Integral Bridge Midas Seminar

Soil Structure Interaction in Integral Bridges

Vidish A. Iyer Structural Engineer and CAE consultant at Midas IT

Bridging Your Innovations to Realities

Bridging Your Innovations to RealitiesClick to edit Master title style Bridging Your Innovations to Realities

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• About Midas IT• About Midas Civil• About Integral Bridges• Modeling Philosophy and Soil Structure Interaction• Software Demo – analysis and design

CONTENTS

Bridging Your Innovations to RealitiesClick to edit Master title style

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Bridging Your Innovations to Realitiesmidas Civil

CONTENTS


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MIDAS Programs were being developed since 1989 and have been used commercially since 1996.

With our headquarters in South Korea , we currently have 7 branches around the world – viz : in China , Russia , India , USA , UK, Japan and recently Singapore .

With over 40 distributors present in over 150 countries.

One of the Largest civil analysis software developers

Proven Reliability with over 5,000 project applications

Intensive quality control system

Analyses verified by various institutions

CONTENTS




ABOUT MIDAS IT

MIDAS Programs were being developed since 1989 and have been used commercially since 1996.

With our headquarters in South Korea , we currently have corporate offices in Beijing, Shanghai, Detroit, Dallas, Europe, India and Japan and are ever expanding .

One of the Largest civil analysis software developers

Proven Reliability with over 5,000 project applications

Intensive quality control system

Analyses verified by various institutions

CONTENTS




ABOUT MIDAS IT


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Midas NFX midas Gen

midas Design +

midas DShop

midas Civil

midas FEA

midas GTS NX

Soilworks midas FX+

FEPartner (PMC in Japan)

Building Eng. Civil Eng. Geotechnical Eng. Mechanical Eng.

OUR PRODUCTS

Integrated Solution System for Bridge and Civil Engineeringmidas Civil

What is midas Civil?

General Purpose

Special Purpose

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Structural Engineer

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Bridge Underground Structure Building

Plant Tunnel Dam

Why midas Civil

CONTENTS




WHAT IS MIDAS CIVIL ?

2-D 3-D


What kind of bridge type can midas Civil handle?

Conventional Bridge

Staged Segmental Bridge

Cable-stayed Bridge & Suspension Bridge

Why midas Civil

CONTENTS




WHAT TYPES OF BRIDGES CAN IT HANDLE ?


CONTENTS




About Integral Bridges


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Four main types :

• Frame abutments (fully integral bridges) • Bank pad abutments • Flexible support abutments • Semi-integral end screen abutments

Forms of Integral Bridges


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• Effectively a portal frame• Full moment continuity between the deck beams and the supporting

structure at the ends

Frame Abutments


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• End Supports – integral with deck but can rotate and/or slide on soil• Abutment forms an ‘end screen’ wall that extends the full width of the

road formation• Soil pressure on end screen – limit equilibrium methods• SSI – if bank pad supported on fully embedded piles

Bank Pad Abutments


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• Helpful in avoiding soil pile interaction• Form sleeves of precast concrete manhole rings around piles • For smaller piles - polythene or UPVC piping • Concerns include buckling length within sleeve

Flexible Support Abutments


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• End screen wall that is integral with the deck beams, but does not provide support to the beams

Semi-integral end screen abutments


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Semi-integral end screen abutments


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Advantages :

• Lower construction and maintenance costs due to elimination of joints ( Yang et aI., 1985; Greimann et aI.1987; Soltani and Kukreti, 1992 ; Hoppe and Gomez, 1996 ).

• Improved seismic performance (Hoppe and Gomez, 1996).

• Fewer piles are required for foundation support (Soltani and Kukreti, 1992; Hoppe and Gomez, 1996).

• No battered piles are needed (Burke, 1996).

• Construction is simple and rapid (Burke, 1996; GangaRao et aI., 1996; Wasserman and Walker, 1996).

• Greater end span ratios are achievable (Burke, 1996; Wasserman and Walker, 1996).

Why Integral Bridges ?


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Disadvantages :

• Using uncompacted backfill to reduce passive pressure on abutment creates settlement at backfill (Arsoy et al 1999 ; Russel et al, 1994 ; Thompson, 1999 )

• Drainage problems can occur close to abutments ( Russel et al, 1994 )

• Cracks in wing walls due to rotation and contraction of superstructure ( Arsoy et al 1999 ; Russel et al, 1994 )

• Skewed integral bridge may rotate with cyclical loading variations in earth pressure ( Arsoy et al 1999 )

• Limit on length of integral bridges (Arsoy et al 1999; Burke 1993; Burke 1990 )

• Integral Abutments suitable if lateral movement of each abutment < 51 mm (Burke, 1993)

Why Integral Bridges ?


CONTENTS




SOIL STRUCTURE INTERACTION


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• Soil is inherently nonlinear

• Initially SSI was thought beneficial for structures under dynamic actions

• Larger natural period may lead to long period ground vibration (Mylonakis and Gazetas ; 2000 )

• SSI is an important consideration for seismic analysis and also for improving the overall certainty of structural stability

SSI AND ITS IMPORTANCE


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MODELING PHILOSOPHY


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Abutment is modeled as plate/solid elements . Pile modeled as a vertical beam element

Three main modeling techniques :

• Equivalent Cantilever ( for piles )• Equivalent Spring ( for abutment and piles )• Meshed Finite Element model for SSI

MODELING


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• Most common modeling method • Pile behavior simplified by using equivalent pile length based

on stiffness properties of soil and pile

EQUIVALENT CANTILEVER


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EQUIVALENT CANTILEVER LENGTH


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ADVANTAGES

• It is an easy method• Gives tolerable results for simple soil conditions

DISADVANTAGES

• Ignores the soil resistance over pile length• Ignores Pile Group interaction• Different cantilever lengths for displacement and moment

considerations

ADVANTAGES/ DISADVANTAGES OF EQUIVALENT CANTILEVER METHOD


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SOFTWARE APPROACH


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• Soil Springs – equivalent stiffness of soil backfill• Consideration of nonlinear soil behavior • Theories :

- Petterson et al ( 2002 )- Lehane et al ( 1999 )- Lade et al ( 1987 )

In this presentation - Lehane for Abutment backfill - Matlock and Reese (1974) for Pile Springs

SOIL SPRINGS


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ABUTMENT SPRINGS

1

'0h SP K

'0hP

ab

c

Spring Force

Relationship between lateral displacement and lateral stress Abutment soil spring behavior


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ABUTMENT SPRINGS


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PILE SPRINGS

• Formulation by Reese and Matlock ( 1970 )


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ADVANTAGES

• Considers the effect of soil stiffness on the pile length• Behavior of the whole pile can be seen

DISADVANTAGES

• Ignores Pile Group interaction if single pile p-y curve is used• Accuracy is a function of distance between spring nodes.

ADVANTAGES/ DISADVANTAGES OF EQUIVALENT SPRING METHOD


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EQUIVALENT SPRING VS EQUIVALENT CANTILEVER


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• Accurate representation of local and global responses.• Analysis options can range from linear elastic to fully nonlinear analysis- depending on

requirement

• Material Models :

- Mohr Coulomb - Drucker-Prager- Von Mises- Hyperbolic ( Duncan-Chang ) - Jardine - D-min- Towhata - Bowles - …and many others

FINITE ELEMENT MODELING


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FOR ADVANCED GEOTECHNICAL APPLICATIONS


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Contact : [email protected] [email protected]

THANK YOU

mailto:[email protected]

mailto:[email protected]

Documents

Integral Bridge Midas Seminar