15 meters Height: 42 meters Volume: 44.000 m3 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 m2 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 it’s 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 windloads, 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 tensileelements 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 userfriendly 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
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