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Open Rib Steel Orthotropic Decks

Description:

This research presents an opportunity to decrease costs, increase safety, and extend the life of bridge decks.

In orthotropic decks, closed rib construction presents material efficiencies as compared to the use of open ribs and thus have comprised the majority of projects in the past several decades. However, closed ribs are more difficult to fabricate and require extensive destructive and non-destructive testing.

Based on a pilot project comparing grid decks, open rib decks, and closed rib decks, it was determined that an open rib deck would* greatly reduce costs of overall fabrication and construction* while nearly matching the weight per foot of steel for closed rib decks. Additional advantages of open ribs include:

  • Easier welding, using fillet welds instead of more difficult, expensive partial and full penetration welds

  • Easier fabrication, improving the competitiveness of domestic fabricators

  • Faster fabrication, reducing overall construction schedules and costs

  • Improved safety, providing inspection and maintenance access to all parts of the orthotropic system with no hidden areas.

Additional research is necessary to complete the comparison of open rib decks to closed rib deck fabrication for the full LRFD design truck and fatigue evaluation. The research is expected to demonstrate that rib efficiency is not the deciding factor for the ultimate cost of the structure, and that when including total design, material, and fabrication costs an open rib system will be the preferred configuration.

Objective:

This project has the potential to revolutionize how we think about steel bridge decks by demonstrating that open rib decks cost less and are safer than closed rib decks.

Benefits:

Urgency:

A large number of long span bridges in US have been in service for many years. The capacities of main load carrying members, such as trusses or main cables, have been diminishing gradually. Extending the capacities and service lives of these long span bridges is of paramount importance. One of the most effective methods is to reduce dead loads by replacing existing heavy concrete or concrete-filled grid decks with lightweight orthotropic steel decks. Thus, there is great value in improving the economy, constructability, and inspectability of steel orthotropic decks, especially in the case of domestic fabrication.

Potential Benefits: This research will demonstrate the superior economy, constructability, and inspectability of open rib orthotropic steel decks, and will provide a complete LRFD design truck and fatigue evaluation. This will enable design professionals to confidently choose open rib orthotropic steel decks for retrofit and new design of long span bridges, leading to less expensive, safer, and more inspectable steel orthotropic structures.

Related Research:

All research since the publication of AISC’s Orthotropic design guide in 1963 has focused on closed rib construction. This study will be unique in its focus on an open rib system that has already demonstrated potential success in a proof of concept study.

Tasks:

Tasks critical to the project include:

  • Cost comparison

    • Side-by-side design of open vs. closed rib orthotropic deck design

      • Evaluation of cost for fabrication and delivery
  • Proof of concept Fabrication and testing

    • Fabrication of best value specimen Laboratory fatigue life testing constant with AASHTO LRFD Level 1 Design
Implementation:

Two Phases are proposed for the study.

Phase 1

The research will involve side-by-side design of existing closed rib structures as redesigned with open ribs for a direct comparison to existing structures, a minimum of 4 designs will be completed varying floorbeam and diaphragm spacing. The designs will be evaluated by a minimum of 5 fabricators (3 North American, 2 foreign) to provide an accurate cost estimate for complete delivery of the fabricated deck including all materials, labor, inspection, and shipping costs for delivery to a hypothetical bridge location near New York, NY.

Expected final product: Summary report including cost comparisons and structural drawings

Phase 2

One fabricator will be selected to create one demonstration panel that represents the lowest cost and highest value from their Phase 1 bid (not necessarily the lowest bid). The panel will be tested in a laboratory for fatigue performance in conformance with the AASHTO Level I Design for new Orthotropic panels. Expected final product: Summary report including complete fatigue testing results and proposed details for open rib panels.

Relevance:

The Target Audience are bridge design engineers, bridge owners, and researchers. Adoption of the results will be completed through AASHTO/NSBA Task Group 16 and AASHTO SCOBS. Those currently in need of and requesting this information include Delaware River Port Authority; MTA Bridges and Tunnels, New York City Department of Transportation.

Sponsoring Committee:AFF20, Steel Bridges
Research Period:24 - 36 months
Research Priority:High
RNS Developer:Duncan Paterson
Source Info:Selected relevant research documents include:
• AASHTO LRFD Bridge Design Specifications (2014), 7th Edition with 2016 Interims
• Manual for Design, Construction, and Maintenance of Orthotropic Steel Deck Bridges, FHWA, 2012. The 2012 FHWA publication of the Orthotropic Manual brought orthotropic design to the modern era, adapting the 1963 AICS manual to include modern analysis methods. However, it is not an exhaustive document. Fabrication is included as a part of Chapter 7 in the manual, but it does not address the consequence of relative costs for open vs. closed ribs as it relates to design decisions.
• Design Manual for Orthotropic Steel Plate Deck Bridges, AISC, 1963
• Qi Ye Report to AASHTO/NSBA TG-16 joint collaboration meeting (meeting minutes, unpublished)
Date Posted:03/19/2018
Date Modified:04/20/2018
Index Terms:Bridge decks, Orthotropic, Bridge design, Bridge construction,
Cosponsoring Committees: 
Subjects    
Construction
Design
Bridges and other structures
History

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