Cubierta Hiperbólico-parabólica

Spokane Church in the State of Washington has been attractively roofed with a parabolic-hyperbolic pre-stressed concrete shell. According to the author, this type of shell structure, normally accepted to be of simple analysis, can present certain difficulties as regards stability. Theories deriving from the study of a membrane are not enough because, if the shell is large enough certain secondary stresses appear which quickly affect stability. In this case the shell, which is symmetrical along one axis only, has two overhangs of 15 and 31 meters respectively, which required a special study. In an attempt to smooth out the difficulties of an exact calculation the author tried as far as possible to even up the bending moments of the whole shell, thus allowing the indétermination conditions to be lessened. To do this he gave the shell a 7.5 centimeter thick overhang of light concrete at the back and a 12 centimeter thickness of ordinary concrete at the front. The front walls are strengthened by the shell, which they support. The light supports at the back will not take any load over the normal design load. To calculate the stress of the shell and around the rim, the membrane theory was applied, and it was assumed that the shell was symmetrical about two axes; this analysis gave a maximum stress of 14 kg/cm2. Considering that the boundary area was subject to axial compressive stresses, in principle, it was thought that only normal reinforcement would be needed over the whole shell, without needing it to be pre-stressed; but it was realised that the secondary stresses would be decisive in the general behaviour of the shell. The shrinkage of the concrete would be another cause of these secondary stresses, and likewise the differential shrinkage and elastic shortening of several parts of the structure. The object of the pre-stressing was to apply uniform pressure on the whole shell. To achieve this a stress of 16 tons was applied on each 1-meter wide band of the shell. In the direction of the two stirrups the pre-stress was 10 tons per meter, to avoid the possibility of cracks.La iglesia de Spokane, del Estado de Washington, se ha cubierto, graciosamente, con una, lámina parabólico-hiperbólica, de hormigón pretensado. Este tipo de láminas, dice el autor, de análisis corrientemente admitido sencillo, puede presentar ciertas dificultades en su estabilidad. No son suficientes las teorías que el estudio de una membrana proporciona, ya que, si las dimensiones de estas láminas alcanzan ciertas proporciones, aparecen esfuerzos secundarios que rápidamente surgen al intervenir en la estabilidad de la lámina. En este caso la lámina, simétrica solamente según un eje, presenta dos voladizos de 15 y 31 m, respectivamente, lo que ha constituido un estudio particular. El autor, con objeto de al lanar dificultades de un cálculo exacto, intentó igualar, en la medida de lo posible, los momentos flectores en toda la lámina, admitiendo, con ello, que las condiciones de indeterminación se verían reducidas. Para proceder asi se le dio a la lámina un espesor de 7,5 cm de hormigón ligero en la parte posterior formando ménsula y de 13 cm en la parte anterior de hormigón del tipo ordinario. Los muros frontales se han solidarizado con la lámina, a la que le sirven de apoyo. Los soportes, ligeros, de la parte posterior, no permiten sobrecargas superiores a las normales previstas. Para el cálculo de las tensiones de la lámina y de los elementos de borde se aplicó la teoría de membrana y se supuso que la lámina era simétrica respecto de los dos ejes, de cuyo análisis resultó una tensión máxima de 14 kg/cm2. Por creer que los elementos del borde estaban sometidos a esfuerzos axiles de compresión, en un principio todo hacía resumir que sólo se necesitarían armaduras nominales en toda la lámina, sin que fuera necesario el pretensado; sin embargo, se pudo apreciar que los esfuerzos secundarios dominarían el comportamiento general de la lámina. La retracción del hormigón sería otra de las causas de dichos esfuerzos secundarios. También influían en estos esfuerzos secundarios la retracción diferencial y acortamiento elástico de varias partes de la estructura. El pretensado tenía por objeto introducir una presión uniforme en toda, la lámina. Para lograrlo se aplicó una tensión de 16 toneladas por banda de un metro de anchura de lámina. En la dirección de los dos estribos, la tensión de pretensado ha sido de 10 toneladas por metro, para evitar la fisuración

Riociguat treatment in patients with chronic thromboembolic pulmonary hypertension: Final safety data from the EXPERT registry

Objective: The soluble guanylate cyclase stimulator riociguat is approved for the treatment of adult patients with pulmonary arterial hypertension (PAH) and inoperable or persistent/recurrent chronic thromboembolic pulmonary hypertension (CTEPH) following Phase

Puente pretensado, en Oakland (U. S. A.)

This is a four span bridge, which is prestreesed in four dimensions, and runs over a number of railway lines. The design has been awarded a number of prizes. The axis of the bridge is circular, and consequently the weight of the bridge imposes torsional moments on the structure. The most original feature of this project is the placing of the prestressing along three space coordinates, and also the regulation of the prestressing forces as functions of time. The prestressing is very densely distributed along the curved part of the structure. This counteracts the effects of the dead weight, and enables the structure to be statically considered as if its spans were straight. Owing to the large torsional moments, the bridge consists of seven T section beams, to reduce the weight and the number of prestressing cables. Another interesting feature of this design is that the springers have been readjusted 25 cm, in order to regain the original compressive constraints, which would have been lost in time, due to creep phenomena. Precast units were not used, as they were not the most apt to work under torsion, and for similar reasons only two dilation joints were fitted.Este puente, de cuatro tramos, pretensado en las cuatro dimensiones, salva una serie de vías férreas y ha obtenido diferentes premios. Las alineaciones del eje forman ángulos de 47 y 20°, y como sus desarrollos correspondientes son curvas circulares se crean momentos importantes de torsión debidos al peso propio. Lo más original de esta obra consiste en la ordenación del pretensado según las tres coordenadas espaciales y una cuarta, temporal, que nos da el valor de las tensiones en función del tiempo

The Application of Dual‐Layer, Mussel‐Inspired, Antifouling Polyglycerol‐Based Coatings in Ventricular Assist Devices

Continuous‐flow ventricular assist devices (VADs) have established themselves as a lifesaving therapy option in patients with severe cardiovascular disease. Unfortunately, complications with VADs resulting from the shear‐induced formation of surface blood clots are common. In the current work, an antifouling coating based on the combination of mussel‐inspired dendritic polyglycerol (MI‐dPG) and linear polyglycerol (lPG) is tested for its cell‐repelling properties, biocompatibility, and complement activating properties. Furthermore, the adhesion and activation of blood platelets are tested under static and flow conditions. The adhesion and proliferation of two cell types are studied by means of LIVE/DEAD cell staining, and it is clearly observed that the lPG‐functionalized MI‐dPG coating prevents cell adhesion. Additionally, no cell mortality is observed on all substrates, indicating the biocompatibility of the tested coatings. All coatings show lower (or equal) complement‐activating properties than bare titanium, which is considered a highly biocompatible material. Most importantly, the lPG‐functionalized system prevents the adhesion and activation of blood platelets under static and flow conditions. Finally, a prototype VAD is successfully coated with MI‐dPG under flow conditions. In the current study, the efficient lPG‐functionalization of the MI‐dPG coating is proved to obtain cell‐ and platelet‐repelling surfaces