AASHTO LRFDLTS INTERIM-2017 Interim Revisions to the LRFD Specifications for Structural Supports for Highway Signs Luminaires and Traffic Signals (First Edition).pdf

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1、 2016 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.ISBN: 978-1-56051-655-2 Pub Code: LRFDLTS-1-I1-OL American Association of State Highway and Transportation Officials 444 North Capitol Street, NW, Suite 2

2、49 Washington, DC 20001 202-624-5800 phone/202-624-5806 fax www.transportation.org 2016 by the American Association of State Highway and Transportation Officials. All rights reserved. Duplication is a violation of applicable law. 2016 by the American Association of State Highway and Transportation O

3、fficials.All rights reserved. Duplication is a violation of applicable law.2017 INTERIM REVISIONS TO THE LRFD STRUCTURAL SUPPORTS INSTRUCTIONS AND INFORMATION FOR HIGHWAY SIGNS, LUMINAIRES, AND TRAFFIC SIGNALS iii 2017 INTERIM REVISIONS INSTRUCTIONS AND INFORMATION General AASHTO has issued interim

4、revisions to the LRFD Structural Supports for Highway Signs, Luminaires, and Traffic Signals, First Edition (2015). This packet contains the revised pages. They are designed to replace the corresponding pages in the book. Affected Articles Underlined text indicates revisions that were approved in 20

5、16 by the AASHTO Highways Subcommittee on Bridges and Structures. Strikethrough text indicates any deletions that were likewise approved by the Subcommittee. A list of affected articles is included below. All interim pages are displayed on a pink background to make the changes stand out when inserte

6、d in the first edition binder. They also have a page header displaying the section number affected and the interim publication year. Please note that these pages may also contain nontechnical (i.e., editorial) changes made by AASHTO publications staff; any changes of this type will not be marked in

7、any way so as not to distract the reader from the technical changes. 2017 Changed Articles SECTION 3: LOADS 3.8.7 C3.8.7 SECTION 5: STEEL DESIGN 5.3 5.12.1 C5.12.1 SECTION 10: SERVICEABILITY REQUIREMENTS 10.4.2.1 C10.4.2.1 SECTION 11: FATIGUE DESIGN 11.5.1 11.7.2 C11.9.3 C11.9.3.1 SECTION 12: BREAKA

8、WAY SUPPORTS 12.1 C12.1 APPENDIX B: DESIGN AIDS B.2 2016 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.2017 INTERIM REVISIONS TO THE LRFD STRUCTURAL SUPPORTS INSTRUCTIONS AND INFORMATION FOR HIGHWAY SIGNS,

9、LUMINAIRES, AND TRAFFIC SIGNALS ivTHIS PAGE LEFT BLANK INTENTIONALLY 2016 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.2017 INTERIM REVISIONS TO THE LRFD STRUCTURAL SUPPORTS FOR HIGHWAY SIGNS, LUMINAIRES,

10、AND TRAFFIC SIGNALS SECTION 3: LOADS 3-173.8.6Gust Effect Factor G C3.8.6 The gust effect factor, G, shall be taken as a minimum of 1.14. G is the gust effect factor and it adjusts the effective velocity pressure for the dynamic interaction of the structure with the gust of the wind. Information pre

11、sented in ASCE/SEI 7-10 states that if the fundamental frequency of a structure is less than one Hz or if the ratio of the height to least horizontal dimension is greater than 4, the structure should be designed as a wind-sensitive structure. Thus, virtually all structures addressed by these Specifi

12、cations should be classified as wind-sensitive structures based on the height to least horizontal dimension ratio. It is not appropriate to use a nonwind-sensitive gust effect factor, G, for the design of sign, luminaire, and traffic signal structures. Special procedures are presented in the comment

13、ary of ASCE/SEI 7 for the calculation of the gust effect factor for wind-sensitive structures. The ASCE/SEI 7 calculation procedure requires reasonable estimates of critical factors such as the damping ratio and fundamental frequency of the structure. These factors are site and structure dependent.

14、Relatively small errors in the estimation of these factors result in significant variations in the calculated gust effect factor. Therefore, even though sign, luminaire, and traffic signal support structures are wind sensitive, the benefits of using the ASCE/SEI 7 gust effect factor calculation proc

15、edure do not outweigh the complexities introduced by its use. If the designer wishes to perform a more rigorous gust effect analysis, the procedures presented in ASCE/SEI 7 may be used with permission of the Owner. 3.8.7Drag Coefficients C d C3.8.7 The wind drag coefficient, Cd, shall be determined

16、from Table 3.8.7-1. Cv shall be taken as: Cv = 0.8 for the Extreme Limit State Cv= 1.0 otherwise The wind drag coefficients in Table 3.8.7-1 were established based upon the work of several research projects as noted in the footnotes. Some coefficients are a strong function of Reynolds number. The te

17、rm CvVd is a simplified form of Reynolds using units convenient for LTS design. The algebraic form of these equations is somewhat different ; however, the behavior is similar as illustrated in Figure C3.8.7-1 and C3.8.7-1 and C3.8.7-2 where different shapes and equations are shown. The typical extre

18、me event wind speed is 105 mph or greater. Therefore, for diameters 8-in. or greater, the Cdis associated with the turbulent case, CvVd 78 mph-ft, and the Cdis a constant (rightmost column of Table 3.8.7-1). For smaller members, ASCE/SEI 07-10 wind speeds will tend to lower the Cdterm compared to pa

19、st practice. The Cvterm at the extreme limit state adjusts the wind speed to correspond to past drag coefficients used for elements subject to wind. For the fatigue limit state, the wind speeds are on the order of 10 mph and the CvVd will be low and the Cdwill be the larger value in the leftmost col

20、umn of Table 3.8.7-1. Between these extremes, the equations can the be used. This observation simplifies the load application where speed varies with height, etc. The reliability calibration used these bounds in determining the load and resistance factors. See NCHRP 796 (Puckett et al, 2014). 2016 b

21、y the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.2017 INTERIM REVISIONS TO THE LRFD STRUCTURAL SUPPORTS 3-18 FOR HIGHWAY SIGNS, LUMINAIRES, AND TRAFFIC SIGNALS Figure C3.8.7-1 Cd for various shapes (6in., 0.5ft

22、)Figure C3.8.7-2 Cd for cylinder for various diameters 0.000.200.400.600.801.001.200 50 100 150 200 250CdV, mphCylinder0.5 ft0.67 ft1.0 ft2.0 ft 2016 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.2017 INTER

23、IM REVISIONS TO THE LRFD STRUCTURAL SUPPORTS FOR HIGHWAY SIGNS, LUMINAIRES, AND TRAFFIC SIGNALS SECTION 3: LOADS 3-19Table 3.8.7-1Wind Drag Coefficients, C d PaSign Panel Lsign/Wsign= 1.0 2.0 5.0 10.0 15.0 1.12 1.19 1.20 1.23 1.30 Traffic SignalsPb1.20 Luminaires (with generally rounded surfaces) 0.

24、50 Luminaires (with rectangular flat side shapes) 1.20 Elliptical Member (D/do 2) Broadside Facing Wind 1.7 1 2dDooD DCdd Narrow Side Facing Wind 1410.7 1ddoDCdTwo Members or Trusses (one in front of other) (for widely separated trusses or trusses having small solidity ratios see note c) 1.20 (cylin

25、drical) 2.00 (flat) Dynamic Message Signs (CMS)Pg1.70 Attachments Drag coefficients for many attachments (cameras, luminaires, traffic signals, etc.) are often available from the manufacturer, and are typically provided in terms of effective projected area (EPA), which is the drag coefficient times

26、the projected area. If the EPA is not provided, the drag coefficient shall be taken as 1.0. Continued on next page 2016 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.2017 INTERIM REVISIONS TO THE LRFD STRUC

27、TURAL SUPPORTS 3-20 FOR HIGHWAY SIGNS, LUMINAIRES, AND TRAFFIC SIGNALS Table 3.8.7-1Wind Drag Coefficients, C d PaPContinued Single Member or Truss Member CvVd 39 mph-ft 39 mph-ft CvVd 78 mph-ft CvVd 78 mph-ft Cylindrical 1.10 1.3(129)vVdC0.45 FlatPd1.70 1.70 1.70 Hexdecagonal: 16-Sides 0 rc 0.26 1.

28、10 v1.37 1.08145 3C6cvcVd VdCrr0.83 1.08rcHexdecagonal: 16-Sides rc 0.26Pe1.10 78.20.5571vCVd0.55 DodecagonalPeP: 12-Sides 1.20 0.610.8vVdC0.79 OctagonalPeP: 8-Sides 1.20 1.20 1.20 Square 2.0 6rsfor rs11 mph). For Alaskainlands, use Ranges E and F B (9-11 mph). For all Hawaiiislands use Range Ranges

29、 E and F B (9-11 mph). Designers are cautioned of the effects of topography when considering location-specific mean wind velocity in their design. These effects can cause considerable variation NCHRP Report 718 is the basis for fatigue loads identified in this section. Prior to 2012, these Specifica

30、tions made no distinction between high-mast lighting towers and other signal or sign support structures. Failures resulting from wind-induced fatigue led to field testing, laboratory wind tunnel testing, and analytical studies to determine appropriate load models for the fatigue design of HMLTs. The

31、 combined wind load specified for HMLTs was derived from the effects of the entire wind-load spectrum and therefore includes all ranges of wind speed. It is recocognized that the drag coefficient varies with wind speed. The value of PFLSis intended to produce the same fatigue damage generated by the

32、 variable amplitude spectrum using a single equivalent constant amplitude load (PCW). PFLSwas derived using constant values of Cd(using Section 3) and the values of PCWmeasured at each pole (NCHRP 718) to simplify the approach. Hence use of values other than those in Section 3 will result in erroneo

33、us estimates of PCW. The in-service performance of HMLTs shorter than 55 ft appears to suggest that fatigue is not a critical limit state. Cracking has been primarily observed in HMLTs greater than 100 ft tall. The limit of 55 ft was selected somewhat arbitrarily to be well below the 100 ft height.

34、However, although these specifications do not require HMLTs shorter than 55 ft to be designed for fatigue, fatigue resistance details should be selected and careful installation practices followed. If the Engineer suspects that the HMLT will be subjected to high yearly mean wind speeds, the HMLT is

35、placed in a location where local wind effects may be great (e.g., on a bluff), or previous performance of similar HMLTs 2016 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.2017 INTERIM REVISIONS TO THE LRFD

36、STRUCTURAL SUPPORTS FOR HIGHWAY SIGNS, LUMINAIRES, AND TRAFFIC SIGNALS SECTION 11: FATIGUE DESIGN 11-11in wind speed. For locations with more detailed wind records, the yearly mean wind velocity may be modified at the discretion of the Owner. has been poor, consideration should be given to designing

37、 the structure for fatigue using the provisions contained herein. For normal installations, the height shall be defined as the distance from the bottom of the base plate to the tip of the pole, not including the distance the lighting fixture may extend beyond the top. The fatigue-limit-state static

38、pressure range values listed in Table 11.7.2-1 account for fatigue importance factors and variation in mean wind speed. The combined wind pressure range includes the cumulative fatigue damage effects of vortex shedding. Figure 11.7.2-1 serves as a broad guide for determining regional mean wind speed

39、. Local conditions are known to vary and may not necessarily be represented by the map. NCHRP Reports 412 and 718 found the design method to be conservative in most cases; however, designers are encouraged to check local wind records and/or consider topographical effects in choosing a yearly mean wi

40、nd speed for design if the local wind conditions are suspected to be more severe than suggested by Figure 11.7.2-1. It is not recommended to use design pressure ranges less than suggested by Figure 11.7.2-1. Table 11.7.2-1Fatigue-Limit-Sta te Pressure Range for HMLT Design, PFLS Fatigue Design Case

41、Importance Category I II Vmean 9 mph 6.5 psf 5.8 psf 9 mph 11 mph 7.2 psf 7.2 psf Figure 11.7.2-1 Yearly Mean Wind Speed, mph No separate load is specified to account for vortex shedding since it is incorporated in the equivalent static combined wind pressure range, PCW used for fatigue design in Ar

42、ticle 11.7.2. High-mast lighting towers are highly susceptible to vibrations induced by vortex shedding, leading to the rapid accumulation of potentially damaging stress cycles that lead to fatigue failure. NCHRP Report 718 studied the response 2016 by the American Association of State Highway and T

43、ransportation Officials.All rights reserved. Duplication is a violation of applicable law.2017 INTERIM REVISIONS TO THE LRFD STRUCTURAL SUPPORTS 11-12 FOR HIGHWAY SIGNS, LUMINAIRES, AND TRAFFIC SIGNALS Where serviceability and maintenance requirements due to vortex shedding induced vibrations are an

44、 issue, devices such as strakes, shrouds, mechanical dampers, etc. may be used to mitigate the effect. 11.8DEFLECTION Galloping and truck gust-induced vertical deflections of cantilevered single-arm sign supports and traffic signal arms and non-cantilevered supports should not be excessive. Excessiv

45、e deflections can prevent motorists from clearly seeing the attachments, and may cause concern about passing under the structures. 11.9FATIGUE RESISTANCE 11.9.1Detail Classification All fatigue sensitive details in the connections and components in support structures shall be designed in accordance

46、with their respective detail classifications. Detail classifications for typical components, mechanical fasteners, and welded details in support structures are tabulated in Table 11.9.3.1-1. All connections shall be detailed as required in Article 5.6. of these structures in the field and determined

47、 that the previous edition did not properly quantify vortex shedding. Rather than separate the effect of vortex shedding from all other wind phenomena, a loading spectrum was developed to encompass all possible wind load effects. The fatigue-limit-state static wind pressures listed in Table 11.7.2-1

48、 represent this combined wind load effect. Maintenance and serviceability issues resulting from vortex shedding may have a detrimental effect on the performance of HMLTs. Issues with anchor bolts loosening and rattling of the luminaire have been known to occur. Where fatigue-prone details exist whic

49、h may shorten the life of HMLTs due to a lower fatigue resistance than initially considered, or in cases where the service life of an HMLT initially designed for a finite lifetime may wish to be extended, mitigation devices have proved reliable in reducing the number of damaging stress cycles. Information pertaining to the performance and sizing of strakes and shrouds on HMLTs is presented in NCHRP Report 718 and FHWA-WY-10/02F Report Reduction of Wind-Induced Vibrations in High-mast Light Poles (Ahearn