Helmut Saal

Buckling loads of tank shells with imperfections

Buckling tests were performed with four tank structures under vacuum pressure with diameters ranging from 10 to 70 m. After discussion of geometric imperfections tolerated by the standards and methods of measuring geometric imperfections of that size the results of the measurements are reported. Some of these results are far beyond the tolerance criteria of standards for stability design of shells. However, the loads where a buckling failure of the tank occurs is underestimated with the application of these standards. Numerical investigations of the buckling behaviour of the shell with geometric imperfections of eigenmode-shape show that with the size recommended for this purpose by standards the analysis will miss the buckling phenomenon. Different shapes of imperfections are investigated in the numerical analysis with a sector model of the tank shell. Only the numerical investigation with a model of the complete tank shell with the measured imperfections gave results which agreed with the buckling phenomenon observed in the tests as well for the loads as for the location of the buckling loads.

Flexibility factors for nozzles in the knuckle region of dished pressure vessel heads

Nozzles in the spherical part of pressure vessel heads may be designed according to BS5500 and/or with the solutions based on the work of Bijlaard. However, no solution has been available so far if the nozzle is in the knuckle region of the pressure vessel head. Furthermore the restraint forces and moments at the nozzles and thus the stresses due to them may be reduced if the flexibility of the support at the nozzle is taken into account in the calculation. This paper reports on the flexibilities and how they can be taken into account in the design.

Calculation of the bearing capacity of fillet welds depending on the weld metal and the welding parameters

Publisher Summary The chapter discusses the calculations of the bearing capacity of fillet welds depending on weld metal and welding parameters. Welded connections of lower strength steel welded with filler metals (FM) approved for that steel have a considerable overstrength compared to the parent metal (PM) independent of the welding process and the welding parameters. Thus, there is no need to differentiate with respect to the parameters influencing the strength in the weld metal (WM). For welded connections of S460 and even more for S690, this overstrength decreases. A design rule allowing a safe design independent of the type of PM, FM and the welding parameters will be uneconomic for a large number of applications. The chapter presents material properties in the WM of high strength steel, depending on the welding parameters. Despite numerous parameters influencing these material properties, FE calculations and large scale tests show that the bearing capacity of fillet welds can be calculated with a simple rule.

Lateral torsional buckling of rafters in tank structures and the stabilizing influence of the roof

Publisher Summary The chapter discusses lateral-torsional buckling of rafters in tank structures and the stabilizing influence of the roof. The chapter focuses on the structural failure due to lateral-torsional buckling of the radial rafters caused by external loading or internal vacuum pressure. The lateral-torsional buckling strength of the rafters is studied with respect to the supporting effect of the tangential trusses and the stabilizing influence of the roof plates. The influence of the supporting effects is investigated for six real roof structures with diameters ranging from 20 to 45 meters and compared with German codes. Recommendations for the interpretation of numerical investigations in considering conceivable factors such as boundary conditions or the loosely attached thin steel roofing are given in the chapter. The chapter presents the results of a recent study on the carrying behavior of rafters of tank roofs prone to lateral-torsional buckling.