Lightweight foamed concrete (LWFC) is a concrete having structural strength with lightweight density and high flowability. High-performance lightweight foamed concrete (HPLWFC) is used in modern concrete technology and intensively in the construction of high-rise buildings, long-span concrete structures, road sub-bases and other applications. The present work deals with the fresh and hardened properties of LWFC. The fresh properties of LWFC are measured with the flow and fresh density tests. The hardened properties tests include compressive strength, flexural strength, flexural toughness, static modulus of elasticity, ultrasonic pulse velocity, water absorption and oven-dry density. In addition, the study focuses mainly on the effect of the fibres added to LWFC mixes. Two types of fibre have been used: glass fibres and polypropylene fibres, and the combination of glass fibres (GF) and polypropylene fibres (PPF) to obtain hybrid fibres (GF+PPF).This study also focuses on the effect of hybrid fibres on the flexural toughness of HPLWFC. Trial mixes have been used to choose the optimum mix. The definition for choosing the best mix depended on three parameters: oven-dry density, flowability and compressive strength. The volume fraction of glass and polypropylene fibres are 0.06, 0.2, 0.4 and 0.6 %, and 0.2, 0.6, 1 and 1.4 % respectively. The percentages of hybrid fibres “GF + PPF” are “0.2 + 0.6”, “0.4 + 0.6”, “0.2 + 1” and “0.4 + 1” %. The results show that the greatest increments in the compressive and flexural strengths of LWFC are 51 and 21 % respectively due to the use of 0.6 % glass fibres. On the other hand, LWFC reinforced with polypropylene fibres exhibits only a minor increase in compressive, splitting tensile and flexural strengths. The best percentage of hybrid fibres yielding the highest increment in LWFC is “0.4 % GF + 0.6 % PPF”. The results of flexural toughness tests indicate that the polypropylene fibres denote a higher efficiency in the flexural toughness than is the case with glass fibres. The flexural toughness results increase with the volume fraction of the fibres. The hybridization shows the best flexural toughness values due to the cooperative work of the glass and polypropylene fibres boost the performance of flexural toughness in pre-crack and post-crack zones. Therefore, the use of 0.4 %GF + 1 %PPF gives the best results in this regard.

This paper summarizes the results of the development of advanced fibre-reinforced concrete intended for explosion-resistant applications. Experimental research was carried out with the aim of contributing to understanding the effect of different types of reinforcement on the behaviour of high-performance fibre-reinforced concrete subjected to a blast load. The fine-grained concrete matrix was reinforced by various types of dispersed fibre - metallic, carbon, mineral and polymer - in different lengths (6-55 mm) and combinations, while the volume content (3 %) of fibres was kept constant. Physico-mechanical and explosion tests were performed on prismatic and slab-shaped specimens and the effect of different kinds of reinforcement on the blast resistance and mechanical performance of the concrete samples was evaluated. The accelerations of the specimens within the blast load were ascertained. The material characteristics and explosion test data obtained were used to create a finite element model in LS-DYNA. The numerical and experimental investigations resulted in the design of concrete elements for population protection which are able to resist an explosion defined by the weight and placement of the charge. The resistance of the newly designed concrete element was confirmed by a field blast test.

Fibre-reinforced concrete (FRC) without any traditional reinforcement is used particularly extensively in structures such as pavements and tunnels. The fib Model Code for Concrete Structures 2010 introduced the possibility of using FRC for structural design and it is becoming a reference document for such structures. The application of fib Model Code 2010 suggestions for flexural and axial forces, once the constitutive relationships of the material are defined, allows for safe design. However, shear verification is often a cause of discussion in the design community. The aim of this paper is to clarify this aspect and provide a procedure that can be followed in the design process. A case study is also presented.

A method of analysis for predicting the shear strength and behaviour of shear-dominated reinforced concrete beams is presented in this paper. The proposed model is based on the softened membrane model that accounts for the Poisson's effect on the behaviour of reinforced concrete beams subjected to the combined effect of shear and flexure. The softened membrane model is appealing for modelling the shear behaviour of concrete elements as it is based on solid mechanics of materials fundamentals. The accuracy of the proposed mathematical model was validated against the experimental results of 66 reinforced concrete elements tested under pure shear as well as 167 shear-dominated RC beams available in the literature. Analysis results showed that the proposed model could satisfactorily predict the shear strength as well as the entire shear stress-shear strain behaviour of shear-dominated beams.

Strain penetration of the longitudinal reinforcement in reinforced concrete (RC) members at the joints and/or footings results in fixed-end rotations at the member ends. Several experimental studies have shown that fixed-end rotations caused by strain penetration contribute significantly (up to 50 %) to the total displacement capacity of RC members. Hence, accurate determination of these fixed-end rotations at yielding and ultimate limit states is of primary importance when defining the structural response of RC members. The purpose of this study is to present the theoretical background to and the assumptions made for the most common relationships found in the literature for determining strain penetration-induced fixed-end rotations at yielding and ultimate. Furthermore, new simple relationships are proposed on the basis of realistic and mechanically based assumptions. Comparisons between the existing and proposed relationships demonstrate the limitations of the former. Finally, the proposed relationships are calibrated against experimental measurements of RC column specimens subjected to cyclic loading with recorded fixed-end rotations due to strain penetration in the adjacent joints and/or footings.

A reliability-based investigation into the ductility measures for reinforced concrete (RC) beams designed according to the current fib Model Code for Concrete Structures 2010 is presented in this paper. Based on the ductility ratio (= ratio of strain in tensile rebar to yield stress of steel), a limit state to ensure adequate ductility in RC beams is proposed. Results show that the ductility ratio generally follows a right-skewed distribution, and due to variability in the material properties and model error, there is high variability in the strain ductility. This high variability in the ductility ratio leads to a high probability of non-ductile behaviour for RC beam designs based on the code. This is more pronounced for normal-strength concrete and grade S500 steel. Based on a target probability taken from the literature, a modification to the allowable neutral axis depth advised by the code is proposed. The results presented in this paper indicate that more reliability-based studies of the safety factors provided by fib Model Code 2010 are needed in order to ensure adequate ductility in RC beams.

In engineering practice, the prevention of early-age cracking in massive concrete structures is of great importance to their serviceability during the whole life cycle. From the scientific viewpoint, this engineering concern requires the control of the early-age performance of concrete structures. Following earlier research projects against the background of the Hong Kong-Zhuhai-Macao Link, the focus of this work is to obtain insights into the evolution of the early-age behaviour of precast concrete in an immersed tunnel. To this end, a full-scale test was performed, from which the behaviour of early-age concrete could be observed directly. After validating the constitutive model developed with the test results, the early-age performance during the entire fabrication process of the precast concrete immersed tunnel is evaluated numerically. It was also found that stress relaxation plays a major role in stress development in the immersed tunnel, although the thermal strain is the main source of early-age stresses. This in-depth investigation resulted in a comprehensive understanding of the early-age behaviour of an actual precast concrete immersed tunnel. What is more important, the early-age performance of concrete structures can be accurately evaluated and further adjusted or controlled with the help of the validated numerical modelling, which is no doubt beneficial for the control of early-age cracking in massive concrete structures in engineering.

The coupling of subsequent rings in the circumferential joints of tunnel lining systems is of particular interest in mechanized tunnelling and a controversial issue in discussions. On the one hand, interlocking systems such as “cam & pot” can be of use in limiting the lining's deformation. But on the other hand, unfavourable conditions often lead to repetitive and significant damage that decreases the tunnel's lifetime. This paper describes the experimental results of a three-part optimization concept (structural analysis, topological optimization and experimental verification) that was tested for concrete linings using the example of the shear coupling mechanism. First, geometrical dependencies are analysed which reveal predominantly stronger cams than corresponding pots. Hence, pot bearing capacities are increased, transferring topological optimization results to reinforcement concepts featuring micro-mesh reinforcement, steel fibre cocktails and rebars welded to anchor plates. The latter especially resulted in comparatively stronger pots along with considerably better ductility. Nevertheless, pots still represent the weaker part and are crucial for the design. Therefore, a concept with steel dowels and predefined static boundary conditions was tested. The results are characterized by a significantly lower scatter of bearing capacities accompanied by much better ductility.

Keine Kurzfassung verfügbar.

RILEM-fib MoC | A continuing evolution | fib on LinkedIn^TM | ICCRRR 2015 | Departure of fib Secretary General Petra Schumacher | fib Bulletin 76 | fib MC2020 | Short notes | A.G.S. Bruggeling 1923-2015 | George Somerville OBE FREng 1934-2015 | Congresses and symposia | Acknowledgement

Keine Kurzfassung verfügbar.

Keine Kurzfassung verfügbar.

Komplette Monatsausgabe

Keine Kurzfassung verfügbar.

Handwerker fordern Neuregelung für Mängelbeseitigung
ÖPP-Projekte sollen transparenter werden
“Die Energie- und Wärmewende muss weitergehen!”

Seit Jahren erfreut sich die Bohrbranche eines ständig wachsenden Marktes. Es gibt viele technische Weiterentwicklungen. Technische Regelwerke werden ergänzt und fortgeschrieben. Diese Entwicklungen sind bei der grabenlosen Leitungsverlegung im Horizontalspülbohrverfahren (Horizontal Directional Drilling, HDD) sowie in der Geothermie bei der Herstellung von Erdwärmesonden mit Teufen bis 100 Meter besonders deutlich erkennbar. Doch mit ihr geht auch die Zunahme von Sach- und Vermögensschäden und der daraus folgenden Streitfälle einher. Spätestens dann stellt sich die Frage: Was hätte wer wann wissen können und müssen? Unser UBB-Hauptaufsatz nimmt eine Standortbestimmung vor.

BauFordSiG: Auch Erwerber haben Baugeld!
Ablehnung eines Beweisantrages im Zivilverfahren

Nicht selten kommt es bei Bauvorhaben zum Streit zwischen Bauherr und Architekt/Ingenieur hinsichtlich der Höhe von Honoraren. Spätestens vor Gericht hat der Architekt die Voraussetzungen seines Honoraranspruchs darzulegen und zu beweisen. Dabei spielt die Prüfbarkeit der Honorarschlussrechnung eine zentrale Rolle. Wendet der Auftraggeber (AG) die fehlende Prüfbarkeit einer Rechnung innerhalb der Prüffrist ein, wird der Honoraranspruch nicht fällig (vgl. § 15 Abs. 1 HOAI) und kann nicht durchgesetzt werden. Daneben kann der AG im Prozess die Forderungshöhe bestreiten, so dass der Auftragnehmer (AN) seine Ansprüche prüfbar darlegen muss.

D&O-Versicherungen (Directors-and-Officers-Versicherung, auch Organ- oder Manager-Haftpflichtversicherung) sind in Managerkreisen ein heißes Thema. Wer sie hat, wähnt sich in Sicherheit. Dass dem nicht notwendig so ist und deshalb auch die Manager-Gehälter eher relativ zu betrachten sind, meint Franz M. Held, Mitglied der Geschäftsleitung VOV GmbH.

In den nächsten Wochen steht bei den meisten Unternehmern die Gewinnermittlung 2014 auf dem Plan. Wer dringend Betriebsausgaben benötigt, sollte die eine oder andere Steuerstrategie fahren. Hier die besten Steuertipps, mit denen Unternehmen der Baubranche die Steuerlast 2014 drücken können.

Keine Kurzfassung verfügbar.

Keine Kurzfassung verfügbar.

Keine Kurzfassung verfügbar.

Die denkmalgeschützte Domschule in Güstrow wurde zur Nutzung durch das benachbarte John-Brinckman-Gymnasium saniert und umgebaut. Es handelt sich um das älteste erhaltene Schulgebäude in Mecklenburg-Vorpommern mit über 400-jähriger durchgehender Nutzung. Der Renaissancebau wurde 1868 durch einen Backsteinbau ergänzt und erhielt nun ein neues Erschließungsbauwerk, s. Meldung S. 283. (Foto: Natalie Toczek, Berlin)

Keine Kurzfassung verfügbar.