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.

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60th Birthday of Harald Müller
65th Birthday of Joost Walraven
Recent activities of fib Commission 8
Honorary doctorate to M. Curbach
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Acknowledgement

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The 22 February 2011 Mw 6.2 Christchurch (Lyttelton) earthquake was a particularly severe test for both modern seismically designed and existing non-ductile reinforced concrete (RC) buildings. Some 16.2 % of 833 buildings with RC systems within the Christchurch central business district (CBD) were severely damaged. There were 182 fatalities, 135 of which were the unfortunate consequences of the complete collapse of two medium-rise RC buildings. As with the post-Northridge 1994 earthquake, the design performance of “modern” structures is being scrutinized - with the inevitable question: is “life safety” but irreparable damage still a valid performance target? This brief paper presents a summary of RC building damage from a broad performance-based earthquake engineering perspective. Several preliminary lessons, not all of them surprising, and the issues that have arisen will be discussed using case study buildings, with suggestions for urgently needed research areas.

The Christchurch region of New Zealand experienced a series of major earthquakes and aftershocks between September 2010 and June 2011 which caused severe damage to the city's infrastructure. The performance of tilt-up precast concrete buildings was investigated and initial observations are presented here. In general, tilt-up buildings performed well during all three major earthquakes, with mostly only minor, repairable damage occurring. For the in-plane loading direction, both loadbearing and cladding panels behaved exceptionally well, with no significant damage or failure observed in panels and their connections. A limited number of connection failures occurred due to large out-of-plane panel inertia forces. In several buildings, the connections between the panel and the internal structural frame appeared to be the weakest link, lacking in both strength and ductility. This weakness in the out-of-plane load path should be prevented in future designs.

Fabric formwork entails the use of fabrics as the main contact material for a concrete mould. The fabric is either hung or prestressed in a supporting falsework frame. Beams or trusses cast in fabric formwork are inherently non-prismatic and have been shown to offer potential for structurally efficient shapes. The casting of beams or trusses in fabric formwork is a highly non-linear problem due to the interaction of the fluid concrete with the woven, prestressed fabric material. Numerical models need to be developed for the engineering of these elements. To this end, it is demonstrated that it is feasible to integrate manufacturing constraints in an automatic optimization process. This is achieved by creating an automated computational framework that includes fabric form-finding and finite element analysis, which operate within an optimization process that uses principles from biological evolution. The results show structurally efficient and manufacturable beams and demonstrate potential for optimization in general that explicitly includes fabrication considerations.

The purpose of this paper is to provide information on the behaviour of steel prestressing wires under likely conditions that could be expected during a fire or impact loads. Four loadings were investigated: a) the influence of strain rate - from 10-3 to 600 s-1 - at room temperature, b) the influence of temperature - from 24 to 600 °C - at low strain rate, c) the influence of the joint effect of strain rate and temperature, and d) damage after three plausible fire scenarios.
At room temperature it was found that using “static” values is a safe option. At high temperatures our results are in agreement with design codes. Regarding the joint effect of temperature and strain rate, mechanical properties decrease with increasing temperature, although for a given temperature, yield stress and tensile strength increase with strain rate. The data provided can be used profitably to model the mechanical behaviour of steel wires under different scenarios.

This paper studies the effects of cross-sectional shape and rebar configuration on the reliability indices of concrete columns. Three sections with rectangular, square and circular shapes are selected. Using the Monte Carlo simulation technique, the statistical parameters for reinforced column resistance are calculated along several load eccentricities using the most recent statistical data available in the literature. The statistical parameters show that the magnitude and the variation of bias factors and the coefficients of variation are not similar for the sections selected. The coefficients of variation of the square and circular sections are greater than that of the rectangular section. The results of reliability analysis indicate the importance of sectional shape, especially at low load eccentricities. In some cases, the effect of cross-sectional shape or reinforcement configuration is found to be more important than the effect of the compressive strength of the concrete. It is recommended to include the shape factor and the reinforcement configuration in the code calibration process for the capacity reduction factors.

This paper documents the results of a joint research project dealing with the loading of formwork systems used with highly flowable concretes. First calculation approaches concerning the pressure of fresh concrete on vertical formwork were developed on the basis of the investigations conducted on the material behaviour of highly flowable concretes. In doing so, construction management questions regarding, for instance, process design and quality assurance in the application of highly flowable concretes were also investigated. Different scientists from German research institutes collaborated in a research group to pool their knowledge in the field of the pressure of fresh concrete. Because of the extent and complexity of the tasks to be tackled, the joint research project was divided into five subprojects (A to E), which were performed by the research institutes according to their individual respective capacities.

• fib General Assembly approves the Model Code 2010
• fib Symposium 2012
• Earthquake resistance short course, Athens
• fib Bulletins
• New fib website launched
• Elices receives Spanish prize
• Hans Wittfoht † 1924-2011
• Andrew Beeby † 1939-2011
• Congresses and symposia
• Acknowledgement
• 2011 reviewers

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The fib Model Code is a recommendation for the design of reinforced and prestressed concrete which is intended to be a guiding document for future codes. Model Codes have been published before, in 1978 and 1990. The draft for fib Model Code 2010 was published in May 2010. The most important new element in this Model Code is “Time” in the sense of service life. Additionally, the Model Code contains an extended state-of-theart chapter on the structural materials concrete and steel but regards non-metallic reinforcement and fibres as reinforcement as well. Many loading conditions are considered, ranging from static loading to non-static loading, considering earthquake, fatigue and impact/explosion. Five methods are offered to verify structural safety. Attention is given to verification of limit states associated with durability, robustness and sustainability. Finally, verification assisted by numerical methods and by testing is considered. Other elements that are links in the chain of life cycle design are construction and conservation. In the part on conservation the conservation strategy is treated in combination with conservation management, condition survey and assessment, and evaluation and decision-making.

Data has been collected from several European ready-mixed concrete plants in order to analyse some data-based statistical aspects of the concrete family concept. Concrete strength records of concrete families were obtained from seven different concrete plants. This data is used to investigate the presence of autocorrelation in the transposed data of concrete family strength records. Further, strength records from two Belgian concrete plants are investigated in more detail and used to investigate how the concrete family concept, the applied transformation method and the family composition guidelines influence the general quality of accepted batches.

It is proposed to build concrete bridges with tendons fully encapsulated in plastic ducts and without the use of reinforcing steel. In this case the durability of the proposed bridge depends only on the durability of the concrete because corrosion is no longer a determining factor regarding the lifetime of the structure. The requirements of the serviceability and ultimate limit states are fulfilled by providing post-tensioned tendons with strands fully encapsulated in plastic ducts and watertight anchorages. Since the proposed bridge does not contain any steel, which would be endangered by material-related corrosion, there is no need for insulation to the deck. Consequently, there is also no need for pavement and edge beams. This concept of building bridges represents a breakthrough with regard to sustainability and durability of concrete bridges and is applicable to small and mediumsized bridges. The method has already been implemented for the design of the Egg-Graben Bridge in the Großarl valley in the province of Salzburg, Austria. Prior to the actual construction of the bridge, large-scale tests were performed to obtain practical values for the serviceability, ductility and loadbearing capacity of this structural system.

The concept of casting concrete in fabrics, fabric formwork technology, has resurfaced at various times and in different forms throughout the past century. The following paper traces developments that have used fabrics for concrete formwork, including different types of flexible formwork, controlled permeability formwork and pneumatic formwork. This paper presents a comprehensive historical overview of fabric formwork, listing key innovators, technological developments and their advantages, and offering examples of structures built with these methods. The information gathered is used to present a taxonomy of these related formwork technologies as well as a formal definition of the term “fabric formwork” that encompasses them. The paper is intended to introduce readers to these technologies and offer readers already familiar with these methods additional historical background.

The purpose of this paper is to improve the performance of a twodimensional finite element approach, called the Rotating Compression Field Model (RCFM). The RCFM capability for reproducing the non-linear behaviour of reinforced concrete (RC) beams, tested in shear with monotonic load increase, has been tested and amended. Concrete is treated as a quasi-orthotropic material with smeared cracks and smeared reinforcement. A modified version of the Sargin relationship for concrete in compression is adopted, introducing a new model for the softening branch of the stress-strain compression curve in the RCFM to take into account compression softening and the effect of confinement due to inplane reinforcement. In addition, this paper considers out-ofplane confinement effects using the model suggested by Eurocode 2.
A key issue in the RCFM approach consists of relating the decay of effective concrete strength to the deviation angle between the inclination of the compression stress field at first cracking and its inclination at the load level considered. The validity of this relation has been extended from the original 15° up to more than 30°.
A new stress-strain curve is implemented in the code to model the tensile behaviour of concrete without reinforcement (tension softening) in addition to the tension stiffening effect already present for concrete with reinforcement. This model leads to a successful comparison with experimental results on RC beams for a significant range of design parameters and mechanical material properties.

A deformation criterion is proposed for the fatigue failure of concrete in tension. According to the criterion, a fatigue failure is imminent when the total deformation approaches the deformation at maximum stress in a corresponding static test. This criterion was originally proposed for bond slip by Balázs in 1991. It is tested on two series of new and old concrete cylinders loaded in cyclic tension. How the criterion may be used to predict the number of load cycles to failure for existing structures under cyclic tensile loading is also shown.

Strengthening reinforced concrete (RC) beams in shear using carbon fibre-reinforced polymer (CFRP) has been found to enhance, significantly, the shear capacity of existing RC beams. In previous studies the use of steel plates bonded externally to the RC beams was found to improve the shear performance of these beams. Most of the previous work was conducted on RC beams having rectangular sections. The main objective of this paper is to gain a better understanding and enhance the experimental database of shear behaviour of RC T-beams strengthened with externally bonded reinforcement (EBR) systems. The present study encompasses some of the important parameters such as direction of EBR fibre alignment and the strengthening materials made of carbon-fibre sheets, steel plates or steel bars for shear strengthening. The contribution of EBR to the shear capacity of the T-beams was computed using three design codes and compared with the experimental output. A series of RC T-beams was tested experimentally with the CFRP and steel strips carefully aligned and spaced. A reference T-beam and a rectangular beam were tested as well to explore the effect of the internal shear reinforcement and the existence of the flange on the shear capacity of the beam.

• fib Symposium 2011 in Prague
• 2011 fib Medal of Merit
• fib Symposium in 2013, Tel-Aviv
• 2011 fib AAYE presented in Prague
• PBS Workshop, Leipzig
• fib UK group strengthens ties
• fib Bulletins
• New Task Groups in Comm 8
• Arie Gerritse †, 1929-2011
• Hendrik Lambotte †, 1925-2011
• Congresses and symposia
• Acknowledgement

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