An Immune System for Buildings

Turning Sensors into a Digital Nervous System

This measurement method is called Structural Health Monitoring (SHM) and is used worldwide—primarily for bridges, offshore wind turbines, or tunnels. Effectively, SHM acts as a nervous system for buildings. Its functionality is based on strategically placed sensors that continuously track vibrations, temperatures, or material strain. These raw data streams are transmitted to central computing units, where specialised algorithms analyse even the smallest deviations from normal structural behaviour—long before they become visible to the human eye.

The decisive advantage of this method is obvious: damage and material fatigue can be detected early on before they develop into critical impairments, saving massive maintenance costs. "Our data provide the owner with vital information on how flexibly and safely the diving tower responds under load," Dragos explains. The doctoral candidate, who studied civil engineering at the Aristotle University of Thessaloniki, now leads the Smart Monitoring working group at IDAC and splits his working time between Hamburg and his hometown of Thessaloniki. "Through the measurements, we provide indications of potential damage and highlight concretely which areas should be examined more closely."

The swimming pool is currently undergoing refurbishment, meaning the Hamburg measurement data flows directly into the official structural and static assessment. Dragos notes that the rare deployment of SHM systems on everyday buildings like residential housing is purely pragmatic: "Ultimately, deploying an SHM system is always the result of a cost-benefit analysis by the owners. Right now, this technology is systematically prioritised for public, safety-critical infrastructure like bridges or pipelines."

However, equipping safety-critical structures with monitoring systems also brings dangers, warns Professor Kay Smarsly, director of the Institute of Digital and Autonomous Construction (IDAC) at TUHH. "In the future, civil engineering structures will increasingly be equipped with sensor systems that are available online. This opens the door wide to cyberattacks," Smarsly explains. "A structure can therefore be intact while its online-networked monitoring system is faulty or compromised—and vice versa." The comprehensive digital networking of infrastructure makes buildings smarter, but it also leaves them more vulnerable.

Critical Infrastructure in the Crosshairs

"For a modern bridge or tunnel, we can no longer just look at the physical concrete structure," Smarsly says. "The structure, its sensors, the communication networks, the data processing, and the ensuing decisions form a tightly coupled cyber-physical system." According to Smarsly, such an integrated system can be impaired in three distinct ways: by structural damage to the building itself, by internal monitoring faults—such as a defective sensor—and by cyberattacks.

The most realistic threat today is not a spectacular, Hollywood-style "bridge collapse via a mouse click," Smarsly notes, but rather attacks on the digital eyes and nerves of the infrastructure. Data streams could be manipulated, monitoring services disabled, urgent warnings suppressed, or disruptive false alarms triggered. As a consequence, vital maintenance might get neglected, or expensive, unnecessary closures could threaten cities. The danger escalates dramatically if attackers compromise actuators—the controllable mechanical components that operate tunnel ventilation or moving swing bridges.

Learning from Biological Defense Mechanisms

To counter this new threat landscape, the German Research Foundation (DFG) is funding a joint cooperation project titled "Digital Immunization of Civil Infrastructure". The initiative bridges IDAC with the Laboratory of Experimental Strength of Materials and Structures at the Aristotle University of Thessaloniki. The project’s unique twist: the research team maps the exact functional logic of the biological immune system onto physical structures.

The human body protects itself through a fast, innate defense layer and builds a memory against future attacks via its adaptive immunity. Following this model, the digital protection architecture of bridges and tunnels is designed to become adaptive, enabling it to fend off threats independently. "In our digital counterpart, sensors, diagnostic modules, digital threat markers, and reaction memories assume comparable functional roles," Smarsly explains.

The IDAC team is performing true pioneering work worldwide. Until now, the construction industry lacked a reference architecture that mirrors the biological defense cascade—from entire cells down to signaling molecules—and transfers it onto digital components.“ For Kosmas Dragos, the system represents the next logical step for a well-established and proven technology: "While the term digital immunisation sounds completely novel, the technology is based on the consistent advancement of real, existing tools—such as digital twins." A digital twin is a virtual model of the real structure on a computer, which is fed with all live sensor data to replicate its behavior dynamically.

If the self-protecting building of the future detects a threat, it triggers a staged, automated defense chain. First, a suspicious sensor value is cross-checked against measurement data from neighbouring sensors and expected structural models. If the suspicion is confirmed, the affected data stream or hacked network node can be isolated de-centrally. At this point, a form of digital self-healing is designed to step in. A computationally generated "virtual sensor" temporarily replaces the failed hardware, allowing the monitoring to continue operating until the defective sensor can be physically replaced. This self-healing is made possible by physics-based models. Since the algorithm incorporates the mechanical laws of the building, it can reconstruct the missing measurements using model-based estimation.