Characterization and modelling of seismic action Report of WG2: Earthquake resistance Dan Lungu*, Aurel Stratan** & Radu Vacareanu* * Technical University of Civil Engineering of Bucharest, Romania ** "Politehnica" University of Timisoara, Romania COST C26: Urban Habitat Constructions under Catastrophic Events Final Conference, 16-18 September 2010, Naples, Italy
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COST C26: Urban Habitat Constructions under Catastrophic ... · Dan Lungu*, Aurel Stratan** & Radu Vacareanu* * Technical University of Civil Engineering of Bucharest, Romania **
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Characterization and modelling of
seismic action
Report of WG2: Earthquake resistance
Dan Lungu*, Aurel Stratan** & Radu Vacareanu*
* Technical University of Civil Engineering of Bucharest, Romania
** "Politehnica" University of Timisoara, Romania
COST C26: Urban Habitat Constructions under Catastrophic Events
Final Conference, 16-18 September 2010, Naples, Italy
State of the art
Ground motion produced at a
site is characterised by the
two orthogonal horizontal
components and the
vertical component
Ground motion representation
for structural design may be in
the form of:
– Time histories
– Power spectral density
– Response spectra (elastic or inelastic)
Ground motion modelling
Main characteristics of the ground motion time history:
– Peak ground acceleration (PGA), peak ground velocity (PGV) and
peak ground displacement (PGD);
– Motion duration;
– Frequency content.
PGA and PGV
– Very simple measures of severity of the ground shaking
– Random variables
– Prediction of the peak ground parameters at a site is the target of
the probabilistic seismic hazard analysis (PSHA)
Motion duration
– Time interval between two specified fractions of
the total cumulative energy of accelerogram
– It represents the time interval over which the
motion power is almost constant and near its maximum
E [a(t)] dttot
2
0
t d
Ground motion modelling
Frequency content - concept crucial for understanding
the structural damage potential of ground motion.
Frequency content can be described:
– Directly, by the power spectral density function (PSD), obtained
from stochastic modelling of the acceleration process;
– Indirectly, by the response spectra.
Stochastic measures of frequency content:
– The dimensionless indicators (Cartwright & Longuet - Higgins)
and q (Vanmarcke);
– The f10, f50 and f90 fractile frequencies of the total cumulative
power of PSD and the frequencies f1, f2 and f3 corresponding to
the highest 1, 2, 3 peaks of the PSD.
Deterministic measures of frequency content are the
control frequencies and corresponding control periods
TB, TC, TD.
Modelling of response spectra
EPA and EPV. Elastic response spectrum.
Effective peak acceleration (EPA)
and effective peak velocity (EPV)
characterize the intensity of a
ground motion by averaging the
effects of shaking on the
structures most exposed to that spectral content
The elastic response spectrum is given as smoothed
acceleration spectrum (for 5% damping) having a
specified probability to be exceeded; 0.5 median, 0.1, etc.
Seismic input motions must be
compatible with local soil condition,
intensity of shaking, seismic source
mechanism and hypocentral distance
0.1 0.5
2.5
smean of SAEPA
0.8 1.2
2.5
smean of SVEPV
Design spectrum
Acceleration-displacement response spectra
Design spectra:
– Behaviour factor q used to
reduce spectral accelerations,
accounting for inelastic
structural response (ductility,
redundancy and overstrength)
– Lower bound ag
The acceleration-
displacement response
spectra (ADRS)
– An alternative representation of
response spectra
– Periods are represented by a
series of radial lines extending
from the origin of the plot.
Bucharest'86 - 16 free-field motions
0
50
100
150
200
250
300
0 1 2 3 4 5 6 7 8 9
SD , cm
SA
, cm
/s2
Probabilistic seismic hazard assessment (PSHA)
A cornerstone position for the prediction of the strong
ground motion likely to occur at a particular site
The general PSHA is based on the following
methodology:
– Identification of independent sources of seismic activity and
determination of recurrence relationships;
– Fitting the attenuation relationship on a ground motion
parameter;
– Calculating the peak ground motion
parameter at the site with a specified
probability of non-exceedance during
structure lifetime;
– Delineation of isoseismal maps;
– Construction of uniform hazard
response spectra for design.
Vrancea seismic
subcrustal source
Hazard curve for Iasi City
1.E-04
1.E-03
1.E-02
1.E-01
50 150 250 350 450
PGA , cm/s2
PGA
Contribution to the research development Seismic motion leading to exceptional actions on structures
Seismic action is characterised by high uncertainty and
can be specified in probabilistic terms only
Mistakidis, E., Apostolska, R., Dubina, D., Graf, W.,