No abstract

<p>The weight and design speed of the railway vehicles increases in time. As a result, the values of design loads grow up. In old Bulgarian standard [1] the equivalent nosing force is prescribed as 60kN. In the present EN1991-2 [2] this value is 100kN. Meanwhile, a significant part of the very old bridges is not designed for nosing forces. In cases of long span between cross girders of the “open type” deck and lack of nosing braces, the load bearing capacity of longitudinal girders, concerning out of plane bending moments due to nosing forces, is insufficient. To investigate the value of equivalent nosing force are provided “in situ” measurements on the longitudinal girders of “open type” deck of a steel riveted railway bridge in exploitation in the Republic of Bulgaria. The strains and horizontal linear deformations are measured in the midspan of the longitudinal beams for real trains. The equivalent nosing force is calculated using developed procedures.</p>

Steel silos are interesting, complicated facilities. In order to ensure unloading of whole amount of stored product by gravity, they are often placed on supporting structure. Values of stresses in joints between thin sheets and supporting frame elements are very high, which could cause local loss of stability in thin shells. Many researchers have worked on values and distribution of the meridional stresses in that joints. Their traditional approach is to divide in their minds cylindrical shell on two parts - discretely supported ring beam and continuously supported shell above it. As a result of their efforts critical height of shell Hcr and ideal position of intermediate stiffening ring on shell are determined. The scientific results are based on semi-membrane theory of Vlasov, in which influence of vertical stiffeners and internal pressure is not accounted. On other hand all steel silos are loaded with an internal pressure and majority of them have vertical stiffeners above supports. Is it possible the obtained scientific results to be applied to these silos? In a present article the author will show that stiffeners and pressure should not be ignored in an analysis.

The steel silos are interesting complex facilities. In order to ensure unloading of whole amount of stored product by gravity, the steel silos are often placed on supporting frame structure. Values of stresses in the joints between the thin walled shell and supporting frame elements are very high. It can causes local loss of stability in the shell. To prevent its local buckling, many designers put stiffening elements above the supports. Here the question is how high should be the stiffening elements? The right solution is that they should reach that level till which the values of the meridional normal stresses above the supports and in the middle between them are equalized. Under this level the cylindrical shell will be considered as a ring beam, stiffened by elements above the supports. Above it, the cylinder can be calculated as continuously supported shell. But where is this level? A lot of researchers worked on values and way of distribution of normal meridional stresses above the supports of the cylindrical shells. As a result of their efforts are determined critical height Hcr of the shell and the ideal position HI   of intermediate stiffening ring. But these heights are considerably different between each other. To which of them our vertical stiffening elements should achieve?

In order to ensure unloading of whole amount of stored product by gravity, steel silos are often placed on supporting structure. The simplest way to design these complicated facilities is to divide cylindrical shell on two parts in our minds - discretely supported ring beam and continuously supported shell above it. Obviously, to ensure continuously support of shell, bending stiffness of ring beam should be high. In European standard EN 1993-4-1, that concept is recognized but it keeps silence about recommended stiffness of ring beam. Another way to design is to know law of distribution of compressive axial stresses due to discrete column reactions R, by height of shell. Knowing it, we could calculate the effective width leff of distribution of compressive stresses on every level. Where effective width is equal to distance between discrete supports, there critical height of shell ends and above it cylindrical body is continuously supported. Unfortunately the above quoted standard EN 1993-4-1 does not give an information how to calculate leff. The questions here are; should we accept linear distribution of compressive forces by height? In addition, could we use directly the results of Whitmore (1952), where angle of distribution α = 30°? Or, even to accept a far more brave opinion that α = 45°, used by many of the elder designers? Moreover, is value of angle α constant or does it depend on various influencing factors?