15 meters
Height:
42 meters
Volume:
44.000 m
3
Mass:
approximately 160.000 kN
Why is this project important?
The existing courthouse in Zwolle dates from the 1970's and
was designed by Jo Kruger. It has a very monumental design
and a beautiful travertine façade. For a number of years now
the existing courthouse is too small to facilitate all its functions
and personnel.
A design contest
was held between five
architects to expand the existing building with an additional
20.000 m
2
of various functions.
The
winning design by
Gunnar
Daan
was partly chosen
because it respects the existing design and cleverly locates
part of the new floor area above the existing building instead
of next to it. This project is important because it is the main
element on which a new city plan of the surrounding area
"the Haaglanden" is based.
Why is this project so special?
Te decision of the architect to locate part of the expansion
above the existing building created a large challenge for the
structural engineer.
After studying several possibilities, a
design was chosen in which a cantilevered structure of 52
meters hangs above the existing building. A similar volume on
the other side balances this load. The total structure is carried
by two sets of diagonal pylons,
which are connected at the
top by a tensile element. The office building stands on the
"bridge deck"
which is suspended from the pylons using
massive tie-rods.
Use of ESA-Prima Win
Description of the technical questions to be solved
with ESA-Prima Win:
One of the largest design challenges of this structure is how to
control the displacements, both during and after construction.
The overall structure is relatively flexible and the displacements
due to dead load and live load are quite large. Another
important aspect is that the construction phasing has a
significant impact of the resulting displacements and internal
member forces. During the construction stage the vertical
displacements of the bridge deck are controlled at set times by
using jacks at the bottom connection of the tie-rods. The
calculation of the necessary jack force and the influence on
the rest
of the
structure
are
an important
design
consideration. By using the option of active/non-active
elements of ESA-Prima
Win its possible to calculate the
necessary jack forces with only the elements that are present
at the time of construction.
Using fictional temperature loads
simulates the loads of the jacks. The jack-procedure can be
modelled as an individual load-case. This procedure makes it
possible to use just one overall
model for all load cases and
load combinations, and thereby saves a lot of time because it
is not necessary to "manually add" results from several
computer models for each construction stage.
The option of active/non-active elements
was also used to
model elements that are not active during construction but
only during the actual useful life of the structure. This is for
instance the case for the concrete slab of the bridge deck. This
floor is cast at the end of the construction phase because
during the jack-procedure the additional stiffness
would
create problems. In the end situation the floor is necessary for
the stability of the wind forces and is therefore introduced in
the model in the final situation and only active under wind-
loads, temperature loads and live loads.
Another important design aspect is the serviceability under
wind loads. Because of the large cantilever over the existing
buildings the maximum acceleration under wind gusts has to
be checked carefully. By using the module '
Dynamics" from
ESA-Prima Win was possible to get an accurate estimate of the
eigenfrequencies of the structure and their corresponding
eigenmodes. The foundation piles are modelled as bi-linear
elements in order to guarantee proper modelling of the forces
in the foundation blocks.
The second-order effects of the structure are difficult to check
with a simple calculation. The extension of the tensile-
elements is not subjected to second-order effects so the
normal
enlargement factor
n/n-1
would
yield
over
conservative results. By using the advanced structural analysis
model (non-linear, p-delta effect) these complex calculations
were successfully carried out.
A description of your experience with ESA-Prima Win
when realising the project:
Due to the complexity and the dimensions of the structure, a
very detailed 3-D model had to be developed.
As mentioned
previously, some specific functions, such as time dependent
active elements and foundation models were primordial to
model properly this structure.
ESA Prima Win seemed at this time the most suitable software
to use as it had the options needed as well as a really user-
friendly graphical interface,
which is very helpful
when
working on such structure.
Moreover, the few examples files
displayed on the web site allow a very fast learning of the basis
of the program.
The linear, non-linear and dynamic analyses were performed
in a fashionable time. The results were obtained in a very clear
manner and once again the graphical interface helped to give
a rapid first evaluation of the structure behaviour. The
possibility to extract specific results in different formats was a
very useful tool to investigate the output with software such
as
Math lab and Excel. Finally, the new updates of the
program were very much appreciated, as new options, such
as section analyses,
were available.
The only problems encountered were related to the display of
the output relative to the shell elements. Those graphical
results did not always display properly, and made the use of
shell elements sometimes
unpractical. I
would like to
acknowledge all the persons working at the ESA Prima Win
help desk for their technical support, their enthusiasm and
their kindness. They have been of great help to exploit the
many options of this software.
Modules used:
Base
Pre processor
Advanced structural analyses
Steel and concrete design: section evaluation (forces and
moments), steel code checks, shell analyses
Universal: intelligent document, international languages
53
SCIA User Contest Catalog
