design of water treatment tanks
Haswell Consulting Engineers
customised LUSAS Civil & Structural to analyse geotechnical problems involving
soil/structure interaction. Extensive use was made of the LUSAS parametric facilities to
automate the modelling and analysis of various types and sizes of ground bearing and piled
water treatment tanks.
An important feature of all LUSAS products is the ability to allow
engineers to automate analyses of structures having a similar layout or arrangement. This
is done by creating Wizards using the in-built scripting language. After defining an
initial model, the scripting language can be used convert the model data into a form for
use with variable dimensions and attributes. Graphical menus and on-screen dialogs are
added to allow engineers to enter data and build models of different structural dimensions
and properties with the minimum of effort.
of underground water treatment tanks has traditionally been based on conventional hand
calculation procedures which take into account the behaviour of the soil and of the
structure independently. Hand calculation procedures also require three dimensional
problems to be idealised in two dimensions. These two factors lead to inaccuracies in the
soil/structure interaction and the effect on the structure. Parametric modelling of the
soil and structure with LUSAS Civil & Structural can combine the soil and the
structure in one three-dimensional model, allowing engineers and analysts with only a
basic knowledge of finite element methods to create tank models, perform analyses and
With Haswell's tank designs, variables such as wall and slab dimensions,
number and location of piles, concrete properties, backfill properties, and number of soil
horizons are all entered via on-screen user-defined forms. Various loading conditions can
be selected allowing for any number of the following:
- Hydrostatic pressures from differing water levels in adjacent tank bays.
- Uplift due to pore water pressure.
- Piled foundations with a tension and/or compression capacity.
processing scripts for each tank type allow predetermined sets of results to be produced.
By following another sequence of on-screen prompts the location and angle of view on the
structure can be specified to give the stress plots and data output required. In a
comparison with manual calculations, bending moment values obtained from both rectangular
and conical tank designs showed close correlation under a range of loading conditions.
By using LUSAS for tank design many of the simplifications made in
conventional analyses are unnecessary and more accurate results can be achieved. The
soil/structure interaction can be investigated both globally and locally in 3D with
stresses, strains, bending moments and displacements being obtained. The soil and
structure can be analysed in one model with easy modification of geometry and material
Dr Ala Sainak the engineer responsible for developing the range of
parametric programs used said: 'The use of LUSAS parametric modelling techniques reduces
the need for specialist finite element expertise and makes repetitive analyses easier to
perform for less experienced users.'