180
X3
Category 3: Industrial Buildings and Plants
Software: Scia Engineer
Steel Structure for Biomass Boiler and Service Platforms - Elblag, Poland
General Description of the Structure and Supported
Devices
• Overall dimensions of the structure envelope:
21 x 24 x 33 m
• Structure Weight: 215 tonnes
• Number of bars in the structure: 2,254
• Number of joints: 1,254
• Weight of supported technology: 625 tonnes
The presented steel structure serves to secure the
operation of the steam three-draught boiler for biomass
combustion. The first draught of the boiler is formed
by a combustion chamber of the boiler with membrane
walls and a membrane top wall, on which there are
suspended systems of ribbed tubes. The combustion
chamber, with dimensions of 8 x 8 x 25 m and a weight
of 295 tonnes, is mounted to slide on a bearing steel
structure. Friction bearings along with a guideway in
appropriate directions enable the chamber to transform
its shape due to considerable heat dilatation. Dilatation
movements are enabled from the fixed point on the
substructure outwards and upwards in the guideway
directions. The bottom of the combustion chamber
is formed by a vibration resonance grid, which has
been placed on a separate steel concrete structure.
The bearing structure of the second and third draught
has been designed as a multistage spatial frame.
The interconnecting of the structures of the individual
draughts has been solved in a way which enables
misalignments of the assembly to be compensated.
Duct systems supported by this structure are divided
into several dilatation units, which are always mounted
to slide on the steel structure with the guideway.
Another structure serves to support sheet metal ducts
and pipelines for water and steam, and to secure the
access to technological devices by means of platforms.
The whole structure is situated inside the boiler house,
to which it is connected on several levels. The method
for interconnecting the boiler structure to the boiler
house has been chosen so as to hinder the transfer of
horizontal forces between individual structures.
Software and Model
The whole structure has been solved as a 3D-framed
structure. The greater part of the joints has been
modelled as hinged with negligence of the rotary
stiffness of the connection. Frame joints have been
designed in joints of spar pieces of main structures,
where the stability of the structure could not be
secured by means of vertical bracing. The influence
of the second order has been examined by means
of the “Stability” module, with which the maximum
critical number of the structure has been determined.
As results from the stability assessment, influences
of the second order have to be considered. These
influences have been implemented into the model in the
form of horizontal forces acting to columns within the
independent loading cases.
Particular attention has been paid to the structure below
the combustion chamber and the structure below the
vibration grid. The structure below the chamber was
interesting especially in the field of solving details of the
chamber’s friction bearing. These details have been
made without the usage of bearings, with the application
of sliding lacquers and appropriate friction coefficients
for the determination of horizontal forces.
The structure below the vibration grid was examined
dynamically by means of a modal analysis with the
development to natural shapes.
Following the execution of the linear static, dynamic
and stability analysis, the Scia Engineer program was
applied. In this program, we successfully achieved an
optimised design structure design. We also managed
all the design phases thanks to the application of the
transfer of geometry into the Scia program from the
AdvanceSteel program by means of the IFC- and XML-
Export.
