Abstract:
This study explores three-dimensional nonlinear
dynamic responses of typical tall buildings with and without
setbacks under blast loading.These 20 storey reinforced concrete
buildings have been designed for normal (dead, live and wind)
loads. The influence of the setbacks on the lateral load response
due to blasts in terms of peak deflections, accelerations,
inter-storey drift and bending moments at critical locations
(including hinge formation) were investigated. Structural
response predictions were performed with a commercially
available three-dimensional finite element analysis programme
using non-linear direct integration time history analyses.
Results obtained for buildings with different setbacks were
compared and conclusions made. The comparisons revealed
that buildings having setbacks that protect the tower part
above the setback level from blast loading show considerably
better response in terms of peak displacement and interstorey
drift, when compared to buildings without setbacks.
Rotational accelerations were found to depend on the periods
of the rotational modes. Abrupt changes in moments and
shears are experienced near the levels of the setbacks. Typical
twenty storey tall buildings with shear walls and frames that
are designed for only normal loads perform reasonably well,
without catastrophic collapse, when subjected to a blast that is
equivalent to 500 kg TNT at a standoff distance of 10 m.
