Wind Drag Coefficients for Highway Signs and Support Structures (2023)

Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

2023 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 RESEARCH REPORT 1012 Wind Drag Coefcients for Highway Signs and Support Structures George Constantinescu University of Iowa, IIHR—Hydroscience & Engineering and Department of Civil and Environmental Engineering Iowa City, IA Asghar Bhatti University of Iowa, Department of Civil and Environmental Engineering Iowa City, IA a n d Hao Wu University of Iowa, IIHR—Hydroscience & Engineering and Department of Civil and Environmental Engineering Iowa City, IA Subscriber Categories Bridges and Other Structures • Design • Highways Research sponsored by the American Association of State Highway and Transportation Ofcials in cooperation with the Federal Highway Administration

NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM Systematic, well-designed, and implementable research is the most effective way to solve many problems facing state departments of transportation (DOTs) administrators and engineers. Often, highway problems are of local or regional interest and can best be studied by state DOTs individually or in cooperation with their state universities and others. However, the accelerating growth of highway transporta- tion results in increasingly complex problems of wide interest to high- way authorities. These problems are best studied through a coordinated program of cooperative research. Recognizing this need, the leadership of the American Association of State Highway and Transportation Officials (AASHTO) in 1962 ini- tiated an objective national highway research program using modern scientific techniques—the National Cooperative Highway Research Program (NCHRP). NCHRP is supported on a continuing basis by funds from participating member states of AASHTO and receives the full cooperation and support of the Federal Highway Administration (FHWA), United States Department of Transportation, under Agree- ment No. 693JJ31950003. The Transportation Research Board (TRB) of the National Academies of Sciences, Engineering, and Medicine was requested by AASHTO to administer the research program because of TRB’s recognized objectivity and understanding of modern research practices. TRB is uniquely suited for this purpose for many reasons: TRB maintains an extensive com- mittee structure from which authorities on any highway transportation subject may be drawn; TRB possesses avenues of communications and cooperation with federal, state, and local governmental agencies, univer- sities, and industry; TRB’s relationship to the National Academies is an insurance of objectivity; and TRB maintains a full-time staff of special- ists in highway transportation matters to bring the findings of research directly to those in a position to use them. The program is developed on the basis of research needs iden- tified by chief administrators and other staff of the highway and transportation departments, by committees of AASHTO, and by the FHWA. Topics of the highest merit are selected by the AASHTO Special Committee on Research and Innovation (R&I), and each year R&I’s recommendations are proposed to the AASHTO Board of Direc- tors and the National Academies. Research projects to address these topics are defined by NCHRP, and qualified research agencies are selected from submitted proposals. Administration and surveillance of research contracts are the responsibilities of the National Academies and TRB. The needs for highway research are many, and NCHRP can make significant contributions to solving highway transportation problems of mutual concern to many responsible groups. The program, however, is intended to complement, rather than to substitute for or duplicate, other highway research programs. Published research 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 by going to https://www.mytrb.org/MyTRB/Store/default.aspx Printed in the United States of America NCHRP RESEARCH REPORT 1012 Project 15-67 ISSN 2572-3766 (Print) ISSN 2572-3774 (Online) ISBN 978-0-309-69825-2 Library of Congress Control Number 2023931048 © 2023 by the National Academy of Sciences. National Academies of Sciences, Engineering, and Medicine and the graphical logo are trade- marks of the 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. Permission is given with the understanding that none of the material will be used to imply TRB, AASHTO, APTA, FAA, FHWA, FTA, GHSA, or NHTSA endorsement of a particular product, method, or practice. It is expected that those reproducing the material in this document for educational and not-for-profit uses will give appropriate acknowledgment of the source of any reprinted or reproduced material. For other uses of the material, request permission from CRP. NOTICE The research report was reviewed by the technical panel and accepted for publication according to procedures established and overseen by the Transportation Research Board and approved by the National Academies of Sciences, Engineering, and Medicine. The opinions and conclusions expressed or implied in this report are those of the researchers who performed the research and are not necessarily those of the Transportation Research Board; the National Academies of Sciences, Engineering, and Medicine; the FHWA; or the program sponsors. The Transportation Research Board does not develop, issue, or publish standards or speci- fications. The Transportation Research Board manages applied research projects which provide the scientific foundation that may be used by Transportation Research Board sponsors, industry associations, or other organizations as the basis for revised practices, procedures, or specifications. The Transportation Research Board; the National Academies of Sciences, Engineering, and Medicine; and the sponsors of the National Cooperative Highway Research Program do not endorse products or manufacturers. Trade or manufacturers’ names or logos appear herein solely because they are considered essential to the object of the report.

e National Academy of Sciences was established in 1863 by an Act of Congress, signed by President Lincoln, as a private, non- governmental institution to advise the nation on issues related to science and technology. Members are elected by their peers for outstanding contributions to research. Dr. Marcia McNutt is president. e National Academy of Engineering was established in 1964 under the charter of the National Academy of Sciences to bring the practices of engineering to advising the nation. Members are elected by their peers for extraordinary contributions to engineering. Dr. John L. Anderson is president. e National Academy of Medicine (formerly the Institute of Medicine) was established in 1970 under the charter of the National Academy of Sciences to advise the nation on medical and health issues. Members are elected by their peers for distinguished contributions to medicine and health. Dr. Victor J. Dzau is president. e three Academies work together as the National Academies of Sciences, Engineering, and Medicine to provide independent, objective analysis and advice to the nation and conduct other activities to solve complex problems and inform public policy decisions. e National Academies also encourage education and research, recognize outstanding contributions to knowledge, and increase public understanding in matters of science, engineering, and medicine. Learn more about the National Academies of Sciences, Engineering, and Medicine at www.nationalacademies.org. e Transportation Research Board is one of seven major programs of the National Academies of Sciences, Engineering, and Medicine. e mission of the Transportation Research Board is to provide leadership in transportation improvements and innovation through trusted, timely, impartial, and evidence-based information exchange, research, and advice regarding all modes of transportation. e Board’s varied activities annually engage about 8,000 engineers, scientists, and other transportation researchers and practitioners from the public and private sectors and academia, all of whom contribute their expertise in the public interest. e program is supported by state transportation departments, federal agencies including the component administrations of the U.S. Department of Transportation, and other organizations and individuals interested in the development of transportation. Learn more about the Transportation Research Board at www.TRB.org.

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 CRP STAFF FOR NCHRP RESEARCH REPORT 1012 Christopher J. Hedges, Director, Cooperative Research Programs Waseem Dekelbab, Deputy Director, Cooperative Research Programs, and Manager, National Cooperative Highway Research Program Sid Mohan, Associate Program Manager, Implementation and Technology Transfer, National Cooperative Highway Research Program Ahmad Abu-Hawash, Senior Program Officer Sheila Moore, Senior Program Assistant Natalie Barnes, Director of Publications Heather DiAngelis, Associate Director of Publications NCHRP PROJECT 15-67 PANEL Field of Design—Area of General Design Hussam Z. Fallaha, Virginia Department of Transportation, Richmond, VA (Chair) Harold L. Adcock, Iowa Department of Transportation, Ames, IA Xiaohua Hannah Cheng, New Jersey Department of Transportation, Trenton, NJ Bryan A. Davis, HAPCO, Bristol, VA Karl W. Larson, Virginia Department of Transportation, Richmond, VA Jean A. Nehme, FHWA Liaison Stephen F. Maher, TRB Liaison AUTHOR ACKNOWLEDGMENT Dr. James Buchholz developed the experimental procedure, including designing the force measurement apparatus and the different protocols needed to ensure the accuracy of the measurements. Mohammad Elsouht and Dr. Buchholz performed the wind-tunnel experiments. Dr. Buchholz also provided the infor- mation in Appendix A on the experimental facility and instrumentation used to conduct the experiments and to estimate the drag coefficients for validation of the numerical model.

NCHRP Research Report 1012: Wind Drag Coefficients for Highway Signs and Support Structures presents the results of a comprehensive project to estimate wind loads acting on highway signs and their support structures. The research made use of numerical simulations and wind-tunnel testing. The report presents a list of recommended design specification revisions for consideration by the American Association of State Highway and Transporta- tion Officials (AASHTO) in the next update of the AASHTO Load and Resistance Factor Design Specifications for Structural Supports for Highway Signs, Luminaires, and Traffic Signals (LRFDLTS-1). The research findings will be used by structural engineers respon- sible for designing and evaluating highway sign support structures at state departments of transportation. The proposed new wind load estimation methods will give engineers a better understand- ing of the behavior of sign support structures subjected to wind loading. New wind drag coefficients that account for sign geometry and placement, support structure type, wind direction, and other important variables will result in more accurate wind load estimation and better design. Under NCHRP Project 15-67, the University of Iowa research team was asked to develop methods for estimating wind loads and to propose updates to the AASHTO LRFDLTS-1 in order to incorporate new wind drag coefficients. The research team performed three- dimensional numerical simulations to estimate the pressure, stress distributions, and wind loads. Subsequently, the wind loads were used to calculate the drag coefficients. The results from the numerical simulations were validated by comparing wind load predictions and the corresponding drag coefficients with those measured experimentally in wind tunnels and the field. New wind-tunnel testing was performed to supplement data available from past testing. The research team illustrated the proposed methods in a series of design examples presented in the report. NCHRP Research Report 1012 documents the entire research effort. F O R E W O R D By Ahmad Abu-Hawash Staff Officer Transportation Research Board

1 Summary 6 Chapter 1 Introduction and Research Approach 6 1.1 Problem Description and Problem Statement 7 1.2 Knowledge Gaps 9 1.3 Research Objectives 9 1.4 Research Approach 11 1.5 Research Tasks 13 Chapter 2 Findings 13 2.1 Drag Coefficients for Highway Signs 13 2.1.1 Preliminary Simulations 17 2.1.2 Validation for Isolated Rectangular Signs Using Wind-Tunnel Data 18 2.1.3 Validation for Isolated Rectangular Signs Using Field Data 19 2.1.4 Validation for Rectangular Signs that Include an Add-on Sign, Using Wind-Tunnel Data 20 2.1.5 Validation for Side-by-Side Rectangular Signs, Using Wind-Tunnel Data 23 2.1.6 Isolated Rectangular Highway Signs 28 2.1.7 Rectangular Highway Signs that Include an Add-On Sign 30 2.1.8 Side-by-Side Highway Signs 34 2.1.9 Isolated Highway Signs Placed on a Monotube Support Structure 35 2.1.10 Isolated Highway Signs Placed on a Truss Support Structure 43 2.1.11 Isolated Highway Signs Placed on a Grade Separation Structure 53 2.1.12 Side-by-Side Highway Signs Placed on a Monotube Support Structure 55 2.1.13 Side-by-Side Highway Signs Placed on a Truss Support Structure 58 2.2 Wind Loads on Sign Support Structures 58 2.2.1 Drag Coefficients for Isolated and Back-to-Back Members of Infinite Length 61 2.2.2 Drag Coefficients for Finite-Length Members 63 2.2.3 Wind Loads on Monotubes Supporting Highway Signs 68 2.2.4 Wind Loads on Trusses Supporting Highway Signs 87 Chapter 3 Proposed Methods for Estimating Wind Drag Coefficients and the Associated Wind Loads 87 3.1 Overall Procedure to Determine Wind Loads 88 3.2 Wind Drag Coefficients for Estimation of Wind Loads Applied Normal to the Highway Signs 88 3.2.1 Base Wind Drag Coefficient for an Isolated Rectangular Sign, Cd0 89 3.2.2 Wind Drag Coefficient Cd for a Highway Sign 91 3.2.3 Wind Drag Coefficient Cd for a Sign Mounted on a Grade Separation Structure C O N T E N T S

92 3.2.4 Wind Drag Coefficient Cd for Wind Acting Perpendicular to the Lateral Faces of Thick Signs 92 3.2.5 Wind Drag Coefficient Cd for Multiple Signs on a Vertical Column 93 3.3 Wind Drag Coefficients for Members of a Sign Support Structure with Wind Applied Normal to the Plane of the Sign Support Structure 93 3.3.1 Base Wind Drag Coefficient Cd0 for Circular Members 93 3.3.2 Base Wind Drag Coefficient Cd0 for L-Shaped Members 94 3.3.3 Wind Drag Coefficient Cd for Monotube Support Structures 95 3.3.4 Wind Drag Coefficient Cd for Chord Members of Truss Structures 97 3.3.5 Wind Drag Coefficient Cd for Secondary Members of Truss Structures 98 3.3.6 Wind Drag Coefficients Cd for Gusset Plates in Truss Structures 99 3.4 Wind Drag Coefficient for Members of Sign Support Structure with Wind Applied Transverse to the Plane of Sign Support Structure 99 3.5 Wind Drag Coefficient for Vertical Columns Supporting Monotubes and Trusses 101 Chapter 4 Conclusions 101 4.1 Applicability of Results to Improving Current Practice 102 4.2 Conclusions and Recommendations 104 4.3 Suggested Research 106 References A-1 Appendix A Wind-Tunnel Experimental Facility and Instrumentation B-1 Appendix B Design Examples