Design of Pedestrian Bridge LFRD

ATTACHME ATTACHMENT NT A – 2009 2009 AGEND AGENDA A ITEM ITEM

- T-5 (WAI (WAI 31)

NCHRP 20-07 TASK 244 LRFD GUIDE SPECIFICATIONS SPECIFICATIONS FOR THE DESIGN OF PEDESTRIAN BRIDGES FINAL DRAFT

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LRFD LRFD GUIDE GUIDE SPECIF SPECIFICA ICATI TIONS ONS FOR FOR THE DESIG DESIGN N OF PEDE PEDESTR STRIAN IAN BRID BRIDGES GES

TABLE OF CONTENTS 1—GENERAL.................... —GENERAL................................... ............................ ........................... ............................ ............................ ............................ ............................ ............................ ............................ ............................ ................ 1 1.1—SCOPE.......................... 1.1—SCOPE........................................ ............................ ............................ ............................ ........................... ............................ ............................ ............................ ............................ .......................... ............. 1 1.2—PROPRIETA 1.2—PROPRIETARY RY SYSTEMS .......................... ......................................... ............................ ............................ ............................ ............................ ............................. ........................... ................... ...... 1 1.3—COLLISI 1.3—COLLISION ON MITIGATION......... MITIGATION....................... ............................ ............................ ............................ ............................ ............................ ............................ ............................ ........................ .......... 1 2—PHILOSOPHY..... 2—PHILOSOPHY................... ............................ ............................ ............................ ............................ ............................ ............................ ............................ ............................ ............................ ........................ .......... 2 3—LOADS 3—LOADS ........................... .......................................... ............................. ............................ ............................ ............................ ............................ ........................... ............................ ............................ .......................... ............. 2 3.1—PEDESTRI 3.1—PEDESTRIAN AN LOADING LOADING (PL)........................ (PL)...................................... ............................ ............................ ............................ ............................ ............................ ............................ ................. ... 2 3.2—VEHICLE 3.2—VEHICLE LOAD (LL)............................... (LL)............................................. ............................ ............................ ............................ ............................ ............................ ............................ ........................ .......... 3 3.3—EQUESTRIA 3.3—EQUESTRIAN N LOAD (LL)................................... (LL)................................................. ........................... ............................ ............................ ............................ ............................ .......................... ............. 4 3.4—WIND 3.4—WIND LOAD (WS)............................... (WS)............................................. ............................ ............................ ............................ ............................ ............................ ............................ ............................ ................ 4 3.5—FATIGUE 3.5—FATIGUE LOAD (LL)............................... (LL)............................................. ............................ ............................ ............................ ............................ ............................ ............................ ........................ .......... 5 3.6—APPLICA 3.6—APPLICATION TION OF LOADS........................ LOADS...................................... ............................ ............................ ............................ ............................ ............................ ............................ ...................... ........ 5 3.7—COMBINA 3.7—COMBINATION TION OF LOADS............................. LOADS........................................... ............................ ............................ ............................ ............................ ............................ ............................ ................ 5 4—FATIGUE 4—FATIGUE .......................... ........................................ ............................ ............................ ............................ ............................ ............................ ............................ ............................ ............................ ........................ .......... 5 4.1—RESISTA 4.1—RESISTANCE NCE ........................... .......................................... ............................ ............................ ............................. ............................ ............................ ........................... ............................ ........................... ............ 5 4.2—FRACTURE...... 4.2—FRACTURE.................... ............................ ............................ ............................ ............................ ............................ ............................ ............................ ............................ ............................ ........................ .......... 6 5—DEFLECTIONS... 5—DEFLECTIONS................. ............................ ............................ ............................ ............................ ............................ ............................ ............................ ............................ ............................ ........................ .......... 6 6—VIBRATIONS 6—VIBRATIONS .......................... ........................................ ............................ ............................ ............................ ............................ ............................ ............................ ............................ ............................ ................. ... 6 7—STABILITY........... 7—STABILITY......................... ............................. ............................ ............................ ............................ ........................... ............................ ............................ ............................ ............................ ...................... ........ 7 7.1—HALF-THRO 7.1—HALF-THROUGH UGH TRUSSES .......................... ........................................ ............................ ............................ ............................ ............................ ............................ ............................ ................. ... 7 7.1.1—Latera 7.1.1—Laterall Frame Frame Design Force................ Force.............................. ............................ ............................ ............................ ............................ ............................ ............................ ...................... ........ 7 7.1.2—Top 7.1.2—Top Chord Stability Stability .......................... ........................................ ............................ ............................ ............................ ............................ ............................ ............................ ........................ .......... 7 7.1.3—Alter 7.1.3—Alternativ nativee Analysis Analysis Procedures................ Procedures.............................. ............................ ............................ ............................ ............................ ............................ ............................ ................ 9 7.2—STEEL 7.2—STEEL TWIN I-GIRDER I-GIRDER AND SINGLE TUB GIRDER SYSTEMS .............................. ............................................ ............................ .................... ...... 10 7.2.1—Gener 7.2.1—General........... al......................... ............................ ............................ ............................ ............................ ............................ ............................ ............................ ............................ ............................ ................ 10 7.2.2—Lateral Torsional Buckling Resistance - Twin I-Girder........... ........... .......... ........... ........... .......... .......... .... 10 7.2.3—Lateral-Torsional Buckling Resistance-Singly Symmetric Sections ........... .......... ........... .......... ........... ..... 11 8—TYPE SPECIFIC SPECIFIC PROVISIONS PROVISIONS .......................... ........................................ ............................ ............................ ............................ ............................ ............................ ............................ ................ 11 8.1—ARCHES........... 8.1—ARCHES......................... ............................ ............................ ............................ ............................ ............................ ............................ ............................ ............................ ............................ ...................... ........ 11 8.2—STEEL 8.2—STEEL TUBULAR MEMBERS MEMBERS ........................... .......................................... ............................ ............................ ............................ ............................ ............................ ........................ ........... 11 8.2.1—Gener 8.2.1—General........... al......................... ............................ ............................ ............................ ............................ ............................ ............................ ............................ ............................ ............................ ................ 11 8.2.2—Detai 8.2.2—Detailing ling .......................... ......................................... ............................. ............................ ............................ ............................ ............................ ........................... ............................ ......................... .......... 12 8.2.3—Tubular Fracture Critical Members.............. ........... .......... ........... ........... .......... .......... ........... .......... ........... 12 8.3—FIBER 8.3—FIBER REINFORCED REINFORCED POLYMER POLYMER (FRP) MEMBERS MEMBERS .......................... ......................................... ............................ ............................ ............................ ................. .... 13 REFERENCES REFERENCES .......................... ........................................ ............................ ............................. ............................ ............................ ............................ ........................... ............................ ............................ .................... ...... 13

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LRFD GUIDE SPECIFICATIONS PECIFICATIONS FOR THE DESIGN OF PEDESTRIAN BRIDGES

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1—GENERAL 1.1—SCOPE

C1.1

These Guide Specifications address the design and constr construct uction ion of typica typicall pedest pedestria rian n bridge bridgess which which are desi design gned ed for, for, and and inte intend nded ed to carr carry, y, prim primar aril ily y pedest pedestria rians ns,, bicyc bicyclis lists, ts, equest equestria rian n riders riders and light light maintenance vehicles, but not designed and intended to carry typical typical highway highway traffic. traffic. Pedestria Pedestrian n bridges with cable cable suppor supports ts or atypic atypical al struct structura urall system systemss are not specifically addressed. These These Guide Guide Specif Specifica icatio tions ns provi provide de additi additiona onall guidance on the design and construction of pedestrian bridges in supplement to that available in the AASHTO LRFD Bridge Design Specifications (AASHTO LRFD). Only Only those those issues issues requi requirin ring g addit addition ional al or differ different ent treatmen treatmentt due to the nature of pedestria pedestrian n bridges bridges and thei theirr load loadin ings gs are addr addres esse sed. d. In Artic Article le 3 of this this document, document, the load definiti definitions ons and abbreviati abbreviations ons are taken taken from from AASHTO Alumin inum um and and wood wood AASHTO LRFD LRFD. Alum structure structuress are adequately adequately covered in AASHTO LRFD, and as such are not specifically addressed herein. Implem Implement entati ation on of the wind wind loadin loading g and fatigu fatiguee loading loading provision provisionss require require reference reference to the AASHTO Standar Standard d Specif Specifica icatio tions ns for Struct Structura urall Suppor Supports ts for Hig Highw hway ay Sign Signs, s, Lumi Lumina nari ries es and and Traf Traffi ficc Sign Signal alss (AASHTO Signs).

This This edit editio ion n of the the Guid Guidee Spec Specif ific icat atio ions ns was was developed developed from the previous previous Allowable Allowable Stress Design (ASD) (ASD) and Load Load Factor Factor Design Design (LFD)(LFD)-bas based, ed, editio edition n ( AASHTO evalua uati tion on of avai availa labl blee fore foreig ign n AASHTO 1997 ). An eval specifica specifications tions covering covering pedestria pedestrian n bridges, bridges, and failure failure investigation reports as well as research results related to the behavior and performance of pedestrian bridges was performed during the development of the LRFD Guide Specifications.

1.2—PROPRIETARY SYSTEMS

C1.2

Where proprietary systems are used for a pedestrian bridge crossing, the engineer responsible for the design of the system shall submit sealed calculations prepared by a licensed Professional Engineer for that system.

It is important to clearly delineate the responsibilities of each party when proprietary bridge systems are used. All portions of the design must be supported by sealed calculati calculations, ons, whether whether from the bridge bridge manufactu manufacturer, rer, or the the spec specif ifyi ying ng engi engine neer er.. The inte interf rfac acee betw betwee een n the the proprietary system and the project-specific substructures and foundations needs careful attention.

1.3—COLLISION 1.3—COLLISION MITIGATION

C1.3

Articl clee 2.3.3 2.3.3.2 .2 spec specif ifie iess an AASH AASHTO TO LRFD LRFD Arti increase increased d vertical vertical clearance clearance for pedestria pedestrian n bridges bridges 1.0 ft. higher than for highway bridges, in order to mitigate the risk from vehicle collisions with the superstructure. Should Should the the owner owner desire desire additio additional nal mitig mitigati ation, on, the following steps may be taken:

In most most cases cases increa increasin sing g verti vertical cal cleara clearance nce is the most cost effective method of risk mitigation.



Increasing vertical clearance in addition to that contained in AASHTO LRFD



Prov Proviidin ding struct ructu ural ral conti ontinu nuiity of the the superstruc superstructure ture,, either either between between spans or with the substructure



Increasing the mass of the superstructure




Incr Increa easi sing ng the the superstructure

late latera rall

resi resist stan ance ce

of

2

the the

2—PHILOSOPHY Pedestrian bridges shall be designed for specified lim limit stat states es to achi achiev evee the the obje object ctiv ives es of safe safety ty,, servicea serviceabili bility ty and constructa constructabilit bility, y, with due regard regard to issue issuess of inspec inspectab tabili ility, ty, econom economy, y, and aesthe aesthetic tics, s, as spec specif ifie ied d in the the AASHT These G ui uide AASHTO O LRFD LRFD. Specif Specifica icatio tions ns are based based on the LRFD LRFD philos philosophy ophy.. Mixing provisions from specifications other than those refe refere renc nced ed here herein in,, even even if LRFD LRFD base based, d, shou should ld be avoided. 3—LOADS 3.1—PEDESTRIAN 3.1—PEDESTRIAN LOADING (PL)

C3.1

Pedestrian bridges shall be designed for a uniform pedest pedestria rian n loading loading of 90 psf. psf. This This loadin loading g shall shall be patt patter erne ned d to prod produc ucee the the maxi maximu mum m load load effe effect cts. s. Cons Consid ider erat atio ion n of dyna dynami micc load load allo allowa wanc ncee is not not required with this loading.

The previous previous edition of these Guide Specifica Specifications tions used a base nominal loading of 85 psf, reducible to 65 psf based on influence influence area for the pedestrian pedestrian load. With the LFD LFD load load fact factor ors, s, this this resu result ltss in fact factor ored ed load loadss of 2.17(85 2.17(85)) = 184 psf and 2.17(65) 2.17(65) = 141 psf. psf. The Fourth Fourth Edition of AASHTO LRFD specif specified ied a consta constant nt 85 psf regard regardles lesss of influenc influencee area. area. Multi Multiply plying ing by the load factor, factor, this results results in 1.75(85) 1.75(85) = 149 psf. This falls within within the range of the previous factored loading, albeit toward the lower end. European codes appear to start with a higher nominal load (approx 105 psf), but then allow reductions based on loaded loaded length. length. Additi Additiona onally lly,, the load factor factor applie applied d is 1.5, resulting in a maximum factored load of (1.5)105 = 158 158 psf. psf. For For a long long loade loaded d leng length th,, this this load load can can be reduced to as low as 50 psf, resulting in a factored load of (1.5)50 (1.5)50 = 75 psf. The effect effect of resistance resistance factors factors has not been been acco accoun unte ted d for for in the the abov abovee disc discus ussi sion on of the the Europe European an codes. codes. There There are, however, however, warning warningss to the design designer er that that a reduct reduction ion in the the load load based based on loaded loaded length may not be appropriate for structures likely to see significant crowd loadings, such as bridges near stadiums. Cons Consid ider erat atio ion n might ight be give given n to the the maxi maximu mum m credible credible pedestrian pedestrian loading. loading. There is a physical physical limit limit on how much load can be applied to a bridge from the static weight weight of pedestrians. pedestrians. It appears that that this load is around 150 150 psf, psf, base based d on work work done done by Nowak Nowak (200 (2000) 0) from from wher wheree Figu Figure ress C1 thro throug ugh h C3 were were take taken. n. Alth Althoug ough h there there does does not appear appear to be any availabl availablee inform informati ation on relating to the probabilistic distribution of pedestrian live loading, loading, knowing the maximum credible credible load helps to define the limits of the upper tail of the distribution of load. The The use of a 90 psf nomi ominal live load in combination with a load factor of 1.75 results in a loading of 158 psf, psf, which which provi provides des a margi marginal nal,, but suffic sufficien ient, t, reserve compared with the maximum credible load of 150


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psf.

Figure C3.1-1 —Live Load of 50 psf



3.2—VEHICLE 3.2—VEHICLE LOAD (LL)

C3.2

Wher Wheree vehi vehicu cula larr acce access ss is not not prev preven ente ted d by permanent physical methods, pedestrian bridges shall be

The vehicle loading specified are equivalent to the H-trucks shown in Article 3.6.1.6 of AASHTO LRFD at


designed designed for a maintena maintenance nce vehicle load specifie specified d in Figure 1 and Tab Table 1 for the Strength I Load Combination unless otherwise specified by the Owner. A single truck shall be placed to produce the maximum load load effect effectss and shall shall not be placed placed in combin combinati ations ons with the pedestria pedestrian n load. The dynamic dynamic load allowance allowance need not be considered for this loading.

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the time of this writing (2009) and contained in previous Standard Specificat Specifications ions for versio versions ns of the AASHTO Standard Highway Bridges.

Table 3.2-1—Design Vehicle Clear Deck With 7 to 10 feet Over 10 feet

Design Vehicle H5 H10

Figure 3.2-1—Maintenance Vehicle Configurations.

3.3—EQUESTRIAN 3.3—EQUESTRIAN LOAD (LL)

C3.3

Decks intended to carry equestrian loading shall be designed for a patch load of 1.00 kips over a square area measuring 4.0 inches on a side.

The equestrian load is a live load and intended to ensure ensure adequate adequate punching punching shear capacity of pedestrian pedestrian bridge decks where horses horses are expected. The loading was deriv derived ed from from hoof hoof pressu pressure re measu measurem rement entss report reported ed in Roland Roland et. al. (2005). (2005). The worst loading loading occurs during during a canter where the loading on one hoof approaches 100% of the total weight weight of the horse. The total factored factored load load of 1.75 kips is approximately the maximum credible weight of a draft horse.

3.4—WIND LOAD (WS)

C3.4

Pedestrian bridges shall be designed for wind loads as specified in the AASHTO Signs, Articles 3.8 and 3.9. Unless Unless otherw otherwise ise direct directed ed by the Owner, Owner, the the Wind Wind Importan Importance ce Factor, Factor, I r, shall all be tak taken as 1.15. 1.15. The The loading shall be applied over the exposed area in front

AASHTO Signs Signs The The wind wind load loadin ing g is take taken n from from AASHTO specification rather than from AASHTO LRFD due to the potentially flexible nature of pedestrian bridges, and also due to the potenti potential al for traffic traffic signs signs to be mounte mounted d on them.


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elevat elevation ion includi including ng enclos enclosure ures. s. Wind Wind load load on signs supported by the pedestrian bridge shall be included. In addi additi tion on to the the wind wind load load spec specif ifie ied d abov above, e, a vertical uplift line load as specified in AASHTO LRFD Article 3.8.2 and determined as the force caused by a pressure of 0.020 ksf over the full deck width, shall be applied applied concurrent concurrently. ly. This loading loading shall be applied at the windward quarter point of the deck width.

For porous wind enclosures, the wind pressure may be reduced but pressures less than 85% of the pressure on a solid enclosure are not recommended.

3.5—FATIGUE 3.5—FATIGUE LOAD (LL)

C3.5

The The fati fatigu guee load loadin ing g used used for for the the fati fatigu guee and and fracture limit state (Fatigue I) shall be as specified in Section 11 of the AASHTO Signs. The Natu Natural ral Wind Wind Gust specified in Article 11.7.3 and the Truck-Induced Gust Gust specif specified ied in Articl Articlee 11.7.4 11.7.4 of that that specif specifica icati tion on need only be considered, as appropriate.

Wind Wind load loadss are are not not part part of the the Fati Fatigu guee I load load com combina binati tion on for vehi vehicu cula larr brid bridge ges. s. This This arti articl clee designates wind as a live load for pedestrian bridges, via the designati designation on LL. Wind should should be considered considered a fatigue fatigue live load for pedestrian bridges. Neither the pedestrian live load nor the maintenance vehi vehicl clee load load used used for for stre streng ngth th and and serv servic icea eabi bili lity ty is appropriate as a fatigue design loading due to the very infreq infrequen uentt nature nature of this this loadin loading. g. The fatigue fatigue loadin loading g specified is consistent with the treatment of sign support struct structure ures. s. For bridges bridges crossi crossing ng roadwa roadways, ys, the trucktruckinduce induced d gust gust loadin loading g should should be consid considere ered. d. The other other loadings specified in AASHTO Signs are not applicable to pedestrian bridges due to their decreased susceptibility to galloping or vortex shedding vibrations.

3.6—APPLICATION 3.6—APPLICATION OF LOADS

C3.6

When When determ determini ining ng the the patter pattern n of pedest pedestria rian n live live loading which maximizes or minimizes the load effect on a given member, the least dimension of the loaded area shall be greater than or equal to 2.0 ft.

The dimension given is meant to represent a single line line of pedest pedestria rians; ns; any width width less than than this this would would not represent a practical loading scenario.

3.7—COMBINATION 3.7—COMBINATION OF LOADS

C3.7

The types of bridges identified in Article 1.1 shall be designed for the load combinations and load factors specif specified ied in AASHTO AASHTO LRFD LRFD Table Table 3.4.1-1 3.4.1-1,, with with the following exceptions:

Load combination combination Strength II is meant for special special permi permitt trucks trucks,, which which is not applic applicabl ablee to pedest pedestria rian n bridges. bridges. Strength Strength IV is for dead load dominant dominant structures structures such as long span trusses, and would not likely apply to pedest pedestria rian n bridge bridges. s. Streng Strength th V addres addresses ses the case of strong wind combined with reduced live loading, which is not likely likely to occur for pedestri pedestrian an bridges. bridges. For unusual unusual case casess wher wheree the the excl exclud uded ed load load comb combin inat atio ions ns have have a reas reason onab able le chan chance ce of occu occurr rrin ing, g, they they shou should ld be considered in the design. design. The fatigue loading specified specified in AASHTO Signs and referenced herein was calibrated for a load factor of 1.0 and the design condition of infinite life.

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Load combinations combinations Strength II, Strength Strength IV, and Strength V need not be considered.

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The The load oad factor ctor for the Fatig atigu ue I loa load comb combin inat ation ion shal shalll be take taken n as 1.0, 1.0, and and the the Fati Fatigu guee II load load com combina binati tion on need need not not be considered.

4—FATIGUE 4.1—RESISTANCE The fatigu fatiguee resist resistanc ancee for steel steel compon component entss and AASHTO AASH TO LRFD LRFD, detail detailss shall shall be as specif specified ied in the Article 6.6.1.2.5 for the Fatigue I load combination. For


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those components and details not covered in AASHTO LRFD, the nomina nominall fatigu fatiguee resis resistan tance ce may be taken taken from Table 11.3 of AASHTO Signs or Figure 2.13 of AWS D1.1 Structural Welding Code – Steel. The fatigue fatigue resistanc resistancee for steel reinforceme reinforcement nt in concrete structures shall be as specified in the AASHTO LRFD Article 5.5.3. 4.2—FRACTURE

C4.2

Except Except as specif specifie ied d herein herein,, all of the provis provision ionss AASHTO LRFD LRFD spec specif ifie ied d in Arti Articl clee 6.6.2 6.6.2 of the the AASHTO relating relating to Charpy V-notch (CVN) fracture fracture toughness requir requirem ement ents, s, includ including ing Fractu Fracture re Criti Critical cal Member Member (FCM) (FCM) and Main Member Member designati designation, on, shall shall apply to steel steel pedest pedestria rian n bridge bridges. s. Design Design of tubul tubular ar memb members ers shal shalll also also sati satisf sfy y the the prov provis isio ions ns of Arti Articl clee 8.2. 8.2. If supp suppor orte ted d by the the char charac acte teri rist stic icss of the the site site and and appl pplication, on, the Own Owner may waive the the FCM FCM requirements.

For For pede pedest stri rian an brid bridge gess cros crossi sing ng lowlow-vo volu lum me wate waterw rway ayss and and road roads, s, or area areass not not acce access ssib ible le to the the general public, FCM treatment may not be appropriate.

5—DEFLECTIONS

C5

Deflecti Deflections ons should should be investig investigated ated at the service service limit limit state using load combination combination Service Service I in Table AASHTO LRFD LRFD. For 3.4.1 3.4.1-1 -1 of AASHTO For span spanss othe otherr than than cantilever arms, the deflection of the bridge due to the unfact unfactore ored d pedest pedestria rian n live live loadin loading g shall shall not exceed exceed 1/500 of the span length. length. Deflection Deflection in cantilever cantilever arms due to the pedestrian live loading shall not exceed 1/300 of the cantilever cantilever length. Horizontal Horizontal deflecti deflections ons under unfactored wind loading shall not exceed 1/500 of the span length.

AASHTO O LRFD LRFD contains Table Table 2.5.2 2.5.2.6 .6.1 .1-1 -1 of AASHT guidance on span-to-depth ratios that may be invoked by an owner.

6—VIBRATIONS

C6

Vibrations shall be investigated as a service limit state using load combination Service I in Table 3.4.1-1 of AASHTO LRFD. Vibration Vibration of the structu structure re shall not cause cause discom discomfor fortt or concer concern n to users users of a pedest pedestria rian n bridge bridge.. Except Except as specif specified ied herein, herein, the the fundam fundament ental al frequency frequency in a vertical vertical mode of the pedestrian pedestrian bridge without live load shall be greater than 3.0 hertz (Hz) to avoid avoid the first first harmoni harmonic. c. In the the latera laterall direct direction ion,, the fundamental frequency of the pedestrian bridge shall be grea greate terr than than 1.3 Hz. Hz. If the the fund fundam amen enta tall freq freque uenc ncy y cann cannot ot sati satisf sfy y thes thesee limi limita tati tion ons, s, or if the the seco second nd harmon harmonic ic is a concer concern, n, an evalu evaluati ation on of the dynami dynamicc perf perfor orma manc ncee shal shalll be made made.. This This eval evalua uati tion on shal shalll consider:

Due Due to the the vibr vibrat atio ion n probl problem emss expe experi rien ence ced d in London on the Millennium bridge, there have been many publi publicat cation ionss in the techni technical cal liter literatu ature, re, primari primarily ly in Euro Europe pe,, on this this topi topic. c. Desp Despit itee this this larg largee body body of knowledge, it does not appear there has been convergence toward one method of evaluation, or development of any specification that adequately covers this issue. These provisions address the issue of vibration from two directions: maintaining a minimum natural vibration freq freque uenc ncy y abov abovee thos thosee indu induce ced d by pede pedest stri rian ans, s, and and spec specif ifyi ying ng a mini minimu mum m weig weight ht to lim limit vibr vibrat atio ion n amplitude amplitudess if the frequency frequency limits limits are not met. Although Although somewh somewhat at outdat outdated, ed, both both of these these approa approache chess are still still viable and have the great advantage of simplicity. The techni technical cal guide guide publis published hed by Setra Setra (Servi (Service ce d’Etudes d’Etudes Techniques Techniques des Routes Routes et Autoroute Autoroutes) s) (2006) appears to present a relatively straightforward method for addressing vibration issues when the frequencies of the bridge fall within the pacing frequencies of pedestrians. The “lock-in” phenomenon refers to the tendency of

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The frequency frequency and magnitud magnitudee of pedestria pedestrian n footfall loadings

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The The phas phasin ing g of loadi oading ng from rom multi ltiple ple pedest pedestria rians ns on the bridge bridge at the same time, time,


including the “lock-in” phenomena

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Appropriate estimation of structural damping

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Frequency Frequency dependent dependent limits limits on accelerati acceleration on and/or velocity

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people people to synchr synchroni onize ze their their pacing pacing freque frequency ncy to the late latera rall freq freque uenc ncy y of the the brid bridge ge when hen the the late latera rall displacem displacements ents begin to grow. In other words, words, instead of random frequencies and phasing among the loading from pedest pedestria rians ns on the the bridge bridge,, the freque frequenci ncies es and phases phases becomes fully correlated with the bridge motion.

In lieu of such evaluation in the vertical direction the bridge may be proportioned such that either of the following criteria are satisfied:

 180    W 

f  2.86 ln

(6-1)

or W  180e ( 0.35

f )

(6-2)

where: W =

the weight weight of the suppor supported ted struc structu ture, re, includ including ing only dead load (kip)

f

the fun fundam damenta ntal frequ requen ency cy in the vert vertiical cal direction (Hz)

=

7—STABILITY 7.1—HALF-THROUGH 7.1—HALF-THROUGH TRUSSES 7.1.1—Lateral Frame Design Force

C7.1.1

The verti vertical cal truss truss member members, s, the floor floor beams beams and their connections shall be proportioned to resist a lateral force applied at the top of the the truss verticals. The lateral force force shall shall not be less less than than 0.01/K 0.01/K times times the averag averagee factored design compressive force in the two adjacent top chord chord membe members, rs, where where K is the design design effect effective ive length length factor factor for the the indivi individua duall top chord chord memb members ers supported supported between between the truss vertical verticals. s. In no case shall the valu alue for 0.01 0.01//K be less ess than than 0.00 0.003 3 when hen determining the minimum lateral force, regardless of the K-value used to determine the compressive capacity of the top chord. chord. The lateral lateral frame frame design force force shall be applied concurrently with the loading used to determine the average compressive force above. End posts shall be designed as a simple cantilever to carry its applied axial load combined with a lateral load of 1.0% of the end post axial load, applied laterally at the upper end.

This This articl articlee modif modifies ies the provis provision ionss of AASHTO LRFD by replacing the 300 pounds per linear foot design requirements for truss verticals with provisions based on research research reported reported in Galambos Galambos (1998). These provisions provisions establish establish the minimum minimum lateral strength of the verticals verticals based on the degree of lateral support necessary for the top chord chord to resis resistt the maxim maximum um design design compre compressi ssive ve force.

7.1.2—Top Chord Stability

C7.1.2

The top chord shall be considered as a column with elas elasti ticc late latera rall supp suppor orts ts at the the pane panell poin points ts.. The The contri contribut bution ion of the the connec connectio tion n stiff stiffnes nesss betwee between n the

The use of the 1.33 facto factorr appli applied ed to the the factor factored ed compression load to determine Pc is in recognition that for for unif unifor orml mly y load loaded ed stru struct ctur ures es ther theree is a high higher er


floor beam and the vertical member shall be considered in dete determ rmin inin ing g the the stif stiffn fnes esss of the the elas elasti ticc late latera rall supports. The procedure for determining the resistance of a compression member in AASHTO LRFD may be used to determine the resistance of the compression chord with a value for the effective length factor, K, based on a late latera rall U-fr U-fram amee and and obtai obtaine ned d from from Table Table 1. In this this table, C

=

late latera rall stif stiffn fnes esss of the the U-fra U-fram me made made of the truss verticals and the floorbeam taken as P/Δ (kip/in.)

P

=

arbit arbitrar rary y latera laterall load load as shown shown schema schemati tical cally ly in Figure 1 (kips)

Δ

=

latera laterall deflect deflection ion resul resultin ting g from later lateral al load load P and shown schematically in Figure 1 (in.)

L

=

length length of the chord chord betwe between en panel panel points points (in.) (in.)

Pc =

desired desired critical critical buckling buckling load (kip), (kip), which which shall shall be taken as 1.33 times the factored compressive load,

n

numb number er of pane panels ls in the the trus trusss

=

Figure 7.1.2-1—Lateral U-Frame

8

probability of the maximum compression force occurring simult simultane aneous ously ly in adjace adjacent nt truss truss panels panels.. For further further discussion refer to Galambos (1998). Interpola Interpolation tion of values values between between those given in the table is acceptable.


9

Table 7.1.2-1—Values of 1/K for various Values of CL/Pc and n 1/K

n=4

n=6

n=8

n=10

n=12

n=14

n=16

1.000

3.686

3.616

3.660

3.714

3.754

3.785

3.809

0.980

3.284

2.944

2.806

2.787

2.771

2.774

0.960

3.000

2.665

2.542

2.456

2.454

2.479

0.950

2.595

0.940

2.754

2.303

2.252

2.254

2.282

0.920

2.643

2.146

2.094

2.101

2.121

0.900

3.352

2.593

2.263

2.045

1.951

1.968

1.981

2.460

2.013

1.794

1.709

1.681

1.694

2.313

1.889

1.629

1.480

1.456

1.465

2.147

1.750

1.501

1.344

1.273

1.262

1.955

1.595

1.359

1.200

1.111

1.088

1.739

1.442

1.236

1.087

0.988

0.940

1.639

1.338

1.133

0.985

0.878

0.808

1.517

1.211

1.007

0.860

0.768

0.708

1.362

1.047

0.847

0.750

0.668

0.600

1.158

0.829

0.714

0.624

0.537

0.500

0.886

0.627

0.555

0.454

0.428

0.383

0.530

0.434

0.352

0.323

0.292

0.280

0.187

0.249

0.170

0.203

0.183

0.187

0.250

0.135

0.107

0.103

0.121

0.112

0.200

0.045

0.068

0.055

0.053

0.070

0.180

0

0.150

0.017

0.031

0.029

0.025

0.139

0

0.100

0.003

0.010

0.097

0

0.850 0.800

2.961

0.750 0.700

2.448

0.650 0.600

2.035

0.550 0.500

1.750

0.450 0.400

1.232

0.350 0.300

0.121

0.293

0

0.259

0

0.114

0

0.085

0

7.1.3—Alternative Analysis Procedures

C7.1.3

The use use of a seco second nd-o -ord rder er nume numeri rica call anal analys ysis is procedure to evaluate the stability of the top chord of a half-through truss is acceptable in lieu of the procedure above, provided the following aspects are included in the model:

Given the increasing availability of software that is capable of second order analyses, such an analysis is a practical alternative to the method given in Article 7.1.2. Howev However er,, the the desi design gn equa equati tion onss in AASHTO AASHTO LRFD LRFD accoun accountt for the issues issues identi identifi fied, ed, and any altern alternati ative ve meth method od shoul should d also also addr addres esss thes these. e. One meth method od that that migh mightt be foll follow owed ed woul would d be to use use the the secon second d orde orderr numerical analysis to determine the K factor for a given chord size and panel point frame stiffness, and then the AASHTO LRFD LRFD to determ design design equations equations of AASHTO determine ine the the corresponding resistance.



Effect Effectss of initi initial al out-of out-of-st -strai raigh ghtne tness, ss, both both betwe between en panel panel points points and across across the entire entire length of the compression chord



Effect Effectss of residu residual al stress stresses es in compre compressi ssion on members due to fabrication and construction



Effects of the stiffness of vertical to floorbeam connections


10

7.2—STEEL TWIN I-GIRDER AND SINGLE TUB GIRDER SYSTEMS 7.2.1—General

C7.2.1

For potentially torsionally flexible systems such as twin I-girder I-girder and single tub girder girder structura structurall systems, systems, the designer shall consider:

Severa Severall incide incidents nts have have highl highlig ighte hted d the the need need for a careful evaluation of the stability of pedestrian bridges, especi especiall ally y during during the constr construct uction ion stages. stages. Struct Structura urall system systemss consis consistin ting g of two parall parallel el girder girderss can exhibi exhibitt very different behavior during construction depending on the bracing bracing systems used. If no lateral lateral bracing bracing is present, present, during construction the out-of-plane (transverse) bending stiffn stiffness ess can be much much less less than than the in-pla in-plane ne (verti (vertical cal)) stiffness stiffness and lateral-tors lateral-torsional ional buckling buckling can occur. occur. After After the deck is cast, the section is effectively a “c” shape, which which is singly singly symmetr symmetrica ical. l. Use of the appropr appropriat iatee late latera rall-to tors rsio iona nall buck buckli ling ng equa equati tion on is crit critic ical al,, and and reference reference should should be made to Galambos Galambos (1998). Further Further information is contained in Yura and Widianto (2005), as well as Kozy and Tunstall (2007).



The out-of-plane stiffness of twin I-girders, prior becoming composite with a concrete deck, can be significantly smaller than the inplane, or vertical, vertical, stiffness. This can lead to to a lateral-torsional buckling instability during construction



Single tub girders, prior to becoming composite with a concrete deck, behave as singly symmetric sections with a shear center below the bottom flange. AASHTO LRFD Article 6.7.5.3 requires top lateral bracing in tub section members to prevent lateral torsional buckling of these sections.



Prior to becoming becoming composite composite with a concrete concrete deck deck,, twin twin I-gi I-gird rder erss with with bott bottom om flang langee bracing, will behave as a tub girder and exhibit the same tendencie tendenciess toward toward laterallateral-tors torsional ional buckling. Top lateral bracing bracing shall be provided as for tub sectio sections, ns, or the the stabil stability ity shall shall be checked as a singly symmetric member.

7.2.2—Lateral Torsional Buckling Resistance - Twin I-Girder For evaluating the stability of twin I-girder systems with withou outt a comp compos osit itee deck deck or late latera rall brac bracin ing, g, the the equation given by Yura and Widianto (2005) may be used:

M n  M cr 



2

s E 2

L

I yo I xo

 M px (7.2.2-1)

where: E = I xo = I yo = L

=

M cr cr =

modulu moduluss of elasti elasticit city y of steel steel (ksi) (ksi) in-p in-pla lane ne mom momen entt of ine inert rtia ia of of one one gird girder er 4 (in. ) out-of out-of-pl -plane ane momen momentt of inerti inertiaa of one girde girderr 4 (in. ) effect effectiv ivee buckli buckling ng lengt length h for latera laterall-tor torsi siona onall buckling (ft) crit critic ical al elas elasti ticc late latera rall tors torsio iona nall buck buckli ling ng


M px = M n = s

=

11

moment of one girder (kip-in.) in-p in-pla lane ne plas plasti ticc mom momen entt of of one one gird girder er (kip (kip-in.) nomin nominal al in-p in-pla lane ne fle flexu xura rall res resis ista tanc ncee of one one girder (kip-in.) spac spacin ing g betw betwee een n gird girder erss (in. (in.))

Where a concrete deck is used, continuous twin Igirder systems shall be made composite with the deck for the entire length of the bridge. 7.2.3—Lateral-Torsional 7.2.3—Lateral-Torsional Buckling Resistance-Singly Symmetric Sections

C7.2.3

The laterallateral-tors torsional ional stability stability of singly singly symmetri symmetricc secti ection onss not cov covered ered in Artic rticle le 7.2. 7.2.2 2 shall all be inve invest stig igat ated ed usin using g info inform rmat atio ion n avai availa labl blee in the the literature.

Equa Equati tion onss for for the the dete determ rmina inati tion on of the the late latera ralltorsional buckling moment in singly symmetric sections are given in the “Guide to Stability Design Criteria for Metal Metal Structure Structures” s” by Galambos Galambos (1998), (1998), specific specifically ally in chap chapte terr 5. Equa Equati tion on 5.9 5.9 of that that chap chapte terr pres presen ents ts the the genera generall formu formula la for bendin bending g membe members. rs. Method Methodss for accoun accountin ting g for locati location on of loadin loading g with with respec respectt to the shear center are provided, as well as for determining the approp appropria riate te buckli buckling ng length lengthss consid consideri ering ng rotati rotationa onall restraints.

8—TYPE SPECIFIC PROVISIONS 8.1—ARCHES Arches Arches shall shall be design designed ed in accord accordanc ancee with with the provisions of the AASHTO LRFD with guidance from Nettleton (1977). 8.2—STEEL TUBULAR MEMBERS 8.2.1—General The capaci capaciti ties es and resis resistan tances ces for the design design of connections for welded tubular steel members shall be in accordance with the Chapter K of the specifications and comment commentary ary of AISC AISC (2005) (2005) or AASHTO Signs. Resistanc Resistances es for fatigue design shall be in accordance accordance with the Structural Welding Code – Steel ANSI/AWS D1.1 Section 2.20.6 or Section 11 of AASHTO Signs. All loads, load factors, and resistance factors shall be as AASHTO TO LRFD LRFD and spec specif ifie ied d by AASH and thes thesee Gui Guide Spec Specif ific icat atio ions ns.. For For membe emberr desi design gn othe otherr than than connections:



Flex Flexur uree resi resist stan ance ce of rect rectan angu gula larr tubul tubular ar members shall be according to AASHTO LRFD Article 6.12 as box sections.



Shea Shearr resi resist stan ance ce of rect rectan angu gula larr tubu tubula larr AASHTO LRFD members shall be according to Article 6.11.9 as box sections.




12

Tension Tension and compressi compression on resistance resistance shall be according to AASHTO LRFD Article 6.8.2 and 6.9.2, respectively.

For electric-resistance-welded tubular members, the design wall thickness shall be taken as 0.93 times the nominal wall thickness. 8.2.2—Detailing

C8.2.2

The minimum metal thickness of closed structural tubul tubular ar membe members rs shall be 0.25 inch. inch. These These memb members ers shall either be completely sealed to the atmosphere, or be hot-dipped galvanized and provided with drain holes.

Different philosophies exist on how best to protect tubu tubula larr memb member erss from from corr corros osio ion. n. One One meth method od is to comple completel tely y seal seal the interi interior or of the member member from from the the atmo atmosp sphe here re.. This This requ requir ires es care carefu full deta detail ilin ing g of the the connections, as even a small opening will allow moisture laden air into the interior, and over time this can result in a large accumulat accumulation ion of water. Box members members in a large truss that were supposedly sealed to the atmosphere have been found to contain several feet of water. Another method of corrosion protection is to vent the interior of the tube adequately and to provide some form of surface treatment, often a galvanized finish, to prevent corrosion. corrosion. Issues Issues to consider consider include include the size of the field pieces pieces to be galvan galvanize ized, d, the size size of local local galvan galvanizi izing ng kettles, and the service environment of the bridge. FHWA FHWA Tech Techni nica call Advi Adviso sory ry T 5140 5140.2 .22 2 (198 (1989) 9) provides guidance in the use of weathering steels.

8.2.3—Tubular Fracture Critical Members

C8.2.3

The AASH AASHTO/ TO/AW AWS S Frac Fractu ture re Cont Contro roll Plan Plan for for Nonredund Nonredundant ant Members Members contained contained in AASHTO/AWS AASHTO/AWS D1.5, Section 12, shall be applied to tubular members, where required by AASHTO LRFD Articles 6.6.2 and C6.6.2, with the following modifications:

No current specification adequately covers the use of tubu tubula larr memb member erss in a frac fractu ture re crit critic ical al capa capaci city ty.. AASH AASHTO/ TO/AW AWS S D1.5 D1.5 speci specifi fica call lly y excl exclud udes es tubu tubula larr members. members. It appears significa significant nt research research is required required to address the unique aspects of both the longitudinal weld used to create the closed shape, as well as the one-sided groov roovee welds lds with ithout out bac backing king bars bars used used in the connection connectionss of HSS. Until such such time as this research research is performed, the procedure specified herein represents the best best availa available ble metho method d for addres addressi sing ng fract fracture ure criti critical cal issues in HSS construction.



ASTM A500, A501, A847, and A618 shall be added to those listed in Article12.4.1



For the purposes of determining preheat and interpass temperatures, the values for A709 Grade 50 shall be used.



Steel for tubular sections shall conform to the Charpy v-notch requirements defined in A70907. Filler Filler metal metal shall be treated as A709 and conform to the requirements of AWS D1.5 Table 12.1.



Welding details for cyclically loaded tubular members specified by AASHTO/AWS D1.1 shall be used.



All welds welds require require qualif qualifica icatio tion n using using AWS D1.1 Figure 4.8.


13

8.3—FIBER REINFORCED REINFORCED POLYMER (FRP) MEMBERS

C8.3

The minimum minimum thickness thickness of closed closed structur structural al FRP membe embers rs (suc (such h as tube tubes) s) shal shalll be 0.25 0.25 inch inch.. The The minimum minimum thickness thickness of open structura structurall FRP members members (such as channels) including connection plates shall be 0.375 inch.

For design of FRP members members in pedestria pedestrian n bridges, bridges, reference may be made to the AASHT AASHTO O Guid Guidee Specif Specifica icati tions ons for Design Design of FRP Pedest Pedestri rian an Bridge Bridgess Litt Little le info inform rmat atio ion n is curr curren entl tly y avai availa labl blee (2008). regarding regarding resistanc resistancee equations equations or resistanc resistancee factors factors for this this mater material ial used in bridge bridge struct structure ures. s. Severa Severall design design spec specif ific icat ation ionss cove coveri ring ng FRP FRP pult pultru rude ded d shap shapes es are are currently under development by the American Society of Civil Engineers and may be of use in the future for the design of FRP pedestrian bridges.

REFERENCES AASHTO. 1997. Guide Specifications for Design of Pedestrian Bridges , American Association of State Highway and Transportation Officials, Washington, DC. AASHTO. 2001. Standard Specifications for Structural Supports for Highway Signs, Luminaries and Traffic Signals, 4th Edition, LTS-4, American Association of State Highway and Transportation Officials, Washington, DC. AASHTO. 2002. Standard Specifications for Highway Bridges, 17th Edition , American Association of State Highway and Transportation Officials, Washington, DC. AASHTO. 2007. AASHTO LRFD Bridge Design Specifications, 4th Edition, 2008 and 2009 Interim, American Association of State Highway and Transportation Officials, Washington, DC. AASHTO. 2008. AASHTO Guide Specifications for Design of FRP Pedestrian Bridges , 1st Edition. American Association of State Highway and Transportation Officials, Washington, DC. AISC. 2005. Specification for Structural Steel Buildings, ANSI/AISC 360-05 , American Institute of Steel Construction, Chicago, IL. Allen, D. E. and Murray, T. M. 1993 “Design Criterion for for Vibrations Due to Walking,” AISC Journal, 4 th Quarter, pp. 117-129. AWS. 2008. Bridge Welding Code, AASHTO/AWS D1.5M/D1.5:2008, American Welding Society, Miami, FL. AWS. 2006. Structural Welding Code - Steel , AASHTO/AWS D1.1M/D1.1M:2006, American Welding Society, Miami, FL. Bachmann, H. “Lively footbridges - a real challenge”. Proceedings of the International Conference on the Design and Dynamic Behavior of Footbridges, Paris, France, November 20–22, 2002, pp.18–30. Blekherman, A.N. 2007 “Autoparametric “Autoparametric Resonance in a Pedestrian Pedestrian Steel Arch Arch Bridge: Solferino Bridge, Bridge, Paris,” Journal of Bridge Engineering, Volume 12, Issue 6, pp. 669-676 Dallard, P., Fitzpatrick, T., Flint A., Low A., Smith R.R., Willford M., and Roche M. ”London Millennium Bridge: Pedestrian-Induced Lateral Vibration”. Journal of Bridge Engineering , Volume 6, Issue 6, 2001, pp. 412-417.


Dallard, P., et al. “The London Millennium Footbridge”. Structural Engineering , 79(22), 2001, pp.17–33. FHWA, 1989. Uncoated Weathering Steel in Structures, Technical Advisory T 5140.22, Federal Highway Administration, US Department of Transportation, Washington, DC. Galambos, T.V. 1998. Guide to Stability Design Criteria for Metal Structures, 5th Edition , John Wiley & Sons, Inc., New York , NY Kozy, B. and Tunstall, S. 2007 “Stability Analysis Analysis and Bracing for for System Buckling in Twin I-Girder Bridges,” Bridge Structures: Assessment, Design and Construction , Vol 3 No.3-4, pp 149-163 Nettleton, D. A. 1977. Arch Bridges, Bridge Division, Office of Engineering, Federal Highway Administration, U.S. Department of Transportation, Washington, DC. Nowak, Nowak, A.S. and Collins, Collins, K.R. 2000. Reliability of Structures , McGraw-Hill International Editions, Civil Engineering Series, Singapore, Poston, Randall W., West, Jeffery S. “Investigation of the Charlotte Motor Speedway Bridge Collapse,” Metropolis & Beyond 2005 - Proceedings of the 2005 Structures Congress and the 2005 Forensic Engineering Symposium, April 20.24, 2005, New York, NY, ASCE Roberts, T. M. M. 2005 “Lateral Pedestrian Excitation Excitation of Footbridges,” Footbridges,” Journal of Bridge Engineering, Volume 10, Issue 1, pp. 107-112. Roland, Roland, E. S., Hull, M. L., and Stover, S. M. 2005. “Design “Design and Demonstra Demonstration tion of a Dynamomet Dynamometric ric Horseshoe for Measuring Ground Reaction Loads of Horses during Racing Conditions,” Journal of Biomechanics, Vol. 38, No. 10, pp. 2102-2112. SETRA. SETRA. 2006. Technical Guide – Footbridges -Assessment of Vibrational Behaviour of Footbridges under Pedestrian Loading, Service d’Etudes Techniques des Routes et Autoroutes, Association Francaise De Genie Civil, Paris, France. Willford, M. “Dynamic actions and reactions of pedestrians”. Proceedings of the International Conference on the Design and Dynamic Behavior of Footbridges, Paris, France, November 20–22, 2002. Yura, J. A. and Widianto. 2005. “Lateral Buckling and Bracing of Beam – A Re-evaluation after the Marcy Bridge Collapse.” 2005 Annual Technical Session Proceedings, April 6-9, 2005 in Monreal, Quebec, Canada, Structural Stability Research Council. Rolla, MO. Zivanovic, S., Pavic, A., and Reynolds, P. “Vibration serviceability of footbridges under human-induced excitation: a literature review”. Journal of Sound and Vibration , 279(1-2), 2005, pp. 1-74.

14

Design of Pedestrian Bridge LFRD

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