67 research outputs found
Chlamydia trachomatis in the Dutch population: epidemiology, serological responses, and host genetics
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Reverse Engineering of existing reinforced concrete slab bridges
No full textMost bridges in the Dutch infrastructure are built before 1985 and have experienced increasing traffic intensities and loads. On the other hand, the structural (design) codes have changed over the years. A frequently faced problem in practice is that the original design calculations and technical drawings of a large percentage of the existing bridge stock are unknown or lost. Therefore, the current capacity of the bridge is unknown. The currently used method to map the reinforcement dimensions and amounts in an existing bridge is by (X-ray) scanning. As an alternative, this work proposes Reverse Engineering of the existing bridges, by redoing (a correct) former bridge design with a known design year and load class as a starting point. Consequently, the Reverse Engineered bridge design can be assessed according to the current Eurocodes. A parametric study reveals different capacity margins in former structural bridge design than expected beforehand. Bending moment seems to be the governing failure mode where the main focus in literature laid on shear failure.Accepted Author ManuscriptIntegral Design & ManagementConcrete Structure
Monitoring and assessing concrete bridges with intelligent techniques
No full textConstruction Management and EngineeringStructural EngineeringCivil Engineering and Geoscience
Balancing of an Ultra Precision Indexing Tool for SPDT Lathes
No full textMicro and Nano EngineeringPrecision and Microsystems EngineeringMechanical, Maritime and Materials Engineerin
On the injuries of the vertebrae and spinal marrow: prognostic factors & classifications.
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83224.pdf (Publisher’s version ) (Open Access)The general aim of this thesis was to critically appraise current concepts of prognostication and classification of spinal column and spinal cord injuries.
To date, only a few reliable, validated spinal column injury classifications exist. Moreover, the scientific validity of currently known prognostic factors, including risk factors for complications, in the spinal trauma population is limited. Based on literature findings and clinical data, methodological recommendations are provided to facilitate future research initiatives which aim to identify valid risk factors or to introduce a novel classification system for the spinal column injury population.
Whereas reliable and validation classification systems are scarce in the field of spinal column injuries, spinal cord injury (SCI) physicians from all over the world rely on the methodologically-sound ‘International Standards for Neurological Classification of SCI’ for over a decade. In collaboration with the ‘European Multicenter study for human Spinal Cord Injury’ (EM-SCI) network, two research projects were conducted and presented in this thesis. In the first project, the reproducibility and construct validity of the most prevalent syndrome in SCI, the traumatic central cord syndrome, was evaluated. In the second project, the predictive value of the initial neurological examination on ambulation outcomes after traumatic SCI was studied. This latter project resulted in the introduction of a novel and validated clinical prediction rule for independent ambulation outcomes after traumatic SCI.
Based on his thesis, the author concludes the following: ‘Before progressing into an era of comparative therapeutic trials, a clear insight into the most relevant prognostic factors influencing patient outcomes is warranted. Furthermore, as patients are commonly stratified by spinal cord and/or spinal column injury severity in clinical trials, categorizations and classification of these injuries should ideally have been validated by demonstrating their clinical relevance, reliability, and accuracy. With regard to the methodological quality of clinical studies in the field of spinal trauma, there is considerable room for improvement. To improve the quality of everyday spinal trauma care in the future, it is our duty to improve the validity of future clinical studies’ findings.’Radboud Universiteit Nijmegen, 21 december 2010Promotores : Veth, R.P.H., Geurts, A.C.H. Co-promotores : Hosman, A.J.F., Meent, H. van de280 p
Beam or truss mechanism for shear in concrete: Problems converting a beam into a truss
No full textAn unpublished study by Prof. A.W. Beeby shows the differences in strength capacity between a reinforced concrete beam without shear reinforcement and the same beam with a cut-out section at the middle of the span. The cut-out section exists at the bottom part of the beam while the reinforcement still remains. It remarkably turns out that the strength capacity of the beam with the cut-out section is 1.6 times larger compared to the reference beam. The reference beam fails by a flexural shear crack which does not arise in the beam with the cut-out section. On the occasion of Beeby’s experiments and the lack of a simple physical model for a flexural shear crack this thesis has the objective to clarify the difference between a beam and a truss mechanism and the failure due to flexural shear cracks. The study is based on a simple supported beam without shear reinforcement subjected to a oncentrated load with a three point bending test with a slendernessratio of 2.45 and a reinforcement ratio of 0.89%. An analytical study describes the difference between the beam and a simplified truss mechanism. Linear analyses show the differences in stress distributions and deflections. The study shows the same difference in strength capacity as the experiments of Beeby. In addition quite a difference is revealed in the displacements of both mechanism. The truss mechanism shows a larger deformation compared to the beam mechanism. Finite element modelling with DIANA has been used to gain better insight in the difference of the strength capacity. The models use a total strain fixed crack model. The Hordijk-curve describes the tensile properties and an ideal relation describes the compressive properties. The decrease of the poisson ratio and the shear resistance around a crack have been taken into account by a damaged based shear retention model and a damaged based crack model. The finite element models show differences of the strength capacity within the same level of Beeby’s experiments. The force mechanism in both systems is different before the flexural shear crack arises in the beam. After a flexural shear crack occurs both mechanism seems to change into a similar truss mechanism, but detailed analyses show important deviations from this expectation. Variation of the cut-out dimensions shows that a too small gap results in a flexural shear crack and a too large gap in the failing of the cantilever part. Gaps between these limits all change into a truss mechanism which reaches the same level of failure load as the basic truss. The decrease of stiffness of the beam results in more compressive stresses in the truss mechanism preventing the occurrence of the shear crack. If the shear crack does not occur in the beam it results in a higher strength capacity. A dedicated shaped beam which has initially exactly the shape of a shear cracked beam without the concrete part below the crack, has a different strength capacity compared to a regular shear cracked beam. The dedicated shaped beam proves that the crack shape itself has no influence on the ability of converting into a truss. It turns out that in the regular beam it is impossible to develop a perfect truss mechanism after a flexural shear crack due to the concrete that is still present beneath the crack. The concrete beneath the crack causes a different stress distribution in the top of the beam compared to the dedicated shaped beam without this concrete. A hypothesis is given for the failure of the shear crack. The acquired knowledge of the influence of the concrete beneath the crack and the stiffness of the beam allows other design possibilities. It is possible to design a concrete truss, if among other, the yielding of steel, crushing of the concrete and the deformation capacity of the truss are taken into account. Further research is for instance possible for unbonded reinforcement and beams with a descending height.Structural and Building EngineeringStructural EngineeringCivil Engineering and Geoscience
Automated Structural Assessment of existing reinforced concrete underpasses
No full textMuch of the Dutch infrastructure was built in the 1960s and 1970s and includes an estimated 55.000 bridges and viaducts. These aging structures have reached the end of their designed service life or will reach it in the short term. It is estimated that 15% of these structures have a box-shaped cross-section as being reinforced concrete underpasses and culverts. Replacing all these structures in the short term is not practical and financially feasible. In order to preserve these structures, it must be demonstrated based on a structural assessment that the structural safety is guaranteed. So many assessments will be performed by different engineers which is a time-consuming process and results in a non-consistent assessment where unnecessary disapproval occurs which in turn leads to unnecessary costs and loss of time. The aim of this thesis is to set up a structured consistent automated method with which unnecessary disapproval and unjustified approval is avoided, a necessary efficiency improvement is achieved and structures where structural safety is at risk can be identified. Quantitative research has been conducted in which numerical data from parameter studies is collected and analysed to investigate relationships between the studied variables, find patterns and generalize results. First a data analysis of existing underpasses and culverts in the Netherlands was carried out, after which the modeling of the load effect and the capacity of existing reinforced concrete structures was investigated. An automated analytical model was created for the first step to determine the load effect, including the method of Guyon-Massonnet for traffic load distribution for the determination of bending moments and an application of method 7.3-7 from CEB-fib model code 2010 to determine the shear force as a result of the local tandem system loads. The determination of the capacity of existing concrete structures was investigated arithmetically. As a second step to determine the load effect, a model refinement was performed by automating a 2,5D FEM plate model. Structures from the database were assessed with both the analytical model and the 2,5D FEM model and a sensitivity analysis was performed based on theoretical structures within the boundaries derived from the data analysis. It is concluded that it is the most efficient method to first assess the large batches with the analytical model and that the 2,5D FEM plate model for structures with an intersection angle smaller than 80gon and structures that are disapproved with the analytical model offers added value in terms of a lower UC. From the comparison with the 2,5D FEM plate model it is concluded that the method as an extension of method 7.3-7 from (CEB-fib, 2010) results in too optimistic values for the occurring shear force as a result of the tandem system load due to an overestimation of the vertical load distribution. This research shows that an automated structural assessment can be of added value on the classic approach of assessing existing concrete underpasses and culverts by significantly improving efficiency and therefore to realize a cost-efficient method.Civil Engineering | Structural Engineering | Concrete Structure
Reverse Engineering of existing reinforced concrete slab bridges
No full textMost bridges in the Western European road networks are ageing. The vast majority of about 90% of these bridges have reinforced concrete as a building material. The traffic intensity, as well as the axle, and the average vehicle weight have increased since these structures were opened to traffic. Furthermore, the structural (design) codes have changed over the years. Therefore, there is a need to investigate if existing structures meet the safety/reliability level described by the current codes. However, a frequently faced problem in practice is that the original design calculations and technical drawings of a large percentage of the existing bridges are unknown or lost. Especially for bridges in the lower road network, often designed for the lower load classes B/45 and maintained by a local government, the documentation is missing. The national road network, designed for load classes A/60 is maintained by the national government and faces the same problem but to a lesser extent. Bridges within this scope have different detailing rules and execution practices than used nowadays. Plain reinforcement was in general used which is bend-up at a support. Therefore, the study is twofold: first, Reverse Engineering is applied to determine the reinforcement of existing reinforced concrete slab bridges, second the capacity margin of RE bridges are examined with the current assessment codes. A Reverse Engineering-tool is developed to automate the dimensioning of the required reinforcement according to the former design codes. This tool uses the year of design, load class and the geometric dimensions of the bridge as input parameters. A parametric study is performed to examine bridges from different design periods. Consequently, the Reverse Engineering-tool is used to assess the Reverse Engineered bridge according to the current assessment codes. The validation of the model shows for the majority of the Reverse Engineered bridges that the Reverse Engineered reinforcement is slightly less than the reinforcement amounts from the technical drawings. This proves a conservative approach where the actual structural capacity is underestimated. Consequently, an assessment of the Reverse Engineered bridge can be performed with sufficient robustness.The computer code ran with the input parameters having a normal distribution, showed the largest effect for the uncertainty in the design year and load class especially around 1940 and 1962. Therefore, the design year and load class are crucial in Reverse Engineering and assessment of an existing bridge. The capacity margin of the Reverse Engineered bridges is assessed according to the current Eurocode based design codes. The traffic- and permanent load including load factors according to the general assessment codes from the NEN8700/NEN8701 and the RBK-1-1, and the decentralised load model from TNO are applied. The assessment with the Eurocode including the load factors from the NEN8700 showed Unity Checks for bending moment at the mid-supports and mid-spans of larger than 1.0, where the Unity Checks for shear forces resulted below 1.0. The assessment with the Decentralised load model showed Unity Checks for bending moment at the mid-supports and mid-spans and shear force below 1.0. In case the amount of support reinforcement is based on the amount of span reinforcement, the bending capacity margin at the mid-supports is insufficient for large spans. Significant bending capacity margins are obtained in structural design of RC slab bridges in the period 1930-1970. The main contribution of this research is that bridges designed between 1940 and 1962 show the most critical Unity Checks for bending in the assessed period. In this period account the following design methods: The dynamic amplification factor introduced in the GBV1940 for concrete bridges, the traffic load class from the VOSB1933, the N-method to determine the cross-section capacity and the effective width method from the GBV1940 and from the Guyon Massonnet method.The capacity margin for shear is found to be almost independent of the design period. Here can be concluded that the slenderness of the bridge deck is the main contribution in the shear capacity. Bridges designed in the period 1940-1962 with the support reinforcement based on the span reinforcement and with a span length >10m designed for load class B/45 or with a span length of >11m designed for load class A/60, form the group with the most critical bending capacity. However, the size of the group of former bridges designed according to these conditions is unknown.From the results can be concluded that bridges designed between 1940-1962 with RE reinforcement are found to be legally unsafe for bending according to the parametric assessment with the Eurocode.Civil Engineering | Structural Engineering | Concrete Structure
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