Cross-Facility Validation of Dynamic Centrifuge Testing - SERIES
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Cross-Facility Validation of Dynamic Centrifuge Testing Ulas Cilingir, Stuart Haigh, Charles Heron, UCAM Gopal Madabhushi, Jean-Louis Chazelas, Sandra Escoffier
LCPC
Facilities
UCAM
LCPC
Test Programme
• To date, LCPC have carried out 15 tests and Cambridge have carried out 6.
Bearing Pressure
55% Relative Density
No structure
50 kPa
100 kPa
UCAM
UCAM
UCAM
LCPC 80%
UCAM LCPC
LCPC UCAM
300 kPa
LCPC
UCAM LCPC
LCPC
Structural Properties
• Initial structures have composed lumped masses on a flexible web with base and top weights changed to alter bearing capacity. All the buildings have been tuned to a fixedbase natural frequency of 50Hz. Bearing Pressure (kPa)
50
100
300
Base Width (m)
4
4
4
Superstructure-Foundation Mass Ratio
1.3
0.9
2.6
Fixed Base Damping (%)
0.5
0.8
Centre of Gravity (mm from base)
58
52
81
Bearing Capacity
• Testing at LCPC has investigated the static bearing capacity of the structures.
So construction settlements will range from 5 to 60mm for the modelled structures
Settlements during earthquakes
• UCAM shows a clear trend of decreased earthquakeinduced settlements, both absolute and relative to the soil with increasing relative density.
Settlements during earthquakes
• UCAM shows a clear trend of increased earthquake-induced settlements relative to the soil with increasing bearing pressure. • For a 0.3g PGA shake of 25s duration, this gave settlements on dense soil of: • 20mm for 100 kPa structure • LCPC 30mm • 15mm for 50 kPa structure • These are approximately twice the settlements during construction
Input Earthquakes
Prototype Acceleration (g)
• Because of the limitations of the current UCAM mechanical earthquake actuator, the earthquakes which can be compared fall into 2 categories. • “sinusoidal” earthquakes 0.2 0 -0.2 0
0.1
0.2
0.3 Time (s)
Prototype Acceleration (g)
• “sine-sweep” earthquakes
0.4
0.5
0.6
0.2 0 -0.2 0
0.2
0.4
0.6
0.8 Time (s)
1
1.2
1.4
1.6
Model Characterisation
• LCPC characterise models using an in-flight CPT Loose
0.95 1 1.05 1.1 1.15 1.2 1.25 Normalized ampl. of 1 Hz peak - g 100 kPa building on Hostun Sand 50 - 57% - 1 Hz
depth - m
-3.9
depth - m
- solid : under the footing
-3.9
1.05
1.1
1.15 1.2 1.25 1.3 1.35 Normalized ampl. of 1 Hz peak - g
amplification
1.4
1.45
1.5
depth - m
Amplification Profiles In Hostun sand ID = 57%
Depthdepth -m -m
50 kPa building on Hostun Sand 50 - 57% - 1 Hz
0.5
1 1.5 Normalized ampl. of 3 Hz peak - g 3 Hz
2
-11.7
2.5
300 kPa
-15.6 -19.5 0.6
0.8
1
1.2
1.4
1.6
1.8
2
Normalized ampl. of 3 Hz peak - g amplification
2.2
2.4
2.6
Acceleration (g)
Acceleration (g)
Acceleration (g)
Structural Response – UCAM Example
UCAM_CH01_EQ3 Model Scale ID = 55%
Model Base Input Acceleration 20 0 -20
0
0.2
0.4
0.6 0.8 1 1.2 Structure Base Acceleration
1.4
1.6
1.8
0
0.2
0.4
0.6
1.4
1.6
1.8
0
0.2
0.4
0.6
1.4
1.6
1.8
20 0 -20
0.8 1 1.2 Superstructure Acceleration
50 0 -50
0.8 1 Time (s)
1.2
Moment-Rotation Loops
• Inertial acceleration of superstructure provides force • Rotations calculated from double integral of vertical accelerometers • Can observe rotational stiffness variation with change in relative density • Area of loop representative of energy dissipation Acceleration, a
Resulting overturning force, F = ma Superstructure mass, m
Soil-Structure Interaction 50k P a S truc ture - M om ent-Rotation P lot 8 6
Moment (Nm)
4 2 0 -2 -4 -6
CH02 EQ2
UCA M Data -8 -0.8
-0.6
-0.4
-0.2 0 Rotation (degrees )
0.2
0.4
0.6
ID = 80%
Soil-Structure Interaction – 100kPa 10 8 6
Moment (Nm)
4 2 0 -2 -4 -6 UCAM Data LCPC Data
-8
UCAM_CH01_EQ1 LCPC_5_1_EQ7 -10 Model Scale -0.2 ID = 55%
• Qualitatively, the behaviour observed at UCAM and LCPC matches well. • Some numerical values differ slightly, highlighting differences between experimental facilities and techniques at different centers. • Further analysis of the data is required to clarify what is affecting the data and possibly to standardise some techniques for future testing.
Inter-structure interaction
No significant interaction effects are observed from the vertical base accelerations at frequencies below 300 Hz (6Hz prototype)
Inter-structure interaction
The lack of interaction becomes even more clear when examining the superstructure response
