Authors:
G. Vu, J. J. Timothy, E. H. Saenger, C. Gehlen, G. Meschke

Abstract:
Early identification and prevention of damage in concrete structures can significantly reduce maintenance and repair costs. Weak material degradation, such as load-induced microcracking, generally is a precursor of localized damage in concrete structures can be detected by means of ultrasonic signals. To reliably identify and quantify damage, a systematic method that translates ultrasonic coda signals into the damage state is required. To this end, the effect of material degradation on the coda variations at the specimen level is systematically investigated using a combination of multiscale computational modeling, wave propagation simulations, and Coda Wave Interferometry. The study reveals a strong correlation between relative velocity variation and stiffness variations under stress, confirming the method’s sensitivity to microstructural changes. Simulations of mesoscale concrete models in a virtual lab reveal that relative velocity change increases linearly with stress during initial deformation (up to 1.23%) and decreases significantly during the microcracking stage (−3%), correlating reasonably with experimental data. Additionally, the computational framework enables testing across a robust sample set to estimate the probability of failure, supporting more informed decision-making in structural health monitoring. Finally, a strategy for using specimen scale information to predict the state of damage at the structural scale is presented.

Link to the open access publication:

The lecture dates for the summer term 2025 are online.

On November 22, 2024, the German Research Foundation decided to fund the Collaborative Research Centre 1683 (CRC 1683) with the title “Methods of interaction for the modular reuse of existing load-bearing structures“ (shortened “Modular Reuse”).

Instead of recycling old concrete, researchers of the CRC 1683 will investigate existing concrete elements, e.g. ceilings, walls, supports and foundations, regarding their quality, reusability and adaptability. All these information will be gathered to build a modular construction kit, which in turn will give the base to build up a building from recently produced and adapted old structures.
This innovative concept aims to reduce greenhouse gas emissions and curb the accumulation of unmanageable masses of construction waste.

The Institute for Structural Mechanics is involved with two sub-projects in this research:

A2 - Simulation methods for modular connections of reused concrete elements
This project focuses on the development of numerical methods for the modelling and digital design of joints of reused concrete modules. Design optimisation algorithms based on robust mathematical formulations are developed considering several aims, such as minimising the added material, minimising costs and manufacturing emissions, and maximising strength and durability. It is also crucial to develop reliable simulation models that can accurately describe the mechanical behaviour of the joints, taking into account contact stress, prestressing and concrete damage.

Koussay Daadouch, Roger Sauer, Günther Meschke.

A5 - Reliability-based structural performance assessment considering polymorphic uncertainties of reused concrete elements
The aim of this subproject A05 is to develop concepts for determining and ensuring the reliability of structures made of reused concrete elements. The consistent consideration of uncertainties at the concrete element level and at the structural level in combination with dedicated nonlinear computational models allows to realistically investigate the structural performance during the intended service life under consideration of ageing and the environmental impact.

Gerrit Neu, Steffen Freitag.


See also RUB News:
https://news.rub.de/presseinformationen/wissenschaft/2024-11-25-neuer-und-verlaengerter-sfb-alte-betonteile-fuer-neue-gebaeude-nutzen