Design of bulkheads and
diaphragms
Design of flexible retaining structures:
diaphragms and bulkheads. The problem of dimensioning and verifying these
structures is solved by Diadim II through a finite elements model (F.E.)
especially designed to evaluate the interaction between terrain and structure.
The
distribution and magnitude of the loading and resisting forces exerted on the
structure are, as a matter of fact, strongly influenced by the deformation of
the combination terrainstructure, hence it is necessary to use an advanced
numerical method that takes into account both the nonlinear behaviour of the
materials and the temporary phases of excavation operation.
The optimisation of the calculation algorithms
and the and the user interface specifically dedicated to the problem, enable one
to analyse and verify quite complex situations with high precision but within
very short time. Given the terrain’s stratigraphy and the position of the
aquifer uphill and downhill 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 with different methods based on the geotechnical characterisation
of the terrain.
The
elastic characteristics of the structure can be explicitly defined in terms of
rigidity to flexion or be automatically calculated on the base of description of
the very section; as a matter of fact the program can calculate continuous
diaphragms in reinforced cancrete, beam bulkheads, sheet piles and piles in
reinforced concrete. The user can, furthermore, choose various fastening
conditions of the top and bottom of the diaphragm.
The program enables one to apply to the
structures external moments and horizontal distributed or point loads. It is
possible to define multiple anchoring levels, that can tie rods (eventually
prestressed) resistant to traction only or as rigid braces that can also absorb
compression forces.
The removal of earth, downhill from the
structure, can be separated, in the numerical simulation, in different phases.
This is an important characteristic of the program as it enables one to take
into account the deformations resulting from previous excavation phases and to
recalculate the response curve of the terrain downhill from the structure at
each excavation phase.
After
calculating the loads on the diaphragm the program goes over to the structural
analysis phase properly said. The structure is, as a matter of fact, tested for
pressure and flexion and, in case of reinforced piles the shear resistance due
to reinforcement is verified.
Verification of the moment and normal stress is
performed in the section under the highest stress with the Ultimate Limit State
method, Eurocode 2, that takes into account the mechanical nonlinearity of
materials and the nonlinearity of the structure.
The program determines the bending moment and
the normal stress of the calculation and confronts these respectively with the
ultimate bending moment before failure and ultimate normal resistive stress.
Shear Verification: this is performed with the
standard method described under Eurocode 2. The program determines the maximum
shear force acting on the section and that this is smaller than the bearing
capacity of reinforced concrete beams (Vrd2) and of the reinforcements (Vrd3).
