The
problem of dimensioning and verifying these structures is solved
by Diadim through a finite differences model (FDM) that has been
especially designed to evaluate the interaction between soil and
structure.
The
distribution and magnitude of the loading and resisting forces exerted
on the structure are, in fact, greatly influenced by the deformation
of the terrainstructure combination, hence it is necessary to use
an advanced numerical method that takes into account both the nonlinear
behaviour of the materials and the time phases of the excavation
operations.
The optimisation of the calculation algorithms and the user interface
dedicated to specificity of the problem, enable one to analyse and
verify quite complex situations with high precision but in extremely
very short times.
Given
the stratigraphy of the terrain and the position of the aquifer
above and below to the work during the different excavation phases,
the program calculates the diaphragm as an elastic beam on elastoplastic
supports.
The
characteristics and deformability of the terrain are defined in
terms of underground modulus that can be defined directly by the
user at each stratigraphic level, or, alternatively, can be calculated
automatically using different methods based on the geotechnical
characterisation of the terrain.
The
elastic characteristics of the structure can be explicitly defined
in terms of bending stiffness or be automatically calculated on
the basis of a description of the section itself; the program can
in fact calculate continuous diaphragms in reinforced concrete,
beam bulkheads, sheet piles and piles in reinforced concrete.
The
user can also choose various constraint conditions of the top and
bottom of the diaphragm. The program also enables one to apply external
moments and distributed horizontal loads or point loads to the structures.
It
is possible to define multiple anchoring levels, that can be schematised
as tie rods (possibly prestressed) that are only resistant to traction
or as rigid braces struts that are also able to absorb compression
stresses.
The
removal of earth, downhill to the structure, can be divided into
different phases, in the numerical simulation. This is an important
characteristic of the program as it enables one to take into account
the deformations that result from previous excavation phases and
to recalculate the response curve of the terrain downhill to the
structure during each excavation phase.
After
having calculated the loads on the diaphragm, the program switches
to the actual structural analysis phase. The structure is in fact
tested for combined compressive and bending stress and, in the case
of reinforced piles, the shear resistance due to the reinforcement
is verified.
Verification
of the moment and normal stress is performed in the section subject
to the highest stress using the Ultimate Limit State method, according
to Eurocode 2, which takes the mechanical nonlinearity of the materials
and the nonlinearity of the structure into account.
The
program determines the bending moment and the normal stress of the
calculation and compares these with the ultimate bending moment
before failure and the ultimate normal resistive stress, respectively.
The
verification of the Shear is performed with the standard method
prescribed by Eurocode 2. The program determines the maximum shear
force acting on the section and verifies that this is smaller than
the bearing capacity of the reinforced concrete beams (Vrd2) and
of the reinforcements (Vrd3).
