Krista Morris Wakota Bridge Monitoring and Analysis

Wakota Bridge Monitoring and Analysis
Krista Morris
Wakota Bridge Monitoring and Analysis
Introduction
• Project overview
• Analysis to date
• Future investigation
Krista Morris
Wakota Bridge Monitoring and Analysis
Objectives
•Gain a better understanding of the changes in
member forces in twin-walled fixed bridge piers
due to thermal loading, through the modeling and
instrumentation of the Wakota Bridge
•Evaluate AASHTO design specifications regarding
thermal loading
•Verify common design procedures for
determining the stiffness of the piers
Krista Morris
Wakota Bridge Monitoring and Analysis
Bridge background
• South St. Paul, MN
• Across the Mississippi
River
– 2 bridges, 5 lanes each
– 4 spans, 4 piers
• Post-tensioned,
segmental construction
– Cast-in-place, cantilever
construction
Krista Morris
Wakota Bridge Monitoring and Analysis
Bridge Background
Krista Morris
Wakota Bridge Monitoring and Analysis
Project Overview
• Previous modeling work
– Comparing common design methods
– Differences between Procedures A and B of
AASHTO thermal design in Minnesota
– Models developed will be calibrated using
field data
Krista Morris
Wakota Bridge Monitoring and Analysis
Instrumentation
• Vibrating wire
strain gages in
both
superstructure
and piers
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• Linear string
potentiometers in
each abutment
Wakota Bridge Monitoring and Analysis
Instrumentation: Piers
•
Top Instrumented section
Elev. 223.16 ft.
(225.1 ft for Pier 4)
•
•
Bottom Instrumented
section Elev. 214.00 ft.
Krista Morris
Instrumented at
two elevations
(top and bottom
of pier wall)
Total of 28 gages
in Pier 2
Total of 16 gages
in Pier 4
Wakota Bridge Monitoring and Analysis
Instrumentation: Piers
• Oriented vertically to capture axial force
• Paired along widths of pier walls to capture bending in
both directions
Krista Morris
Wakota Bridge Monitoring and Analysis
Instrumentation: Superstructure
String Pot
Section P4-6D
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Section P2-4U
Wakota Bridge Monitoring and Analysis
Instrumentation: Superstructure
= VW Gage
1000
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• Spans 3 and 4
instrumented with 40
gages to determine
“locked in forces” due to
temperature changes
• Oriented horizontally to
capture axial forces
• Linear string
potentiometer at each
abutment to measure
overall expansion and
contraction
Wakota Bridge Monitoring and Analysis
Data: Strain change
Strain vs. Time
Gage 2TDR1, Pier 2
100
50
0
-5011/18
-100
-150
-200
-250
-300
-350
-400
1/7
2/26
4/17
500
6/6
7/26
9/14
Date
Strain (microstrain)
Strain (microstrain)
Strain vs. Time
Gage 2TUR1, Pier 2
400
300
200
100
0
11/18
-100
1/7
100
80
60
40
20
0
11/18
1/7
2/26
4/17
Date
Krista Morris
6/6
4/17
Date
6/6
7/26
9/14
Temperature vs. Time
Gage 2TDR1, Pier 2
7/26
9/14
Temperature (degrees F)
Temperature (degrees F)
Temperature vs. Time
Gage 2TUR1, Pier 2
2/26
100
80
60
40
20
0
11/18
1/7
2/26
4/17
Date
6/6
7/26
9/14
Wakota Bridge Monitoring and Analysis
Data: Strain change
100
50
0
-50 0
-100
-150
-200
-250
-300
-350
-400
Strain vs. Temperature
Gage 2TDR1, Pier 2
500
20
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40
60
Temperature (degrees F)
80
100
Strain (microstrain)
Strain (microstrain)
Strain vs. Temperature
Gage 2TUR1, Pier 2
400
300
200
100
0
-100
0
20
40
60
Temperature (degrees F)
80
100
Wakota Bridge Monitoring and Analysis
Data
Daily temperature and strain fluctuation
Strain at 4:00 PM
Top of Pier 4
3750
3350
3150
Up - Left
2950
30
25
20
Up - Left
15
Up - Right
10
Down - Left
5
Down - Right
0
1/7 1/12 1/17 1/22 1/27 2/1
Air Temperature, 1/10 - 2/9
Down - Left
2550
Down - Right
2350
2150
1/9 1/13 1/17 1/21 1/25 1/29 2/2
Date
Krista Morris
2/6 2/10 2/14
2/6 2/11 2/16
Date
Up - Right
2750
Temperature (degrees F)
Strain (microstrain)
3550
Temperature (degrees F)
Temperature at 4:00 PM
Top of Pier 4
30
20
10
0
1/9
-10
1/19
1/29
Date
2/8
Wakota Bridge Monitoring and Analysis
Cross-section Modeling
10
00
z
10
00
Krista Morris
Wakota Bridge Monitoring and Analysis
Analysis
• Linear interpolation of values at gages
to find stress distribution along
sections
– Integrated across area of each subdivision
area to find forces, sum of forces from
each
Krista Morris
Wakota Bridge Monitoring and Analysis
Results
– Through June 14
– 84 degree F
temperature
range
600
500
Force (kips)
• Force at Pier 2
cross-sections
Avg. Temperature vs. Axial force
at 732.15 ft
400
300
200
100
0
-100 0
20
40
60
Temperature (degrees F)
80
100
Avg. Temperature vs. Axial Forces
at 702.1 ft
800
Force (kips)
600
400
200
0
-200
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0
20
40
60
Temperature (degrees F)
80
100
Wakota Bridge Monitoring and Analysis
Results
– Through June 14
– 82 degree F
temperature
range
500
400
Force (kips)
• Force at Pier 4
cross-sections
Avg. Temperature vs. Axial load
at 738.5 ft
300
200
100
0
-100 0
10
-200
20
30
40
50
60
70
60
70
Temperature (degrees F)
Avg. Temperature vs. Axial load
at 702.1 ft
40
Force (kips)
30
20
10
0
-10 0
-20
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10
20
30
40
50
Temperature (degrees F)
Wakota Bridge Monitoring and Analysis
Conclusions
• Significant differences in axial forces
calculated for AASHTO Procedures A
and B
– Significant changes in temperatures
• Analyses can be designed to simulate
changes in stiffness of piers
• Direct change in strain and internal
forces due to temperature
Krista Morris
Wakota Bridge Monitoring and Analysis
Future work
• Analysis of axial forces and moments
on piers will continue
– More complex cross-sections
– Additional six months of field data
– Calibration of models using field data
– Additional analytical studies
Krista Morris
Wakota Bridge Monitoring and Analysis
Thank you!
Questions?
Krista Morris