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Romero, Manuel L.; Cajot, Louis-Guy; Conan, Yves; Braun, Matthias Fire design methods for slim-floor structures Steel Construction 2/2015 102-109 Articles

Kurzfassung

Slim-floor beams are well-known, sustainable and economical solutions for residential, commercial and industrial buildings. However, despite their widespread use, Eurocode 4 contains no specific simplified calculation methods for the fire resistance of integrated and shallow floor beams. There is a clear need for an improved understanding of the performance of structures in fire plus clear and cost-effective design guidance. This paper presents a set of simplified rules for determining thermal fields in the lower flange, web, rebars and slab of slim or integrated floor beams. This calculation methodology is based on existing formulas taken from different parts of Eurocode 4 except for the temperature calculation in the lower flange, which is deduced from a parametrical study using the SAFIR software.

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New technology paves the way for greener steel Steel Construction 2/2015 109 News

Kurzfassung

Keine Kurzfassung verfügbar.

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Hicks, Stephen; Peltonen, Simo Design of slim-floor construction for human-induced vibrations Steel Construction 2/2015 110-117 Articles

Kurzfassung

This paper presents a simplified design method for evaluating the vibration response of composite floors with slim-floor beams. The methodology is amenable to hand calculations and is appropriate for floors with regularly spaced grids and vibrations that are occasioned by walking activities. From in situ tests that have been undertaken on six floors, it is shown that slim-floor construction can easily satisfy the demanding ISO 10137 response limits for operating theatres and laboratories together with limits recommended by industry for car parks and shopping malls. Comparisons with measurements show that the simplified method presented here provides conservative predictions, and may therefore be used with confidence in design.

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Leskela, Matti V.; Peltonen, Simo Effect of unzipping connection behaviour on the composite interaction of shallow floor beams Steel Construction 2/2015 118-121 Articles

Kurzfassung

Unzipping connection behaviour is not referred to in EN 1994-1-1 - only ductile and non-ductile shear connections are classified. It might be clear that unzipping connections belong to the non-ductile ones, but not all the non-ductile connections are unzipping ones. Characteristic of unzipping connection behaviour is that, initially, connection stiffness is high and composite action is efficient. However, as the load increases, so the connection loses its shear stiffness very rapidly, and after the onset of plastic behaviour in the beam, the decking no longer contributes to the bending resistance of the initially composite member. This behaviour is most typically seen in shallow floor beams (abbreviated to SF beams) supporting hollow-core decking. This is a companion paper to the one in which the composite action in SF beams with ductile shear connections is discussed.

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Kuhlmann, Ulrike; Just, Adrian; Leitz, née Froschmeier, Bernadette; Grabe, Jürgen; Schallück, Christoph Simplified criteria and economic design for king piles in combined steel pile walls according to Eurocode 3, part 1-1 Steel Construction 2/2015 122-132 Articles

Kurzfassung

The steady growth in world trade leads to a demand for more port and harbour facilities. One of the most common forms of construction for deep-water harbour quays is the combined steel pile wall. It consists of up to 45 m long H-section king piles plus Z-section intermediate sheet pile infill elements. The intermediate elements and the quay both transfer all forces to the king piles, which as a result are loaded with (bi)axial bending and axial force, so their stability must be checked. Up to now the effect of the soil surrounding the piles was used just in terms of best practice - buckling about the weak axis and lateral torsional buckling were neglected completely. Considering these stability phenomena in design without taking the soil into account would lead to a very conservative approach. As verification of lateral torsional buckling according to EN 1993-1-1 (EC3-1-1) becomes relevant when the embedment is neglected, a more refined analysis has been developed.
This article presents simplified criteria that quickly exclude stability phenomena (flexural buckling about the weak axis and lateral torsional buckling) while taking into account the effects of the soil. For the cases in which the criteria are not fulfilled, the article presents economic solutions that consider the embedment of the king piles in the soil in the design for stability.

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Eleventh edition of the Edoardo Benvenuto Prize Steel Construction 2/2015 132 News

Kurzfassung

Keine Kurzfassung verfügbar.

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Helbig, Thorsten; Kamp, Florian; Oppe, Matthias An Eye to the Sky - Inclined grid shell dome of 90 m in Astana, Kazakhstan Steel Construction 2/2015 133-138 Report

Kurzfassung

A 6500 m² glazed grid shell dome covers the Nazarbayev Centre in Astana, Kazakhstan. Located near the Presidential Palace, this futuristic building, designed by Foster Partners in London, is one of a whole series of prominent architectural buildings in Astana.
The 20° inclined glass roof spans across various levels of the reinforced concrete structure and slopes down to the north. The dome has a span of over 90 m and a rise of about 11 m. A sufficient in-plane stiffness of the rectangular grid of the dome is achieved by the rigidly connected rectangular hollow sections, which are framed by a strong circumferential edge beam. Connections of the grid and edge beam are bolted mainly as a means to cope with the ambitious time schedule that required fast erection during the strong Kazakh winter. By means of a statically determined support, the roof grid and edge beam of the glazed dome remain largely independent of the concrete structure’s long-term and deformation behavior. A major issue for the roof structure was the verification of global buckling of the dome. In order to minimize tolerances, all connection surfaces of bolt joints were CNC milled. This article summarizes the design philosophy of the dome steel grid and the relationship between glazed dome and main concrete structure.

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News: Steel Construction 2/2015 Steel Construction 2/2015 138 News

Kurzfassung

The DVS EXPO will focus on robotics and virtual welding trainers
Upgrade for Hot Strip Mill in Port Talbot

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ECCS News: Steel Construction 2/2015 Steel Construction 2/2015 139-142 ECCS News

Kurzfassung

Events
Announcements
Technical Committees (TC) activities
TC News

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Stadsbrug Nijmegen: a beauty with waves and curves Steel Construction 2/2015 142-143 News

Kurzfassung

Keine Kurzfassung verfügbar.

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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

Kurzfassung

Keine Kurzfassung verfügbar.

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

Kurzfassung

Keine Kurzfassung verfügbar.

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

Kurzfassung

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

Kurzfassung

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

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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