shaking table tests on the seismic performance of bridge
TRANSCRIPT
SHENG LIAN（Outline of Master Thesis, September 2020)
Department of Civil Engineering, The University of Tokyo, Japan
Shaking Table Tests on The Seismic Performance of Bridge Abutments with EPS And Soil Reinforcements in The Backfill
.
Geotechnical Engineering Laboratory, The University of Tokyo 2020
Introduction
Experimental models
Results & Discussion
Previous large earthquakes reported numerous damage cases on bridge abutmentssuch as residual lateral displacements of abutment body and relative settlements atbackfill-abutment wall interface. These damages disrupted normal traffic operationand hence posed a threat to post-earthquake rehabilitation and economic activities.
In light of it, this study focuses on different soil reinforcement methods in thebackfill in order to determine the optimal aseismic countermeasure layout that is botheffective and practically applicable on site. Tohoku earthquake
(2011)Kumamoto earthquake
(2016)
Previous researchExpanded Polystyrene (EPS), geogrids and soil nails are three main types of soilreinforcement methods adopted in the field. Previous research focused on thecombined use of these reinforcements for existing structures, but the effects ofdifferent geometries or material properties of reinforcements were not fully studied.This study hence investigated how EPS stiffness and nail length/diameter affect overallstructure seismic performance. Specifically, EPS of lower stiffness and through-out soilnails penetrating from the top of abutment body to subsoil layer were adopted. EPS of lower stiffness
Through-out type soil nails
LoadcellsScale： 1:20；Material: AluminumWeight : 48.7kg； Volume: 0.0194m3
Unit weight: 25.1kN/m3à simulate comparable seismic responses as prototype
Static load
GirderSupporting
frame Abutment
Rollers
Backfill
Surcharge
Soil foundation
Shaking table Shaking direction
Scale： 1:20one end: attached to abutment top via hingesthe other end： with rollers on a supporting frameàfacilitates girder sliding under seismic input.
Lead ingots
Rubber bands
0.39kPa
0
2
4
6
8
10
12
14
0 500 1000
Tilti
ng a
ngle
(deg
rees
)
Base acceleration (gal)
Through-out
Through-out + softer EPS
No countermeasuresShortened
Through-out + ordinary EPS1. Softer EPS, more
suppressed tilting
2. Shortened nail not adequate
00.20.40.60.81
1.21.41.61.8
0 500 1000
Net s
eism
ic so
il fo
rce
(kN/
m)
Base acceleration (gal)
Shortened
Through-out + softer EPS
No countermeasures
Through-out + ordinary
EPS
1. Addition of EPS, profound reductionin soil force
2. Softer EPS, further attenuation & more gradualincrease
Through-out
020406080100120140160180
0 500 1000 1500
Settl
emen
t (m
m)
Base acceleration (gal)
Through-out
Through-out + softer EPS
Through-out + ordinary EPS
1. Through-out nail alone not enough in inhibiting settlement
No countermeasures
Shortened3. Addition of EPS , improve settlement (EPS uplifting)
2. No further reduction despite softer EPS
No reinforcement
Through-out nail
Shortened through-out nail
Through-out + softer EPS
Through-out + ordinary EPS
Experimental cases5 out of the 12 cases were selectedfor parametric study purpose. Seismicperformance of the abutment modelwas evaluated against parametersshown in the figure circled.
Conclusions
Merits:✓ consistent and continuous tensile force (nail)✓ better attenuation of seismic soil force (softer EPS)✓ practical applicability (shallow excavation)
Proposed
Through-out + softer EPS
① To confirm benefit of through-out type nails
② To verify length effect
③ To investigate benefit of EPS backfill
④ To check stiffness effect of different EPS
Tilting and lateral displacement ↓
- Inadequate if shortened /- Deep nail penetration needed
- Relative settlement ↓ (uplift)- Soil force & overturning moment ↓
- Soil force & moment further↓ (if softer)- Settlement condition almost unchanged