overview of new practices & policy - deck issues

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Overview of New Overview of New Practices & PolicyPractices & Policy

Deck IssuesDeck Issues

TopicsTopics

Stakeholder ResponsibilitiesStakeholder ResponsibilitiesDeflection Control MeasuresDeflection Control MeasuresChanges to Plan RequirementsChanges to Plan Requirements

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Stakeholder ResponsibilitiesStakeholder ResponsibilitiesDesignerDesigner

The The DesignerDesigner is responsible for designing a is responsible for designing a superstructure that maintains minimum cover & superstructure that maintains minimum cover & deck thickness throughout placement.deck thickness throughout placement.

Stakeholder ResponsibilitiesStakeholder ResponsibilitiesContractorContractor

The The ContractorContractor is responsible for designing is responsible for designing falsework & finishing machine support that falsework & finishing machine support that minimizes deflection during placement.minimizes deflection during placement.

Note: The Contractor assumes responsibility for Note: The Contractor assumes responsibility for maintaining minimum cover and deck maintaining minimum cover and deck thickness when deviating from plan thickness when deviating from plan requirements.requirements.

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Deflection Control MeasuresDeflection Control Measures

Construction Design

Deflection Control MeasuresDeflection Control MeasuresConstructionConstruction

IssueIssue::Place concrete in a manner that minimizes Place concrete in a manner that minimizes differential deflections across the transverse differential deflections across the transverse section.section.Specification Change #1Specification Change #1: : CMS 511.10 & 511.19CMS 511.10 & 511.19For structures with a skew angle greater than For structures with a skew angle greater than fifteen (15) degrees and up to fifty (50) degrees, fifteen (15) degrees and up to fifty (50) degrees, load and finish the concrete at the skew angle.load and finish the concrete at the skew angle.

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Current Typical Method of PlacementCurrent Typical Method of Placement


Revised Method of Placement Revised Method of Placement


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IssueIssue::Place concrete in a manner that minimizes Place concrete in a manner that minimizes differential deflections across the transverse differential deflections across the transverse section.section.Specification Change #2Specification Change #2: : CMS 511.10 & 511.19CMS 511.10 & 511.19For structures with a skew angle greater than fifty For structures with a skew angle greater than fifty (50) degrees, load the concrete at the skew angle (50) degrees, load the concrete at the skew angle and finish the concrete at fifty (50) degrees. The and finish the concrete at fifty (50) degrees. The furthest the concrete shall precede the finishing furthest the concrete shall precede the finishing machine is 20 ft.machine is 20 ft.


Revised Method of Placement Revised Method of Placement

50°>50°

20’ Max.

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IssueIssue::Reduce the potential for web distortion (“oilReduce the potential for web distortion (“oil--canning”) under overhang bracket loading.canning”) under overhang bracket loading.Specification Change #3Specification Change #3: : CMS 508.02CMS 508.02Locate the lower contact point of overhang Locate the lower contact point of overhang falsework within 8 inches (200 mm) of the top of falsework within 8 inches (200 mm) of the top of the rolled beam or steel girder’s bottom flange.the rolled beam or steel girder’s bottom flange.


8” Max.

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IssueIssue::Reduce potential for unanticipated girder Reduce potential for unanticipated girder deflection during deck placement.deflection during deck placement.Specification Change #4Specification Change #4: : CMS 513.26CMS 513.26Permanently fasten all cross frames and lateral Permanently fasten all cross frames and lateral bracing before deck placement begins.bracing before deck placement begins.

Deflection Control MeasuresDeflection Control Measures

Construction Design

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Deflection Control MeasuresDeflection Control MeasuresDesignDesign

IssueIssue::Reduce potential for deck thickness loss due to Reduce potential for deck thickness loss due to web distortion (“oilweb distortion (“oil--canning”) under overhang canning”) under overhang bracket loading.bracket loading.Policy Change #1Policy Change #1: : BDM 302.4.1.7BDM 302.4.1.7For steel girder web depths > 78”, specify Item For steel girder web depths > 78”, specify Item 508.02 “as per plan” and specify the lower 508.02 “as per plan” and specify the lower contact point of overhang falsework in the plans. contact point of overhang falsework in the plans.


70” Absolute

Max.

50” Preferred

Max.

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IssueIssue::Reduce potential for deck thickness loss due to web Reduce potential for deck thickness loss due to web distortion (“oildistortion (“oil--canning”) under overhang bracket loading.canning”) under overhang bracket loading.Policy Change #2Policy Change #2: : BDM 302.2BDM 302.2For steel girder web depths > 78”, determine amount of For steel girder web depths > 78”, determine amount of girder twist from “oilgirder twist from “oil--canning” canning” ((φφoo) ) andand associated associated screed rail deflection (screed rail deflection (δδleftleft & & δδ rightright) and deck thickness ) and deck thickness loss. loss. Stiffen web as necessary by reducing transverse Stiffen web as necessary by reducing transverse stiffener spacing, thickening web or providing design for stiffener spacing, thickening web or providing design for temporary web bracing in the plans. temporary web bracing in the plans.


NNooδδrightright

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IssueIssue::Reduce potential for deck thickness loss due to girder Reduce potential for deck thickness loss due to girder warping between crossframes under the overhang load.warping between crossframes under the overhang load.

Policy Change #3Policy Change #3: : BDM 302.2BDM 302.2Designers shall determine amount of girder twist from Designers shall determine amount of girder twist from girder warping between crossframes girder warping between crossframes ((φφww)) andandassociated screed rail deflection (associated screed rail deflection (δδleftleft & & δδ rightright) and deck ) and deck thickness loss.thickness loss.Reducing crossframe spacing and stiffening flanges of Reducing crossframe spacing and stiffening flanges of main members can reduce the effect of girder warping.main members can reduce the effect of girder warping.


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φφwwδδrightright


IssueIssue::Minimize global deformation (i.e. “Minimize global deformation (i.e. “frowniefrownie face” face” ))across the transverse section of across the transverse section of NEWNEW steel or steel or prestressed superstructures. prestressed superstructures. Policy Change #4Policy Change #4: : BDM 302.2BDM 302.2Layout the transverse section such that the tributary Layout the transverse section such that the tributary deck load carried by the fascia member does not exceed deck load carried by the fascia member does not exceed 110%110% of the average tributary deck load carried by of the average tributary deck load carried by interior members.interior members.A Line Girder Analysis of the superstructure is A Line Girder Analysis of the superstructure is acceptable and twist acceptable and twist ((φφgg)) due to global deformation may due to global deformation may be neglected.be neglected.

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IssueIssue::Minimize global deformation (i.e. “Minimize global deformation (i.e. “frowniefrownie face” face” ))across the transverse section of across the transverse section of EXISTINGEXISTING steel or steel or prestressed superstructures. prestressed superstructures. Policy Change #5Policy Change #5: : BDM 302.2BDM 302.2Layout the transverse section such that the tributary Layout the transverse section such that the tributary deck load carried by the fascia member does not exceed deck load carried by the fascia member does not exceed 115%115% of the average tributary deck load carried by of the average tributary deck load carried by interior members.interior members.A Line Girder Analysis of the superstructure is A Line Girder Analysis of the superstructure is acceptable and twist acceptable and twist ((φφgg)) due to global deformation may due to global deformation may be neglected.be neglected.


“Frownie Face”

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IssueIssue::If global deformation cannot be minimized, reduce the If global deformation cannot be minimized, reduce the potential for deck thickness loss due to global potential for deck thickness loss due to global deformation across transverse section.deformation across transverse section.

Policy Change #6Policy Change #6: : BDM 302.2BDM 302.2When the tributary deck load carried by the fascia When the tributary deck load carried by the fascia member does not meet the previous requirements, member does not meet the previous requirements, perform a Refined Analysis of the superstructure to perform a Refined Analysis of the superstructure to determine twist due to global deformation determine twist due to global deformation ((φφgg)) and and associated screed rail deflection (associated screed rail deflection (δδleftleft & & δδ rightright) and deck ) and deck thickness loss.thickness loss.

TTributary Areas ributary Areas –– ExampleExampleNew Steel SuperstructureNew Steel Superstructure

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A=5.3 ft2


A=5.3 ft2 A=6.0 ft2

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A=5.3 ft2 A=6.0 ft2 A=7.0 ft2

5.3 ft2 < 6.0(1.10)=6.6 ft2 < 7.0 ft2


IssueIssue::Reduce potential for deck thickness loss on prestressed Reduce potential for deck thickness loss on prestressed II--Beam superstructures due to insufficient lateral bracing Beam superstructures due to insufficient lateral bracing during deck placement.during deck placement.Policy Change #7Policy Change #7: : BDM 302.5.2.6BDM 302.5.2.6Designers shall analyze the diaphragms for the Designers shall analyze the diaphragms for the overturning loads applied by the overhang brackets overturning loads applied by the overhang brackets during deck placement. Additional diaphragms or during deck placement. Additional diaphragms or temporary bracing details may be required.temporary bracing details may be required.“Oil“Oil--canning” and warping effects associated with steel canning” and warping effects associated with steel superstructures may be neglected.superstructures may be neglected.

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IssueIssue::Design a superstructure that maintains minimum Design a superstructure that maintains minimum cover & deck thickness throughout placement.cover & deck thickness throughout placement.Policy Change #8Policy Change #8: : BDM 302.2BDM 302.2The total loss of deck thickness from the three The total loss of deck thickness from the three sources of girder twist sources of girder twist ((φφoo φφww and and φφgg) ) shall not shall not exceed ½ in.exceed ½ in.

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δδrightright

φφooφφoo

δδleftleft

“Oil-Canning”

φφww

δδrightright

φφww

δδleftleft

“Warping”

φφgg

δδrightright

φφgg

δδleftleft

“Global Deformation”


IssueIssue::How should global deformation (How should global deformation (φφgg)) for a structure with for a structure with complex geometry (e.g. curvature, skews > 50°, multiple complex geometry (e.g. curvature, skews > 50°, multiple skews, etc.) be determined?skews, etc.) be determined?

Policy Change #9Policy Change #9: : BDM 302.2BDM 302.2For structures with complex geometry, the designer For structures with complex geometry, the designer should consider a more detailed analysis of the pour sequence to determine if the sequence itself leads to potential cover loss in excess of ½” at specific locations throughout the deck.

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IssueIssue::Reduce potential for unanticipated girder Reduce potential for unanticipated girder deflection during deck placement.deflection during deck placement.Policy Change #10Policy Change #10: : BDM 302.4.2.3BDM 302.4.2.3Slotted holes shall not be used in crossframe Slotted holes shall not be used in crossframe connections. Crossframe connections shall be connections. Crossframe connections shall be fully welded or designed to prevent slip during the fully welded or designed to prevent slip during the deck placement operations.deck placement operations.


IssueIssue::What is the maximum pouring width for a wide What is the maximum pouring width for a wide skewed bridge?skewed bridge?Policy Change #11Policy Change #11: : BDM 302.2BDM 302.2The paving width as measured along the skew The paving width as measured along the skew should be kept less than 120’. Introducing should be kept less than 120’. Introducing longitudinal construction joints may be required.longitudinal construction joints may be required.Contact the ODOT Office of Construction Contact the ODOT Office of Construction Administration if a paving width > 120’ can not be Administration if a paving width > 120’ can not be avoided.avoided.

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Changes to Plan RequirementsChanges to Plan Requirements

Deflections Deflections -- ScreedsScreedsGeneral NotesGeneral Notes

Changes to Plan RequirementsChanges to Plan RequirementsDeflections Deflections -- ScreedsScreeds

For Line Girder AnalysisFor Line Girder Analysis::Divide deck load evenly to all beams/girders to Divide deck load evenly to all beams/girders to determine deflections used to establish screed determine deflections used to establish screed elevations.elevations.

Assumes all beams deflect uniformly (i.e. as Assumes all beams deflect uniformly (i.e. as a unit).a unit).Accounts for the influence of crossframes on Accounts for the influence of crossframes on overall girder deflection.overall girder deflection.Limited to transverse sections with balanced Limited to transverse sections with balanced tributary loads to main memberstributary loads to main members

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Changes to Plan RequirementsChanges to Plan RequirementsDeflections Deflections -- ScreedsScreeds

For Refined AnalysisFor Refined Analysis::Use the deflections from each beam/girder to Use the deflections from each beam/girder to establish individual screed elevations.establish individual screed elevations.

Allows the Designer to anticipate girder twist Allows the Designer to anticipate girder twist due to global deflections (due to global deflections (φφgg).).

Screed elevations can be adjusted to Screed elevations can be adjusted to account for differential deflections between account for differential deflections between girders due to global deflections.girders due to global deflections.

Changes to Plan RequirementsChanges to Plan RequirementsGeneral NotesGeneral Notes

All assumptions that a Designer makes regarding Contractor means, methods and equipment that affect the design provided in the plans should be included in the General Notes.

Examples Include:• Special pouring sequences• Finishing machine loads• Locations of overhang brackets• etc.

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SummarySummary

An itemized summary is provided at the back of the seminar handout and is available for download at our website:

www.dot.state.oh.us/se/skew/skew.htm

Questions ??Questions ??

Email Questions to:

[email protected]

overview of new practices & policy - deck issues

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