Post on 06-Feb-2018
Aristotle University Thessaloniki, Department of Civil Engineering, Structural Division
Seismic assessment of bridges accounting for Seismic assessment of bridges accounting for nonnon--linear material and soil response linear material and soil response
and varying boundary conditions and varying boundary conditions
A.J. Kappos, Professor, Aristotle University ThessalonikiA. Sextos, Lecturer, Aristotle University Thessaloniki
Coupled site and soil-structure interaction effects with application to
seismic risk mitigationNATO ESP.EAP.ARW 983188
Aristotle University Thessaloniki, Department of Civil Engineering, Structural Division
Problem statementProblem statement
Nonlinear static (pushover) analysisNonlinear static (pushover) analysis has become a popular tool for the seismic has become a popular tool for the seismic assessment of assessment of buildings, later also of bridgesbuildings, later also of bridges
Nonlinearity is associated associated (in most studies) with(in most studies) with material behaviourmaterial behaviour→→ yieldingyielding of reinforced concreteof reinforced concrete (R/C) sections
? additionaladditional material nonmaterial non--linearity mechanismslinearity mechanisms (in foundation and/or backfill soil) ? nonnon--linearitylinearity in in boundary conditionsboundary conditions (activation of control components such as
bearings, ‘stoppers’, or seismic joints)
The goalgoal of this paper, is to focus on a real bridge structure in order to assess the assess the importance of considering over neglecting importance of considering over neglecting various nonvarious non--linearity sources, thelinearity sources, the actual actual
stiffnessstiffness of the abutments and embankments, and the foundation subsystems.
Aristotle University Thessaloniki, Department of Civil Engineering, Structural Division
Overcrossings (overpasses) Overcrossings (overpasses) in Egnatia Motorwayin Egnatia Motorway
OverpassesOverpasses UnderpassesUnderpasses
Aristotle University Thessaloniki, Department of Civil Engineering, Structural Division
Overview of the bridge studiedOverview of the bridge studied
monolithic pier-to-deck connectiondeck is connected through two pot bearings that permit
sliding along the two principal bridge axes longitudinal 12cm joint separates deck from backwalltransverse displacement blocked at the abutments
19.0m 32.0m 19.0m
60.0m
A1 P1 P2 A2
Aristotle University Thessaloniki, Department of Civil Engineering, Structural Division
Overview of the bridge studiedOverview of the bridge studied
PiersPiers P1P1, , P2P2
Pile capPile cap
2x2 Pile 2x2 Pile GroupGroup
DeckDeck
Pier top flexural reinforcementPier top flexural reinforcement::136.4136.4cmcm22
UncrackedUncracked section propertiessection propertiesconsidered in designconsidered in design
Aristotle University Thessaloniki, Department of Civil Engineering, Structural Division
Overview of the bridge studiedOverview of the bridge studied
0
0.4
0.8
1.2
1.6
2
2.4
2.8
3.2
0.00 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 1.80 2.00 2.20 2.40 2.60 2.80 3.00
Rd
(m/s
ec2 )
Κατακόρυφη Συνιστώσα Rd,z
Οριζόντια Συνιστώσα Rd,y
Οριζόντια Συνιστώσα Rd,x
Design spectrumDesign spectrum
Time (sec)
Sa
(m/s
ec2 )
Horizontal component x-x (qx = 2.5)
Horizontal component y-y (qy = 3.5)
Vertical component z-z (qz = 1.0)
Soil category CPGA = 0.16g (Zone I)
‘Non-seismic’ design according to German Norms DIN 1055, 1045, 1072, 1075, 1054, 4227, 4085, 4014
Seismic Design according to Greek Seismic Code EAK2000 and Greek standards E39/99 for seismic design of bridges
Aristotle University Thessaloniki, Department of Civil Engineering, Structural Division
Numerical Analysis: static soil stiffness Numerical Analysis: static soil stiffness
MultiMulti--linear plinear p--y,y,ppuu(z) from API (z) from API
(1991)(1991)
yy5050 = 0.05= 0.05yyuu = 15 = 15 ×× yy5050CCuu = = 3030 -- 200 200 ΚΚPaPaγγ = 1= 177 –– 22 kN/m22 kN/m33
(Model 4)
Aristotle University Thessaloniki, Department of Civil Engineering, Structural Division
Numerical Analysis: Numerical Analysis: stiffness assumptionsstiffness assumptions
P-y29% EI4
P-y29% EI3
Fixed37% EI2
Fixed100% EI1
Foundation modellingPier EIeff
FE Model
ID#
4 alternative models developed 4 alternative models developed
for the bridge for the bridge
additional, separate models for the abutment and for additional, separate models for the abutment and for the abutmentthe abutment--embankmentembankment--foundation soil systemfoundation soil system
Aristotle University Thessaloniki, Department of Civil Engineering, Structural Division
Numerical Analysis: static soil stiffness Numerical Analysis: static soil stiffness
80.0% y-yTranslational (transverse)1.090.5054
80.1% y-yTranslational (transverse)1.080.5013
81.7% y-yTranslational (transverse)1.070.4962
81.7% y-yTranslational (transverse)1.000.4631
modal participation
factor2nd Mode shapePeriod of 2nd
mode (sec)
FE Model
ID#
98.8% x-xTranslational (longitudinal)1.971.0124
98.9% x-xTranslational (longitudinal)1.870.9593
99.7% x-xTranslational (longitudinal)1.380.708 2
98.9% x-xTranslational (longitudinal)1.000.5121
modal participation
factorFundamental Mode shapeRatio
Ti/T1
Fundamental Period T (sec)
FE Model
ID#
Dynamic characteristics of the 4 Dynamic characteristics of the 4 alternative FE modelsalternative FE models
??
Mode 1
Longitudinal
Mode 2
Transverse→ transverse stiffness controlled by blocked displacement at the abutments!
Aristotle University Thessaloniki, Department of Civil Engineering, Structural Division
Finite Element Analysis Finite Element Analysis Separate pushover Separate pushover analysis for the abutment analysis for the abutment in both directionsin both directions
Soil yieldingSoil yieldingPile flexural failurePile flexural failure
PilePile head shear failurehead shear failure
Backfill soil yielding (in Backfill soil yielding (in transverse direction)transverse direction)
Sliding joint (in the Sliding joint (in the
longitudinal direction)longitudinal direction)
pile shear capacity/demand
Aristotle University Thessaloniki, Department of Civil Engineering, Structural Division
Detailed modelling of the backfill-embankment-foundation soil system
ABAQUS Tetrahedral solid elements (C3D4),
different E and φ for each soil type
Aristotle University Thessaloniki, Department of Civil Engineering, Structural Division
Detailed modelling of the backfill-embankment-foundation soil system
Longitudinal direction
Longitudinal direction
0
2000
4000
6000
8000
10000
12000
14000
0 0.02 0.04 0.06 0.08 0.1Displacement (m)
Forc
e (k
N)
Transverse direction
0
2000
4000
6000
8000
10000
12000
14000
0 0.05 0.1 0.15 0.2
Displacement (m)
Transverse direction
ABAQUS Tetrahedral solid elements (C3D4), different E and φ for
each soil type
→→ reasonable match only in the reasonable match only in the ttransverse directionransverse direction
Aristotle University Thessaloniki, Department of Civil Engineering, Structural Division
Pushover curve and seismic assessment of the overall system Pushover curve and seismic assessment of the overall system (longitudinal direction)(longitudinal direction)
Pier yieldingPier yieldingJoint closure at δ=12cm
Backfill yielding Ultimate state due to unrecoverable abutment damage (δ=22cm)4 plastic hinges exhausting 35-49% of the available plastic rotation
Soil yielding
stiffsofter soil
2E2EEEEE 2E2E
Aristotle University Thessaloniki, Department of Civil Engineering, Structural Division
Abutment pile head shear failure
Stiffness mainly provided by middle piers Collapse
Pushover curve and seismic assessment of the overall system Pushover curve and seismic assessment of the overall system (transverse direction)(transverse direction)
Soil y
ieldin
gPier yi
elding
Stiffness provided mainly by middle piers
2E2EEE EE 2E2E
??
The abutment piles fail in shear at their head, the The abutment piles fail in shear at their head, the abutment abutment becomes unstable at its base,becomes unstable at its base, and the and the high ductility of the piers is never high ductility of the piers is never mobilisedmobilised
No joints existNo joints exist
Aristotle University Thessaloniki, Department of Civil Engineering, Structural Division
Conclusions
additional material non-linearity mechanisms(of the foundation and/or backfill soil)
BC non-linearity mechanisms (activation of control components such as ‘stoppers’ or seismic joints)
→ must be considered in analysis and design
The problem is even more complex…
Definition of system ductility
Ratcheting effect
Dynamic bridge abutment-embankment interaction (see presentation by Sextos…)