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Schlaich, Jörg Hyperbolic structures. Shukhov's Lattice Towers - Forerunners of Modern Lightweight Construction. From Beckh, M. Steel Construction 2/2015 143-144 Book review

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Keine Kurzfassung verfügbar.

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Announcement: Steel Construction 2/2015 Steel Construction 2/2015 144 Announcement

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Keine Kurzfassung verfügbar.

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Contents: Structural Concrete 2/2015 Structural Concrete 2/2015 Contents

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Keine Kurzfassung verfügbar.

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Andrade, Carmen Modelling the concrete-real environment interaction to predict service life Structural Concrete 2/2015 159-160 Editorial

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Keine Kurzfassung verfügbar.

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Kromoser, Benjamin; Kollegger, Johann Pneumatic forming of hardened concrete - building shells in the 21st century Structural Concrete 2/2015 161-171 Technical Papers

Kurzfassung

Double-curvature shells, used as supporting structures, are strong and save materials. Major parts of the applied loads can be carried by normal forces. Thus, the stresses are distributed very uniformly and efficiently over the entire cross-section, and long spans can be built with small thicknesses. The state of the art in the construction of shell structures is characterized by a high labour input for formwork and falsework. A new construction method without formwork and falsework has been invented at the Institute for Structural Engineering at Vienna University of Technology. The idea of this new construction method is to build concrete shells with a double curvature originating from an initially plane plate. During the transformation process, the hardened concrete plate is lifted and the elements are bent with the aid of pneumatic formwork until the required curvature is reached. Non-linear finite element calculations, tension tests, bending tests and bonding tests were carried out in order to determine a suitable combination of concrete and reinforcement. The second part of the paper describes a large-scale experiment for the erection of a 17.6 × 10.8 m, 2.9 m high free-form shell. Finally, different applications for the new method are explained.

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Galmarini, Andreas; Locher, Daniel; Marti, Peter Predicting the responses of reinforced concrete slab strips subjected to axial tension and transverse load - a competition Structural Concrete 2/2015 172-183 Technical Papers

Kurzfassung

Six large-scale tests on reinforced concrete slab strips were carried out at the Swiss Federal Institute of Technology (ETH) in Zurich, Switzerland, in order to investigate the loadbearing behaviour of reinforced concrete slabs subjected to axial tension and transverse load. Four of these tests were used for an international competition to predict the responses of the test specimens. The specimens differed in the axial tension applied and the presence of stirrups.
This paper presents the test concept, the four test specimens, the test results and the predictions received, and also evaluates the results of the competition. Simplified hand calculation analyses of the experiments are also included.
The tests showed that there is significant shear strength in reinforced concrete slabs under axial tension, and that the system capacity of such slab strips is not limited by a local shear failure. The prediction competition revealed that the modelling of a cracked reinforced concrete slab strip is still a significant challenge, even for experienced researchers using the latest analysis tools.

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Kassem, Wael Shear strength of deep beams: a mathematical model and design formula Structural Concrete 2/2015 184-194 Technical Papers

Kurzfassung

This paper presents a proposal for estimating the shear capacity of reinforced concrete deep beams. The proposed model is based on the fixed-angle softened truss model and utilizes a newly proposed formula for the effective transverse compressive stress acting on the beam web. The proposed formula is developed using a stepwise multiple linear regression analysis of the reported shear capacity values of 445 experimental deep beams. The validity of the mathematical model is examined by comparing its response with the experimental results as well as the predictions of other formulas available in the literature, and it results in the one best fitting the measured shear strengths. The mathematical model leads to an explicit single closed-form expression for computing the shear strength of deep beams. The proposed expression is dimensionless and contains four variables that express the horizontal and vertical reinforcement ratios, the concrete strength and the shear span-to-depth ratio. On the basis of the results of this paper, a design formula is proposed with predictions that are more consistent and also more reliable than those of the ACI Code and the Eurocode.

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Classen, Martin; Herbrand, Martin Shear behaviour of composite dowels in transversely cracked concrete Structural Concrete 2/2015 195-206 Technical Papers

Kurzfassung

In steel-concrete composite girders, innovative composite dowels can be used to transfer the shear forces between the concrete slab and the steel section. Today, composite dowels are predominately used in engineering structures such as prefabricated composite bridges. However, due to their ease of manufacture, good loadbearing and deformation properties and suitability for slender concrete slabs, these composite dowels are being used more than ever in building construction as well. The present article describes shear tests on puzzle-shaped composite dowels for slender concrete slabs with a depth of only 10 cm. Aside from different reinforcement configurations, the influence of different longitudinal stress states and transverse cracking in the concrete slab have been investigated. In previous studies of the shear force capacity of composite dowels, the influence of transverse cracking has been neglected. However, our own experiments described in this paper show that the shear capacity of composite dowels is significantly affected by concrete cracking. In order to simulate the experiments performed and to analyse the shear behaviour of the composite dowels in cracked and uncracked concrete, a three-dimensional, non-linear finite element model of the shear tests was set up. The results of both the experimental and numerical investigations are summarized in this paper.

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Fernández-Montes, David; González Valle, Enrique; Díaz Heredia, Elena Influence of axial tension on the shear strength of floor joists without transverse reinforcement Structural Concrete 2/2015 207-220 Technical Papers

Kurzfassung

The mechanism governing shear strength in reinforced concrete members without transverse reinforcement subjected to both bending and tensile stress is complex. Further, formulas used to estimate shear failure are inconsistent with each other and do not fit well with experimental findings. This article highlights the differences between the results of experimental tests and the shear strength values estimated with the equations of ACI 318-11, Eurocode 2 (EC2) and modified compression field theory (MCFT). The tests considered are the ones reported in the literature consulted and the tests carried out for this experimental investigation, some with high-performance concrete. The review also puts forward a proposal for improving the method and fitting procedure when estimating the shear failure in a longitudinal reinforced concrete member without transverse reinforcement due to an excessive principal tensile stress in its web.

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Schlicke, Dirk; Tue, Nguyen Viet Minimum reinforcement for crack width control in restrained concrete members considering the deformation compatibility Structural Concrete 2/2015 221-232 Technical Papers

Kurzfassung

The current design code EC2 [1] regulates the minimum reinforcement for crack width control in restrained concrete members by taking up the cracking force of the cross section. Although this concept gives straightforward results, its consistent application can lead to high reinforcement amounts with increasing member thickness. The reason is the simplifying assumption of an infinite member length neglecting the deformation compatibility.
The cracking force approach was therefore empirically modified to reflect practical experience, see [2]. However, the main modification of a limited tensile strength seems particularly dubious, as the primarily affected thick members have already a strong developed tensile strength before any risk of cracking occurs at all.
Finally, this circumstance leaves the structural designer with the dilemma of being either uneconomic or having no mechanical proof in a possible case of damage.
However, the mechanically consistent estimation of the minimum reinforcement for crack width control can be achieved by considering the deformation compatibility of the restrained member, see [3]. With the introduction of [4], this deformation-based design concept became state of the art for mass concrete members of hydraulic structures.
This contribution presents the general application of the deformation-based design concept due the findings of [5]. The reliability and the practicability of this approach will then be illustrated by the deformation-based minimum reinforcement design of a trough structure.

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Costa, Ricardo Joel Teixeira; Providência, Paulo; Dias, Alfredo Considering the size and strength of beam-column joints in the design of RC frames Structural Concrete 2/2015 233-248 Technical Papers

Kurzfassung

Some experimental research studies have reported that longitudinal reinforcement in beams and columns exhibits larger strains inside the joint than at the joint periphery (defined as the intersection of the outer surfaces of beam and column). This may explain why several technical specifications and state-of-the-art programs recommend basing the design of beams and columns on internal force values larger than those at the joint periphery. These results and procedures are questionable and are investigated in this paper. The non-linear finite element analysis presented here for reinforced concrete frames under gravity and quasi-static monotonic lateral loads examines (i) the stress fields in reinforcement inside interior, exterior and roof exterior joints, and (ii) the load-carrying capacity of representative sub-frame models incorporating such joints. The results prove that it is actually safe, with respect to the joint load capacity, to base the design of longitudinal reinforcement in beams and columns on the internal force values at the joint periphery. This result also contributes to the recommendation to use real-size beam-column joint models in the analysis procedure.

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Xiao, Jianzhuang; Sun, Chang; Jiang, Xinghan Flexural behaviour of recycled aggregate concrete graded slabs Structural Concrete 2/2015 249-261 Technical Papers

Kurzfassung

This paper proposes a new concept for “recycled aggregate concrete graded slabs”, which can be achieved through graded distribution for the mechanical properties of the recycled aggregate concrete (RAC). In this study, one four-point bending test was used to investigate six RAC graded slabs and three homogeneous slabs with RAC. The major parameters considered were the layers with different recycled coarse aggregates (RCAs) replacement percentages (0, 50 and 100%), the grading pattern (different casting methods) and the reinforcement ratio. It has been concluded that RAC graded slabs have similar flexural behaviour to that of homogeneous slabs with RAC. The reinforcement ratio, the layers with different RCA replacement percentages and the grading pattern can influence the flexural behaviour of RAC graded slabs. Furthermore, the effects of the three factors on both the flexural capacity and the deflection of the RAC graded slabs were studied with finite element method (FEM) simulation using ABAQUS software. Both the experiments and the FEM analysis indicate that the flexural behaviour of RAC slabs can be improved by using this suitable grading method.

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Colombo, Matteo; Martinelli, Paolo; di Prisco, Marco A design approach for tunnels exposed to blast and fire Structural Concrete 2/2015 262-272 Technical Papers

Kurzfassung

A design procedure based on a simplified FE model for underground tunnels subjected to internal explosion and possibly preceded by fire accidents is proposed in this article. The procedure can provide a valuable tool for designers who have to check the structural safety of a tunnel for the case of an internal blast event. The tunnel geometry considered is the same adopted for the metro line in Brescia, Italy. It has an internal diameter of about 8.15 m, is about 13.7 km long and is located about 23.1 m below the surface. Six segments and a smaller key segment (6+1) make up the tunnel. The ring has an average width of about 1.5 m. The FE model is first tested under static serviceability loads. Dynamic analyses are carried out in order to reproduce the blast scenario. The aim of this work is to generate pressure-impulse (p-i) diagrams for underground tunnels for the case of internal explosion and pre-explosion fire actions. An ultimate limit state criterion based on the eccentric ultimate flexural capacity and capable of including fire-blast interaction is introduced. An innovative layered precast tunnel segment solution made of different fibre-reinforced cementitious composites is compared with a traditional solution with the lining section made of reinforced concrete. The potential applications of this new solution are also discussed in the paper.

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Van Tittelboom, Kim; Gruyaert, Elke; De Backer, Pieter; Moerman, Wim; De Belie, Nele Self-repair of thermal cracks in concrete sandwich panels Structural Concrete 2/2015 273-288 Technical Papers

Kurzfassung

Although the use of insulated concrete sandwich panels results in more energy-efficient buildings, the presence of this insulation layer can induce thermal cracks. As cracks form a preferential path for aggressive agents to enter and degrade the concrete matrix, and as they are not wanted in this application from an aesthetical point of view, they need to be treated. The aim of this study was to seal the cracks in concrete sandwich panels invisibly in an autonomous way. Therefore, the efficiency of various encapsulated healing agents was compared by inducing thermal cracks in concrete sandwich panels, thus causing capsule breakage and the release of the agents into the cracks. It was shown that encapsulation of both polyurethane and a water-repellent agent can result in a reduction in the water uptake by cracks. However, only when a water-repellent agent was released cracks were healed in an almost invisible way. This study has shown that the self-healing approach involving encapsulated polymer-based healing agents can also be applied to concrete sandwich panels, although more research will be needed to meet the specific healing requirements of this application.

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Gang, Xu; Yun-pan, Li; Yi-biao, Su; Ke, Xu Chloride ion transport mechanism in concrete due to wetting and drying cycles Structural Concrete 2/2015 289-296 Technical Papers

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The transport mechanism of chloride ions in concrete during wetting and drying cycles of varying duration is evaluated in this paper. The experimental test results were used to validate a numerical simulation model in order to assess the influence of diffusion coefficient, surface chloride ion concentration and ratio of dry-wet cycle durations on the transport mechanism of chloride ions in concrete. Experimental and numerical analysis results indicate that the maximum transmission depth of chloride ions in concrete depends on the diffusion coefficient and the dry-wet cycle regime but has little relationship with the surface concentration of chloride. The chloride ion transmission in the surface zone accelerates only if the dry-wet ratio is > 1. As the dry-wet ratio increases, so the chloride ion transmission accelerates. It tends to become stable when the dry-wet ratio reaches 5:1. The dry-wet cycles accelerate the transport process of chloride ions within a certain distance from the surface; beyond this distance, chloride ions in the complete immersion specimen migrate more rapidly than those under dry-wet cycles. The peak concentration of chloride ions within the convection zone has a relationship with the diffusion coefficient, the surface chloride ion concentration and the dry-wet regime. The smaller the diffusion coefficient, the higher the surface chloride concentration; the greater the dry-wet ratio, the higher the peak of convection can be.

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Hajali, Masood; Alavinasab, Ali; Shdid, Caesar Abi Effect of the location of broken wire wraps on the failure pressure of prestressed concrete cylinder pipes Structural Concrete 2/2015 297-303 Technical Papers

Kurzfassung

The effect of the location of broken prestressing wire wraps on the overall strength of prestressed concrete cylinder pipes (PCCP) is investigated here. An advanced computational model based on non-linear finite element analysis is used to study three possible locations of broken wire wraps: at the spigot joint, at the bell joint and in the barrel of the pipe. A sensitivity analysis was performed to evaluate the cracking of the concrete core and the yielding of the prestressing wires and steel cylinder with increasing internal pressure and with an increasing number of broken wire wraps. Two classes of 2.44 m embedded cylinder pipe (ECP) were modelled with 5, 35, 70, and 100 wire wrap breaks. The results show that broken wire wraps at the joint, and especially the spigot joint, decrease the overall strength of PCCP more so than those at the bell joint or in the barrel of the pipe. The intensity of this effect increases with increasing internal pressure and with a larger number of broken wire wraps.

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fib-news: Structural Concrete 2/2015 Structural Concrete 2/2015 305-311 fib-news

Kurzfassung

Wider scope for Commission 1; A first for FRP in Ghent; Presidium meets in Lausanne; fib Bulletin 74; ‘Innovative Concretes’ in Ulm; Short notes; Congresses and symposia; Acknowledgement

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Inhalt: UnternehmerBrief Bauwirtschaft 2/2015 UnternehmerBrief Bauwirtschaft 2/2015 Inhalt

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Keine Kurzfassung verfügbar.

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Ernst & Sohn (Hrsg.) Gesamtausgabe UBB 2/2015 UnternehmerBrief Bauwirtschaft 2/2015 1-24 Gesamtausgabe

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Komplette Monatsausgabe

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Schalk, Günther Viel Freud und Leid im Familienbetrieb... UnternehmerBrief Bauwirtschaft 2/2015 1 Editorials

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Keine Kurzfassung verfügbar.

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

Kurzfassung

Vergaberecht soll anwenderfreundlicher werden
Städte sollen grüner und barrierefreier werden
“Aufzeichnungspflichten sind ein Bürokratiemonster”

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Otto, Jens Was passiert mit BGK, AGK und WuG bei Änderung des Bau-Soll? UnternehmerBrief Bauwirtschaft 2/2015 3-8 Berichte

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Der sichere Umgang mit der Berechnung von Vergütungsansprüchen bei EP-Verträgen für Baustellengemeinkosten (BGK), Allgemeine Geschäftskosten (AGK) sowie des Anteils für Wagnis (W) und Gewinn (G) bei vom AG geänderten Bauleistungen bereitet oft Schwierigkeiten. Dabei stellt sich stets die Frage, ob für den in Menge oder Qualität abweichenden Leistungsumfang grundsätzlich ein Vergütungsanspruch des AN für die genannten Anteile des Angebotspreises besteht und wenn ja, in welcher Höhe. Die Abweichungen können entstehen durch Mehr- und Mindermengen (§ 2 Abs. 3 VOB/B), entfallene Leistungen (§ 2 Abs. 4 VOB/B, § 8 Abs. 1 VOB/B), geänderte Leistungen (§ 2 Abs. 5 VOB/B), zusätzliche Leistungen (§ 2 Abs. 6 VOB/B) sowie gestörte Bauabläufe. Der UBB-Hauptaufsatz versucht, etwas Licht ins Dunkel der Anspruchssysteme und -berechnungen zu bringen.

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Bach, Thorsten Familie oder Fremde - wer soll das Unternehmen weiterführen? UnternehmerBrief Bauwirtschaft 2/2015 9-11 Berichte

Kurzfassung

Laut Institut für Mittelstandsforschung in Bonn stehen jährlich mehr als 25.000 Unternehmensinhaber in Deutschland vor der Herausforderung, ihr Unternehmen an eine Nachfolgegeneration zu übergeben. Dies bietet für viele Inhaber unternehmerische Chancen, birgt aber auch viele Risiken sowie persönliche und emotionale Herausforderungen. Nach dem erfolgreichen Aufbau des eigenen Unternehmens stellt die Nachfolgeregelung eine der wichtigsten Herausforderungen im Leben eines Unternehmers dar. Sie stehen vor der Frage: Bleibt das Unternehmen weiterhin in der Familie oder geht es über in die Hände einer familienfremden Unternehmensführung?

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Neues zur Erbschafts- und Schenkungssteuer bei Betriebsübergang UnternehmerBrief Bauwirtschaft 2/2015 12 Berichte

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Ein Urteil des Bundesverfassungsgerichts (BVG) vom 17.12.2014 (Az. 1 BvL 21/12) zur Erbschafts- und Schenkungssteuer von Betriebsvermögen sorgt für Schlagzeilen. Worum ging es dabei? Welche Folgen sind zu erwarten? Wie sollten Baufirmen und Bauhandwerksbetriebe vorgehen, wenn die Betriebsnachfolge in naher Zukunft stattfinden soll? Der UBB gibt Antworten.

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Englert, Florian Aktuelles aus der Rechtsprechung UnternehmerBrief Bauwirtschaft 2/2015 13-14 Berichte

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Mangel nicht anerkannt - Fristsetzung entbehrlich?
Haftung des Architekten: unendlich?

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