When a multilayer concrete beam is built, several concrete mixtures could be poured sequentially. Usually concrete used in external layers are higher resistance than those placed in internal layers. Time between the pouring of the different layers could have influence on the beam behaviour. The goal of this paper is to study how temporary offset on manufacturing the multilayer concrete beams has influence on their mechanical behaviour. Some has test have been run out to some beams which let us know the different behavior between each other. Finally it has been determinate if the construction process is the cause or other factors lead to produce the founded differences.
In this paper an analysis of building frames under horizontal actions is presented. Firstly the theoretical behavior is studied, and then a strut and ties model is proposed based on results obtained in an auxiliary finit element model. Thus, it has been first described the particular features of the structural problem, on the one hand the seismic action and on the other structural mechanism that it involves. Then a particular analysis of a node has been carried out, in the case of a frame with a specific configuration. This fem model allows to check the hypothesis adopted for the strut and ties calculations that are proposed as the solution of the problem. In this way, the main intention of this article is not to show a general approach to the issue of portal frames under seismic forces. Instead of this, the main goal of this paper is to propose a methodology based on simple calculation models that let solve the structural problem.
La defoliación arbórea es uno de los mejores indicadores para evaluar el estado fitosanitario de los bosques. Existen varias redes en España que toman esta información: Red Europea de Seguimiento de Daños en Bosques de ICP-Forests, Redes Autonómicas de Seguimiento de Daños, y Red de Seguimiento y Evaluación de Parques Nacionales. El objetivo de este estudio es el análisis de la dinámica de la defoliación en regiones bioclimáticas, tipos de masas y principales especies de coníferas (Abies alba, Pinus uncinata, Pinus sylvestris, Pinus nigra, Pinus halepensis, Pinus pinaster, Pinus pinea) y frondosas (Castanea sativa, Fagus sylvatica, Quercus pyrenaica, Quercus robur, Quercus ilex, Quercus suber, Quercus faginea y Olea europaea) de la España peninsular y Baleares. Se armonizó la información de las diferentes redes de daños en una red integrada compuesta por un total de 2858 parcelas con datos entre 1986 y 2015. Los resultados muestran un incremento en la defoliación general media (12.3% en 1986 a un 25.2% en 2015). En coníferas, Pinus uncinata (región alpina), Pinus pinaster (región atlántica) y Pinus halepensis (región mediterránea), mostraron los valores más altos de defoliación en 2015. En frondosas, los valores más elevados se encontraron en Quercus pyrenaica, Quercus faginea, Quercus robur y Castanea sativa, tanto en la región mediterránea como en la atlántica. Se constata la idoneidad de la armonización e integración de las diferentes redes de daños para hacer un seguimiento a largo plazo del estado sanitario de los bosques. Estos resultados ponen en relieve la importancia de contar con una red actualizada e integrada de la información de daños en los bosques como herramienta para una gestión que garantice su sostenibilidad a largo plazo.
El Gobierno de Paraguay, en vistas del crecimiento de la ciudad y de la saturación del tráfico rodado sobre el único puente existente sobre el río Paraguay, ha decidido proyectar un nuevo cruce. El cauce del río Paraguay cuenta con un ancho en época de estiaje de unos 700m, el cual puede aumentar en época de lluvias a unos 1500m, debiéndose además respetar un tramo central navegable de 150x30m. El volumen del tráfico a soportar implicaba disponer un tablero de 28’50m de ancho. Estos condicionantes planteaban la necesidad de una estructura que se dividía en tres tramos diferenciados: un primer tramo de acceso desde Asunción, el puente principal sobre el cauce navegable y un tramo de acceso desde la orilla opuesta a Asunción sobre la zona inundable del río. En fases preliminares del estudio se analizaron alternativas para el vano principal: tableros sección cajón sencillo o dobles para ejecución por voladizos, celosías metálicas empujadas, tableros extradosados y puentes atirantados de pilono sencillo o doble. Las alternativas que se juzgaron más adecuadas fueron el tablero en sección cajón con un vano principal de 180 m de luz y el puente atirantado de doble pilono y 260 m de luz. La primera alternativa presentaba un esquema de luces de 90+180+90m. La sección adoptada consistía en un cajón con un núcleo de 10’60 m de ancho el cual se ampliaba hasta los 28’45m necesarios de plataforma mediante el uso de jabalcones. Los cantos previstos eran un mínimo de 4’00 m en centro del vano principal y de 9’00 m sobre las pilas intermedias. La alternativa atirantada, finalmente seleccionada, se conformaba por un tablero de hormigón de canto constante de 2’45 m, suspendido de sus bordes mediante dos familias de cables en semiarpa que acometían contra un pilono en diamante con fuste central único.
Cable-stayed bridges represent one of the most developed structural typologies being used recently as it has a span range that can extend beyond 1000m. Furthermore, when it comes to bridges that span to a medium range we could say their shape and resistance are features that make this kind of bridge suitable for many different applications.Moreover, due to this type of bridge being used newly more extensively it has allowed for a better understanding of the theoretical knowledge of the various technical aspects both at a structural and simulation level in order to improve the constructions process of this type of bridge. Knowledge and development of these bridges can be attributed to the increasing apprehension of I.T. skills and the development of more advanced computer software with regards to structural calculations. The latter can aide more demanding analysis that was previously difficult to ascertain Defining features of this type of structure, besides its hyper static attributes, is the importance of the construction process, namely the cable tensioning process, which determines whether the requirements set out in the construction process will be met once the bridge is finished and traffic loads are applied. This is why much research has been conducted into the optimisation of the axial forces to be applied to the cables.Focus, of part of this research, goes into the possible influences of random geometrical and mechanical parametres on the forces applied to the structure.We have therefore proceeded to develop research in which we have tried to gain more in depth knowledge which considers these aspects so that we can validate the hypothesis which are currently established in the regulations Firstly, the purpose of this thesis is to provide a new method to introduce random errors on the forces or deformations of cable tensioning so that this technique can be extended to various models of cable-staying bridges.It is important to highlight that this thesis has focused on cable-stayed bridges built through the balanced cantilever method and with concrete girders and considering there are many actual bridges with these characteristics the research has focused on a specific yet extensively applied method. vi INDICE vii
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