PMSS Project Details

Project ID:	FHWA-PROJ-08-0024
Project Name:	Improved Analytical Techniques for Historic Covered Bridges
Status:	Programmed
Contact:	Last Name: Duwadi First Name: Sheila R Telephone: 202-493-3106 E-mail: sheila.duwadi@dot.gov
Organization:	Federal Highway Administration - Turner-Fairbank Highway Research Center (TFHRC)
Office:	Office of Infrastructure Research and Development
Team:	Hazard Mitigation Team
Roadmap/Focus area(s):	Historic Preservation Infrastructure Research and Technology Strategic Plan and Roadmap
Project Findings:	Data not yet available
Project Description:	Covered bridges are complex structures to analyze as they are constructed with timber, which is highly variable and with designs that are redundant with material properties influencing the behavior. When combined, it is easy to understand why some analyses conclude that some bridges shouldn’t even be standing. As noted in FHWA publication FHWA-HRT-04-098, Covered Bridge Manual, there are inconsistencies with the assumptions of the traditional, simple, static analysis of trusses. Generally in most covered bridge analyses, it is assumed that the primary truss elements behave in a manner similar to steel trusses. However, the fact that timber trusses are more significant means that covered bridge members tend to behave more like frame members (i.e., have both axial and bending forces) than as truss members (i.e., axial forces only). Some of the complexities involve eccentric connections at the joints, various load paths from the stringers and floor beams to the truss, uncertainty of the connections between the trusses and the arches, and interaction between the trusses and their housing. Most engineers are relatively comfortable with completing a standard truss analysis but are unprepared to complete a sophisticated 2-D or 3-D frame analysis. As such, much simplified and inaccurate analyses are often performed with overly conservative safety factors applied to account for known inaccuracies. In addition, many covered bridge trusses consist of multiple kingpost trusses superimposed with an arch that has complex connectively between the various elements. An accurate analysis of such systems clearly requires sophisticated analysis techniques with which most engineers are not familiar. Because of the issues discussed above, it is clear that engineers need assistance with the analysis and modeling of covered bridges. This is especially true as they conduct repair and load rating calculations.
Laboratories:	Not Applicable
Start Date:	September 8, 2008
End Date:	September 30, 2013
Funding Amount:	$130,000.00
FHWA Program Name:	National Historic Covered Bridge Preservation Program
Goals:	This study will develop guidelines for improving the analysis of covered bridges.
Project Type:	Offsite
Background Information:	Data not yet available
Test Methodology:	It is envisioned this will be done through collection of specific behavior data such that modeling geometries and configurations can be optimized and validated. Specific areas of interest include: intersection/ interconnection of lattice members, impact of classic arch behavior, behavior and interaction of bolster beams, floor systems, distribution beams, influence of bracing, and others. To collect the needed behavioral information, a number of covered bridges need to be instrumented and response data (e.g., strain, deflection, etc.) collected while controlled loads cross the bridge. This data is necessary to develop and calibrate modeling methodologies.
Other Information:	Funding is $130,000 (Federal Highway Administration) + $39,000 (Forest Service—Forest Products Laboratory)
Partners:	Data not yet available
More Information URL(s):
Fieldtest:	Data not yet available
Expected Benefits:	Data not yet available
Deliverables:	Name: Analytical Techniques for Historic Covered Bridges Product Type(s): Research report, Techbrief Description: The report will provide guidance on analyzing timber trusses for use by designers. Audiences: Researchers, Bridge design professionals, Federal Turner-Fairbank Highway Research Center staff, State highway agencies Secondary Audiences:
Related URL(s):
FHWA Topics:	Roads and Bridges--Design Roads and Bridges--Structures
TRT Terms:	covered bridges trusses
FHWA Disciplines:	Design Structures
Subject Areas:	Bridges and other structures History