Prof. Dr.-Ing. Martina Schnellenbach-Held

Institute for Structural Concrete
University of Duisburg-Essen

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  • An approach to evaluate the strengthening requirement of concrete bridges - Evaluation of structural and damage data using methods of the risk assessment [Ein Ansatz zur Bewertung des Verstärkungsbedarfs von Massivbrücken: Auswertung von Bauwerks- und Schadensdaten mit Methoden der Risikobewertung]
    Peeters, M. and Schnellenbach-Held, M.
    Beton- und Stahlbetonbau 115 (2020)
    An approach to evaluate the strengthening requirement of concrete bridges – Evaluation of structural and damage data using methods of the risk assessment. Due to the condition of the bridges and the constantly increasing traffic load, there is an enormous need for bridge strengthening relevant to bearing capacity in addition to the replacement construction. Therefore, the available financial resources for the maintenance of the bridge stock and for the maintenance of a functioning infrastructure must be used efficiently and effectively within the maintenance management. The presented approach to determine the basic strengthening requirement of concrete bridges provides a further feature for the decision-making which bridge categories require a strengthening and which bridges can be considered as rather uncritical with regard to a strengthening. The determination is made on the basis of risk assessment methods and on the basis of real damage data on superstructures of about 1,240 concrete bridges in the course of federal trunk roads. The risk assessment was carried out on the one hand by using level-frequency diagrams, considering the risk matrices, and on the other hand by using risk numbers, each separately for the assessment attribute of stability and durability. © 2020, Ernst und Sohn. All rights reserved.
    view abstract10.1002/best.201900096
  • Consistent management and evaluation of building models in the early design stages
    Abualdenien, J. and Schneider-Marin, P. and Zahedi, A. and Harter, H. and Exner, H. and Steiner, D. and Singh, M.M. and Borrmann, A. and Lang, W. and Petzold, F. and König, M. and Geyer, P. and Schnellenbach-Held, M.
    Journal of Information Technology in Construction 25 (2020)
    The early stages of building design involve the consideration of different design variants and their assessment regarding various performance criteria including energy consumption and costs. During the design process, the involved experts from different disciplines frequently exchange building information to develop a design that satisfies the project's requirements and objectives. In the course of this iterative process, the building design evolves throughout multiple refinement stages. At the same time, different variants are developed. In BIM-based projects, the maturity of the design information provided by the model is expressed by the notion of Level of development (LOD). So far, however, there is no method to formally define the information requirements of a LOD. In particular, there are no means for expressing the uncertainty involved with the provided information. By contrast, despite the insufficient information available in early design stages, a BIM model appears precise and certain. This situation leads to false assumptions and model evaluations, for example, in the case of energy efficiency calculations or structural analysis. Hence, this paper presents an overview of a set of approaches that were developed to alleviate and preserve the consistency of the designed solutions. The approach includes the development of a multi-LOD meta-model, which allows one to explicitly describe the LOD requirements of each building component type incorporating the possible uncertainties, e.g. concerning the building dimensions. On the basis of this multi-LOD model, methods for evaluating a building design's performance regarding the building's structure and life cycle energy performance are proposed that take the defined uncertainties into account. To support the management of design variants in one consistent model, a graph-based approach is introduced. Finally, a minimized communication protocol is described to facilitate the workflow and communicate the evaluation results for supporting the decision-making process. © 2020 The author(s). This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 International (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
    view abstract10.36680/j.itcon.2020.013
  • Experimental investigation on a hole edge supported slab with punching shear reinforcement [Experimentelle Untersuchungen zu lochrandgestützten Flachdecken mit Durchstanzbewehrung]
    Mucha, R. and Welsch, T. and Schnellenbach-Held, M.
    Beton- und Stahlbetonbau 115 (2020)
    Experimental investigation on a hole edge supported slab with punching shear reinforcement. In order to prevent the punching of conventional flat slabs, various design concepts resting upon numerous experiments have been developed and enshrined in design codes. Hole edge supported flat slabs with a small load application area have not been considered in these design codes. Previous experimental and numerical investigations showed the different load bearing behavior of conventional flat slabs and hole edge supported flat slabs with a small load application area. It was found that, resulting from these differences and depending on the kind of hole edge support, the punching shear capacity of hole edge supported flat slabs is possibly overestimated when using existing design codes. Linked to this the question raised how the use of punching shear reinforcement will lead to an increased punching shear capacity of hole edge supported slabs. In order to answer this question, a tentative test analogous to previous experiments was carried out on a flat slab specimen with punching shear reinforcement in the form of stud rails. In the following, the results of this test are reported and compared to the findings of the previous investigations. © 2020, Ernst und Sohn. All rights reserved.
    view abstract10.1002/best.201900095
  • Experimental investigations on the punching shear behavior of hole edge supported slabs with a small load application area [Experimentelle Untersuchungen zum Durchstanztragverhalten lochrandgestützter Platten mit kleiner Lasteinleitungsfläche]
    Welsch, T. and Mucha, R. and Schnellenbach-Held, M. and Held, M.
    Beton- und Stahlbetonbau 115 (2020)
    Experimental Investigations on the Punching Shear Behavior of Hole Edge Supported Slabs with a Small Load Application Area. Due to their benefits regarding freedom of flexible floorplan design, flat slabs have established as an important part of building construction. In case of use of very slender construction members with a high load carrying capacity, such as columns of high strength concrete, spun concrete or composite columns, the problem of the vertical load transmission through the normal strength slab arises. Special construction members have been developed with high-strength cores penetrating the slab in order to enable a direct vertical force closure between the columns. In this case only a reduced load application area with a ring-shape remains for the load introduction from the slab into the column. Preliminary investigations based on finite element simulations revealed that this has an influence on the punching shear behavior and the failure loads of flat slabs, depending on the size of the reduced load application area and the kind of the core design. Subsequently the results of the first experimental investigations on that special kind of punching problem and the accompanying finite element simulations are presented. © 2020, Ernst und Sohn. All rights reserved.
    view abstract10.1002/best.201900066
  • Influence of thermal treatment on the strength of fine-grained Ultra-High Performance Concrete (UHPC/RPC) [Einfluss der thermischen Behandlung auf die Festigkeiten von feinkörnigem ultrahochfestem Beton (UHPC/RPC)]
    Rhau, M. and Schnellenbach-Held, M. and Welsch, T.
    Beton- und Stahlbetonbau 113 (2018)
    Influence of Thermal Treatment on the Strength of Fine-Grained Ultra-High Performance Concrete (UHPC/RPC). By means of targeted specific thermal post-treatment, the bending tensile strength and compressive strength of Ultra-High Performance Concrete (UHPC) can significantly be increased. In most publications, a pre-storage time of 1–2 days, a holding temperature of 60–90 °C and a dwell time of 24–48 hours are recommended [1, 2]. Own preliminary investigations on the thermal treatment of fine-grained UHPC (RPC) at the Institute for Structural Concrete of the University Duisburg-Essen showed that improved results could be achieved by other variations. Therefore, more detailed investigations were carried out on the pre-storage time and the holding temperature of two different UHPC mixtures. Furthermore, the influence of protection of the samples against dehydration during the thermal treatment was investigated. The results of these studies are documented and evaluated in this publication. It was found that the treatment temperature has the greatest influence on the compressive strength. The protection of the samples was crucial for the flexural strength. It should also be noted that different thermal treatment regimes led to the best results for the various mixing compositions. © 2018, Wilhelm Ernst and Sohn. All rights reserved.
    view abstract10.1002/best.201800006
  • Building Information Modeling - implementation within structural design
    Kepplin, R. and Schnellenbach-Held, M. and Held, M.
    Bautechnik 94 (2017)
    Building Information Modeling (BIM) radically changes the planning process of construction projects. This implies that all planning partners have to familiarize oneself with new working structures and new software tools. A three-dimensional building design and its object-oriented database form the basis for this new working method. Special applications, developed for the BIM planning process, assist the structural designer by providing features for an automated transformation from the building design over an analytical model in a calculation model. As a chain of reasoning three-dimensional calculation models are used for the static proof by this workflow. The application of 3d-static software in practice can already be noticed. Three-dimensional calculation models concerning structural engineering were realized according to the BIM workflow for scientific research and designed in its entirety. This article points out difficulties of the transformation process, limits of structural detailing and problems of a 3d structural analysis based on experiences gained on three-dimensional analytic and calculation models. Additionally options to implement intelligent methods in the BIM workflow are presented.
    view abstract10.1002/bate.201700003
  • High performance aerogel concrete
    Welsch, T. and Schnellenbach-Held, M.
    High Tech Concrete: Where Technology and Engineering Meet - Proceedings of the 2017 fib Symposium (2017)
    Aerogel Concrete is a promising approach to fulfill the requirements for the thermal insulation of buildings. So far, Aerogel Concretes exhibit very low thermal conductivities of 0.06 < λ < 0.10 W/(mK) and very low corresponding compressive strength of fcm ≤ 2.5 MPa. Thus, the suitability of Aerogel Concrete as a building material for load bearing walls was worthy of discussion. Previous efforts to achieve considerable compression strength in the range of normal strength concretes (fcm ≈ 20 MPa) were accompanied by a significant increase of the thermal conductivity up to λ ≈ 0.55 W/(mK). By embedding silica aerogel granules in a high strength cement matrix, the Institute for Structural Concrete (ISC) at the University of Duisburg-Essen developed in cooperation with the German Aerospace Center (DLR) so called High Performance Aerogel Concrete (HPAC) with an improved correlation between compression strength and thermal conductivity. The thermal conductivities of the new material are in the range of 0.09 W/(mK) ≤ λ ≤ 0.25 W/(mK) for the High Performance Aerogel Concretes considered with compression strength between 2 MPa and 25 MPa. The dry bulk density at the same amounts of aerogel granule is less compared to previous investigations on Aerogel Concrete. The Young's modulus related to the dry bulk density is comparable to that of Lightweight Aggregate Concrete; the flexural strength is considerable less. The mixtures are flowable, nearly self-compacting and show a short hydration process as well as an increased tendency to shrink. Subsequently, the results of the investigations on HPAC are presented in detail. © Springer International Publishing AG 2018.
    view abstract10.1007/978-3-319-59471-2-15
  • Entwicklung von Hochleistungsaerogelbeton
    Schnellenbach-Held, M. and Welsch, T. and Fickler, S. and Milow, B. and Ratke, L.
    Beton- und Stahlbetonbau 111 (2016)
    Development of High Performance Aerogel Concrete. Because of requirements for thermal insulation the realization of single-leaf walls made of normal concrete is not feasible for a couple of decades. Thus, additional means such as external thermal insulation systems or cavity walls with core insulation are normally necessary, which are accompanied by creative, constructive or economical disadvantages. Previous attempts to produce single-leaf walls with lightweight concretes lead to huge wall thicknesses due to the low compressive strength or the higher thermal conductivities of lightweight concretes. By embedding silica aerogel granules in a high strength cement matrix, the Institute for Structural Concrete (ISC) at the University of Duisburg-Essen developed a High Performance Aerogel Concrete (HPAC) in cooperation with the Institute of Materials Research of the German Aerospace Center (DLR). The HPAC exhibits a remarkable relation between compressive strength and thermal conductivity [1]. The following report covers the mechanical and the building physics properties of the new material. Copyright © 2016 Ernst & Sohn Verlag für Architektur und technische Wissenschaften GmbH & Co. KG, Berlin
    view abstract10.1002/best.201600017
  • Praxiserfahrungen zum Verstärken von Betonbrücken
    Welsch, T. and Reißen, K. and Schnellenbach-Held, M. and Hegger, J. and Von Weschpfennig, D. and Haardt, P.
    Beton- und Stahlbetonbau 111 (2016)
    Steigende Beanspruchungen insbesondere durch Schwerlastverkehr und altersbedingte Tragfähigkeitsdefizite älterer Brückenbauwerke führen dazu, dass zahlreiche Betonbrücken instand gesetzt oder verstärkt werden müssen. Um einen Beitrag zur konstruktiv und wirtschaftlich erfolgreichen Durchführung zukünftiger Verstärkungsmaßnahmen zu leisten, wurde im Auftrag der Bundesanstalt für Straßenwesen (BASt) eine Erfahrungssammlung zu "Verstärkungen älterer Beton- und Spannbetonbrücken" erstellt [1]. In der Dokumentation wird ein Überblick über den Stand der Technik der im Massivbrückenbau eingesetzten Verstärkungstechniken gegeben, und insgesamt 76 durchgeführte Verstärkungsmaßnahmen werden ausgewertet. Repräsentative Verstärkungsmaßnahmen werden in anonymisierter Form detailliert vorgestellt. Der vorliegende Bericht gibt einen Überblick über die in Kürze erscheinende Erfahrungssammlung [1], wobei die wesentlichen Erfahrungen der ausgewerteten Anwendungsfälle vorgestellt werden. Experiences on the Strengthening of Concrete Bridges Increasing loads, in particular by heavy-duty traffic, and age-related load-bearing deficits of older bridges result in the need of repairing and strengthening numerous concrete bridges. In order to contribute to a successful realization of future strengthening measures, a collection of experiences focusing on economical and constructive perspectives was provided on behalf of the German Federal Highway Research Institute (BASt). In this documentation [1], an overview is given on the state of the art of strengthening technologies for reinforced and prestressed concrete bridges, and the experiences of 76 strengthening measures are summarized. Representative strengthening measures are presented in anonymized form. This report describes the new documentation [1], and essential experiences of the evaluated cases of application are introduced. © 2016 Ernst & Sohn Verlag für Architektur und technische Wissenschaften GmbH & Co. KG, Berlin.
    view abstract10.1002/best.201600005
  • Development of high performance aerogel concrete
    Fickler, S. and Milow, B. and Ratke, L. and Schnellenbach-Held, M. and Welsch, T.
    Energy Procedia 78 (2015)
    Current massive wall-building materials can be characterized by having either low thermal conductivities and thus low bulk densities and low compression strength or high compressions strength, high bulk densities and high thermal conductivities. In this paper, the first results of a research project are presented, in which a new aerogel-based construction material is developed that exhibits extra ordinary heat-insulating and load-carrying properties. By embedding silica aerogel granules in a high strength cement matrix "High Performance Aerogel Concrete" is developed, which combines the benefits of conventional concrete (compressive strength, unlimited moldability) with the properties of a heat insulating material. So far, various mixtures were examined in terms of their compressive strength and thermal conductivity. The first results are very promising with compressive strength between 3.0 MPa and 23.6 MPa and thermal conductivities between 0.16 W/(mK) and 0.37 W/(mK). © 2015 Published by Elsevier Ltd.
    view abstract10.1016/j.egypro.2015.11.684
  • Bionic optimization of concrete structures by evolutionary algorithms
    Schnellenbach-Held, M. and Habersaat, J.-E.
    Structural Engineering International: Journal of the International Association for Bridge and Structural Engineering (IABSE) 24 (2014)
    Floor slabs represent a large volume of concrete in buildings. The goal of this research is to achieve a structure that has an optimized bearing capacity. The optimization implies economic efficiency and sustainability. This paper describes a bionic optimization process that is applied in a project of the German Research Foundation (DFG) Priority Programme called "Concrete light. Future concrete structures using bionic, mathematical and engineering formfinding principles". The project involves adaption of three different natural structures that lead to a natural flow of forces. These natural structures are (a) spider webs, (b) hollow parts of bones and (c) geometries of structures such as the bottom side of water lilies or seashells. This scientific paper deals with the implementation of an optimization process for a configuration of reinforcement inspired by a spider web. Evolutionary Algorithms (EAs) are used for the development and optimization of an innovative and useful configuration of reinforcement. The EAs use reproduction, mutation and selection as mechanisms, inspired by biological evolution, to solve technical problems gradient-free. In this project the EA is combined with physical nonlinear finite element analyses. The EA is embedded into a C# application, in which the slab structure is generated and the finite element programme is started. The quality of the results is characterized by the fitness of each individual (reinforcement configuration), which is, for this example, the midspan displacement of the generated slab multiplied by the steel volume per slab. Accordingly, the midspan displacement is to be minimized during the process, with the minimum possible amount of reinforcement. The optimization variables are the angles and the number of rebars per slab. Several constrains need to be included to get comparable results between the developed slabs and the conventional slabs with orthogonally configured reinforcement. This paper presents the results of an optimized reinforcement configuration thus found by EA and comparisons with the behaviour of conventional slabs with a similar reinforcement ratio.
    view abstract10.2749/101686614X13830790993564
  • Self-tuning closed-loop fuzzy logic control algorithm for adaptive prestressed structures
    Schnellenbach-Held, M. and Steiner, D.
    Structural Engineering International: Journal of the International Association for Bridge and Structural Engineering (IABSE) 24 (2014)
    Constantly increasing traffic loads, unpredictable influences on and unplanned conditions of bridges represent new challenges in the field of engineering. Innovative strategies and construction techniques are required to meet these and future challenges. Adaptive prestressing offers great potential to increase a structure's load-carrying capacity and to optimize its load-induced stresses. In this manner, cost efficiency and sustainability of constructions can be enhanced. Therefore, a control algorithm with high reliabi lity and redundancy is required to meet the new challenges. In this paper, an adaptive fuzzy logic-based closed-loop control system for realization of adaptive prestressed structures is presented. Based on the new concept, two different specialized control algorithms are developed. In order to decrease deflections, the prestressing force of an aluminium truss is controlled. The algorithm includes a fuzzy system with model-based knowledge base. The learning process is established on direct synchronization of the calculated deflections of the model with the measured reactions of the structure. Another fuzzy system for adaptive prestressing of a reinforced concrete T-beam uses a model-free knowledge base. Optimization of load-induced stresses is accomplished utilizing expert knowledge. An incremental learning process is performed in accordance with the algorithm's basic rules. Experiments on the two prototypes are conducted to investigate the functionality of the developed algorithms. In addition to efficiency, high reliability and redundancy are shown by the control system. In this article, the potential of fuzzy-controlled adaptive prestressing is illustrated.
    view abstract10.2749/101686614X13830790993528
  • Innovations in bridge construction
    Friedrich, H. and Empelmann, M. and Hamm, S. and Freundt, U. and Schnellenbach-Held, M. and Butz, C. and Mangerig, I. and Tusche, J.
    Beton- und Stahlbetonbau 108 (2013)
    The Federal Ministry of Transport, Building and Urban Development (BMVBS) together with the Federal Highway Research Institute (BASt) created a long-term framework research program called "Road in the 21st Century". The design of futurecompliant roads requires an integral approach also including bridges and structural technology. The following article deals with three completed and two current research projects with the focus on Innovations in Bridge Construction. © 2013 Ernst & Sohn Verlag für Architektur und technische Wissenschaften GmbH & Co. KG, Berlin.
    view abstract10.1002/best.201300001
  • Execution quality of reinforced and prestressed concrete bridges on federal roads
    Winter, G. and Schnellenbach-Held, M. and Gusia, P.J.
    Beton- und Stahlbetonbau 107 (2012)
    The research project "Execution quality of reinforced and prestressed concrete structures on federal highways" was conducted in the 1990s. The current research project based on this preliminary project aims to inspect whether the regulations for execution are implemented successfully in practice and how they have influenced the quality of workmanship. As part of the research project 53 construction site inspections on 19 structures were carried out in less than two years to observe the main stages of execution. In comparison to the preliminary project a decrease in the number of defects per site visit as well as the "seriousness" of the defects is registered. Planning and design documents were improved. The construction supervision offices have shown considerably better knowledge of applicable regulations. The regulations for execution introduced in 2003 have also been implemented successfully in the bridge construction industry. The deficiencies could have been avoided by implementing the existing rules. © 2012 Ernst & Sohn Verlag für Architektur und technische Wissenschaften GmbH & Co. KG, Berlin.
    view abstract10.1002/best.201100078
  • Swellable acrylatgels - An alternative maintenance method for expansion joints at navigable waterway constructions?
    Maisner, M. and Eßer, A. and Kwenjeu, A. and Westendarp, A. and Schnellenbach-Held, M.
    Beton- und Stahlbetonbau 107 (2012)
    Could swellable acrylatgels offer an interesting application possibility for navigable waterway constructions? Within a research and development project three for other applications commercially used acrylatgels were investigated with respect to this application. The maintenance of expansion joints is currently unregulated. Concerning the manufacturer two gels are applicable for the maintenance of joints. Selected physical properties of the gels were determined. For statements concerning the compatibility with structural elements, which are in contact with the gels within the joint, concrete models were developed and constructed. The focus on the investigations was on the harmful impacts of waterstop types like PVC and Elastomer and of build-in parts of steel, incl. concrete reinforcement steel. On investigations concerning the injectability of acrylatgels on reinforced concrete the applicability against heavy water pressure was questioned. Furthermore, considerations concerning the ecological relevance of such measures using acrylatgels were carried out. Copyright © 2012 Ernst & Sohn Verlag für Architektur und technische Wissenschaften GmbH & Co. KG, Berlin.
    view abstract10.1002/best.201200030
  • Micro-reinforced Ultra High Performance Concrete (UHPC) - Structural behaviour
    Schnellenbach-Held, M. and Prager, M.
    Beton- und Stahlbetonbau 106 (2011)
    With intent to provide a ductile failure and to use UHPC to full capacity usually steel fibres are added during the mixing process. The impaired workability as well as random orientation and spreading of the fibres are beside the spots of corrosion resulting from near-surface fibres the main disadvantages of the use of steel fibres. Within this paper a micro-reinforcement as replacement for steel-fibres is introduced with respect to the structural behaviour of the composite material. To outline the comparability in structural behaviour the results of the experimental investigations on micro-reinforced UHPC are constantly compared to the results of fibered UHPC. Additional investigations concerning the orientation of the micro-reinforcement show an influence on the structural failure. Beside the experimental tests nonlinear finite element simulations were performed. The simulations and the test results show substantial similarities in crack propagation, ultimate deformation and bearing capacity. © 2011 Ernst & Sohn Verlag für Architektur und technische Wissenschaften GmbH & Co. KG, Berlin.
    view abstract10.1002/best.201100030
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  • mechanical properties

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