As part of the Research Academy Ruhr's "Research Explorer Ruhr" program, PhD Tulio Antunes Pinto Coelho from the Federal University of Mato Grosso do Sul, Brazil, visits our institute from 22 June to 5 July 2025.

The program offers prospective and early postdocs the opportunity to learn about the research landscape of the University Alliance Ruhr, as well as its funding opportunities and career paths. At best, the program will lead to further research collaborations and proposals.

We would like to thank Tulio Antunes Pinto Coelho for enriching us – in particular the institute’s research group “Structural Intelligence and Reliability” – with his knowledge from the research areas of fire design of reinforced concrete as well as uncertainty modeling and reliability analyses.

We are looking forward to further deepening this scientific exchange in research.

The research paper titled "Mechanics of longitudinal joints in segmental tunnel linings: A semi-analytical approach" has been witten by Zhen Liu, Xian Liu, Abdullah Alsahly, Yong Yuan, and Günther Meschke.
It is now published in "Tunnelling and Underground Space Technology" by Elsevier.

Abstract:
To meet basic structural serviceability and durability requirements throughout the life of tunnels, the design and evaluation of segmental tunnel linings requires accurate structural models. Considering that segmentation introduces non-trivial kinematics to the lining system, it is important to properly evaluate the moment-rotation relationship for longitudinal joints. In this study, a nonlinear semi-analytical model is proposed to assess the mechanical behavior of the longitudinal joint, taking into account the nonlinear behavior of the concrete in the vicinity of the joint and the contact deformation induced by the roughness of the contact surface. Through the proposed model, the moment-rotation relationship of the joint and the stress distribution in the vicinity of the joint are obtained simultaneously without the need for highly resolved finite element analyses. It is demonstrated how the proposed model can be applied to parametric analysis of joint configurations and to predict tensile stresses that may cause spalling and splitting cracks. The performance of segmental joints is systematically investigated, revealing a more accurate distribution of the contact pressure and the deformations and the stress field within the joint influence zone. To fully consider the influence of the joint, the effective joint rotation angle is defined to consider the additional rotational flexibility resulting from the joint-induced deformations, which attributes to the contact deformation and the disturbed stress field within the joint influence zone. Since the joint rotation angle calculated based on the classical rigid plate assumption (nominal joint rotation angle) tends to overestimate the effective joint rotation angle, a correction factor relating the nominal and the effective joint rotation angles is proposed for practical applications.

The full paper is providing a 50 days' free access and is avialable until June 24, 2025: Personalized Share Link
or is available via

"A finite strain model for fiber angle plasticity of textile fabrics based on isogeometric shell finite elements" by Thang X. Duong and Roger A. Sauer has been published in "Journal of the Mechanics and Physics of Solids" Volume 200, July 2025, 106158 by Elsevier.

Abstract:
This work presents a shear elastoplasticity model for textile fabrics within the theoretical framework of anisotropic Kirchhoff–Love shells with bending of embedded fibers proposed by Duong et al. (2023). The plasticity model aims at capturing the rotational inter-ply frictional sliding between fiber families in textile composites undergoing large deformation. Such effects are usually dominant in dry textile fabrics such as woven and non-crimp fabrics. The model explicitly uses relative angles between fiber families as strain measures for the kinematics. The plasticity model is formulated directly with surface invariants without resorting to thickness integration. Motivated by experimental observations from the picture frame test, a yield function is proposed with isotropic hardening and a simple evolution equation. A classical return mapping algorithm is employed to solve the elastoplastic problem within the isogeometric finite shell element formulation of Duong et al. (2022). The verification of the implementation is facilitated by the analytical solution for the picture frame test. The proposed plasticity model is calibrated from the picture frame test and is then validated by the bias extension test, considering available experimental data for different samples from the literature. Good agreement between model prediction and experimental data is obtained. Finally, the applicability of the elastoplasticity model to 3D shell problems is demonstrated.

The open access article is available here:

A new publication titled "A Multiscale Model for Predicting the Young’s Modulus and the Thermal-Expansion Coefficient of Concrete at High Temperatures” by Simon Peters, Giao Vu, Günther Meschke has been released in the journal Construction and Building Materials by Elsevier.

Abstract:
A semi-analytical micromechanical model is proposed to predict the evolution of the Young’s modulus and thermal-expansion coefficient of concrete at elevated temperatures, considering three scales of observation, namely cement paste, mortar and concrete. After validation with various experimental data sets, the model quantifies different sources of damage to concrete at elevated temperatures, indicating that the chemical decomposition of cement paste has a minor influence on the evolution of the Young’s modulus, while the thermal degradation of the aggregate plays a major role. At higher temperatures, cracking is the main mechanism driving the reduction of the Young’s modulus of the investigated concretes.

With regard to the thermal-expansion coefficient evaluated at multiple scales, load-induced thermal strains highly effect the homogenized total strains at the mortar level. Moreover, it is demonstrated that the dehydration degree of C-S-H increases proportionally with the measured load-induced thermal strains.

You can read the full paper as open access publication here:

On Monday, 28. April 2025 at 1PM, the doctoral defense of Stefanie Schoen took place. The title of her dissertation was: Reliability analysis and design of RC and SFRC structures considering Polymorphic Uncertainties.


Dear Stefanie, congratulations on your successful defense! We wish you all the best as you take on further achievements.

Abstract:
Ensuring structural safety requires a precise understanding of uncertainties in material properties, environmental conditions, and modeling assumptions. This dissertation advances the design of reinforced concrete (RC) and steel fiber-reinforced concrete (SFRC) structures by integrating polymorphic uncertainties – combining aleatory and epistemic uncertainties – into a reliability-based framework. While aleatory uncertainties account for inherent randomness, such as material heterogeneity, epistemic uncertainties stem from limited knowledge, including variations in fiber orientation.

Building on semi-probabilistic safety concepts, this study employs probabilistic methods to quantify failure probabilities across ultimate and serviceability limit states. However, accurately estimating low failure probabilities requires a large number of realizations, making finite element simulations computationally prohibitive. To overcome this challenge, reliability analysis is combined with a Transformer-based model for uncertainty quantification.

Finally, reliability-based design optimization reveals that while steel fibers can partially replace conventional reinforcement, their greatest value lies in complementing its – substantially reducing crack width sensitivity to stochastic loads and enhancing durability. Hence, this thesis underscores the importance of integrating uncertainties and the strategic use of steel fibers in the sustainable and durable design of concrete structures.

For further information please check: