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Prudente dos Santos, João Pedro de Oliveira Dias; Crémona, Christian; Campos da Silveira, António Paulo; de Oliveira Martins, Luís CaladoReal-time damage detection based on pattern recognitionStructural Concrete3/2016338-354Technical Papers

Kurzfassung

Structural health monitoring (SHM) can be defined as the process of developing and implementing structural damage detection strategies. Ideally, this detection should be carried out in real-time before damage reaches a critical state and impairs structural performance and safety. Hence, it must be based on sensorial systems permanently installed on the target structures and on fully automatic detection methodologies.
The ability to detect damage in real-time is vital for controlling the safety of old structures or for post-retrofitting/post-accident situations, where it might even be mandatory for ensuring a safe service. Under these constraints, SHM systems and strategies must be capable of conducting baseline-free damage identification, i.e. they must not rely on comparing newly acquired data with baseline references in which structures must be assumed as undamaged.
The present paper describes an original strategy for baseline-free damage detection based on the application of artificial neural networks and clustering methods in a moving windows process. The proposed strategy was tested on and validated with numerical and experimental data obtained from a concrete cable-stayed bridge and proved effective for the automatic detection of small stiffness reductions in single stay cables as well as the detachment of neoprene pads in anchoring devices, requiring only a small number of inexpensive sensors.

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Zhao, Yuxi; Zhang, Dawei; Shen, Shijun; Ueda, TamonAxial loading capacity of concrete-jacketed RC columns with pre- and post-corrosion damageStructural Concrete3/2016355-364Technical Papers

Kurzfassung

The main objective of this study is to investigate the effect of pre- and post-jacketing corrosion and loading damage on concrete-jacketed reinforced concrete (RC) columns under uniaxial loading and to develop a methodology for predicting the corresponding compressive strength. The pre- and post-damage involved preloading up to 50 % of the peak load of the core column, an electrochemical process to accelerate the migration of chlorides from an external electrolyte into the test columns and a wetting-drying cycle process with a controlled current to speed up the corrosion of the steel reinforcing bars in the test columns. Uniaxial loading tests were performed to determine the structural performance of the concrete-jacketed columns with and without corrosion damage. The failure mode and load-displacement and load-strain responses of the test columns were recorded, and the related mechanisms are discussed. A model capable of evaluating the compressive strength of unjacketed or jacketed RC columns with and without corrosion damage was then developed. The analytical approach considered the effect of reinforcement corrosion on the effective loadbearing area of the concrete and the confinement effect of the stirrups. The analytical results agree well with the experimental results, indicating the reliability and effectiveness of the models developed.

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Debernardi, Pier Giorgio; Taliano, MaurizioAn improvement to Eurocode 2 and fib Model Code 2010 methods for calculating crack width in RC structuresStructural Concrete3/2016365-376Technical Papers

Kurzfassung

The analysis of the mechanical behaviour of a reinforced concrete tie subjected to a monotonic loading in the stabilized cracking stage is performed here by way of a theoretical general model that considers the effect of the so-called Goto cracks (secondary cracks). It is shown, in particular, that the average bond stress along the transmission length depends not only on the concrete strength as assumed by the fib Model Code for Concrete Structures 2010, but also on reinforcement ratio and bar diameter. In this regard, tabulated theoretical values of the average bond stress are proposed as a function of the aforementioned parameters. Moreover, the secondary cracks reduce the effect of tension stiffening on the relative mean strain. On the basis of the main results obtained with the general model, some improvements are suggested for the calculation methods proposed by fib Model Code 2010 and Eurocode 2 concerning the average value of the bond stress and taking into account the influence of the secondary cracks on the mean deformation. An improved calculation method is therefore performed. Finally, the theoretical results of crack spacing and crack width obtained with the general and improved methods are compared with experimental data obtained from extensive research on RC ties.

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Visintin, Phillip; Oehlers, Deric J.Mechanics-based closed-form solutions for moment redistribution in RC beamsStructural Concrete3/2016377-389Technical Papers

Kurzfassung

When it comes to the efficient design of reinforced concrete beams and frames, moment redistribution is used to: reduce the absolute maximum magnitude of the moment in the critical region, equalize the critical moments on either side of interior columns and fully utilize the capacity of the non-critical regions of a member. Although important, historically, moment redistribution has proved to be difficult to quantify due to the complexity of quantifying hinge rotations. Although numerous empirical expressions exist for plastic hinge lengths, i.e. the length over which the ultimate curvature can be integrated in order to give hinge rotations, a comparison with a global dataset yields poor results. Using a recently developed mechanics-based moment-rotation approach, it is possible to quantify the moment-rotation characteristics of reinforced concrete hinges. In the tension region, the approach applies partial interaction theory directly to simulate the mechanisms associated with slip of the reinforcement relative to the surrounding concrete as cracks widen, whereas in the compression region, partial interaction shear-friction theory is used to describe the formation and failure of concrete softening wedges. It is shown how the moment-rotation approach explicitly allows for the size dependency. Furthermore, mechanics-based solutions for moment redistribution are then derived and it is shown how these can be simplified at the ultimate limit state for use in the design office.

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di Prisco, Marco; Martinelli, Paolo; Dozio, DanieleThe structural redistribution coefficient KRd: a numerical approach to its evaluationStructural Concrete3/2016390-407Technical Papers

Kurzfassung

Structures made of a material with a very high standard deviation, such as fibre-reinforced concrete, exhibit an exceptionally safe prediction of the maximum bearing capacity when this is derived from characteristic values identified by means of small specimens. This is emphasized when the structures are characterized by high redundancy. In this regard, two reference tests representing two extreme situations are considered: a) simply supported unnotched full-scale beams characterized by a statically determinate loading scheme and b) full-scale slabs on the ground characterized by a statically indeterminate loading scheme. The Italian standard and, more recently, the fib Model Code for Concrete Structures 2010 have introduced a coefficient (structural redistribution factor) that is able to take into account the reduced variability of mechanical bearing capacity when associated with a large volume involved in the failure process and/or when the structure is able to redistribute stresses significantly, thus favouring the average rather than the minimum strength. A numerical procedure taking into account the expected heterogeneity of the mechanical characteristics in the structure is introduced for the first time to evaluate the redistribution factor.

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Atta, Ahmad; Zaher, Fahmy; Etman, EmadStructural performance of continuous RC slabs strengthened in negative moment regions with a mineral-based compositeStructural Concrete3/2016408-424Technical Papers

Kurzfassung

An experimental programme was proposed and carried out to assess the effectiveness of the mineral-based composite (MBC) technique for the flexural strengthening of negative moment regions in continuous reinforced concrete slabs. In addition to the testing of the two reference specimens, the experimental programme included the testing of nine continuous RC slab specimens with different strengthening techniques, namely, using ordinary steel bars and MBC material. This experimental programme was conducted to study the failure modes, the load-deflection behaviour and the failure loads.
Furthermore, we present and describe a comparative study between the two strengthening techniques, namely, steel reinforcing bars with MBC or steel bars with epoxy mortar. Based on the experimental results presented, both strengthening techniques for continuous slabs are evidently efficient. In this study the measured results for the average crack spacing were compared with the limits stipulated in CEB-FIP code 1990 and the failure load calculations were extended with an analytical approach based on the ultimate theory for the failure load calculation. In conclusion, the results obtained from the analytical model are in agreement with the experimental results.

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D'Antino, Tommaso; Triantafillou, Thanasis C.Accuracy of design-oriented formulations for evaluating the flexural and shear capacities of FRP-strengthened RC beamsStructural Concrete3/2016425-442Technical Papers

Kurzfassung

Fibre-reinforced polymer (FRP) composites have been employed in the last few decades largely for the strengthening and seismic retrofitting of existing reinforced concrete (RC) structures. Several studies are available in the literature and different analytical models have been proposed for evaluating the FRP contribution in strengthened RC elements. This paper analyses the accuracy of analytical models widely used for evaluating the flexural and shear contributions provided by the FRP. Some of those models are included in design guidelines. In particular, the analytical models for evaluating the FRP strain at intermediate crack-induced debonding failure are analysed. The accuracy of each formulation is assessed comparing the analytical provisions with the experimental results collected from two databases, one for bending and one for shear. The results obtained show that most of the analytical flexural models achieve a good level of accuracy and only a few models provide inadequate results. A new formulation proposed for evaluating the FRP shear contribution is shown to be generally conservative, which comes at the expense of accuracy.

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Lee, Deuck Hang; Han, Sun-Jin; Kim, Kang SuDual potential capacity model for reinforced concrete beams subjected to shearStructural Concrete3/2016443-456Technical Papers

Kurzfassung

The shear resistance mechanisms of a reinforced concrete (RC) member with shear reinforcement can be divided into the contributions of the concrete and the shear reinforcement. The shear resistance mechanisms of concrete can be further divided into the shear resistance of the intact concrete in the compression zone, the aggregate interlock in the cracked tension zone and the dowel action of the longitudinal tension reinforcement. The shear demand curves and potential shear capacity curves for both tension and compression zones have been derived in this study, with the assumption that the shear failures of RC members are dominated by the flexural-shear strength. The shear capacity model was also proposed on this basis. In the proposed model, the crack width and the local stress increase in reinforcement were calculated based on the bond behaviour between the reinforcement and its surrounding concrete. Further, the crack concentration factor was introduced to consider the formation and propagation of the critical shear crack that developed from the flexural cracks. The results of a total of 1, 018 shear tests were collected and compared with the analysis results provided by the proposed model. It was demonstrated that the proposed model provides a good estimate of the shear strengths of RC beams.

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Ricker, Marcus; Siburg, CarstenPunching shear strength of flat slabs - critical review of Eurocode 2 and fib Model Code 2010 design provisionsStructural Concrete3/2016457-168Technical Papers

Kurzfassung

The fib Model Code for Concrete Structures 2010 introduces a new design concept for punching shear based on critical shear crack theory. This paper presents and provides the background to the design provisions for punching shear according to fib Model Code 2010, Eurocode 2 and the corresponding German National Annex to Eurocode 2. The different punching shear design provisions are critically reviewed by means of parameter studies and a comparison of the calculated resistances and test results. The safety levels of the code provisions are verified and the influence of the different punching parameters on the calculated resistances is examined in detail.

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Oviedo, Rodrigo; Gutiérrez, Sergio; Santa María, HernánExperimental evaluation of optimized strut-and-tie models for a dapped beamStructural Concrete3/2016469-480Technical Papers

Kurzfassung

Strut-and-tie modelling constitutes a powerful tool for the design of complex structural reinforced concrete elements. It has been proved numerically that strut-and-tie (ST) models obtained using structural optimization methods produce designs that are more efficient. However, to the best of the authors' knowledge, no experimental evidence of such results has been published. This paper presents experimental results for nine test specimens; five of them were designed using optimal models derived from a full homogenization structural optimization algorithm, and the remaining four using conventional ST models for comparison purposes. Although all specimens carry loads higher than the factored design load, specimens based on ST models derived using full homogenization with reinforcement parallel to the ties exhibit better structural performance regarding crack growth control, more ductile modes of failure and a greater increase in load capacity.

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Herfelt, Morten A.; Poulsen, Peter N.; Hoang, Linh C.; Jensen, Jesper F.Numerical limit analysis of keyed shear joints in concrete structuresStructural Concrete3/2016481-490Technical Papers

Kurzfassung

This paper concerns the shear capacity of keyed joints that are transversely reinforced with overlapping U-bar loops. It is known from experimental studies that the discontinuity of the transverse reinforcement affects the capacity and the failure mode. However, to the best knowledge of the authors, previous theoretical works and current design equations in standards do not account for this important effect. This paper introduces a detailed model based on finite element limit analysis to assess the effect of the discontinuous reinforcement. The model is based on the lower bound theorem and uses the modified Mohr-Coulomb yield criterion, which is formulated for second-order cone programming. The model provides a statically admissible stress field as well as the failure mode. Twenty-four different test specimens were modelled and the calculations compared with the experimental results. The results of the model show satisfactory agreement with the experimental observations. The model produces estimates of the shear capacity that are significantly better than those of the Eurocode 2 design equations.

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Zhou, Lin-Yun; Liu, ZhaoInvestigation of the buckling behaviour of thin-walled hollow concrete piersStructural Concrete3/2016491-501Technical Papers

Kurzfassung

Tall hollow concrete piers with high width-to-thickness ratios are commonly used in long-span box girder bridges. Such thin-walled structures present the possibility of failure due to local buckling. So, in common practice, diaphragms are usually included in hollow piers to improve the local stability; however, is that necessary? Although experimental research on the buckling behaviour of hollow piers has been conducted extensively, few analytical attempts have been performed to reveal the effects of the width-to-thickness ratio on local buckling behaviour. To this end, an analytical model has been proposed to investigate the local buckling behaviour of hollow piers. Following the Ritz-Timoshenko method, an analytical formula for critical local buckling stress has been developed and verified to have good accuracy compared with finite element analyses. Based on the buckling failure mode of a hollow pier with a slenderness ratio > 6, it can be reasonably postulated that the strength of the hollow pier will be unaffected by local compression flange buckling when the wall width-to-thickness ratio is < 24, and it is entirely unnecessary to include diaphragms in hollow piers for stability. Additionally, it is equally interesting that the critical width-to-thickness ratio of a hollow pier with a slenderness ratio > 4 derived using the proposed model is the same as the value given by the current AASHTO-LRFD Bridge Design Specifications.

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Buitrago, Manuel; Adam, Jose M.; Calderón, Pedro A.; Moragues, Juan J.; Alvarado, Yezid A.Estimating loads on shores during the construction of RC building structuresStructural Concrete3/2016502-512Technical Papers

Kurzfassung

When constructing reinforced concrete (RC) building structures, knowing the loads to which the shoring system will be subjected during the entire process is one of the key aspects for ensuring safety during the work. Although various simplified methods of estimating the load transmission between shores and slabs during construction have been proposed to date, none of these methods can estimate the loads on individual shores during the different construction phases. This paper proposes a calculation method that allows the loads on individual shores to be calculated for each construction phase without having to resort to the use of advanced software. The proposal was validated by comparison with the results obtained from two actual buildings under construction and represents a step forward in the construction of RC building structures, as it is the first method that offers the possibility of estimating the loads acting on each shore during all the construction phases.

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fib-news: Structural Concrete 3/2016Structural Concrete3/2016513-519fib-news

Kurzfassung

Technical Council meets in Madrid
2017 AAYE
Redefining fib Commission 3
fib Bulletin 78
ICCS16
Short notes
Congresses and symposia

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Inhalt: UnternehmerBrief Bauwirtschaft 3/2016UnternehmerBrief Bauwirtschaft3/2016Inhalt

Kurzfassung

Keine Kurzfassung verfügbar.

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Schalk, GüntherVon Smart homes und Wintergärten...UnternehmerBrief Bauwirtschaft3/20161Editorials

Kurzfassung

Keine Kurzfassung verfügbar.

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Ernst & Sohn (Hrsg.)Gesamtausgabe UBB 3/2016UnternehmerBrief Bauwirtschaft3/20161-24Gesamtausgabe

Kurzfassung

Komplette Monatsausgabe

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Kurz informiert: UnternehmerBrief Bauwirtschaft 3/2016UnternehmerBrief Bauwirtschaft3/20162Kurz informiert

Kurzfassung

Gutachten des Bundesrechnungshofs stärkt BVMB den Rücken
“Serielles Bauen” soll Nachhaltigkeit im Wohnungsbau sichern
Gute Stimmung in der Planungsbranche

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Karl, Christian K.Bauen in Vietnam: Gute Chancen für deutsches Know-howUnternehmerBrief Bauwirtschaft3/20163-8Berichte

Kurzfassung

In Asien ist nicht nur China als ein potenzielles Marktwachstumsland für ausländische Investoren interessant. Auch Vietnam entwickelt sich von einem einst durch Krieg verwüsteten Land zu einer wirtschaftlichen Erfolgsgeschichte Asiens. Seit der Wirtschaftserneuerungsreform “Doi moi” im Jahr 1986 hat Vietnam nach China die am zweitschnellsten wachsende Wirtschaft. Aktuell sind über 250 deutsche Firmen auf dem vietnamesischen Markt aktiv. Geringe Lohnkosten, eine sehr junge Bevölkerung und die relativ stabile politische Lage machen Vietnam zu einem attraktiven Investitionsstandort. Dieser UBB-Beitrag, basierend auf einer Studie aus dem Bereich Bautechnik & Baudidaktik der Universität Duisburg-Essen, gibt einen Überblick über die konjunkturelle Lage Vietnams. Außerdem wird die Entwicklung der Bauwirtschaft mit ihren verschiedenen Sparten vorgestellt sowie zukünftige Potenziale in der vietnamesischen Bauindustrie aufgezeigt.

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Talebitari, Burkhard"Wir wollen den Mittelstand gern dabei haben"UnternehmerBrief Bauwirtschaft3/20169-10Berichte

Kurzfassung

Gute Stimmung bei den Mitgliedsunternehmen - selbst wenn man sich informell umhörte, ca. 550 Gäste und Verkehrsminister Alexander Dobrindt als Festredner des Abends. Dass es Probleme zwischen dem Mittelstand und dem Verkehrsministerium gibt, ist dabei weniger überraschend als der Umstand, dass viele von ihnen altbekannt sind: Planungsprozesse besonders im Bereich Schienenwege und Bundesfernstraßenbau, ÖPP, Bauvertragsrecht, Nachwuchs- und Fachkräftegewinnung, das Erbschaftssteuergesetz, Neustart des sozialen Wohnungsbaus nebst Schaffung steuerlicher Anreize für Investoren ...

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Schneider, Christoph Thomas; Schonert, KatharinaVertrauen und Vorsicht: Spannung bei der PersonalauswahlUnternehmerBrief Bauwirtschaft3/201611-13Berichte

Kurzfassung

Insbesondere im Mittelstand müssen Fach- und Führungskräfte bereits nach kurzer Einarbeitungszeit die erwartete - und von den Bewerbern ja ebenso in Aussicht gestellte - Leistung erbringen. Dabei bauen die Erwartungen des Bauunternehmens auf den Angaben des Bewerbers auf. Aber stimmen diese? Was, wenn nicht? Und wie erkennt man falsche Angaben? Der UBB gibt Tipps für die Sichtung und Auswahl von Bewerbern.

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Schalk, GüntherAktuelles aus der RechtsprechungUnternehmerBrief Bauwirtschaft3/201614-15Berichte

Kurzfassung

Bauzeitverlängerung auch bei “normaler” Witterung?
BAG stellt klar: Zeugnis muss nicht “gut” oder “sehr gut” sein
Hat die Baufirma eine Verkehrssicherungspflicht?

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UBB-SteuertrendsUnternehmerBrief Bauwirtschaft3/201616Berichte

Kurzfassung

Keine Kurzfassung verfügbar.

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Bauleistung: Vertrauensschutz?UnternehmerBrief Bauwirtschaft3/201616Berichte

Kurzfassung

Im Chaos zur Steuerschuldnerschaft bei Bauleistungen können Baufirmen einen entscheidenden Etappensieg feiern. Der Bundesfinanzhof hat entschieden, dass ernstliche Zweifel an der Rechtmäßigkeit des § 27 Abs. 19 UStG bestehen. Wir erklären Ihnen, was das bedeutet.

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Neue GestaltungsüberlegungenUnternehmerBrief Bauwirtschaft3/201617Berichte

Kurzfassung

Trägt eine Kapitalgesellschaft Kosten für die Tochtergesellschaft, stellt sich die Frage, ob die Muttergesellschaft diese Kosten als sofort abziehbare Betriebsausgaben behandeln darf oder ob sie diese Kostenübernahme als verdeckte Einlage behandeln und die Kosten deshalb auf die Beteiligung aktivieren muss. In der Praxis haben Mutter- und Tochtergesellschaft hier interessante Gestaltungsmöglichkeiten.

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