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Nüsse, Gregor Developing a high quality sandwich-panel envelope-system for office and multi-storey buildings (P 977) Steel Construction 4/2016 372 News

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Keine Kurzfassung verfügbar.

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Announcements: Steel Construction 4/2016 Steel Construction 4/2016 372 Announcements

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Keine Kurzfassung verfügbar.

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Contents: Structural Concrete 4/2016 Structural Concrete 4/2016 Contents

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Keine Kurzfassung verfügbar.

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Doniak, Íria LíLcia Oliva Local and global integration for a sustainable future Structural Concrete 4/2016 520-521 Editorials

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Keine Kurzfassung verfügbar.

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von Greve-Dierfeld, Stefanie; Gehlen, Christoph Performance-based durability design, carbonation part 2 - Classification of concrete Structural Concrete 4/2016 523-532 Technical Papers

Kurzfassung

At present, prescriptive regulations with regard to concrete cover and composition are applied to provide sufficient durability of reinforced concrete members under exposure conditions with different degrees of severity. In view of current knowledge on deterioration mechanisms and their modelling, it is planned to change from these deemed-to-satisfy specifications to a performance-based design approach in future standards. In such specifications, concrete durability design is based on the statistically characterized performance of concrete, determined in standardized tests with respect to defined classes of concretes with similar performance.
This paper presents the results of a study in which concrete mixes were tested and analysed with respect to their carbonation resistance. Compositions with similar performance are grouped into carbonation resistance classes. These classes are described statistically and requirements for performance testing are given. In addition, composition requirements are introduced in order to determine concrete performance depending on mix composition prescriptively. Finally, an example is given for the assessment of concrete performance with regard to carbonation.
This work was carried out at the request of JWG under CEN TC 250/SC2 and CEN TC 104/SC1 as an input and starting point for the ongoing committee work to implement the methodology from the fib Model Code for Concrete Structures 2010 in the next generation (2021) of European concrete standards.

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Andrade, Carmen; Cesetti, Alessandro; Mancini, Giuseppe; Tondolo, Francesco Estimating corrosion attack in reinforced concrete by means of crack opening Structural Concrete 4/2016 533-540 Technical Papers

Kurzfassung

The corrosion of reinforcement in concrete is the most common degradation phenomenon of reinforced concrete structures. Reinforced concrete elements subjected to corrosion generally crack due to the expansive nature of oxides. One very important task is estimating the corrosion level using a non-destructive method in order to establish both the actual safety of the structure and a priority intervention plan.
Many researchers have studied the relationship between the corrosion phenomenon and the corresponding crack openings and their evolution; several statistical analyses, based on test data from experimental campaigns under a wide range of test conditions, are available.
The present work attempts to contribute to finding a relationship between the crack opening and the amount of corrosion induced in the reinforcing bars. The result of the analysis is that only a reduced number of tests can be used to establish an empirical model based on a reliable set of test data. A simple relationship between crack opening and corrosion penetration is not recommended, due to the different parameters that are able to influence this correlation. Therefore, two fundamental parameters, the ratio of the concrete cover to the rebar diameter and the concrete strength, have also been considered. The considerations made regarding these parameter test results have been rearranged and the result is a formulation that shows reduced scatter.

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Hussein, Luaay; Amleh, Lamya Analytical modelling of bond stress at steel-concrete interface due to corrosion Structural Concrete 4/2016 541-552 Technical Papers

Kurzfassung

An analytical model is proposed for bond stresses at the corroded steel-concrete interface in reinforced concrete. The concrete around the corroded bar is modelled as a thick-walled cylinder - consisting of an inner cylinder of an anisotropic material and an outer cylinder made of an isotropic material - subjected to internal pressure exerted by the growth of corrosion products on the concrete wall at the interface. A frictional model is used to combine the action of confining pressure due to radial pressure produced by principal bar ribs and the pressure resulting from expansion of corrosion products. The analysis results using the proposed model show good agreement with the experimental results of several researchers.

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Zych, Mariusz Modification of the simplified method of crack control included in EN 1992-3 Structural Concrete 4/2016 553-563 Technical Papers

Kurzfassung

The methods of crack control for liquid-retaining RC tank walls are analysed taking into account external load (EN 1992-1-1) and imposed strain occurring at the construction stage (EN 1992-3), i.e. during the concrete-hardening period. The convergence ranges of the simplified method of crack control included in EN 1992-3 and the detailed calculation methods included in EN 1992-1-1 and EN 1992-3 are defined. Apart from the compatibility areas, overestimation of the acceptable reinforcing bar diameter &phgr;s*, illustrated in Fig. 7.103N in EN 1992-3, was proved. Coefficients k&phgr;1 and k&phgr;2 are defined, which enable the calculation of the acceptable reinforcing bar diameter &phgr;s* in order to obtain the values complying with the direct calculations. For practical purposes, graphs have been plotted to facilitate the definition of coefficients k&phgr;1 and k&phgr;2 without performing direct calculations. On the basis of the analyses performed and the relations proposed, it can be concluded that there is a possibility or a necessity to increase or decrease the acceptable reinforcing bar diameter &phgr;s* depending on the concrete mechanical properties and geometrical properties of an RC tank wall.

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Tian, He; Zhang, Y. X.; Yang, Chunhui; Ding, Yining Recent advances in experimental studies of the mechanical behaviour of natural fibre-reinforced cementitious composites Structural Concrete 4/2016 564-575 Technical Papers

Kurzfassung

This paper presents a review of recent research and development work involving natural fibre-reinforced concrete (NFRC). The recent developments in NFRC reinforced with different types of natural fibre, such as sisal fibre, bagasse fibre, coir fibre, banana fibre, eucalyptus fibre, flax fibre, jute fibre and pinus radiate fibre, are covered. Natural fibres and their modification methods are introduced first and the development history of natural fibre-reinforced concrete and the relevant research into the mechanical behaviour of NFRC in both the short- and long-term are reviewed. The applications of NFRC are also summarized.

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irgulis, Giedrius; vec, Old ich; Geiker, Mette Rica; Cwirzen, Andrzej; Kanstad, Terje Variation in fibre volume and orientation in walls: experimental and numerical investigations Structural Concrete 4/2016 576-587 Technical Papers

Kurzfassung

Previous research with fibre-reinforced slab elements has shown that the surface roughness of formwork and the presence of rebars affect fibre orientation and fibre volume distribution. This paper discusses the orientation and volume distribution of steel fibres in wall elements cast from a single point. Aparticular focus of the work was the effect of formwork tie ba rs on fibre orientation and distribution. Numerical simulations and X-ray computed tomography were appliedto quantify the fibre orientation and distribution, and the mechanical performance was determined using three-point bending tests on sawn beams. The Thorenfeldt model (applied in the Norwegian proposal for the new fibre-reinforced concrete guideline) was used to estimate the residual flexural tensile strength based on fibre orientation and distribution.
The simulation results show that the fibre orientation can be related to the flow pattern. The results indicate a large variation in fibre orientation, which was confirmedexperimentally. The fibre volume distribution was mostly uniform, except for an area with fewer fibres at the casting point. The large variation in fibre orientation was reflected in a large variation in residual flexural tensile strengths. Weak zones due to anisotropic fibre orientation, caused by formwork tie bars, were observed.

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di Prisco, Marco; Martinelli, Paolo; Parmentier, Benoit On the reliability of the design approach for FRC structures according to fib Model Code 2010: the case of elevated slabs Structural Concrete 4/2016 588-602 Technical Papers

Kurzfassung

This paper focuses on the reliability of the design approach proposed in the fib Model Code for Concrete Structures 2010 for estimating the ultimate capacity of fibre-reinforced concrete (FRC) elevated slabs on the basis of different tests for material characterization. The fracture properties of the material are determined through three-point bending tests on notched beams and through double edge wedge splitting (DEWS) tests carried out on cylinders cored in the full-size test structure. As a case study, an FRC elevated flat slab 0.2 m thick is considered which consists of nine bays (panels) measuring 6 × 6 m (overall size 18.3 × 18.3 m) and is supported by 16 circular concrete columns. The ultimate bearing capacity of the slab determined experimentally is compared with the design value predicted by means of a procedure based on limit analysis following fib Model Code 2010. The results show that the method proposed in fib Model Code 2010 using the characteristic values and the classification is reliable. Even if the tests are affected by a significant standard deviation and the two experimental campaigns with three-point bending tests give a significant difference between class “5c” and class “3e”, the structural test results in a loadbearing capacity that is always larger than the predicted one, which considers a safety coefficient for the material &ggr;F = 1.5.

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Simões, João T.; Bujnak, Jan; Ruiz, Miguel Fernández; Muttoni, Aurelio Punching shear tests on compact footings with uniform soil pressure Structural Concrete 4/2016 603-617 Technical Papers

Kurzfassung

Punching shear is usually the governing failure criterion when selecting the depth of reinforced concrete footings. Despite the fact that large experimental programmes aimed at the punching strength of slender flat slabs have been performed in the past, only a few experimental campaigns on full-scale compact reinforced concrete footings can be found in the literature. This paper presents the results of an experimental programme including eight reinforced concrete footings with a nominal thickness of 550 mm. These experiments investigated the influence of column size, member slenderness and the presence of compression and shear reinforcement. The tests were performed using an innovative test setup to ensure a uniform soil pressure. The experimental results show that slenderness influences the punching shear strength as well as the effectiveness of the shear reinforcement. The experiments also show that an important interaction occurs between bending and shear for high levels of shear force near the column (the typical case of compact footings or members with large amounts of shear reinforcement). Different continuous measurements recorded during the experimental tests allow a complete description of the kinematics and strains at failure. On that basis, experimental evidence is obtained showing that crushing of the concrete struts near the column is the phenomenon that triggers the punching failure of compact footings.

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Mobin, Jalal Salehi; Kazemi, Mohammad Taghi; Attari, Nader K.A. Cyclic behaviour of interior reinforced concrete beam-column connection with self-consolidating concrete Structural Concrete 4/2016 618-629 Technical Papers

Kurzfassung

A significant amount of research on self-consolidating concrete (SCC) technology has been devoted to evaluating the suitability of the material for its use in structural applications. However, more research is required to confirm the adequacy of SCC structural members for resisting gravity and seismic loads. This study focuses on the experimental investigation of the seismic performance of interior reinforced concrete beam-column connections with SCC. Four beam-column connection specimens, three with SCC and one with normally vibrated concrete (NC), were designed for this experimental study. Factors such as concrete type (SCC or NC) and axial load ratio (0, 7.5 and 15 % of column section capacity) were assumed to be the variables in designing the specimens. Beam-column connections made with NC and SCC were studied and compared under reversed cyclic loading. The performance of SCC specimens is comparable with NC specimens in terms of strength, displacement and ductility, but SCC specimens show lower energy dissipation capacity.

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von der Haar, Christoph; Marx, Steffen Development of stiffness and ultrasonic pulse velocity of fatigue loaded concrete Structural Concrete 4/2016 630-636 Technical Papers

Kurzfassung

Damage processes in fatigue loaded concrete structures depend on the number and amplitude of the load cycles applied. Damage evolution is linked to a reduction in concrete stiffness, and it is thought that this reduction causes stress redistributions at component level which have a favourable impact on the service life of a structure. Until now, the stiffness reduction and stress redistribution have never been successfully measured in laboratory tests or in situ. It is only known that the real service life is longer than the calculated one and that indicators of stiffness reduction, such as component deflection, increase with the number of load cycles applied.
Ultrasonic measurement techniques are considered to be well suited to detecting degradation processes caused by cyclic loading. It is expected that the stiffness reduction in fatigue loaded concrete structures can be recorded reliably with ultrasonic pulse velocity measurements. In the light of this, fatigue tests were performed on small-scale concrete specimens. The aims of the tests were to understand the correlation between the observed stiffness degradation of the specimens and the results of ultrasonic pulse velocity measurements and to estimate the potential for using ultrasonic pulse velocity measurements in continuous structural health monitoring.

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Hümme, Julian; von der Haar, Christoph; Lohaus, Ludger; Marx, Steffen Fatigue behaviour of a normal-strength concrete - number of cycles to failure and strain development Structural Concrete 4/2016 637-645 Technical Papers

Kurzfassung

The fatigue behaviour of concrete is gaining new relevance against the backdrop of continuous developments in concrete construction. Modern types of concrete are achieving ever higher strengths; hence, concrete structures are becoming increasingly attractive for new fields of application such as onshore and offshore wind turbines. The fatigue of concrete has a special relevance for these cyclically loaded structures and knowledge of the number of cycles to failure is no longer sufficient for their design. There are further questions concerning strain and stiffness development and the combination of fatigue loading and maritime environmental conditions which have been investigated with new testing methods at Leibniz Universität Hannover within the scope of the “ProBeton” research project. The first results of this project, which is supported by the Federal Ministry for Economic Affairs and Energy, are presented here.

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Classen, Martin; Herbrand, Martin; Kueres, Dominik; Hegger, Josef Derivation of design rules for innovative shear connectors in steel-concrete composites through the systematic use of non-linear finite element analysis (FEA) Structural Concrete 4/2016 646-655 Technical Papers

Kurzfassung

Today, the development of innovative shear connectors for steel-concrete composites is accompanied by a large number of experimental investigations, which are obligatory when proposing suitable design formula and carving out their limitations of use. Using the example of the so-called pin connector, the present paper illustrates to what extent validated finite element models of novel shear connectors can be used to replace expensive and time-consuming shear tests and how these finite element models can support the deduction of design concepts. The pin connector considered was developed for connecting steel sections to very slender high-strength concrete slabs in which conventional shear connectors such as headed studs cannot be used due to the limited embedment depth. In order to clarify the shear behaviour and load-carrying mechanisms of these novel connectors, non-linear finite element models were set up using the commercial FE software Abaqus. Subsequently, the FE models were used to perform systematic parametric studies. This paper describes the numerical results and also explains the stepwise development of an entire engineering model for determining the longitudinal shear capacity of small-scale pin connectors, including all the necessary limitations of use. The proposed modelling strategy and the methodology for the deduction of design rules can be transferred and assigned to other types of shear connectors.

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López-López, Andrés; Tomás, Antonio; Sánchez-Olivares, Gregorio Behaviour of reinforced concrete rectangular sections based on tests complying with seismic construction requirements Structural Concrete 4/2016 656-667 Technical Papers

Kurzfassung

The prediction of the seismic behaviour of reinforced concrete elements using numerical models has become a field of growing interest in recent years due to the importance of the effects induced by seismic loads applied to reinforced concrete structures. The simulation of the hysteretic behaviour of the plastic hinges generated in the structure when the seismic load acts requires the use of models that are able to describe the sectional behaviour of structural members. Thus, the main objective of the present paper is the adjustment of several empirical expressions that reduce the computational time needed to simulate the yield and ultimate behaviour of a given reinforced concrete rectangular section under either monotonic or cyclic loading. The expressions are calibrated with a selection of tests, taken from a published database of more than 1000 tests, according to the criterion that the selected specimens comply with the seismic construction requirements of the main international building codes (EC-2, EC-8 and ACI-318). Owing to their robustness and the acceptable computation time for low-dimensional problems, genetic algorithms are used for this calibration. The equations proposed can be employed by structural engineers for the design and analysis of actual structural elements used in ordinary reinforced concrete buildings located in seismic areas, and provide more accurate results than other expressions.

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Ma, Chau-Khun; Awang, Abdullah Zawawi; Omar, Wahid; Liang, Maybelle; Jaw, Siow-Wei; Azimi, Mohammadamin Flexural capacity enhancement of rectangular high-strength concrete columns confined with post-tensioned steel straps: experimental investigation and analytical modelling Structural Concrete 4/2016 668-676 Technical Papers

Kurzfassung

The load-carrying capacity and deformability of concrete columns can be substantially enhanced by confining with post-tensioned steel straps. As interest in high-strength concrete (HSC) grows among structural engineers and researchers due to its superior performance, this confining technique is being extended to HSC columns with the hope that it can eliminate the undesired properties of HSC, especially its brittleness. However, experimental studies involving confined HSC columns subjected to eccentric loads are comparatively limited. It can be seen from past research that most studies of external confinement were conducted on small-scale normal-strength concrete (NSC) cylinders subjected to concentric loads. Since most columns are subjected to eccentric loads in reality, the scarcity of test data has prevented the potential of this confining technique from being fully exploited. In this paper, this confining technique is called the steel-strapping tensioning technique (SSTT) for brevity. Nine HSC columns were tested under eccentric loads. The specimens were grouped into three groups with each group having an unconfined HSC column as a control specimen, a two-layer SSTT-confined HSC column and a four-layer confined HSC column. The experimental results show that the flexural capacities of HSC columns can be enhanced with SSTT. The deformability of confined HSC columns is significantly improved with such confinement.

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Gupta, Pramod K.; Khaudhair, Ziyad A.; Ahuja, Ashok K. A new method for proportioning recycled concrete Structural Concrete 4/2016 677-687 Technical Papers

Kurzfassung

A new modified mix proportioning method for producing normal-strength concrete using recycled concrete aggregate, called the equivalent coarse aggregate mass (ECAM) method, is proposed in this paper. The basic concepts of the proposed method with calculations for mix design are presented by designing 14 mixes and testing 99 concrete samples (57 cubes and 42 cylinders). Experimental work was carried out in two phases. In the first phase, an experimental programme was conducted to verify the proposed mix design method by studying a single parameter - uniaxial compressive strength. Five different mixes with initial 0, 25, 50, 75 and 100 % replacement by mass were designed, cast and tested in this phase. It was concluded from the first phase that the proposed method can be adopted for designing the recycled concrete up to a nominal replacement ratio of 50 %. Accordingly, the second phase of experimental study was carried out to design three different grades of concrete strength using the proposed method to investigate the mechanical properties of the recycled concrete. Seven different mechanical properties - compressive strength, splitting tensile strength, modulus of elasticity, Schmidt hammer test, ultrasonic pulse velocity test, fresh density and hardened density - were investigated and are presented and discussed here.

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fib-news: Structural Concrete 4/2016 Structural Concrete 4/2016 688-695 fib-news

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11th fib PhD International Symposium in Tokyo
CONSEC 2016
fib Bulletin 79
New COM7
Brazil NMG hosts fib event
Short notes
Obituaries
Congresses and symposia

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Inhalt: UnternehmerBrief Bauwirtschaft 4/2016 UnternehmerBrief Bauwirtschaft 4/2016 Inhalt

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Keine Kurzfassung verfügbar.

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Gesamtausgabe UBB 4/2016 UnternehmerBrief Bauwirtschaft 4/2016 1-24 Gesamtausgabe

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komplette Monatsausgabe

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Schalk, Günther Von neuen Schlössern und Haushaltslöchern... UnternehmerBrief Bauwirtschaft 4/2016 1 Editorials

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Kurz informiert: UnternehmerBrief Bauwirtschaft 4/2016 UnternehmerBrief Bauwirtschaft 4/2016 2 Kurz informiert

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BVMB: “Bürokratieabbau darf kein Lippenbekenntnis bleiben!”
“Zertifizierungs-Wahnsinn verteuert das Bauen!”
“Deutsche HOAI verstößt gegen den EU-Vertrag”

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Siegel, Caroline; Traut, Johannes Mindestlohn bei Subunternehmern: Haftungsrisiko! UnternehmerBrief Bauwirtschaft 4/2016 3-8 Berichte

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Baufirmen stehen vielfach unter Druck. Nicht nur hinsichtlich der Herstellung der Bauleistungen, die sie täglich erbringen, nimmt die Zahl der Vorschriften immer mehr zu. Auch haben Bauunternehmen beispielsweise Regelungen aus dem Arbeitsrecht zu beachten. Von hoher Praxisbedeutung sind hier insbesondere die Vorschriften zu Mindestarbeitsbedingungen und zum Mindestlohn am Bau. Werden Mindestarbeitsbedingungen des Baugewerbes - ob im eigenen Betrieb oder durch Subunternehmer - nicht eingehalten, bestehen massive Haftungs- und Bußgeldrisiken. Der UBB stellt in diesem Beitrag die Anforderungen im Überblick dar und gibt Tipps zur Risikobegrenzung.

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