Walter Kaufmann

Last Name

Kaufmann

First Name

Walter

ORCID

0000-0002-8415-4896

Organisational unit

09469 - Kaufmann, Walter / Kaufmann, Walter

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Publications 1 - 10 of 189

Potentials of Steel Fibres for Mesh Mould Elements
Pfändler, Patrick; Wangler, Timothy; Mata Falcón, Jaime; et al. (2018)
RILEM Bookseries
Kirchhoff-Love Plate Deformations Reinterpreted
Marti, Peter; Kaufmann, Walter; Seelhofer, Hans; et al. (2022)
Journal of Engineering Mechanics
The deformations of Kirchhoff–Love plate elements are usually characterized by three components describing the strains in the middle plane and three components describing the bending of the plate element. It is shown that alternatively onemay consider pure bending deformations about two neutral axes that generally are not in the same plane and skew to each other. This interpretation provides an intuitive understanding of the plate deformations and is particularly useful when analyzing the behavior of reinforced concrete plate elements subjected to combined bending moments and membrane forces. After a recapitulation of the conventional interpretation of Kirchhoff–Love plate deformations and their implications on the strain distribution in plate elements, this paper presents the alternative interpretation and illustrates its application for a special case with orthogonal neutral axes.
Ausziehversuche randnaher Bewehrung
Kaufmann, Walter; Galkovski, Tena (2019)
Der vorliegende Bericht dokumentiert die Vorbereitungen, die Durchführung sowie die Auswertung von Ausziehversuchen an randnahen, einbetonierten und nachträglich installierten Bewehrungsstäben. Die Versuche wurden in Anlehnung an den Versuch AC308 (acceptance criteria for adhesive anchor systems in concrete elements, gemäss acceptance criteria for post- installed adhesive anchors in conrete elements der ICC-ES, 2013) durchgeführt, womit ein Spaltversagen des Betons angestrebt wird. Prüfparameter waren die Lage der Stäbe beim Betonieren (Unterseite oder Oberseite) und die Art des Verbundes (einbetoniert oder nachträglich installiert, mit vier unterschiedlichen Hilti Verbundmitteln). Die Einbindelänge, die Betonsorte sowie der Stabdurchmesser wurden nicht variiert. Es wurden acht prismatische Versuchskörper mit jeweils vier in den Ecken angeordneten Bewehrungsstäbe verwendet, wobei die Stäbe in einer Diagonale jeweils gleich ausgeführt wurden: einbetoniert oder nachträglich installiert. Somit lagen beim Betonieren pro Prüfkörper jeweils ein einbetonierter und ein nachträglich installierter Stab auf der Unterseite (geschalte Fläche) und auf der Oberseite (ungeschalte Fläche). Als Messsysteme wurden Digitale Bildkorrelation (DIC, engl. Digital Image Correlation) für die Deformationen an der Betonoberfläche entlang der Einbindelänge und kontinuierliche faseroptische Dehnungsmessungen an den Bewehrungsstäben eingesetzt (FO, engl. Fibre Optics). Diese Messsysteme ermöglichen einen vertieften Einblick in das Verhalten, insbesondere bezüglich der Interaktion zwischen Beton und Bewehrungsstahl (Verbund).
Identifying Levers for Mass Market Penetration of Digital Fabrication
Bischof, Patrick; Mata Falcón, Jaime; Kaufmann, Walter (2021)
fib Symposium Proceedings ~ Concrete Structures: New Trends for Eco-Efficiency and Performance, Proceedings of the fib Symposium 2021
The construction industry produces buildings and infrastructure and, hence, satisfies basic needs of modern society. It provides a considerable portion of total value added and worldwide jobs. At the same time, it is responsible for more than 11% of CO2 energy-related carbon dioxide (CO2) emis-sions worldwide. Digital concrete fabrication is a young, yet already broad research discipline which brings about potential for the necessary reduction of the ecological impact and for further industrial-isation of the construction industry, while being compatible with the specific requirements of flexi-bility and individuality. Still, it has not succeeded to penetrate the mass-market, largely due to lack-ing competiveness and compliance with structural integrity requirements. The present contribution comprehensively considers features of conventional construction processes to identify benefits when using digital concrete fabrication. Thereby, it addresses not only a complete substitution of conven-tional construction methods, but also solutions taking advantages of the synergic combination of traditional and novel technologies. It assesses traditional construction methods (in-situ construction and prefabricated construction) and clusters their features in order to elaborate their strengths and persistent challenges. Following a customised review on the digital fabrication methods, it identifies some new levers and opportunities for mass-market penetration of digital concrete fabrication tech-nologies in structural and civil engineering construction works.
Large‐scale experiments on concrete hinges under general loading
Markic, Tomislav; Kaufmann, Walter (2023)
Structural Concrete
The structural behavior of concrete hinges under general loading is far from being properly understood, which is to a large extent due to the lack of pertinent experimental data. This paper contributes to filling this knowledge gap by presenting and discussing the results of an experimental campaign on one-way Freyssinet concrete hinges. Seven large-scale concrete hinges were tested in the Large Universal Shell Element Tester, which allowed the investigation of their behavior under general loading by all six stress resultants. A combination of digital image correlation and distributed fiber optic measurements allowed a deeper insight into the structural behavior of the specimens. The tested hinges could sustain very high axial stresses exceeding 4.5 times the uniaxial concrete compressive strength, large rotations of over 60 mrad, and shear stresses in transverse and longitudinal directions up to 2.24 times the axial compressive stress. The resistance to bending moments about the strong axis and torques also proved to be significant. A moderate amount of reinforcement crossing the hinge throat considerably increased the shear resistance at low axial stresses and produced a ductile shear behavior.
Modeling locally corroded reinforced concrete structures in non-linear finite element analyses
Reckinger, Nathalie; Haefliger, Severin; Thoma, Karel; et al. (2025)
Structural Concrete
The ingress of chlorides, originating from the use of de-icing salts or proximity to the sea, may cause severe local reinforcement corrosion in concrete structures such as bridges, tunnels, galleries, and retaining walls. Methods are urgently required to realistically assess the load-bearing capacity of such deteriorated structures, accounting for the effects of the local damage. However, modeling local corrosion in concrete structures using the finite element method is not straightforward. On the one hand, analyzing the local effects of corrosion requires finite elements that are magnitudes smaller than appropriate element sizes used to efficiently model an entire concrete structure, making this approach unviable even when using high-performance computers. On the other hand, when modeling a structure with comparingly large elements, local damage introduces a discontinuity in the affected FE, which are thus no longer a continuum as presumed in standard element formulations. Hence, the influence of the discontinuities needs to be captured consistently and independently of the element size. This paper presents a mechanically consistent approach to deal with discontinuities by defining an influence volume and a correspondingly aligned constitutive relationship. The approach is demonstrated using the existing Corroded Tension Chord Model as a constitutive relationship and validated against the analytical solution for a reinforced concrete tie affected by local corrosion and three experiments on continuous slab strips with and without local damage. The load-deformation behavior of the reinforced concrete tie is accurately captured by the numerical simulation. The load-deflection behavior and failure modes observed in the experiments can be accurately predicted without mesh size dependency, thus proving the suitability of the proposed approach.
Load-bearing and local bond behavior of two-span concrete slab strips with hybrid steel/CFRP reinforcement
Näsbom, Andreas; Thoma, Karel; Reckinger, Nathalie; et al. (2025)
Structural Concrete
Utilizing brittle components in structural concrete challenges state-of-the-art verification procedures based on limit theorems of the theory of plasticity. Unresolved questions regarding deformation capacity, force redistribution, and the influence of generally unknown self-equilibrated stress states impede universally applicable verification frameworks for concrete structures without regions that can fully plasticize. A prerequisite for establishing such frameworks is a detailed understanding of the mechanical behavior, the interaction of brittle and ductile reinforcement components and the impact of self-equilibrated stress states. This paper investigates the structural behavior of two-span concrete slab strips with hybrid steel/CFRP reinforcement, that is, the combination of conventional ribbed steel reinforcing bars (ductile elements) with sand-coated CFRP rods (linear elastic, brittle elements). The study focuses on (i) the global load-bearing behavior, (ii) the influence of self-equilibrated stress states, and (iii) the local bond behavior, which are all discussed regarding initial (backbone) and cyclic loading, respectively. Statistical evaluations of nominal bond shear stress as a function of slip and reinforcement strains-all obtained from Distributed Fiber Optical Measurements-allowed for reliable quantification of the bond behavior and provided consistent insight despite considerable scatter. All data gathered in the presented tests are published open source together with a separate data repository guide.
Tension chord model for CFRP-prestressed structural concrete
Näsbom, Andreas; Merz, Paul; Thoma, Karel; et al. (2025)
Structural Concrete
This paper introduces a mechanical model for steel-reinforced concrete prestressed with bonded CFRP rods and presents the findings of an experimental campaign conducted to validate the model. The study is part of a project aiming at developing a railway bridge system in Switzerland that utilizes stainless steel reinforcing bars combined with pretensioned sand-coated CFRP rods to (i) maximize durability and (ii) achieve reasonable plastic deformation capacity despite the inherent brittleness of the prestressing material. The proposed Tension Chord Model for CFRP-prestressed Structural Concrete (TCM-cfrp) extends the established Tension Chord Model for Structural Concrete by introducing a constant, rigid-perfectly plastic bond shear stress-slip relationship between concrete and CFRP, allowing for computationally efficient closed-form solutions to determine the load-deformation behavior, crack widths, and reinforcement stresses. The validation against the experimental results reveals (i) satisfactory model predictions of the mean strains, the stresses at the crack and the crack widths and (ii) insensitivity of the structural behavior on local bond shear stress distributions, thus supporting the simplification of assuming constant bond shear stresses. The TCM-cfrp is capable of capturing all stress states in tension chords of railway bridge girders and other structural elements relevant for serviceability, ultimate, and to some extent, fatigue limit state verifications. The limitations of the model lie in (i) the simplified treatment of the crack formation process, overestimating deformations but underpredicting crack widths prior to stabilized cracking and (ii) its inability to realistically model local strain and stress distributions between the cracks, which is however of limited relevance for most structural engineering purposes.
Structural Behaviour of a CFRP-prestressed Railway Bridge Prototype
Näsbom, Andreas; Thoma, Karel; Kaufmann, Walter (2025)
Structural Engineering International
This paper discusses the structural behaviour of a 6.5 m long and 1.7 m wide CFRP-prestressed, steel-reinforced concrete railway bridge prototype consisting of four pretensioned longitudinal girders, three pretensioned transverse girders and a deck slab. The prototype test covered key aspects of the structural behaviour of railway bridges in terms of (i) serviceability and fatigue, both related to the prestress efficiency and the behaviour in cyclic loading and (ii) the ultimate limit state, where the presence of the brittle CFRP challenges established design and verification concepts which presume ductile reinforcement. The specimen was loaded in four-point bending with a transverse eccentricity, including a total of 60 000 load cycles at three different load levels and the subsequent loading to failure. Yielding of the reinforcing steel first occurred at approximately 73% of the ultimate load and propagated to significant parts of the bending tensile zones of three out of four longitudinal girders before failure occurred due to concrete crushing in the deck slab. This failure mechanism did not lead to a brittle collapse of the system. Instead, deformations kept increasing at the approximately constant peak load. Distributed fibre optical strain measurements, primarily along the reinforcing steel, allowed for detailed insight into the load-bearing behaviour.
Strip loading in reinforced concrete: Mechanical modeling and experimental validation
Morger, Fabian; Kenel, Albin; Kaufmann, Walter (2025)
Structural Concrete
Strip loading of reinforced concrete is a common problem in engineering practice. The concrete compressive strength at the load introduction can be several times higher than the uniaxial concrete compressive strength, which can be attributed to geometrical and passive confining stresses caused by load dispersion and reinforcement, respectively. However, current design provisions do not allow combining these two confining effects, leading to overly conservative designs. Furthermore, experimental data on strip-loaded concrete members with pronounced passive confinement and moderate load concentration ratios, common, for example, in longitudinal joints of segmental tunnel linings, are scarce. This article presents different models for strip loading as well as an experimental campaign of 15 concrete blocks subjected to strip loading. The test parameters included (i) the reinforcement ratio and type, (ii) the width and position of the loaded area, and (iii) the concrete strength. Digital image correlation was applied to determine the crack widths. The experimental results give insight into the mechanical behavior and were used to compare the different model approaches for strip loading, including the recently published Dual-Wedge stress field and a simplification of the same. The models are presented in detail and adjusted for strip loading with moderate load concentration ratios where required. Furthermore, it is discussed how passive confinement can be accounted for with regular and irregular reinforcement spacings. The bearing capacity predictions of models accounting for the combined effect of load dispersion and passive confinement are in good agreement with the tests and allow for an efficient and safe design, whereas the simplification stands out for its ease of use and lowest coefficient of variation.

Publications 1 - 10 of 189

Walter Kaufmann

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