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Classen, Martin; Herbrand, MartinShear behaviour of composite dowels in transversely cracked concreteStructural Concrete2/2015195-206Technical 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, ElenaInfluence of axial tension on the shear strength of floor joists without transverse reinforcementStructural Concrete2/2015207-220Technical 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 VietMinimum reinforcement for crack width control in restrained concrete members considering the deformation compatibilityStructural Concrete2/2015221-232Technical 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, AlfredoConsidering the size and strength of beam-column joints in the design of RC framesStructural Concrete2/2015233-248Technical 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, XinghanFlexural behaviour of recycled aggregate concrete graded slabsStructural Concrete2/2015249-261Technical 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, MarcoA design approach for tunnels exposed to blast and fireStructural Concrete2/2015262-272Technical 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, NeleSelf-repair of thermal cracks in concrete sandwich panelsStructural Concrete2/2015273-288Technical 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, XuChloride ion transport mechanism in concrete due to wetting and drying cyclesStructural Concrete2/2015289-296Technical Papers

Kurzfassung

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 AbiEffect of the location of broken wire wraps on the failure pressure of prestressed concrete cylinder pipesStructural Concrete2/2015297-303Technical 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 2/2015Structural Concrete2/2015305-311fib-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 2/2015UnternehmerBrief Bauwirtschaft2/2015Inhalt

Kurzfassung

Keine Kurzfassung verfügbar.

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Ernst & Sohn (Hrsg.)Gesamtausgabe UBB 2/2015UnternehmerBrief Bauwirtschaft2/20151-24Gesamtausgabe

Kurzfassung

Komplette Monatsausgabe

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Schalk, GüntherViel Freud und Leid im Familienbetrieb...UnternehmerBrief Bauwirtschaft2/20151Editorials

Kurzfassung

Keine Kurzfassung verfügbar.

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Kurz informiert: UnternehmerBrief Bauwirtschaft 2/2015UnternehmerBrief Bauwirtschaft2/20152Kurz informiert

Kurzfassung

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

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Otto, JensWas passiert mit BGK, AGK und WuG bei Änderung des Bau-Soll?UnternehmerBrief Bauwirtschaft2/20153-8Berichte

Kurzfassung

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, ThorstenFamilie oder Fremde - wer soll das Unternehmen weiterführen?UnternehmerBrief Bauwirtschaft2/20159-11Berichte

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 BetriebsübergangUnternehmerBrief Bauwirtschaft2/201512Berichte

Kurzfassung

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, FlorianAktuelles aus der RechtsprechungUnternehmerBrief Bauwirtschaft2/201513-14Berichte

Kurzfassung

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

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Schweibenz, BerndInformationsbeschaffung bei der Stellensuche am BauUnternehmerBrief Bauwirtschaft2/201515-16Berichte

Kurzfassung

Wie suchen sich Unternehmen als Arbeitgeber und potenzielle Arbeitnehmer vom künftigen Auszubildenden bis zum Studienabsolventen gegenseitig? Welche Wege nutzen beide, um Nachwuchs für den Betrieb zu suchen beziehungsweise um sich nach einem passenden möglichen Arbeitgeber umzusehen? Die Hochschule Biberach hat sich des Themas angenommen. Zwei Absolventen haben im Rahmen ihrer Abschlussarbeiten entsprechende Untersuchungen angestellt. Die Ergebnisse können sowohl Unternehmen als auch Bewerbern wichtige Tipps geben.

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Neues von der Steuer 2015UnternehmerBrief Bauwirtschaft2/201517-19Berichte

Kurzfassung

Im Zollkodex-Anpassungsgesetz, kurz Jahressteuergesetz 2015, und in zahlreichen Schreiben des Bundesfinanzministeriums sind wichtige Steueränderungen für 2015 enthalten, die Unternehmer seit dem 1.1.2015 umsetzen müssen. Der UBB gibt Ihnen einen Überblick über die wichtigsten Steueränderungen 2015.

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BIM - das Allheilmittel für die Zukunft des Bauens?UnternehmerBrief Bauwirtschaft2/201520Berichte

Kurzfassung

BIM hat das Potenzial, die deutsche Bauwirtschaft nachhaltig zu verbessern, so viel steht am Ende des 5. BRZ-Mittelstandsforums fest. Das Forum des BRZ ist längst so etwas wie ein Klassiker und eine hervorragende Kontaktbörse obendrein. Im Februar und März stehen weitere an.

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UBB-VeranstaltungstippsUnternehmerBrief Bauwirtschaft2/201520Veranstaltungen

Kurzfassung

Keine Kurzfassung verfügbar.

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Inhalt: Bauphysik 1/2015Bauphysik1/2015Inhalt

Kurzfassung

Keine Kurzfassung verfügbar.

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Jahresinhaltsverzeichnis 2014Bauphysik1/2015Jahresinhaltsverzeichnis

Kurzfassung

Keine Kurzfassung verfügbar.

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Zirkelbach, Daniel; Stöckl, BeateHygrothermische Bemessung von Gründächern - Modellentwicklung und praktische AnwendungBauphysik1/20151-7Fachthemen

Kurzfassung

Trotz schwieriger Feuchteschutzbemessung - Gründächer sind von der Bemessung mit Hilfe des Glaserverfahrens nach DIN 4108-3 ausgeschlossen - setzen sich Dachbegrünungen in der Praxis immer mehr durch. Häufige Argumente sind die ansprechende Optik und die Verbesserung des Arbeits- und Wohnumfeldes für die Nutzer, so dass die Nachfrage nach begrünten Flachdächern in den vergangenen Jahren stark gestiegen ist. Doch neben weiteren Vorteilen wie sommerlicher Wärmeschutz, Regenwasserrückhalt, Schutz der Dachabdichtung oder Lärm- bzw. Schallschutz, bergen vor allem Gründächer in Holzbauweise aufgrund des auch im Sommer geringen Trocknungspotentials ein gewisses Schadensrisiko. Im Rahmen eines Forschungsprojekts wurden die Grundlagen geschaffen, um Dachbegrünungen mit Hilfe hygrothermischer Simulationen zuverlässig berechnen und planen zu können.
Basierend auf Messungen in Holzkirchen, Leipzig, Wien, Kassel und Mailand wurden die spezifischen Oberflächenübergangskoeffizienten und die Materialeigenschaften verschiedener Substrate ermittelt. Die auf diese Weise entwickelten Gründachmodelle bieten Planern und Bauproduktherstellern eine möglichst genaue und zuverlässige Grundlage für die Planung der Feuchtesicherheit von extensiv begrünten Dächern.
Auf Basis der neuen Untersuchungen können allgemeine Empfehlungen zur Ausführung von begrünten Leichtbaudächern für die Praxis erarbeitet werden. Für die Planung von Neubauten sollte demnach der Grenzwert von 18 M.-% nach DIN 68800 nicht überschritten werden, so dass bei fast allen Konstruktionen eine zusätzliche Überdämmung der äußeren Schalung notwendig ist. Ohne Überdämmung erreicht das Feuchteniveau meist höhere Werte. Bei Bestandskonstruktionen ohne Überdämmung, die bisher schadensfrei sind, muss im Einzelfall ein eventueller Handlungsbedarf überprüft werden.

Hygrothermal design of green roofs - new models and practical application.
Despite challenging moisture control design issues - the German standard for moisture control excludes steady state diffusion methods from being used for vegetated roofs - green roofs have become very popular. Most frequently mentioned reasons are the attractive appearance and the improvement of the working - and living environment for the people. Therefore the percentage of green roofs among flat roofs shows a strong increase in the past years. But beside their advantages like cooling effect in the summer months, storage of rain water, protection of the roofing membrane or noise control, the application of green roofs - especially on wooden constructions - involves a certain risk of damage because of the low drying potential in the summer months. Within a research project a new model to calculate green roofs reliably by the help of hygrothermal simulations was established.
On the basis of existing and new measurements in Holzkirchen, Leipzig, Vienna, Kassel and Milan the specific surface transfer coefficients and the material properties of different substrates were determined. The models developed in this way provide to planners and manufacturers of building materials and constructions a reliable basis for the design of the moisture safety of extensive green roofs.
Based on these results general practice recommendations for wooden light-weight green roofs were worked out. For design purposes the limit value of 18 M.-% (e. g. according to the German DIN 68800) shouldn’t be exceeded. Therefore an additional insulation above the exterior sheathing is often necessary. Without such an additional insulation layer moisture levels in the wooden structure may exceed safety limits within a couple of years. For existing, damage free buildings the need for action has to be determined individually.

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