Composite Bridge Decking, Final Project Report
Project Description and Objectives
FHWA's Highways for LIFE Technology Partnerships program was established “to work with the highway construction industry to accelerate the adoption of promising innovations… to refine or improve existing equipment, materials, practices, or processes that have been demonstrated but have not become adopted as routine or common practice in the highway industry…. and to fund innovations that have been developed to a prototype and require further refinement, testing, evaluation and first application in a real-world setting before they would be available for purchase, or conventional practice.”1 The Composite Bridge Decking project (originally called Composite Bridge Decking for Moveable Bridges) was selected for funding under the Technology Partnerships Program to build on 7 years of applied research that had been conducted at the University at Buffalo for the New York State Department of Transportation.2 Although a hybrid material design had been proven technically in a laboratory environment, the prototype used for testing was made using a hand lay-up method, which is not particularly cost-effective. The purpose of the Composite Bridge Decking project is to show that a high-quality deck section meeting all American Association of State Highway and Transportation Officials (AASHTO) service requirements can be produced economically.
There is a need for lightweight decks on moveable bridges, historic bridges, and other structures that were not designed for heavy concrete decks. Many existing bridges were built with open steel grating, but long-term durability of the deck has been a maintenance problem because of corrosion and fatigue cracking. Lack of a solid surface can also contribute to the deterioration of the superstructure itself because steel is exposed to the elements, road salt, and sandy debris that can trap moisture.
Although many of the more than 100 fiber-reinforced polymer (FRP) composite decks/structures that are in service were used because of their light weight, widespread use of these systems has not been attained for a variety of reasons. Most have been proprietary in nature, which is generally not attractive to bridge owners. Public sector purchasing regulations were written to foster competition with the goal of cost reduction. Proprietary systems do not conform to this model, so adoption of the technology may be hindered. There also have been some troubles with bonded wearing surfaces cracking, spalling, and delaminating.
The product intent is a solid-surface, lightweight system that is corrosion resistant, fatigue resistant, modular and easy to install, one that provides good skid resistance, low noise levels, is cyclist friendly, is repairable, and requires little maintenance while in service.
This document summarizes the final deck design that was derived from the cost sharing provided by the project team and FHWA. Through finite element analysis, validated by material, component, and system testing, this design has been shown to be capable of functioning in a wide range of applications, with a support spacing of up to 5 feet. The system is adaptable to different support conditions, so strength and stiffness requirements can be met with just minor adjustments to the material architecture. The design yields a generous factor of safety for strength, as well as a controlled failure mode. At the same time, the deck is sufficiently stiff to avoid any serviceability issues related to local deflections, including the wearing surface cracking that has occurred in the past. The project began July 15, 2010, and the deck was installed on a bridge in Allegany County, New York, during August 2012. Appendix A provides lessons learned from Allegany County’s perspective.
Project Scope and Tasks
A wide range of bridges could benefit from the deck discussed in this report. Although variations of the deck can be used on almost any bridge, the project scope originally targeted moveable bridges, since the demand for a lightweight system is most pressing in that situation. Other bridges that would benefit from a lightweight composite deck are historic bridges that were not designed for a heavy deck. Bridges that are weight restricted because of excessive dead load and those whose load-carrying capacity is diminished due to rust and section loss also would benefit from this type of deck. Sites with poor soil conditions may also benefit.
Project tasks that contributed to this outcome included:
- Material evaluation and selection.
- Development of appropriate fabrication methods and installation details.
- Testing of subcomponents and full-scale structural panels to validate finite models.
- Installation and evaluation of the installation procedures.
Specific tasks are listed in table 1.
|2||Preliminary Design||Define Performance Objectives|
|3||Set Deck Geometrics|
|4||Create Finite Element Model|
|6||Design Review I (Preliminary Design Review)|
|8||Qualify Tube Subcomponents|
|9||Consider Alternative Assembly Methods|
|10||Fabricate & Test 3-ft by 10-ft Test Panels|
|13||Design Review II (After-Test Review)|
|14||Final Design||Set Final Design, Materials & Assembly Method|
|15||Design Review III (Final Design Review)|
|16||Update Finite Element Model|
|17||Field Installation||Fabricate "Proof of Concept" Panels|