Page 123 - AGC_EN_iBook

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tHe WIND BRaCINGS
The horizontal loads (wind loads and horizontal forces exerted by ground movements or earthquakes) are absorbed by steel wind bracings that link the columns to the oor plates diagonally.The number of wind bracings has been kept to a minimum so that the free expansion of the oor plates (or the building) is not restricted. Only a few of these bracings are still visible as part of the exterior structure of the building, where they have been treated as decora- tive elements within the spaces they occupy.The others have all been concealed within the building’s technical areas. At ground level just a single wind bracing has been xed, to enable the most ef cient use of the available car park; it is positioned centrally, within a grid of four columns.
The site at Louvain-la-Neuve is situated within a potential risk zone for signi cant ground movements and earth tremors. In order to increase the resistance of the rare wind bracings with regard to these movements, the oblique columns have been lled with con- crete in order to increase their buckling limits, and the upper metal wind bracings have been modi ed to enable a plasti cation of the assemblings prior to a rupture.The equivalent horizontal forces depend on the zone (0.06 g for the region of Louvain-la-Neuve),
the type of soil, and especially the exibility of the construction. This building is atypical given the absence of lift cores, of concrete stairs and of rigid facades down to the foundations, and given the large horizontal surfaces (a square building whose side measures 83 m), the heavy weight of the solid slabs (the total weight of the building is about 190,000 kN, equally distributed over 143 columns) and the fact that the building catches the wind well. As a result, the percentage of the total weight that has to be taken into account to determine the horizontal stresses in the seismic calculation, even
if it is reduced in absolute value, becomes proportioning.
For accidental load combinations (such as earth tremors), the wind load should not be taken into account.
2012.06.02
the latent threat of earth tremors was a continual cause of uncertainty during the construction phase. For this reason, the load-bearing capacity was increased by the use of additional wind bracings during the building of the east wings.these were removed once construction of the central gallery and the west wing had progressed suf ciently.