768
Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
To assess the consequences of allowing the soil-structure
interface to undergo some plastic deformation, a comparative
calculation with the global model is made, with the following
changes:
- gapping elements deactivated
- all non-linear springs linearised with the initial stiffness
- horizontal material damping incorporated by dashpot
Thus, the soil-structure interface will behave fully linearly.
The impact of this for the bridge structure can be assessed by
observing the extreme moment envelope, which is plotted for
the north tower in Figure 17.
Figure 15. Bridge longitudinal displacements, NCE series 1, s-y- corner
point, north tower.
Figure 16. S-axial stress-displacement curves, NCE series 1, s-y- corner
point, north tower.
Figure 17. Envelopes of extreme moment in the north tower, NCE
event, average of the seven series.
It should be noted that all design effects were evaluated as
the average for the seven time histories, cf. EN 1998-1, clause
4.3.3.4.3(3). It can be observed that the linear soil interface in
general provides more onerous moments in the north tower, on
average 13% more than the reference interface which allows for
some plastic deformation.
6 CONCLUSIONS
An advanced, non-linear model of the soil-structure interaction
for the tower foundations has been established. The model
includes distributed springs for three-dimensional dynamic
analyses. Compared to single-point linear supports, this has the
following benefits:
- Possibility to calculate distributed stresses under the
foundation directly during time-history analyses
- Direct modelling of the horizontal shear capacity in the
soil-structure interface, dependent on the interface
friction coefficient and on the time-varying vertical
force,
F
,
< ⋅
.
- Thus, proper modelling of foundation gapping is also
achieved, and the overall moment-rotation curve is
directly made dependent on the vertical force.
-
The shear stresses in the interface does also incorporate
shear from torsional moment (
).
-
Separate indication of displacements in the gravel
bed/foundation interface and in the subsoil.
-
Possibility to calibrate with pseudo-static continuum
finite element models with good accuracy; also for
varying vertical force, which normally is difficult.
Thus, by the detailed modelling of dynamic behaviour, it is
possible to implement in a practical manner a displacement-
based verification for large earthquakes, where seismic energy
is dissipated by foundation rocking with gapping, some
controlled and limited sliding and permanent horizontal
displacements within the subsoil.
7 ACKNOWLEDGEMENTS
The authors gratefully acknowledge the permission by Owner
NÖMAYG / Nurol-Özaltin-Makyol-Astaldi-Yüksel-Göçay and
Contractor IHI Infrastructure Systems CO., Ltd. to publish this
paper.
8 REFERENCES
Fédération internationale du béton (FIB) 2001.
Seismic bridge design
and retrofit - structural solutions. State-of-art report.
Bulletin 39.
Sprint-Digital-Druck, Stuttgart.
Gazetas G. 1991. Foundation vibrations, Chapter 15 in H. Y. Fang
(Ed.):
Foundation Engineering Handbook.
Van Nostrand Reinhold,
New York.
Kramer S. L. 1996.
Geotechnical earthquake engineering
. Prentice-
Hall, New Jersey.
Law H.K. & Lam I.P. 2001. Application of periodic boundary for large
pile group.
Journal of Geotechnical and Geoenvironmental
Engineering
127 (10), 889-892.
Lam I.P., Law H.K. and Martin G.R. 2007.
Bridge Foundations:
Modeling Large Pile Groups and Caissons for Seismic Design
.
Technical Report MCEER-07-0018, 12/1/2007. U. S. Department
of transportation, Federal Highway Administration.
Sørensen K.A., Jakobsen P.F. and Andersen G.B. 1990. IBDAS, an
integrated bridge design and analysis system.
3rd Int. Conf. on
Short and Medium Span Bridges
, 105-116, Toronto.
Yang D., Dobry R. and Peck, R.B. 2001. Foundation-soil-inclusion
interaction modeling for Rion-Antirion Bridge seismic analysis.
4th
Int. Conf. on Recent Advances in Geotechnical Earthquake
Engineering and Soil Dynamics
, San Diego.
th tower by
h the push-
Figure 14. Force vs. relative displacement between foundation and soil
in the bridge longitudinal direction. NCE seismic time histories, north
tower.
The difference in the maximum value of the shear stress in
the soil and gravel springs is due to the radiation dashpot in
parallel with the horizontal soil spring, cf. Figure 5.
5.4
Impact of non-linear effects
To assess the consequ nc s of allowing the soil-structure
interf ce to underg om plastic deformation, a c mpa ative
calculation with the global model is made, with the following
ch nges:
- gapping elements deactivated
- all non-lin ar springs linearised with the initial stiffness
- horiz tal m terial damping ncorpora ed by d shpot
Thus, the soil-structure interface will behave fully linearly.
The impac of this for the bridge structure can be assessed by
obs rving the extreme moment envelope, which is plotted for
the north tower in Figure 17.
Figure 15. Bridge longitudinal displacements, NCE series 1, s-y- corner
point, north tower.
Figure 16. S-axial stress-displacement curves, NCE series 1, s-y- corner
point, north tower.
Figure 17. Envelopes of extreme moment in the north tower, NCE
event, average of the seven series.
It should be noted that all design effects were evaluated as
the average for the s ven time histories, cf. EN 1998-1, clause
4.3.3.4.3(3). It can be observed tha th linear soil interfa e in
general provides more onerous moments in the n rth tower, on
av rage 13% more than the eference interface which all s for
some plastic deformatio .
6 CONCLUSIONS
An advanced, non-linear model of the soil-structure interaction
for the tow r foundations has been e tablished. The model
includes distributed spri gs for three-dimensional dynamic
analyses. Compared to ingle-point linear supports, this has the
following benefits:
- Possibility to calculate distributed stresses under the
foundat on directly d ring time-history analy es
- Direct m dell ng of the horizontal hear c pacity in the
soil-structure
terface, dependent on the interface
friction coefficient and on the time-varying vertic l
fo ce,
F
,
< ⋅
.
- Thus, proper modelling of foundation gapping is also
achieved, and the overall momen -rotation curve i
directly made ependent on the vertical f rce.
-
The shear stress s i the interface does also incorporate
shear from to sional mome t (
).
-
Separate indication of displacements in the gravel
bed/foundation in erface an in th subsoil.
-
Possibility to calibrate with pseudo-static continuum
finite element models with good accuracy; also for
varying v rtical force, which normally is difficult.
Thus, by the detailed modelling of dynamic behaviour, it is
possible to implement in a practical man er a displacement-
based v rification for large earthquakes, where seismic energy
is dissipated by
undation rocking wit gapping, some
controlled and limited sl ding and permanent horizontal
displacements within th subsoil.
7 ACKNOWLEDGEMENTS
The authors gratefully acknowledge the permission by Owner
NÖMAYG / Nurol-Özaltin-Makyol-Astaldi-Yüksel-Göçay a d
Contractor IHI Infrastructure Systems CO., Ltd. to publish this
paper.
8 REFERENCES
Fédération internationale du béton (FIB) 2001.
Seismic bridge design
and retrofit - structural solutions. State-of-art report.
Bulletin 39.
Sprint-Digital-Druck, Stuttgart.
Gazetas G. 1991. Foundation vibrations, Chapter 15 in H. Y. Fang
(Ed.):
Foundation Engineering Handbook.
Van Nostrand Reinhold,
New York.
Kramer S. L. 1996.
Geotechnical earthquake engineering
. Prentice-
Hall, New Jersey.
Law .K. & Lam I.P. 2001. Application of periodic boundary for large
pile group.
Journal of Geotechnical and Geoenvironmental
Engineering
127 (10), 889-892.
Lam I.P., Law H.K. and Martin G.R. 2007.
Bridge Foundations:
Modeling Large Pile Groups and Caissons for Seismic Desig
.
Technical Report MCEER-07-0018, 12/1/2007. U. S. Department
of transportation, Federal Highway Administration.
Sørensen K.A., Jakobsen P.F. and Andersen G.B. 1990. IBDAS, an
integrated bridge design and analysis system.
3rd Int. Conf. on
Short and Medium Span Bridges
, 105-116, Toronto.
Yang D., Dobry R. and Peck, R.B. 2001. Foundation-soil-inclusion
interaction modeling for Rion-Antirion Bridge seismic analysis.
4th
Int. Conf. on Recent Advances in Geotechnical Earthquake
Engineering and Soil Dynamics
, San Diego.
