenance measures.
A type of 3rd generation management system is under development, in which efficiency gains are expected, for example, when tablets are used to automatically introduce information during inspections, remote access, intercommunication and business intelligence with modules for probability prediction.
Some companies are also starting to adopt a broader asset management policy, which will allow them to have a holistic and coordinated view of interfering with various components: sidewalks, works of art (bridges, tunnels, etc.), equipment (signage) and operations management.
Many municipalities are unaware of the state of the art of maintaining the infrastructure for which they are responsible, and in some cases do not have their full inventory.
However, there are still bridges that are not part of this regular inspection effort, namely bridges that are inspected by more than 300 municipalities. Although some have already taken the initiative to develop their own strategy, most municipalities have financial constraints and a lack of organic capacity. The government can delegate powers, but it cannot delegate responsibilities. It is therefore up to her to propose a national bridge inspection program among municipalities to determine the operational status of this type of infrastructure. Note that many municipalities are not aware of the state of the art of the infrastructure they are responsible for and in some cases do not have their full inventory.
Despite the efforts made, monitoring the structural condition of the bridges, especially during routine inspections, is still very susceptible to human interpretation. Although new technologies such as drones are now being used to photograph and measure cracks, the scientific community needs to develop more technology to minimize the risk of human error. The 4th industrial revolution will certainly bring more technology for the intelligent detection of anomalies and for the automatic digitization of information in the near future.
We need to study the effects of climate change on bridges. More studies are needed to develop adaptation strategies that will be implemented today to avoid disastrous consequences in the future
There are also some surveillance technologies that could be used more widely by the entities. However, it is important to develop and implement a technical regulation for monitoring the structural integrity of bridges. China developed itself in 2014. There are developments in Europe to convert a number of technical recommendations into a regulation. This is an important milestone in the application of established surveillance techniques, namely the installation of devices that can be used to control the depth of the bed.
In addition, the effects of climate change on bridges need to be investigated. One of the effects expected for Portugal is precisely the increase in the frequency of intense rainfall for short periods of time, causing particularly higher rivers in the rivers of the smaller hydrographic basins, flooding and, in borderline cases, greater erosion of the bed next to the foundations. More studies are needed to develop adaptation strategies that will be implemented today to avoid disastrous consequences in the future. The construction of bed protection against erosion in the vicinity of the pillars cannot be ruled out here. At the same time, the coordinating bodies for the management of water resources must be held accountable in order to prevent interventions that lead to the destruction of the dynamic equilibrium of the rivers. Floods and bridges are not a harmonious couple.
After 20 years of the collapse of the Hintze-Ribeiro Bridge, we must acknowledge the efforts of key units, but there are still many challenges to make our bridges more resilient.
The author writes according to the new orthographic convention