In this study the effect of
near-fault ground motions are investigated, along with
other seismological parameters such as earthquake
magnitude and distance from the fault, to evaluate the
seismic response of an eight-story RC combined
structural system building (MRF and Shear walls), and
perform a damage assessment for that building under
certain earthquake events. Those near field ground
motions are from Italian Aquila and Norcia earthquakes,
due to the similarity in the geo tectonic environment
between Greece and Italy. Furthermore, suggesting
appropriate solutions to mitigate the damage reached in
practically applicable and economic approach.
Figure showing the building layout
The Reinforced concrete building consists of beams which
are simulated as T-sections in the interior spans while
are considered as L-sections at the perimeter of the
building. Shear walls, Beams and Columns are modeled as
inelastic forced based plastic hinge elements
(infrmFBPH), while the slabs are considered as rigid
diaphragms as illustrated in the following figure.
The structure was modelled using the building modeler of
Seismostruct program, the height of each floor was taken
approximately 3m. The dead loads are the own weight of
the members, floor covering and wall loads, since the
walls are divided into exterior and interior walls. The
interior wall loads are distributed on the slabs while
the exterior wall loads are uniformly distributed on the
beams. All dead and live loads are transferred to the
beams as distributed loads.
Figure showing the 3D modelling of the building in
Seismostruct
Using Seismostruct software, a static non-linear
pushover analysis is performed, in order to calculate
the yield acceleration of the building (ay) which is
used later in picking up the suitable ground motion
records expected to cause considerable damage.
Subsequently, a nonlinear inelastic dynamic time history
analysis is performed, using a sample of 16 near fault
ground motion records from Aquila and Norcia earthquakes
in Italy, to obtain the displacement time history of
each record, which will be used to determine the damage
limit states achieved according to “T. Rossetto, A.
ElNashai” vulnerability relationships.
Afterwards, Chilean code assumptions and provisions were
implemented in the case study herein as the existing
building was strengthened by a certain number of shear
walls in order to make the ratio of shear wall in the
one principal direction (Y) of the building to the floor
area (Aw/Af) about 3% in each floor to check the
enhancement or improvement of the building seismic
response taking into account reducing the existed shear
walls and core reinforcement.
Figure showing the layout of the strengthened
building in Seismostruct
After implementing the Chilean code provisions and
investigating the building in Y-direction only, a
comparison is established between the behaviour of the
original and strengthened building under the same near
field ground motion records.
The dynamic time history results have shown a
significant improvement in the building response and a
reduction in the damage limit states reached for most of
the records.
After reviewing all the results, it was found that the
moment magnitude value isn’t the predominant affecting
factor, and the acceleration time history density is
more effective in the damage caused by the near field
records.
Eventually, it was concluded that the sensitivity of the
estimation of damage is mostly affected by the energy
contained in the ground motion which is introduced as
the “energy flux” index which is the time interval of
the squared ground velocity. This index is in the case
of a directivity velocity pulse this measure takes
abruptly large values at the beginning of the ground
motion duration.
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