MPC
Research Projects (2009-10)

Identifying Number

MPC-338

Project Title

Use of Wind Power Maps to Establish Fatigue Design Criteria for Traffic-Signal and High Mast Poles, Phase II

University

University of Wyoming

Project Investigators

Dr. Jay A. Puckett, P.E.
V.O. Smith Professor
University of Wyoming, Civil and Architectural Engineering Department
Phone: (307)760-5919
Fax: (307)766-2221
E-mail: puckett@uwyo.edu

Dr. Michael G. Barker, P.E.
Professor
University of Wyoming, Civil and Architectural Engineering Department
Phone: (307)766-2916
Fax: (307)766-2221
E-mail: barker@uwyo.edu

Description of Project Abstract

Design criteria for traffic-signal and luminaire structures relies upon fatigue load criteria that are producing significant increases in structure and joint size and cost. The cognizant design specification is the Fifth Edition of the AASHTO Luminaire and Traffic Signal Specification (2009). See Figure 1 below for examples of large connections. Without the fatigue requirements, these connections would be significantly different.

Colorado DOT Box	Colorado DOT Plate with clamps and gussets	Wyoming DOT Stiffened Box

Figure 1. Three Typical Large Connections

Connection designs, specifically in the windy plains, coastal and mountain states, are significantly affected because of higher than average wind speeds. A new approach (or significant refinements in the present) is required to better define where fatigue design is truly required.

Phase I illustrated that the use of Wind Resource Maps (power maps) for traffic signal structures shows significant promise in predicting fatigue damage and locations where fatigue design is critical. Additionally, and just as important, where fatigue design is not critical and, therefore, more economical joints could be used.

Phase II work will focus on obtaining updated inspection data from the Phase I states considered and including more states in the database. In short, more data are necessary in order to develop the seminal work and write guidelines that could be considered by the AASHTO T12 Signs and Luminaires Committee for inclusion in the specifications.

Project Objectives

Validate the use of wind power maps to predict fatigue damage in traffic signal poles using DOT fatigue inspection data as the basis. Suggest specification modifications based upon the findings for traffic-signal and high-mast poles.

Project Approach/Methods

The following tasks will be performed:

1. Collect more inspection data to expand the database from state and local DOTs in windy/mountainous areas and in non-windy areas.
2. Correlate the inspection data with the wind power in each area. Independently examine fatigue predictors.
3. Draw conclusions regarding the application of wind power maps for thefatigue design of signal and sign structures.
4. Write draft specifications.
5. Submit final report.
6. Submit a technical paper to the Transportation Research Board.

MPC Critical Issues Addressed by the Research

#6 Work Zone Safety
#11 Traffic Operations and Management
#18 Economic Analysis of Investments and Impacts

Contribution/Potential Applications of Research

Overview: Connection details within traffic signal and sign structures are cracking and several failures have occurred. This issue has been the subject of several investigations and the AASHTO specification for design of these structures has been modified to address fatigue.

Vibrations in traffic signal structures are initiated by several wind-induced phenomena. Fatigue damage is cumulative and is a function of wind characteristics, including the velocity and time over which the wind is present. Wind power density spectra developed for electric power generation planning were correlated to signal pole inspection data in Phase I. The correlation shows promise, see Figure 2.

Prior to the Phase I work, no research has combined the wind power spectra developed for power generation with the fatigue problem. Correlation with wind power could lead to criteria for specification-based design referencing existing wind-power maps developed by DOE to locate generators (see http://rredc.nrel.gov/wind/pubs/atlas/). The research is novel.

Wind Power as a Predictor: Because the factors desired for wind power production are similar to those believed to cause wind-induced vibrations in traffic-signal structures, a correlation between wind power classes and incidences of fatigue cracks in traffic signal structures has have a significant impact on economy of signal and light structures. More data are necessary to accomplish this goal.

Phase I work illustrated:

• Orientation of the signal with respect to the dominate wind direction is a predictor.
• Age of pole in-service could help guide inspection frequency (failures are early (3yrs) or late after 12yrs).
• High-mast pole failures are not directly related to wind power but rather the complete velocity spectra in the area. A more detailed approach will be necessary as the aeroelastic load response is different than for signal poles (vortex shedding in high masts).
• Connect type and details are important.
• Manufacturers are strongly correlated to connection type.
• Mast-arm length is not a strong predictor.
• Wind power class is a strong predictor, see Figure 2.

Figure 2 suggests that a correlation exists between wind power density and fatigue crack incidences. The highest percentages of crack occurrences are typically found in regions with a wind class region of 3 or higher. This figure represents approximately 2500 structures - the weighted mean values are shown in the figure (dots).

Since the Phase I project began, several more states have inspected their traffic-signal and high-mast inventories. Importantly, states are located in a variety of wind power regions. Summary -- The phase I work definitely confirmed the research hypothesis; however more data are necessary for implementation.

Research Methodology: More data from several DOTs are required in order to validate this approach to the level of confidence required for specification adoption. The inspection data from state and local DOTs located in windy areas and non-windy areas will be obtained.

The additional data will be quantified in a manner similar to Phase I. These data will also provide records based upon independent inspections and procedures in case there is any bias particular to specific DOTs. Data will be studied as an aggregate and also by segregating the data by agency and region.

Technology Transfer Activities

The authors hope to present this work at TRB and/or in a journal. They will also report to the AASHTO Subcommittee on Bridges and Structures (T-12) that helps to maintain the AASHTO Specifications associated with the design of ancillary structures.

Time Duration

July 1, 2009 through June 30, 2010

Total Project Cost

$99,943.00

MPC Funds Requested

$49,535.00

TRB Keywords

Fatigue, vortex shedding, structural engineering, wind power