The automated analysis and design of underground concrete nuclear shelters

Two topics are covered in this thesis; the implementation of the SemiLoof shell element into ANSYS and a .finite element analysis of an underground nuclear shelter subjected to a blast load, using SemiLoof shells.
The SemiLoof Shell is an eight noded, isoparametric, thin shell element. Its main advantage over its competitors is its faster matrix calculation and solution time due mainly to the fact that it has only 32 degrees of freedom (3 translationals at each node, plus 2 rotationals at each midside node), rather than the usual 48 degrees of freedom (6 at each node).
The User Element Utility was used to link the original SemiLoof Fortran subroutines into ANSYS as a linear element. As these subroutines were already available, the main task was to design and write interfacing subroutines which were required to translate parametric and array names, serve subroutine callingmarguments and overcome inconsistencies in the arrangement of the ANSYS/SemiLoof degree of freedom sets. The original SemiLoof calculations are limited to displacements, element forces and bending moments, hence further stress calculation subroutines had
to be written in order to make the element of practical use to the engineer. SemiLoof is referenced by ANSYS as Stif100 can be used in the same way as any other ANSYS element. All the linear analysis types, pre- and postprocessing features and wave front solution are available for use by SemiLoof, which can also be mixed with other ANSYS elements having a suitable degree of freedom set. Benchmark tests on SemiLoof in ANSYS have shown it to be a quick
and accurate performer and a useful alternative to ANSYS's eight node thin shell - Stif93.
SemiLoof in ANSYS was then used to analyse an underground, reinforced concrete nuclear shelter, subjected to an impulsive blast load. The aim of this analysis was to determine if the design data-bending moments were of a realistic magnitude. The SemiLoof analyses showed that they were less than adequate and that the shelter is probably slightly underdesigned. It suggested in this thesis that the design criteria of moderate damage was unsuitable for the purposes of the shelter and that it would be advantageous to design the shelter so that it would remain in good condition after the blast load, and thereby service the basic needs of comfort and hygiene for the occupants.