Shrinkage plays an important, sometimes crucial, role in the design of many types of concrete structures as well as in their behaviour after construction. However, the uncontrolled strains are often larger than the expected values. As a matter of fact, there is as yet no perfectly satisfactory physical explanation for shrinkage. In this work, a large database has been set up for shrinkage testing performed by several research centres in Europe. On the basis of the statistical analysis of this database and by observing real structural behaviour, it becomes possible to investigate the current codes of practice regarding the computation of time-dependent shrinkage strains. As comparison with experimental tests has shown that predictions are often inaccurate, a correction factor is proposed in this work to improve the European Code, Eurocode 2, and lead to more satisfactory results.

Fatigue design according to CEB-FIP Model Code 90 is limited to concrete grades up to C80. In addition, the design rules include a strength-dependent reduction in the fatigue reference strength, which leads to uneconomical design of high-strength concrete. Considering comprehensive knowledge now available concerning the fatigue behaviour of normal-strength and high-strength concretes, the amount of this reduction can no longer be justified. A new design model for compressive fatigue loading and its derivation is presented in this article. A comparison between the new design model and the current standard ones reveals that the new design model ensures safe and economical design of normal-strength, high-strength and ultra-high-strength concrete. This new design model is included in the new fib Model Code 2010.

Many box girder bridges are constructed with doubly unsymmetrical precast beam units. The aim of this paper is to present special considerations for the optimum arrangement of pretensioned strands in a simply supported precast pretensioned beam with a doubly unsymmetrical section. The goal of the optimum arrangement is to minimize the distortion (lateral sway phenomenon) caused by the doubly unsymmetrical characteristic of the beam section at transfer. The study shows that the distortion of the unsymmetrical section is minimized when the resultant stresses at transfer are constant over all of the top flange and over all of the bottom flange of the precast beam for most of the sections within the beam length. In this case, the neutral axes of these sections will be horizontal with respect to the beam section. This approach is verified with the help of two different finite element models. In the first model, the beam is modelled as one-dimensional space frame elements; in the second model, the beam is modelled using three-dimensional solid elements. A practical example of a box girder bridge made from doubly unsymmetrical precast pretensioned beams in the APM (Automated People Mover) elevated bridge project in Saudi Arabia is also presented.

• Focus on sustainability at the 2012 fib symposium in Stockholm
• 2012 fib Medals of Merit awarded in Stockholm
• 9th International fib Ph.D. Symposium in Karlsruhe
• Bond in Concrete 2012 held in Brescia, Italy
• Sustainability short course held in Naples
• fib Bulletins
• Rüdiger Rackwitz † 1941-2012
• Impact factor
• Short notes
• Congresses and symposia
• Acknowledgement

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This paper examines the problems of the seismic design of precast concrete structures as indicated by the effects of the L'Aquila earthquake of 2009. The behaviour of such structures on that occasion is analysed on the basis of detailed surveys performed on site on a relevant number of buildings just after the earthquake.
Following this analysis, which points out the inadequacy of the cladding panel connections, the paper presents a systematic definition of the problem, examining the behaviour of the whole system of structure + panels. Proposals are made for the typology of one-storey buildings for industrial uses, some possible alternative solutions that ensure the stability of all the construction elements. Specific calculations for a typical precast building give the order of magnitude of the forces and/or displacements for which the connections are to be designed.

This research deals with the behaviour of grouted dowels used in beam-to-column connections in precast concrete structures. The research focuses primarily on the theoretical and experimental analysis of the resistance mechanism of the dowels. The experimental programme included 15 models for analysing the following variations in dowel parameters: a) dowel diameters of 16, 20 and 25 mm, b) dowel inclinations of 0° (i.e. perpendicular to the interface), 45° and 60°, c) compressive strength of classes C35 and C50 for the concrete adjacent to the dowels, and d) the absence or presence of compressive loads normal to the interface. The experimental results indicate that the ultimate capacity and shear stiffness of the inclined dowels are significantly higher than those of the perpendicular dowels. Based on these results, an analytical model is proposed that considers the influence of the parameters studied regarding the capacity of the dowel.

Knowledge of the stress-strain relationship of concrete under uniaxial compression is crucial for the design of concrete members. This study focuses on the stress-strain behaviour under compression and especially the strain-softening of self-compacting concretes produced with limestone fillers. Four self-compacting concretes (SCC) and three conventional vibrated concretes (VC) were used to produce cylindrical test specimens with an h/d ratio of 3. The &sgr;-&egr; diagram at five different ages (3-91 days) was recorded during uniaxial compressive tests. The peak strain of the SCC cylinders was shown to be higher than the ones recorded for VC concretes. However, the specific toughness of both concrete types turned out to be comparable.

This paper confirms that the structural behaviour of ground-supported slabs is a non-linear function of the structural properties of slabs as well as the supporting soil. The findings reported emphasize that the suggested equations used in design codes pay insufficient attention to the effect of the supporting ground stiffness within the context of the mechanical behaviour of slabs as far as ductility is concerned. The results presented demonstrate that ground stiffness has a significant effect on the ductility of ground-supported slabs. It also pays particular attention to the possibility of determining the ductility limit of slabs.

Experience with the analysis and performance of 15 lightweight concrete footbridges is presented from the point of view of their dynamic response caused by moving people. The footbridges are formed either by a stress ribbon or by a slender deck supported by arches or suspended from pylons. The dynamic response was determined according to a procedure given in a 1998 draft of Eurocode 2: Design of Concrete Structures - Part 2: Concrete Bridges. Thirteen footbridges have been built and so far no complaints about their dynamic behaviour have been recorded.

The predominant failure mode of concrete members reinforced with fibre-reinforced polymer (FRP) bars is flexural, due to either concrete crushing or FRP rupture. Many design tools have been developed for the flexural design of FRP-reinforced concrete. These tools are sufficiently accurate, but an iterative procedure is required when dealing with flexural failure due to FRP rupture. In addition, despite the fact that the design concepts involved are similar to those used for conventional steel-reinforced concrete, the changes in the design philosophy and the linear behaviour up to rupture of the FRP bars lead to the sectional properties having a different influence on the design, which not everyone may be familiar with. Therefore, this study proposes a general methodology for evaluating the design flexural capacity of FRP-reinforced concrete sections. This methodology is based on the design provisions of Eurocode 2 and comprises non-dimensional, closed-form equations, derived independently of the concrete and FRP characteristics. The proposed methodology can be used to derive universal dimensionless design charts as well as tables. The accuracy of the proposed design tools has been verified by comparing the predictions with the experimental results of 98 beams, which are available in the published literature.

• Latin American seminar on conceptual design and applications of precast concrete structures
• fib days India 2011
• MC2010 presentations
• 3rd International Symposium on UHPC (HiPerMat 2012)
• fib short course: Concrete Structures in Fire, South Africa
• 2013 fib Achievement Award for Young Engineers
• fib Bulletins
• ICCS13, Tokyo: Call for papers
• Ibero-American congress 2012
• What is the “Impact Factor”?
• Short notes
• Congresses and symposia
• Acknowledgement

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The magnitude 6.3 earthquake that struck Christchurch on 22 February 2011 caused widespread damage throughout Christchurch's central business district (CBD), where a large proportion of the building stock consists of reinforced concrete (RC) buildings. Damage to the façades of these buildings was a clear contributor to overall building damage. This paper presents the damage assessment of the façade systems of these RC buildings. A survey of 173 RC buildings in the Christchurch CBD is conducted here, focusing on the damage to the façade systems of the buildings. The survey covers only buildings greater than three storeys in height, excluding the majority of unreinforced masonry façades, the damage to which has been well documented. The façade type and modularity is classified for each system, as well as the connection type where possible. The level of damage to each façade is determined in terms of the following performance levels: Operational, Immediate Occupancy, Life Safety and High Hazard. Further investigation is also made into three precast concrete panel systems. These case studies examine the damage, detailing and construction practice of each particular system.

In less than six months, the city of Christchurch, New Zealand, experienced two major earthquakes: on 4 September 2010 and 22 February 2011. The former was generated by the rupture of the previously unknown Greendale fault, releasing a magnitude Mw 7.1 earthquake 30-40 km away from the Central Business District (CBD); the latter event, of magnitude Mw 6.2, was less than 10 km from the CBD on an unknown buried fault at the edge of the city. There was widespread damage to the lifelines covering not only Christchurch City but also the closest districts of Selwyn and Waimakariri. The different nature of the fault ruptures and locations of the two events resulted in a variation in damage levels between the earthquakes throughout the region.
Teams from various organizations performed inspections on over 800 bridges throughout the affected Canterbury region. No major collapses were registered among concrete bridges and only 20 bridges required closure due to damage caused by the two earthquakes. Owing to the nature of the Canterbury soils, extensive liquefaction and lateral spreading occurred throughout the region. It was this lateral spreading that caused most of the traffic disruption and closure of bridges, due to damage to the abutments and approaches, foundation settlement and rotation.
The authors aim to give a detailed overview of the damage assessment and seismic performance of the Canterbury bridges during these two earthquakes, emphasizing unexpected issues that are still not properly detailed in New Zealand and overseas standards.

EN 13791 applies when assessing the in situ compressive strength of structures and precast concrete components. According to the code itself, it may be adopted when doubt arises about the compressive strength of a concrete. For assessing the structural safety of existing structures, however, the method given in EN 13791 does not seem to be applicable and may lead to an unsafe approach for determining the characteristic concrete strength. This paper presents an alternative method for determining the characteristic concrete strength from cylinders obtained in situ. The method proposed is based on EN 1990 (Eurocode basis of design) and the corresponding Annex D. The method according to EN 13791 is outlined in this article. Moreover, the practical implementation of the method in accordance with clause 5.2 of EN 1990 is explained and an example is given. Finally, both methods are compared with each other. It is demonstrated that EN 13791 does not apply to safety assessments of existing concrete structures and the use of this code may lead to unsafe situations.

In order to address how new knowledge influences design expressions, design codes have in most cases become significantly more complex over the last decades. However, this tendency is leading to codes that are too complicated for preliminary design but still not sufficiently accurate for assessing existing structures (where even more realistic models of behaviour are sometimes required). An alternative code strategy is that proposed by codes based on a levels-of-approximation (LoA) approach. This approach is based on the use of theories based on physical parameters where the hypotheses for their application can be refined as the accuracy required increases. The approach proposes adopting safe hypotheses during the first stages of design, leading to relatively quick and simple analyses. In cases where such a degree of accuracy is not sufficient (e.g. design of complex structures, assessment of existing structures, significant potential economic savings), the hypotheses can be refined in a number of steps, leading to better estimates of the behaviour and strength of members. This approach, recently adopted in the first complete draft of Model Code 2010 for a number of design issues, is discussed within this paper with reference to punching shear provisions.

In a bridge construction process, where large concrete elements are rotated with the aid of strand lifting units (lowering of arch halves, balanced lift method), the tendons have to be deviated over saddles with small radii of curvature. Since information on the ultimate strength of curved strand tendons was not available at the time, a test programme was carried out in order to determine the ultimate strength as a function of radius of curvature (R = 0.5 m, R = 1.0 m, R = 3.0 m, straight tendons), number of strands (1 to 55) and type of strand (0.5″ and 0.6″). The results of the full scale experiments showed almost no decrease in efficiency with regard to single strand tendons and only moderate losses regarding multistrand tendons. Based on the experimental results and a biaxial failure criterion, an analytical model was developed which is able to predict the ultimate strength of curved tendons.

An analytical model for the calculation of the pressure of concrete on vertical formwork has been developed on the basis of experimental tests on highly flowable concretes in the fresh state (see companion paper “Material investigations and large-scale tests”). The model takes into account the time-dependent material parameters of the fresh concrete, the specific properties of the highly flowable vibrated concretes and self-compacting concretes (SCC) as well as operational aspects. A proposal for the design of formwork was developed based on the experimental tests and the semi-probabilistic safety concept. It was found that the design load is often lower than the hydrostatic concrete pressure - even for highly flowable concretes. On construction sites, the pressure can be best controlled by limiting the casting rate. Insufficient experience of personnel in the handling of highly flowable concretes increases the uncertainties with respect to the design values and the safety risk.
Further investigations into construction management-related aspects regarding the use of highly flowable concretes cover the risk assessment during concreting, design of the processes on the construction site and the development of the basis for a documentation system.

fib Symposium 2013, Tel Aviv: Call for papers
ICCS13: Call for papers
fib Symposium Stockholm
ICI-fib Workshop, New Delhi
60th Birthday of Harald Müller
65th Birthday of Joost Walraven
Recent activities of fib Commission 8
Honorary doctorate to M. Curbach
fib Bulletins
Congresses and Symposia
Acknowledgement

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