35W and 10 Years of Change - UMN CCAPS · 1/30/2018 1 35W and 10 Years of Change Ed Lutgen| Bridge...
Transcript of 35W and 10 Years of Change - UMN CCAPS · 1/30/2018 1 35W and 10 Years of Change Ed Lutgen| Bridge...
1/30/2018
1
35W and 10 Years of ChangeEd Lutgen| Bridge Construction and Maintenance Engineer
Catherine French | Professor, University of MinnesotaKevin Western | State Bridge Engineer
Topics
2
• Bridge Info, Collapse, and Initial Response
• On Site Perspective
• National Transportation Safety Board (NTSB) Findings
• Changes in MnDOT and National Processes
• New Bridge – Selection, Design, and Construction
• U of M Research
• Chapter 152 Funding
• Final Thoughts
1/30/2018
3
I-35W Bridge
Universityof
Minnesota
DowntownMinneapolis
http://maps.google.com/1/30/2018
I‐35W Bridge
4
Bridge Background• Bridge Completed in 1967
• 1907 Feet Long
•3 span continuous truss
• Main span 456’
• 2 trusses
• 11 approach spans
• Continuous steel multi beam
• Continuous concrete slabs
• Average Daily Traffic (ADT) 141,000
• 4 lanes each direction
• Structurally Deficient – SR 50.0
• Annually Inspected – In depth Fracture Critical
• MnDOT 20 year plan called for Replacement 2020‐25July 1967
1/30/2018
1/30/2018
2
51/30/2018
Two Studies of Fatigue Potential
6
• 2001 University of Minnesota –Fatigue Evaluation of the Deck Truss of Bridge 9340
• 2007 – URS – Fatigue Evaluation and Redundancy Analysis
• Multi Girder Approach Spans Had Required Retrofits for Fatigue Cracks
1/30/2018
Previous Bridge Modifications
• 1977 Concrete overlay
• 1998 Railing repair, drainage system, minor deck repair
• 1999 Painting portion of truss spans
• 1999 Anti icing system
• 2001 Curb & slab repair
Average yearly MnDOT Maintenance Hours: 500
71/30/2018
Contract Maintenance Work at Time of Collapse
• Contract to replace concrete overlay, repair joints and lighting, and install guardrail
• Work completed:North bound – two inside lanesSouth bound – two outside lanes
• Scheduled completion date was September 30, 2007
• Cost ‐ $9 million
• Contractor employees and MnDOT inspectors on bridge at collapse
81/30/2018
1/30/2018
3
August 1, 2007: The Collapse
Collapse occurs at 6:05 p.m.Wednesday, August 1, 2007
9
Over 100 vehicles on the bridge at the time
13 fatalities140 injuries1/30/2018 10
North End – I 35W Bridge – South End• 1/30/2018
11North End• 1/30/2018 12
Pier 7 North End Main Span• 1/30/2018
1/30/2018
4
13Main Span
• 1/30/2018 14Pier 6 South End Main Span• 1/30/2018
15South Spans• 1/30/2018 161/30/2018
1/30/2018
5
Emergency Response
• 6:05 p.m.
• Numerous concurrent calls to State Patrol Dispatch (911) and from field employees to RTMC and Maintenance Dispatch
• Motorists on bridge, construction workers, citizens in area assist injured
• Emergency personnel from Twin Cities and Western Wisconsin respond
• 6:10 p.m.
• District Emergency Operations Center activated
• Immediate traffic control for ramp and freeway closures provided by FIRST units, maintenance units, and contractors in the vicinity
17
MnDOT’s Regional Transportation
Management Center (RTMC)
1/30/2018
Response the First 12 Hours
• 6:20 p.m. – State Emergency Operations Center
• Unified command center set up on collapse site. Authority in command changed as incident progressed:
• Minneapolis Fire Department in charge of rescue
• Hennepin County Sheriff in charge of recovery (MnDOT assisted with some demolition)
• MnDOT assumed command after recovery was completed
181/30/2018
First 12 Hours – (continued)
6:20 p.m.
• Started converting I‐35W temporary traffic control measures to longer term traffic control standards with barriers and signs
• 20 changeable message signs activated
• MnDOT Metro District provides maintenance staff and equipment for security efforts
• 800 megahertz communication system was critical for responders
191/30/2018
First 12 Hours – (continued)
• 7:00 p.m.• Over 150 employees activated, most just
returned without a call• MnDOT structural engineers called to site
• 10:00 p.m.• Governor and Mayor provide an update to
public. Number of victims unknown.• Rescue Operations Ended; Recovery
Begins• 11:00 p.m.
• Detour maps for morning rush posted on MnDOT web site
• Overnight• Expanded signing and barricades of closed
I‐35W • Converted T.H. 280 to a freeway
201/30/2018
1/30/2018
6
I‐35W Detour Map
211/30/2018
August 2, 2008
– Recovery operations continue– Engineers assess stability of wreckage for recovery personnel
–NTSB leads investigation–MnDOT contacts Wiss Janney Elstner (WJE) and TranSystems/Lichtenstein for investigation
– Engineering team begins to organize for rapid replacement
221/30/2018
Media Coverage August 2nd
– Governor conducts interviews throughout morning
– 2:00 pm Press Conference:Governor announces
• Emergency statewide bridge inspections beginning with underdeck trusses
• Forensic Investigation Team• Review of MnDOT Inspection
Program
23
NTSB Chairman Mark Rosenker
1/30/2018
Managing Media Requests
24
• Held Daily 2:00 pm Press Conference• Only means to manage volume of requests• Format was statement, update on specific issue,
open to questions• Length was held to a reasonable time – 30 to 45
minutes• When it ended, held questions till next day
• Governor and Commissioner directed MnDOT to be transparent
• Document requests were overwhelming• Website posting of plans, inspection reports,
bridge studies• Dedicated I‐35W Website includes all documents• Document Management System established to
gather and store all bridge information• Later removed inspectors names after harassing
phone calls to their homes1/30/2018
1/30/2018
7
Managing Media Requests (continued)
• Our Priority was local media requests
• Within 24 hours media began their own investigations and speculation.
• Our time was consumed correcting misinformation
• After 3 weeks ended face to face interviews and responded to written questions.
251/30/2018 26
U.S. Navy Dive Team
Recovery of Victims and Bridge Removal• Access to site controlled by police and fencing – 24/7
• Site protocol followed during recovery of victims
• Navy Divers from Norfolk, VA assist in recovery
1/30/2018
• Aug. 20 – Navy Divers recover 13th victim, site turned over to MnDOT
• Sept. 6 ‐ Navigation channel opened to commercial traffic
• Sept. 27 – Final steel removed from river
271/30/2018
Topics
1/30/2018 28
• My Experiences
• Inspection Changes
• Construction Changes
• Load Rating Changes
• Maintenance Changes
• Programming Changes
1/30/2018
8
My Experiences – August 1
1/30/2018 291/30/2018
My Experiences – August 1
1/30/2018 30
My Experiences – August 2
1/30/2018 31
My Experiences ‐ Visuals
1/30/2018 32
1/30/2018
9
My Experiences ‐ Documentation
1/30/2018 33
My Experiences – Bohemian Flats
1/30/2018 34
My Experiences ‐ Afton
1/30/2018 35
My Experiences – Final Report
1/30/2018 36
1/30/2018
10
My Experiences ‐ Pieces
1/30/2018 37
• 35W Steel Pieces
• Historical Society
• Victims
• First Responders
• Educational
• Recycling
My Experiences ‐ Universities
1/30/2018 38
The Cause ‐ U10W
1/30/2018 39
The Cause – U10W
1/30/2018 40
Compression diagonal
Tension diagonal
Stress
Yieldstress
0
Orange and red shading: exceeds yield stress
Allowable
1/30/2018
11
The Cause – U10W
Compressiondiagonal
Tensiondiagonal
1/30/2018 41
The Cause – U10W
1/30/2018 43
Vertical U10‐L10
Tension Diagonal U10‐L11
Top Chord U9‐U11
Compression Diagonal U10‐L9
The Cause – U10W
1/30/2018
Center of spanU10
44L9
Pier
1/30/2018
12
The Cause
U2 U4 U6 U8 U10 U12 U14
L1L3 L5
L7 L9L11 L13
U0
1/2” thick gusset plate (50 ksi) 10 of 29 gusset plates5/8” thick gusset plate (50 ksi) 4 of 29 gusset plates1” thick gusset plate (50 ksi) 13 of 29 gusset plates1 3/8” thick gusset plate (100 ksi) 2 of 29 gusset plates
1/30/2018 45
NTSB/WJE Theories Considered
• Corrosion damage• Fracture of a floor truss• Pre‐existing cracking or fatigue• Locked bearings and piers• Terrorism• Sinkhole south side of river• Railroad vibrations• Seismic movement• Approach creep• Material deficiencies• Fire truck loading (overload)• Scour undermining the footing• Thermal loads• Overloaded bridge (contractor and traffic)• Drilled shaft hinging• Settling or moving piers• U of MN coal tunnel 1/30/2018 46
Why Change
“Failure is a great teacher, and I think when you make mistakes and you recover from them and you treat them as valuable learning experiences, then you’ve got something to share.”
Steve Harvey, famous actor and author
1/30/2018 47
Failures Lead to Change
• 1967 – Silver Creek bridge in WV/OH collapse
• 1987 – Schoharie Creek in NY collapse
• 2007 – 35W bridge
1/30/2018 48
1/30/2018
13
Inspections – FHWA
Bridge Inspection Reference Manual (BIRM) 2006
• Gusset plate only briefly mentioned couple times
• “By contrast, a slightly deteriorated gusset plate at a panel point of a truss may not be critical.” page 4.4.4
1/30/2018 49
2006 BIRM
Inspections – FHWA
Bridge Inspection Reference Manual (BIRM) 2012
• Added Chapter 10.8.1 specifically for gusset plates.
• Over 30 pages of details, failure mechanisms, repairs, inspection techniques, conditions to look for and document.
1/30/2018 50
2012 BIRM
Inspections – Gusset Plate
• New Inspection Elements for Trusses
• Element 162: gusset plates
• Element 120:trusses
• Element 113: stringer
• Element 152: floorbeam
1/30/2018 51
Inspections – FHWA
23 FHWA Inspection Metrics
• Assesses compliance with NBIS at 23 CFR Part 650, subpart C
• Compliance levels
• Compliance
• Substantial compliance
• Conditional compliance
• Non‐compliance
1/30/2018 52
1/30/2018
14
• MN has 205 agencies with at least 1 bridge
• Agencies broken into classes based on number of eligible structures
Inspections – Bridge Office Audit
1/30/2018 53
Inspections – Bridge Office Audit
1/30/2018 54
• Constant improvement since 2012 implementation
• All metrics have shown similar improvements
Inspections – Bridge Office Audit
70%
75%
80%
85%
90%
95%
100%
2011 2012 2013 2014 2015 2016
Metric 6 Compliance
1/30/2018 55
Inspections – Section Loss
Pre 2007 inspection notes for gusset plate
• Up to 3/16” section loss on a ½” plate
• 3/16” / ½” = 38%
• Take entire critical cross section not localized damage
1/30/2018 56
1/30/2018
15
Inspections – Section Loss
Better Inspection Documentation
• BSIPM pages section loss guidance B.4.1.2
• UT and Phased array
1/30/2018 57
Inspections – Fracture Critical
• All FC inspections for state and local agencies performed by Bridge Office
• Best access equipment
• More NDT trained staff
• Consistent documentation
• Meet FHWA Metric 10 and 16
• Fracture critical bridges have an independent structural review every 2 years.
1/30/2018 58
Inspections – SIMS
SIMS – Structure Information Management System
• All inspection reports
• Pictures
• Migrated old Pontis data into SIMS
• Reports for inspections due
• Queries of data
• Program Administrator reviews
• Bridge maintenance module
1/30/2018 59
Construction – Specs
1/30/2018 60
Figure 16 NTSB Final ReportNTSB Factual Report
1/30/2018
16
Construction – Specs
1/30/2018 61
Specification 1513 Load Restrictions
• Material 65,000 lb per 1000 ft2
• Materials 25,000 lb per 100 ft2
• Truck 80,000 lb
• All truck, material 200,000 lb
1/30/2018 62
• Prior 2007
• No gussets analyzed
• Simple span trusses only
• Post 2007
• All trusses
• Structural gussets
Load Rating – Analysis
Truss and Gusset Plate Rating
• Blatnik
• Winona
• Osceola
• DeSoto
1/30/2018 63
Truss ProjectsTruss Projects
1/30/2018 64
Truss Projects
1/30/2018
17
Bolt Replacement
65
Maintenance ‐ Resources
Tipped Bearing
Debris Removal
In response to an identified condition.
Rail Repair
Approach panel foam jacking
Spall Repair
1/30/2018 66
Identify Maintenance Tasks from: • Inspection Reports • Assessments• Flushing• Date Last Performed• Condition of Elements
Maintenance – Work
1/30/2018
Maintenance ‐ Data Tracking and Reporting
67SIMS Maintenance Module
Oracle Business Intelligence
1/30/2018
Bridge Maintenance Training
68
Bridge Maintenance Training
• Bridge Maintenance Academy (BMA I – III)
• Welding
• Shotcrete
• High Angle Rescue
• Statewide annual worker conferences
1/30/2018
1/30/2018
18
Bridge Maintenance Training
69
Bridge Maintenance Training• Preventive Maintenance eLearning Modules
• Crack Sealing
• Gland Repair
• Flushing (in progress)
• Poured Joint Sealing (in progress)
• BMA I (in progress)
• http://www.dot.state.mn.us/bridge/training.html
• Bridge Maintenance Manual – soon to be on the MnDOTBridge Office website
1/30/2018
Bridge Planning ‐ BRIM
• BRIM Process:
• Ranking each bridge based on the probability and consequence of a service interruption (Bridge Planning Index).
• Identifying preservation and improvement needs.
• Conducting an expert review.
1/30/2018 70
Risk Assessment
• Work Type• Costs• Timeframe
District Review
35W Bridge Replacement
• Process for Contractor Selection
• Design, Construction and Innovation
• What Went Well and Challenges
• Health Monitoring (Cathy)
• Final Thoughts
711/30/2018
New Bridge is Needed Quickly
• 141,000 cars a day used the bridge
• One of the busiest bridges in Minnesota
• Serves major traffic areas of:
• U of M
• Downtown Minneapolis
• $400K a day estimated in road users costs
• MnDOT needs to demonstrate abilities and begin rebuilding public confidence
721/30/2018
1/30/2018
19
Planning for Replacement Begins Early Morning Hours of August 2
• Replacement team begins to form
• Discussion begins on delivery method
• Need quality, buildable replacement bridge plan
731/30/2018
New Bridge
• August 2nd• Design build best value procurement method
selected• August 3rd
• Core team identified• Three experienced design build project managers
on team• Bridge Office personnel
• Three bridge designers• Two construction engineers with bridge
experience• Empowered to be decision makers
741/30/2018
Design Build – Why?
75
• Considers quality and cost
• 7th design build best value project
• Past design build projects successful
• Geometric improvements desired
• Public input/communication and
visual quality important
• High level of national interest
• Utilize expertise of DB teams
• Allows construction to begin quickly
• First complex bridge with design build process
1/30/2018
Challenges of I‐35W Site
1/30/2018 76
• Demolition – when will it be completed
• 24/7 work will be necessary
• Hydraulic scour at site
• Work adjacent to lock and dam
• Substantial winter work required
1/30/2018
20
Procurement Process
• Issued Statement of Qualification on August 4
• Held daily confidential meeting with each proposing team
• Held public meetings, DBE and utility coordination meetings
• Addressed media and public questions
• Developed Request for Proposals in 3 weeks
• Responded to clarifications and issued addenda
1/30/2018 77
Established Procurement Timeline
• August 1 – Collapse occurs• August 4 – Issue Request for Qualifications• August 8 – Short listed teams• August 23 – Request For Proposals released• September 14 ‐ Technical proposals received• September 18
• Evaluation and Scoring Completed• Financial Proposals Received
• September 19 – Project Letting• September 20 – City of Minneapolis Grants
Municipal Consent• Project Award – Early October
1/30/2018 78
WHAT DID WE HEAR?“Slow Down; You are Moving Too Fast”
• A landmark bridge should be considered
• You don’t know why the previous bridge collapsed
• No ugly freeway‐style bridge
• Design bridge for a future light rail line
• Minnesota politics
1/30/2018 79
RFP Evaluation/Scoring Criteria
• Quality (50 percent)
• Quality control/quality assurance
• Safety
• Aesthetics/Visual Quality (20 percent)
• Visual enhancements to the structure
• Enhancements (15 percent)
• Public Outreach/Involvement (15 percent)
• Impacts to the public
• Approach to communication
1/30/2018 80
1/30/2018
21
Co‐Housing
• Important to establish a partnership relation
• All team members represented
• 24/7 work until design was way ahead of construction
• Scheduled and just‐in‐time meetings every day
• Prioritizing review tasks a continual challenge
1/30/2018 81
Oversight – Peer Review Team
• Parsons Transportation Group brought concrete box expertise to the team
• First test of our Peer Review process• Bridge Modeling – In parallel with EOR
• Established protocol for results comparisons
• Reviewed temporary works as well
• Same team (and members) provided field support• Great benefit in understanding what is important
• Unique staff with both experiences and background
1/30/2018 82
Bridge Description
•Four‐span bridge approximately 1225’ in length
•Cast‐in‐Place approach spans and Precast Segmental river span (120 segments)
•Variable depth superstructure 25’ to 11’
1/30/2018 83
Bridge Description• Two parallel bridges, each with two box girders
• Striped for 5 lanes each direction (10 total) with 13’ and 14’ shoulders (actual design loading considers for 7 lanes each direction)
• Future configuration of 4 lanes each direction plus light rail line or bus transit lane (lane drop for ramps)
1/30/2018 84
90’4”
11’
1/30/2018
22
100 Year Design Life
1/30/2018 85
•Include corrosion resistant design details with post‐tensioning
•Utilize high performance materials
•Provide multiple layers of protection of key structural elements
•Provide high quality construction
High Performance Concrete
• Performance specifications • Impacts on schedule and quality• Strength, permeability, chloride resistance
• Slag, fly ash, micro silica• Self consolidating concrete
• Primarily used for drilled shafts• Viscosity Modifying Admixtures (VMA)
• Helped prevent segregation in mix• Contractor and supplier innovation
• Developed mix designs• 45 mix designs• Silica Fume in Superstructure (approx. 4% by vol)• Used high range water reducing agents and
retarders• Multiple test pours and mock ups
1/30/2018 86
Public Input in Design
1/30/2018 87
• First time charrette process used in MN
• Pier shape
• Rail type
• Native stone abutments
More than 400 peoattended on July 5
Sidewalk Talk: More than 400 people attended on July 5, 20081/30/2018 88
1/30/2018
23
Safety Management
• Partnership• MnDOT• Flatiron‐Manson• Mn/OSHA
• Training of all workers assigned to project• Required escorts for visitors
• Large safety team
• Audits performed weekly
• Consistency from top to bottom
• MnDOT incentive
1/30/2018 89
Falsework System
1/30/2018 90
1/30/2018 91
Segment Casting and Delivery
• Contractor used 35W roadway
• Long line casting method
• First time in Minnesota
• 8 separate beds
• Travelling housing
• Side by side segments with closure pour
1/30/2018 92
1/30/2018
25
Transporting Segments1/30/2018 97 1/30/2018 98
Segment Erection1/30/2018 99 1/30/2018 100
1/30/2018
26
Aesthetic Lighting
1/30/2018 101
Open to Traffic September 19, 2008
1/30/2018 102
Completed in 11 Months – 3 Months Early
1/30/2018 103
Schedule and Budget
• Schedule• Contract completion date: December 24, 2008• Open to traffic: September 18, 2008• Substantial completion reached 90 days ahead of schedule
• Budget• Little cost growth (1% ±)• Incentives
• $18 million on time• $7 million No‐Excuse Bonus
1/30/2018 104
1/30/2018
27
35W ‐ What went well
• High performance concrete
• Mass concrete
• Self‐consolidating concrete
• Cold weather protection
• Involvement of Engineer of Record
• LED lighting
• Smart Bridge Technology
1/30/2018 105
35W – What Went Well
• Safety• Quality
• Engineer of Record
• Peer Review
• MnDOT staff
• Team Partnership
• Project Communication
1/30/2018 106
35W ‐ Challenges
• Anti‐icing system
• Definition of falsework requirements in project documents
• Long‐term creep for strength and fatigue design of modular joints
• Litigation ‐ but did validate selection process
1/30/2018 107
Health Monitoring
1/30/2018 108
1/30/2018
28
Department of Civil, Environmental, and Geo- Engineering13 February 2018 - Structural Seminar Series 109
I35W St. Anthony Falls BridgeSmart Bridge System
Catherine French, Carol Shield, Brock Hedegaard, Lauren Linderman, Ben Jilk Department of Civil, Environmental, and Geo‐ Engineering
University of Minnesota – Twin Cities
Department of Civil, Environmental, and Geo- Engineering13 February 2018 - Structural Seminar Series 110
Project Background – Planning/Construction Phase
Design‐build project awarded to Flatiron/Manson & FiggBridge Engineers featured a “Smart Bridge” system
• strain gages• thermistors• fiber optic sensors• linear potentiometers• accelerometers• corrosion sensors
• strain gages• thermistors• fiber optic sensors• linear potentiometers• accelerometers• corrosion sensors
UMN invited to participate in instrumentation plan discussions Proposed modifications/additions to address MnDOT issues of interest Gathered material samples
“Smart Bridge” consisted of
over 500 sensors
Department of Civil, Environmental, and Geo- Engineering13 February 2018 - Structural Seminar Series 112
Originally Proposed Instrumentation – Strain Gages
• Originally proposed Strain gages at midspans and supports
Behaviors of interest:• Curvatures
Department of Civil, Environmental, and Geo- Engineering13 February 2018 - Structural Seminar Series 113
195 vibrating wire (VW) strain gages (38 at midspan of Span 2)
Behaviors of interest:• Load distribution (curvatures)• Shear• Torsion
Installed Instrumentation: VW, thermistors
26 VWSG 38 VWSG
243 thermistors
• Thermal gradient
Transverse VW strain gageLongitudinal VW strain gage
6 in.
Instrumented Sections
1/30/2018
29
Department of Civil, Environmental, and Geo- Engineering13 February 2018 - Structural Seminar Series 114
Installed Instrumentation: Fiber optic sensors
12 Fiber optic sensors (12 ft. lengths)(6 pairs along SB Span 2)
Behaviors of interest:• Load distribution (average curvatures)
SB Span 2
Instrumented Sections
Department of Civil, Environmental, and Geo- Engineering13 February 2018 - Structural Seminar Series 115
• Originally proposed Accelerometers at midspans
Behaviors of interest:• Deflections
Originally Proposed Instrumentation – Accelerometers
Department of Civil, Environmental, and Geo- Engineering13 February 2018 - Structural Seminar Series 116
Installed Instrumentation: Accelerometers
Instrumented Sections
26 accelerometers(bottom of deck in each box)10 moveable along the length of SB Span 2
Behaviors of interest:• Frequencies• Mode shapes• Damping
Department of Civil, Environmental, and Geo- Engineering13 February 2018 - Structural Seminar Series 117
Installed Instrumentation: Linear Potentiometers
Instrumented Sections
12 Linear potentiometersin each box at each expansion joint(4 @ abutment 1, 8 @ pier 4)
Behaviors of interest:• Overall movement of bridge
1/30/2018
30
Department of Civil, Environmental, and Geo- Engineering13 February 2018 - Structural Seminar Series 118
Project originally intended to be review of previously performed and available technologies…
…became demonstration project of how available technologies play a role in foundation health monitoring
State of the Practice and Art forStructural Health Monitoring ofBridge SubstructuresPUBLICATION NO. FHWA-HRT-09-040 MAY 2014
led by Prof. Gray Mullins, U of S Florida, Tampa
Project Background – Planning/Construction Phase
FHWA Project on Drilled Shafts
Department of Civil, Environmental, and Geo- Engineering13 February 2018 - Structural Seminar Series 119
FHWA Project on Drilled Shafts
Photos from FHWA-HRT-09-040 May 2014Photos from FHWA-HRT-09-040 May 2014
Department of Civil, Environmental, and Geo- Engineering13 February 2018 - Structural Seminar Series 120
Instrumentation of Pier 2
Photos from FHWA-HRT-09-040 May 2014
Department of Civil, Environmental, and Geo- Engineering13 February 2018 - Structural Seminar Series 121
Summary of Bridge Instrumentation
LP Accelerometer VWSG
Fiber Optic
ThermistorsSB
NB
1/30/2018
31
Department of Civil, Environmental, and Geo- Engineering13 February 2018 - Structural Seminar Series 122
Sensor wiring completion after closure pour
Department of Civil, Environmental, and Geo- Engineering13 February 2018 - Structural Seminar Series 123
UMN Assisted with “Punch List”
Department of Civil, Environmental, and Geo- Engineering13 February 2018 - Structural Seminar Series 124
Lightning Strikes
https://i.pinimg.com/736x/17/2c/a4/172ca4cf5b7615b8d57a519b9d2ba2b4--photo-and-video-lightning.jpghttps://www.johnweeks.com/i35w/ms32.html
• Isolation transformers installed for surge protection • Metal‐oxide varistors (MOVs) installed to help against lightning strikes.
Department of Civil, Environmental, and Geo- Engineering13 February 2018 - Structural Seminar Series 125
Project Background – UMN’s role in monitoring
Objectives:• Investigate structural characteristics and changes over time• Evaluate design assumptions
(load distribution, deformations, response to environmental effects)• Evaluate effectiveness of the selected instrumentation• Develop long‐term monitoring system
1/30/2018
32
Department of Civil, Environmental, and Geo- Engineering13 February 2018 - Structural Seminar Series 126
Truck Tests• 8 trucks for a total load of 400 kips (1.8MN)
• 5 static load configurations at multiple locations
• Additional dynamic load configurations
Establish “baseline behavior” – Truck Tests
Establish a baseline
Department of Civil, Environmental, and Geo- Engineering13 February 2018 - Structural Seminar Series 127
Measured Strain Data for First Five Years
Daily changes: ~100 με(approximately 500 psi)
Total changes: ~400 με
*Plot represents mechanical strain plus creep and shrinkage strains
Challenges of Developing Monitoring System
8 fully loaded trucks (400 k) induce at most 50 µε
Department of Civil, Environmental, and Geo- Engineering13 February 2018 - Structural Seminar Series 128
• Data from multiple sources in multiple formats collected with multiple data acquisition systems at multiple rates (static and dynamic data)
• Most individual sensor data not meaningful Groups of sensors through section required to determine curvatures,
thermal gradients,… Groups of curvature readings required to determine load distribution “Baseline” data varies over course of day/season due to thermal and
time‐dependent effects (need to combine multiple types of data)
• VOLUME OF DATA…
Model Development• Historical Data• Finite Element Model
Data Processing
• What is “normal” behavior?• How might damage manifest itself in data?
Challenges of structural monitoring
Department of Civil, Environmental, and Geo- Engineering13 February 2018 - Structural Seminar Series 129
Finite Element Model (Overview)Constructed using ABAQUS to model Spans 1‐3 of SB Bridge
Pinned Pinned
ExpansionExpansion
BCs pinned @ Piers 2 and 3, rollers @ Abutments 1 and Pier 4
1/30/2018
33
Department of Civil, Environmental, and Geo- Engineering13 February 2018 - Structural Seminar Series 130
FEM Development and Calibration
Department of Civil, Environmental, and Geo- Engineering13 February 2018 - Structural Seminar Series 131
Calibration with measured results
Used measured data to validate models
Considered load effects (truck tests) and environmental effects (temperature/gradient)
Incorporated information from material tests Creep Shrinkage Coefficient of Thermal Expansion
Department of Civil, Environmental, and Geo- Engineering13 February 2018 - Structural Seminar Series 132
Bridge Instrumentation
Linear Potentiometers
12 linear potentiometers located at expansion joints
Behaviors of interest:• Overall movement of bridge due
to time dependent effects and temperature
Department of Civil, Environmental, and Geo- Engineering13 February 2018 - Structural Seminar Series 133
Challenges of Long-Term Monitoring
• Bridge behavior depends on many complex natural phenomena.
• Damage is not necessarily sudden and can be masked by normal, safe variations in behavior.
Ideal Case Typical Case
1/30/2018
34
Department of Civil, Environmental, and Geo- Engineering13 February 2018 - Structural Seminar Series 134
Monitoring and Modeling the I35W Bridge
GoalIntegrate monitoring data into maintenance and inspection strategies to extend bridge life.
ChallengesDamage is not necessarily sudden, whilechanging operating conditions cause large variations in behavior.
ApproachDevelop data normalization and anomaly detection techniques for extracting unexpected changes in the structural behavior.
Department of Civil, Environmental, and Geo- Engineering13 February 2018 - Structural Seminar Series 135
Thermal Gradients
Five largest measured thermal gradients compared to design thermal gradients from AASHTO LRFD (2010) and Priestley (1978).
Longitudinal stress at midspan estimated from measured mechanical strains compared to FEM stresses computed using AASHTO LRFD (2010) and Priestley (1978) gradients.
Parameters that affect behavior
Department of Civil, Environmental, and Geo- Engineering13 February 2018 - Structural Seminar Series 136
Uniform Temperature
Common design assumption that coefficient of thermal expansion (CTE) is constant.
Estimates of short blocks of measured data show that CTE varied by 20% with concrete temperature.
Believed to be caused by changes in internal relative humidity and surface tension of adsorbed water.
Parameters that affect behavior
Coefficient of thermal expansion measured from VWSGs in south span of the southbound bridge
Internal relative humidity in concrete dependent on temperature (Grasley and Lange, 2007)
Department of Civil, Environmental, and Geo- Engineering13 February 2018 - Structural Seminar Series 137
Hydration Concrete strength and modulus increase with time after casting.
Creep Continued deformation under constantly applied load.
Shrinkage Loss of water in concrete as cement cures and hardens.
Time‐dependent effects
Parameters that affect behavior
1/30/2018
35
Department of Civil, Environmental, and Geo- Engineering13 February 2018 - Structural Seminar Series 138
Post‐tensioning losses
Post‐tensioning stresses reduce with time, possibly leading to tension and cracking.
Increaseddeflections
Structure continues to deform, either leading to serviceability problems or (in extreme cases) safety issues.
Monitoring and predictions
If monitoring a structure, we will need to differentiate between normal time‐dependent behavior and slow degradation of structure.
Parameters that affect behavior
Time‐dependent effects – Why of concern?
Department of Civil, Environmental, and Geo- Engineering13 February 2018 - Structural Seminar Series 139
• Time‐dependent behavior of concrete widely recognized, but many different approaches exist:
– AASHTO LRFD (2010)– ACI‐209 (1982)– CEB‐FIP Model Code (1978, 1990)
– B3 (Bažant and Baweja, 1995)– GL2000 (Gardner and Lockman, 2001)
• Creep models are very different among the listed methods.
“Asymptotic” creep limits to some maximum value
“Logarithmic” creep approaches line in log‐time space
Parameters that affect behavior
Department of Civil, Environmental, and Geo- Engineering13 February 2018 - Structural Seminar Series 140
Creep and Shrinkage
Creep and Elastic StrainH = 64%V/S = 8 in.f’c = 7450 psiσ = 1900 psi @ 10 days
Logarithmic Models:– B3 (Bažant and Baweja, 1995)
– GL2000 (Gardner and Lockman, 2001)
Asymptotic Models:– AASHTO LRFD (2010)– ACI‐209 (1982)– CEB/FIP Model Code (1978, 1990)
When compared to NU‐ITI creep and shrinkage database, all models have large coefficients of variation, ranging from 25% to 35%.
Parameters that affect behavior
Department of Civil, Environmental, and Geo- Engineering13 February 2018 - Structural Seminar Series 141
Data Normalization
Need to predict the expected behavior due to temperature and time‐dependent phenomena in order to identify anomalous readings.
Challenges• Time‐dependent behavior uncertain• Temperature dependence dominates data
Short‐term (e.g., bearing lock‐up) Long‐term (e.g., slow degradation)
1/30/2018
36
Department of Civil, Environmental, and Geo- Engineering13 February 2018 - Structural Seminar Series 142
Data Normalization
• Use linear regression on measured data:
j
jjx
ttHtDI
zTdA
A
dAT
A
TdAy ,653
2
21
Uniform Temperature
Thermal Gradient
Time‐Dependent
Error and Data Jumps
• Given: Measured data y, temperature T• Unknown: Coefficients αi, time‐dependent D(t)• Technique: Assume time‐dependent behavior,
compute coefficients, and remove temperature‐dependent behavior.
Department of Civil, Environmental, and Geo- Engineering13 February 2018 - Structural Seminar Series 143
Data Normalization
LP Deflection
Extract time‐dependent
Bridge TemperatureLP Deflection
Bridge Temperature
The rate of creep and shrinkage of concrete depend on the bridge temperature.
Longitudinal deflections are measured by LPs at the expansion joints.
Department of Civil, Environmental, and Geo- Engineering13 February 2018 - Structural Seminar Series 144
Node 3
Northbound Span 1
Total LP
Time‐dependent deflection Temperature‐dependent deflection
Data Normalization
Department of Civil, Environmental, and Geo- Engineering13 February 2018 - Structural Seminar Series 145
Data Normalization
Transform the time‐scale using the Arrhenius equation:
Converts readings with temperature history T(t′) to an equivalent adjusted age assuming constant temperature T0.
0
0
1 1'
0 'QtR T T t
adjt
t t e dt
Bridge TemperatureLP Deflection
Normalized time‐dependent behavior follows line in log‐time.
Transform time‐scale
1/30/2018
37
Department of Civil, Environmental, and Geo- Engineering13 February 2018 - Structural Seminar Series 146
To compare measured deflections with time‐dependent predictions, the time can be adjusted using the Arrhenius equation:
Warmer temperatures “stretch” time. Colder temperatures “contract” time.
0
0
1 1'
0 'cUt
R T T t
adjt
t t e dt
LP DeflectionBest fit of time‐dependent predictions
Data Normalization
Department of Civil, Environmental, and Geo- Engineering13 February 2018 - Structural Seminar Series 147
Data Normalization
Benefits of Data Normalization
AnomalyDetection
Deviations easier to detect from expected time‐dependent behavior than from total strains and deflections.
FEM ComparisonMeasured data using adjusted age can be compared to constant temperatureFEM results.
VersatilityEffective for temperature‐ and time‐dependent longitudinal strains and deflections.
Department of Civil, Environmental, and Geo- Engineering13 February 2018 - Structural Seminar Series 148
Time-Dependent FEM• Includes aging, creep,
shrinkage, and relaxation for 150 adjusted age years
• Uses Kelvin chain model to compute viscoelastic behavior
• Includes full erection procedure to accurately capture initial stress state.
Department of Civil, Environmental, and Geo- Engineering13 February 2018 - Structural Seminar Series 149
Time-Dependent FEM
LP Data and FEM Results
Southb
ound
Sp
an 1
Southb
ound
Sp
an 3
1/30/2018
38
Department of Civil, Environmental, and Geo- Engineering13 February 2018 - Structural Seminar Series 150
Prototype Monitoring System
Features of Prototype Monitoring System
• Monitors expansion joint deflections, but can be expanded to other system.
• Computes short‐term errors based on predictions using Bayesian regression.
• Computes long‐term errors based on unexpected changes in slope.
• Sends automatic email updates.
Department of Civil, Environmental, and Geo- Engineering13 February 2018 - Structural Seminar Series 151
Linear Potentiometer Monitoring
Benefits of Using Time‐Dependent Readings
Time‐dependent deflection from Node 4 (SB Span 1)
Narrow bounds over the course of several months
Always increasing, but at a slower rate each year
Thermal behavior is assumed not to change with time, and is therefore easier to remove from LP data than the time‐dependent behaviors.
Department of Civil, Environmental, and Geo- Engineering13 February 2018 - Structural Seminar Series 152
Anomaly Detection
Approach to Anomaly Detection
Linear Potentiometer
Data
Temperature Data
Data NormalizationTime‐
Dependent Data
Finite Element Model Results
Bayesian Regression(FEM = prior dist.)
Posterior Distribution
Training Set
Test Set
Diagnose Anomalies(Short and Long‐term)
Department of Civil, Environmental, and Geo- Engineering13 February 2018 - Structural Seminar Series 153
Anomaly Detection
Short‐Term Anomaly Detection• Use Bayesian regression to predict the time‐
dependent behavior over a specified test set.• Prior distribution taken from FEM results and
uncertainty of creep and shrinkage models.
95%‐credible bounds for Southbound south span LP using 1990 CEB Model Code
Prior Distribution
Posterior Distribution
1/30/2018
39
Department of Civil, Environmental, and Geo- Engineering13 February 2018 - Structural Seminar Series 154
Linear Potentiometer Monitoring
Monitoring System for LP Readings
Short‐term check Every month, ensure that the time‐dependent readings lie within of the defined bounds.
Long‐term checkEvery month, ensure that the annual time‐dependent deflections are (1) positive and (2) less than the deflections from the previous year.
Bearing location Given the LP readings, output the location of the bearing and how much is left for expansion.
Thermal ResponseEnsure that the linear regression coefficients for the thermal response have not changed since the previous year.
Department of Civil, Environmental, and Geo- Engineering13 February 2018 - Structural Seminar Series 155
Anomaly Detection
Short‐Term Anomaly Detection• Posterior distribution provides rational bounds
for detecting anomalous readings.
Southbound south span LP measured data with bearing lock‐up introduced 10 days from end of test set
Normalized time‐dependent data compared to posterior distribution clearly shows anomaly
Department of Civil, Environmental, and Geo- Engineering13 February 2018 - Structural Seminar Series 156
Anomaly Detection
Long‐Term Anomaly Detection• Compute slope of time‐dependent data with
respect to adjusted age.• Slope is always decreasing and never negative.
Southbound south span LP
0.25 in. ramp over 18 months starting here
Southbound south span LP
Measured slope with respect to adjusted age
Posterior distribution compared to slope of measured time‐dependent data
Posterior distribution compared to slope with 0.25 in. drift over 18 months
Department of Civil, Environmental, and Geo- Engineering13 February 2018 - Structural Seminar Series 157
Summary of Monitoring System
Data Normalization
Account for expected safe changes in measured structural behavior.
ModelingCreate computational models to estimate future performance of structure.
Anomaly Detection
Use Bayesian regression to derive rational bounding values for detecting deterioration and damage.
1/30/2018
40
Department of Civil, Environmental, and Geo- Engineering13 February 2018 - Structural Seminar Series 158
• Difficult to identify problems with systems that may have defects prior to instrumentation.
• Truck load tests and environmental effects can be used to establish “baseline” behavior—periodically repeat tests to identify changes.
• Temperature and time‐dependent effects have prominent influence on concrete bridge behavior, possibly masking deterioration that may occur over time (e.g., corrosion).
• Data normalization on temperature can allow the measured time‐dependent behavior to be compared to FEM results and used in monitoring system.
• FEM in combination with historical data can be used to establish expected metrics and error limits.
• Anomaly detection technique using Bayesian regression has successfully been implemented to detect short‐term and long‐term problems
• Long‐term monitoring can assist in maintenance plans/strategies.
Summary and Conclusions
Department of Civil, Environmental, and Geo- Engineering13 February 2018 - Structural Seminar Series 159
AcknowledgementsMinnesota Department of Transportation
Minnesota Supercomputing Institute
Truck Test and Lab Helpers: Paul Bergson, Rachel Gaulke, Andrew Gastineau, Andrew Morgan, Anna Flintrop, Ben Jilk, Damien Teichner, Dan Slegh, Dave Klaseus, Joel Petersen‐Gauthier, Max Halverson, Sarah Noe
Department of Civil, Environmental, and Geo- Engineering13 February 2018 - Structural Seminar Series 160
Questions?
Department of Civil, Environmental, and Geo- Engineering13 February 2018 - Structural Seminar Series 161
References• American Association of State Highway and Transportation Officials (2010). AASHTO LRFD Bridge Design Specifications, Fifth
Edition, Washington, DC.• American Concrete Institute (1982). “Prediction of creep, shrinkage and temperature effects in concrete structures.” ACI‐209R‐82,
ACI Committee 209, Detroit. • Bažant, Z.P. and Baweja, S. (1995). “Creep and shrinkage prediction model for analysis and design of concrete structures ‐ model
B3,” Materials and Structures, RILEM TC 107‐GCS, Vol. 28, No. 180, pp. 357‐365.• Bažant, Z.P., and Prasannan, S. (1989a). “Solidification theory for concrete creep. I: Formulation,” Journal of Engineering Mechanics,
Vol. 115, No. 8, pp. 1691‐1703.• Bažant, Z.P., and Prasannan, S. (1989b). “Solidification theory for concrete creep. II: Verification and application,” Journal of
Engineering Mechanics, Vol. 115, No. 8, pp. 1704‐1725.• Bažant, Z.P., and Xi, Y. (1995). “Continuous Retardation Spectrum for Solidification Theory of Concrete Creep,” Journal of
Engineering Mechanics, Vol. 121, No. 2, pp. 281‐288.• Comité Euro‐International du Béton (CEB) and the Fédération International de la Précontrainte (FIP) (1978). CEB‐FIP model code
1978.• Comité Euro‐International du Béton (CEB) and the Fédération International de la Précontrainte (FIP) (1990). CEB‐FIP model code
1990.• Gardner, N.J., and Lockman, M.J. (2001). “Design provisions for drying shrinkage and creep of normal‐strength concrete,” ACI
Materials Journal, Vol. 98, No. 2, pp. 159‐167. • Grasley, Z.C., and Lange, D.A. (2007). “Thermal dilation and internal relative humidity of hardened cement paste,” Materials and
Structures, Vol. 40, No. 3, pp. 311‐317.• Hedegaard, B.D., Shield, C.K., and French, C.E.W. (2013). “Finite element modeling of the viscoelastic behavior of reinforced and
prestressed concrete,” Journal of Structural Engineering.• Hedegaard, B.D., French, C.E.W., and Shield, C.K. (2013). “Investigation of thermal gradient effects in the I‐35W St. Anthony Falls
Bridge,” Journal of Bridge Engineering, Vol. 18, No. 9, pp. 890‐900.• Priestley, M.J.N. (1978). “Design of concrete bridges for temperature gradients,” ACI Journal, Vol. 75, No. 5, pp. 209‐217.• Sohn, H. (2007). “Effects of environmental and operational variability on structural health monitoring,” Philosophical Transactions
of the Royal Society A, Vol. 365, pp. 539‐560.
1/30/2018
41
Final Thoughts
1/30/2018 166
Design Quality
• Incorporated peer review of major bridge designs
• Required quality management plans for all consultant contracts
• Modified quality processes within Bridge Office
1/30/2018 167
Transportation Funding
• Previous Minnesota legislative proposals in 2006 & 2007
• 2008 transportation bill & veto override• License plate fee increase
• 5 cent gas tax Increase
• $1.8 billion in bonding of which $600M for bridges
• Up to 3.5 cent added gas tax for bond payments
• By June 2018, replace or rehab all bridges identified in the bill.
1/30/2018 168
Chapter 152 Funds
• 172 bridges were identified• Fracture critical
• Structurally deficient
• Approximately 137 bridges will be replaced or rehabbed
• 123 completed
• Several notable large, important bridges were replaced or rehabbed
1/30/2018 169
1/30/2018
43
Stillwater Lift Bridge (St. Croix)1741/30/2018
St. Croix Crossing1751/30/2018
Red Wing1761/30/2018
Red Wing1771/30/2018
1/30/2018
44
DeSoto Bridge (St. Cloud)1781/30/2018
Granite City Bridge (St. Cloud)1791/30/2018
Kennedy1801/30/2018
Kennedy1811/30/2018
1/30/2018
45
Baudette1821/30/2018
Baudette1831/30/2018
A few final thoughts …
1/30/2018 184
Media
• Daily news conferences are manageable; individual interviews are overwhelming.
• When conference is over, address further questions the next day.
• Be factual and calm; avoid speculation.
• Use non‐engineering terms when possible.
• Keep accusatory questions in perspective – lives have been lost.
1/30/2018 185
1/30/2018
46
Employee Wellness
• Our employees responded on August 1‐2, returning without being called. They have tremendous strength.
• Stress debriefings were valuable tools to share emotions.
• Watch for signs of employee struggles with mental and physical health. Reassign to other duties as needed.
• Protect employees’ privacy; others won’t hesitate to call them at home.
• Communicate with employees as often as possible, rather than having the news be their source.
1/30/2018 186
Other Observations
• Existing partnerships/relationships with the FHWA, City of Minneapolis, and other agencies were key in responding to the tragedy.
• Dedicating a team solely to rapid replacement was needed. Others dealt with collapse.
• Understand politics will be part of it.
1/30/2018 187
Within tragedy is also the impetus to review processes
and improve.
Be open to the opportunity.
1/30/2018 188
Thank you!
Catherine [email protected]
1/30/2018 189
Kevin [email protected]