Potential Solutions

Potential SolutionsPotential Solutions

Goals for Design – What are we concerned Goals for Design – What are we concerned about?about?– Primary Goal: Get the deck on successfullyPrimary Goal: Get the deck on successfully

Stability during deck pourStability during deck pour Girder plumbnessGirder plumbness Deck thickness, cover, smoothnessDeck thickness, cover, smoothness

– Secondary GoalSecondary Goal Design efficiencyDesign efficiency

Potential Solutions- Background:Potential Solutions- Background:Current DesignsCurrent Designs

Potential Solutions- BackgroundPotential Solutions- BackgroundCurrent DesignsCurrent Designs

“On skewed structures, in order to accommodate differential dead load deflections of adjacent stringers that exceed ½ inch at any intermediate crossframe location, the erection bolt holes in the crossframe members should be detailed as slotted holes. Hole dimensions shall be 1/16” wider than the nominal bolt diameter and ¾” longer than the nominal bolt diameter. Holes in the stiffeners shall be 3/16” larger than the diameter of the erection bolts. Final bolting and welding shall not be completed until after the deck concrete has been placed.“

Potential Solutions- Background:Potential Solutions- Background:Current DesignsCurrent Designs

Potential SolutionsPotential Solutions

One obvious solution – reduce or eliminate skewOne obvious solution – reduce or eliminate skew

Solution 1 – Erect Girders PlumbSolution 1 – Erect Girders Plumb Solution 2 – Erect Girders Out of Plumb (Pre-Solution 2 – Erect Girders Out of Plumb (Pre-

twist girders)twist girders) Solution 3 – Stiffen Superstructure Solution 3 – Stiffen Superstructure Solution 4 – Lean-on BracingSolution 4 – Lean-on Bracing

Potential Solutions – Potential Solutions – Solution 1Solution 1Erect Girders PlumbErect Girders Plumb Erect girders plumbErect girders plumb Install all crossframes (welded) Install all crossframes (welded) Girders rotate out of plumb during deck placement Girders rotate out of plumb during deck placement Girders will be permanently twistedGirders will be permanently twisted

““Business as Usual” SolutionBusiness as Usual” Solution

Potential Solutions – Potential Solutions – Solution 1Solution 1Erect Girders PlumbErect Girders Plumb

IssuesIssues How much twist is too much ?How much twist is too much ?

– GirdersGirders– BearingsBearings– CrossframesCrossframes

Potential Solutions – Potential Solutions – Solution 2Solution 2Erect Girders out of PlumbErect Girders out of Plumb

Erect girders out of plumb (twisted) and Erect girders out of plumb (twisted) and girders rotate to plumb during deck girders rotate to plumb during deck placementplacement


AASHTO/NSBA

Guidelines for Constructability

AASHTO/NSBA Guidelines for Constructability

Method for Erecting Girders Out of Plumb


IssuesIssues– Steel fit-up during erectionSteel fit-up during erection– Ability of erectorsAbility of erectors– Where has it been done before ? Is it really Where has it been done before ? Is it really

feasible?feasible?– Steel detailing done correctly ?Steel detailing done correctly ?– Potential finger pointing (detailer, erector, designer, Potential finger pointing (detailer, erector, designer,

owner)owner)

Potential Solutions – Potential Solutions – Solution 3Solution 3Stiffen SuperstructureStiffen Superstructure

Stiffen superstructureStiffen superstructure– Add steel Add steel

Bigger flangesBigger flanges Deeper websDeeper webs

– Add girder line(s)Add girder line(s)– Use shored constructionUse shored construction

Benefit – girder twist reduces with increased Benefit – girder twist reduces with increased girder stiffnessgirder stiffness


Shored ConstructionShored Construction

AdvantageAdvantage– Composite for all dead and live loadsComposite for all dead and live loads


DisadvantagesDisadvantages– Cost of temporary shoringCost of temporary shoring– Need good foundations for shoringNeed good foundations for shoring– Can’t put shoring in trafficCan’t put shoring in traffic– Undesirable to put shoring in waterwayUndesirable to put shoring in waterway– Serious issues with redecking Serious issues with redecking


Example 1: Single span, 150’ span, 60 deg., 50 ksiExample 1: Single span, 150’ span, 60 deg., 50 ksi

Differential Differential DeflectionDeflection

No. of No. of GirdersGirders

Max. Girder Max. Girder RotationRotation

Total Girder Total Girder WeightWeight

No No RestrictionsRestrictions 55 0.99 deg.0.99 deg. 276 k276 k

1” Max.1” Max. 55 0.50 deg.0.50 deg. 443 k443 k

½” Max.½” Max. 66 0.38 deg.0.38 deg. 670 k670 k


Example 2: Single span, 166’ span, 63 deg. SkewExample 2: Single span, 166’ span, 63 deg. Skew

No. of GirdersNo. of Girders Max. Girder Max. Girder RotationRotation

Total Girder Total Girder WeightWeight

66 2.16 deg.2.16 deg. 410 k410 k

88 1.11 deg.1.11 deg. 750 k750 k

Potential Solutions – Potential Solutions – Solution 4Solution 4Lean-on BracingLean-on Bracing

Lean on BracingLean on Bracing What is it ?What is it ?

Potential Solutions – Potential Solutions – Solution 4Solution 4 Lean-on Bracing Lean-on Bracing

Potential Solutions – Potential Solutions – Solution 4Solution 4 Lean-on Bracing Lean-on Bracing

www.steelbridges.org

“Lean-on Cross Frame Bracing for Steel Girders with Skewed Supports”

http://www.steelbridges.org/

http://www.steelbridges.org/

Potential Solutions – Potential Solutions – Solution 4Solution 4 Lean-on Bracing - Lean-on Bracing - DefinitionsDefinitions

Internal Lean on Bracing (Solution “4I”)Internal Lean on Bracing (Solution “4I”)

External Lean on Bracing (Solution “4E”)External Lean on Bracing (Solution “4E”)

Potential Solutions – Potential Solutions – Solution “4I”Solution “4I”Internal Lean-on BracingInternal Lean-on Bracing

X XX

X XX

A

A

Section A-A

Potential Solutions – Potential Solutions – Solution “4E”Solution “4E”

External Lean-on BracingExternal Lean-on Bracing

Potential Solutions – Potential Solutions – Solution “4E”Solution “4E”External Lean-on BracingExternal Lean-on Bracing

Top & Bottom Angles, Single Bolt at Each End

Bolted Crossframe

Bolted Crossframe


Place Deck – Middle Girders Deflect


Install and Weld X-framesRemove

Crossframe; Place Deck

Remove Crossframe; Place Deck


Install and Weld X-frames Install and Weld X-frames


Place Closure Pour Place Closure Pour

Miscellaneous IssuesMiscellaneous Issues

BearingsBearings Deck Joints & End CrossframesDeck Joints & End Crossframes Semi-integral bridgesSemi-integral bridges

Miscellaneous IssuesMiscellaneous IssuesBearingsBearings

Longitudinal slope issuesLongitudinal slope issues


Cambered Beam Before Deck Placement


Beam After Deck Placement


Before Deck Placement


After Deck Placement


Bearing Movement and Restraint IssuesBearing Movement and Restraint Issues


Longitudinal Displacements

Fixed

Expansion


Transverse Displacements


Lateral restraint issuesLateral restraint issues

Fixed Expansion


Lateral Restraint

Semi-integral Retainers


Lateral Restraint

Seismic Pedestals

Miscellaneous IssuesMiscellaneous IssuesBearings - SummaryBearings - Summary

For Skewed / Wide Bridges, May Need to:For Skewed / Wide Bridges, May Need to: Design for individual loadsDesign for individual loads Design for permanent long. & lat. bearing rotationsDesign for permanent long. & lat. bearing rotations Design for additional longitudinal translationDesign for additional longitudinal translation Design for lateral translationDesign for lateral translation Prevent or design for lateral restraint forcesPrevent or design for lateral restraint forces

– Bearing anchors or other restraintsBearing anchors or other restraints– Seismic pedestalsSeismic pedestals– Semi-integral retainers Semi-integral retainers

Miscellaneous IssuesMiscellaneous IssuesEnd CrossframesEnd Crossframes

Miscellaneous IssuesMiscellaneous IssuesSemi-integral BridgesSemi-integral Bridges

QUESTIONS ?QUESTIONS ?E-mail questions to:E-mail questions to:

[email protected]@dot.state.oh.us

Potential Solutions

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