Fatigue Design - · PDF fileStructural Welding Code 01.1-Steel. Fatigue de ... Section 11:...

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i \ Section 11: Fatigue Design Constant-amplitude tatiguethresholeJ-also known as constant-amplitude fatigue limit (CAFL) or endur- ance limit, a stress range below which a fatigue life appears to be infinite. SPECIFICATIONS 11.1 SCOPE 1his section contains provisions for the fa- tigue design of cantilevered steel and aluminum structural supports for highway signs, luminaires, and traffic signals. COMMENTARY This section focuses on fatigue, which is de- fined herein as the damage that may result in fracture after a sufficient number of stress fluctua- tions. It is based on NCH RP Report 412, Fatigue Resistant Design of Cantilevered Signal, Sign and Light Supports (Kaczillski et al. 1998). The study focused on critical support structures that show A Fatigue-c-damage resulting in fracture caused by stress fluctuations. In-plane bending-bending in-plane for the main member (column). At the connection of an arm or arm's built-up box to a vertical column, the in-plane bending stress range in the column is a result of galloping or truck-induced gust loads on the arm and/or arm's attachments. Limit state wind load effect-a specifically defined load criteria. Load bearing attachment-attachment to main member where there is a transverse load range in the at- tachment itself in addition to any primary stress range in the main member. Non-load bearing attachment-attachment to main member where the only significant stress range is the primary stress in the main member. Out-ot-plane bending-bending out-of-plane for the main member (column). At the connection of an arm 'or arm's built-up box to a vertical column, the out-of-plane bending stress range in the column is a result of natural wind gust loads on the arm and the arm's attachments. Pressure range-c-magnitude of force, in terms of pressure, of a limit state wind load effect. Stress range-c-magnitude of stress fluctuations. Yearly mean wind velocity-long-term average of the wind speed for a given area. 11-1

Transcript of Fatigue Design - · PDF fileStructural Welding Code 01.1-Steel. Fatigue de ... Section 11:...

i\

Section 11:

Fatigue Design

Constant-amplitude tatiguethresholeJ-also known as constant-amplitude fatigue limit (CAFL) or endur­ance limit, a stress range below which a fatigue life appears to be infinite.

SPECIFICATIONS

11.1 SCOPE

1his section contains provisions for the fa­tigue design of cantilevered steel and aluminumstructural supports for highway signs, luminaires,and traffic signals.

COMMENTARY

This section focuses on fatigue, which is de­fined herein as the damage that may result infracture after a sufficient number of stress fluctua­tions. It is based on NCH RP Report 412, FatigueResistant Design of Cantilevered Signal, Sign andLight Supports (Kaczillski et al. 1998). The studyfocused on critical support structures that show

A

Fatigue-c-damage resulting in fracture caused by stress fluctuations.

In-plane bending-bending in-plane for the main member (column). At the connection of an arm or arm'sbuilt-up box to a vertical column, the in-plane bending stress range in the column is a result of galloping ortruck-induced gust loads on the arm and/or arm's attachments.

Limit state wind load effect-a specifically defined load criteria.

Load bearing attachment-attachment to main member where there is a transverse load range in the at­tachment itself in addition to any primary stress range in the main member.

Non-load bearing attachment-attachment to main member where the only significant stress range is theprimary stress in the main member.

Out-ot-plane bending-bending out-of-plane for the main member (column). At the connection of an arm'or arm's built-up box to a vertical column, the out-of-plane bending stress range in the column is a result ofnatural wind gust loads on the arm and the arm's attachments.

Pressure range-c-magnitude of force, in terms of pressure, of a limit state wind load effect.

Stress range-c-magnitude of stress fluctuations.

Yearly mean wind velocity-long-term average of the wind speed for a given area.

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Standard Specifications for Structural Supports for Highway Signs, Luminaires and Traffic Signals

SPECIFICATIONS

11.3 NOTATIONS

COMMENTARY

bCddDEtntn1(F)n9H

Ilavg

Itop

Ibottom

Ii:

LLLLPGPNWPTG

PvsrRSnSRttbtctpVcVmean

Wwpa.a.t!..cr

= flat-to-flat width of a multisided section (m, ft)= appropriate drag coefficient from Section 3, "Loads," for given attachment or member= diameter of a circular section (m, ft)= inside diameter of exposed end of female section for slip-joint splice (mm, in)= modulus of elasticity (MPa, ksi)

first natural frequency of the structure (cps)= first modal frequency (cps)= fatigue strength (CAFL) (MPa, ksi)= acceleration of gravity (9810 mm/s2, 386 in/s2)

= effective weld throat (mm, in)= moment of inertia (mm4, in4)

average moment of inertia for a tapered pole (mm4, in4)= moment of inertia at top of tapered pole (mm4, in4)= moment of inertia at bottom of tapered pole (mm4, in4)= importance factors applied to limit state wind load effects to adjust for the desired level of

structural reliabilitylength of the pole (Article 11.7.2) (mm, in)slip-splice overlap length (example 1 of Figure 11-1) (mm, in)length of reinforcement at handhole (example 13 of Figure 11-1) (mm, in)

= length of longitudinal attachment (examples 12, 14 and 15 of Figure 11-1) (mm, in)= galloping-induced vertical shear pressure range (Pa, psf)

,= natural wind gust pre~sur,e rClnge(Pa, psf)= triJck-il1duc'ed gust, pressure range (Pa, psf) , _~~i"

~" .,~. - •••• ~ ~ "<. _ T' •

" = ' ~,vortex ·snedding-induced'pressure range (Pa, psf)= .racji(,Jsof c~ordor column (mm,~in),=·-tra~sit~onraqiu§9fIOl")gitudinal attaqhment (mm,in): ".' .. -:," .- .Strouhaln-umber '. ",= .. nomina:! stre'ss range o(the !)iainmember or branching member (MPa;'ksi)= thickness (mm,in)= wall thickness of branching member (mm, in)= wall thickness of main member (column) (mm, in)= plate thickness of attachment (mm, in)= critical wind velocity for vortex shedding (mis, fUs)= yearly mean wind velocity for a given area (mis, mph)= weight of the luminaire (N, k)= weight of the pole per unit length (N/mm, k/in)= damping ratio= angle of transition taper of longitudinal attachment (example 14 of Figure 11-1) (deg)

ovalizing parameter for bending in the main member (note b of Table 11-2)indication of stress range in member resulting from applicable axial loadings or moments

/. -t ..

11.4 APPLICABLE STRUCTURE TYPES

Design for fatigue shall be required for thefollowing cantilevered-type structures:

a:) overhead cantilevered sign structures,

b) overhead cantilevered traffic signalstructures, and

c) high-level lighting structures.

The fatigue design procedures outlined in thissection may be applicable to steel and aluminumcantilevered structures in general. However, onlyspecific types of cantilevered structures are identi­fied for fatigue design in this article. Commonlighting poles and roadside signs are not includedsince they are smaller structures and normallyhave not exhibited fatigue problems. An exceptionwould be square lighting poles, as they have ex-

11-2

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(....~.;,;

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Section 11: Fatigue Design

SPECIFICATIONS

11.5 DESIGN CRITERIA

Cantilevered support structures shall be de­signed for fatigue to resist each of the applicableequivalent static wind load effects specified inArticle 11.7, and modified by the appropriate im­portance faCtors given in Article 11.6. Stressesdue to these loads on all components, mechani­cal fasteners, and weld details shall be designedto satisfy the requirements of their respectivedetail categories within the constant-amplitudefatigue thresholds provided in Table 11-3. Asummary of typical fatigue-sensitive cantileveredsupport structure connection details is presentedin Table 11-2 and illustrated in Figure 11-1.

COMMENTARY

hibited poor fatigue performance. Square cross­sections have been much more prone to fatigueproblems than round cross-sections. Cautionshould be exercised regarding the use of squarelighting poles even when a fatigue design is per­formed. The provisions of this section are not ap­plicable for the design of span wire (strain) poles.

In general, overhead cantilevered sign andtraffic signal structures should be designed for fa­tigue due to individual loadings from galloping,natural wind' gusts, and truck-induced wind gusts.High-level lighting structures should be designedfor fatigue for loadings from natural wind gusts.Vortex shedding should be considered for single­member cantilevered members that have tapersless than 0.0117 m/m (0.14 in/ft) , such as lightingstructures or mast arms without attachments.

NCH RP Report 412, Fatigue Resistant Designof Cantilevered Signal, Sign and Light Supports(Kaczinski et al. 1998) is the basis for the fatiguedesign provisions for cantilevered structures. Otherstructures, including overhead bridge support

","strlJctur(3s for signs and signals, are, also suscepti~'\:',ble tt)"',fati~j'ue'dariiage: SOmehofthe design pro\ii~~'

sionsof this section can also be applicable to non-, ",_cafl,ti!E?V~J~q,,~tr~:~tur,e.s.;'.A' r'e.searc,t"1project isc:ur~ j;._.L .. ,:­

" ' rentJy underWay to deverop"compret€r'tatigu~de~"-:';;'-""~' ,"pign proyi~iolJs" J9r ,I,.or)ca,ntil,E;)y.ereq,$"'upporj"sJrlJc~ ..

tiJres.'

Accurate load spectra and life prediction tech­niques for defining fatigue loadings are generallynot available. The assessment of stress fluctua­tions and the corresponding number of cycles forall wind-induced events (lifetime loading histogram)is practically impossible. With this uncertainty, thedesign of cantilevered sign, luminaire, and trafficsignal supports for a finite fatigue life becomes im­practical. Therefore, an infinite life fatigue designapproach is recommended and considered soundpractice. It is generally based on the constant­amplitude fatigue limit (CAFL). The CAFL valuesprovided in Table 11-3 are approximately thesame as those given in Table 1O.3.1.A of the Stan­dard Specifications for Highway Bridges (AASHTO1996).

An infinite-life fatigue approach was devel­oped in an experimental study that consideredseveral critical welded details (Fisher et al. 1993).

11-3

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Standard Specifications for Structural Supports for Highway Signs, Luminaires and Traffic Signals

SPECIFICATIONS COMMENTARY

The infinite-life fatigue approach can be used whenthe number of wind load cycles expected duringthe lifetime of the structures is greater than thenumber of cycles at the CAFL. This is particularlythe case for structural supports where the windload cycles in 25 years or greater lifetimes are ex­pected to exceed 100 million cycles, whereas· typi­cal weld details reach the CAFL at 10 to 20 millioncycles.

Fatigue critical details should be designedwith nominal stress ranges that are below the ap­propriate CAFL. To assist designers, a categoriza­tion of typical cantilevered support structure detailsto the existing AASHTO and American WeldingSociety (AWS) fatigue design categories is pro­vided in Table 11-2 and Figure 11-1. Based on areview of state departments of transportation stan­dard drawings and manufacturers' literature, theabove referenced list of typical cantilevered sup­port structure connection details was produced.This list should not be considered as a completeset of all possible connection details, but rather it isintended to remove the uncertainty associated withapplying the provisions of the Standard Specifica-

tions for Highway Bridges to. the fatigue design ofcantilevered support structures .

. This detailed categorization of fatigUe~sensitive connection 9E!tails..can be us~d ..by de-

. 'signersand fabricators to produce more fatigue­resistant cantilevered support structures. Properdetailing will improve the fatigue resistance ofthese structures, and it can eliminate or reduceincreases in member size required for less fatigue­resistant details.

The notes for Table 11-2 specify the use ofStress Category K2- This stress category corre­sponds to the category for cyclic punching shearstress in tubular members specified by the AWSStructural Welding Code 01.1-Steel. Fatigue de­sign for the column's wall under this condition mayrequire sizes of the built-up box connection or col­umn wall thicknesses that are excessive for practi­cal use. For this occurrence, an adequate fatigue­resistant connection other than the built-up boxshown in Figure 11-1 should be considered.

Regarding full-penetration groove-weldedtube-to-transverse plate connections, NCHRP Re­port 412 did not fully investigate the effects fromthe possible use of additional reinforcing filletwelds. Additional research and testing of thesetypes of detail configurations are needed to sup­port future updates of this section.

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Section 11: Fatigue Design

SPECIFICATIONS

11.6 FATIGUE IMPORTANCE FACTORS

An importance factor, IF, that accounts forthe degree of hazard to traffic and damage toproperty shall be applied to the limit state windload effects specified in Article 11.7. Importancefactors for cantilevered traffic signal, sign, andluminaire support structures exposed to the fourwind load effects are presented in Table 11-1.

COMMENTARY

Importance factors are introduced into theSpecifications to adjust the level of structural reli­ability of cantilevered support structures. Impor­tance factors should be determined by the owner.For combined structures, such as traffic signal andluminaire combined structures, use of the more con­servative importance factor is recommended.

Three categories of cantilevered supportstructures are presented in Table 11-1. Structuresclassified as category I present a high hazard inthe event of failure and should be designed to re­sist rarely occurring wind loading and vibrationphenomena. It is intended that only the most criti­cal cantilevered support structures be classified ascategory I. Some examples of structures thatshould be considered for category I classificationinclude the following: large sign structures (includ­ing variable message signs [VMS]), traffic signalstructures with long mast arms, and high-levellighting poles in excess of 30 m (98 ft) that are in­stalled on highways where the vehicle speed issuch that the consequences of excessive deflec­

.•tiol}9r'a cpllisiol1 with a f!3-lIenstnJcture .is intoler­able. Category II and III structures are not lesslikely to expe[i~ncethe full limit state wind loadsassociated 'with' category I. If category II or IIIcan­tilevered support structures· experience the limitstatel6ads ()Ver. a' peti6doftime: they woilldbeexpected to experience fatigue damage. Soundengineering judgment shall be used in the classifi­cation process.

Table 11-1. Fatigue Importance Factors, IFFatigue Category

Importance Factor, IF

GallooinqVortex SheddinqNatural Wind GustsTruck-Induced Gusts

ISign 1.0X 1.0 1.0

Traffic Signal1.0X 1.0 1.0

Liqhtinqx1.0 1.0 x

IISign 0.65X0.750.89

Traffic Signal0.65X0.800.84

Lightingx0.65 0.72x

IIISign 0.31X0.490.77

Traffic Signal0.30X0.590.68

Liqhtinqx0.30 0.44x

Note:x-Structure is not susceptible to this type of loading.Category Descriptions:I -Critical cantilevered support structures installed on major highways.II-Other cantilevered support structures installed on major highways and all cantilevered supportstructures installed on secondary highways.III-Cantilevered suooort structures installed at all other locations.

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Standard Specifications for Structural Supports for Highway Signs, Luminaires and Traffic Signals

SPECIFICATIONS

11.7 FATIGUE DESIGN LOADS

To avoid large-amplitude vibrations and topreclude the development of fatigue cracks invarious connection details and at other critical

locations, cantilevered support structures shall bedesigned to resist each of the following applicablelimit'state equivalent static wind loads actingseparately. These loads shall be used to calcu­late, nominal stress ranges at fatigue-sensitiveconnection details," as described in Article 11.5.The calculated nominal stress range shall notexceed the CAFL values given in Table 11-3 foraparticular connection detail.

In lieu of using the equivalent static pres­sures provided in this specification, a dynamicanalysis of the structure may be performed usingappropriate dynamic load functions derived fromreliable data. '

, ;, ~

11.7.1 Galloping

, Overhead cantilevered sign and traffic signalsupport structures shall be designed for gallop­ing-induced cyclic loads by applying an equiva­lent static shear pressure vertically to the surfacearea, as viewed in normal elevation of all sign

COMMENTARY

Cantilevered support structures are exposedto several wind phenomena that can produce cyclicloads. Vibrations associated with these cyclicforces can become significant. NCHRP Report 412has identified galloping, vortex shedding, naturalwind gusts, and truck-induced gusts as wind­loading mechanisms that can induce large ampli­tude vibrations and/or fatigue damage in cantile­vered traffic signal, sign, and light support struc­tures. The amplitude of vibration and resultingstress ranges are increased by the low levels ofstiffness and damping possessed by many of thesestructures. In some cases, the vibration is only aserviceability problem because motorists cannotclearly see the mast arm attachments or are con­cerned about passing under the structures. In othercases, where deflections mayor may not be con­sidered excessive, the magnitudes of stressran-gas induced in these structures have resulted inthe development of fatigue cracks at various con­nection details including the anchor bolts.

", _The wind-loading phenomena specified in thissection possess the greatest potential for creatinglarge .amplitude vibrations in cantilevered support

pstructures.ln partiqJlar, galloping and vortex shed-'ding are aeroelastic instabilities that will typicallyinduc!3vibratibns at the, natural frequency of the "structure (Le., resonance). These conditions canlead to fatigue failures in a relatively short period oftime.

Design pressures for each of the four possiblefatigue wind-loading mechanisms are presented asan equivalent static wind pressure range, or ashear stress range in the case of galloping. Thesepressure (or shear stress) ranges should be ap­plied to the structure as prescribed by this sectionin a simple static analysis to determine stressranges at fatigue-sensitive details. In lieu of de­signing for galloping or vortex-shedding limit statefatigue wind load effects, mitigation devices maybe used as approved by the owner. Mitigation de­vices are discussed in NCHRP Report 412.

Galloping, or Den Hartog instability, results inlarge' amplitude, resonant oscillations in a planenormal to the direction of wind flow. It is usuallylimited to structures with nonsymmetrical cross­sections, such as sign and traffic signal structures

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Section 11: Fatigue Design

SPECIFICATIONS COMMENTARY

panels and/or traffic signal heads and backplatesrigidly mounted to the cantilevered horizontalsupport. The magnitude of this vertical shearpressure range shall be equal to the following:

In lieu of designing to resist periodic gallop­ing .forces, cantilevered sign and traffic signalstructures may be erected with approved vibra­tion mitigation devices. Vibration mitigation de­vices should be approved by the owner, and theyshould be based on historical or research verifi- .cation onts vibration damping characteristics.

(Pa)

(psf)

Eq.11-1

with attachments to the horizontal cantileveredarm. Structures without attachments to the cantile­

vered horizontal support are not susceptible togalloping induced wind load effects.

The results of wind tunnel (Kaczinski et al.1998) and water tank (McDonald et al. 1995) test­ing, as well as the oscillations observed on cantile­vered support structures in the field, are consistentwith the characteristics of the galloping phenom"ena. These characteristics include the sudden on­

set of large-amplitude, across-wind vibrations thatincrease with increases in wind velocity. It is im­portant to note, however, that galloping is typicallynot caused by support structure members, butrather by the attachments to the horizontal cantile­vered arm, such as signs and traffic signals.

Alternatively, for traffic signal structures,the owner may choose to install approved vibra­tion mitigation devices if structures display a gal­loping problem. The mitigation devices must beinstalled as quickly as possible after the gallopingproblem appears.

........... Th~,ovynE3r may. choose to .exclude gal~. loping' loads for the fatigue design of overhead

..J.._ __._._._.~.~_t:1!i!e.Y§!r(3~.~Jg~.suPP9J:t,._~~~~t~i~.~\'Jj~h,gl,lc:i_~ri~__. ,~ ". chord (Le:;four-chbrd) h'orizontal trusses ...

The geometry and orientation of these at­tachments, as well as the wind direction, directlyinfluence the susceptibility of cantilevered supportstructures to galloping. Traffic signals are moresusceptible to galloping when configured with abackplate. In particular, traffic signal attachmentsconfigur'ed with or without a backplate are moresusceptible. to galloping' when subject to flow from

'the Tear: .Galloping of sign attachments is lnde-_.,-pen,dent-of-:aspeet ratio~nd is r;nore,8f,ev~le.n!'y.'ith-

wind flows from the front of the'structure. - . ,__•. *_ .....••.. ; ., r.••• · ._." , .•..._ .•.••. _ •...

By conducting wind tunnel tests and analYticalcalibrations to field data and wind tunnel test re­

sults, an equivalent static vertical shear of 1000 Pa(21 psf) was determined for the galloping phenom­ena. This vertical shear range should be applied tothe entire frontal area of each of the sign and trafficsignal attachments in a static analysis to determinestress ranges at critical connection details. For ex­ample, if a 2.5 m by 3.0 m (8 ft by 10ft) sign panelis mounted to a horizontal mast arm, a static forceof 7500 x IF, N (1680 X IF, Ib) should be appliedvertically to the structure at the center of gravity ofthe sign panel.

A pole with multiple horizontal cantileveredarms may be designed for galloping loads appliedseparately to each individual arm, and need notconsider galloping simultaneously occurring onmultiple arms.

Overhead cantilevered sign support struc­tures with quadri-chord horizontal trusses do notappear to be susceptible to galloping because oftheir inherent high degree of three-dimensionalstiffness.

11-7

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Standard Specifications for Structural Supports for Highway Signs, Luminaires and Traffic Signals

SPECIFICATIONS COMMENTARY

Two possible means exist to mitigate gallop­ing-induced oscillations in cantilevered supportstructures. The dynamic properties of the structureor the aerodynamic properties of the attachmentscan be adequately altered to mitigate galloping.The installation of a device providing positive aero­dynamic damping can be used to alter the struc­ture's response from the aerodynamic effects onthe attachments.

A method of providing positive aerodynamicdamping to a traffic signal structure involves in­stalling a sign blank mounted horizontally and di­rectly above the traffic signal attachment closest tothe tip of the mast arm. This method has beenshown to be effective in mitigating galloping­induced vibrations on traffic signal support struc­tures with horizontally-mounted traffic signal at­tachments (McDonald et al. 1995). For vertically­mounted traffic signal attachments, a sign blankmounted horizontally near the tip of the mast armhas mitigated large amplitude galloping vibrationsoccurring in traffic signal support structures. Thi~sign blank is placed adjacent to a traffic signal at­tachment,' and a separatiOn __~xistsbetween thesign,blank an~ the, top of the mast arm. In bothcases, ,the sign blanks are required, to provide a

_,u sufficient -surface-·area' for rnitigationto occur.'U However,. the installation of sign blanks may influ­'; enqe Jhe, designoLstructures for truck-induced

wind gusts by increasing the projected area on ahorizontal plane. NCHRP Report 412 provides ad­ditional discussion on this possible mitigation de­vice, and on galloping susceptibility and mitigation.

(

11.7.2 .Vortex Shedding

Nontapered lighting structures shall be de­signed to resist vortex shedding-induced loads forcritical wind velocities less than approximately 20m/s (65 fps; 45 mph).

The critical wind velocity, Vc (mis, ft/s), atwhich vortex shedding lock-in can occur may becalculated as follows:

The shedding of vortices on alternate sides ofa member may result in resonant oscillations in aplane normal to the direction of wind flow. Typicalnatural frequencies and member dimensions pre­clude the possibility of most cantilevered sign andtraffic signal support structures from being suscep­tible to vortex shedding-induced vibrations.

where fn is the first natural frequency of thestructure (cps); d and b are the diameter and flat-

Vc = fnd (for circular sections)Sn

Vc = fnb (for multisided sections)Sn

Eq. 11-2

Eq. 11-3

Cantilevered mast arms and lighting struc­tures that have tapers less than 0.0117 m/m (0.14in/ft) may be required by the owner or designer toresist vortex shedding-induced loads.

Structural elements exposed to steady, uni­form wind flows will shed vortices in the wake be­hind the element in a pattern commonly referred toas a von Karmen vortex street. When the fre­quency of vortex shedding approaches one of the

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Section 11: Fatigue Design

SPECIFICATIONS COMMENTARY

(\

to-flat width of the horizontal mast arm or poleshaft for circular and multi-sided sections (m, ft),respectively; and Sn is the Strouhal number. TheStrouhal number shall be taken as 0.18 for circu­lar sections, 0.15 for multisided sections, and0.11 for square or rectangular sections. For a ta­pered pole, d and b are the average diameterand width.

natural frequencies of the structure, usually the firstmode, significant amplitudes of vibration can becaused by a condition termed lock-in. The criticalvelocity at which lock-in will occur is defined by theStrouhal relationship:

Eq. C 11-1

The equivalent static pressure range to beused for the design of vortex shedding-inducedloads shall be:

In lieu of designing to' resist periodic 'vortex .shedding forces, approved vibration mitigationdevices may be used.

where Vc is expressed in m/s (ft/s); Cd is the dragcoefficient specified in Section 3, "Loads;" and {3

is' the damping ratio, which is conservatively es-timated. as 0.005: .-

Eq.11-4(Pa)

A lower bound wind speed can be establishedfor traffic signal and sign structures. Although vor­tices are shed at low wind velocities for wind

speeds less than 5 mls (16 fps, 11 mph), the vorticesdo not impart sufficient energy to excite moststructures. Typical natural frequencies and mem-ber diameters for sign and traffic signal supportstructures result in critical wind velocities well be-low the 5 mls (16 fps, 11 mph) threshold for the oc­currence of vortex shedding. Because of extremelylow levels of damping inherent in many nontaperedsupport structures, vortex shedding may exciteresonant vibration. At wind speeds greater thanabout 20 m/s (65 fps, 45 mph) enough natural turbu­lence is generated to disturb the formation of vortices. -.:..._.

The <equivalent static pressure range' Pvs Aithough possible; recent'tests (Kaczinskietshall be applied transversely to poles (Le.,.hori- al. 1998; McDonald et al. 1995) have indicated that

- .. - -. - 'zontal'-direction) and horizontal" mast:" arms--:(Le.,>:.' ·theoccurrenceof· '{ortexshedding: froQ:1-attach-- - - .. ' verticalcHrection).· ..... u.'· merits to cahtilevered sfgnand traffic sr~Ynalsup- .~..

......PQetstructuresJs.l1otcriJical., Ih fact, Jh·es!'Lattach~._:,...ments are' more susceptible to galloping-induced .vibrations. Finally, support structures composed oftapered members do not appear susceptible tovortex-induced vibrations when tapered at least0.0117 m/m (0.14 in/ft). The dimensions of mosttapered members result in critical wind velocitiesbelow the threshold velocity; and, furthermore, anyvortices that may form are correlated over a shortlength of the member, and they consequently gen­erate insignificant vortex-shedding forces.

Calculation of the first modal frequency forsimple pole structures (Le., without mast arms) canbe accomplished using the following equations:

fn1 = 1.75 J Eig1& wL4

(without luminaire mass)

Eq. C 11-2

f 1 = 1.732 I Eign 21& V We + 0.236we(with luminaire mass)

Eq. C 11-3

where W is the weight of the luminaire (N, k), w isthe weight of the pole per unit length (N/mm, klin),

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Standard Specifications for Structural Supports for Highway Signs, Luminaires and TrafficSignals

SPECIFICATIONS COMMENTARY

9 is the acceleration of gravity, L is the length ofthe pole (mm, in), and I is the moment of inertia ofthe pole (mm4, in\ For tapered poles, lavg is sub­stituted for I, where:

Itop + Ibottom

lavg = 2 Eq. C 11-4

where Cd is the appropriate drag coefficientspecified in Section 3, "Loads," for the consideredelement to which the pressure range is to be ap­plied. The natural wind gust pressure range shallbe applied in the horizontal direction to the ex­posed area of all support structure members,signs, traffic signals, and/or miscellaneous at­tachments. Designs for natural wind gusts shallconsider the application of wind gusts for any di­rection of wind.

Cantileve'r~d overhead sign, overhead traffic .. ". Be.cause of the inhere~t v,arii3.9ility in the ye~: .,~":_h'""signal; a[1d .high;le"vel; lighting 'supports 'shall be'" hlo"cifY- ~uid 'direCtion"of air. fiow', natural wind gusts

designed to resist an equivalent static natural are the most basic wind phenomena that may in-wind gust pressure range of: duce vibrations in wind-loaded structures. The

equivalent static natural wind gust pressure rangespecified for design was developed with data ob­tained from an analytical study of the response ofcantilevered support structures subject to randomgust loads (Kaczinski et al. 1998). This parametricstudy was based on the 0.01 percent exceedancefor a yearly mean wind velocity of 5 m/s (11.2mph), which is a reasonable upper-bound of yearlymean wind velocities for most locations in thecountry. There are locations, however, where theyearly mean wind velocity is larger than 5 m/s(11.2 mph). For installation sites with more detailedinformation regarding yearly mean wind speeds(particularly sites with higher wind speeds), thefollowing equivalent static natural wind gust pres­sure range shall be used for design:

11.7.3' Natural Wind Gust·.... -- '. ' .... - ._- ---- -- ..- ..-.- --.-.-"-"

(Pa) Eq.11-5

Itop is the moment of inertia at the tip of the poleand Ibottom is the moment of inertia at the bottom ofthe pole.

Determining the first modal frequency forpoles with mast arms, however, is best accom­plished by a finite element based modal analysis.The mass of the luminaire/mast arm attachmentsshall be included in the analysis to determine thefirst mode of vibration transverse to the wind direc­tion. Poles that may not have the attachments in­stalled immediately shall be designed for thisworst-case condition. Because the natural fre­quency of a structure without an attached mass istypically higher than those with an attachment, theresultil19 critical wind speed and vortex sheddingpressure range will also be higher.' .

('.

The design natural wind gust pressure rangeis based on a yearly mean wind speed of 5 m/s(11.2 mph). For locations with more detailed windrecords, particularly sites with higher windspeeds, the natural wind gust pressure may bemodified at the discretion of the owner.

P.= 250C (V;ean )NW d 25 F

P. = 5.2C (V;ean )NW d 125 F

11-10

(Pa)

(psf)

Eq. C 11-5

Section 11: Fatigue Design

SPECIFICATIONS

11.7.4 Truck-Induced Gust

COMMENTARY

The largest natural wind gust loading for anarm or pole with a single arm is from a wind gustdirection perpendicular to the arm. For a pole withmultiple arms, such as two perpendicular arms, thecritical direction for the natural wind gust will usu­ally not be normal to either arm. The design naturalwind gust pressure range shall be applied to theexposed surface areas seen in an elevation vieworientated perpendicular to the assumed wind gustdirection.

Overhead sign and traffic signal supportstructures shall be designed to resist an equiva­lent static truck gust pressure range of:

where Cd is the appropriate drag coefficient fromSection 3, "Loads," for the considered element to ,which theu pressure range is to beapPlied>Thepressure range shall be applied in the vertical

direction to the cantilevered horizontal support. as___welL as the_area of alLsigns, attachments,walk" .

ways, and/or. fighting fixfures projected on' ahOri-______ ._z:QD!i3t R!c:lllE!~Tb!s..P[~§gJre Gln9.~Lsb_aIJJ:~~_~ppJi€Zd_:_.

along the· lull: length- of any sign pan­els/enclosures or the outer 3.7 m (12 ft), which­ever is greater~ The equivalent static truck pres­sure range lTlay be reduced for locations wherevehicle speeds are less than 30 m/s (65 mph),

{" The truck-induced gust loading may be ex-+ 1 eluded for the fatigue design of overhead cantile-

l vered traffic signal support structures, as allowedby the owner...•.

(Pa)

(psf)

Eq. 11-6

The passage of trucks beneath cantileveredsupport structures may induce gust loads on theattachments mounted to the horizontal support ofthese structures. Although loads are applied inboth the horizontal and vertical direction, horizontalsupport vibrations caused by forces in the verticaldirection are most critical. Therefore, truck gustpressures are applied only to the exposed hori­zontal surface of the attachment and horizontalsupport.

A pole "'lith multiple horizontal cantilever ar.msmay be designed for truck gust loads applied sepa­ratelyto each.individucil arm and need not consider

. trLJ9kgw3tloads· applied. simultaneouslY to multiplearms.

-Recent vibration problems on sign structures'

with large projected areas in the horizontal plane,such as VMS enclosures, have focused attentionon vertical gust pressures created by the passageof trucks beneath the sign. To improve fuel econ­omy, many trucks are outfitted with deflectors todivert the wind flow upward and minimize the dragcreated by the trailer. It has been proposed to rep­resent this gust pressure as that imposed by a 30m/s (65 mph) wind to approximately coincide withexisting vehicle speed limits (DeSantis and Haig1996).

The equivalent static truck gust pressure isdetermined by utilizing the wind pressure formulain Section 3, "Loads," where the velocity is 30 m/s(65 mph) and the height factor is 1.0. To accountfor an increase in the relative truck speed causedby head winds, a factor of 1.3 is also included. Asthe truck passes under the structure, a pressure isapplied upward, and then suction pressure is ap­plied downward. Therefore, the load is doubledbased on the assumption that on the first cycle thedownward and upward forces are equal. Forstructures installed at locations where the posted

11-11

Standard Specifications for Structural Supports for Highway Signs, Luminaires and Traffic Signals

SPECIFICATIONS COMMENTARY

speed limit is much less than 30 mts (65 mph), thedesign pressure may be recalculated based on thislower wind velocity. The following equation may beused: '

,( V )2Pm = 1760Cd ' / IF (Pa)30 m s

Pm = 36.6Cd ( V r IF (psf)65 mph

Eq. C 11-6

, ,. ".o-'-.~··''''·.-...~.•.......

where V is the truck speed in m/s (mph).

Utilizing appropriate drag coefficients (Cd), thetruck gust pressure range can then be applied toall horizontally projected areas, which include boththe horizontal support and any attachments. Forstructures with large sign panels, pressures shallbe applied along the entire length of the horizontalareas to recognize the possibility of passage of twotrucks side-by-side. For structures without largesign panels, the equivalent static truck gust pres­sure,sh?II ..be ?ppJied. to the. outer 3.7_m (12.ft).

-length Of the horizqriJaLsupport and to any attach-ments located within this length, '

A drag coefficient yalu$.of ~,.20was,u~ed :,'bYUeSantis'arid Hai£f' (1996) to determine an'u equivalent. static.-tr~uck 'gust pres.sure range :on

VMS .. ' ,

The magnitude of applied pressure resultingfrom a truck-induced gust will vary depending onthe elevation of the horizontal support and the ele­vation of the attachments above the truck. Eq. 11­6 neglects any decreases in design pressure re­sulting from increasing elevations above the trucks.Fatigue Related Wind Loads on Highway SupportStructures (Dexter and Johns 1998) includes arecommendation for the variation of truck-induceddesign pressures for a range of elevations abovethe road surface.

The given truck-induced gust loading may beexcluded for the fatigue design of overhead canti­levered traffic signal structures, as allowed by theowner. Many traffic signal structures are installedon roadways with negligible truck traffic. In addi­tion, the typical response of cantilevered traffic sig­nal structures from truck-induced gusts can be sig­nificantly overestimated by the design pressuresprescribed in this article. However, some cantilevertraffic signal structures have experienced large­amplitude vibrations from truck-induced gusts ap­plied under the right conditions.

11-12

Section II: Fatigue Design

SPECIFICATIONS

11.8 DEFLECTION

Galloping and truck-gust induced verticaldeflections of cantilevered single-arm sign sup­ports and traffic signal arms should not be exces­sive so as to result in a serviceability problem,because motorists cannot clearly see the arm'sattachments or are concerned about passing un­der the structures.

---_ .. ,.~.... _._._._-'. _._- --- ..--.-.--

COMMENTARY

Because of the low levels of stiffness and

damping inherent in cantilevered single mast armsign and traffic signal support structures, evenstructures that are adequately designed to resistfatigue damage may experience excessive verti­cal deflections at the free end of the horizontalmast arm. The primary objective of this provisionis to minimize the number of motorist complaints.

NCHRP Report 412 recommended that thetotal deflection at the free end of single-arm signsupports and all traffic signal arms be limited to200 mm (8 in) vertically, when the equivalentstatic design wind effect from galloping and truck­induced gusts are applied to the structure. Dou­ble-member or truss-type cantilevered horizontalsign supports were not required to have verticaldeflections checked because of their inherentstiffness. There were no provisions for a dis­placement limitation in the horizontal direction.

11-13

Standard Specifications for Structural Supports for Highway Signs, Luminaires and Traffic Signals

Table 11-2. Fatigue Details of Cantilevered Support Structures

Construction

Plain Members

MechanicallyFastenedConnections

1.

2.

3.

Detail

With rolled or cleaned surfaces. Flame-cut

edges with ANSI/AASHTO/AWS D5.1 (Ar­ticle 3.2.2) smoothness of 1,000 micro-in.or less.

Slip-joint splice where L is greater than orequal to 1.5 diameters.Net section of fully-tightened, high-strength(ASTM A325, A490) bolted connections.

Stress

Cat~A

B

B

Application.

High-level lightingpoles.

Bolted joints.

Example

2

4. Net section of other mechanically fastenedconnections:

Steel:Aluminum:

5. Anchor bolts or other fasteners in tension;stress range based on the tensile stressarea. Misalignments of less than 1:40 withfirm contact existing between anchor boltnuts, washers, and base plate.

6. Connection of members or attachment of

miscellaneous signs, traffic signals, etc.with clam s or U-bolts.

Holes and Cutouts 7. Net section of holes and cutouts.

~.r~~~~:~k~et~·_·~1~;~~·~~-~~~~I~~~ig~~~:I~~I~~;~I:~~~I~hedi-. - rection of Hie applied stress.9. Full-penetration groove-welded splices with

...... "cL·. '. welds ground tdprbvideasriibothfransi~-

_ _--'- _1~_:.tiC>fl~e~~en ..me.rT1~~.rsj'Nith()r 'lVit~()u.!-.--------:.r bacKing ring removed).10. Full-penetration groove-welded splices with

weld reinforcement not removed (with orwithout backing ring removed).

11. Full-penetration groove-welded tube-to­transverse plate connections with thebacking ring attached to the plate with afull-penetration weld.

12. Full-penetration groove-welded tube-to­transverse plate connections.

E I Column or mast arm

butt-splices.

E I Column-to-base-plateconnections.

Mast-arm-to-flange­rl plate connections.E' Column-to-base-plateconnections.

Mast-arm-to-flange­rl plate connections.E Column or mast armrl lap splices.E Angle-to-gusset con-nections with weldsterminated short of

plate edge.Slotted tube-to-gusset

connections withrl coped holes.E' Angle-to-gusset con-nections.

Slotted tube-to-gussetconnections without

coped holes.

8

3

4

5

5

5

3

2,6

2, 6

··6- ...

Anchor bolts.Bolted mast-arm-to­

column connections.

Wire outlet holes.

Drainage holes.Unreinforced hand-

holes.

Longitudinal seam ~.: ..welds~ -

Column or mast.armbutt-splices:'

DED

D

D-

D

B'

14. Members with axial and bending loads withfillet-welded end connections withoutnotches perpendicular to the appliedstress. Welds distributed around the axis ofthe member so as to balance weldsstresses.

13. Fillet-welded lap splices.

15., Members with axial and bending loads withfillet welded end connections with notchesperperidicular to the applied stress. Weldsdistributed around the axis of the memberso as to balance weld stresses.

Fillet-WeldedConnections

11-14

Section 11: Fatigue Design

Table 11-2. Fatigue Details of Cantilevered Support Structures (continued)

Application I Example( ConstructionI Detail

Fillet-Welded

16.Fillet-welded tube-to-transverse plateConnections

connections.(continued)

117.Fillet-welded connections with one-

l--psided welds normal to the direction of

the applied stress.18.

Fillet-welded mast-arm-to-column l--Ppass-through connections. 19.

Fillet welded T-, Yo, and K-tube-to-

I

Seetube, angle-to-tube, or plate-to-tube

notesconnections.

a and b

Attachments 20. Non-load bearing longitudinal attach­ments with partial- or full-penetrationgroove welds, or fillet welds, in whichthe main member is subjected to lon­gitudinalloading:

L < 51 mm (2 in):

- 51mrn(2 in) 5, L5,12t and102mm(4 in):

C

D

Column-to-base-plate or I 7, 8mast-arm-to-flange­plate socket connec­tions

Built-up box mast-arm- I 8to-column connections.

Mast-arm-to-column pass- I 9through connections.

Chord-to-vertical or I 8, 10, 11chord-to-diagonal trussconnections (see note a).

Mast-arm directly weldedto column (see note b).

Built-up box connection(see note b).

Weld terminations at I 12, 13ends of longitudinalstiffeners.

Reinforcement at hand­holes.

,. ' .. , ~... "- -

L> 12tor 102 mm(4 in) when t 5, 25 mm(1 in):

____ 21; Non-I()Cld_bearingJongitudinalgttach~~-",I- ments with-:L > 102-mm (4 in) and-full--,­

. pe'netration groove welds. The main-_____n.-:,;: - -:-- _:'-'u ------ --:_-'--- ---;::':"1':::""': :::-membe rig-subJeCted tolongitudfnal ~::---

- -- loading and weld tem;ination embodiesa transition radius or taper with the weldtermination ground smooth:

E

, Welds terminatioosat-ends of longitudinal -_~stiffeners_, _

14

. -.---- ..

R2:152mm(6in)or a:S; 15°: I C

152mm(6in) > R> 51 mm (2 in) or 15°< a 5, 60°: I D

R5,51mm(2in)ora>500: I E

22. Non-load bearing longitudinal attach­ments with L> 102 mm (4 in) and filletor partial-penetration groove welds. Themain member is subjected to longitudi­nalloading and the weld terminationembodies a transition radius or taperwith the weld termination ground smooth:

Weld terminations at

ends of longitudinalstiffeners.

14

R> 51 mm (2 in) or 15° < a :s;60°:

R :s;51 mm (2 in) or a > 60°:

23. Transverse load-bearing fillet-weldedattachments where t:s; 13 mm (0.5 in)and the main member is subjected tominimal axial and/or flexural loads.[When t> 13 mm (0.5 in), see note d].

11-15

D

E

C Longitudinal stiffenerswelded to base plates.

12,14

-------------~---'---'-~-'~=--'----------------------

Standard Specifications for Structural Supports for Highway Signs, Luminaires and Traffic Signals

Table 11-2. Fatigue Details of Cantilevered Support Structures (continued)

Construction DetailStressApplicationExampleCategoryAttachments

24. Transverse load-bearing longitudinalGusset -p late- to-cho rd15(continued)

attachments with partial- or full- attachments.penetration groove welds or fillet welds, in which the nontubular main member issubjected to longitudinal loading andthe weld termination embodies a transi-tion radius that is ground smooth:

R> 51 mm(2in)or 15° < a ~ 60°:

D

R ~ 51 mm(2in) or a> 60°;

ESee note c

Notes:

a) Stress category ET with respect to stress in branching member provided that !..- J 24 for the chord member. Whent

0.7

!..- > 24 ,then the fatigue strength equals: (F) = (.1F)Er X(y;24Jt n n r

t

Stress category E with respect to stress in chord.

b) Stress category ET with respect to stress in branching member.

( ET,where .1F ) n is the CAFL for category ET.

.. " ... ,,', ' " ,- --"-, -. - - r

Stress category K2 withrespect to stress in main m.ember (column) Rfc:>yidedthat ~ ~24. for the main member.

, .,.---------"."~::::.,-.-"-.--, ..:~-- ..• -- .. '. - .,.,," : tc ,',' "._ ., ' " 0.7

~~en'~:2~~,t~i;L:;~~~s~~~-(~)~(:;"f{xJ ,whem(.d~istheCAFl fo, categoryK,--:.:~---tc""---:-:, --, -- ,•.... , ,,' ,--." --,n ., n - r tc - .. ---, - n '

The nominal stress range in the main member equals: (5R ) main member = (5R ) branching member ( ~: )a,Where tb is the wall thickness of the branching member, tc is the wall thickness of the main member (column), and

ex is the ovalizing parameter for the main member equal to 0.67 for in-plane bending, and equal to 1.5 for out-of­

plane bending in the main member. (5R ) branching member is the calculated nominal stress range in the branching

member induced by fatigue design loads. (See commentary of Article 11.5.)

The main member shall also be designed for stress category E using the section modulus of the main member andmoment just belo"w the connection of the branching member.

c) First check with respect to the longitudinal stress range in the main member per the requirements for non-loadbearing longitudinal attachments. The attachment must then be separately checked with respect to the transversestress range in the attachment per the requirements for transverse load-bearing longitudinal attachments.

d) When t > 13 mm (0.5 in), the fatigue strength shall be the lesser of category C or the following:

where (.1Ft is the CAFL for category C, H is the effective weld throat (mm, in), and tp is the attachment platen

thickness (mm, in). ,

11-16

i\

i\

Section 11: Fatigue Design

Table 11-3. Constant-Amplitude Fatigue Thresholds

Detail

SteelAluminumCategory

ThresholdThreshold

MPa

ksiMPaksi

A

165247010.2

B

11016416.0

B'

8312324.6

C

6910284.0

D

487172.5

E

314.5131.9

E'

182.671.0

ET

81.230.44

K2

71.02.70.38

_____ .. . . "'"'"'~_;._.' __....:....d_. ._._.~_.-.;.. ..__._." -,."_0 __ .-

--_._~--_.,--- . ___ '__ " • ": .. __ •••• _. •__ .~ • •• • ._ •• _. 0_" .••u •__ .__·._~+ .._·~'_

11-17

'I'I : ! !

~;::

§-i3..

~""C')

'Si2:::1-.c;::""

~..,Vl::;­;::C')..•.;::

i:!-Vl{;'15ca.~..,

::x::

~'"~Vl

~'~""

t'-<;::~S'!:I::;.'"""

!:I;::~~§,';:J)C')

VlaQ';::!:I1;;'

Fillet Weld(Detail 13)

ShmdnnJ IIlIlt

(Delull 4)

Backing Ring

+ 60

"-~M

Fillet· Welded Lap-Splice

Example 3

~6a

Example 5

l'iIIct Weld·(UclnilI4)

lIi!:h Strenglh lJolls(Detail 3)

Gruuve-Welded Tube-Iu-Trunsverse 1>loleConnection

, t.

Hole amI/or Culuut(Detail7)

,.

. ,

Duubhi.AlIgle-l·russ Gusset

Examille 2

·Weld slopped.sbu~t of gusset edge•

i

,i

Backing Rllig

Grouve Wetd(Del'alllO) ,

,.,

Gusset

Fillet W Cld

(DclaIl15)

; 60

~M

Grouve-Welded Dutt-Slllice

Example 4

~

fl. = 1.5x ()----I._

~ 60

; 60

Groove Weld(DelDll 9)

Slip-Joint Splice

Example 1

~Slip Splice(Delall 2)

"to's=..•(p....•....•I....•-!»

~Iy

2"UI-..•!»-<t(pm><!»3'tICDUI

<..~ ..~-•...,

'"

C/'.)'"<">

:::toc;:::

..........",

~~";::'"t1'"""

aQ';:::

Gussel

Coped Hole

Fillet Weld

(Detail 14)

Example 6

Section A-A

SluUed Tube-tu-Gusset Connection

l<'illetWeld

(Detail 16)

Fillet Weld

(DetoilIS)

Gusset

Seum Weld

(Detail 8)

,

: Example 6: .. ' !

:.• 't 11~

'1":

, !Section A·A ,to ;

'Fillet Weld.(DetaiI16)

~. ,

'I.

I:!

'I . ! "

Sh)~tcd 'l't,be-to-Gusset Cunnectiun

FilM Weld

Seam Weld

(Detail 8)

l.A

Example 6

~ 110

SluUed Tube-to-Gusset Connection

.....110

i:III..•...•DI..•.<"CD

m)(DI

3"tJCDIII

"cQ'e..•.CD

-"-"I-"-

C"":"'"

....•.

....•.I

....•.

<D

;Ih

Fi1~et-W~lded Socket Connection:,

:!,,~

: :Expmptc 7".

i'

t"<

;::;:s

5'~::j'~'"~;::~~§,';::R

C")

CI)~.;::~~

CI)

~;::

!}~~~

C")

'SiC")

~:::t,c;::'"

~.,CI)~;::C")•..•;::~...•CI)

.§'1:3ca.

~.,::t:

~';::..~~CI)

~';::~'"

~D.a

Fillet Weld(DelaIl19)

Fillel Weill

(Delaill'J)

Fillel Weill

(Uelail 17)

"--

~lIcr

~cr

Example II

Sec!iull/l·/l

Fillet· Welded Angle-to-Tube Connection

Exalllple 11

JIt:t;!P

~D.cr

Fillet Weld(OcIIlIl19)

Fillet- Welded Mil.~I-l\rJIl-tu-Cohllllll COlllledioll

(Built-Up Hux)

Fillet Weld\Uel:1i116J

Ui~1I Slrell!:11I Hult

(\)e(all SJ

i,

EXllluule 10'. .

;--;

, ., ,

1

Tl~i,I '.. 1\

.,

~.

lIa.: :

lrillct- WcldcdTubc-tu-Tubc Couucc Iiun, ...

Fillet Weld(Deta\l18)

Fillet Weld(Detll\l18)

Fillet Weld(Detail I?)

I'illel Weld

(Oelulll 'J)

Fillet. Welded Must-I\rm-tu-Columll Connectioll

(Buill·Up Uox)

Example 8

.,

~D.cr

t tJ.a

Fillet Weld(DclaIl16)

t1\

Fillet-Welded Tube-to-Tube Colullln

.Pass-Through Connection

EX8l1ll)le9

"TI

10'e:...•. (1)....•....•I....•

~I

~

e:

III-...•DI-<'(1)m><DI3"0(j)III

,. '

~<-~"--.

if

: ! .....

Non-Loud llearingLollgiludinal Attachmenl.' ,I :. ; 'l .

E~ample 12 '',. ", i

VJ<1:>

""

~"c;:::

....•

....•",

~~,

!:::'"

I;::,'"'"aQ'

;:::

FilM Weld(Detail 23)

Fillet Weld

(Delail 2U)

Section A-A

o, ~ Fillet Weld' (Delail 20)

ickness = tReinforcement,ih

,,.!

11.

i +" '

t, .Acr ;:" ", '

. ' .. ,' ,.. " ,

i" '6. ~ ,i 'i ;"; ."1' •

:\'I; ,

,;1

, 11...

Handhole : i

"j>:

Reillrorcem~'nti

i;

--,A

"T110'"I:..,(I)....•.....•.I....•.

~,-"-" I:

+ 6CJ

~I1/1

..•...,III..•.<'(I)m><III3

f-

"C

CD

A

1/1

Reinforced Handhole

Example 13

i'",,'

!

Reinforced Halldhole

Exumple 13

iIIi!,

fI,

'1'"

q't-!

Standard Specifications for Structural Supports for Highway Signs, Luminaires and Traffic Signals

'""'- c...• "-:: ..,.- •.....•

/I.,-

,-

i\.

Figure 11-1 (e). Illustrative Examples

11-22

/\.

Section 11: Fatigue Design

11.9 REFERENCES

/ American Association of State Highway and Transportation Officials. AASHTO Standard Specifications forHighway Bridges. Washington, D.C.: AASHTO, 1996.

·./Cook, R. A, D. Bloomquist, A M. Agosta, and K. F. Taylor. Wind Load Data for Variable Message Signs.Report no. FUDOT/RMC/0728-9488. City, Fla.: University of Florida, Florida Department of Trans­portation, 1996 .

./ Creamer, B. M., K. G. Frank, and R. E. Klingner. Fatigue Loading of Cantilever Sign Structures from TruckWind Gusts. Report no. FHWA/TX-79/10+209-1F. Austin, Texas: Center for Highway Research,Texas State Department of Highways and Public Transportation, 1979 .

./ DeSantis, P. V. and P. Haig. "Unanticipated Loading Causes Highway Sign Failure." Proceedings ofANSYS Convention, 1996.

Dexter, R. J. and K. W. Johns. Fatigue-Related Wind Loads on Highway Support Structures. AdvancedTechnology for Large Structural Systems, report no. 98-03. Bethlehem, Pa.: Lehigh University,1998.

<> Fisher, J. W., A Nussbaumer, P. B. Keating, and B. T. Yen. NCHRP Report 354: Resistance of WeldedDetails Under Variable Amplitude Long-Life Fatigue Loading. TRB, National Research Council,Washington, D.C., 1993.

v'Kaczinski, M. R.; R. J. Dexter, and J. P. Van Dien. NCHRP Report 412: Fatigue Resistant Design of Canti­

levered Signal, Sign and Light s.upports. T~B~ ,N(3.tional R~~earc~ 9ounc)I,. Was_hing!qn, D ..~.,1998'.. n'

McDonald, J. R.; et al. Wind toad Effects on Signals, Luminaires and Traffic Signal Structures. Report no.

.... - -~~~,.~.30~-.~.~~~~~~ock,.·T~~~~;~~!n.~,E~9~n.e.er.inQRes~rq.h y~.!1ter!..I~.X9-~.T-~~h.d~l/tliy.~~~Jty;1.~~!?-,".d.:: , .._'_' . _--.--- ." .--- . ----," .

11-23