Eurocode 2 and the corresponding National Annex were introduced in Germany in 2012. Most of the design provisions for these new standards were adopted from Model Code 1990 and provide a new design approach for ground slabs and footings. For the fib Model Code for Concrete Structures 2010, the punching shear design concept has been revised and introduced in Swiss standard SIA262:2013. This paper presents in detail the design equations for determining the punching capacity according to Eurocode 2, the German National Annex to Eurocode 2, fib Model Code 2010 and SIA 262:2013.
Parametric studies have been used to examine the influence of the main parameters (shear span-depth ratio, effective depth, longitudinal reinforcement ratio and concrete compressive strength) on the punching shear resistance of footings. To quantify the level of safety and the efficiency, the design provisions are compared with systematic test series.

In this work, gene expression programming (GEP), as a new tool, has been used to predict the bond strength of fibre-reinforced polymer-to-concrete composite joints as the performance symbol of this structure. Some 238 datasets were collected from the literature, divided into 192 and 46 sets at random and then trained and tested respectively by means of GEP. The parameters width of prism, concrete cylinder compressive strength, width of fibre-reinforced polymer (FRP), thickness of FRP, modulus of elasticity of FRP and bond length were used as input parameters. Using these input parameters, the bond strength of FRP-to-concrete composite joints in different conditions was predicted in the GEP model. The training and testing results in the GEP model show that GEP is a powerful tool for predicting the bond strength values of the FRP-to-concrete composite joints in the range considered.

This paper presents investigations carried out at the Technical University of Denmark (DTU) on a prototype series for a super-lightweight prestressed concrete deck element called the SL-Deck.
The intention behind making a new prefabricated deck element is to improve performance with respect to flexibility, sound insulation and fire resistance compared with present-day prefabricated structures.
Full-scale tests and theoretical investigations show that the deck structure performs as intended. Also, that it is possible to assess by calculation the loadbearing capacity in bending and shear, and assess the pull-out strength of prestressing wires, the fire resistance and the acoustic insulation. Based on the results of the investigations, recommendations are given for further development of the structure before fully automated mass production is established.

When it comes to dynamically loaded concrete structures, determining the real degree of fatigue damage of a structure on site is a very demanding process that has not been explored in depth. Calculation concepts according to current codes and specifications (e.g. fib Model Code for Concrete Structures 2010 [1]) do not offer efficient results for this task. However, the permanent monitoring from the erection of a structure up to the end of its lifetime is seen as a very promising possibility for assessing the degree of damage constantly. This article takes a closer look at the concrete fatigue concept of fib Model Code 2010 [1], shows an FE simulation of a time-dependent fatigue process for an offshore wind turbine foundation and presents a fatigue monitoring concept including laboratory tests, which enables the detection of the real degree of deterioration in a concrete structure. During tests, the use of ultrasound was identified as the most appropriate method. Measuring wave velocity enables the determination of the dynamic E-modulus, which correlates to the degree of damage within the cross-section of the structure considered.

An internally confined hollow RC (ICH RC) column offers strong and durable confinement owing to the reinforcement provided by the inner tube. The strength and ductility of the column are enhanced because of the continuous confining stress provided by the inner tube. The excellent structural performance of ICH RC columns makes them particularly suitable for applications in high-rise buildings. However, if a high-rise building is damaged by fire, it will collapse without fire resistance performance. Also, lack of evacuation measures endangers human life. Thus, to predict the status of structures in fires, their behaviour should be evaluated in terms of fire time. In this study, the fire resistance performance of an ICH RC column was analysed during an ISO 834 standard fire and with certain initial conditions. Furthermore, the effects of hollow ratio, thickness of inner tube and thickness of cover concrete on the fire resistance performance were analysed. The results could be used for designing fire-resistant ICH RC columns.

Private households consume about 30 % of Germany's total primary energy and cause about 15 % of the total CO2 emissions, and so this sector represents a key sector for climate protection targets. Whereas primary energy consumption in buildings is limited by regulations, the production of carbon emissions-intensive materials is only moving slowly into the focus of legislation, regulations and, ultimately, the perception of society. Considering a thermally conditioned building during its life cycle, most environmental effects are during operation. Nevertheless, the grey energy of a concrete structure can add up to 20 % in individual cases. Owing to the carbon-intensive cement production, concrete as a material causes relatively high environmental impacts. Logical options appear to be substituting cement with so called by-products or using recycled additives. In fact, there are only a few projects that have used a resource-saving concrete. In 2010 in Ludwigshafen, one building in a group of buildings was chosen as the first building in Germany to be built almost completely from recycled concrete without increasing the cement content. It was built as a low-energy construction and in a zero-carbon-emissions area. The project was supported scientifically by the Institute of Energy and Environmental Research in Heidelberg and the Brandenburg University of Technology Cottbus. The buildings won the Construction Prize 2011 with the distinction “best relation between quality and costs”. This paper discusses integral aspects of the use of recycling concrete from the structural design, eco-accounting and materials properties perspectives. It demonstrates the potential and opportunities for the quality-assured use of recycling concrete for sustainable resource management.

When reinforcing bars are post-installed in holes drilled in cured concrete, adhesive mortars are used to create a bond between concrete and bars. Appropriate adhesives can develop higher bond strengths than standard ribbed bars cast into concrete. A detailed design concept for the anchorage length of reinforcing bars has been developed by taking into account splitting/spalling of the concrete and pullout. Pullout and splitting tests on reinforcing bars set in concrete were carried out with different adhesive mortars and with varying concrete strengths and concrete covers. When higher bond strengths than those recommended for cast-in reinforcement are taken into account, it is important to check deformations and crack widths at the serviceability limit state (SLS) separately. For this reason, structural tests on slabs and corbels were carried out. Moreover, pullout tests on post-installed reinforcing bars were performed in order to measure displacements at service load level.

Fatigue loading and its sometimes inevitable fatigue failure are common in many civil engineering construction projects. The behaviour of vibrated concrete (VC) under this type of loading is well understood. However, the fracture and fatigue resistance of self-compacting concrete (SCC) is poorly documented in literature. Considering the substantially different composition of the two concrete types (VC and SCC), it is uncertain whether their mechanical properties are similar or not. This paper describes the results of a series of destructive static and cyclic four-point bending tests on inverted T-shaped reinforced concrete beams, made from VC and SCC in equal quantities and of equal compressive strength. A comparison of the two concrete types is made, based on deflection, strain, crack width evolution and failure mechanism. The experiments prove that these mechanical properties of VC and SCC, subjected to a fatigue load, in some cases relate differently from a static loading process. Furthermore, the results reveal a faster concrete strain and crack width development for SCC during the fatigue tests. Regarding the number of cycles to failure, the applied load level is crucial.

Keine Kurzfassung verfügbar.

Structural changes in the fib; 60 years of setting standards; Summer studies in Milan; fib Bulletin 73; New fib Presidium; HPC conference and MC2010 workshop in Beijing; Short notes; Congresses and symposia; Acknowledgement

Keine Kurzfassung verfügbar.

Keine Kurzfassung verfügbar.

Keine Kurzfassung verfügbar.

Keine Kurzfassung verfügbar.

This article explains the process of developing a new method, called the balanced lift method, for constructing bridges based on an alternative to the bridge construction techniques used nowadays. The most common methods of building bridges are those using falsework or the cantilever method, but a rather uncommon method, the lowering of arches is seen as the origin of the balanced lift method. The idea was to create a method that would allow a bridge to be built in a very fast manner without the need for falsework, using prefabricated elements and assembling all parts together in a position - in this case vertically - that would simplify the construction process. In order to reach the final state of the bridge, the parts assembled vertically are rotated into their final horizontal position. This article contains descriptions of the development of the method, a large-scale test and two bridges already designed using the balanced lift method.

The use of reinforced concrete (RC) piles in integral abutment bridges (IABs) has not been widespread due to concerns over pile flexibility and the potential for concrete cracking. This is the reason why the use of steel piles is the preferred solution in the United States. However, in various countries where IABs are still seldom used, RC piles are more readily available and economical. Hence, an understanding of the behaviour of IABs with RC piles can lead to a wider implementation of integral solutions. This paper presents the results of a parametric study conducted to evaluate how both the design variables and the accuracy of the modelling approach influence the potential use of integral solutions with RC piles in prestressed concrete bridges up to 200 m long. Finite element modelling was used and four levels of approximation (LoA) were established for the analyses, ranging from simple linear-elastic to more complex non-linear models. The results show that existing concerns over concrete cracking control can be overcome if adequate options in design are used together with the adequate LoAs in structural analysis. Integral solutions with RC piles for bridges up to 200 m long can generally be adopted, although in comparisons with non-integral designs a significant additional amount of prestressing steel is to be expected. The results also include a set of charts with practical estimates to help designers in their first approach to the preliminary design of an IAB.

The design of large concrete structures is a very complex area which requires specialized skills and specialized tools. Tools are available to design these structures efficiently. However, these design tools are based on inconsistency between what is assumed in the structural analysis and the sectional design. This inconsistency is believed to be conservative, but is such an approach always safe and cost-effective? In light of this, a design tool has been developed to eliminate this inconsistency. The program is called ShellDesign and the new method is called the “consistent stiffness method”. The method can be used in practical design and is a more efficient alternative to running non-linear analysis programs. In order to obtain a more rational and consistent design method for transverse shear, implementation of the modified compression field theory (MCFT) in ShellDesign is almost finished. The main advantages of developing ShellDesign are to increase the competitiveness of concrete structures, contribute to increased safety and also to increase operability and document robustness in existing structures.

The aim of this research is to compare the predictions of the design load-carrying capacity of slabs obtained with simplified analytical and numerical procedures which can be readily used by analysts in the current design process. The research fits into a research programme initiated by the Dutch Ministry of Infrastructure and the Environment for the re-examination of the load-carrying capacity of existing bridges and viaducts, and the beams and slabs they include, through the use of non-linear finite-element analyses. The behaviour of reinforced concrete slabs subjected to concentrated loads close to their supports is investigated in this contribution. Three tests from a series of 18 slabs with a total of 108 tests, tested at Delft University of Technology, were selected as case studies and analysed with non-linear finite-element analyses and analytical models either proposed by design codes or available in the literature. The research agrees well with the philosophy of the fib Model Code for Concrete Structures 2010, which offers different analytical and numerical calculation methods for evaluating the design shear resistance of reinforced concrete members according to different levels of approximation. For the three slabs investigated in this study, it indeed pays to use higher levels of approximation. The highest level (level IV) based on non-linear finite element analysis gives the highest design load resistance, but still well below the resistance obtained experimentally.

Punching tests on 13 specimens under uniform soil pressure were conducted to evaluate the punching shear behaviour of footings with practical dimensions. The test series included square footings with and without punching shear reinforcement. The dimensions of the footings varied between 1.20 × 1.20 m and 2.70 × 2.70 m and the slab thickness varied between 0.45 and 0.65 m, resulting in shear span-depth ratios a&lgr;/d between approx. 1.25 and 2.00.
In addition to the measured steel strains in the flexural reinforcement and the stirrups, the increase in the slab thickness as well as the saw-cuts were examined to investigate the internal cracking and failure characteristic. In combination with previous tests conducted at RWTH Aachen University, this test series permits a description of the effect of the main parameters on the punching shear strength of footings. These parameters are the size effect of the effective depth, the concrete compressive strength, the flexural reinforcement ratio and the punching shear reinforcement.

This paper is an attempt to provide a detailed procedure for the finite element modelling and simulation of concrete-filled steel tubular (CFST) columns subjected to axial compression using the commercial software package ANSYS 12. A modified material model for modelling the concrete core is described and explained. Composite action is modelled between the concrete core and the steel tube and the procedure is presented with the recommended properties for modelling such behaviour. The proposed model is then validated by comparing its numerical results with selected experimental results available in the literature. The proposed model is used to investigate numerically the load transfer mechanism of CFST columns filled with different grades of concrete in order to study the effect of this parameter - i.e. compressive strength of concrete core - on the load transfer mechanism in such columns. Further, the proposed model has been employed for investigating the confining pressure provided by the steel tube on the concrete core along the length of the CFST column.

Steel composite hollow columns have been studied in order to ease their construction. Welding or bolting are mostly used for connecting the steel tubes of precast steel composite hollow columns. However, welding generally results in temperatures of about 20000 °C in the welding zone and 1300 °C around the welding zone. Thus, the strength of the concrete in regions close to a welding zone is reduced. In this paper, the effects of arc welding and electro-slag welding - two widely used methods for connecting the column modules of steel composite hollow columns - on the temperature change in the welding zone are studied by performing heat transfer analysis. The changes in the strength of the concrete are investigated for each welding method. The rate of decrease in concrete strength due to electro-slag welding was greater than that due to arc welding. In addition, an effective method using ceramic fibres is suggested for preventing strength reduction in concrete due to welding heat.

The prescriptions provided by codes of practice for assessing the minimum reinforcement amount for strength purposes in reinforced concrete beams usually disregard the non-linear contribution of concrete in tension and size-scale effects. In the present paper, these phenomena are taken into account correctly in the description of the flexural failure in lightly reinforced concrete beams by means of a numerical algorithm based on non-linear fracture mechanics. In this context, the application of dimensional analysis permits a reduction in the number of governing parameters. In particular, it is demonstrated analytically that only two dimensionless parameters, referred to as reinforcement brittleness number and stress brittleness number, are responsible for the brittle-to-ductile transition in the mechanical response. According to this approach, new formulae suitable for evaluating the minimum reinforcement in practical applications is proposed for both rectangular and T-sections. A comparison with experimental results demonstrates the effectiveness of the proposed model for different reinforcement percentages and beam depths.

This paper aims to put into perspective the influence of long-term effects, such as concrete creep and shrinkage, on concrete cracking. Long-term experimental results obtained at the Centre for Infrastructure Engineering & Safety (CIES) are reported and compared to design estimates made using the fib Model Code for Concrete Structures 2010. The influence of factors such as stirrup spacing and concrete cover are discussed. Results show that time-dependent shrinkage-induced cracking can considerably modify the cracking patterns obtained in short-term tests. For crack control in real structures and for the development of models for inclusion in codes of practice, it is strongly recommended that account be taken of time-dependent effects. Limiting observations to those made in short-term tests may lead to erroneous conclusions that are simply not applicable for structures that are more than a few weeks old.

The experimental results for quasi-brittle materials such as concrete and fibre-reinforced concrete exhibit high variability due to the heterogeneity of their aggregates, additives and general composition. An accurate assessment of the fracture-mechanical parameters of such materials (e.g. compressive strength fc and specific fracture energy Gf) turns out to be much more difficult and problematic than for other engineering materials. The practical design of quasi-brittle material-based structures requires virtual statistical approaches, simulations and probabilistic assessment procedures in order to be able to characterize the variability of these materials. A key parameter of non-linear fracture mechanics modelling is the specific fracture energy Gf and its variability, which has been a research subject for numerous authors although we will mention only [1, 2] at this point. The aim of this contribution is the characterization of stochastic fracture-mechanical properties of four specific, frequently used classes of concrete on the basis of a comprehensive experimental testing programme.

After a concrete structure has been exposed to fire, a combination of destructive and non-destructive testing, expert judgment and calculations is used to decide whether the structure should be demolished or repaired, or can continue to be used without repairs or rehabilitation. However, there are many uncertainties associated with both the fire duration and the effect of elevated temperatures on the residual mechanical properties of the materials. Consequently, the maximum service load after fire exposure should be assessed based on reliability considerations in order to provide an adequate level of safety. As this type of calculation is too complex and time-consuming for practical use, a reliability-based assessment tool has been developed for concrete structures and applied to slabs to determine the maximum service load after fire. When using the proposed method, a safety level is targeted which is comparable with the safety level associated with the Eurocode format for the design of new structures. It is concluded that the proposed assessment method is both user-friendly and directly applicable in practice.