prefabricated bridges - strategies, challenges & · pdf filedesign plans review group design...

8/4/2008
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Structures Design Plans Review GroupDesign
Conference 08 Prefabricated Bridges
Prefabricated Bridges - Strategies, Challenges & Opportunities
Roadmap: Will discuss state-of-the-art technologies related to prefabricated rapid bridge construction for both steel and
b idconcrete bridges. Prefabricated
Bridges
Thomas A. Andres P.E.Assist. State Structures
Design Engineer
Where have we been?
Where are we headed?
Prefabricated Bridges
Design Engineer

8/4/2008
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Design Engineer
Design Engineer

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Design Engineer
Why Prefabricate Bridges?FasterCan be cheaperImprove qualityMinimizes traffic impactsCan be easier to constructCa be eas e to co st uctImproves construction zone safetyMinimizes environmental impactsCan allow for more aesthetic opportunities
Design Engineer

8/4/2008
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FHWA Framework for Prefabricated B id El t d S t (PBES)Bridge Elements and Systems (PBES) Decision-Making
http://www.fhwa.dot.gov/bridge/prefab/framework.cfm
Design Engineer
Project SelectionHigh ADTFHWA Framework for Prefabricated Bridge High ADTEmergency replacement/ repairWhere conventional construction requires long detoursWhere bridge location creates problems w/ ready-mix concrete delivery
Prefabricated Bridge Elements and Systems (PBES) Decision-Making
Where time spent on the water affects labor/ insurance costsDoes site access allow for prefabricated components and heavy lifting equipment?Is casting yard available?
Design Engineer

8/4/2008
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Project Selection (cont.)Does variability within project allow forFHWA Framework for Prefabricated Bridge Does variability within project allow for formwork reuse? Will long construction times create adverse economic impacts?
Ramps to international airportBridge into major port
Prefabricated Bridge Elements and Systems (PBES) Decision-Making
Major hurricane evacuation routeConstruction finish time may affect tolling revenues
Is the bridge construction on the critical path for the project?
Design Engineer
The Devil is in the DetailsConsiderations:Co s de o s:
Fit-upDurability of connections
Design Engineer

8/4/2008
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Deck Replacements: p
Precast Deck Panel Replacements Using Near-Surface Mounted Reinforcement as a Splicing Method
Design Engineer
Design Engineer

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Saw Cut Existing Deck
Night One Lane ClosureSaw Cut Existing Deck
Design Engineer
Lift Out DamagedSection of Deck
Night One Lane Closure
Design Engineer

8/4/2008
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Lift-In FullDepth PrecastPanel w/ Strong
Night One Lane Closureg
Backs
Design Engineer
Epoxy GroutBetween Existing
Deck and New PrecastPanels
Design Engineer

8/4/2008
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Remove Strong BacksAnd Open to Traffic
Design Engineer
Night Two Lane ClosureTypical Transverse GrooveCross Section
Cut-in Transverse GroovesInstall FRP or Fiberglass Reinforcing & Epoxy Grout
Design Engineer
Near-Surface Mounted Reinforcement Splice

8/4/2008
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Short Span Prefabricated BridgesStandard Index 20350 - Prestressed Slab Units w/ -Unit thickness of
1 0 d 1 3 6 Topping New Standard to be Published in Jan -09
1-0 and 1-3
- Spans up to 50
-No Transverse Post-tensioning
-Pre-wetting of units prior to placing topping
Design Engineer
Steel Fibers Placed in Topping to Reduce Differential Shrinkage Cracking
placing topping
PRECAST SUBSTRUCTURE STANDARD FOR SMALL OVERPASS BRIDGES
Need Management Aesthetic Buy-inChoices Limited Due to Need to St d di F k
Design Engineer
Standardize Formwork Lifting Weights May Require Multiple Pier Caps Across Bridge Width

8/4/2008
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Column and Cap Elements can beElements can be PrecastWhereas Large Projects can Justify Using Project Specific Precast ShapesShapes,Small Overpass Projects Require Standardization Because of Forming Costs
Design Engineer
StandardizeShape of PierCap to Allow Reuse of Formwork

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Single ColumnPier
Two ColumnPier

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Two ColumnPier
X may vary from 5-0 to24-0 in 6 steps
Three ColumnPier
X f 5 0 t
Keep maximum lifting weight < 65 tonsX may vary from 5-0 to24-0 in 6 steps

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Variable Bridge Width
Keep maximum lifting weight < 65 tonsLifting Weights Require Multiple Pier Caps Across Bridge Width
Maximum Lifting Weight Drives Crane Requirements for ProjectDrives Overhead Costs

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StandardizeShape of PierColumn to Allow Reuse of Formwork
Circular Column Oval Column
Rebar Coupler
Allow Texture & RusticationChoices Of Column Element

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How Much to Precast?
Can Entire Bridge be Prefabricated and Rolled or Skidded into Place?
FHWA Manual on Use of Self-Propelled Modular Transporters to Remove and R l B idReplace Bridges
http://www.fhwa.dot.gov/bridge/pubs/07022/Prefabricated
Bridges
Design Engin

prefabricated bridges - strategies, challenges & · pdf filedesign plans review group design...

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