Verification of the bursting and spalling formulas in the FIB model code by finite element analyses of anchorage zones of pretensioned girders

In order to predict the stress and possible crack distribution in the anchorage zones of pretensioned girders several models have been developed as can be found in the fib Model Code, the ASHTOO code or Eurocode 2. In this paper, the bursting and spalling formulas from the fib Model Code are evaluated by finite element calculations since some issues could be raised when applying the proposed formulas for industrial applications, especially for beams of limited dimensions. The effect of the upper strands, the assumed stress distribution at the opposite side of the equivalent symmetric prism, the stress transfer diagram along the strands and the effects of the strand position relative to the simplified resultant forces remain unclear. Accordingly two-dimensional finite element models were developed to gain insight into the bursting and spalling formulations from the fib Model Code. The numerical models render stresses and the stress flow results, which allow a more clear coupling to well-known strut-and-tie models. The results indicate that for various strand configurations, especially for small beams, the fib formulations may be too conservative

Nonlinear analysis of the end zones of prestressed concrete girders

Pretensioned concrete girders have been used for many years in construction. Nevertheless, optimization is still possible, especially regarding the anchorage zones. These are typically subjected to different types of stresses due to the local transmission of the prestressing force. By using a 3D nonlinear finite element model, the stresses and cracks in the anchorage zone due to the prestressing forces can be predicted in a more reliable manner. In this paper two 3D FE models are developed by using the concrete damage plasticity model in Abaqus. In the first model, the load transfer is defined by creating a shear force around each strand. In the second model, the interaction between the strands and the concrete is created by using surface-to-surface contact elements with friction. Finally, to validate the models, the results are compared with strain measurements on a precast beam during production at a precast concrete plant

Non-linear 3D finite element analysis of the anchorage zones of pretensioned concrete girders and experimental verification

This paper focuses on the modelling of the anchorage zone of a pretensioned girder. The finite element software Abaqus was used to create a 3D non-linear finite element model (FEM). This analysis was performed on a full-scale pretensioned girder with end blocks and with various types of strand modelling, where accurate contact properties between prestressing steel and concrete are essential. The model has been validated by comparing the numerical strain results with the strain measurements on a full-scale girder with end blocks, which was produced in a precast concrete plant. At the same time, a parametric study was executed to determine the value of the coefficient of friction between the strands and the concrete and to examine the sensitivity of the input parameters of the model. The results have indicated that an accurate determination of the concrete properties at the time of release is very important. Furthermore, the Hoyer effect is analysed. It is found that the radial expansion of the strand in the finite element model is in good agreement with the theoretically calculated expansion of the strand which demonstrates the accuracy of the finite element model. In addition, it is shown that the Hoyer effect influences the force transfer of two adjacent strands. The aim of this research is to investigate the potential of an alternative FE model of a pretensioned girder based on strand to concrete frictional behaviour, rather than the commonly used models based on an assumed shear stress distribution along the transfer length

Numerical and experimental analysis of the transfer length and its influence on the anchorage zone design of pretensioned concrete members

In order to optimize the end block of a prestressed girder, nonlinear finite element models are frequently used. This way the stresses and possible cracks in the anchorage zones can be predicted in a more reliable manner. However, a preliminary parametric study of nonlinear finite element models has shown that the transfer length has a major influence on the stresses in the concrete and in the reinforcement, and on the crack formation. In this paper this transfer length is examined, firstly by performing a parametric study of the formulations found in literature, secondly by measurements on beams produced at a precast concrete plant. The aim of this parametric study and the experimental research is to get further insight into the transfer length function as required for further numerical analysis of the end zones

New insights into the anchorage zones of precast pretensioned concrete girders

Pretensioned concrete girders are widely used in the construction sector. Nevertheless, optimisation is still possible considering the end zones. These end zones are subject to different types of stress due to the local transmission of the prestress force. In order to optimise these regions, a 3D non-linear finite element model was developed using the Abaqus software. Different from other attempts, a full scale girder with multiple strands is modelled. The accuracy of the FE model was verified by comparing the numerical results with experimental data. A full scale test in a precast concrete plant during normal production is carried out, and a good fit between the experimental and numerical results is obtained. Finally, the model was used to design a girder without end block. The calculation of the additional reinforcement was based on vector plots of the tensile stresses, extracted from the FEM

Design of anchorage zones of pretensioned concrete girders : a comparison of nonlinear 3D FEM results with measurements on a full scale beam

Featured Application The end zones of pretensioned beams have been investigated for many years, and many simplified analysis methods have been proposed. Detailed nonlinear finite element analysis-based design, has only become available in the last years. The paper provides an experimentally validated nonlinear FE based technique which opens perspectives for a further optimization of these end zones. Pretensioned concrete beams are widely used for constructing large load-bearing structures and bridging long spans. Crack formation may occur in the end zones of these elements due to tensile splitting, spalling and bursting actions. Investigation of these zones is typically done by means of analytical methods, strut and tie modelling, 2D linear or nonlinear analysis, or full 3D nonlinear analysis. Especially challenging in this last approach is the modelling of the force transfer from the strands to the surrounding concrete as it strongly influences the magnitude of the tensile stresses. This paper presents a 3D nonlinear analysis of the anchorage zone of a pretensioned girder, and a comparison with experimental results (mechanical strain measurements, embedded strain gauges). Material modelling, steel-concrete interaction properties, as well as convergence problems are addressed systematically. The comparison indicates that a good agreement is found, both for concrete and rebar strains, and that a friction coefficient of 0.7 can be adopted, although the results for values from 0.5 to 0.9 do not differ that much. The results demonstrate that a 3D nonlinear analysis provides an excellent insight in the behavior of the end zones of pretensioned girders which opens perspectives for an optimization of the end zone design based on this type of analysis

Fiets 'Ersatzpaard': de etymologische kwestie revisited en beslecht?

To date there is no convincing etymology of the Dutch word fiets 'bicycle'. This is not surprising, as the origin of the word seems to lie in Germany. It is attested there, along the border with the Netherlands, but also more inland. In German, as in Dutch, several folk etymological transformations of the original word for 'bicycle' (the French vélocipède) occur, more often than not based on the notion that bicycles are substitutes for horses. The Latinate prefix vice- serves exactly this purpose. The German pronunciation of vice-, however, made the etymology of fiets unrecognizable to Dutch speakers

Growth stimulatory angiotensin II type-1 receptor is upregulated in breast hyperplasia and in situ carcinoma but not in invasive carcinoma

Two different receptors which bind angiotensin II specifically have been identified in humans and were designated angiotensin II type-1 receptor (AT(1)) and angiotensin II type-2 receptor (AT(2)). They only have 34% sequence homology and act through different signalling pathways. AT(1) stimulation has been implicated in hypertrophy and hyperplasia in various tissues. In order to study the involvement of AT(1) in tissues from controls (n=10) and patients with hyperplasia (n=33), ductal carcinoma in situ (DCIS) (n=23) and invasive carcinoma of the breast (n=25), we tested biopsies and breast-derived cell lines using immunocytochemistry, in situ hybridisation and cell proliferation techniques. The results show specific overexpression of AT(1) receptor on the cytoplasmic membrane of cells of hyperplastic lesions with and without atypia and on DCIS of the breast. Evidence for growth stimulation is provided by in vitro experiments showing growth induction by angiotensin II of T47D cells which express the AT(1) but not the AT(2) receptor. The expression of AT(1) on the cell membrane disappears in invasive breast cancer cells suggesting a regulatory pathway which is no longer needed in invasive carcinoma. The specific AT(1) expression upregulation might well be an important step in the pathogenesis of hyperplasia of the breast, which is regarded as a precursor lesion for breast cancer

Vitrification negatively affects the Ca2+-releasing and activation potential of mouse oocytes, but vitrified oocytes are potentially useful for diagnostic purposes

Research question: To what extent does vitrification affect the Ca2+-releasing and activation potential of mouse oocytes, which are commonly used to determine the oocyte activation potential of human spermatozoa? Design: The effect of mouse oocyte vitrification on Ca2+ dynamics and developmental competence after oocyte activation was assessed and compared with fresh mouse oocytes. Moreover, the Ca2+ store content of the endoplasmic reticulum was determined at different time points during the vitrification–warming procedure. Finally, the Ca2+ pattern induced by cryoprotectant exposure was determined. Results: After human sperm injection into mouse oocytes, Ca2+ dynamics but not fertilization rates were significantly altered by vitrification warming (P < 0.05). Ca2+ dynamics in response to SrCl2 or ionomycin were also altered by oocyte vitrification. In contrast, activation and blastocyst rates after SrCl2 exposure were not affected (P > 0.05), whereas activation rates after ionomycin exposure were significantly lower in vitrified–warmed oocytes (P < 0.05); blastocyst rates were not affected (P > 0.05). Cryoprotectant exposure was associated with a strong drop in endoplasmic reticulum Ca2+ store content. Oocytes rapidly recovered during warming and recovery in Ca2+-containing media; a threshold area under the curve of Ca2+ dynamics to obtain activation rates above 90% was determined. Conclusions: Vitrified–warmed mouse oocytes display reduced Ca2+-releasing potential upon oocyte activation, caused by cryoprotectant exposure. With adapted classification criteria, these oocytes could be used for diagnosing oocyte activation deficiencies in patients. Evaluating the Ca2+-signalling machinery in vitrified–warmed human oocytes is required