structural steel design fabrication and construction 00

7/28/2019 Structural Steel Design Fabrication and Construction 00

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Structural Steel Design,Fabrication, and Construction

Jamie F. Farris, P.E.TxDOT Bridge Division

October 11, 2011


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Design

Fabrication

Construction

NSBA/AASHTO


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Bridge Design Manual - LRFD


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TxDOT Preferred Practices

TxDOT

FHWA Consultants

Academics

Fabricators Detailers

Steel Mill reps

Texas Steel

Quality Council


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Material Selection


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Unpainted Weathering Steel Preferred

A 709 Grades 50W and HPS 70W

More economical

Consider location conditions before choosing

Use details to prevent concrete staining


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Prevent Concrete

Staining

Include drip tabs on

all girders

Additional options

Stainless steel trays

Paint area over Bent

Weathering Steel


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Painted Steel

System IV noncoastal newconstruction

System III coastalnew construction

More info - See Item446 of TxDOT SpecBook


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Span Configuration & Geometry

3 and 4 span continuous Preferred

Interior Spans 20-30% longer then End Spans

Check uplift at the ends of continuous girders

Avoid high skews or major differentials wherepossible

L L1.2L to 1.3LInteriorExterior Exterior


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Girder Spacing I-girders

Limit CL-CL spa to 10 ft Min of 4 girders for vehicular bridge span

Tub girders Limit web spacing to 10 ft

Min of 3 girders for vehicular bridge span Consider use of PCPs for straight girders


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I-Shaped Plate Girders


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Geometric Constraints for

Straight Girders

Flange Width

D/4Flange Width 15 in

in Flange Thick 3 in

Web Thick in

0.25D

Min.

D

0.50 in

Min.

0.75 in Min.

3.00 in Max.


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Flange Width D/4

Flange Width 15 in

1 in Flange Thick 3 in

Web Thick in

0.25D

Min.

D

0.50 in

Min.

1.00 in Min.

3.00 in Max.

Geometric Constraints for

Curved Girders


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Flange Criteria

Flange Width

Constant

Transitions at field splices

Top = Bottom

Flange Thickness Use 10 ft min length

Use only a few sizes

In lieu of lateral bracing flange thickness

Use similar thicknesses

across girders


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Flange Criteria

Flange splices extend thicker flangesbeyond theoretical flange splice location

Theoretical Location


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Web Criteria

Web Depth

Whole inch increments

Dapped Ends: No more than 40% of web

depth

Do not use haunched webs

Web Thickness

Eliminate need for transverse stiffeners Discourage use of fully stiffened web

designs

Optimal designs have few sizes


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Web Criteria

Dont use Longitudinal stiffeners unlessweb depth > 120 in

Present

fabrication and

fatigue problems


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Field Splices

Show in plans as welded Offer bolted splice option

Locate at points of DL

contraflexure Girder field length ~ 130 ft max

Limit shipping width to 6 ft and

height to 9 ft Web splice locations at least

10 apart


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Bolted Field Splices

Galvanized bolts forpainted steel

1, 7/8, Dia

Class A surface

conditions Splice PL thickness

Add 1/8 tomin edge distancesin AASHTO LRFD


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Splice Fill Plates

Steel grade specified for girders not

available in thicknesses less than 3/8

Allow optional fill plate material (A 606, A

570, etc.)

Spec Book 447.4.B


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A325 vs. A490 Bolts

Contractors preferA325

A325 bolts can beretightened

A490 bolts aresensitive to tighteningprocedures

A490 bolts requireimpact wrenches thatmight not be available


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Max Spacing Straight = 30 ft

Curved = 20 ft

Provide at all endbearings

Straight - Set parallel

to skew up to 20o. Set

radial beyond 20o

Curved set radial to

girders

Diaphragms & X-Frames


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X-frame Half Pipe Stiffeners

Research Project0-5701

Gives girders

higher bucklingcapacities

Serves as abearing stiffener

Coming soon:Added to SGMDStandard

Skewed Bridges


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Lean On Bracing

Research Project 0-1772

Struts transfer forces to 1 or 2 X-frames

Minimize LL induced brace forces Reducing number of braces

Straight Bridges


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Stud Connectors

Full length of

girder

Min longitudinalSpa 4d

SGMD Standard

Not required ontop of flange splice

plates


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Bearings

Select from TxDOT

SGEB standard

Triple check bearing

seat elevations

Avoid costly HLMR,

disc, pot bearings

Bent Cap geometry


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Steel Tub Girders

Only use if this isthe best solution

Consider for long,

narrow, curved,bridges with tightradius

NSBA Practical

Steel Tub GirderDesign


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Tub Girders

Constant shape Rotated with x-slope

Top flange and Web

same requirements asI-girder

Avoid details more

critical than Cat. C


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Bottom Tension Flange

> thick

w/t 80

Classified as fracture-critical for 2-girder spans

All bottom flange edges

extend 2 in + beyondweb CL


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Inspection Access


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Slabbing and Stripping

Top View

Girder Elevation


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Multiple Head Cutting Bed -

Strips Out Flanges From

Wider Plates

Slabbing and Stripping


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Narrow Gap Electroslag Welding

Welding TimeApprox. =10- 20%

of multiple pass

weld

Minutes

versus

Hours


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Analyze girder system using grid analysis

Predict the behavior of girder system

once bridge is fully constructed


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Critical Stages of Stability

Girder Erection

Before concrete deck placement


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Research Study 0-5574

Curved Plate Girder Design for Safeand Economical Construction

Justify recommendations in PreferredPractices

Create uniformity among analyticalrequirements of curved I-girders during

early stages of construction

Girder erection and concrete slab

placement


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Field Monitoring Parametric Finite

Element Modeling

Survey of GirderErection Practices

PC Based

Analytical tools

Research Study 0-5574

Lifti P i t L ti


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Lifting Point Locations

Sh i I


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Shoring Issues

High costs

Prematureremoval

Site access issues


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UT Lift 1.1

ANALYTICAL TOOLS

Spreadsheet Behavior of girder

segments during

lifting Determines optimallift locations

Girderdeformations

Predicts girdertwist


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3D Finite Element

Program

Partially

constructed girdersystems

Staged deck

placementUT Bridge 1.5

ANALYTICAL TOOLS


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National Steel Bridge Alliance


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AASHTO/NSBA


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AASHTO/NSBA


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Guidelines for Steel

Girder Analysis Shop Detail Drawing

Review

Fabrication

Sample OwnersQuality AssuranceManual

Erection Guide Spec Coating Systems

Guide

AASHTO/NSBA


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AASHTO/NSBA


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Final published inEarly 2012

23 Chapters including Analysis

Load Combinations

Splice Design Substructure Design

Bearing Design

Deck Design

Design for Fatigue 7 Example Problems

A k l d t


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Acknowledgements

Brian Merrill, TxDOT BRG

John Holt, TxDOT BRG

Tom Schwerdt, TxDOT CST

Mike Hyzak, TxDOT BRG

Greg Turco, TxDOT BRGMichelle Romage-Chambers, TxDOT BRG

Todd Helwig, University of Texas

Karl Frank, Hirschfeld Industries

Jason Stith, Michael Baker, IncUniversity of Texas Researchers

TxDOT BRG Construction Section


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structural steel design fabrication and construction 00

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