Structural assessment of concrete railway bridges : Non-linear analysis and remaining fatigue life

This research focused on the biochemical composition of organic matter and its change during the process of decomposition in natural conditions of the local climatic community of Quercetum farnetto-cerris Rudski (1940) 1949 s.lat. The experiment was conducted on leaf fall of edificators in this forest, i.e. Hungarian and bitter oak and a combination of the two, material analysed at three time spans (following leaf fall, after six months and after one year). The aim of this research was to determine the value of each of the above mentioned edificators for the ecosystem functioning as well as their impact in the formation of soil organic horizon. In addition to biochemical content analysis, concentrations of C, N, C:N ratio and lignin:N ratios in organic matter were analyzed. In tandem with these examinations (at three time spans) concentrations of soil humus were also determined (0-10cm 10-20cm, and 20-30cm) aimed at comprehending their time distribution. It transpired that Hungarian oak organic matter had a more favourable ratio of readily-soluble matter and resistant matter, as opposed to the bitter oak organic matter. This fact directly influenced decomposition altitude of examined species: Hungarian oak (51.25%), Hungarian and bitter oak (48.33%) and bitter oak (28.52%). On the basis of an empirically obtained annual constant (k), Oslon decomposition model was designed to give a prognosis of decomposition to the state of almost complete mineralization. The humus time analysis in this community indicated degradation processes within.Na osnovu obavljenih istraživanja mogu se izvesti sledeći zaključci. Postoji statistički potvrđena razlika u brzini razlaganja između organske materije sladuna i cera, kombinacije sladuna i cera i same organske materije cera. Relevantni parametri dekompozicije (C, N i odnos C:N) su potvrdili razliku u razlaganju. Organska materija sladuna imala je presudnu ulogu u metabolizmu ove zajednice u prvoj godini istraživanja, dok će organska materija cera (zahvaljujući svom rezistentnijem biohemijskom sastavu) imati presudnu ulogu u budućim fazama dekompozicije. Za skoro potpunu mineralizaciju (99%) organskog opada ove zajednice biće potrebno oko 7.7 godina. Organski otpad edifikatora ekosistema sladuna i cera razlaže se u opsegu karakterističnom sa listopadne šume umerene zone. Vremenska analiza količine humusa je ukazala na ozbiljnost degradacionih procesa u ovoj zajednici i na narušenost balansa između procesa mineralizacije i humifikacije organske materije zemljišta koja ce se u bliskoj budućnosti odraziti na produktivnost ovog šumskog staništa.nul

Non-Linear Analysis and Remaining Fatigue Life of Reinforced Concrete Bridges

The work provides methods for non-linear structural analysis and fatigue safety evaluation in assessment of existing railway bridges. The use of non-linear analysis leads to higher load carrying capacities, but also to improved understanding of the structural response, forming a better basis for decisions in the assessment. The methods for fatigue assessment lead to increased remaining service life of reinforced concrete railway bridges. The achievements of the work are: • Models for assessment of concrete bridges by non-linear analysis are described, and examples and general recommendations for practical application of the methods aregiven. • An overview of the effect of corrosion on the bond properties has been developed through non-linear analyses and tests found in literature. Recommendations for practical assessment of anchorage capacity in corroded railway concrete bridges are presented. • The determination of reliable in-situ material properties in old concrete bridges is described,including properties for fully probabilistic analysis. A particular aim was to develop better methods to describe development of concrete properties with age and degree of hydration. • Recommendations are given regarding re-distribution of sectional forces and moments, obtained through linear structural analysis (with FEM). In a case study, a typical slab bridge was designed using different methods, and its response evaluated through nonlinearanalyses. • A good understanding of the load-carrying mechanisms in combined bending-shear-torsion gives a possibility to make more accurate assessments than with standard code methods. Methods and examples are presented. • A state-of-the-art review of fatigue behaviour of reinforced concrete railway bridges is presented and a methodology to assess the remaining fatigue life of existing reinforced concrete bridges subjected to railway traffic is developed.EC Sixth Framework Program, Sustainable Bridges – Assessment for Future Traffic Demands and Longer Lives, TIP3-CT-2003-00165