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Naji, ArashModelling the catenary effect in the progressive collapse analysis of concrete structuresStructural Concrete2/2016145-151Technical Papers

Kurzfassung

Progressive collapse is a phenomenon in which local failure of a structural component due to a gas explosion or blast may lead to failure of the entire structure or a significant part of it. RC structures can resist progressive collapse through various mechanisms such as frame action and catenary action.
In this paper, the effect of catenary action on the resistance of concrete frame structures to progressive collapse is modelled using limit analysis. Non-linear optimization is performed for this. It is observed that although frame action is known to be the main mechanism resisting progressive collapse, at the end of this action, after rupture of bottom bars, catenary effects may bring about a noticeable increase in the resistance of the structure. The results show good agreement with the experimental results of other researchers.

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Müller, Frank; Kohlmeyer, Christian; Schnell, JürgenA new approach for calculating the internal forces, moments and deflections of sandwich panels with reinforced concrete facingsStructural Concrete2/2016152-161Technical Papers

Kurzfassung

Software for calculating the internal forces, moments and deflections of sandwich elements with reinforced concrete facings has been developed as part of a research project at Technische Universität Kaiserslautern. Sandwich elements with stiff concrete facings are internally statically indeterminate. Cracking of the concrete facings leads to a redistribution of the internal forces and moments over the length and across the cross-section of the element. This redistribution must be considered in the structural design of such elements.
An existing program for calculating metal-faced sandwich elements was considerably extended by an iterative approach that allows the internal forces and moments to be calculated with the exact stiffness of the cracked facings. This iterative approach and the calculation algorithm behind the new software, called swe2+, are explained in this paper. A verification of the calculation results and a parametric study of a two-span sandwich element are also presented.

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Vatteri, Ahsana Parammel; Rao, K. Balaji; Bharathan, Anoop M.Time-variant reliability analysis of RC bridge girders subjected to corrosion - shear limit stateStructural Concrete2/2016162-174Technical Papers

Kurzfassung

Chloride-induced corrosion of reinforced concrete (RC) bridge girders has led to a huge loss of national resources. One of the important concerns affecting RC bridge girders is corrosion of the stirrups, which can even cause the failure mechanism to change from a ductile flexural mode to a brittle shear mode. Hence, analysis of the reduction in shear capacity overtime is essential in the reliability assessment of bridge girders, which is the topic of the paper. This paper proposes a stochastic modelling approach for estimating the time-variant shear capacity and reliability within the framework of a Monte Carlo simulation, which assists in the sustainability-based service life design of bridge girders. Such modern design concepts require methodologies for estimating whole life cost at the design stage itself. The development of such methodologies would provide the designer with various options for arriving at an optimum design having the desired performance level during the service life. The proposed approach takes into account: 1) the randomness in basic variables, 2) the effect of micro-environments and the spatial variation of corrosion, 3) the number of stirrups resisting web shear failure, and 4) the ductile to brittle transition of stirrup steel as corrosion propagates. The incorporation of this transition is found to have a significant influence on the time-variant reliability of the girder. Although PFA concrete is known to have better durability characteristics than OPC concrete, this paper gives a framework for its quantification in terms of time-variant reliability.

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Zhou, Lin-Yun; He, Zhi-Qi; Liu, ZhaoInvestigation of optimal layout of ties in STM developed by topology optimizationStructural Concrete2/2016175-182Technical Papers

Kurzfassung

Strut-and-tie models (STMs) have been wildly used for the design of disturbed regions in structural concrete members. The STM developed based on the load path method or with the aid of stress trajectories is not unique and varies with the designer's intuition and past experience. As a result, topology optimization methods have been adopted to generate STMs in reinforced concrete structures. However, such models are just a preliminary configuration and the detailed layout of ties in an STM cannot be determined by the optimal topology. This is because reinforced concrete is assumed to be a uniform elastic continuum. Therefore, the effect of the steel reinforcement on the load transmission cannot be considered in the optimization process. Recently, the criterion of minimum strain energy has been proposed to determine the optimal layout of STMs obtained by the modified optimization method. However, the strain energy criterion does not work when the minimum strain energy in ties is zero when evaluated by mathematical equations. To address this issue, the maximum stiffness criterion is proposed to discover the optimal layout of ties in STMs by evaluating the stiffnesses of strut ties.

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Classen, Martin; Gallwoszus, Joerg; Stark, AlexanderAnchorage of composite dowels in UHPC under fatigue loadingStructural Concrete2/2016183-193Technical Papers

Kurzfassung

In steel-concrete composite structures, innovative composite dowels can be used for the connection of ultra-high-performance concrete (UHPC) slabs and high-strength steel members. In addition to sufficient shear capacity, composite dowels have to ensure the transmission of tensile forces in the composite connection in order to prevent lifting of the concrete slab. This may lead to structural problems, particularly in the very slender concrete slabs of high-strength composite beams, where composite dowels have very small embedment depths. Although findings concerning the structural anchorage behaviour of composite dowels under static loads are already available, studies on the fatigue of composite dowels under cyclic pull-out loading are still lacking. As fatigue behaviour is crucial for applications in bridge construction, the present paper introduces cyclic pull-out tests on composite dowels in UHPC slabs in which the influence of different load-dependent parameters (upper load level and load range) as well as the use of transverse reinforcement has been investigated. Furthermore, an approach to assess the lifetime of composite dowels in UHPC under cyclic pull-out loading is proposed.

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Pantazopoulou, Stavroula J.; Tastani, Souzana P.; Thermou, Georgia; Triantafillou, Thanasis; Monti, Giorgio; Bournas, Dionysios; Guadagnini, MaurizioBackground to the European seismic design provisions for retrofitting RC elements using FRP materialsStructural Concrete2/2016194-217Technical Papers

Kurzfassung

This paper is a comprehensive background document on the state of the art in European seismic design provisions which was assembled by fib committee 5.1 to support the development of design guidelines regarding the use of externally applied fibre reinforced polymer (FRP) materials in the seismic retrofitting of reinforced concrete structures. In the context of developing design guidelines, the underlying mechanistic models that support the derivation of provisions were assembled following critical evaluation of the existing proposals and with careful reference to the experimental evidence available, the comparative assessment of past models in the literature and requirements established from first principles.

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Ziaadiny, Hadi; Abbasnia, RezaUnified cyclic stress-strain model for FRP-confined concrete circular, square and rectangular prismsStructural Concrete2/2016220-234Technical Papers

Kurzfassung

The behaviour and modelling of concrete columns confined with FRP composites under monotonic compression has been extensively studied, but far fewer studies of the cyclic behaviour of FRP-confined circular and rectangular columns have been carried out. A reliable model indicating the cyclic stress-strain behaviour of FRP-confined columns is of great importance, especially for seismic retrofits and the design of these columns. In this paper, based on the results from a series of cyclic compressive loading tests on FRP-confined specimens, a unified cyclic stress-strain model is proposed for circular, square and rectangular columns confined with FRP composites. The model contains different parts of the cyclic stress-strain curve, including plastic strain, maximum strain in unloading path and corresponding stress, stress deterioration, effect of loading history, partial unloading and partial reloading. New expressions are also proposed for predicting unloading and reloading paths. The proposed model agrees well with the test results.

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Zhang, WeiExperimental study on fatigue behaviour of CFRP plates externally bonded to concrete substrateStructural Concrete2/2016235-244Technical Papers

Kurzfassung

The behaviour of the bond between fibre-reinforced polymers (FRP) and concrete greatly influences the behaviour of concrete structures strengthened with FRP composites. Although numerous experimental studies have investigated this bond, experimental data concerning fatigue tests on carbon FRP plates attached to concrete blocks are still lacking. Therefore, a series of double-lap shear tests under monotonic and fatigue loadings were performed on concrete prismatic specimens reinforced with CFRP plates. First, a series of experimental investigations are summarized. Thereafter, the fatigue behaviour of CFRP plate debonding is characterized using S-N diagrams that represent the relationship of the upper-limit fatigue load with the monotonic load strength and the number of cycles to debonding on a semi-logarithmic scale.

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irgulis, Giedrius; vec, Old ich; Geiker, Mette Rica; Cwirzen, Andrzej; Kanstad, TerjeInfluence of reinforcing bar layout on fibre orientation and distribution in slabs cast from fibre-reinforced self-compacting concrete (FRSCC)Structural Concrete2/2016245-256Technical Papers

Kurzfassung

Fibre orientation and volume distribution affect the post-cracking tensile strength, which is one of the main design parameters of fibre-reinforced concrete (FRC). This paper discusses the influence of unidirectional and grid reinforcement on fibre orientation and distribution in FRC slabs. Slabs without conventional reinforcing bars were used as a reference. The slab size was 1200 × 1200 × 150 mm. Numerical simulations were used to predict the fibre orientation and X-ray computed tomography (CT) to determine the actual fibre orientation and distribution. Beams were sawn from each slab, CT-scanned and tested in three-point bending tests in accordance with EN 14651. Both the numerical simulations and the CT results show that the rebars caused a more isotropic fibre orientation in the lower halves of the slabs. This was confirmed in the bending tests, where the lowest variation and highest residual tensile strengths were documented for beams sawn from slabs with grid reinforcement. Fibre migration from the upper layer to middle and lower layers of the slabs due to gravity was observed in all slabs, and in the reinforced slabs, migration also depended on the distance from the casting point. The reinforcement led to an accumulation of fibres above the rebars in the middle layer of each reinforced slab. A set of mechanisms is proposed to explain the experimental results.

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Ai, Qing; Yuan, Yong; Mahadevan, Sankaran; Jiang, XiaomoProbabilistic degradation modelling of circular tunnels assembled from segmental liningsStructural Concrete2/2016257-273Technical Papers

Kurzfassung

Cross-section deformation is considered an important indicator for assessing the structural safety in the inspection and maintenance of tunnels. The way it increases over its lifetime is an indication of the gradual degradation in structural performance. In order to take timely and appropriate maintenance measures before the tunnel reaches the ultimate limit state, a predictive degradation model of cross-section deformation should be established. In this paper, a probabilistic degradation model is developed based on an average uniform rigidity ring model for circular tunnels assembled from segmental linings. By considering the uncertainties and relevant performance of parameters that vary over time, the model is able to supply probabilistic and time-dependent predictions. Critical parameters are identified and the model is simplified following sensitivity analysis. Based on the measuring data, a Bayesian updating method is proposed to improve the input assumptions and predictions of the model. This research provides a perspective on the degradation modelling of the cross-section deformation of circular tunnels assembled from segmental linings and methods for improving the proposed predictive model.

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Chen, Lin; Qu, Wenjun; Zhu, PengLife cycle analysis for concrete beams designed with cross-sections of equal durabilityStructural Concrete2/2016274-289Technical Papers

Kurzfassung

Durability at the corners of the cross-section is relatively weak in the concrete beams of bridges; the reinforcement at the corners therefore corrodes first. In order to delay durability failure at the corners, measures should be taken such as the application of corner concrete coatings or adjustments to the reinforcement at the corners. In this way, the durability resistance would be adjusted to be equal in the section, which is called the equal durability design method. In this paper, the life cycle analyses of a component designed with equal durability and one designed in the traditional way - both in a carbonation environment - are conducted and compared. A probabilistic model of service life is established based on empirical degradation models. Service life distribution is calculated with the Monte Carlo simulation method. Costs associated with durability failure are estimated based on the service life distribution. Related influencing factors are analysed as well. Finally, life cycle cost analyses of the component designed with equal durability and the one designed in the traditional way are conducted and compared. The results show that the component designed with equal durability is more economic over the life cycle if construction cost is kept within about 1.1 times that of the component designed traditionally.

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Shaik_, Faiz Uddin Ahmed; Mali, SarveshProperties of stabilized recycled plastic concretes made with three types of cementStructural Concrete2/2016287-297Technical Papers

Kurzfassung

The growing concern for the ready-mixed concrete industry is the disposal of returned unused concrete. In its plastic state, the concrete is a perishable product and the disposal of any unused concrete presents a set of challenges. An increase in environmental regulations requires the industry to implement the best practices that effectively reduce the quantity of by-product materials requiring disposal. This paper describes a preliminary experimental study on the effect of commercial stabilizer on the plastic and hardened properties of concretes made with three different types of cement commonly used in Australia, namely, general-purpose Portland cement (GP) (100 % ordinary Portland cement (OPC)), general-purpose blended (GB) cement (75 % OPC + 25 % class F fly ash (FA)) and low-heat (LH) cement (35 % OPC + 65 % blast-furnace slag). The effect of various stabilizer dosages on the efflux time (flow time) of GP, GB and LH cement grouts was studied in the initial phase. The results show that for a constant efflux time, the holding duration of the grouts increases with increasing stabilizer dosages (or amounts) and in the case of GB and LH cement grouts, the holding duration is longer than the GP cement grout for the same stabilizer dosage. In the next phase, the predicted stabilizer dosage was added to concretes made with the above three cements to evaluate the plastic and hardened properties of fresh concretes, stabilized concretes and blends of fresh concretes with 10, 25 and 50 % stabilized concretes. The results show that the initial slump values are within the tolerance, except they are higher when the stabilizer dosage is added after 1 h, but the final slump is within the tolerance of the control concrete. After stabilization of the concretes, the initial and final setting times of stabilized concretes increased to > 24 h. The initial and final setting times of the blended concrete containing fresh concrete and 10, 25 and 50 % stabilized concretes are similar to those of fresh concrete for all cement types. The stabilized concretes do not have any significant effect on the compressive strength and shrinkage compared with the control concrete.

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fib-news: Structural Concrete 2/2016Structural Concrete2/2016298-305fib-news

Kurzfassung

The fib in Slovakia
fib Bulletin 77
HiPerMat
Short notes
Congresses and symposia
Acknowledgement

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Inhalt: UnternehmerBrief Bauwirtschaft 2/2016UnternehmerBrief Bauwirtschaft2/2016Inhalt

Kurzfassung

Keine Kurzfassung verfügbar.

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Ernst & Sohn (Hrsg.)Gesamtausgabe UBB 2/2016UnternehmerBrief Bauwirtschaft2/20161-24Gesamtausgabe

Kurzfassung

Komplette Monatsausgabe

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Schalk, GüntherDie Baufirma ist immer der Mörder?UnternehmerBrief Bauwirtschaft2/20161Editorials

Kurzfassung

Keine Kurzfassung verfügbar.

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Kurz informiert: UnternehmerBrief Bauwirtschaft 2/2016UnternehmerBrief Bauwirtschaft2/20162Kurz informiert

Kurzfassung

BVMB fordert: Bauverwaltungen spürbar verstärken!
Erwartungen zum Jahresstart “saisontypisch verhalten”
“Grenzwerte ohne erneuerbare Energien nicht einzuhalten”

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Cadez, IvanAllgemeine Geschäftskosten: Kalkulation nach neuem VerfahrenUnternehmerBrief Bauwirtschaft2/20163-9Berichte

Kurzfassung

Die Allgemeinen Geschäftskosten (AGK) sind ein wesentlicher Bestandteil der vertraglich vereinbarten Vergütung und spielen auch im Rahmen von Ansprüchen aus gestörtem Bauablauf eine wichtige Rolle. Obwohl die AGK das Ergebnis der Baustelle und des Unternehmens entscheidend beeinflussen, schenken viele Bauunternehmen der Bestimmung der baubetriebswirtschaftlich angemessenen Höhe der AGK in der Angebotsphase keine besondere Beachtung. In unserem UBB-Hauptaufsatz stellen wir ein neu entwickeltes Verfahren zur Ermittlung der Höhe der AGK in der Angebotskalkulation vor, das wesentliche Vorteile bei der Erzielung der geplanten Ergebnisse bezüglich der AGK-Deckung bei der Ausführung von Bauleistungen bietet.

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Gilka, Michael"Der Verbrecher ist nicht immer der Bauunternehmer...!"UnternehmerBrief Bauwirtschaft2/201610-11Berichte

Kurzfassung

Manchmal ist die Welt wirklich ungerecht. Vergleichen Sie mal schlechte Nachrichten aus der Autoindustrie und aus der Bauwirtschaft. Was passiert, wenn namhafte Autoproduzenten aus dem Premiumsegment umfangreiche und millionenschwere Rückrufaktionen durchführen müssen, etwa weil die Fahrzeuge schwerwiegende Mängel aufweisen? Erfolgt deshalb ein Aufschrei in der Bevölkerung? Wendet sich der Käufer gar von seinem bisherigen Autoproduzenten ab? Kauft er sein nächstes Auto nur noch bei der Konkurrenz? Nimmt das Image des betreffenden Autoproduzenten einen Schaden? Nein, nichts dergleichen passiert. Ganz im Gegenteil: Die Kunden bleiben ihrem Premiumproduzenten treu und kaufen Jahr für Jahr sogar noch mehr Fahrzeuge.

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Geburtstagsfeier auf Kosten des Finanzamts?UnternehmerBrief Bauwirtschaft2/201612Berichte

Kurzfassung

Feiert ein GmbH-Gesellschafter-Geschäftsführer mit der Belegschaft und mit Kunden seinen Geburtstag, kann er die Kosten der Feier als Werbungskosten in Anlage N seiner Einkommensteuererklärung eintragen. Damit das Finanzamt mitspielt, muss er sich jedoch an ein paar Spielregeln halten.

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News, Urteile und AnweisungenUnternehmerBrief Bauwirtschaft2/201612Berichte

Kurzfassung

Keine Kurzfassung verfügbar.

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Schalk, GüntherAktuelles aus der RechtsprechungUnternehmerBrief Bauwirtschaft2/201613-14Berichte

Kurzfassung

Keine Kurzfassung verfügbar.

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Bach, ThorstenFührungskräfte am Bau: Suche, Sicherung und EntwicklungUnternehmerBrief Bauwirtschaft2/201615-17Berichte

Kurzfassung

Die deutsche Bauindustrie steht vor der Herausforderung, in ihrer Personalpolitik die sogenannten Mega-Trends zu bewältigen. Dazu zählen die demografische Entwicklung, der Mangel an Fach- und Führungskräften sowie der kulturelle Wandel im Arbeitsleben. Somit gilt es für die Unternehmen mehr denn je, ihre Mitarbeiter entsprechend zu suchen, zu binden und zu entwickeln. Mit diesem Aufsatz möchte ich Anregungen und Hilfestellungen geben, wie Unternehmen diese Herausforderungen meistern können.

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Risikogeschäfte der GmbH ohne steuerliche FolgenUnternehmerBrief Bauwirtschaft2/201618Berichte

Kurzfassung

Investiert eine GmbH Geld in Risikogeschäfte und erleidet daraus Verluste, ist für das Finanzamt die Sache meist klar. Nicht die GmbH ist die treibende Kraft für solche Risikogeschäfte, sondern der an der GmbH beteiligte GmbH-Gesellschafter-Geschäftsführer. Fatale Folge: Die Verluste stellen eine verdeckte Gewinnausschüttung (vGa) dar. Doch von dieser sehr fiskalischen Auffassung rückt das Bundesfinanzministerium (BMF) nun ab.

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Umsatztantieme ist nicht automatisch verdeckte AusschüttungUnternehmerBrief Bauwirtschaft2/201619Berichte

Kurzfassung

Gönnt sich ein GmbH-Gesellschafter-Geschäftsführer zusätzlich zu seinem Fixgehalt eine Umsatztantieme, sehen die meisten Prüfer und Sachbearbeiter in den Finanzämtern Rot. Die Umsatztantieme ist ihrer Meinung nach eine verdeckte Gewinnausschüttung (kurz vGA).

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