@inproceedings{FischerSawadeBeuletal., author = {Fischer, Christian and Sawade, Gottfried and Beul, Willibald and Krause, Hans-Joachim}, title = {Anwendung der magnetischen Streufeldmessung zur Bestandsanalyse von Br{\"u}ckenbauwerken}, series = {Erstes Br{\"u}ckenkolloquium: Beurteilung, Ert{\"u}chtigung und Instandsetzung von Br{\"u}cken, Ostfildern (Germany)}, booktitle = {Erstes Br{\"u}ckenkolloquium: Beurteilung, Ert{\"u}chtigung und Instandsetzung von Br{\"u}cken, Ostfildern (Germany)}, pages = {521 -- 526}, language = {de} } @article{FischerOžboltGehlen, author = {Fischer, Christian and Ožbolt, Joško and Gehlen, Christoph}, title = {Experimentelle und numerische Untersuchungen zum Einfluss der Bewehrungskorrosion auf das Verbundverhalten zwischen Stahl und Beton}, series = {Beton- und Stahlbetonbau}, volume = {105}, journal = {Beton- und Stahlbetonbau}, number = {5}, issn = {1437-1006}, doi = {10.1002/best.201000005}, pages = {284 -- 293}, abstract = {Im vorliegenden Aufsatz werden Ergebnisse aus experimentellen und numerischen Untersuchungen an so genannten Balkenend (engl. beam end) Probek{\"o}rpern zum Einfluss der Stahlkorrosion auf das Verbundtragverhalten vorgestellt. Dabei wurden geometrische Einfl{\"u}sse, wie Stabdurchmesser und Betondeckung sowie Einfl{\"u}sse aufgrund von B{\"u}gelbewehrung und deren Schw{\"a}chung durch die Korrosion untersucht. Insgesamt ergaben sich sechs verschiedene Probek{\"o}rpertypen, an denen Ausziehversuche ohne Korrosion und zu unterschiedlichen Korrosionsstadien durchgef{\"u}hrt wurden. Dabei wurden korrosionsbedingte, maximale Rissbreiten von bis zu rd. w = 1,3 mm mit dazugeh{\"o}rigen Korrosionsabtr{\"a}gen von maximal bis zu xcorr = 500 μm untersucht. Die Untersuchungen ergaben, dass die Verbundfestigkeit von Probek{\"o}rpern ohne B{\"u}gelbewehrung mit zunehmender Korrosion exponentiell abnimmt. Probek{\"o}rper mit B{\"u}geln weisen hingegen kaum Verbundfestigkeitsverluste bis zur untersuchten Rissbreite von w = 0,6 mm auf. Die umschließende Wirkung der B{\"u}gel wurde unter den untersuchten Bedingungen nicht beeinflusst. Ein erarbeitetes numerisches FE-Modell konnte die experimentellen Ergebnisse gut reproduzieren.}, language = {en} } @phdthesis{Fischer, author = {Fischer, Christian}, title = {Auswirkungen der Bewehrungskorrosion auf den Verbund zwischen Stahl und Beton}, doi = {10.18419/opus-464}, abstract = {Carbonation and chloride induced reinforcement corrosion influences the load bearing behaviour of reinforced concrete structures and consequently shortens its durability. This occurs basically due to the following three points: (i) the loss of steel cross section, (ii) the loss of concrete cross-section due to cracking and spalling, and (iii) the loss of bond action between steel and concrete. The present work is limited to studies on the influence of chloride induced reinforcement corrosion on bond behaviour between steel and concrete. In this context the question arises of which components to ensure bond integrity are affected in any manner by reinforcement corrosion? To solve these issue primarily experimental studies on different specimen geometries were performed in the past. These include concentric and eccentric pull-out specimens and bending beams. There have been studies performed both with and without transverse reinforcement, which is in this work uniformly called stirrup or stirrup reinforcement. Due to the long periods of time for both the depassivation of the concrete cover as well as the progress of reinforcement corrosion, almost all previous studies have been accelerated in this regard. In previous studies it was determined that the degree of acceleration affects the date of the initial cracking and the change in bond strength. Both, this fact and the great variety of different test specimens led to a large variation in bond strength values with respect to the corrosion of reinforcement. For this reason it has been difficult to assign the geometric and corrosion parameters to certain effects on the bond behaviour. As a contribution to disentangle these issues, experimental studies on beam-end specimens were performed, which serve as the basis for the fundamental mechanisms of bond under corrosive attack. The corrosion of the reinforcement was accelerated potentiostatically, but this was done in comparison with the known studies in a most gentle manner with only five fold in excess of the maximum corrosion rate occurring in nature. The focus of the study was on the nature and distribution of corrosion products, the relationship between corrosion rate and measurable crack width in the concrete cover and the effects of reinforcement corrosion on bar end displacement as well as on bond strength. The tests were performed separately for specimens with and without stirrups, and the specimens with stirrups were further divided into two groups. First, the stirrups were electrically connected to the longitudinal bars, so that the stirrups corroded accelerated. Secondly, the stirrups were electrically decoupled from the longitudinal bars, whereby only the longitudinal bars corroded accelerated. This allowed a qualitative statement about the influence of weakened stirrups on bond behaviour. Subsequently, the obtained results were discussed in the context of results from other researchers. From this e.g. new insights into the dependence of the bond strength of the acceleration of reinforcement corrosion are obtained. Furthermore qualitative statements about the influence of geometrical parameters such as bar diameter and concrete cover on the change of bond strength are made. More precise statements in this regard were possible by numerical studies of finite element models. As part of the numerical investigations, which covered especially more geometrical parameter variations, the influence of different bar diameters and concrete covers on bond strength at different stages of corrosion was investigated. In addition by means of numerical investigations, a quantitative statement on the utilization of the stirrup reinforcement could be made. Using the above findings, a model was created that allows an estimation of the residual bond strength. The model consists of calculating the so-called reference bond strength with no corrosion effect, a description of the decrease in confining action of concrete and the effect if existing of a stirrup reinforcement, which is also weakened by corrosive action. This model distinguishes itself on one hand from purely empirical models that have emerged from the regression of experimental data. Compared to very complex analytical models, the proposed model impresses with its simplicity and user-friendly form.}, language = {en} } @incollection{GehlenMayerThieletal., author = {Gehlen, Christoph and Mayer, Till Felix and Thiel, Charlotte and Fischer, Christian}, title = {Lebensdauerbemessung}, series = {Beton Kalender 2021}, booktitle = {Beton Kalender 2021}, isbn = {978-3-433-61020-6}, doi = {10.1002/9783433610206.ch1}, pages = {1 -- 57}, abstract = {Christoph Gehlen, Till Felix Mayer, Charlotte Thiel und Christian Fischer beschreiben die Lebensdauerbemessung von Beton. Umfassend werden Transport- und Sch{\"a}digungsmodelle vorgestellt, die die Mechanismen der Carbonatisierung, der Chlorideindringung, der Korrosion und der korrosionsinduzierten Rissbildung im Stahlbeton beschreiben. Die damit einhergehende Verbundthematik wird erl{\"a}utert. Auch wird auf alle Mechanismen der Betonkorrosion eingegangen. Die Bemessung in Bezug auf die Dauerhaftigkeit und damit Absch{\"a}tzungen f{\"u}r die Lebensdauer von Beton wird in drei unterschiedlich genauen Formaten gef{\"u}hrt. Neben dem vollprobabilistischen Format wird beschrieben, wie Bemessungen auch auf Grundlage von Nachweisen basierend auf Teilsicherheitsbeiwerten durchgef{\"u}hrt werden k{\"o}nnen. Daran anschließend wird aufgezeigt, welche deskriptiven Bemessungsans{\"a}tze sich daraus ableiten lassen. An einigen exemplarisch herausgegriffenen Objektbeispielen wird die Lebensdauerbemessung konkret vorgef{\"u}hrt.}, language = {en} } @inproceedings{FischerOžbolt, author = {Fischer, Christian and Ožbolt, J.}, title = {An appropriate indicator for bond strength degradation due to reinforcement corrosion}, series = {Proceedings of the 8th international conference on fracture mechanics of concrete and concrete structures, FraMCoS 2013}, booktitle = {Proceedings of the 8th international conference on fracture mechanics of concrete and concrete structures, FraMCoS 2013}, language = {en} } @incollection{FischerOzboltGehlen, author = {Fischer, Christian and Ozbolt, J. and Gehlen, C.}, title = {Verbundfestigkeit von korrodierter Bewehrung in Beton - Teilprojekt B2: Teil 2: Dauerhaftigkeitsbemessung}, number = {602}, edition = {1.}, publisher = {Beuth Verlag}, address = {Berlin}, isbn = {978-3-410-65224-3}, issn = {0171-7197}, pages = {47 -- 88}, language = {en} } @inproceedings{FischerOzbolt, author = {Fischer, Christian and Ozbolt, J.}, title = {Influence of bar diameter and concrete cover on bond degradation due to corrosion in: J. Cairns, G. Metelli, G. Plizzari}, series = {Proceeding of 4 th international symposium: Bond in Concrete 2012: Bond, Anchorages, Detailing}, booktitle = {Proceeding of 4 th international symposium: Bond in Concrete 2012: Bond, Anchorages, Detailing}, pages = {17 -- 20}, language = {en} } @article{BuetefuehrFischerGehlenetal., author = {B{\"u}tef{\"u}hr, M. and Fischer, Christian and Gehlen, C. and Menzel, K. and N{\"u}rnberger, U.}, title = {On-site investigations on concrete resistivity - a parameter of durability calculation of reinforced concrete structures}, series = {Materials and Corrosion}, volume = {57}, journal = {Materials and Corrosion}, number = {12}, issn = {1521-4176}, doi = {10.1002/maco.200604019}, pages = {932 -- 939}, abstract = {For determination the electrolytic resistivity of concrete, resistances of realistic designed probes are measured during a one and two year period, respectively. Measurements are made with a commercially available instrument normally used for measuring earth resistances. Comparison to other usually applied methods show not only that the used method GEOHM is qualified for measuring the electrolytic resistance of concrete but also that the magnitude of measured values is realistic. To obtain electrolytic resistivities from these measurements the individual cell constant for the investigated system was derived from experimental research. First results of the in-situ stored specimens are presented, intended future activities are sketched.}, language = {en} } @incollection{FischerGehlenOžbolt, author = {Fischer, Christian and Gehlen, J. and Ožbolt, C.}, title = {DFG Research Group 537: Modelling reinforcement corrosion - Numerical modelling of bond strength of corroded reinforcement}, series = {Concrete Repair, Rehabilitation and Retrofitting II}, booktitle = {Concrete Repair, Rehabilitation and Retrofitting II}, publisher = {CRC Press}, isbn = {978-0-429-10359-9}, pages = {2}, abstract = {The calculations were performed with four different specimen types (see Table 1). Each type was calculated without expansion (reference calculation) as well as with five different expansion values. The expansion was simulated before the application of the pull-out load.}, language = {en} } @inproceedings{Fischer, author = {Fischer, Christian}, title = {Experimental investigations on the effect of corrosion on bond of deformed bars}, series = {Proceedings of the 8th fib PhD Symposium}, booktitle = {Proceedings of the 8th fib PhD Symposium}, language = {en} } @article{DrenkardFischerSaueretal., author = {Drenkard, Hannah and Fischer, Christian and Sauer, Veit and Gehlen, Christoph}, title = {On the Chloride Distribution in Concrete and Mortar Samples after an RCM Test}, series = {Materials}, volume = {16}, journal = {Materials}, number = {8}, issn = {1996-1944}, doi = {10.3390/ma16082952}, pages = {2952 -- 2952}, abstract = {It is of essential need to face the challenges of CO2 reduction in industrial cement and concrete production reliable test methods in order to evaluate the performance of concretes, especially with regard to the service life of our infrastructure. The rapid chloride migration test (RCM test) is a standard method to assess the resistance against chloride ingress of concrete. However, during our study, certain critical questions arose with regard to the chloride distribution. The sharp chloride ingress front based on the model assumptions contradicted the shallow gradient of the experimental data. For this reason, investigations on chloride distribution in concrete and mortar samples after RCM tests were performed. The focus was on the factors influencing the extraction, e.g., time after RCM test and the location on sample. Furthermore, differences between concrete and mortar samples were investigated. The investigations showed that no sharp gradient on concrete samples was found due to the extremely uneven chloride front. In contrast, the theoretical profile shape was instead demonstrated on mortar specimens. The prerequisite for this result is that the drill powder must be taken directly after the completion of the RCM test from very uniform penetration areas. Thus, the model assumptions on the chloride distribution via the RCM test could be confirmed.}, language = {en} } @incollection{OehlFischerKonradetal., author = {{\"O}hl, Natalie and Fischer, Jenny and Konrad, Robert and Bauer, Christian}, title = {Erhebung und Bewertung von User Experience und Usability technischer Pflegeinnovationen - Implikationen f{\"u}r die praktische Methodenanwendung}, series = {Pflegeinnovationen in der Praxis}, booktitle = {Pflegeinnovationen in der Praxis}, editor = {Krick, Tobias and Zerth, J{\"u}rgen and Rothgang, Heinz and Klawunn, Ronny and Walzer, Stefan and Kley, Tobias}, publisher = {Springer Fachmedien Wiesbaden}, address = {Wiesbaden}, isbn = {9783658393014}, doi = {https://doi.org/10.1007/978-3-658-39302-1_3}, pages = {37 -- 53}, language = {de} }