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Ignatiadis, Anett; Fingerloos, Frank; Hegger, Josef; Teworte, Frederik Eurocode 2 - analysis of National Annexes Structural Concrete 1/2015 3-16 Technical Papers

Kurzfassung

Eurocode 2 consists of four parts that have to be applied in conjunction with the respective National Annexes of the CEN member states. The National Annexes were introduced, in particular, to maintain national safety levels and to account for regional aspects in the different states.
The CEN (European Committee for Standardization) will revise and extend all structural Eurocodes by 2018. As part of that process, two main objectives for revising Eurocodes have been formulated: a reduction in the number of Nationally Determined Parameters (NDP) and improving the “ease of use”.
In order to reduce the number of NDP, improve the ease of use and allow for further harmonization without changing the main structure and the design models of Eurocode 2, the National Annexes of EN 1992-1-1 for the different CEN member states have been compared and analysed. Furthermore, the analysis of the National Annexes may help to identify some main aspects for the revision of Eurocode 2.
This paper summarizes the analysis of the National annexes of EN 1992-1-1 and makes first proposals for further harmonization.

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Wang, Lijie; Caspeele, Robby; Van Coile, Ruben; Taerwe, Luc Extension of tabulated design parameters for rectangular columns exposed to fire taking into account second-order effects and various fire models Structural Concrete 1/2015 17-35 Technical Papers

Kurzfassung

Fire, as one of the most severe load conditions, has an important impact on concrete structures. Not only does a fire affect the material strength, it affects structural stiffness and stability as well. A concrete column, compared with other structural members, in most cases has to cope with both vertical forces and bending moments transferred by slabs and beams. Consequently, it is essential to find a reliable and practical way of establishing interaction curves for the overall structural behaviour of concrete columns subjected to fire. In this paper, a cross-sectional calculation method based on the material models of Eurocode 2 is explained and adopted in order to calculate interaction curves for a typical rectangular column exposed to the ISO 834 standard fire. Subsequently, an iterative approach is introduced to develop interaction curves taking into account second-order effects in the case of all the four faces of a column exposed to fire. The maximum permissible slenderness ratios for columns in different fire durations are obtained and compared with Eurocode 2 provisions. Finally, this method is used to calculate the maximum permissible slenderness ratios for columns exposed to hydrocarbon and natural fires.

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Duplan, François; Abou-Chakra, Ariane; Turatsinze, Anaclet; Escadeillas, Gilles; Brûlé, Stéphane; Javelaud, Emmanuel; Massé, Frédéric On the use of European and American building codes with low-strength mortars Structural Concrete 1/2015 36-44 Technical Papers

Kurzfassung

The standard European building specifications, grouped in a nine-volume Eurocode, describe different approaches for determining the properties of commonly used building materials such as steel, aluminium, concrete, etc.
The American Concrete Institute (ACI) also offers different reports concerning concrete structures (ACI 318R), lightweight concrete (ACI 213R) and the long-term mechanical behaviour (ACI 209R) of concrete. Those reports, used as building codes, are applicable when the properties and composition of the material respect various criteria.
All those materials that do not meet the scope criteria of Eurocode 2 or ACI reports because of their composition, property values or application cannot be used in the design of structures with those building codes. Regarding cement-based materials, concretes and mortars whose compressive strength is lower than the minima might not be useful for structures; however, they present an interesting potential for applications such as infrastructure materials, slabs-on-ground, etc. When designing structures and infrastructures in those materials, the accuracy of any formula offered by those building codes should be checked before being used.
This article compares experimental measurements and predictive formulas for the engineering properties (compressive and tensile strengths, modulus of elasticity). The results show that the addition of specific aggregates with low stiffness and strength modifies the relation between those engineering properties, thus reducing the accuracy of some of the predictive formulas suggested in ACI reports or Eurocodes.

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Cairns, John Bond and anchorage of embedded steel reinforcement in fib Model Code 2010 Structural Concrete 1/2015 45-55 Technical Papers

Kurzfassung

This paper describes the changes to design provisions for embedded steel reinforcement in the fib Model Code for Concrete Structures 2010. The changes introduce new coefficients for steel grade and clear spacing between bars, and extend the range of concrete strengths covered. The way in which the contribution of hooks or anchorages is calculated has been revised and the contribution of end bearing to laps and anchorages of compression bars is recognized. The revised rules represent a move away from a distinction between laps and anchorages per se towards a distinction based on the presence or absence of transverse pressure perpendicular to the bar axis within the bond length. The benefits of staggering laps with only a proportion of bars lapped at a section are also reviewed. Finally, the potential impact of lap and anchorage performance on structural robustness is discussed, and it is concluded that this can only be achieved if bar yield precedes splitting mode bond failures.

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Prince, M. John Robert; Singh, Bhupinder Bond behaviour of normal- and high-strength recycled aggregate concrete Structural Concrete 1/2015 56-70 Technical Papers

Kurzfassung

The effect of concrete grade on the bond between 12 mm diameter deformed steel bars and recycled aggregate concrete (RAC) has been investigated with the help of 45 pullout tests with concentric rebar placement for coarse recycled concrete aggregate (RCA) replacement levels of 25, 50, 75 and 100%. For all the three concrete grades, the measured bond-slip relationships indicate similar mechanisms of bond resistance in the RAC and the natural aggregate (NA) concrete. The most accurate and least conservative predictions of the measured bond strengths were obtained from the local bond-slip model in the fib Model Code for Concrete Structures 2010. Bond strength normalized to fc(3/4) resulted in an improved match with test data and increased with an increase in the RCA replacement levels and decreased with an increase in compressive strength. An attempt to explain this behaviour has been sought in terms of brittleness index, an analogous parameter from rock mechanics. An empirical bond stress versus slip relationship has been proposed for the 12 mm diameter bar and it is conservatively suggested that similar anchorage lengths for this bar in all three concrete grades can be adopted for the RAC and the NA concretes.

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Mihaylov, Boyan Five-spring model for complete shear behaviour of deep beams Structural Concrete 1/2015 71-83 Technical Papers

Kurzfassung

This paper presents a five-spring model capable of predicting the complete pre- and post-peak shear behaviour of deep beams. The model stems from a two-parameter kinematic theory (2PKT) for the shear strength and displacement capacity of deep beams under single curvature. Four of the springs of the model represent the shear resistance mechanisms of the beam, while the fifth spring models the flexural behaviour. The model predicts not only the load-displacement response, but also the deformation patterns of the beam and how these patterns change with increasing load. Validation studies are performed by using 28 tests from the literature, showing excellent results. The model is used to interpret the tests and to draw conclusions about the behaviour of deep beams. It is shown that shear strength variations of up to 60 % between nominally identical specimens can be caused by variations in the path of the critical shear cracks. It is also demonstrated that loss of bond of large reinforcing bars increases the shear capacity of deep beams. Finally, the five-spring model is shown to predict the post-peak shear behaviour effectively, which is important for the analysis of structures under extreme loading.

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Zhou, Lin-Yun; Liu, Zhao; He, Zhi-Qi Further investigation of transverse stresses and bursting forces in post-tensioned anchorage zones Structural Concrete 1/2015 84-92 Technical Papers

Kurzfassung

In the post-tensioned anchorage zone, the load transfer path of an anchor force can be visualized by an infinite number of isostatic lines of compression (ILCs). The method was initially proposed by Guyon and recently attracted significant interest from a number of researchers. Based on the work of these predecessors, an updated mathematical model has been proposed in order to analyse the bursting forces and the distribution of transverse stresses in the anchorage zone. Compared with the results of a finite element analysis, the updated equations are more accurate than the previous ones. Based on the observation that the sixth-order polynomial expression is better than the fourth-order one, as far as the solution of bursting stresses is concerned, it can be reasonably postulated that a de facto function of the ILCs must exist. Additionally, it is equally interesting that the bursting forces derived with the updated analytical model are the same as those obtained with the formula in the current AASHTO-LRFD Bridge Design Specifications based on numerical stress analyses.

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Amin, Ali; Foster, Stephen J.; Muttoni, Aurelio Derivation of the &sgr;-w relationship for SFRC from prism bending tests Structural Concrete 1/2015 93-105 Technical Papers

Kurzfassung

The material characterization of steel fibre-reinforced concrete (SFRC), which is required for its implementation in design codes, should be based on nominal properties that describe its post-cracking strength in tension. In the case of brittle and quasi-brittle materials, such as concrete, the tensile parameters are often derived indirectly. However, for materials with more ductility, such as SFRC, there is conjecture as to whether or not an indirect measure may be used to establish the stress versus crack opening displacement relationship, such as the use of a three- or four-point prism test combined with an inverse analysis. In this paper a simple and efficient inverse analysis technique is developed and shown to compare well with data obtained from direct tension tests. Furthermore, the methodology proposed by the fib Model Code for Concrete Structures 2010 has been investigated and recommendations made to improve its accuracy.

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Scholzen, Alexander; Chudoba, Rostislav; Hegger, Josef Thin-walled shell structures made of textile-reinforced concrete - Part I: Structural design and construction Structural Concrete 1/2015 106-114 Technical Papers

Kurzfassung

At RWTH Aachen University recently, a pavilion was constructed with a roof shell made of textile-reinforced concrete (TRC), a composite material consisting of a fine-grained concrete and high-strength, non-corroding textile reinforcement in the form of carbon fibres. The thin-walled TRC shell structure demonstrates impressively the loadbearing capacity of this innovative composite material. The present paper discusses the practical issues concerning the construction, such as the fabrication of the TRC shells using shotcrete, the concepts developed for the arrangement of the textile reinforcement and the erection of the shells on top of the precast concrete columns. The issues concerning the design, assessment and numerical simulation of the loadbearing behaviour of TRC shells are presented in the companion paper (Part II).

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Scholzen, Alexander; Chudoba, Rostislav; Hegger, Josef Thin-walled shell structures made of textile-reinforced concrete - Part II: Experimental characterization, ultimate limit state assessment and numerical simulation Structural Concrete 1/2015 115-124 Technical Papers

Kurzfassung

The present paper describes a design approach for textile-reinforced concrete (TRC) shells which reflects the interaction between normal forces and bending moments based on the cross-sectional strength characteristics of the material determined experimentally. The influence of oblique loading on the composite strength of TRC elements with flexible reinforcement is included in a normalized interaction diagram for combined loading. As an example, the design approach is applied to the ultimate limit state assessment of a TRC shell in double curvature. Furthermore, the general applicability of the design approach is discussed in the light of the non-linear loadbearing behaviour of TRC. Due to its strain-hardening tensile response, stress redistributions within the shell result in loadbearing reserves. Details of the structural design and production solutions developed and applied during the realization of the TRC shell structure are described in the companion paper (Part I).

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Jung, Bastian; Morgenthal, Guido; Xu, Dong; Schröter, Hendrik Quality assessment of material models for reinforced concrete flexural members Structural Concrete 1/2015 125-136 Technical Papers

Kurzfassung

Non-linear constitutive models for concrete in compression are frequently defined in design codes. The engineer generally uses either the linear (in SLS) or non-linear (in ULS) compression model. However, a large variety of different approaches exists for describing the behaviour of the cracked concrete tension zone, and the selection of a corresponding model is usually based on qualitative engineering judgement. The aim of this paper is to assess the prediction quality of several concrete material models in order to provide a quantitative model selection. Therefore, uncertainty analysis is applied in order to investigate the model and parameter uncertainty in the bending stiffness prognosis for flexural members. The total uncertainty is converted into a prognosis model quality that allows a quantitative comparison between the material models considered. The consideration of the reinforced concrete in tension is based on the characterization of the tension stiffening effect, which describes the cracking in an average sense. In the interest of the practical applicability of the models considered, even for large structures, no discrete crack simulations based on fracture mechanics are considered. Finally, the assessment identifies that the prediction quality depends on the loading level and, furthermore, the quality across the models can be quantitatively similar as well as diverse.

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Holomek, Josef; Bajer, Miroslav; Barnat, Jan; Schmid, Pavel Design of composite slabs with prepressed embossments using small-scale tests Structural Concrete 1/2015 137-148 Technical Papers

Kurzfassung

The loadbearing capacity of steel-concrete composite slabs using thin-walled steel sheeting with prepressed embossments is in most cases determined by their resistance in longitudinal shear. The design of composite slabs still requires full-scale laboratory bending tests to be performed. Small-scale shear tests cannot include all of the influences affecting the bent slab. However, by using an appropriate procedure, the shear characteristics obtained from such tests can be used to determine the bending capacity of the slab. Two such procedures are compared in this paper.
End restraints effectively increase the loadbearing capacity of the composite slabs. Two different types of easily assembled additional end constraints are also tested and compared in this paper. Small-scale tests are used to obtain their shear bearing characteristics and to predict the loadbearing capacity of bent slabs using these restraints.

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fib-news: Structural Concrete 1/2015 Structural Concrete 1/2015 149-157 fib-news

Kurzfassung

The fib in Russia: new standards; Worldwide representation at ACF 2014; DISC2014: the past and the future; Old for new: Penang Bridge; A venerable institute turns 80; JPEE2014 in Lisbon; fib MC2010 course in Brazil; Short notes; Nigel Priestley † 1943-2014; Congresses and symposia; Acknowledgement

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Inhalt: UnternehmerBrief Bauwirtschaft 1/2015 UnternehmerBrief Bauwirtschaft 1/2015 Inhalt

Kurzfassung

Keine Kurzfassung verfügbar.

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UBB-Steuertipps spezial. Betriebsprüfung: Hilfe, der Prüfer des Finanzamts kommt ... UnternehmerBrief Bauwirtschaft 1/2015 E1-E4 Berichte

Kurzfassung

Wenn sich ein Prüfer des Finanzamts für eine Betriebs-, Umsatzsteuer- oder Lohnsteuerprüfung anmeldet, herrscht in den meisten Baubetrieben höchste Alarmstufe. Denn vor allem in der Baubranche sind die Prüfer besonders streng. In unserem Sonderteil zum Jahresstart zeigt Ihnen der UBB, was die Unternehmensführung oft gar nicht weiß, was der Prüfer alles über Ihren Betrieb weiß. Wir geben Ihnen einen Verhaltensknigge an die Hand, wie Sie bestimmte “klassische” Situationen richtig interpretieren, wie Sie sich entsprechend “richtig” verhalten und verraten Ihnen typische Prüfungspunkte, die bei Betriebsprüfungen immer wieder besonders relevant werden.

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Jahresinhaltsverzeichnis 2014 UnternehmerBrief Bauwirtschaft 1/2015 Jahresinhaltsverzeichnis

Kurzfassung

Keine Kurzfassung verfügbar.

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Schalk, Günther Neustart in das Bau-Jahr 2015: Weiter rauer Wind in der Bauwirtschaft ... UnternehmerBrief Bauwirtschaft 1/2015 1 Editorials

Kurzfassung

Keine Kurzfassung verfügbar.

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Kurz informiert: UnternehmerBrief Bauwirtschaft 1/2015 UnternehmerBrief Bauwirtschaft 1/2015 2 Kurz informiert

Kurzfassung

Herbstbelebung 2014 ausgefallen. Auftragspolster der Baufirmen schmilzt weiter ab
Anlagevermögen rückläufig. “Wertverlust der deutschen Straßen stoppen!”
Neue Regelung. Mittelständler müssen zum Energie-“TÜV”

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Schalk, Günther Öffentlich-private Partnerschaften - Sparmodell oder Trugschluss? UnternehmerBrief Bauwirtschaft 1/2015 3 Berichte

Kurzfassung

ÖPP-Projekte werden in der Bauwirtschaft durchaus kontrovers diskutiert. ÖPP (“Öffentlich-private Partnerschaften”, auch: “PPP”) sind eine vertraglich geregelte Zusammenarbeit zwischen öffentlicher Hand und Unternehmen der Privatwirtschaft, die eine außergewöhnliche Form der Arbeitsteilung regelt: Der “private” Partner, in der Regel ein Zusammenschluss aus Baufirmen, stellt das Bauvorhaben in eigener Verantwortung her. Das soll in erster Linie Effizienz garantieren. Der öffentliche Auftraggeber hofft darauf, dass eine Projektrealisierung in ÖPP-Form die angespannten öffentlichen Haushalte entlastet, da der private Partner letztlich die Vorfinanzierung stemmt. Seine Vergütung erhält er zum Beispiel im Wege einer Konzession.

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Kulle, Bernward ÖPP: Chance für den Mittelstand? UnternehmerBrief Bauwirtschaft 1/2015 4-6 Berichte

Kurzfassung

Öffentlich-private Partnerschaften (ÖPP) sind eine Chance für den Mittelstand, langfristig sichere Verträge mit der öffentlichen Hand einzugehen. Schon heute ist über die Hälfte der deutschen Hochbau-ÖPP-Projekte von Mittelständlern abgeschlossen. Die Marktanteile zeigen, dass der Mittelstand von ÖPP in Deutschland profitierten kann.

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Iding, Andreas ÖPP - Pragmatismus ist gefragt!! UnternehmerBrief Bauwirtschaft 1/2015 7-9 Berichte

Kurzfassung

Die alternative Beschaffungsvariante ÖPP muss sich in den letzten Jahren wie ein geprügelter Hund vorgekommen sein. Im Zuge der Finanzkrise und deren Ausläufer erfuhr eine sich zunächst stetig gut entwickelnde Organisationsform einen Sturm der Entrüstung, der teilweise mit medialer Begleitung über sie niederging. Nachläufer sind auch heute immer noch wahrnehmbar. Nicht wenige stimmten schon in den Abgesang ein, obwohl ÖPPs noch gar nicht im Vergleich zu anderen Ländern sich etabliert geschweige denn abgehoben hatten. In den letzten Monaten hat sich die Stimmungslage ein wenig geändert. Sehr subtil zwar, die Indikatoren für diesen gefühlten Wandel sind jedoch im Zusammenhang gesehen durchaus repräsentativ. Sprichwörtlich ist es wohl nicht die Ruhe vor, sondern vielmehr die Ruhe nach dem Sturm. Eine gute Zeit, um nach vorn zu schauen!

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GmbH-Gesellschafter: Weniger Steuer für Dienstwagennutzung UnternehmerBrief Bauwirtschaft 1/2015 10 Berichte

Kurzfassung

Stößt ein Prüfer des Finanzamts bei der Prüfung einer GmbH auf einen Passus zum Dienstwagen im Arbeitsvertrag eines GmbH-Gesellschafter-Geschäftsführers und stellt fest, dass statt eines Mitteklassewagens ein teurerer Dienstwagen gefahren wird, unterstellt er schnell eine verdeckte Gewinnausschüttung. Sagt der Prüfer A, muss er aber auch B sagen. Denn unterstellt der Prüfer eine Dienstwagengestellung aus gesellschaftsrechtlichen Gründen, hat das nach einem Urteil des Bundesfinanzhofs Auswirkungen auf die Höhe der ans Finanzamt abzuführenden Umsatzsteuer für die Dienstwagengestellung.

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Weniger Arbeitsunfälle am Bau UnternehmerBrief Bauwirtschaft 1/2015 11 Berichte

Kurzfassung

Die Zahl der Arbeitsunfälle auf deutschen Baustellen ist laut Berufsgenossenschaft Bauwirtschaft (BG BAU) weiter zurückgegangen. Genau 105.248 Beschäftigte verunglückten 2013 bei der Arbeit. Das sind fast 4.000 weniger als im Vorjahr und beinahe 50.000 weniger als noch vor zehn Jahren. Zu dieser erfreulichen Entwicklung beigetragen haben laut BG BAU gezielte Initiativen zur Prävention und ein gewachsenes Bewusstsein für einen verbesserten Arbeitsschutz in den Unternehmen.

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Sindermann, Thomas; Mechnig, Michael Ist die gerichtsfeste Baustellendokumentation eine Utopie? Ansprüche aus Bauablaufstörungen setzen konkrete Nachweise voraus UnternehmerBrief Bauwirtschaft 1/2015 12-14 Berichte

Kurzfassung

Spätestens, wenn eine Baufirma vor Gericht versucht, Ansprüche wegen gestörten Bauablaufs oder Mehrvergütungsansprüche wegen geänderter oder zusätzlicher Leistungen geltend zu machen, wird den Teilnehmern nicht selten schmerzlich bewusst: Dokumentation spielt eine entscheidende Rolle. Das OLG Köln (Urteil vom 28.01.2014 - 24 U 199/12) etwa hat im Januar 2014 unter Bezugnahme auf Grundsatzentscheidungen des BGH aus den Jahren 1986, 2002 und 2005 vor Augen geführt, welche Maßstäbe die Rechtsprechung an die Darlegung von Ansprüchen aus Bauablaufstörungen stellt. Neben der “adäquat-kausalen Nachweisführung” und einer “bauablaufbezogenen Darstellung” wird auch der “Baustellendokumentation” eine zentrale Bedeutung beigemessen. Eine unzureichende Dokumentation geht regelmäßig zu Lasten des Auftragnehmers.

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Englert, Florian Aktuelles aus der Rechtsprechung UnternehmerBrief Bauwirtschaft 1/2015 15-16 Berichte

Kurzfassung

Nachtragskampf: Baufirma darf in engen Grenzen die Leistung verweigern!
Komplettheitsklauseln: komplett als AGB wirksam!

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