Design methodology for cross-life structural monitoring with unknown damage process.

Classical structural monitoring is usually used to a) monitor known deterioration processes and their temporal development in older existing structures or b) check the assumptions made in the design of new structures with a high degree of innovation. In these applications, however, the monitoring duration is limited to a few months to a few years and the physical quantities to be monitored and their effect locations are clearly defined.
In the future, electronic continuous monitoring will be an important tool in the maintenance of infrastructure structures, with the following novel challenges:
- considerably longer monitoring duration (several decades to entire structure lifetime) and
- initially unknown damage mechanism, time of occurrence and location.

The objective of the subproject (TP) is to develop a design methodology that can be used to reliably design a sensor concept for the new application area "cross-life monitoring systems". This objective can be divided into two sub-areas: a building-related area and a measurement system-related area. The interface between these areas is the definition of the physical quantities to be measured or the sensor technology to be used, see Fig. 1. In the first phase of the priority program, the focus of the project is on the building-related area. Furthermore, due to the necessary focus in the TP, the developments are limited to prestressed concrete bridges, even though the basic methodology is transferable to other types of structures.

The scientific challenge of the TP is based on the fact that currently available measurement methods can only monitor selective or narrowly defined areas in sufficient resolution. Since monitoring in the sense of fully digitized maintenance is to begin at the beginning of the structure's service life, no damage processes are yet underway on the object. Complete sensor-based monitoring would thus require a very dense sensor network over the entire structure, which would be neither economically justifiable nor technically reasonable.
The scientific gain of knowledge of the TP consists in how a reliable and economical measurement concept can be designed in case of initially unknown damage mechanism as well as time and place of occurrence. The question has to be answered which physical quantities have to be recorded at which resolution (local, temporal, measuring range) at a specific structure.

To answer the question, a cluster-based and an object-based approach are followed. The cluster-related approach is based on the systematic evaluation of existing similar buildings. For this purpose, a comparison group with similar properties is formed for the concrete object. The object-related approach is based on a specific analysis of a concrete building. For this purpose, the typical evaluation methods for existing structures are placed in the context of future metrological monitoring.
Both approaches are to be coupled in the methodology to be developed and tested on the validation structure Nibelungenbrücke Worms.