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.

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.

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.

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.

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.

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.

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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No short description available.

Eurocode 2 consists of four parts that have to be applied in conjunction with the respective National Annexes of the CEN member states. The National Annexes were introduced, in particular, to maintain national safety levels and to account for regional aspects in the different states.
The CEN (European Committee for Standardization) will revise and extend all structural Eurocodes by 2018. As part of that process, two main objectives for revising Eurocodes have been formulated: a reduction in the number of Nationally Determined Parameters (NDP) and improving the “ease of use”.
In order to reduce the number of NDP, improve the ease of use and allow for further harmonization without changing the main structure and the design models of Eurocode 2, the National Annexes of EN 1992-1-1 for the different CEN member states have been compared and analysed. Furthermore, the analysis of the National Annexes may help to identify some main aspects for the revision of Eurocode 2.
This paper summarizes the analysis of the National annexes of EN 1992-1-1 and makes first proposals for further harmonization.

Fire, as one of the most severe load conditions, has an important impact on concrete structures. Not only does a fire affect the material strength, it affects structural stiffness and stability as well. A concrete column, compared with other structural members, in most cases has to cope with both vertical forces and bending moments transferred by slabs and beams. Consequently, it is essential to find a reliable and practical way of establishing interaction curves for the overall structural behaviour of concrete columns subjected to fire. In this paper, a cross-sectional calculation method based on the material models of Eurocode 2 is explained and adopted in order to calculate interaction curves for a typical rectangular column exposed to the ISO 834 standard fire. Subsequently, an iterative approach is introduced to develop interaction curves taking into account second-order effects in the case of all the four faces of a column exposed to fire. The maximum permissible slenderness ratios for columns in different fire durations are obtained and compared with Eurocode 2 provisions. Finally, this method is used to calculate the maximum permissible slenderness ratios for columns exposed to hydrocarbon and natural fires.

The standard European building specifications, grouped in a nine-volume Eurocode, describe different approaches for determining the properties of commonly used building materials such as steel, aluminium, concrete, etc.
The American Concrete Institute (ACI) also offers different reports concerning concrete structures (ACI 318R), lightweight concrete (ACI 213R) and the long-term mechanical behaviour (ACI 209R) of concrete. Those reports, used as building codes, are applicable when the properties and composition of the material respect various criteria.
All those materials that do not meet the scope criteria of Eurocode 2 or ACI reports because of their composition, property values or application cannot be used in the design of structures with those building codes. Regarding cement-based materials, concretes and mortars whose compressive strength is lower than the minima might not be useful for structures; however, they present an interesting potential for applications such as infrastructure materials, slabs-on-ground, etc. When designing structures and infrastructures in those materials, the accuracy of any formula offered by those building codes should be checked before being used.
This article compares experimental measurements and predictive formulas for the engineering properties (compressive and tensile strengths, modulus of elasticity). The results show that the addition of specific aggregates with low stiffness and strength modifies the relation between those engineering properties, thus reducing the accuracy of some of the predictive formulas suggested in ACI reports or Eurocodes.

This paper describes the changes to design provisions for embedded steel reinforcement in the fib Model Code for Concrete Structures 2010. The changes introduce new coefficients for steel grade and clear spacing between bars, and extend the range of concrete strengths covered. The way in which the contribution of hooks or anchorages is calculated has been revised and the contribution of end bearing to laps and anchorages of compression bars is recognized. The revised rules represent a move away from a distinction between laps and anchorages per se towards a distinction based on the presence or absence of transverse pressure perpendicular to the bar axis within the bond length. The benefits of staggering laps with only a proportion of bars lapped at a section are also reviewed. Finally, the potential impact of lap and anchorage performance on structural robustness is discussed, and it is concluded that this can only be achieved if bar yield precedes splitting mode bond failures.

The effect of concrete grade on the bond between 12 mm diameter deformed steel bars and recycled aggregate concrete (RAC) has been investigated with the help of 45 pullout tests with concentric rebar placement for coarse recycled concrete aggregate (RCA) replacement levels of 25, 50, 75 and 100%. For all the three concrete grades, the measured bond-slip relationships indicate similar mechanisms of bond resistance in the RAC and the natural aggregate (NA) concrete. The most accurate and least conservative predictions of the measured bond strengths were obtained from the local bond-slip model in the fib Model Code for Concrete Structures 2010. Bond strength normalized to fc(3/4) resulted in an improved match with test data and increased with an increase in the RCA replacement levels and decreased with an increase in compressive strength. An attempt to explain this behaviour has been sought in terms of brittleness index, an analogous parameter from rock mechanics. An empirical bond stress versus slip relationship has been proposed for the 12 mm diameter bar and it is conservatively suggested that similar anchorage lengths for this bar in all three concrete grades can be adopted for the RAC and the NA concretes.

This paper presents a five-spring model capable of predicting the complete pre- and post-peak shear behaviour of deep beams. The model stems from a two-parameter kinematic theory (2PKT) for the shear strength and displacement capacity of deep beams under single curvature. Four of the springs of the model represent the shear resistance mechanisms of the beam, while the fifth spring models the flexural behaviour. The model predicts not only the load-displacement response, but also the deformation patterns of the beam and how these patterns change with increasing load. Validation studies are performed by using 28 tests from the literature, showing excellent results. The model is used to interpret the tests and to draw conclusions about the behaviour of deep beams. It is shown that shear strength variations of up to 60 % between nominally identical specimens can be caused by variations in the path of the critical shear cracks. It is also demonstrated that loss of bond of large reinforcing bars increases the shear capacity of deep beams. Finally, the five-spring model is shown to predict the post-peak shear behaviour effectively, which is important for the analysis of structures under extreme loading.

In the post-tensioned anchorage zone, the load transfer path of an anchor force can be visualized by an infinite number of isostatic lines of compression (ILCs). The method was initially proposed by Guyon and recently attracted significant interest from a number of researchers. Based on the work of these predecessors, an updated mathematical model has been proposed in order to analyse the bursting forces and the distribution of transverse stresses in the anchorage zone. Compared with the results of a finite element analysis, the updated equations are more accurate than the previous ones. Based on the observation that the sixth-order polynomial expression is better than the fourth-order one, as far as the solution of bursting stresses is concerned, it can be reasonably postulated that a de facto function of the ILCs must exist. Additionally, it is equally interesting that the bursting forces derived with the updated analytical model are the same as those obtained with the formula in the current AASHTO-LRFD Bridge Design Specifications based on numerical stress analyses.

The material characterization of steel fibre-reinforced concrete (SFRC), which is required for its implementation in design codes, should be based on nominal properties that describe its post-cracking strength in tension. In the case of brittle and quasi-brittle materials, such as concrete, the tensile parameters are often derived indirectly. However, for materials with more ductility, such as SFRC, there is conjecture as to whether or not an indirect measure may be used to establish the stress versus crack opening displacement relationship, such as the use of a three- or four-point prism test combined with an inverse analysis. In this paper a simple and efficient inverse analysis technique is developed and shown to compare well with data obtained from direct tension tests. Furthermore, the methodology proposed by the fib Model Code for Concrete Structures 2010 has been investigated and recommendations made to improve its accuracy.

At RWTH Aachen University recently, a pavilion was constructed with a roof shell made of textile-reinforced concrete (TRC), a composite material consisting of a fine-grained concrete and high-strength, non-corroding textile reinforcement in the form of carbon fibres. The thin-walled TRC shell structure demonstrates impressively the loadbearing capacity of this innovative composite material. The present paper discusses the practical issues concerning the construction, such as the fabrication of the TRC shells using shotcrete, the concepts developed for the arrangement of the textile reinforcement and the erection of the shells on top of the precast concrete columns. The issues concerning the design, assessment and numerical simulation of the loadbearing behaviour of TRC shells are presented in the companion paper (Part II).

The present paper describes a design approach for textile-reinforced concrete (TRC) shells which reflects the interaction between normal forces and bending moments based on the cross-sectional strength characteristics of the material determined experimentally. The influence of oblique loading on the composite strength of TRC elements with flexible reinforcement is included in a normalized interaction diagram for combined loading. As an example, the design approach is applied to the ultimate limit state assessment of a TRC shell in double curvature. Furthermore, the general applicability of the design approach is discussed in the light of the non-linear loadbearing behaviour of TRC. Due to its strain-hardening tensile response, stress redistributions within the shell result in loadbearing reserves. Details of the structural design and production solutions developed and applied during the realization of the TRC shell structure are described in the companion paper (Part I).

Non-linear constitutive models for concrete in compression are frequently defined in design codes. The engineer generally uses either the linear (in SLS) or non-linear (in ULS) compression model. However, a large variety of different approaches exists for describing the behaviour of the cracked concrete tension zone, and the selection of a corresponding model is usually based on qualitative engineering judgement. The aim of this paper is to assess the prediction quality of several concrete material models in order to provide a quantitative model selection. Therefore, uncertainty analysis is applied in order to investigate the model and parameter uncertainty in the bending stiffness prognosis for flexural members. The total uncertainty is converted into a prognosis model quality that allows a quantitative comparison between the material models considered. The consideration of the reinforced concrete in tension is based on the characterization of the tension stiffening effect, which describes the cracking in an average sense. In the interest of the practical applicability of the models considered, even for large structures, no discrete crack simulations based on fracture mechanics are considered. Finally, the assessment identifies that the prediction quality depends on the loading level and, furthermore, the quality across the models can be quantitatively similar as well as diverse.

The loadbearing capacity of steel-concrete composite slabs using thin-walled steel sheeting with prepressed embossments is in most cases determined by their resistance in longitudinal shear. The design of composite slabs still requires full-scale laboratory bending tests to be performed. Small-scale shear tests cannot include all of the influences affecting the bent slab. However, by using an appropriate procedure, the shear characteristics obtained from such tests can be used to determine the bending capacity of the slab. Two such procedures are compared in this paper.
End restraints effectively increase the loadbearing capacity of the composite slabs. Two different types of easily assembled additional end constraints are also tested and compared in this paper. Small-scale tests are used to obtain their shear bearing characteristics and to predict the loadbearing capacity of bent slabs using these restraints.

The fib in Russia: new standards; Worldwide representation at ACF 2014; DISC2014: the past and the future; Old for new: Penang Bridge; A venerable institute turns 80; JPEE2014 in Lisbon; fib MC2010 course in Brazil; Short notes; Nigel Priestley † 1943-2014; Congresses and symposia; Acknowledgement

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No short description available.