992 research outputs found
Maximum dynamic stress on bridges traversed by moving loads
No full textMost current research on dynamic effects due to traffic load on simply supported bridges focuses on the mid-span section of the bridge, since this location corresponds to the worst static bending moment. However, the maximum total moment allowing for dynamics, may differ considerably from the maximum moment at mid-span. This paper shows how the maximum can occur in a section relatively far from mid-span with a significant difference in magnitude.Other funderJournal websitewww.bridgesjournal.comEuropean 6th Framework Programme ARCHES (Assessment and Rehabilitation of Central European Highway Structures)Publisher requires the journal URL to appear on the record: www.bridgesjournal.com. Could use Description web link: Journal website as in http://hdl.handle.net/10197/2437? - AV 1/11/2010 au ke SB. 15/11/'1
Impact of Liver and Kidney Function on Vitamin D3 Metabolism in Female and Male Patients Undergoing Allogeneic Hematopoietic Stem-Cell Transplantation
No full textWe previously described that elevated levels of the active vitamin D3 metabolite 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) during the early phase of allogeneic hematopoietic stem-cell transplantation (HSCT) can predict one-year transplant-related mortality (1y-TRM). Given that the liver and kidneys are the primary organs responsible for the effective conversion of vitamin D3, we investigated whether liver and/or kidney function, inflammation, or patient sex might influence vitamin D3 metabolism and, consequently, patient outcomes during transplantation. We found that female patients exhibited higher levels of 1,25(OH)2D3 at the time of transplantation compared with male patients. However, 1,25(OH)2D3 levels were associated with 1y-TRM in both sexes. No correlation was found between liver-associated markers, such as bilirubin, or the inflammation marker C-reactive protein (CRP) and serum levels of vitamin D3 metabolites in either female or male patients. However, serum levels of 1,25(OH)2D3, but not 25(OH)D3 correlated with the creatinine-based estimated glomerular filtration rate (eGFR), indicating that 1,25(OH)2D3 levels are associated with kidney function in HSCT patients. However, a Cox regression analysis, adjusted for baseline risk factors, demonstrated that high peri-transplant levels of 1,25(OH)2D3 (measured from days −2 to 7) remained a significant predictor of patient survival, even when eGFR was taken into account (hazard ratio = 0.99; p = 0.004). These findings suggest that optimal serum levels of 1,25(OH)2D3 may not be achievable in some HSCT patients and that kidney function alone cannot explain why some patients fail to reach the optimal 1,25(OH)2D3 threshold. These data support the potential use of 1,25(OH)2D3 as a prophylactic agent, particularly in patients with pre-existing kidney disease
Load Tests on Bridges
No full textThis chapter presents an overview on the state-of-the-art procedures for load tests on bridges and on the applicable sensing and data acquisition technologies. Best practices for the planning, preparation and execution of load tests are presented. The discussion is supported by practical applications in which the authors have been involved during the last 20 years. Selected case studies are used to illustrate the role of load tests during commissioning of new bridges, during rehabilitation works and as part of the assessment of existing bridges. (c) 2023, The Author(s), under exclusive license to Springer Nature Switzerland AG
Mega Floating Concrete Bridges
No full textIntroduction This graduation project has been initiated to research the technical feasibility of floating bridges. The project has been done in co-operation with the FDN engineering company and Delft technical university. A design is made of a continuous pontoon floating bridge, which connects a mainland to an island. Floating bridges can be constructed where conventional bridges are impractical (under the conditions that are described in section 1.4.2). The buoyancy forces support the bridge in the vertical direction and the mooring system in the horizontal direction. The project contains also a survey of the most known floating bridges in the world. Problem definition Which design limitations and structural parameters can ensure stability of the continuous pontoon floating bridge under wind and wave load? Research The objective of this thesis is to understand the response of the continuous pontoon floating bridges under wind-wave load and traffic load that is described in the euro code which enables us to optimize the structural design procedure. That can be accomplished by studying the influence of the pontoon dimensions and the pontoon connector rotational rigidity on the global stability of the bridge. Determination the principles of response reduction and converting the displacement into internal forces are a relevant part of this thesis as well as the mitigating of the local environmental loads to be redistributed along larger parts of the bridge. The scope of the graduation project is very wide. It contains an overview of floating bridges; its hydrodynamic behaviour will be defined and due to the limited period of time will be not analyzed. The hydrostatic behaviour and analysis of continuous pontoon floating bridges will be researched as a multi-body slender structure with flexible connections. Also the conceptual design of the pontoons and the connections and the shape effects were researched. Detailed design calculations for the case study are included in this thesis. Results Environmental loads are the main loading on the floating bridge. Because of the random form of the sea wave forces and the wind force, it is difficult to expect the precise value and direction of loading on the bridge. The environmental loads twist the bridge and excite it in the horizontal and in the vertical direction. When it is possible to construct a sliding pile mooring system to introduce the wind and wave load in the horizontal direction, the floating bridge will have a satisfactory stability. The efficiency of the mooring cable is lower than the sliding pile due to the relatively large compliance range. That is valid also for the vertical displacement; the bridge response will be introduced by the bridge flexural rigidity, the bridge mass, the water spring, the water damping and the pontoon connector stiffness when discrete pontoons are used. The linear theory is applied to determine the sea wave load. The hydro-static and the hydro-dynamic analysis of a multi-body slender structure consisting of rigidly or flexibly connected elements will be made.. The design procedure of the mooring cables of the offshore structure is applied to design the mooring system. Conclusions and recommendations The connection stiffness of the pontoon has a large influence on the bridge response. The ratio connection stiffness over pontoon stiffness is very important for the bridge structural behaviour. When this ratio is smaller than 10-8 the bridge behaves as rigid bodies connected by hinges. When this ratio is larger than 10-3 the bridge behaves as a continuous elastic beam. The largest deflections, moments, and shear forces occur in the ends of the bridge. Additional supports, masses, or dampers at these ends can reduce these moments and forces strongly. Embedment steel crossheads are used to introduce the large mooring line forces without damaging the concrete walls of the pontoons. Further optimization of the pontoon length is recommended. Fatigue of the prestressing steel and the concrete are shown to be critical and need to be further investigated.Design and ConstructionCivil Engineering and Geoscience
Grothendieck Toposes as Unifying 'Bridges': A Mathematical Morphogenesis
No full textWe present some philosophical principles underlying the theory of topostheoretic ‘bridges’, introduced by the author in 2010 and further developed and
applied in the subsequent years
Development in Roman stone arch bridges
No full textThe long success of the Roman Empire depended in large measure on the vast network of roads that was constructed. At its fullest extent this included more than 300 major stone-arch bridges, many still in use. In this article the author categorizes the bridges in terms of date and three basic parameters - maximum span, overall length, and height. This suggests two major periods of construction: the first century B.C. and the first half of the second century A.D. Large bridges are listed
Self-anchored suspension bridges
No full textSince 1870, only about 25 highway bridges have been executed as a self-anchored suspension bridge. The rise of the cable stayed bridge since 1955 made this suspension type an obsolete alternative for a long period of time. The largest existing main span for a self-anchored suspension bridge is 300 metres and dates from 1999. Main difficulties for this bridge type to reach spans over 300 metres can be blamed on erection problems and the buckling stability of the girder. Erecting the deck structure prior to the main cable makes this bridge technically and economically less attractive than for instance the cable stayed bridge. A dimensional inventory has shown that the deck slenderness is limited to about ? = 1/95 and the sag ratio varies between 1/5-1/8. The deck slenderness is related to the required bending stiffness to have sufficient resistance against buckling. Also the relatively high sag ratios, compared to conventional suspension bridges, are mainly chosen to reduce the normal force in the deck that is imposed by the main cable. A parameter study into the structural behaviour has revealed that the most important bridge parameters are the bending stiffness EIdeck of the deck and the axial stiffness EAmain cable of the main cable. A well chosen ratio between the EIdeck and EAmain cable influences the maximum bending moments and the deflections in the girder. In the pre-design process of a suspension bridge type it is favourable to consider: -A slender stiffening girder, to reduce the maximum bending moment in the girder -A stiff main cable, to increase the global stiffness of the bridge and to reduce the maximum bending moment in the girder -A high sag to span ratio, to reduce the normal force in the deck and the maximum bending moment in the deck.Design and constructionCivil Engineering and Geoscience
Cystine and glutamate transport in renal epithelial cells transfected with human system x—c
No full textCystine and glutamate transport in renal epithelial cells transfected with human system x-c.BackgroundSystem x-c is a heterodimeric transporter, comprised of a light chain, xCT, and heavy chain, 4F2hc, which mediates the sodium-independent exchange of cystine and glutamate at the plasma membrane. In the current study we tested the hypothesis that stable transfection of Madin-Darby canine kidney (MDCK) cells with human xCT and 4F2hc results in the expression of functional system x-c.MethodsMDCK cells were transfected stably with human clones for xCT and 4F2hc. Analyses of time- and temperature-dependence, saturation kinetics, and substrate specificity of L-cystine and L-glutamate transport were carried out in control and xCT-4F2hc-transfected MDCK cells. We also measured the uptake of L-cystine inXenopus oocytes expressing human xCT and/or 4F2hc or xCT and/or rBAT (a heavy chain homologous to 4F2hc).ResultsAll of the different sets of data revealed that transport of L-cystine and L-glutamate increased significantly (twofold to threefold) in the MDCK cells subsequent to transfection with xCT-4F2hc. Moreover, uptake of L-cystine also increased (about tenfold) inXenopus oocytes expressing hxCT and h4F2hc. Biochemical analyses of L-cystine uptake in oocytes verified our findings in the transfected MDCK cells. Interestingly, in oocytes injected with rBAT with or without xCT, uptake of L-cystine was significantly greater than that in water-injected oocytes.ConclusionOur findings indicate that stable transfection of MDCK cells with xCT and 4F2hc results in a cell-line expressing a functional system x-c transporter that can utilize L-cystine and L-glutamate as substrates. This study apparently represents the first stable transfection of a mammalian cell line with system x-c
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
Using Eurocodes and Aashto for assessing shear in slab bridges
No full textReinforced concrete short-span solid-slab bridges are used to compare Dutch and North American practices. As an assessment of existing solid-slab bridges in the Netherlands showed that the shear capacity is often governing, this paper provides a comparison between Aashto (American Association of State Highway and Transportation Officials) practice and a method based on the Eurocodes, and recommendations from experimental research for the shear capacity of slab bridges under live loads. The results from recent slab shear experiments conducted at Delft University of Technology indicate that slabs benefit from transverse force redistribution. For ten selected cases of straight solid-slab bridges, unity checks (the ratio between the design value of the applied shear force and the design beam shear resistance) are calculated according to the Eurocode-based method and the Aashto method. The results show similar design shear forces but higher shear resistances in the North American practice, which is not surprising as the associated reliability index for Aashto is lower
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