The base isolation and damping system in Tranc?o Bridge - Lisbon

The system

As we all know, civil infrastructure is critical for economic growth and social well-being. But, when it comes to seismic events, the risk of infrastructure damage can be significant. This is why it's essential to take the necessary measures to ensure the safety of our infrastructure. One of the most critical structures in Portugal is the viaduct over the Tranc?o river, which is one of the bridges with more traffic in the country (about 85000 vehicles per day). However, its structural behavior was deficient regarding seismic action, which could lead to severe consequences in case of an earthquake.

Fortunately, in 2010, an intervention was carried out to reinforce the bridge's structure, and the adopted solution consisted of introducing a base isolation complemented with a seismic damping system, among other interventions to increase the structural performance of the bridge.

The adopted solution can effectively reduce the amplitude of the vibrations during seismic events, preventing the bridge's collapse and ensuring the safety of the people who use it. This is a clear example of how implementing such solutions can make a significant difference in preventing risks from seismic events on infrastructures, ultimately protecting the population's safety and well-being.

The Bridge

The viaduct over the Tranc?o river has a total development of about 329m and a deck width of 30.29m. The viaduct was entirely built of reinforced concrete in 1959 and consists of 5 spans in the longitudinal direction with a 57m development. Each span is formed by 6 individual arches. At the deck level, there are expansion joints that provide independent behavior to the various spans regarding horizontal actions.

Regarding the structural behavior of the viaduct for seismic action, relevant deficiencies were found regarding the strength and deformation of the structure. Since the viaduct consists of 5 spans separated by expansion joints, each span has an independent dynamic behavior, so during an earthquake, movements of the structure will occur in counter-phase with significant amplitude, leading to impact phenomena and eventually the fall of simply supported deck spans. The main intervention carried out on the viaduct consisted of improving its performance for seismic action. The adopted solution consisted of introducing a base isolation and seismic damping system. The system was introduced at the base of the arches.

Additionally, the continuity of the deck was established at the expansion joints to ensure joint behavior of the structure, functioning as a single dynamic unit. The main execution difficulty consisted of cutting the base of the arches to place high-distortion and damping rubber bearing devices and the placement of viscous dampers, involving complex load transfer processes and displacement control. Source: A2P Consult

Regular or continuous monitoring

The installation of sensors, such as displacements, tilt, temperature and vibration sensors on the bridge is crucial to monitor its behavior, especially after the implementation of the base isolation and damping system. These sensors allow engineers and technicians to collect and analyze data regarding the bridge's performance and to identify any potential issues that may arise, such as structural deformation or excessive vibrations, that could compromise the bridge's safety and functionality.

The base isolation and damping system implemented in the viaduct over the Tranc?o river are designed to absorb and dissipate the energy generated during seismic events, protecting the structure from excessive stress and deformation. However, it's essential to monitor this system's behavior, as it's not a "set it and forget it" solution. Over time, the system may wear out or undergo changes that affect its efficiency, such as the rubber bearings degrading or the fluid in the dampers becoming less viscous.

Seasonal changes in weather conditions, such as temperature and humidity fluctuations, can also affect the behavior of the base isolation and damping system. For example, changes in temperature can cause the rubber bearings in the base isolation system to become stiffer or softer, which can affect the system's efficiency in absorbing and dissipating energy.

By collecting data regularly and/or continuously, we can analyze how the bridge's base isolation and damping system performs during different weather conditions. We can identify any trends in the data and assess whether the system is operating as expected or if adjustments need to be made.

From data to information

In the end, what we want is to have information about the current state of structural integrity and predict its future behavior and maintenance needs. And we have worked intensively on the last years to turn this process as simple as possible, with as little effort as possible. Or in another words, with minimal energy spent from Data Extraction, Transformation, Loading, Analysis and Visualization.

With this in mind, we are using different technologies for data collection (e.g. wireless sensors) and real-time analysis to separate signal from noise and to extract the information we need from data to detect changes on the structural and mechanical behavior of critical assets.