Browsing by Author "Hofmann, Jan"

Now showing 1 - 10 of 10

Open Access
3rd International Symposium on Connections between Steel and Concrete : Stuttgart, Germany, 27th - 29th September 2017 ; proceedings
(Stuttgart : Institute of Construction Materials, University of Stuttgart, 2017) Sharma, Akanshu; Hofmann, Jan
Steel is an integral part of any concrete construction either in the form of anchors connecting structural/non-structural components to the structure or in the form of reinforcement embedded in concrete or sometimes as a part of steel-concrete composite construction. To ensure structural integrity, it is essential to form a reliable connection between steel and concrete. The anchorage must serve its function well to ensure the interaction between the components connected to the structure and the structure itself. The bond between reinforcement and concrete must be ensured to maintain the required flow of forces from concrete to steel and vice-versa. The concrete and steel structural members must be able to interact with each other in a desired way. If the connection between steel and concrete loses its integrity, the integrity of the entire structure comes in jeopardy. In order to ensure the integrity of connections between steel and concrete, it is required to (i) investigate their behavior through high quality experiments, (ii) evaluate their performance with advanced and reliable computational methods, and (iii) summarize them in practical and reliable design rules and models to be used by engineers and practitioners. Although connections between steel and concrete are used ever since the commencement of reinforced concrete construction, there are several aspects which are yet to be fully understood. Advancement in technologies lead to development of new products such as post-installed anchors, anchor channels, high strength reinforcing bars etc., whose performance in concrete need to be investigated. New concrete based materials such as high performance concrete, fiber reinforced concrete, geopolymer concrete etc. are being developed and their compatibility with the steel components and rebar must be verified. The interaction between structure and the anchorages or concrete and steel structure connected through anchorages need to be understood. Innovative fastening solutions between steel and concrete components are being developed for which reliable design models are needed. Furthermore, several general design issues, e.g. anchorages with supplementary reinforcement, fatigue behavior of anchors, long term performance of bonded anchors, anchor channels under different loading combinations, harmonization of design between post-installed and cast-in place reinforcing bars, influence of corrosion on performance of anchorages and reinforcement etc. need in-depth investigations. In addition, globally, structures are exposed to natural and man-made hazards more than ever, which induce extreme loads on the structural components, e.g. earthquakes, fire, impact and combinations thereof. The performance of existing structures against such hazards has exposed several inherent weaknesses in the past. Often, the performance of structures under such hazards is significantly influenced by the performance of connections between steel and concrete. Since the loads induced in the structures by such hazards cannot be reliably estimated and also since under such loads, compatibility requirements between different components result in additional demands on different components, the designs can only be reliably done following a performance based design approach. Similar approaches must also be developed for the design of connections between steel and concrete to ensure a reliable performance from the connections and in turn from the structures against extreme hazards. One of the most important applications of anchorages is in strengthening of structures for connecting the strengthening element and the parent structure. Every strengthening needs a certain type of anchorage and the performance of the strengthening depends largely on the performance of the anchorage itself. The demands posed on the anchorages used in strengthening (e.g. seismic strengthening) could be very challenging, which includes high forces, large crack widths, combined load and crack cycling, limited area and depth to develop the required resistance etc. In order to ensure the safety of structures, therefore, it is essential to develop innovative strengthening methods along with anchorage techniques that would allow the strengthening to serve its desired function. The 3rd International Symposium on Connections between Steel and Concrete (ConSC2017) aims at bringing the experts from around the globe working in the field of steel-concrete connections to share and discuss the current state-of-the-art as well as the possible future directions to improve the safety of structures by making reliable connections between steel and concrete. The previous two symposia were held in Stuttgart in 2001 and 2007. This symposium offers a platform for the academicians, researchers, industry, regulatory authorities, practicing engineers and students to share the knowledge gained through a decade of research and development. With more than 120 high quality research papers along with the keynote addresses and invited lectures from the renowned experts, this symposium is a significant step forward towards the enhancement of knowledge as well as to provide food for thought for the forthcoming research in the field of connections between steel and concrete.
Open Access
Appraisal theories for emotion classification in text
(2020) Hofmann, Jan
Over the last years the automated classification of emotions from text has become an interesting topic in natural language processing with many applications. Theories from psychological studies on emotions have been widely utilized to support the task of the automated assignment of emotions to textual content. Most commonly used theories are the fundamental emotions theory like proposed by Paul Ekman and the dimensional model of affect proposed by Albert Mehrabian and James Russell. However, these theories ignore other psychological theories, namely the cognitive appraisal theories, which explain emotions as a response to an individual interpretation of a given situation. Such appraisal theories have only been minorly used in the attempt to improve performance of emotion classification. In addition, there are no datasets annotated with appraisal dimensions. This work filled this gap by annotating a dataset with appraisal dimensions. Further, this work conducted several experiments in which classification models utilized these appraisal annotations. Although this work was not able to show a clear improvement in a real-world setting, the results show that appraisal dimensions have the potential to improve the performance of classifiers, which predict emotions from text.
Open Access
Bond in concrete - bond, anchorage, detailing : 5th International Conference : Stuttgart, Germany, 25th - 27th July 2022 : proceedings
(Stuttgart : Institute of Construction Materials, University of Stuttgart, 2022) Hofmann, Jan; Plizzari, Giovanni
Although concrete and reinforced concrete structures are not considered particularly sustainable, concrete is one of the most important and widely used building material in the world. Structures such as bridges, power plants or tunnels would be inconceivable without reinforced concrete as a building material. The bond between reinforcement and concrete is an essential factor for achieving the desired response from these different reinforced concrete structures. Moreover, bond plays an important role not only in reinforced concrete structures, but also for strengthening and rehabilitation of structures. Due to the necessity of sustainable building methods and need to reduce the spending of resources, the rehabilitation of structures will play an important role in shaping the sustainable future. In addition, our building materials are changing quite rapidly. This applies not only to concrete, but also to reinforcement. Carbon concrete, extreme lightweight or printed concrete, glass fibre or textile reinforcement are just a few examples. Their properties are significantly different from the previously known materials. In combination this can lead to a completely changed bond behavior, which can no longer be described using the existing models. Consequently, this becomes a challenge for all of us working in this field since results and solutions are expected faster than in the past. Therefore, it is important to have a platform that enables exchange of information on the latest results and future development and is also essential to publish and share the findings with the research community. However, this is not the only motivation for organising the Bond in Concrete Conference. The personal exchange and the development of a social network is an additional motivation, which is becoming more and more essential for both work and successful research. The previous conferences in Paisley (1982), Riga (1992), Budapest (2002) and Brescia (2012) are excellent examples for personal and professional networking. This tradition is something we want to continue in Stuttgart (2022) and use this opportunity to enable, encourage and support interdisciplinary research on “bond”. Looking at the recent developments, the description of the bond models and the underlying theories have been further improved and refined in the last few years. As a result, a larger number of influencing factors and loading conditions are considered for describing and quantifying “bond”. Today we know much more about bond than we did 50 years before. But we still don´t know enough about “bond”, it is important to continue and intensive research in the future. Despite all the adversities, uncertainties, injustices and challenges that our society will have to handle in the upcoming years and decades, I am convinced that each one of us is doing their best to make our future worth living. The 5th Conference on “Bond in Concrete" may contribute to this objective.
Open Access
Concrete cone failure of post installed fasteners during fire
(2023) Lakhani, Hitesh; Hofmann, Jan
The fire resistance of fasteners needs to be verified for all failure modes applicable at ambient conditions. Generally, in most cases, for unprotected fasteners loaded in tension, steel failure mode is decisive. But for fasteners made of stainless steel and/or larger (bolt) sizes, concrete cone failure may be the decisive failure mode for small anchorage depths. Due to practical difficulties associated with loading an anchor during a fire test, very limited experimental data is available in literature and that to for relatively small embedment depths. The paper presents the results (6 nos) of the fire tests conducted on expansion anchors (made of stainless steel) with sizes M12 (hef = 70 mm) and M20 (hef = 100 mm). Moreover, the paper also compares the reduction in the concrete cone capacity with exposure duration, predicted as per the current design guidelines and the new set of experimental data obtained in this study.
Open Access
Coupled thermo-mechanical inelastic analysis of reinforced concrete flexural members subjected to fire loads
(2016) Lakhani, Hitesh; Sharma, Akanshu; Hofmann, Jan
A simplified procedure to evaluate the complete-load-deflection time response of Reinforced Concrete (RC) flexural members subjected to fire loads is presented in this report. The proposed approach is extendable for performance evaluation of RC structures at all three levels of complexity namely member level (e.g. beams, columns), sub assembly level (e.g. beam-column joints) and as well as the structural level. This approach involves the determination of moment-curvature characteristics for the critical sections of the fire affected structural member and performing nonlinear static analysis to determine the load-deflection response of the member exposed to fire loads. The thermal analysis is first performed to determine the temperature distribution across the section, for a given fire duration. Temperature-dependent stress-strain curves for concrete and steel are then utilized to perform a moment-curvature analysis. The moment-curvature relationships are obtained at regular intervals of the fire exposure. These are then utilized to obtain the load-deflection plots following nonlinear static analysis (Pushover Analysis). The load-deflection plots obtained for the different exposure duration's are then used to obtain the deflection-time plots for a particular load level. Moreover, one of the important issues of modeling the initial stiffness giving due consideration to stiffness degradation due to material degradation and thermal cracking has been addressed in a rational manner. The approach is straightforward and can be easily programmed in spreadsheets. Implementation and validation of the proposed approach with various experiments available in literature has been discussed in detail in this report. The report also discusses the in-house code developed for carrying out 2D transient heat transfer analysis and obtaining moment-curvature relationships.
Open Access
Handbuch. I, Entwurf von Anschlüssen zwischen Stahl und Beton
(2014) Kuhlmann, Ulrike; Hofmann, Jan; Wald, Frantisek; Ruopp, Jakob; Sharma, Akanshu; Becková, Sárka; Schwarz, Ivo; Silva, Luis Simoes da; Gervásio, Helena; Gentili, Filippo; Krimpmann, Markus; Kann, Jörg van; Dehan, Véronique
Dieses Handbuch fasst die gewonnenen Forschungsergebnisse des Forschungsprojektes INFASO RFS-CR-2012-00022 "New Market Chances for Steel Structures by Innovative Fastening Solutions between Steel and Concrete" und des Nachfolgeprojekts RFS2-CT-2012-00022 "Valorisation of Knowledge for Innovative Fastening Solutions between Steel and Concrete" zusammen. Dieses Handbuch wurde von Wissenschaftlern zweier unterschiedlicher Forschungsbereiche verfasst. Aus dem Bereich der Befestigungstechnik vertreten durch das Institut für Werkstoffe im Bauwesen der Universität Stuttgart und aus dem Gebiet des Stahlbaus durch das Institut für Konstruktion und Entwurf der Universität Stuttgart und des Department of Steel and Timber Structures der Czech Technical University in Prague. Der Praxisbezug des Projektes wurde sichergestellt, indem Industriepartner und Organisationen maßgeblich am Entstehen beteiligt waren.
Open Access
Handbuch. II, Anwendung in der Praxis von Anschlüssen zwischen Stahl und Beton
(2014) Kuhlmann, Ulrike; Hofmann, Jan; Wald, Frantisek; Ruopp, Jakob; Sharma, Akanshu; Becková, Sárka; Schwarz, Ivo; Silva, Luis Simoes da; Gervásio, Helena; Gentili, Filippo; Krimpmann, Markus; Kann, Jörg van; Dehan, Véronique
Das zweite Handbuch basiert auf Handbuch I "Entwurf von Anschlüssen zwischen Stahl und Beton", in welchem die Forschungsergebnisse des RFCS Forschungsprojektes INFASO RFS-CR-2012-00022 "New Market Chances for Steel Structures by Innovative Fastening Solutions between Steel and Concrete" und des Nachfolgeprojekts RFS2-CT-2012-00022 "Valorisation of Knowledge for Innovative Fastening Solutions between Steel and Concrete" zusammengefasst sind. Innerhalb des Forschungsprojektes INFASO wurden Bemessungsprogramme für drei verschiedene Anschlüsse zwischen Stahl und Beton entwickelt. Diese Programme wurden im Forschungsprojekt INFASO+ überarbeitet. In diesem Handbuch werden Hintergrundinformationen zu den Bemessungsprogrammen gegeben und zusätzlich Anwendungsmöglichkeiten der Programme im Detail beschrieben.
Open Access
Influence of edge proximity on concrete breakout failure in post-installed RC columns foundation joints
(2023) Cattaneo, Sara; Mahadik, Vinay; Genesio, Giovacchino; Hofmann, Jan
This paper discusses findings from an experimental program aimed at investigation of concrete breakout failure within the rebar end anchorage zone of reinforced concrete column-to-foundation joints, with columns located in proximity of foundation edge/s. A total of four tests on full scale column foundation joints are presented. In all specimens the column main reinforcement is anchored in the foundation using post-installed rebar technology. All connections are designed with the objective to trigger concrete breakout failure mode within the rebar end anchorage zone. Finite element analyses were used as a tool to design the specimens. The paper presents discussion of the test results within the framework of expectations outlaid during design of the test specimens. The effects of bending compression from column on the concrete breakout capacity under influence of foundation edges is the specific focus of the present investigation. It is shown that the direction of application of load on the column largely determines the effect of bending compression from column on concrete breakout capacity. The test data presented in this paper offers the necessary benchmark data on concrete breakout behavior in the case of reinforced concrete column foundation joints under influence of foundation edges. This test data along with insights from finite element analyses is employed to explore and possibly identify necessary modifications to the current state-of-the-art consideration of concrete breakout capacity for reinforced concrete connections.
Open Access
Influence on the load‐displacement behaviour of steel‐to‐concrete connections with post‐installed adhesive anchors
(2023) Maçi, Nilde; Hofmann, Jan
Designing frame structures requires knowing the behaviour of each member of the frame (beam, column, joint, etc.) regarding the axial forces, shear forces, and bending moments. Furthermore, the ductility of the structure under seismic loading is essential in earthquake regions. Nowadays, structural frames are built from different materials such as concrete and steel, to achieve better performance. Therefore, the behaviour of the connections between steel and concrete is essential. The steel‐to‐concrete joints were the focus of the INFASO project, where joint solutions with easy fabrication, quick assembly, applicability in old structures, sufficient ductility, and high loading capacity were developed. They proposed the use of anchor plates with welded studs or post‐installed fasteners such as adhesive anchors to connect the steel and concrete members. This paper focuses on the performance of post‐installed adhesive anchors. During their service life, post‐installed anchors are subjected to monotonic, constant, and seismic loading. Each of these loading approaches is described in the current standards. Seismic and constant loading tests are of importance to the long‐term behaviour of the anchors. Seismic loading tests are carried out using a predefined cycle pattern. According to TR049, seismic tests of category C1 (tension and shear) are performed with 140 load cycles, where the load amplitude decreases after 10, 30, and 100 cycles. On the contrary, C2 category tests increase the amplitude within 75 or 59 cycles, depending on the test. Constant loading tests apply when the anchors are installed in cracked concrete. In contrast to the mentioned patterns, this study observes the behaviour of the adhesive anchors when the amplitude of each cycle is increased by 5 % until the anchor fails. Standard short‐term pull‐out tests are carried out to determine the load increments. Various parameters such as the embedment depth, bond line thickness, hole cleaning, wet concrete, and elevated temperatures are studied. Confined and unconfined tests are performed. Overall, the reference short‐term failure loads are higher than those in the tests with incremental and cyclic loading. The anchors installed with reduced hole cleaning, in wet concrete or subjected to elevated temperatures have a lower failure load compared to the reference series. Two additional bond line thicknesses are used for comparison. The increase in the thickness influenced the failure load differently for confined and unconfined test setups.
Open Access
Strengthening of anchor channels on the concrete surface
(2023) Petrasch, Michael C.; Hofmann, Jan
For the installation of curtain wall systems, the positions of anchor channels gradually move closer to the edge of the concrete slabs. But close to the edge of the slab, conventional supplementary reinforcements have problems to redistribute the loads to the reinforcement due to the short bond length that is available after concrete edge failure occurred. Therefore, tests have been conducted to investigate the behaviour of anchors channels, close to the edge. To achieve this, a strengthening system on the surface of the concrete with post installed fasteners was developed. First results indicate a high potential for strengthening the channels close to the edge under shear load. With these test results numerical simulations with Atena Science were performed and, after its calibration, the model was used for further investigation.