Conference Agenda

This study focuses on soil-structure interaction (SSI) under seismic excitation, using a direct hybrid method. During an earthquake, repeated impacts between the soil and the foundation lead to nonlinear dynamic behavior. In this context, a new subdomain coupling method is proposed to treat the contact between the soil integrated in time using a central difference scheme, and the concrete foundation integrated using the Newmark implicit scheme. The approach is implemented and validated in MATLAB through two illustrative applications. First, a one-dimensional benchmark problem involving two bars in contact demonstrates that the formulation accurately reproduces displacements, velocities, and contact forces in excellent agreement with a full explicit algorithm. Then, a two-dimensional case study of soil-concrete foundation interaction subjected to gravity loading highlights reduced computational time compared with the full explicit method. This work pro-vides a robust and efficient framework for simulating nonlinear SSI problems in the time domain.

The LT-Bridge construction method has been developed in recent years at TU Wien. In this method, thin-walled longitudinal (L) girders made of high-strength concrete are combined with transverse (T) deck slab elements and subsequently connected by a layer of in-situ concrete. Compared to the conventional construction of multi-span post-tensioned concrete bridges with full in-situ concrete and temporary supporting structures, the LT-Bridge method enables faster construction and reduced material consumption. The Pinkabach Bridge, completed in 2022, was the first bridge built using this method. Currently, four additional LT-Bridges with lengths of up to 260 m are in the design phase in Austria. The structural design of LT-Bridges follows Eurocode 2. The webs of the thin-walled longitudinal girders typically have a thickness of only 120 mm, yet they must resist considerable shear forces and transverse bending moments that are mainly induced by traffic loads. The interaction formula for shear and transverse bending given in the new Eurocode 2 is conservative and leads to high quantities of stirrup reinforcement in the webs. To address this issue, the application of a layered shell element has been proposed for the design of the longitudinal girder webs. In this element, nonlinear material models are implemented according to Eurocode 2 for both the high-strength concrete C80/95 and the reinforcement (stirrups and longitudinal bars). This allows a realistic assessment of the load-bearing capacity under the combined action of shear and transverse bending moments. While the reinforcement of the webs in the Pinkabach Bridge was designed using the interaction formula of the new Eurocode 2, the LT-Bridges that are currently being designed can achieve further reductions in material consumption by applying nonlinear analysis with the layered shell element.

Delayed Ettringite Formation (DEF) can induce expansive products in the porosity of concrete which leads to internal swelling pressure and damage that can jeopardize the performance of the affected struc-tures. Numerical modelling can provide an appropriate solution to predict such evolution over time especially in the case of massive and critical structures. Such predictive modelling can only be reliable if the modelling hypotheses have been validated and their limitations fully assessed. This work contributes to such purpose using the poromechanical model by Sellier (2021). To evaluate the predictive capacities of the model, we select here a bridge’s pier affected by DEF and show some induced cracking that is monitored and characterized. Blind calculations are done using two distinctive softwares: finite element code Cast3M (open) and the finite volume code FLAC3D (restricted). Eventually, this benchmark aims at exploring the sensitivity to the inputs, modelling hypotheses and tools used.

Ensuring the long-term performance and safety of reinforced concrete (RC) structures depends on the ability to understand their evolving condition and the ability to assess their situation. Within Structural Health Monitoring (SHM), this requires physically meaningful indicators that capture a structure’s inherent ductile or brittle tendencies. This study revisits a validated Integrated Fracture-Based Model (IFBM) and establishes it as a foundation for damage quantification and performance assessment. The IFBM analytically describes lightly reinforced concrete beam behaviour across two key stages; crack propagation with tensile softening and crack rotation with compression softening, through a closed-form solution satisfying equilibrium, compatibility, and constitutive relationships, including bond-slip and post-cracking stress distribution. A dimensionless Ductility Number (DN) is formulated from dimensional analysis of the IFBM, integrating material, geometric, and interface parameters such as reinforcement ratio, concrete strength, elastic moduli, bond stress, and critical crack opening. The DN characterises the stability of cracking, where higher values indicate ductile, bond-controlled failures and lower values correspond to brittle, reinforcement-fracture modes. Validation against Digital Image Correlation experiments confirmed strong correlation between DN and observed failure mechanisms. The DN thus quantifies a structure’s intrinsic ductility potential, enabling SHM systems to interpret sensor data within a mechanical context. As a mechanics-based indicator, it provides a baseline for condition tracking, risk assessment, and early detection of performance deviations in reinforced concrete structures.