Stability Considerations for the Construction of Steel I-

Girder Bridges using the Incremental Launching

MethodMaria Emilia Ponton, Andres Robalino

ADSTREN EngineeringTelmo Andres Sanchez

Universidad San Francisco de Quito

Annual Stability ConferenceStructural Stability Research Council

Orlando, April 12, 2016

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Presentation Outline

• Introduction• Case Study Description• AASHTO Strength Checks• Global Buckling of Two Girder System• Conclusions• Future Work

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Introduction• The incremental launching method (ILM) is used to cross over

an obstacle with minimal intervention from below• The superstructure is assembled behind one abutment and

then, it is pushed forward• When proper considerations are taken, the steel erection with

ILM can be safer, faster, and more cost-effective than other methods

• However, the steel girders may be subject to high strength demands

• How applicable are current AASHTO Specifications to study bridges constructed with ILM?

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Case Study Description• The Maresa Bridge has two superstructures in parallel,

composed of five and four steel I-girders• The bridge is situated in Quito, Ecuador

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Case Study DescriptionBridge Cross-Section:

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Case Study DescriptionGirder Dimensions:

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Case Study DescriptionSequence of Launching Operations:

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Case Study DescriptionSequence of Launching Operations:

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Case Study DescriptionSequence of Launching Operations:

Structure in its final position

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AASHTO Required Strength Checks

The AASHTO Bridge Design Specifications require checking the following limit states for construction of steel I-girder bridges:

bu f h ycf f R F

/ 3bu f h ncf f R F

bu f crwf F

bu f h ytf f R F

u v crV V

- Compression flange yielding

- Compression flange stability

- Web bend-buckling

- Tension flange yielding

- Web shear strength

fl ≤ 0.6Fyf- Maximum level of fl

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AASHTO Required Strength Checks

When the girder webs do not have bearing stiffeners and are subject to concentrated loads, the AASHTO Bridge Design Specifications require checking two additional limit states:

- Web local yielding

- Web crippling

All these limit states need to be considered when constructing a bridge with ILM

u b nyR R

u b ncR R

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AASHTO Required Strength Checks

Finite element models (FEM) are developed in ABAQUS to study the behavior of the Maresa Bridge and to compare to the results of the AASHTO Specification requirements

Illustration of the deformed structure as predicted by the FEM (stresses shown in MPa; deflections scaled by a x5 factor)

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AASHTO Required Strength Checks

0

50

100

150

200

250

300

350

400

35 40 45 50 55 60 65

MPa

x (m)

Fyc G1 (1.5DC) G1 (1.25DC+1.25WS)φf

0

50

100

150

200

250

300

350

400

35 40 45 50 55 60 65

MPa

x (m)

Fnc G1 (1.5DC) G1 (1.25DC+1.25WS)φf

Compression Flange Yielding Compression Flange Stability

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AASHTO Required Strength Checks

Compression Flange Stability Concentrated Load

3.682.86

2.47 2.09

1.71

1.661.28

4.123.23

2.762.32

1.95

1.94

1.45

200

250

300

350

400

450

500

35 40 45 50 55 60 65

MPa

x (m)

Fnc G1 γ(1.5DC) G1 γ(1.25DC+1.25WS)φf

3.68

2.86 2.47 2.09 1.75 1.661.28

4.123.23 2.76

2.32 1.951.94

1.45

0

500

1000

1500

2000

2500

3000

3500

35 40 45 50 55 60 65

kN

x (m)

Rn - Web Local Yielding Rn - Web Crippiling

G1 γ(1.5DC) G1 γ(1.25DC+1.25WS)

φwφb

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Global Buckling of Two Girder System

First buckling mode for the two girder system, cantilever = 65m

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AASHTO Required Strength Checks

0.0

0.5

1.0

1.5

2.0

2.5

50 55 60 65

γ

x (m)

FEA - Two girder system (actual geometry) FEA - Two girder system (uniform section)

Eq. 1 - Two girder system Cb=1 Eq. 1 - Two girder system Cb>1

crt

2 2 2 2 2

2 221.3 4yc yc o eff x

gl bg g g

I J I h I I SEM CL L L

Yura et al. (2008)

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Conclusions• ILM is a method that may be implemented for the construction

of steel I-girder bridges• I-girders are subject to a combination of high bending, high

shear, and concentrated loads• Current AASHTO Bridge Design Specifications do not

necessarily capture the expected capacity of the girders at the cantilever support

• Global buckling resistance may be evaluated by using the methodology discussed in Yura et al (2008), with Cb = 1.0

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Future Work• Investigate the correlation between bending, shear, and

concentrated loads- There is substantial evidence that shows that M and

V are not necessarily correlated- Eurocode 3 considers the M, V, P interaction

• Further studies on the applicability of global buckling strength equation

- Eq. 1 was developed for simply supported beams- Does it apply to other cases? (e.g., cantilever systems)

Questions?

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