08 integral and semi integral abutments

MnDOTMnDOT LRFD Integral & LRFD Integral & SemiSemi––Integral Integral

AbutmentsAbutmentsLRFD Bridge Design WorkshopLRFD Bridge Design Workshop

June 12, 2007June 12, 2007

David David ConkelConkel, P.E., P.E.State Aid Bridge EngineerState Aid Bridge Engineer

Presentation OverviewPresentation Overview

The The JointlessJointless BridgeBridgeIntegral Abutment Integral Abutment SemiSemi--Integral AbutmentIntegral AbutmentTypical Design DetailsTypical Design Details

The The JointlessJointless Bridge Bridge Construction of ChoiceConstruction of Choice

Why a Why a JointlessJointless Bridge?Bridge?Superstructures with deck joints still predominate, but Superstructures with deck joints still predominate, but the trend Nationally is for a the trend Nationally is for a jointlessjointless bridge.bridge.

Eliminates the inherent problems associated with Eliminates the inherent problems associated with installing, maintaining, and repairing deck joints and installing, maintaining, and repairing deck joints and bearingsbearings

Fewer construction joints and simple concrete Fewer construction joints and simple concrete forming, which results in rapid construction, and forming, which results in rapid construction, and reduced initial costsreduced initial costs

Why a Why a JointlessJointless Bridge?Bridge?The FHWA promotes the usage of The FHWA promotes the usage of jointlessjointless bridges bridges where appropriatewhere appropriate

Our sister states, Iowa, North Dakota, South Dakota Our sister states, Iowa, North Dakota, South Dakota and Wisconsin all design and Wisconsin all design jointlessjointless bridges whenever bridges whenever possiblepossible

MnDOT’sMnDOT’s experience, field observations, and years experience, field observations, and years of successful service have demonstrated that of successful service have demonstrated that jointlessjointless bridges do perform well. bridges do perform well.

Integral Abutments Integral Abutments

The integral abutment bridge is characterized by: The integral abutment bridge is characterized by:

Abutment type that eliminates expansion joints in the Abutment type that eliminates expansion joints in the deck deck

Beams cast into a concrete end diaphragm which is Beams cast into a concrete end diaphragm which is rigidly connected to a concrete pile caprigidly connected to a concrete pile cap

Pile cap is supported by a single row of pilesPile cap is supported by a single row of piles

Pile stiffness and flexibility accommodate thermal Pile stiffness and flexibility accommodate thermal expansion and contraction of superstructure expansion and contraction of superstructure

MnDOTMnDOT Integral Abutment Integral Abutment LimitsLimits

Max. bridge length w/ HMax. bridge length w/ H--pile: 300 feetpile: 300 feetMax. bridge length w/ C.I.P. pile: 150 feet Max. bridge length w/ C.I.P. pile: 150 feet Max. beam depth: No limitMax. beam depth: No limitMax. wingwall length: 12 feetMax. wingwall length: 12 feetTypical abutment depth (Bridge seat to bottom of Typical abutment depth (Bridge seat to bottom of footing): 3’footing): 3’--0” below grade, 2’0” below grade, 2’--0” exposed0” exposedMax. skew angle: skew permitted will vary Max. skew angle: skew permitted will vary linearly from 45 degrees for a 100 foot bridge to linearly from 45 degrees for a 100 foot bridge to 20 degrees for a 300 foot bridge. 20 degrees for a 300 foot bridge.

Integral Abutment Skew Integral Abutment Skew LimitsLimits

Maximum Skew of Integral Abutments

Skew = -0.125*(Length) + 57.5Skew = 45

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Integral Abutment Limits Integral Abutment Limits NationallyNationally

Steel GirdersSteel GirdersBridge Length: up to 650 feetBridge Length: up to 650 feetSkew: up to 70 degreesSkew: up to 70 degrees

PrestressedPrestressed Concrete GirdersConcrete GirdersBridge Length: up to 1175 feetBridge Length: up to 1175 feetSkew: up to 70 degreesSkew: up to 70 degrees

Note : Note : MnDOTMnDOT use limits are occasionally use limits are occasionally exceededexceeded

Successful experience will drive future changes in Successful experience will drive future changes in the limitsthe limits

Integral Abutment Pile Integral Abutment Pile Design/AnalysisDesign/Analysis

Typically orient HTypically orient H--piling such that the weak piling such that the weak axis bending occurs longitudinal to the bridge.axis bending occurs longitudinal to the bridge.

Pile penetration into abutment wall is 2’Pile penetration into abutment wall is 2’--6” for 6” for a “fixed head” conditiona “fixed head” condition

Piles are designed to carry vertical loads Piles are designed to carry vertical loads equally and there currently is no explicit equally and there currently is no explicit requirement to consider bending moment in requirement to consider bending moment in piles.piles.

Integral Abutment Pile Integral Abutment Pile Design/Analysis Design/Analysis

WEAK AXIS

2’-6”

Pile Design/AnalysisPile Design/Analysis

A bridge with a total length in excess of 300 feet A bridge with a total length in excess of 300 feet will have larger movement demands and may will have larger movement demands and may require the need for special design require the need for special design considerations, for example:considerations, for example:

Bridge abutments with anticipated movements in Bridge abutments with anticipated movements in excess of 1 inch may require strong axis orientation excess of 1 inch may require strong axis orientation to prevent a plastic hinge under weak axis bendingto prevent a plastic hinge under weak axis bending

Bridge abutments with movements in excess of 1” to Bridge abutments with movements in excess of 1” to 1.5” may require the pile analysis to consider all 1.5” may require the pile analysis to consider all applicable forces including thermal, skew effects and applicable forces including thermal, skew effects and deflections of the superstructure.deflections of the superstructure.

Integral Abutment Integral Abutment Design/AnalysisDesign/Analysis

5.131000

43375Tpullout =⋅

= kips

Back Face Vertical Bar and Back Face Vertical Bar and Longitudinal Deck Bar DesignLongitudinal Deck Bar Design

Integral Abut. Design/AnalysisIntegral Abut. Design/Analysis

Integral Design/Analysis Integral Design/Analysis

Note, the decision was made to delete Note, the decision was made to delete the design requirement for the the design requirement for the longitudinal deck and back face vertical longitudinal deck and back face vertical reinforcement at the abutment to reinforcement at the abutment to withstand 1/2 the fixedwithstand 1/2 the fixed--end moment end moment due to live load. due to live load.


Change was based on:Change was based on:

Feedback from Feedback from MnDOTMnDOT bridge designers bridge designers The requirement was too conservative, and The requirement was too conservative, and required an excessive amount of longitudinal required an excessive amount of longitudinal deck reinforcement. deck reinforcement.

Comparison to pile stiffness Comparison to pile stiffness Research indicates that weak axis pile bending Research indicates that weak axis pile bending will decrease the top tensile stress in the slab will decrease the top tensile stress in the slab caused by dead load and live load. caused by dead load and live load.


Change was based on:Change was based on:

Requirements from other statesRequirements from other states

Based on our discussions at the North Central Based on our discussions at the North Central States Consortium “Bridge Design Committee”, States Consortium “Bridge Design Committee”, a majority of the states do not calculate fixed a majority of the states do not calculate fixed end moments or provide any special design for end moments or provide any special design for the superstructurethe superstructure--abutment joint. abutment joint.

Based on experience and design, I/DOT simply Based on experience and design, I/DOT simply uses #5@12” placed in the top mat to account uses #5@12” placed in the top mat to account for the fixed end moment due to live load. for the fixed end moment due to live load.

SemiSemi--Integral AbutmentsIntegral Abutments

SemiSemi--Integral Abutments Integral Abutments

The semiThe semi--integral abutment bridge is characterized by:integral abutment bridge is characterized by:

Abutment type that eliminates expansion joints in Abutment type that eliminates expansion joints in the deck the deck

Similar to the integral abutment except concrete end Similar to the integral abutment except concrete end diaphragm is not connected to concrete pile capdiaphragm is not connected to concrete pile cap

Thermal movement is accommodated by expansion Thermal movement is accommodated by expansion bearings and a small vertical gap between the end bearings and a small vertical gap between the end diaphragm and pile cap diaphragm and pile cap

Pile cap is typically supported on multiple rows of Pile cap is typically supported on multiple rows of piles or spread footingspiles or spread footings

Use of SemiUse of Semi--Integral Integral Abutment Abutment

SemiSemi--integral abutments are commonly integral abutments are commonly used on designs that require:used on designs that require:

JointlessJointless bridgebridgeSkews less than 30 degreesSkews less than 30 degreesMedium height abutment wallsMedium height abutment wallsSpread foundationsSpread foundationsSupported on drilled shafts Supported on drilled shafts Require multiple rows of pilesRequire multiple rows of piles

MnDOTMnDOT SemiSemi--Integral Integral Abutment LimitsAbutment Limits

MnDOTMnDOT, semi, semi--integral abutment limits have not integral abutment limits have not been entirely established. Limits on max bridge been entirely established. Limits on max bridge length and max grade of bridge will be determinedlength and max grade of bridge will be determined

Max. skew angle permitted will be 30 degrees to Max. skew angle permitted will be 30 degrees to prevent the possibility of damage to wingwall from prevent the possibility of damage to wingwall from non eccentric passive pressure which can force non eccentric passive pressure which can force deck into wingwall deck into wingwall

As we gain more confidence with the semiAs we gain more confidence with the semi--Integral Integral abutment style, the limits will be determined.abutment style, the limits will be determined.

SemiSemi--Integral Abutment Integral Abutment Limits Nationally Limits Nationally

Nationally, semiNationally, semi--integral abutment use is integral abutment use is limited to:limited to:

Max. skew concrete beams: 45 degreesMax. skew concrete beams: 45 degrees

Max. skew steel beams: 40 degreesMax. skew steel beams: 40 degrees

Max. span concrete beams: 200 feetMax. span concrete beams: 200 feet

Max. span steel beams: 200 feetMax. span steel beams: 200 feet

Max. bridge length: 500 feetMax. bridge length: 500 feet

MnDOTMnDOT SemiSemi--Integral Integral Abutment Abutment

Note, Note, MnDOT’sMnDOT’s new new semisemi--integral abutment integral abutment is very similar to I/DOT’s is very similar to I/DOT’s semisemi--integral abutment.integral abutment.

Superstructure expands Superstructure expands and contracts over a and contracts over a fixed abutment.fixed abutment.

Expansion DetailExpansion Detail

(1) (1) -- 24” WIDE WATERPROOF MEMBRANE SYSTEM. MEMBER PLACEMENT SHALL 24” WIDE WATERPROOF MEMBRANE SYSTEM. MEMBER PLACEMENT SHALL BE SUCH THAT A 1” WRINKLE IN THE MEMBRANE WILL BE FORMED OVER THBE SUCH THAT A 1” WRINKLE IN THE MEMBRANE WILL BE FORMED OVER THE E JOINT OPENING TO ALLOW MOVEMENTJOINT OPENING TO ALLOW MOVEMENT

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SemiSemi--Integral Abutment Integral Abutment Design/AnalysisDesign/Analysis

PASSIVE EARTH PASSIVE EARTH PRESSUREPRESSURE

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Requirements:Requirements:

Approach panel length (20 foot min.) to be greater than Approach panel length (20 foot min.) to be greater than wingwall lengthwingwall length

To minimize approach panel length, keep the abutment stem To minimize approach panel length, keep the abutment stem height to a maximum of approximately 15 feetheight to a maximum of approximately 15 feet

B910 to be used for all abutmentsB910 to be used for all abutments

Wingwall outside of barrier and approach panelWingwall outside of barrier and approach panel

Traffic barrier placed on approach panelTraffic barrier placed on approach panel

Backwall designed for full passive earth pressureBackwall designed for full passive earth pressure


Requirements:Requirements:

Maximum expansion length has not been established Maximum expansion length has not been established ((MnDOTMnDOT has recently designed a bridge with a 250’ has recently designed a bridge with a 250’ length, currently not under construction) length, currently not under construction)

Skew up to 30 degrees, shear lug requiredSkew up to 30 degrees, shear lug required

Single span, one abutment to be fixedSingle span, one abutment to be fixed



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Diaphragm Diaphragm BackwallBackwall

SemiSemi--Integral Abutment Integral Abutment Design/Analysis Design/Analysis

Diaphragm backwall:Diaphragm backwall:

Design for passive soil pressure, which results Design for passive soil pressure, which results from bridge expansionfrom bridge expansion

Consider the backwall to be a continuous beam Consider the backwall to be a continuous beam spanning between girders to determine horizontal spanning between girders to determine horizontal reinforcement reinforcement



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Diaphragm Diaphragm Shear LugShear Lug


Diaphragm Shear Lug:Diaphragm Shear Lug:

Design for passive soil pressure, which results from Design for passive soil pressure, which results from bridge expansionbridge expansion

Consider the shear lug to be a cantilever beam to Consider the shear lug to be a cantilever beam to determine vertical reinforcement and shear determine vertical reinforcement and shear reinforcement requirements reinforcement requirements

Special design consideration should be given to Special design consideration should be given to bridges on steep profile grades where the bridge bridges on steep profile grades where the bridge may have a tendency to migrate downhill bringing may have a tendency to migrate downhill bringing lug into contact with abutment stem.lug into contact with abutment stem.



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Abutment Abutment StemStem


Abutment Stem:Abutment Stem:

Design for active earth pressure and a 2’ live load Design for active earth pressure and a 2’ live load surchargesurcharge

Consider the abutment stem as a cantilever beam Consider the abutment stem as a cantilever beam to determine vertical reinforcing to determine vertical reinforcing

Horizontal reinforcement in the abutment stem will Horizontal reinforcement in the abutment stem will be for temperature & shrinkage onlybe for temperature & shrinkage only

Integral Integral vsvs SemiSemi--Integral Integral Abutments Abutments

Abutment type preference:Abutment type preference:

11stst choice: Integral Abutments choice: Integral Abutments

22ndnd choice: Semichoice: Semi--Integral AbutmentsIntegral Abutments

Last choice: Conventional tall or short parapet Last choice: Conventional tall or short parapet abutments with deck joint abutments with deck joint

Railing Inside of WingwallRailing Inside of Wingwall

Elevation/SectionElevation/Section

Approach Slab SupportApproach Slab SupportNo longer specified, No longer specified, slab connection was slab connection was accomplished with accomplished with top horizontal tie top horizontal tie bars.bars.

With settlement, the With settlement, the slab panel behaved slab panel behaved like a cantilever like a cantilever allowing tension allowing tension cracks to develop at cracks to develop at the ends of the tie the ends of the tie bars.bars.

Approach Slab SupportApproach Slab Support

To alleviate this To alleviate this problem, a bar problem, a bar configuration that configuration that facilitates flexible facilitates flexible rotation is opted rotation is opted for.for.

This design This design provides a more provides a more positive connection positive connection allowing inevitable allowing inevitable rotation to occur.rotation to occur.

½” x 2” Bit. Felt

Approach Panel Joints for Approach Panel Joints for JointlessJointless Bridges Bridges

Joints for integral or semiJoints for integral or semi--integral abutments integral abutments are placed at the end of the approach panelsare placed at the end of the approach panels

Typically use Typically use an E8S Joint an E8S Joint Detail, but for Detail, but for longer bridges, longer bridges, an expansion an expansion joint device joint device may be neededmay be needed

Bridge Approach Treatment Bridge Approach Treatment for for JointlessJointless Bridges Bridges

A well graded backfill material should be used A well graded backfill material should be used behind the abutments.behind the abutments.

A granular backfill offers two benefits: A granular backfill offers two benefits: Easily compacted in close spacesEasily compacted in close spacesAids in carrying water away from abutmentsAids in carrying water away from abutments

MnDOTMnDOT has developed a new standard for approach has developed a new standard for approach treatment for integral abutments. treatment for integral abutments.

Details similar to those of the South Dakota DOT Details similar to those of the South Dakota DOT Standard should be available very soonStandard should be available very soon

Bridge Approach Treatment Bridge Approach Treatment for Integral Abutmentsfor Integral Abutments

Note: The designer is encouraged to coordinate with Note: The designer is encouraged to coordinate with road design to assure they are providing the correct road design to assure they are providing the correct backfill treatment for integral abutments. backfill treatment for integral abutments.

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(1) – NATURAL GROUND OR SUITABLE GRADING MATERIAL

(2) – SELECT GRANULAR MATERIAL MODIFIED SHALL COMPLY WITH SPEC. 3149.2B2, MODIFIED TO 10% OR LESS PASSING THE NUMBER 200 SIEVE.

(3) – SUBSURFACE PIPE DRAIN

(4) - SUBSURFACE PIPE DRAIN. SEE BRIDGE STANDARD DETAIL B910 FOR DETAILS.

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SummarySummary

If all the requirements/limitations are met on your If all the requirements/limitations are met on your proposed bridge project, integral abutments proposed bridge project, integral abutments should be utilized should be utilized

More information on the semiMore information on the semi--integral abutment integral abutment bridge is coming. We anticipate their common use bridge is coming. We anticipate their common use on both trunk highway and local roadson both trunk highway and local roads

As we become more comfortable in use of the As we become more comfortable in use of the jointlessjointless bridges, current limits set on span length, bridges, current limits set on span length, bridge length, skew, abutment height, and etc… bridge length, skew, abutment height, and etc… will be adjusted accordingly.will be adjusted accordingly.

SummarySummary

Methods of analysis, details, construction, and Methods of analysis, details, construction, and policy on policy on jointlessjointless bridges will continue to evolve.bridges will continue to evolve.

Additional guidelines will be incorporated as Additional guidelines will be incorporated as additional research and experience is brought additional research and experience is brought forward.forward.

Some other possible opportunities:Some other possible opportunities:integral abutments with curved bridgesintegral abutments with curved bridgesspread footings on MSE fillsspread footings on MSE fillsretrofitting existing bridges to eliminate jointsretrofitting existing bridges to eliminate joints

QuestionsQuestions

08 integral and semi integral abutments

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