Development and Calibration of AASHTO LRFD Specifications for Structural Supports for Highway Signs, Luminaires, and Traffic Signals (2014)

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N A T I O N A L C O O P E R A T I V E H I G H W A Y R E S E A R C H P R O G R A M NCHRP REPORT 796 Development and Calibration of AASHTO LRFD Specifications for Structural Supports for Highway Signs, Luminaires, and Traffic Signals Jay A. Puckett BridgeTech, inc. Laramie, WY Michael G. Garlich collins engineers, inc. Chicago, IL Andrzej (Andy) Nowak Auburn, AL Michael Barker Laramie, WY Subscriber Categories Bridges and Other Structures TRANSPORTAT ION RESEARCH BOARD WASHINGTON, D.C. 2014 www.TRB.org Research sponsored by the American Association of State Highway and Transportation Officials in cooperation with the Federal Highway Administration

NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM Systematic, well-designed research provides the most effective approach to the solution of many problems facing highway administrators and engineers. Often, highway problems are of local interest and can best be studied by highway departments individually or in cooperation with their state universities and others. However, the accelerating growth of highway transportation develops increasingly complex problems of wide interest to highway authorities. These problems are best studied through a coordinated program of cooperative research. In recognition of these needs, the highway administrators of the American Association of State Highway and Transportation Officials initiated in 1962 an objective national highway research program employing modern scientific techniques. 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Published reports of the NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM are available from: Transportation Research Board Business Office 500 Fifth Street, NW Washington, DC 20001 and can be ordered through the Internet at: http://www.national-academies.org/trb/bookstore Printed in the United States of America NCHRP REPORT 796 Project 10-80 ISSN 0077-5614 ISBN 978-0-309-30818-2 Library of Congress Control Number 2014954483 © 2014 National Academy of Sciences. All rights reserved. COPYRIGHT INFORMATION Authors herein are responsible for the authenticity of their materials and for obtaining written permissions from publishers or persons who own the copyright to any previously published or copyrighted material used herein. Cooperative Research Programs (CRP) grants permission to reproduce material in this publication for classroom and not-for-profit purposes. 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C O O P E R A T I V E R E S E A R C H P R O G R A M S AUTHOR ACKNOWLEDGMENTS NCHRP Project 10-80 is a diverse structural engineering project with topic areas ranging from aero-elastic vibrations, to steel and aluminum fatigue, to wide-ranging material types of steel, aluminum, concrete, wood, and fiber-reinforced plastics. The team wishes to thank the 36 DOT agencies who took time to complete its survey. Their input was very helpful. The collaboration of the research team is especially noted, as without their specific expertise and years of practical knowledge, this project would not have been possible. CRP STAFF FOR NCHRP REPORT 796 Christopher W. Jenks, Director, Cooperative Research Programs Christopher Hedges, Manager, National Cooperative Highway Research Program Waseem Dekelbab, Senior Program Officer Danna Powell, Senior Program Assistant Sheila A. Moore, Program Associate Eileen P. Delaney, Director of Publications Doug English, Editor NCHRP PROJECT 10-80 PANEL Area: Materials and Construction—Specifications, Procedures, and Practices Loren R. Risch, Kansas DOT, Topeka, KS (Chair) Joseph M. Bowman, Hapco (retired), Abingdon, VA Timothy Bradberry, Texas DOT, Austin, TX Xiaohua Hannah Cheng, New Jersey DOT, Trenton, NJ Cabrina Marie Dieters, Tennessee DOT, Nashville, TN Carl J. Macchietto, Valmont Industries, Inc., Valley, NE Julius F. J. Volgyi, Jr., (retired) Richmond, VA Justin M. Ocel, FHWA Liaison Stephen F. Maher, TRB Liaison

F O R E W O R D By Waseem Dekelbab Staff Officer Transportation Research Board This report presents proposed AASHTO LRFD specifications for structural supports for highway signs, luminaires, and traffic signals. The proposed specifications are arranged in three divisions: (1) design according to LRFD methodology; (2) construction, including material specifications, fabrication, and installation; and (3) asset management, including inventory, inspection, and maintenance. In addition, the report provides details regarding the reliability calibration process and results. The material in this report will be of immediate interest to highway design engineers. In June 2000, AASHTO and the Federal Highway Administration agreed on an implemen- tation plan for the design of highway structures utilizing the load and resistance factor design (LRFD) methodology. As part of that agreement, all new culverts, retaining walls, and other standard structures on which states initiate preliminary engineering after October 1, 2010, shall be designed according to the LRFD specifications. The current edition of the AASHTO Standard Specifications for Structural Supports for Highway Signs, Luminaires, and Traffic Sig- nals is generally based on the working stress design method. Also, the design, construction, and inspection languages are intertwined in the specifications and commentary, resulting in a document that is cumbersome and difficult to follow. The probability-based specification (i.e., LRFD) will result in structures that are based on a more uniform set of design criteria. The specifications will promote quality construction and fabrication practices and will address the current shortcomings of inspection and maintenance of these ancillary structures. The combination of these efforts will allow agencies to better design, manage, and maintain these transportation assets to improve the safety and reliability of structural supports nation- wide. Agencies will be in a better position to meet the LRFD implementation plan, and the provisions will facilitate the design, construction, inspection, and maintenance of structural supports for highway signs, luminaires, and traffic signals. Research was performed under NCHRP Project 10-80 by BridgeTech, Inc. The objective of this research was to develop proposed AASHTO LRFD specifications for structural sup- ports for highway signs, luminaires, and traffic signals. Additionally, 16 comprehensive design examples were developed to illustrate the application of the new specifications. The report includes the Research Report, which documents the entire research effort, and the Calibration Report (i.e., Appendix A). Appendix B: AASHTO LRFD Specifications will be published by AASHTO. Other appendices are not published but are available on the TRB website. These appendices are titled as follows: • Appendix C: Design Examples, • Appendix D: Survey Results, and • Appendix E: Fatigue Resistance Comparisons.

N O M E N C L A T U R E A N D D E F I N I T I O N S Nomenclature AA—Aluminum Association. ACI—American Concrete Institute. AISC—American Institute for Steel Construction. Arm—A cantilevered member, either horizontal or sloped, which typically attaches to a pole. ASD—Allowable stress design. AWS—American Welding Society. Bridge Support—Also known as span-type support; a horizontal or sloped member or truss supported by at least two vertical supports. Cantilever—A member, either horizontal or vertical, supported at one end only. CMS—Changeable message sign (also known as a dynamic message sign or a variable message sign). Collapse—A major change in the geometry of the structure rendering it unfit for use. Component—Either a discrete element of the structure or a combination of elements requiring individual design consideration. Design Life—Period of time on which the statistical derivation of transient loads is based: 25 years for the specifications in this report. Designer—The person responsible for design of the structural support. Design—Proportioning and detailing the components and connections of a structure. Ductility—Property of a component or connection that allows inelastic response. Engineer—Person responsible for the design of the structure and/or review of design-related field submittals such as erection plans. Evaluation—Determination of load-carrying capacity or remaining life of an existing structure. Extreme Event Limit States—Limit states relating to events such as wind, earthquakes, and vehicle collisions, with return periods in excess of the design life of the structure. Factored Load—Nominal loads multiplied by the appropriate load factors specified for the load combination under consideration. Factored Resistance—Nominal resistance multiplied by a resistance factor. Force Effect—A deformation, stress, or stress resultant (i.e., axial force, shear force, torsional, or flexural moment) caused by applied loads or imposed deformations. FRC—Fiber-reinforced composite. FRP—Fiber-reinforced polymer. High-Level Lighting—Also known as high-mast lighting; lighting provided at heights greater than 55 ft., typically using four to 12 luminaires. High-Mast High-Level Tower—Another description for a pole-type high-level luminaire support. High-Mast Luminaire Tower—Truss-type or pole-type tower that provides lighting at heights greater than 55 ft., typically using four to 12 luminaires. Limit State—A condition beyond which the structure or component ceases to satisfy the provi- sions for which it was designed. Load and Resistance Factor Design (LRFD)—A reliability-based design methodology in which force effects caused by factored loads are not permitted to exceed the factored resistance of the components.

Load Effect—Same as force effect. Load Factor—A statistically based multiplier applied to force effects accounting primarily for the variability of loads, the lack of accuracy in analysis, and the probability of simultaneous occurrence of different loads, but also related to the statistics of the resistance through the calibration process. LRFD—Load and resistance factor design. LRFD Bridge Construction Specifications—LRFD construction specifications for highway bridges. LRFD Bridge Design Specifications (BDS)—LRFD specifications for design of highway bridges. LRFD-LTS—New LRFD specifications for luminaires, traffic signals, and signs. LTS—Luminaires, traffic signals, and signs. Luminaire—A complete lighting unit consisting of a lamp or lamps together with the parts designed to provide the light, position and protect the lamps, and connect the lamps to an electric power supply. Mast Arm—A member used to hold a sign, signal head, or luminaire in an approximately horizontal position. Mean Recurrence Interval (MRI)—The expected time period for the return of a wind speed that exceeds the basic wind speed. The annual probability of exceeding the basic wind in any 1-year period is the reciprocal of this value. Member—A component that is positioned between two physical joints of a structure (or LTS). Model—An idealization of a structure for the purpose of analysis. Monotube—A support that is composed of a single tube. Multiple-Load-Path Structure—A structure capable of supporting the specified loads following loss of a main load-carrying component or connection. NHI—National Highway Institute. Nominal Resistance—The resistance of a component or connection to force effects, as indicated by the dimensions specified in the contract documents and by permissible stresses, deforma- tions, or specified strength of materials. Overhead Sign—A sign mounted over a roadway or near it, and elevated with respect to a travel way. Owner—The person or agency having jurisdiction for the design, construction, and maintenance of the structural support. Pole Top—A descriptive term indicating that an attachment is mounted at the top of a structural support, usually pertaining to one luminaire or traffic signal mounted at the top of a pole. Pole—A vertical support that is often long, relatively slender, and generally rounded or multisided. Rehabilitation—A process in which the resistance of the structure is either restored or increased. Resistance Factor—A statistically based multiplier applied to nominal resistance accounting primarily for variability of material properties, structural dimensions and workmanship, and uncertainty in the prediction of resistance, but also related to the statistics of the loads through the calibration process. Roadside Sign—A sign mounted beside the roadway on a single support or multiple supports. SCOBS—AASHTO’s Subcommittee on Bridges and Structures SEI—Structural Engineering Institute (within ASCE). Service Life—The period of time that the structure is expected to be in operation. Service Limit States—Limit states relating to stress, deformation, and concrete cracking under regular operating conditions. Sign—A device conveying a specific message by means of words or symbols, erected for the purpose of regulating, warning, or guiding traffic. Span Wire—A steel cable or strand extended between two poles, commonly used as a horizontal support for signs and traffic signals. STD—Standard specifications.

Strength Limit States—Limit states relating to strength and stability during the design life. Structural Support—A system of members used to resist load effects associated with self-weight, attached signs, luminaires, traffic signals, and any other applicable loads. Structure—The same as a structural support. T-12—SCOBS technical committee for structural supports for signs, luminaires, and traffic signals. Traffic Signal—An electrically operated traffic control device by which traffic is regulated, warned, or directed to take specific actions. Truss—A structural system composed of a framework that is often arranged in triangles. Variable Message Sign—A sign that illustrates a variable message (see CMS). XML—Extensible markup language. Definitions Rn = nominal resistance V300 = 300-year design wind speed (ASCE/SEI 7-10) V700 = 700-year design wind speed (ASCE/SEI 7-10) V1700 = 1,700-year design wind speed (ASCE/SEI 7-10) V50 = 50-year design wind speed (ASCE/SEI 7-05) Q = random variable representing load R = random variable representing strength CovR = coefficient of variation for strength variable R lR = bias factor for strength variable R CovQ = coefficient of variation for load variable Q lQ = bias factor for strength variable Q CovKz = coefficient of variation for design pressure variable Kz lKz = bias factor for press variable Kz CovCd = coefficient of variation for design pressure variable Cd lCd = bias factor for pressure variable Cd CovG = coefficient of variation for design pressure variable G lG = bias factor for pressure variable G f = phi factor gD1 = dead load design load factor (used in conjunction with dead + wind case) gD2 = deal load design load factor (dead-load–only case) gW = wind load design load factor OSF = (wind) overstress factor Shape Factor = SF Z S = (plastic moment/yield moment) Ilow = importance factor (low) Imed = importance factor (med) Ihigh = importance factor (high)

C O N T E N T S Appendices C through E are posted on the TRB website and can be found by searching for NCHRP Report 796 at www.TRB.org. Appendix B: AASHTO LRFD Specifications will be published by AASHTO. 1 Summary 3 Chapter 1 Introduction and Research Approach 3 Introduction 3 Organization 3 Contents of the LRFD-LTS Specifications 5 Chapter 2 Findings 5 Agency Survey 5 Literature 5 U.S. and International Specifications 5 Research Papers and Reports 5 Textbooks 5 Resistance Sections 5 Fabrication, Materials, and Detailing (Section 14) 8 Construction (Section 15) 8 Inspection and Reporting (Section 16) 8 Asset Management (Section 17) 12 Chapter 3 Interpretation, Appraisal, and Application 12 Load Models and Calibration 12 LRFD Limit-State Format 12 Dead Load Parameters 12 Wind Load Model 15 Wind Load Information from ASCE/SEI 7-10 and Available Literature 15 Statistical Parameters for Wind Load Variables 15 Statistical Parameters of Resistance 17 LRFD Reliability Analysis 17 Flexural Resistance 17 Load 19 Reliability Indices 19 Implementation 20 ASD Reliability Analysis 21 Resistance 22 Implementation 23 Calibration and Comparison 23 Implementation 23 Setting Target Reliability Indices 25 Implementation into Specifications

25 Computed Reliability Indices 26 Sensitivities 26 Scope of Appendix A 26 Calibration Summary 28 Examples 32 Chapter 4 Conclusions and Suggested Research 32 Conclusions 32 Suggested Research 32 Follow-up Tasks 34 Bibliography A-1 Appendices A-1 Appendix A: Calibration Report Note: Photographs, figures, and tables in this report may have been converted from color to grayscale for printing. The electronic version of the report (posted on the web at www.trb.org) retains the color versions.