U.S. Department of Transportation
Federal Highway Administration
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Washington, DC 20590
202-366-4000


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Bridges & Structures

MAE Center research Success with DOTs

Slide 1

Past and Future

Neil M. Hawkins - Professor Emeritus
University of Illinois
MAE Center Annual Meeting - 2002

PowerPoint Version (5 mb)

With sincere appreciation of the contributions of Professors DeRoches and French (Georgia Tech), Aschheim, LaFave and Long (Illinois), Hwang (Memphis), and personnel from GaDOT, IDOT and TDOT and Caltrans


Slide 2

ORGANIZATION OF PRESENTATION

  • BACKGROUND - Lifeline Considerations for Transportation Systems
  • BACKGROUND - The Highway System Lifeline
  • OVERVIEW OF MAE TRANSPORTATION RESEARCH ACTIVITIES AND SUCCESSES
  • VISION FOR FUTURE

Slide 3

THE TRANSPORTATION SYSTEM AS A LIFELINE

  • DESIGN REQUIRES CONSIDERATION OF FACTORS DIFFERING FROM THOSE FOR BUILDINGS
  • ACCEPTABLE PERFORMANCE DEPENDS ON:
    • Functionality of System after Event and Not Life Safety During Event
    • Financial Impact of Event

Slide 4

FINANCIAL IMPACTS

  • REVENUE LOSSES
  • FACILITY REPAIR COSTS*
  • LIABILITY EXPOSURE
  • RESPONSIBILITY TO SOCIETY*
  • Road* vs. Rail

Slide 5

THE HIGHWAY SYSTEM LIFELINE

  • SPACIALLY DISTRIBUTED COMPONENTS INTERCONNECTED OPERATIONALY AND PHYSICALLY
  • REDUNDANCY ALLOWS SOME LEVEL OF LOCAL DAMAGE
  • AGENCY'S JURISDICTION DETERMINES ITS RESPONSIBILITIES
  • SEISMIC HAZARD DEFINED BETTER BY SCENARIO EVENT THAN PROBABILISTIC GROUND MOTION

Slide 6

HIGHWAY LIFELINE SYSTEM DESIGN

  • PERFORMANCE GOALS FOR SCENARIO EARTHQUAKE - 2 Rather than 1.5 on Estimated Ground Motions?
  • IDENTIFICATION AND QUANTIFICATION OF HAZARD - Soil Liquefaction, Permanent Ground Deformations, Structural Movements and Failures, and Importance of EQ Event Relative to Other Hazards.
  • ASSESS DAMAGE STATE FOR SCENARIO EVENT - Functionality of Components, Time and Cost to Repair.
  • EVALUATE SYSTEM FUNCTIONALITY- IDENTIFY RISK REDUCTION OPTIONS (CBE)

Slide 7
Figure 2-4: Integration of Transportation Officials Stakeholder Thrust Area Research with Core Research. Click for long description.
Figure 2-4: Integration of Transportation Officials Stakeholder Thrust Area Research with Core Research

Slide 8

HIGHWAY INVENTORY

NEW MADRID SEISMIC ZONE

This figure is a road map for States in the new Madrid seismic zone, i.e., Illinois, Indiana, Kentucky, Tennessee, Mississippi, Arkansas, and Missouri.
  • CHARACTERISTICS OF SYSTEM WITHIN AREA WITH 0.1g ACCELERATION FOR 500 YEAR RETURN PERIOD
  • Age for 90% of Bridges
  • Interstate 1966 + - 8 years
  • Overpass 1963 + - 8years
  • Type of Bridge
    • 2/3rds Continuous
    • Steel : Concrete
      • 4:1 Overpasses
      • 1:1 Interstate
  • NBI Lacks Information on Bearing, Bent, Foundation, and Soil Characteristics
  • Interstate Bridge Characteristics Different to Secondary Road

Slide 9

HIGHWAY INVENTORY
ILLINOIS SOUTH OF I-70

Transverse elevation of bridge pier and cross-section of bridge superstructure show longitudinal elevation of three-span bridge -This typical bridge has rocker bearings that allow for rotation but are inherently seismically vulnerable. Expansion bearings at B1, B2, and B4 with a fixed bearing B3 only at pier 2 means that all seismic forces must be taken by pier 2, this again is a seismically unsafe situation.
Elevation of Typical Bridge

  • BRIDGE CHARACTERISTICS VERY DIFFERENT TO CALIFORNIA BRIDGES. PIERS NOT INTEGRAL WITH BEAMS OR DECK.
  • 533 Bridges on Primary Emergency Routes (Interstates)
  • For 10% Sample:
    • 2/3rds Steel Continuous
    • Support Type:
      • 50% Multi-Col. Pier
      • 40% Wall-Pier
      • 90% of Foundations Pile Supported
      • 30% on Soil Likely to Liquefy

Slide 10

VULNERABILITY-FUNCTIONALITY RELATIONSHIPS

  • EXPERT OPINION -"EMPIRICAL" RELATIONSHIPS - HAZUS
  • ANALYTICAL RELATIONSHIPS
  • Approach Slabs
  • Major River Crossing
  • Pavement
  • "Standard" Bridge
Illustrates the general order or sequence of steps: 1) Beginning with information from the Highway Bridge Inventory, the lateral load resisting elements are defined, and a structural model developed. 2) Lateral Load resisting characteristics are determined (i.e., natural frequencies of vibration, soil structure interaction). 3) Then Synthetic Ground Motion is developed and the nonlinear pushover analysis done to establish the sequence of deterioration. 4) Then the damage assessment can be made.
  • EQ with 10% probability in 50 years causes little structural damage to as-built interstate bridges.
  • EQ with 2% probability in 50 years causes wide damage to steel bearings, columns and foundations

Slide 11

DAMAGE TYPES

The "brittle" problems occur at relatively low loads and small deformations and can result in rapid loss of strength and stability.
Lateral Load Performance
(Brittle Deficiencies)

BRITTLE

  • Bearing or Pedestal Failure
  • Beam or Column Shear Failure
  • Column Lap Splice
  • Pile Shear or Pullout
The "ductile" behavior tends to reduce the magnitude of the seismic forces, and absorbs the remaining forces as the structure deforms. The structure continues to resist substantial load even in a deformed configuration after yield.
Lateral Load Performance
(Ductile Deficiencies & Displacement)

DUCTILE

  • Bearing Overturning
  • Excessive Pier Drift
  • Excessive Ground Displ.
  • Pile Flexure

Slide 12

RETROFIT STRATEGIES

Methodology- Flow Diagram for Retrofitted Piers
The vulnerability and loss of functionality was determined in steps 1 through 4 on slide 10. Slide 12 shows how an actual seismic retrofit can then be undertaken. At step 5, based on the Damage Assessment, a seismic Retrofit Strategy is selected. At step 6 the structural model is changed, the Synthetic Ground Motion revisited, and the Lateral Load Performance determined for the new structural configuration. At step 8 there is a Damage Re-Assessment. Step 9 is the Loss Reduction Evaluation.
  • Restrainer Cables
  • Elastomeric Bearings
  • Column and Cap Beam Wrapping
  • Micropile Additions

Slide 13

RESTRAINER CABLES

Restrainer cables attached to steel beams and concrete substructure. Model is in laboratory and instrumented for testing.

Restrainer Cables are used to ensure that bridge beams movements relative to the bearings are restricted and beams cannot displace off bearings longitudinally or transversally.


Slide 14

RESTRAINER CABLES

FXB: Fixed Steel Bearing. EXB: Expansion Steel Bearing
The longitudinal elevation of the bridge shows a three span bridge with simple spans. The superstructure is not continuous. The pier columns, caps, bearings and superstructure are shown in the deformed position with dashed lines. The fixed bearings are to the left and the expansion bearings to the right of each span. The hinge openings are shown in the open and closed positions. The lines identified as "Current - pier" and "Current - girder" are for when no restrainer is provided.

Slide 15

RESTRAINER CABLES - TEST RESULTS

Cable Restrainer Load - Displacement
Graph of load displacement behavior of four restrainer systems shown in the following pictures. The restrainer cable appears to be the same in all three cases as is the attachment to the pier. The brackets apparently have a different stiffness. The lines identified as "Current - pier" and "Current - girder" are for when no restrainer is provided. All three connections developed the yield strength of the cable.
A bracket and cable Bracket 1 is a "bent plate"
Bracket 2 is a "stiffened plate" Bracket 3 is a "bearing or shear plate" because the load is in the plane of the plate

Over 100 Restrainer Retrofits Modified by TN DOT


Slide 16

ELASTOMERIC BEARINGS

The Type I elastomeric bearing resists lateral load by deforming in the direction the load is applied. The Type II sliding bearing begins sliding after the frictional resistance is exceeded. The deformation across the elastomer is recovered once the load is removed. The Type III bearing has a shear pin to limit the deformation of the elastomer.
  • Allows for Temperature Effects. While Bearings Compress Little They Deform Easily in Shear.
  • Hysteresis Small W/o Slip at Interface and Large with Slip.
  • Are Hysteresis Characteristics Advantageous for EQ Effects?
  • Does Stiffening of Elastomer with Decreasing Temperature Obviate Beneficial Effects for EQ?

Slide 17

ELASTOMERIC BEARINGS

  • Tests Conducted on New and Used Bearings to Find Changes in Slip, Stiffness and Hysteretic Characteristics with Decreasing Temperature and Increasing Cyclic Deformations.
  • Dynamic Analyses Made For Typical 4 Span Bridge with Fixed Bearing at Central Pier and Elastomeric Type II Bearings at Side Piers and Type I at Abutments.
Span lengths in sequence are: Abutment 1 to Pier 2 = 15.24m, Pier 2 to Pier 3 = 19.81m, Pier 3 to Pier 4 = 19.81m and Pier 4 to Abutment 5 = 15.24m
Bridge Elevation

Slide 18

ELASTOMERIC BEARINGS

  • Temperature Effect Unpredictable. Vary Widely with Materials Used by Manufacturer
  • Elastomeric Bearing Use Can Reduce or Increase Pier Forces. Type and Location Must Be Properly Selected.
Bar-graphs showing peak relative displacement in mm at abutment1, Pier 2, and Pier 3 for four different bearing configurations. The total displacement and the parts due to the slides, elastomeric, and pier are given. Follow link for data and analysis.

Bar-graphs showing peak relative displacement in mm at abutment1, Pier 2, and Pier 3 for four different bearing configurations. The total displacement and the parts due to the slides, elastomeric, and pier are given. Follow link for data and analysis.

Bar-graphs showing peak relative displacement in mm at abutment1, Pier 2, and Pier 3 for four different bearing configurations. The total displacement and the parts due to the slides, elastomeric, and pier are given. Follow link for data and analysis.

Bar-graphs showing peak relative displacement in mm at abutment1, Pier 2, and Pier 3 for four different bearing configurations. The total displacement and the parts due to the slides, elastomeric, and pier are given. Follow link for data and analysis.

Slide 19

COLUMN AND BEAM WRAPPING

  • Prevents Shear and Lap Splice Failures and Increases Flexural Ductility Capacity.
  • Steel or Composite Placed as Bands or as Encasement. Effectiveness Varies with Form and Quality Control.
  • Encasement More Aesthetically Pleasing But Results in Accelerated Deterioration if Located Below Deck Joint.
  • Effective on Deteriorated Members if Member Properly Repaired First.
Image shows steel hoops used to restrain lateral buckling of the vertical reinforcement near the bottom of the column where a plastic hinge would be expected to form.
Image shows encasement of the plastic hinge regions at the top and bottom of the columns with a rap that confines crushing of the concrete and restrains lateral movement of the reinforcement.
Image shows the bottom of pier columns that have four or five bands equally spaced in the plastic hinge region. The bands function similarly to the hoops and wraps.

Slide 20

COLUMN CAPACITY DESIGN RETROFIT

In the As-built condition, the bearing will fail because the column is too stiff.
As-built
The retrofitted column will behave more ductilely (i.e., the modified and wrapped columns will yield while continuing to resist 220 kips). The energy of the earthquake will be dissipated without other elements of the system ever being overloaded.
Retrofitted

Base shear capacity in terms of pier elements


Slide 21

COLUMN AND BEAM WRAPPING

Effect of As-Built versus Retrofit

Follow link for more information.

Slide 22

FOUNDATION IMPROVEMENT WITH MICROPILES

  • To Increase Foundation Capacity or Stiffness
  • To Resist Overturning Where Existing Cap to Pile Connections Are Inadequate
  • To Extend Piles Below Liquefiable Layer While Maintaining Vertical Load Capacity During EQ.
Diagram showing six steps in placement of a micropile. The auger drilling through the soft layer into the bearing stratum (step 1 & 2). The auger is pulled and a grouting tube inserted (step 3 & 4). As the tube is pulled additional grout is pumped enlarging the pile within the bearing stratum (step 5). The pile within the compressible stratum is reinforced and dowels provided in the footing (step 6).
Image of dowels and reinforcement cages for retrofit of pier footing.

Slide 23

FOUNDATION IMPROVEMENT USING MICROPILES

Case Study Foundations

Existing footing is 2.7 meters square with nine piles in a 0.9 m grid. The eight retrofit piles are spaced at 1.8 m. The final pile cap is 4.5 meters square.

3x3 Retrofitted
Pile Group


Existing footing is 2.7 m by 9 m with 30 piles in three rows of ten, all in a 0.9 m grid. The 16 retrofit piles are spaced at 1.8 m except for the first interior pile in the long rows which are 1.35 m from the end rows. The final pile cap is 4.5 m by 10.8 m.

3x10 Retrofitted
Pile Group


Slide 24

FOUNDATION IMPROVEMENT USING MICROPLIES

  • Stiffness Increased 50% with 3x3 Pile Addition.
  • Even With Retrofit Liquefaction Near Surface Substantially Reduced Pier Lateral Stiffness.
  • Dynamic Rotational Stiffness Increased Regardless of Which Soil Layer Liquefied.
  • Stiffness in Field Tests Less Than Predicted
Image showing the piles have load frames and strut rods in place so they can be laterally loaded against each other. There are provisions for measuring lateral movement from established reference points.
Image showing field test to measure micropile lateral stiffness.

Slide 25

VULNERABILITY- FUNCTIONALITY FOR MID-AMERICA BRIDGES

  • Methodology to Derive Relationships, Repair Costs and Recovery Time Developed By Hwang (Memphis).
  • Response of Typical Multi-Span Bridge Controlled by Response of Central Pier.
  • Vulnerability Functions Derived for "Standard" Bridge for Longitudinal (GaTech) and Transverse Directions (UIUC)
The spans of 42.5, 75, 75, and 42.5 feet are typical for an overpass structure.
The elevation and section identify the "standard bridge" type structure that the fragility curves represent, i.e., superstructure - precast concrete beams with poured-in-place slab and diaphragms, integral abutments with no provisions for expansion; substructure - pile supported piers and abutments with battered piles.
This graph demonstrates that smooth curves can be developed from the data. The curves can be used for design decisions. Follow the link for the data this graph is based on.

Slide 26

VISION FOR FUTURE

  • Consensus Criteria Developed for CBE and Performance Based Design of EQ Emergency Routes in NMSZ Using FHWA Pooled Funds.
    • Design All New, and Systematically Upgrade All Existing, Major River Crossings and Their Approaches to AASHTO-LRFD Seismic Criteria.
    • Identify Life Safety Needs of Communities and Design and Upgrade Routes Consistent with Those Needs.
    • Design Other New Structures, and Upgrade Other Existing Structures, to EQ with 10 % PE in 50 years.
  • MAEC Has Developed The Tools and Skilled Personnel to Successfully Complete That Task.
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Updated: 06/13/2013
Federal Highway Administration | 1200 New Jersey Avenue, SE | Washington, DC 20590 | 202-366-4000