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In General
The office building AB2 has been erected in Bratislava as a part of the complex: Polus City Centre.
The investor of this complex is TrigGránit Development Corporation; the architectural solution was handed over by Ateliér Art s.r.o, Slovakia; Stanfford Haensil Architects, Ontario, Canada and Adamson Associated Architects, Ontario, Canada.
The main Contractor was Strabag s.r.o of Slovakia.
The structural design for the building licence was elaborated by ELTER Constructions s.r.o. of Slovakia.
The detail structural design was elaborated by Konstrukt Plus, Slovakia.
The main structural designer for the building was Ing. Daniel Bukov OK TEAM.
Basic Parameters of the Building
The total number of floors is 21 above ground level and one floor below ground level. The total height of the building is 89.8m. The total area is more than 22 000 m², that is more than 1000m² per floor.
The main bearing system of the building is created from cast in place reinforced concrete. In the middle of the building is located a core with the dimension 17.9m.x 10.7m, the thickness of the walls measure from 600 mm to 300 mm. Square columns have dimensions starting from 700x700mm to 400x400 mm in the upper part of the building. Floor slabs have thicknesses of 280 and 250mm.
The building was erected by sliding the shuttering for the core, which was erected two floors before the construction of the floor slabs. The slabs were connected to the core by rectangular holes. This connection was considered stiff. In the opening where the floor slabs connected to the core, reinforcement was not interrupted. |
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Method of Detail Designing
For the computation of the shape of the structure, cross sections, thicknesses and loads were taken into account. New information concerning the openings (location and dimension) were also included in the structural analysis.
For the calculation of the main bearing system, the 3D model is created. For the separate parts, an own model was created (floor slabs, columns, attic etc.). The results from the global calculation are included into separate models as external loads or are included in the proportioning.
All calculations are performed according the Slovak valid codes.
Loads
The self weight of the structure is considered according to the thickness of the bearing parts. The additional dead load lies in the range of 4.0 to 5.0 kappa. The live load on common floors is 3.5 kPa and 5.0 kPa near the core.
Global Structural Calculation
The main bearing system of the building is calculated by a 3D computational model created by the finite element method. The foundation slab, including soil interaction, core walls and columns, is exactly modelled in this space model. Floor slabs are also modelled precisely, but for computational reasons only a very large mesh is used. For the seismic response, the calculation linear response spectra method is used. For a combination of modal responses, the CQC method is used. Soil interaction has been solved with the theory of half space. The proportioning of the foundation slab and core walls is done in this model without any other influence or consideration. The proportioning of the columns is done by separate calculation where also bending moments from floor slabs are taken into consideration. From the global structural calculation, only normal forces have been adopted. All calculation is performed by NEXIS 32.50.05 program (ESA-Prima Win).
For tall buildings it is necessary to take into consideration the influence of the longitudinal deformation of the columns on the main bearing system. Deformations of columns due to high compression have to deal with elastic deformation creeping and shrinkage of the concrete. Some deformation is eliminated by floor slab levelling, some has to be predicted by calculation. It is also necessary to take into the consideration the decreasing normal forces in the columns due to the decreasing effect of the live load depending on the number of the floors above. Influence of the settlement in the core area, which is higher than settlement in the perimeter columns, also plays a role in the designing of the bearing system. For seismic response calculation, different sub grade properties have to be used (stiffness or resistance of the soil in the case of the dynamic loads is higher). At least two models have to be calculated for one proportioning. With ESA-Prima Win we have the possibility to make many calculations in real time. |
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Floor Slab Calculation
Floor slabs are calculated in a separate model, punching shear and connection to the core walls is taken into account. In this model also bending moments in the columns are calculated. Around the columns a more dense mesh is used. On one side, there are decreased bending moments in the columns, and on the opposite side, there are increased positive moments in the floor slab. The proportioning of the slab in the columns is done based on sections and the reinforcement is distributed accordingly.
Conclusion
In order to obtain a solution of such a demanding structure, a very effective program for the calculation of internal forces calculation is needed. It must be able to prepare the structural model and to offer various possibilities to check the results. The incorporation of the proportioning in one package is also big advantage. ESA-Prima Win fulfils these requirements. |
