elgin o’hare western access interchange- flyover...

11/16/2016Stanley Consultants1

ELGIN O’HARE WESTERN ACCESS

INTERCHANGE- FLYOVER RAMPS

Atalay Yargicoglu, Ph.D., P.E., S.E.


Outline

Project Overview

Bridge Type Investigation

Structural Analysis of Curved Girder Bridges

Flyover Ramp B-67

Midas Civil Analyses

Discussion of Results

References

Questions


PROJECT LOCATION


INTERCHANGE PLAN

B-67

I-490

IL-390


Bridge Type Investigation

Five Curved Girder Systems were considered

Steel plate girder

Steel tub girder (3 tub and 2 tub)

Concrete U-Girder (3 tub and 2 tub)

Concrete segmental

Hybrid (part steel spans – part concrete spans)


Typical Plan and Elevation


Erection and Construction Challenges

Active Class 1 Mainline Railroads

- UPRR 40+ trains /day

- All work must stop when train passes through (within 25’ each side of track)

Restricted Boom Heights due to FAA Requirements

Congested Site

- Limited Crane Locations and Girder Storage Areas

Shoring Towers

- 15’ Clearance to each side of Active Tracks

Girder Weight and Length Limitations for Erection & Transportation


Erection and Construction Challenges


Curved Plate Girder

After extensive research into the design, fabrication, and erection

considerations Steel Curved Girder was found to be the best option.


Concrete U-GirderConcrete U-Girder alternate was further evaluated per Tollway request and

found to be a viable option but too risky for project schedule. Many

construction industry challenges need to be overcome:

- Precasters need to “tool-up” their operations. Requires time and investment.

- High capacity cranes and transport vehicles required.

- Non-Standard Shoring Towers/Straddlebents/Strongbacks needed to Support Splice Points

- Specialty Contractors and High Quality Control Required, etc.


Behavior of Steel Girder Bridges

Two major categories:

Primary Bending — Vertical shear, vertical moment, vertical deflections and end rotations, as are experienced by all bridges

Horizontal Curvature and Skew Effects — Torsional stresses, warping and lateral flange bending, load shifting, and warping and twisting deformations


Typical Steel Curved Plate Girder Framing


Horizontal Curvature Effects

V-Load = (M1 + M2) / [(RD)/d]


V-Load Method, 2-Step Process

1. Straighten out curved structure and apply vertical loads. Calculate V-Loads

2. Apply additional fictitious V-loads so that resulting internal forces are the same as those in the curved structure when subjected to vertical load only.


Lateral Flange Bending


Approximate Methods for Curvature Effects

When the global effects of curvature are neglected, lateral flange bending effects in curved girders must be accounted for by using approximate methods to address curvature. This is most commonly done using lateral flange bending equation:

M-lateral = M.d2 / 10 R h

where:

M-lateral = Lateral Flange Bending Moment

M = Primary Bending Moment

d = Cross frame spacing

R = Radius of Curvature

h = Depth of the Girder


Structural Analysis of Curved Girder BridgesStructural engineers currently have a wide array of approximate and refined analysis and design tools at their disposal.

Line-girder methods

- Bridge girders are analyzed individually for non-composite loads

- Composite loads distributed to all girders

- Live loads calculated by Distribution Factors

- V-Load Approximate Methods used for Curvature effects

- Approximate Methods used for Lateral Flange Bending due to Curvature effects

2D-grid and 2D-frame methods

- Girders and cross-frames are modeled as line elements

- Models interaction of girders and bracing system

- Vertical depth of structure is not considered




• Conventional 3D-frame methods

- Centroid and shear center of the girders are modeled at their actual spatial locations

- Cross-frames or diaphragms through the depth is modeled

• Thin-walled Open-Section (TWOS) 3D-frame methods

- Frame element having seven DOFs per node (3-translations, 3-rotations and 1- warping)

- Accurate characterization of bridge I-girder torsional responses

- Capable of matching the results of 3D FEA quite closely



• Plate and eccentric beam methods

- Composite bridge deck is modeled using flat shell (or plate) finite elements

- Girders are modeled using 3-D frame elements

- Rigid links used to represent Girder-Slab connection




• 3D Finite Element Analysis (FEA) methods

- Structure is modeled fully in three dimensions

- Girder flanges are modeled using beam, shell or solid type elements

- Girder webs are modeled using plate, shell or solid type elements

- Cross-frames are modeled using truss, beam, shell or solid elements as appropriate

- Concrete deck is modeled using shell or solid element

It is important that the right model is selected for a given bridge.

11/16/2016Stanley Consultants

23

Bridge Characterization with Respect to

Curvature and Skew (Ref: NCHRP 12-79) Key Bridge Response Indices :

1. Skew Index, Is = w.tan(skew)/Ls (Is<0.3)

2. Connectivity Index, Ic = 15,000/(R(Ncf+1)m) ; m=1 for SS , 2 for CS (Ic<1)

3. Torsion Index, It = Sci/(Sci+Sco) (It<0.65)

4. Girder Length Index, IL = L-Long/L-Short

5. Global Second-Order Amplification Factor, AFG (AFG<1.10)

(indicator of global buckling capacity of bridge unit, Yura et al., 2008)

For B-67:

Is = 0 and Ic = 0.76

C = Curved

S = Straight

P1 = 2-D Grid Model (MDX)

P2 = Plate-Eccentric Beam Model with Low-Resolution Mesh (LARSA)

1D = Line Girder


Cross-Frame Detailing Considerations

Although AASHTO Article C6.7.2 (2010) states that engineers may need to consider the potential for any problematic locked-in stresses for horizontally curved I-girder bridges, engineers practically never include the inherent lack of fit in their structural analysis in current practice. However, the locked-in forces can significantly influence the girder layovers, the cross-frame forces, and the girder major-axis bending and/or flange lateral bending stresses in certain cases.

Since I-girders in curved bridges generally can be plumb only in one load condition, the cross-frames are fabricated to fit in the field as dictated by the girder erection loads and construction methods. The following approaches are employed:

- No Load Fit (NLF) Detailing

- Steel Dead Load Fit (SDLD) Detailing

-Total Dead Load Fit (TDLF) Detailing

For curved-radially supported bridges, NLF detailing is generally an effective approach since the locked in stresses due to SDLF and TDLF detailing are additive with the dead load stresses. The fact that the cross-frame forces tend to be smallest with NLF detailing.

NCHRP 12-79 research suggest that SDLF and TDLF detailing should be avoided in curved radially-supported bridges. Instead, if required, additional Cross-Frames should be employed to control the girder layovers within the spans.


Flyover Ramp B-67


Flyover Ramp B-67

Pier Details


Flyover Ramp B-67

Girder Framing and Erection Sequence


Flyover Ramp B-67

Bearing Layout and Orientation

(HLMR Pot Bearings)


Flyover Ramp B-67

Modular Joint Detail (Swivel Type)



Midas Civil program used to investigate the lateral response of

the structure to investigate:

- Pier Deflections

- Modular Joint Movements

- Lateral Reactions at Abutments

Model Summary:

Steel Composite Wizard

Drilled Shafts at Piers

Soil Springs

Additional Load Cases for Wind, Braking, and Temperature



Drilled Shaft

Model with

Soil Springs



Live Load at Pier 1


Bearing Orientation



Pier Reactions without Soil Interaction



Pier Displacement



Modular Joint Movement



Pier Reactions with Soil-Structure Interaction



Lateral Reactions at Abutment due to Temperature Loading



Discussion of Results

1. Lateral reactions due to Live load effects were distributed to

all supports. This reduced the pier deflections approximately

by a factor of 2 as compared to decoupled analysis using

tributary span.

2. Lateral reactions at abutments increased approximately 25%.

3. Joints movements were about the same as simple calculations

based on expansion length.


References1. American Association of State Highway Transportation Officials (AASHTO), LRFD

Bridge Design Specifications, 7th Edition, 2016.

2. American Association of State Highway Transportation Officials (AASHTO), Guide

Specifications for Horizontally Curved Steel Girder Highway Bridges, 2003.

3. FHWA Steel Bridge Design Handbook, Structural Analysis, Publication No. FHWA-IF-

12-052 - Vol. 8

4. TRB’s National Cooperative Highway Research Program (NCHRP) Report 725:

Guidelines for Analysis Methods and Construction Engineering of Curved and Skewed

Steel Girder Bridges

5. TRB’s National Cooperative Highway Research Program (NCHRP) Report 424:

Improved Design Specifications for Horizontally Curved Steel Girder Highway Bridges

6. TRB’s National Cooperative Highway Research Program (NCHRP) Report 12-79:

Evaluation of Analytical Methods for Construction Engineering of Curved and Skewed

Steel Girder Bridges

USS Structural Report, “Analysis and Design of Horizontally Curved Steel Bridge Girders”

(USS, 1965).


Questions ?

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