ACI 358.1R-92

ANALYSIS AND DESIGN OF REINFORCEDAND PRESTRESSED-CONCRETE

GUIDEWAY ST

CI Reported by A

Hidayat N. Grouni Chairman

T. Ivan Campbell

Michael P. CollinsCharles W. DolanRoger A. DortonThomas T. C Hsu

These recommendations, prepared by Committee 358, pre-sent a procedure for the design and analysis of reinforced andprestressed-concrete guideway structures for public transit. Thedocument is specifically prepared to provide design guidance forelevated transit guideways. For items not covered in this docu-ment the engineer is referred to the appropriate highway and rail-way bridge design codes.

Limit states philosophy has been applied to develop the de-sign criteria. A reliability approach was used in deriving load andresistance factors and in defining load combinations. A target re-liability index of 4.0 and a service life of 75 years were taken asthe basis for safety analysis. The reliability index is higher than thevalue generally used for highway bridges, in order to provide alower probability of failure due to the higher consequences offailure of a guideway structure in a public tramit system The 75year service life is comparable with that adopted by AASHTO fortheir updated highway bridge design specifications.

KEYWORDS: Box beams; concrete construction; cracking (fracturing);deformation; fatigue (materials); guideways; loads (forces); monorailsystems: partial prestressing; precast concrete; prestressed concrete:prestress loss; rapid transit systems; reinforced concrete; serviceablity;shear properties: structural analysis; structural design: T-beams;torsion; vibration.

CONTENTSCHAPTER 1- Scope, Definitions, and Nota-tions, pg. 358.1R-2

1.1 Scope1.2 Definitions1.3 Notations1.4 SI Equivalents1.5 Abbreviations

Cl Committee Reports, Guides. Standard Practices, andommentaries are intended for guidance in designing, planning,

ting, or inspecting construction and in preparing specifications.

ocuments. If items found in these documents are desired to be part

358.1RRUCTURES

Committee 358

Sami W. TabshSecretary

Stephen J. KokkinsAndy MoucessianAndrzej S. NowakHenry G. Russell

CHAPTER 2- General Design Considerations,pg. 358.1R-5

2.1 Scope2.2 Structural Considerations2.3 Functional Considerations2.4 Economic Considerations2.5 Urban Impact2.6 Transit Operations2.7 Structure/Vehicle Interaction2.8 Geometrics2.9 Construction Considerations2.10 Rails and Trackwork

CHAPTER 3 - Loads, pg. 358.1R-153.1 General3.2 Sustained Loads3.3 Transient Loads3.4 Loads due to Volumetric Changes3.5 Exceptional Loads3.6 Construction Loads

CHAPTER 4- Load Combinations and Loadand Strength Reduction Factors, pg. 358.1R-

23

4.1 Scope4.2 Basic Assumptions4.3 Service Load Combinations4.4 Strength Load Combinations

CHAPTER 5- Serviceability Design, pg.358.1R-25

5.1 General5.2 Basic Assumptions5.3 Permissible Stresses5.4 Loss of Prestress5.5 Fatigue5.6 Vibration5.7 Deformation5.8 Crack Control

ACI 358.1R-92 supersedes ACI 358.1R-86, effective Sept. 1, 1992.Copyright 0 1992 American Concrete Institute.All rights reserved including rights of reproduction and use in any

form or by any means, including the making of copies by any photoprocess, or by any electronic or mechanical device. printed, written ororal or recording for sound or visual reproduction or for use in anyknowledge or retrieval system or device, unless permission in writing isobtained from the copyright proprietors.

-1

ETE358.1R-2 MANUAL OF CONCR

CHAPTER 6 - Strength Design, pg. 356.1R-326.1 General Design and Analysis Considerations6.2 Design for Flexure and Axial Loads6.3 Shear and Torsion

CHAPTER 7- Reinforcement Details, pg.358.1R-34

CHAPTER 8 - References, pg. 358.1R-348.1 Recommended References

CHAPTER 1 - SCOPE, DEFINITIONSAND NOTATIONS

1.1- ScopeThese recommendations are intended to

provide public agencies, consultants, and otherinterested personnel with comprehensive criteriafor the design and analysis of concrete guidewaysfor public transit systems. They differ from thosegiven for bridge design in ACI 343R, AASHTObridge specifications, and the AREA manual ofstandard practice.

The design criteria specifically recognize theunique features of concrete transit guideways,namely, guideway/vehicle interaction, rail/structureinteraction, special fatigue requirements, andesthetic requirements in urban areas. The criteriaare based on current state-of-the-art practice formoderate-speed [up to 100 mph (160 km/h)]vehicles. The application of these criteria foradvanced technologies other than those discussedin this report, require an independent assessment.

ACI 343R is referenced for specific items notcovered in these recommendations. These refer-ences include materials, construction consider-ations, and segmental construction.

1.2-DefinitionsThe following terms are defined for general

use in this document. For a comprehensive list ofterms generally used in the design and analysis ofconcrete structures, the reader is referred toChapter 2 of ACI 318 and to ACI 116R. Theterminology used in this document conforms withthese references.

Broken rail - The fracture of a continuouslywelded rail.

Concrete, specified compressive strength of J$ -Compressive strength of concrete used in designand evaluated in accordance with Chapter 5 ofACI 318 is expressed in pounds per square inch

(psi) [Megapascals (MPa)]; wherever this quantityis under a radical sign, the square root of thenumerical value only is intended and the resultantis in pounds per square inch (psi). INSPECTION

Concrete-A mixture of portland cement or anyother hydraulic cement, fine aggregate, coarseaggregate, and water, with or without admixtures.

Continuously welded rail - Running rails that actas a continuous structural element as a result offull penetration welding of individual lengths ofrail; continuously welded rails may be directlyfastened to the guideway, in which case theircombined load effects must be included in thedesign.

Dead load -The dead weight supported by amember, as defined in Chapter 3, without loadfactors.

Design load-All applicable loads and forces andtheir load effects such as, moments and shearsused to proportion members; for design accordingto Chapter 5, design load refers to load withoutload factors; for design according to Chapter 6,design load refers to loads multiplied by appro-priate load factors, as given in Chapter 4.

Flexural natural frequency- The first verticalfrequency of vibration of an unloaded guideway,based on the flexural stiffness and mass distri-bution of the superstructure.

Live load-The specified live load, without loadfactors.

Load factor-A factor by which the service load ismultiplied to obtain the design load.

Service load-The specified live and dead loads,without load factors.

Standard vehicle-The maximum weight of thevehicle used for design; the standard vehicleweight should allow for the maximum number ofseated and standing passengers and should allowfor any projected vehicle weight increases if largervehicles or trains are contemplated for future use.

1.3 - Notation

a = center-to-center distance of shorter dimen-sion of closed rectangular stirrups, in.(mm). Section 5.5.3

a1= side dimension of a square post-tensioning

anchor, or lesser dimension of a rectangularpost-tensioning anchor, or side dimension of

a square equivalent in area to a circularpost-tensioning anchor, in. (mm). Section5.8.2.1

a, = minimum distance between the center-lines*

Scurvature of continuously welded rail, k/inA =

A =

Abs =

Aoh =

Ar =As =

At =

Av =

b =

=

bb =

BR =Cd =CD =Ce =

:> zCL =CR =d =

dc =

D =DR =

GUIDEWAY

of anchors, or twice the distance from thecenterline of the anchor to the nearestedge of concrete, whichever is less, in.(mm). Section 5.8.2.1effective tension area of concretesurrounding the main tension reinforcingbars and having the same centroid as thatreinforcement, divided by the number ofbars, in.2 (mm2); when the main rein-forcement consists of several bar sizes, thenumber of bars should be computed asthe total steel area divided by the area ofthe largest bar used. Section 5.8.1exposed area of a pier perpendicular tothe direction of stream flow, ft2 (m2).Section 3.3.4area of nonprestressed reinforcementlocated perpendicular to a potentialbursting crack, in.2 (mm2). Section 5.8.2.1Area enclosed by the centerline of closedtransverse torsion reinforcement, in.2(mm2). Section 5.5.3Cross-sectional area of a rail, in.2 (mm2).Area of compression reinforcement, in.2

(mm2).Area of one leg of a closed stirrup resis-ting torsion within a distance, in.2 (mm2).Area of shear reinforcement within a dis-tance, or area of shear reinforcement per-pendicular to main reinforcement withina distance for deep beams, in.2 (mm2).Width of compressive face of member, in.(mm).Center-to-center distance of longer dimen-sion of closed rectangular stirrup, in.(mm). Section 5.5.3Width of concrete in the plane of a poten-tial bursting crack, in. (mm). Section 5.8.2Broken rail forces.Horizontal wind drag coefficient.Flowing water drag coefficient.Wind exposure coefficient.Wind gust effect coefficient.Centrifugal force, kip (kN).Collision load, kip (kN).Forces due to creep in concrete, kip (kN).Distance from extreme compressive fiberto centroid of tension reinforcement, in.(mm).Thickness of concrete cover measuredfrom the extreme tensile fiber to thecenter of the bar located closest thereto,in. (mm).Dead load.Transit vehicle mishap load, due to vehiclederailment, kip (kN).

Base of Napierian logarithms.Modulus of elasticity of concrete, psi (Pa).TRUCTURES

Eci =

Es =

EI =

E Q ==

1=

fc =

fc' =

fci' =

kI

8 =c

ffr =

fm =

fpu =

fpy =

fr =

fs =

fsr =

fst =

fsv =

fy =

f1 =Fbs =

Fh =

Fr =

Fsj =

Fv =

FR =

358.1R-3

Section 5.6.3Modulus of elasticity of concrete attransfer of stress, psi (MPa).Modulus of elasticity of reinforcement, psi(MPa)Flexural stiffness of compression mem-bers, k-in2 (kN-mm2).Earthquake force.Modulus of elasticity of rail, psi (MPa).Bursting stress behind a post-tensioninganchor, ksi (MPa).Extreme fiber compressive stress in con-crete at service loads, psi (MPa).Specified compressive strength of concreteat 28 days, psi (MPa).Compressive strength of concrete at timeof initial prestress, psi (MPa).Cracking stress of concrete, psi (MPa).Cracking stress of concrete at the time ofinitial prestress, psi (MPa).

Square root of specified compressivestrength of concrete, psi (MPa).Stress range in straight flexural reinforcingsteel, ksi (MPa).Algebraic minimum stress level, tensionpositive, compression negative, ksi (MPa).Ultimate strength of prestressing steel, psi(MPa).Specified yield strength of prestressingtendons, psi (MPa).Axial stress in the continuously weldedrail, ksi (MPa). Section 3.4.3Tensile stress in reinforcement at serviceloads, psi (MPa).Stress range in shear reinforcement or inwelded reinforcing bars, ksi (MPa).Change in stress in torsion reinforcing dueto fatigue loadings, ksi (MPa).Change in stress in shear reinforcing dueto fatigue loadings, ksi (MPa).Specified yield stress, or design yield stressof non-prestressed reinforcement, psi(MPa).Flexural (natural) frequency, Hz.Total bursting force behind a post-tensioning anchor, kip (kN).Horizontal design pressure due to wind,psi (Pa).Axial force in the continuously weldedrail, kip (kN).Jacking force in a post-tensioning tendon,kip (kN).Vertical design pressure due to wind, psi(Pa).Radial force per unit length due to(Pa/mm).

CR358.1R-4 MANUAL OF CON

g =

h =hf =

H =H =

HF =IICE==Icr =

Ie =

Ig =

jd =

kr =kt =kv =

PL 1LF =LFe =LFn =M =Ma =

Mcr =PS =q =

rv =

r/h =

R =s =

s =

S =

Acceleration due to gravity = 32.2 ft/sec2(9.807 m/sec2).Overall thickness of member, in. (mm).Compression flange thickness of I-andT-sections, in. (mm).Ambient relative humidity. Section 3.4.4Height from ground level to the top of thesuperstructure. Section 3.3.2Hunting force.Impact factor.Ice pressure.Moment of inertia of cracked sectiontransformed to concrete, in.4 (m4).Effective moment of inertia for compu-tation of deflections, neglecting thereinforcement, in.4 (m4). Chapter 5Moment of inertia of the gross concretesection about its centroidal axis neglectingreinforcement, in.4 (m4).Distance between tensile and compressionforces at a section based on an elasticanalysis, in. (mm).Average creep ratio.k,, as a function of time t.A function of rv for creep and shrinkagestrains.Span length, ft (m).Live load.Longitudinal force.Emergency longitudinal braking force.Normal longitudinal braking force.Mass per unit length, lb/in.-se&in. (kg/m).Maximum moment in member at stage forwhich deflection is being computed, lb-in.(N-mm).Cracking moment, lb-m (N-mm).Forces and effects due to prestressing.Dynamic wind pressure, psf (MPa).Chapter 3.Volume-to-surface-area ratio, (volume perunit length of a concrete section dividedby the area in contact with freely movingair), in. (mm).Ratio of base radius to height of trans-verse deformations of reinforcing bars;when actual value is not known, use 0.3.Radius of curvature, ft (m). Chapter 3Shear or torsion reinforcement spacing ina direction parallel to the longitudinalreinforcement, in. (mm).Spacing of reinforcement, in. (mm),Section 5.8.2Service load combinations. Chapters 4 and5.S F =SH =t =

Stream flow load, lb (N). Chapter 3.Forces due to shrinkage in concrete.Time, days.ETE INSPECTION

T = Loads due to temperature or thermalgradient in the structure exclusive of railforces. Chapter 4.

T = Time-dependent factor for sustained load.Section 5.7.2

_^ T = Change in torsion at section due tofatigue loadings. Section 5.5.3

T0 = Stress-free temperature of rail.T1 = Final temperature in the continuouslywelded rail.U = Ultimate load combinations._^ V = Change in shear at section due to fatigue

loadings, kip (kN). Section 5.5.3.V = Velocity of water, wind, or vehicle, ft/sec

(m/sec). Chapter 3.VCF = Vehicle crossing frequency, Hz. Section

3.3.1.wc = Unit weight of concrete, lb/ft

3 (kg/m3).W = Wind load. Chapter 3.WL = Wind load on live load. Chapters 3 and 4.WS = Wind load on structure. Chapters 3 and 4.xm = Location of maximum bursting stress,measured from the loaded face of the end

block, in. (mm).yt = Distance from the centroidal axis of crosssection, neglecting the reinforcement, to

the extreme fiber in tension, in. (mm).Z = A quantity limiting distribution of flexural

reinforcement.a = Coefficient of thermal expansion. Chapter

3.Y = Mass density of water, lb/ft

3 (kg/m3).i = Initial elastic strain.cC, = Concrete creep strain at time t.%k = Concrete shrinkage strain at time t.csku = Concrete shrinkage strain at t = 00.8 = Angle in degrees between the wind force

and a line normal to the guideway center-line.

a = Multiplier for additional long-timedeflection as defined in Section 5.7.2.

P = Density of air in Section 3.3.2pbs = Ratio of nonprestressed reinforcement

located perpendicular to a potentialbursting crack in Section 5.8.2.

P = Compression reinforcement ratio =A,lbd.

4 = Strength reduction factor.11 = A parameter used to evaluate end block

stresses. Section 5.8.2.1.

1.4- SI EquivalentsThe equations contained in the following

chapters are all written in the U.S. inch-pound

system of measurements. In most cases, theequivalent SI (metric) equation is also given;however, some equations do not have definitive SI

STRGUIDEWAY

equivalents. The reader is referred to ACI 318Mfor a consistent metric or SI presentation. Ineither case, the engineer must verify that the unitsare consistent in a particular equation.

1.5-AbbreviationsThe following abbreviations are used in this

report:

AASHTO American Association of StateHighway and TransportationOfficials

ACI American Concrete InstituteAREA American Railway Engineering

AssociationASTM American Society for Testing and

MaterialsAWS American Welding SocietyCRSI Concrete Reinforcing Steel

InstituteFRA Federal Railway Administration,

U.S. Department of Transportation

CHAPTER 2 - GENERAL DESIGNCONSIDERATIONS

2.1- Scope2.1.1- General

Transit structures carry frequent loads throughurban areas. Demands for esthetics, performance,cost, efficiency and minimum urban disruptionduring construction and operation are greater thanfor most bridge structures. The design of transitstructures requires an understanding of transittechnology, constraints and impacts in an urbanenvironment, the operation of the transit systemand the structural options available.

The guideway becomes a permanent feature ofthe urban scene. Therefore, materials and featuresshould be efficiently utilized and built into theguideway to produce a structure which willsupport an operating transit system as well as fitthe environment.

These guidelines provide an overview of thekey issues to be considered in guideway design.They are intended to be a minimum set of re-quirements for materials, workmanship, technicalfeatures, design, and construction which will pro-duce a guideway that will perform satisfactorily.Serviceability and strength considerations are givenin this report. Sound engineering judgment mustbe used in implementing these recommendations.

2.1.2 - Guideway StructuresThe guideway structure must support the tran-sit vehicle, guide it through the alignment andrestrain stray vehicles. Guidance of transit vehiclesUCTURES 358.1R-5

includes the ability to switch vehicles betweenguideways. The guideway must generally satisfyadditional requirements, such as providingemergency evacuation, supporting wayside powerdistribution services and housing automatic traincontrol cables.

Within a modern transit guideway, there is ahigh degree of repeatability and nearly an equalmix of tangent and curved alignment. Guidewaysoften consist of post-tensioned concrete members.Post-tensioning may provide principal rein-forcement for simple-span structures and con-tinuity reinforcement for continuous structures.Bonded post-tensioned tendons are recommendedfor all primary load-carrying applications and theiruse is assumed in this report. However, unbondedtendons may be used where approved, especiallyfor strengthening or expanding existing structures.

2.13-VehiclesTransit vehicles have a wide variety of physical

configurations, propulsion, and suspensionsystems. The most common transit vehicles aresteel-wheeled vehicles running on steel rails,powered by conventional guidance systems. Tran-sit vehicles also include rubber-tired vehicles, andvehicles with more advanced suspension orguidance systems, such as air-cushioned or mag-netically levitated vehicles. Transit vehicles may beconfigured as individual units or combined intotrains.

2.2- Structural Considerations2.2.1-GeneralTransit systems are constructed in four types of

right-of-way: exclusive, shared-use rail corridor,shared-use highway corridor, and urban arterial.The constraints of the right-of-way affect the typeof structural system which can be deployed for aparticular transit operation. Constraints resultingfrom the type of right-of-way may include limitedconstruction access, restricted working hours,limits on environmental factors such as noise, dust,foundation and structure placement, and avail-ability of skilled labor and equipment.

Three types of concrete girders are used fortransit superstructures. Namely, precast, cast-in-place, and composite girders. The types ofguideway employed by various transit systems arelisted in the Committee 358 State-of-the-ArtReport on Concrete Guideways.2.1

2.2.2-Precast Girder ConstructionWhen site conditions are suitable, entire beam

elements are prefabricated and transported to thesite. Frequently, box girder sections are used for

their torsional stiffness, especially for short-radiuscurves. Some transit systems having long-radius

CRE358.1R-6 MANUAL OF CON

horizontal curves have used double-tee beams forthe structure.

Continuous structures are frequently used.Precast beams are made continuous by developingcontinuity at the supports. A continuous structurehas less depth than a simple-span structure andincreased structural redundancy. Rail systemsusing continuously welded rail are typically limitedto simple-span or two-span continuous structuresto accommodate thermal movements between therails and the structure. Longer lengths of con-tinuous construction are used more readily insystems with rubber tired vehicles.

Segmental construction techniques may beused for major structures, such as river crossingsor where schedule or access to the site favorsdelivery of segmental units. The use of segmentalconstruction is discussed in ACI 343R.

2.2.3 - Cast-in-place StructuresCast-in-place construction is used when site

limitations preclude delivery of large precastelements. Cast-in-place construction has not beenused extensively in modern transit structures.

2.2.4 - Composite StructuresTransit structures can be constructed in a

similar manner to highway bridges, using precastconcrete or steel girders with a cast-in-placecomposite concrete deck. Composite constructionis especially common for special structures, such asswitches, turnouts and long spans where theweight of an individual precast element limits itsshipping to the site. The girder provides a work-ing surface which allows accurate placement oftransit hardware on the cast-in-place deck.

2.3- Functional Considerations2.3.1- General

The functions of the structure are to supportpresent and future transit applications, satisfyserviceability requirements, and provide for safetyof passengers. The transit structure may also bedesigned to support other loads, such as automo-tive or pedestrian traffic. Mixed use applicationsare not included in the loading requirements ofChapters 3 and 4.

2.3.2 - Safety ConsiderationsConsiderations for a transit structure must

include transit technology, human safety andexternal safety, in accordance with the require-ments of NFPA 130, Fixed Guideway TransitSystems.2.3Transit technology considerations include bothnormal and extreme longitudinal, lateral, and ver-tical loads of the vehicle, as well as passingclearances for normal and disabled vehicles,TE INSPECTION

vehicle speeds, environmental factors, transitoperations, collision conditions, and vehicleretention.

Human safety addresses emergency evacuationand access, structural maintenance, fire controland other related subjects. Transit operationsrequire facilities for evacuating passengers fromstalled or disabled vehicles. These facilities shouldalso enable emergency personnel to access suchvehicles. In most cases, emergency evacuation isaccomplished by a walkway, which may be adja-cent to the guideway or incorporated into theguideway structure. The exact details of theemergency access and evacuation methods on theguideway should be resolved among the transitoperator, the transit vehicle supplier, and theengineer. The National Fire Protection Associ-ation (NFPA) Code, Particularly NFPA - 130,gives detailed requirements for safety provisionson fixed guideway transit systems.

External safety considerations include safetyprecautions during construction, prevention oflocal street traffic collision with the transitstructure, and avoidance of navigational hazardswhen transit structures pass over navigablewaterways.

2.3.3-LightingThe requirements for lighting of transit struc-

tures should be in accordance with the provisionsof the authority having jurisdiction. Such pro-visions may require that lighting be provided foremergency use only, or for properties adjacent tothe guideway structure, or, alternatively, be de-leted altogether.

2.3.4-DrainageTo prevent accumulation of water within the

track area, transit structures should be designed sothat surface runoff is drained to either the edge orthe center of the superstructure, whereupon thewater is carried longitudinally.

Longitudinal drainage of transit structures isusually accomplished by providing a longitudinalslope to the structure; a minimum slope of 0.5percent is preferred. Scuppers or inlets, of a sizeand number that adequately drain the structureshould be provided. Downspouts, where required,should be of a rigid, corrosion-resistant materialnot less than 4 in. (100 mm) and preferably 6 in.(150 mm) in the least dimension; they should beprovided with cleanouts. The details of thedownspout and its deck inlet and outlet should besuch as to prevent the discharge of water against

any portion of the structure and should preventerosion at ground level. Slopes should be arrangedso that run-off drains away from stations.Longitudinal grades to assure drainage should be

Y S

esthetics for physical appearance. The size andGUIDEWA

coordinated with the natural topography of thesite to avoid an unusual appearance of thestructure.

Architectural treatment of exposed downspoutsis important. When such treatment becomes com-plicated, the use of internal or embedded down-spouts, becomes preferable. For internal orexternal downspouts, consideration must be givento the prevention of ice accumulation in cold-weather climates. This may require localizedheating of the drain area and the downspout itself.All overhanging portions of the concrete deckshould be provided with a drip bead or notch.

2.3.5 -Expansion Joints and BearingsExpansion joints should be provided at span

ends; this allows the beam ends to accommodatemovements due to volumetric changes in thestructure. Joints should be designed to reducenoise transmission and to prevent moisture fromseeping to the bearings. Adequate detailing shouldbe provided to facilitate maintenance of bearingsand their replacement, when needed, during the

life of the structure.Aprons or finger plates, when used, should be

designed to span the joint and to prevent theaccumulation of debris on the bearing seats.When a waterproof membrane is used, the detailshould be such that penetration of water into theexpansion joint and the bearing seat is prevented.

2.3.6 - DurabilityIn order to satisfy the design life of 75 years or

more, details affecting the durability of the struc-ture should be given adequate consideration; theseshould include materials selection, structural de-tailing, and construction quality control.

Materials selection includes the ingredients ofconcrete and its mix design, allowing for a lowwater-cement ratio and air entrainment in areassubject to freeze-thaw action. Epoxy-coated rein-forcement and chloride-inhibitor sealers may bebeneficial if chloride use is anticipated as part ofthe winter snow-clearing operations or if theguideway may be exposed to chloride-laden sprayfrom a coastal environment or to adjacent high-ways treated with deicing chemicals.

In structural detailing, both the reinforcementplacement and methods to prevent deleteriousconditions from occurring should be considered.Reinforcement should be distributed in the sectionso as to control crack distribution and size. Thecover should provide adequate protection to thereinforcement.

Incidental and accidental loadings should beaccounted for and adequate reinforcement shouldbe provided to intersect potential cracks. Stray

currents, which could precipitate galvanic corro-TRUCTURES 358.1R-7

sion, should be accounted for in the design ofelectrical hardware and appurtenances and theirgrounding.

Construction quality control is essential toensure that the design intent and the durabilityconsiderations are properly implemented. Suchquality-control should follow a pre-establishedformal plan with inspections performed as speci-fied in the contract documents.

To satisfy a 75-year service life, regularinspection and maintenance programs to ensureintegrity of structural components should be in-stituted. These programs may include periodicplacement of coatings, sealers or chemicalneutralizers.

2.4 - Economic ConsiderationsThe economy of a concrete guideway is

measured by the annual maintenance cost andcapitalized cost for its service life. It is particularlyimportant that the design process give considera-tion to the cost of operations and maintenanceand minimize them. Therefore, consideration mustbe given to the full service life cost of theguideway structure. The owners should providedirection for the establishment of cost analyses.Economy is considered by comparative studies ofreinforced, prestressed, and partially prestressed-concrete construction. Trade-offs should be con-sidered for using higher grade materials for sensi-tive areas during the initial construction againstthe impact of system disruption at a later date ifthe transit system must be upgraded. For ex-ample, higher quality aggregates may be selectedfor the traction surface where local aggregateshave a tendency to polish with continuous wear.

2.5 - Urban Impact2.5.1 - GeneralThe guideway affects an urban environment in

three general areas: visual impact, physical im-pact, and access of public safety equipment. Visu-al impact includes both the appearance of theguideway from surrounding area and the appear-ance of the surrounding area from the guideway.Physical impacts include placement of columnsand beams and the dissipation of, noise, vibration,and electromagnetic radiation. Electromagneticradiation is usually a specific design considerationof the vehicle supplier. Public safety requiresprovision for fire, police, and emergency serviceaccess and emergency evacuation of passengers.

2.5.2 -Physical AppearanceA guideway constructed in any built-up

environment should meet high standards ofconfiguration of the guideway elements should en-

CRE355.1R-8 MANUAL OF CON

sure compatibility with its surroundings. While therange of sizes and shapes is unlimited in theselection of guideway components the followingshould be considered:

a. View disruptionb. Shade and shelter created by the guidewayc. Blockage of pedestrian waysd. Blockage of streets and the effect on traffic

and parkinge. Impairment of sight distances for traffic belowf. Guideway mass as it relates to adjacent

structuresg. Construction in an urban environmenth. Methods of delivery of prefabricated

components and cast-in-place constructioni. Interaction with roadway and transit vehiclesj. Visual continuity

Attention to final detailing is important. Itemsto be considered should include:

a. Surface finishb. Colorc. Joint detailingd. Provision to alleviate damage from water

dripping from the structuree. Control and dissipation of surface water runofff. Differences in texture and color between

cast-in-place and precast elements

2.5.3 -SightlinessIn the design of a guideway the view of the

surroundings from the transit system itself shouldbe considered. The engineer should be aware thatpatrons riding on the transit system will have aview of the surroundings which is quite differentfrom that seen by pedestrians at street level. Assuch, the guideway placement and sightlinessshould reflect a sensitivity to intrusion on privateproperties and adjacent buildings. In some cases,the use of noise barriers and dust screens shouldbe considered.

The view of the guideway from a higher van-tage point has some importance. The interior ofthe guideway should present a clean, orderly ap-pearance to transit patrons and adjacent observers.Any supplemental cost associated with obtainingan acceptable view must be evaluated.

2.5.4 -Noise SuppressionA transit system will add to the ambient

background noise. Specifications for new con-struction generally require that the wayside noise

50 ft. (15 m) from the guideway not exceed arange of 65 to 75 dBA. This noise is generatedfrom on-board vehicle equipment such as propul-sion and air-conditioning units, as well as fromTE INSPECTION

vehicle/track interaction, especially when jointedrail is used.

It is normally the responsibility of the vehicledesigner to control noise emanating from the ve-hicle. Parapets and other hardware on the guide-way structure should be designed to meet generalor specific noise suppression criteria. Determina-tion of these criteria is made on a case-by-casebasis, frequently in conjunction with the vehiclesupplier.

2.5.5- VibrationTransit vehicles on a guideway generate vibra-

tions which may be transmitted to adjacent struc-tures. For most rubber tired transit systems, thisgroundborne vibration is negligible. In many railtransit systems, especially those systems withjointed rails, the noise and the vibration can behighly perceptible. In these situations, vibrationisolation of the structure is necessary.

2.5.6 -Emergency Services AccessA key concern in an urban area is the accessi-

bility to buildings adjacent to a guideway by fire orother emergency equipment. Within the confinedright-of-way of an urban street, space limitationsmake this a particularly sensitive concern. In mostcases a clearance of about 15 ft. (5 m) betweenthe face of a structure and a guideway providesadequate access. Access over the top of a guide-way may not represent a safe option.

2.6- Transit Operations2.6.1 - GeneralOnce a transit system is opened for service, the

public depends on its availability and reliability.Shutdowns to permit maintenance, operation, orexpansion of the system can affect the availabilityand reliability of the transit system. These con-cerns often lead to long-term economic, opera-tional, and planning analyses of the design andconstruction of the transit system.

In most transit operations, a shutdown periodbetween the hours of 1:00 a.m. and 5:00 a.m.(0100 and 0500) can be tolerated; slightly longershutdowns are possible in certain locations and onholidays. It is during this shutdown period thatroutine maintenance work is performed.

Many transit systems also perform maintenanceduring normal operating hours. This practice tendsto compromise work productivity and guidewayaccess rules and operations in order to provide asafe working space. The transit operators shouldprovide the engineer with guidelines regarding

capital cost objectives and their operation andmaintenance plans.

2.6.2 -Special Vehicles

GUIDEWAY ST

Transit systems frequently employ specialvehicles for special tasks, such as, retrievingdisabled vehicles and repairing support or steeringsurfaces. While the design may not be predicatedon the use of special vehicles, their frequency ofuse, weights, and sizes must be considered in thedesign.

2.6.3 -Expansion of SystemExpansion of a transit system can result in

substantial disruption and delay to the transitoperation while equipment, such as switches, arebeing installed. In the initial design and layout ofa transit system, consideration should be given tofuture expansion possibilities. When expansion iscontemplated within the foreseeable future afterconstruction and the probable expansion pointsare known, provisions should be incorporated inthe initial design and construction phases.

2.7- Structure/Vehicle Interaction2.7.1- General

Vehicle interaction with the guideway canaffect its performance as related to support,steering, power distribution and traction com-ponents of the system. It is usually considered indesign through specification of serviceability re-quirements for the structure. In the final designstage close coordination with the vehicle supplieris imperative.

2.7.2- Ride Quality2.7.2.1- GeneralRide quality is influenced to a great degree by

the quality of the guideway surface. System speci-fications usually present ride quality criteria aslateral, vertical and longitudinal accelerations andjerk rates (change in rate of acceleration) asmeasured inside the vehicle. These specificationsmust be translated into physical dimensions andsurface qualities on the guideway and in the sus-pension of the vehicle. The two elements thatmost immediately affect transit vehicle perform-ance are the support surface and steering surface.

2.7.2.2 - Support SurfaceThe support surface is basically the horizontal

surface of the guideway which supports the transitvehicle against the forces of gravity. It influencesthe vehicle performance by the introduction ofrandom deviations from a theoretically perfectalignment. These deviations are input to thevehicle suspension system. The influence of thesupport surface on the vehicle is a function of thetype of the suspension system, the supportmedium (e.g., steel wheels or rubber tire), and the

speed of the vehicle.

There are three general components of sup-RUCTURES 358.1R-9

port surfaces which must be considered. Namely,local roughness, misalignment, and camber. Localroughness is the amount of distortion on the sur-face from a theoretically true surface. In mosttransit applications, the criterion of a l/8-inch (3mm) maximum deviation from a 10 ft. (3 m)straightedge, as given in ACI 117, is used.

With steel rails, a Federal Railway Admini-stration (FRA) Class 62.2 tolerance is acceptable.The FRA provision include provisions for longi-tudinal and transverse (roll) tolerances. Thesetolerances are consistent with operating speeds ofup to 50 mph (80 km/h). Above these speeds,stricter tolerance requirements have to be applied.

Vertical misalignment most often occurs whenadjacent beam ends meet at a column or otherconnection. There are two types of misalignmentwhich must be considered. The first, is a physicaldisplacement of adjacent surfaces. This occurswhen one beam is installed slightly lower or higherthan the adjacent beam. These types of misalign-ment should be limited to l/16 in. (1.5 mm) asspecified by ACI 117.

The second type of vertical misalignmentoccurs when there is angular displacement be-tween beams. Such an angular displacement mayresult from excessive deflection, sag, or camber.Excessive camber or sag creates a discontinuitywhich imparts a noticeable input to the vehiclesuspension system.

In the design and construction of the beams theeffects of service load deflection, initial camberand long-time deflections should be considered.There is no clear definition on the amount ofangular discontinuity that can be tolerated at abeam joint. However, designs which tend to mini-mize angular discontinuity generally provide asuperior ride. Continuous guideways are particu-larly beneficial in controlling such misalignment.

Camber or sag in the beam can also affect ridequality. Consistent upward camber in structureswith similar span lengths can create a harmonic vi-bration in the vehicle resulting in a dynamicamplification, especially in continuous structures.When there are no specific deflection or cambercriteria cited for a project, the designer shouldaccount for these dynamic effects by analytical orsimulation techniques. The deflection compati-bility requirements between structural elementsand station platform edges should be accountedfor.

2.7.2.3- Steering SurfaceThe steering surface provides a horizontal input

to the vehicle. The steering surfaces may be eitherthe running rails for a flanged steel-wheel-rail

system or the concrete or steel vertical sur-faces that are integrated into the guideway struc-

CENTERED IN THE GUIDEWAY COMPRESSED AGAINSTTHE GUIDEWAY GENERATlNG A SPURIOUS STEERING IMPUT.

truck assembly.Depending upon the relationship between theFig. 2.7.2.3- Interaction between support andsteering

ture, for a rubber tired system. The condition ofthe steering surface is particularly important since

few vehicles have sophisticated lateral suspension

tion-Total Deviation between the theoreti

-Variations from theoretical gage, cross level andper 15 -6 (4.7 m) of track.-The total Deviation in platform areas should be zfrom the platform.cal and the actual alignments at any point along 358.1R-10 MANUAL OF CONCRETE INSPECTION

NORMAL CONFlGURATIONSTEERING WHEELS

ROLLED COFIGURATiONRIGHT STEERING WHEEL

km/h) or less. In steel-rail systems, an FRA Class62.2 rail tolerance has generally proven to besatisfactory for speeds up to 70 mph (112 km/h).Other tolerance limits are given in Table 2.7.2.3.

There is a particular interaction between thesteering surface and the support surface, which istechnology dependent and requires specific consid-eration by the engineer. This interaction resultsfrom a coupling effect which occurs when a ve-hicle rolls on the primary suspension system, caus-ing the steering mechanism to move up and down(Fig. 2.7.2.3). The degree of this up and downmovement is dependent on the steering mechan-ism which is typically an integral part of thevehicle truck (bogie) system, and the stiffness ofthe primary suspension which is also within thesystems. In most existing guideways, the toleranceof a l/8 in. (3 mm) deviation from a 10 ft. (3 m)straightedge, specified by ACI-117, corrected forhorizontal curvature, has proven to be adequatefor rubber tired vehicles operating at 35 mph (56

Table 2.7.2.3 Track Construction Tolerances

Type and Class of Track

-Dimensions are-H=Horizontal. Sup.=Superelevasupport and the steering surfaces, and the supportand guidance mechanisms of the vehicle (primary,in the case of rubber tired system) a couple can becreated between the two, which causes a spurioussteering input into the vehicle. There are nogeneral specifications for this condition. Theengineer should be aware that this condition canexist and, if there is a significant distanceseparating the horizontal and vertical contactsurfaces, additional tolerance requirements for thefinished surfaces have to be imposed. This is inorder to reduce the considerable steering input,which can cause over or under steering, whichleads to an accelerated wear of components anddegraded ride comfort. superelevation are not to exceed l/8 in. (3 mm)

ero towards the platform and l/4 in (6 mm) away

STRGUIDEWAY

2.7.3 -Traction SurfacesTransit vehicles derive their traction from the

physical contact of the wheels with the concrete orrunning rail or through an electromagnetic force.In those systems where traction occurs throughphysical contact with the guideway, specificattention must be given to the traction surface.

In automated transit, the traction between thewheel and the reaction surface is essential to en-sure a consistent acceleration and a safe stoppingdistance between vehicles. It is also important forautomatic control functions. The engineer shoulddetermine the minimum traction required for thespecific technology being employed. If the trac-tion surface is concrete, appropriate aggregatesshould be provided in the mix design to maintainminimum traction for the working life of thestructure.

Operation in freezing rain or snow may alsoaffect traction on the guideway. The engineershould determine the degree of traction mainten-ance required under all operating conditions. Iffull maintenance is required, then the engineershould examine methods to mitigate the effects ofsnow or freezing rain. These mitigating effects mayinclude heating the guideway, enclosing theguideway, or both.

If deicing chemicals are contemplated, propermaterial selection and protection must be con-sidered. Corrosion protection may require consid-eration of additional concrete cover, sealants,epoxy-coated reinforcing steel, and special con-crete mixes.

2.7.4 -Electrical Power DistributionThere are two components to electrical power

distribution: the wayside transmission of power tothe vehicle and the primary power distribution tothe guideway. The wayside power distribution tothe vehicle is normally done through power railsor through an overhead catenary. Provision mustbe made on the guideway for the mounting ofsupport equipment for the installation of thiswayside power.

For systems using steel running rails, wherethe running rail is used for return current, pro-visions must also be made to control any strayelectrical currents which may cause corrosion inthe guideway reinforcement or generate otherstray currents in adjacent structures or utilities.

The primary power distribution network asso-ciated with a guideway may require several sub-stations along the transit route. Power must betransmitted to the power rails on the guidewaystructure at various intervals. This is usually donethrough conduits mounted on or embedded in the

guideway structure.

Internal conduits are an acceptable means ofUCTURES 358.1R-11

transmitting power; they may be used to routepower from the substation to the guideway. How-ever, access to internal conduits is difficult todetail and construct. Sufficient space must beprovided within the column-beam connection andwithin the beam section for the conduit turns;space must also be provided for safe electricalconnections. Exterior conduits can detract fromthe guideway appearance and can cause increasedmaintenance requirements.

2.7.5 - Special EquipmentA guideway normally carries several pieces of

special transit equipment. This equipment mayconsist of switches, signaling, command and con-trol wiring, or supplemental traction and powerdevices. The specialty transit supplier shouldprovide the engineer with explicit specifications ofspecial equipments and their spatial restrictions.For example, the placement of signaling cableswithin a certain distance of the wayside powerrails or reinforcing steel may be restricted.

The transit supplier should also provide theengineer with the forces and fatigue requirementsof any special equipment so that proper connec-tions to the structure can be designed and in-stalled. An example of connection requirementswould be linear induction motor reaction railattachments.

When no system supplier has been selected, theengineer must provide for the anticipated servicesand equipment. In this instance, a survey of theneeds of potential suppliers for the specific appli-cation may be required prior to design.

2.8- Geometries

2.8.1 - GeneralThe geometric alignment of the transit line can

have a substantial impact on the cost of thesystem. Standardization of the guideway compo-nents can lead to cost savings. During the plan-ning and design stages of the transit system, thebenefits of standardizing the structural elements,in terms of ease and time of construction andmaintenance, should be examined and the effec-tive options implemented.

2.8.2 -StandardizationStraight guideway can be produced at a lower

cost than curved guideway. Geometric alignmentsand column locations that yield a large number ofstraight beams tend to be cost-effective. Physicalconstraints at the ground influence column loca-tions. However, when choices are available, theplacement of columns to generate straight beams,

as opposed to those with a slight horizontal orvertical curvature, will usually prove to be more

NCRET358.1R-12 MANUAL OF CO

cost effective.Standardization and coordination of the in-

ternal components and fixtures of the guidewayalso tends to reduce overall cost. These includeinserts for power equipment, switches, or othersupport elements. Methods to achieve this arediscussed in Section 2.9.3.

2.8.3 -Horizontal GeometryThe horizontal geometry of a guideway align-

ment consists of circular curves connected totangent elements with spiral transitions. Mosttypes of cubic spirals are satisfactory for thetransition spiral. The vehicle manufacturer mayprovide additional constraints on the selection ofa spiral geometry to match the dynamic character-istics of the vehicle.

2.8.4 -Vertical GeometryThe vertical geometry consists of tangent

sections connected by parabolic curves. In mostcases, the radius of curvature of the paraboliccurves is sufficiently long that a transition betweenthe tangent section and the parabolic section isnot required.

2.8.5 - SuperelevationSuperelevation is applied to horizontal curves

in order to partially offset the effect of lateralacceleration on passengers. To accomplish the re-quired superelevation, the running surface awayform the curve center is raised increasingly relativeto that closer to the curve center. This results inthe outer rail or wheel track being raised while theinner rail or wheel track being kept at the profileelevation. The amount of superelevation is afunction of the vehicle speed and the degree ofcurvature. It is usually limited to a maximum valueof 10 percent.

2.9- Construction Considerations2.9.1- General

Construction of the guideway in an urbanenvironment has an impact on the residents,pedestrians, road traffic, and merchants along theroute. Consideration should be given to the costand length of disruption, in terms of street closureand construction details.

2.9.2 - Street Closures and DisruptionsThe amount of time that streets are closed and

neighborhoods are disrupted should be kept to aminimum. Coordination with the public shouldbegin at the planning stage. The selection of

precast or cast-in-place concrete components andmethods of construction depend on the availabilityof construction time and on the ease of stockpilingequipment and finished products at the proximityE INSPECTION

of the site. Construction systems which allow forrapid placement of footings and columns and forreopening of the street prior to the installation ofbeams, may have an advantage in the maintenanceof local traffic.

2.9.3 - Guideway Beam ConstructionGuideway beams may be cast-in-place or

precast. In order to ascertain the preferredconstruction technique, the following items needto be considered early in the design process:typical section and alignment, span composition(uniform or variable), structure types, span-depthratios, and major site constraints.

Cast-in-place construction offers considerabledesign and construction flexibility, however, it alsorequires a greater amount of support equipmenton the site. This equipment, especially shoring andfalsework, has to remain in place while theconcrete cures.

Precast concrete beam construction offers thepotential for reduced construction time on site andallows better quality control and assurance.Advantages of precast concrete are best realizedwhen the geometry and the production methodsare standardized.

Two types of guideway beam standardizationappear to offer substantial cost benefits. Namely,modular construction and adjustable form con-struction.

Modular construction utilizes a limited numberof beam and column types to make up the guide-way. Thus, like a model train set, these beams areinterwoven to provide a complete transit guideway.Final placement of steering surfaces and othersystem hardware on the modular elements pro-vides the precise geometry necessary for transitoperation. Modules may be complete beams.Segmental construction also typifies this con-struction technique.

An adjustable form allows the fabrication ofcurved beams to precisely match the geometric re-quirements at the site. For alignments where asubstantial amount of variation in geometry is dic-tated by the site, this solution provides a highdegree of productivity at a reasonable cost.

2.9.4 - Shipping and DeliveryPrior to the completion of final design, the

engineer should be aware of limitations which maybe placed upon the delivery of large precast ele-ments. Weight limitations imposed by local depart-ments of transportation, as well as dimensionallimitations on turnoff radii, width, and length of

beam elements, may play an important role in thefinal guideway design. The deployment of largecranes and other construction equipment along thesite is also a consideration.

STGUIDEWAY

2.9.5- Approval ConsiderationsThese recommendations for transit guideways

are intended to provide procedures based on thelatest developments in serviceability and strengthdesign. Other pertinent regulations issued by state,federal, and local agencies should be considered.

Specific consideration should be given to thefollowing:

- Alternative designs- Environmental impact statements- Air, noise, and water pollution statutes- Historic and park preservation requirements- Permits- Life-safety requirements- Construction safety requirements

2.9.6 -Engineering DocumentsThe engineering documents should define the

work clearly. The project drawings should show alldimensions of the finished structure in sufficientdetail to facilitate the preparation of an accurateestimate of the quantities of materials and costsand to permit the full realization of the design.

The contract documents should define test andinspection methods, as well as the allowable pro-cedures and tolerances to ensure good workman-ship, quality control, and application of unit costs,when required in the contract. The contractorsresponsibilities should be clearly defined. Wherenew or innovative structures are employed, sug-gested construction procedures to clarify theengineers intent should also be provided. Com-puter graphics or integrated data bases can assistin this definition.

2.10- Rails and Trackwork

2.10.1- GeneralGuideways for transit systems which utilize

vehicles with steel wheels operating on steel railsrequire particular design and construction con-siderations, which include, rail string assembly, useof continuous structures, and attachment of therails to the structure.

Two options exist for assembling the rails:They may be jointed with bolted connections instandard 39 ft. (11.9 m) lengths, or welded intocontinuous strings. The rails may be fasteneddirectly to the structure or installed on tie-and-ballast.

2.10.2- Jointed RailThe traditional method of joining rail is by

bolted connections. Sufficient longitudinal railmovement can develop in these connections to

prevent the accumulation of the thermal stressesalong the length of the rails.RUCTURES 358.1R-13

The space between the rail ends presents adiscontinuity to the vehicle support and steeringsystems. Vehicle wheels hitting this discontinuitycause progressive deterioration of the joints, gen-erate loud noise, reduce ride comfort, and in-crease the dynamic forces on the structure.

Because of these limitations, most modern tran-sit systems use continuously welded rail. However,jointed rail conditions will exist in switch areas,maintenance yards and other locations wherephysical discontinuities are required. However,even in these areas, discontinuities can be reducedgreatly by the use of bonded rail joints.

2.10.3 -Continuously Welded Rail

2.10.3.1 -GeneralTo improve the ride quality and decrease track

maintenance, individual rails are welded into con-tinuous strings. There is no theoretical limit to thelength of continuously welded rail if a minimumrestraint is provided.Minimum rail restraintconsists of prevention of horizontal or verticalbuckling of rails and anchorage at the end of acontinuous rail to prevent excessive rail gaps fromforming at low temperatures, if accidental breaksin the rail should occur.

Continuously welded rail (CWR) has becomethe standard of the transit industry over the pastseveral decades. The use of CWR requires par-ticular attention to several design details, whichinclude, thermal forces in the rails, rail break gapand forces, welding of CWR, and fastening ofCWR to the structure. The principal variablesused in the evaluation of rail forces are rail size interms of its cross-sectional area, the characteristicsof the rail fastener, the stiffness of the structuralelements, rail geometry, and operational environ-ment, in terms of temperature range.

In cases where accumulation of the thermaleffects would produce conditions too severe forthe structure, slip joints can be used. Slip jointsallow limited movement between rail strings. Theygenerally cause additional noise and require in-creased maintenance. Their use therefore is notdesirable. Location of rail anchors and rail expan-sion joints will affect the design of the structure.

2.10.3.2 -Thermal ForcesChanges in temperature of continuously welded

rails will develop stresses in the rail and in thestructure. Rails are typically installed at a designstress-free ambient temperature, to reduce the riskof rail buckling at high temperatures and railbreaks at low temperatures. Depending upon themethod of attachment of the rails to the structure,

the structure should be designed for:- Horizontal forces resulting from a rail break

CRET358.1R-14 MANUAL OF CON

- Radial forces resulting from thermal changesin the rails on horizontal or vertical curves

- End anchorage forces

2.10.3.3 -Rail BreaksContinuously welded rails will, on occasion,

fail in tension. This situation occurs because of railwear, low temperature, defects in the rail, defectsin a welded joint, fatigue or some combination ofthese effects. The structure should be designed toaccommodate horizontal thrust associated with thebreak.

2.10.3.4 -Rail WeldingContinuous welded rail is accomplished by

either the them-rite welding process or the electricflash butt welding process. Proper weld proce-dures should ensure that:

- Adjacent rail heads are accurately aligned- Rails are welded at the predetermined stress-

free ambient temperature- Rail joint is clean of debris- The finished weld is free of intrusions- Weld is allowed to cool prior to tightening

the fasteners.

Ultrasonic or x-ray inspection of the welds atrandom locations is suggested.

2.10.4 -Rail Installation2.10.4.1 -GeneralRails are attached to either cross ties on

ballast or directly to the guideway structure. Thepreference in recent years has become direct railfixation as a means of improving ride quality,maintaining rail tolerances, reducing maintenancecosts, and reducing structure size.

2.10.4.2 -Tie and BallastTie and ballast construction is the conven-

tional method of installing rails at grade andoccasionally on elevated structures. Ties are usedto align and anchor the rails. Ballast provides anintermediate cushion between the rails and thestructure, stabilizes the tracks, and preventsthermal forces to be transmitted from the rails tothe structure.

Ballast substantially increases the structuredead load. Tie-and-ballast installations makecontrol of rail break gaps difficult since the tiesare not directly fastened to the primary structure.Rail breaks can develop horizontal, vertical, andangular displacements of the rail relative to the

structure.

2.10.4.3 -Direct FixationDirect fixation of the rail to the structure isE INSPECTION

accomplished by means of mechanical rail fas-tener. Elastomeric pads are incorporated in thefastener to provide the required vertical andhorizontal flex and provisions for adjust-ment between adjacent fasteners and the struc-ture. The elastomeric pads also assist in the re-duction of noise, vibration, and impact.

Important design and construction consider-ations for the direct fixation fasteners include:

- Method of attachment to the structure- Vertical stiffness- Allowance for horizontal and vertical

adjustment- Ability to restrain the rail against rollover- Longitudinal restraint

Direct fixation fasteners are one of the mostimportant elements in the design of the track-work. They are subjected to a high number ofcyclic loads and there are thousands of fastenersin place in any one project. Progressive failuredoes not generally create catastrophic results, butleads to a substantial maintenance effort andpossible operational disruptions.

No industry wide specifications exist for thedefinition or procurement of direct fixation fas-teners. A thorough examination of the charac-teristics and past performance of available fas-teners, and the characteristics of the proposedtransit vehicle should be undertaken prior to fas-tener selection for any specific installation.

2.10.4.4 -Continuous StructureDirect fixation of continuous rail to a con-

tinuous structure creates a strain discontinuity ateach expansion joint in the structure. Fastenersmust be designed to provide adequate slip at thesejoints while still being able to limit the rail-gapsize in the event of a rail break. In climates withextreme ranges in temperature [- 40 F to +90 F(- 40 C to + 30 C)], structural continuity isgenerally limited to 200 to 300 ft. (60 to 90 m)lengths. In more moderate climates, longer runs ofcontinuous structure may be possible.

REFERENCES*

2.1 ACI Committee 358, State-of-the-Art Report onConcrete Guideways, Concrete Intenational, V. 2, No. 7, July1980, pp. 11-32.

2.2 Code of Federal Regulations, 49, Transportation, Parts200-999, Subpart C, Track Geometry, Federal Railroad Admin-

istration, Washington, D.C., Section 213.51-213.63.

2.3 National Fire Codes, Publication NFPA - 130, 1983,Standard on Fixed Guideway Systems, National Fire Protec-tion Association, Battery March Park, Quincy, MA 02269.

STRGUIDEWAY

*For recommended references, see Chapter 8.

CHAPTER 3 -LOADS

3.1 -GeneralThe engineer should investigate all special,

unusual, and standard loadings that may occur inthe guideway being designed. Special or unusualloads may include emergency, maintenance, orevacuation equipment or conditions. The fol-lowing loads commonly occur and are consideredwhen assessing load effects on elevated guidewaystructures.3.1

a. Sustained loads- Dead load- Earth pressure- External restraint forces- Differential settlement effects- Buoyancy

b. Transient loads- Live load and its derivatives- Wind- Loads due to ice- Loads due to stream current

c. Loads due to volumetric changes- Temperature- Rail-structure interaction- Shrinkage- Creep

d. Exceptional loads- Earthquake- Derailment- Broken rail- Collision loads at street level

e. Construction Loads- Dead Loads- Live Loads

3.2 - Sustained loads3.2.1 -Dead Loads, D

Four components of dead load are considered:

- Weight of factory-produced elements- Weight of cast-in-place elements. Weight of trackwork and appurtenances which

includes running and power rails, second-pourplinths and fasteners, barrier walls, and noise-suppression panels. Weight of other ancillary componentsUCTURES 358.1R-15

3.2.2 -Other Sustained LoadsLoads from differential settlement, earth

pressure, effects of prestress forces (PS) or ex-ternal structural restraints should be included inthe design, as they occur. The beneficial effects ofbuoyancy may only be included when its existenceis ensured. References 3.2 and 3.11 may be usedas guides to evaluate the effects of these sustainedloads.

3.3 - Transient Loads3.3.1- Live Load and its Derivatives3.3.1.1- Vertical Standard Vehicle Loads, LThe vertical live load should consist of the

weight of one or more standard vehicles posi-tioned to produce a maximum load effect in theelement under consideration. The weight andconfiguration of the maintenance vehicle are to beconsidered in the design. The weight of pas-sengers should be computed on the basis of 175 lb(780 N) each and should comprise those oc-cupying all the seats (the seated ones) and thosewho are standing in the rest of the space that doesnot have seats (standees). The number of standeesshall be based on one passenger per 1.5 ft.2 (0.14m).

For torsion-sensitive structures, such asmonorails, the possibility of passengers beingcrowded on one side of the vehicle should beconsidered in the design.

3.3.1.2 -Impact Factor, IThe minimum dynamic load allowance3.2.3.3

shown in Table 3.3.1.2 should be applied to thevertical vehicle loads, unless alternative valuesbased on tests or dynamic analysis are approved.

Definition of terms in the Table follow:

vehicle speed, ft/sec (m/sec)VCF = (3-l)

span length, ft (m)

fi = first mode flexural (natural) frequency3.4

of the guideway where,

(3-2)

where

e = span length, center-to-center ofsupports, in. (m)

M = mass per unit length of the guideway,which includes all the sustained loadsthe beam carries including its own mass,

lb/in.-sec2/in. (kg/m)

NCRE

)

er-tisly

>_ 0

10.1

applied as follows:R = radius of curvature, ft (m)

canom-tionints of

ayshis

iclesg = acceleration due to gravity, 32.2 ft/sec/sec(9.82 m/s2)

V = maximum operating speed of the vehicle,ft/sec (m/s2) and,

L = the standard vehicle load, kips (kN)

Emergency braking, LFe = 0.30LNormal braking, LFn = 0.15L

Continuously welded rail trackwork distribute longitudinal forces to adjacent cponents of guideway structures. This distribumay be considered in design. Use of slip jomay prevent transfer and distributionlongitudinal forces.

The load, L, should be applied simultaneouslywith other load combinations (Chapter 4) in orderto produce the maximum force effect on thestructure.

3.3.1.4 -Hunting Force, HFThe hunting (or nosing) force, HF, is caused

by the lateral interaction of the vehicle and theguideway. It should be applied laterally on the

3.3.1.6 - Service Walkway LoadsLive load on service or emergency walkw

shall be based on 85 psf (4.0 kPa) of area. Tload should be used together with empty veh358.1R-16 MANUAL OF CO

Table 3.3.1.2 Dynamic Load Allowance (ImpactI

Structure Types RubbContinuou

Simple-span structures,

I - VCF- - - 0 . 14

Continuous-span structures,

I - VCF- - -0.124

EC = modulus of elasticity of the guideway,psi (Pa)

Ig= moment of inertia of uncrackedsection of the guideway, in.4 (m4)

VCF = Vehicle Crossing Frequency, Hz

The dynamic load allowance should not beapplied to footings and piles.

3.3.1.3 -Centrifugal Force, CFThe centrifugal force, CF, acting radially

through the center of gravity of the vehicle at acurved track may be computed from,

where,

CF = f L, WN) (3-3) Iguideway at the point of wheel-rail contact, as afraction of the standard vehicle load, L, as follows:TE INSPECTION

red andWelded Rail

Jointed rail

.10 >_ 0.30

0 >_ 0.30

Bogie type Hunting force

Nonsteerable 0.08LSteerable 0.06L

When centrifugal and hunting forces can actsimultaneously, only the larger force need beconsidered.

For rail and structure design, the huntingforce would be applied laterally by a steel wheel tothe top of the rail at the lead axle of a transittrain. it need not be applied for rubber tiredsystems; typically, LIM propelled vehicles run onsteel-wheel-and-rail and, hence require consider-ation of hunting effects.

3.3.1.5 - Longitudinal Force, LFThe longitudinal force acts simultaneously

with the vertical live load of a standard vehicle onall wheels. It may be applied in either direction:forward in braking or deceleration or reverse inacceleration. The longitudinal force should beon the guideway, since the walkway load is theresult of vehicles being evacuated.

GUIDEWAY STRUCTURES 358.1R-173.3.1.7-Loads on Safety RailingThe lateral load from pedestrian traffic on

railings should be 100 lb/ft (1.5 kN/m) applied atthe top rail.

3.3.2 -Wind Loads, W3.3.2.1 -GeneralThis section provides design wind loads for

elevated guideways and special structures. Windloads, based on the reference wind pressure, shallbe treated as equivalent static loads as defined inSection 3.5.3.

Wind forces are applied to the structure andto the vehicles in accordance with the load com-binations in Chapter 4. WL is used to designatewind loads applied to vehicle, while WS indicateswind loads applied to the structure only.

The net exposed area is defined as the netarea of a body, member, or combination of mem-bers as seen in elevation. For a straight super-structure, the exposed frontal area is the sum ofthe areas of all members, including the railingsand deck systems, as seen in elevation at 90degrees to the longitudinal axis. For a structurecurved in plan, the exposed frontal area is takennormal to the beam centerline and is computed ina similar manner to tangent structures.

The exposed plan area is defined as the netarea of an element as seen in plan from above orbelow. In the case of a superstructure, the ex-posed plan area is the plan area of the deck andthat of any laterally protruding railings, membersor attachments.

The gust effect coefficient is defined as theratio of the peak wind-induced response of astructure, including both static and dynamic action,to the static wind-induced response.

Buildings and other adjacent structures canaffect the wind forces. Wind tunnel tests may beconsidered as a method to improve wind forcepredictions or to validate design coefficients in thealternative design approach provided in Section3.5.3.

3.3.2.2 - Design for WindThe guideway superstructure should be de-

signed for wind-induced horizontal, Fh and verti-cal, Fv drag loads acting simultaneously. The windshould be considered to act on a structure curvedin plan, in a direction such that the resulting forceeffects are maximized. For a structure that isstraight in plan, the wind direction should betaken perpendicular to the longitudinal axis of thestructure.

The following uniformly distributed load in-tensities may be used for design:Fh = the greater of 50 lb/ft2 (2.4 kPa) or 300

lb/ft (4.4 kN/m)and

Fv = 15 lb/ft2 (0.7 kPa)

The wind loads, Fh and Fv, should be appliedto the exposed areas of the structure and vehiclein accordance with the provisions of sections 4.3and 4.4.

These loads and provisions are consistent withthe recommendations of the AASHTO StandardSpecifications for Highway Bridges3.11 derivedfrom wind velocities of 100 mph (160 km/h). Windloads may be reduced or increased in the ratio ofthe square of the design wind velocity to thesquare of the base wind velocity, provided that themaximum probable wind velocity can be ascer-tained with reasonable accuracy, or provided thatthere are permanent features of the terrain thatmake such changes safe and are viable.

The substructure should be designed forwind-induced loads transmitted from the super-structure and wind loads acting directly on thesubstructure. Loads for wind directions both nor-mal to and skewed to the longitudinal centerlineof the superstructure should be considered.

3.3.2.3 -Alternative Wind LoadThe alternative wind load method may be

used in lieu of that given in Section 3.3.2.1.Alternative wind loads are suggested for projectsinvolving unusual height guideways, unusual gustconditions, or guideway structures that are, in thejudgment of the engineer, more streamlined thanhighway structures.3.7.3.8

The wind load per unit exposed frontal areaof the superstructure, WS, and of the vehicle, WL,applied horizontally, may be taken as:

Fh = qCeCgCd (3-4)

Similarly, the wind load per unit exposed plandeck or soffit area applied vertically, upwards ordownwards, shall be taken as:

Fv = qCeCgCdqc,cgcd (3-5)

Where, Cd = 1.0 and Ce, Cg, and q are defined inSection 3.3.2.4. The maximum vertical windvelocity may be limited to 30 mph (50 km/h).

In the application of Fv, as a uniformlydistributed load over the plan area of the struc-ture, the effects of a possible eccentricity shouldbe considered. For this purpose, the same totalload should be applied as an equivalent vertical

NCRET358.1R-18 MANUAL OF CO

line load at the windward quarter point of thesuperstructure.

3.3.2.4 -Reference Wind PressureThe reference wind pressures at a specific site

should be based on the hourly mean wind velocityof a 75-year return period. A l0-year returnperiod may be used for structures under con-struction.

The reference wind pressure, q, may bederived from the following expression:

where

V = mean hourly velocity of wind, ft/sec (m/s)P = density of air at sea level at 32 F (0 C)

= 0.0765 lb/ft3 (1.226 kg/m3)g = 32.2 ft/sec

2 (9.807 m/s2)

For structures that are not sensitive to wind-induced dynamics, which include elevated guide-ways and special structures up to a span length of400 ft (122m), the gust effect coefficient Cg mayvary between 1.25 and 1.50. For design purposes,a factor of 1.33 may be used for Cg. For struc-tures that are sensitive to wind action, Cg shouldbe determined by an approved method of dynamicanalysis or by model testing in a wind tunnel. Forguideway appurtenances, such as sign posts, light-ing poles, and flexible noise barriers, Cg may betaken as 1.75.

The exposure coefficient or height factor, Ce,may be computed from:

Ce= l/2@, 2 l.O,forIiinfl

=5/8@, 2 l.O,forHinm (3-7)

(3-6)

H is the height from ground level to the top of thesuperstructure. It should be measured from thefoot of cliffs, hills, or escarpments when thestructure is located on uneven terrain, or from thelow water level when the structure is located overbodies of water. Where excessive funneling may becaused by the topography at the site, Ce should beincreased by 20 percent.

The drag coefficient or shape factor, Cd, is afunction of many variables, the most important ofwhich are the skew angle (horizontal angle of

wind), and aspect ratio (ratio of length to width ofstructure). For box or I-girder superstructures andsolid-shaft piers with wind acting at zero skew andpitch angles, Cd may vary between 1.2 and 2.0. AE INSPECTION

factor of 1.50 for Cd may be used for design pur-poses. For unusual exposure shapes, the drag co-efficient, Cd, should be determined from wind-tunnel tests.

Where wind effects are considered at a skewangle of B degrees measured from a line perpendi-cular to the longitudinal axis of a structure, thenCd should be multiplied by 0.0078 for the longitu-dinal wind load component and by (1 - 0.0001813~)for the transverse or perpendicular load compo-nent.

3.3.2.5- Wind Load on Slender Elements andAppurtenances

Slender elements, such as light and signsupports, should be designed for horizontal windloads provided for in Sections 3.3.2.3 and 3.3.2.4,as well as lateral and crosswind load effects causedby vortex shedding. Both serviceability andstrength considerations should be investigated.Details that may cause stress concentrations dueto fatigue or resonance should be avoided. 3.9

The wind drag coefficient, Cd, for sign andbarrier panels with aspect ratios of up to 1.0, of1.0 to 10.0, or more than 10.0, should be 1.1, 1.2,or 1.3, respectively.

For light fixtures and sign supports withrounded surfaces, octagonal sections with sharpcomers, or rectangular flat surfaces, the values ofCd should be 0.5, 1.2, or 1.4, respectively. A Valueof 1.2 for Cd should be used for suspended signalunits.

When ice accretion is expected on the surfaceof slender components, the total frontal areashould include the thickness of ice.

The dynamic effects of vortex shedding shouldbe analyzed and the stress limits for 2 x l06 cyclesof loading shall be applied.

3.3.3 -Loads Due to Ice Pressure, ICEFloating ice forces on piers and exposed pier

caps should be evaluated according to the localconditions at the site. Consideration should begiven to the following types of ice action on pierserected in bodies of water:

Dynamic ice pressure due to ice sheets andice floes in motion caused by stream orcurrent flow and enhanced by wind action,Static ice pressure caused by thermal actionon continuous stationary ice sheets over largebodies of water,Static pressure resulting from ice jams at aguideway site,

Static uplift or vertical loads due to ice sheetsin water bodies of fluctuating level.

Ice loads resulting from freezing rain or con-

Y STRGUIDEWA

solidation of compact snow on the guidewaysuperstructure and vehicle should be included, asappropriate.

3.3.4- Loads due to Stream Current, SF3.3.4.1 -Longitudinal LoadsThe load acting on the longitudinal axis of a

pier due to flowing water may be computed by thefollowing expression.3.5

SF = h CDAV2y (3-8)

where

A = Exposed area of the pier perpendicular tothe direction of stream flow, ft2 (m2)

Y = Mass density of water, 62.4 lb/ft3 (1000kg/m3)

V = Speed of stream flow, ft/sec (m/set)CD = 0.7 for semicircular-nosed piers= 0.8 for wedge-nosed piers

= 1.4 for squared-ended piers and againstdrift lodged on the pier

3.3.4.2 -Transverse LoadsThe lateral load on a pier shaft due to stream

flow and drift should be resolved from the maindirection of flow. The appropriate componentshould be applied as a uniformly distributed loadon the exposed area of the pier, below the highwater level, in the direction under consideration.

3.4 -Loads due to Volumetric Changes3.4.1- General

Provisions should be made for all movementsand forces that can occur in the structure as aresult of shrinkage, creep, and variations in tem-perature. Load effects that may be induced by arestraint to these movements should be includedin the analysis. These restraints include thoseimposed during construction on a temporary basisand those imposed by the rail-fastener interactionon an on-going basis. Effects due to thermal gra-dients within the section should also be con-sidered.3.5

3.4.3 -Temperature, T3.4.2.1. -Temperature RangeThe minimum and maximum mean daily

temperatures should be based on local meteoro-logical data for a 50-year return period. The rangeof effective temperature for computing thermalmovements of the concrete structure should be thedifference between the warmest maximum and thecoldest minimum effective temperatures, whichmay be considered to be 5 F (2.5 C) above or

below the mean daily minimum and maximumtemperatures. If local temperature data are notUCTURES 358.1R-19

available, the structure may be designed for aminimum temperature rise of 30 F (17 C) and aminimum temperature drop of 40 F (23 C) fromthe installation temperature.

3.4.2.2 -Effective Construction TemperatureIf the guideway is to be designed to accom-

modate continuously welded rails, an effectiveconstruction temperature should be selected. Thistemperature, which should be based on the meandaily temperature prevalent for the locality underconsideration, is used to establish the baseline railforce.

3.4.2.3 -Thermal Gradient EffectsCurvature caused by a temperature gradient

should be considered in the design of the struc-ture.

The temperature differential between topand bottom surfaces varies nonlinearly accordingto the depth and exposure of the structuralelements and their locality. A winter differential of15 F (8 C) and a summer differential of 25 F (14C) between the top of the deck and the soffit ofthe structure may be used. The temperaturedifferential should be increased in regions withhigh solar radiation; NCHRP 267 document maybe used as a guide in this respect.3.12

3.4.2.4 -Coefficient of Thermal ExpansionIn lieu of a more precise value, the coef-

ficient of linear thermal expansion for normalweight concrete may be taken as 6.5 x l0-6/deg F(12 x 10-6/deg C).

3.4.3-Rail-Structure Interaction FR and FrContinuously welded rail directly fastened to

the guideway, induces an axial force in the struc-ture through the fastener restraint when the struc-ture expands or contracts due to variations in tem-perature. Continuously welded rail is assumed tobe installed in a zero stress condition at an effec-tive installation temperature, T0. If the CWR isinstalled at a temperature that is different fromthe effective installation temperature, then the railis physically stressed to be compatible with thezero stress condition for which it is designed at theinstallation temperature.3.6

3.4.3.1 -Thermal Rail ForcesAxial rail stress fr due to a change in the

temperature after installation, is expressed by

fr = Er a (T1 - T0) (3-9)

CK = coefficient of thermal expansion

To = the installation temperature (zero-stress

condition)

NCRET358.1R-20 MANUAL OF CO

r, = the final rail temperatureE, = modulus of elasticity of rail steel, given in

Section 5.6.3

For a temperature decrease, T1 may be takenas the minimum effective temperature described inSection 3.4.2.1. For a temperature rise, T1 may betaken as the maximum effective temperature plus20 F (12 C). The corresponding rail force, Fr, isexpressed by:

Fr =SId;=BA&a(Tl-To) (3-10)

where Z implies that the forces in all rails shouldbe summed up. The movement of the structurethrough the fasteners induces either a tensile orcompressive axial force on the rail, depending onwhether the temperature rises or drops, respec-tively, from that at installation.

A vertically or horizontally curved structureexperiences a radial force resulting from thethermal rail forces. This radial force per unitlength of rail is expressed as

where R is the radius of curvature. FR alwaysoccurs in combination with Fr.

The preceding expressions apply where thereis no motion of the rail relative to the structure.Where rail motion may occur, the relaxation ofthe rail must be analyzed to determine its effecton the structure. Rail motion may occur when:

- Rail expansion joints are present or,- Radial or tangential movements of rail and

guideway structure at curves occur, or- A rail break takes place, or- Continuous rails cross structural joints, or- Creep and shrinkage strains in prestressed

concrete elements continue to take place.

3.4.3.2 -Broken Rail ForcesAt very low temperatures, the probability of a

rail break increases. The most likely place for arail break to take place is at an expansion joint inthe structure. A rail break at this location gener-ally creates the largest forces in the structure.

When the rail breaks, it slips through thefasteners on both sides of the break until thetensile force in the rail before the break is

counteracted by the reversed fastener restraintforces. The unbalanced force from the broken railis resisted by both the unbroken rails and theguideway support system in proportion to theirE INSPECTION

relative stiffnesses. The probability that more thanone rail will break at the same time is small, andis generally not considered in the design.

3.4.3.3 - Rail GapThe relative stiffness of the system should be

proportioned so that the magnitude of the gap be-tween broken rail ends be equal to the maximumallowable in order to prevent vehicle derailment.Typically acceptable rail gaps are in the range of2 in. (50 mm) for a 16-in. (0.4-m) diameter wheeland up to 4 in. (100 mm) for larger wheels. Railgap is controlled by the spacing and stiffness ofthe fasteners.

3.4.4 -Shrinkage in Concrete, SHShrinkage is a function of number variables,

the most significant of which are the charac-teristics of the aggregates, the water-cement ratioof the mix, the type and the duration of curing,surface-to-volume ratio of the member, the am-bient temperature and relative humidity at thetime of placing the concrete. For a major transitproject, shrinkage and creep behavior of the con-crete mix should be validated as part of the designprocess. For precast members, only the portion ofshrinkage or creep remaining after the element isintegrated into the structure needs to be con-sidered.

In the absence of more accurate data ormethod of analysis, shrinkage strain r-days aftercasting of normal weight concrete may becomputed from the following expression:3.2

sh =k&tEshu (3-12)

where the ultimate shrinkage strain, E&,,, isexpressed as:

E* = 55o l - iii6[ ( IIH 2 xl04 (3-13)For 0 I r I 12 in. (300 mm),

k, = 1-S[ T

+ 0.5, (3-14)

where rv is in inches,i T1 ,-300 + 0.5,where rv is in mm.

GUIDEWAY STRUCTURES 358.1R-21

For rv z= 12 in. (300 mm)

k = 0.5

3.5 - Exceptional Loads3.5.1 - Earthquake Effects, EQv

where rv ,= volume-to-surface-area ratio, t is thetime in days after the end of curing, and H is therelative ambient humidity, in percent.

k = 1 - e-O.ti (3-15)*

3.4.5-Creep in Concrete, CRCreep is a function of relative humidity,

volume-surface ratio and of time t after appli-cation of load. Creep is also affected by theamount of reinforcement in the section, themagnitude of sustained prestress force, the age ofthe concrete when the force is applied, and theproperties of the concrete mix. If the design issensitive to volumetric change, then an ex-perimental validation of creep behavior, based onthe ingredients to be used, may be necessary.

In the absence of more accurate data andprocedure, creep at r-days after application of loadmay be expressed in terms of the initial elasticstrain, 6 from:3.2

6CT = flak

where,

kr = 4.250 - 0.025H

For 0 4 rv I 10 in. (250 mm)

(3-16)

+ 0.7, (3-17)

where rv is in inches,

I= 1-z[ T250 + 0.7,

where rv is in mm

For rv > 10 in. (250 mm)

k = 0.7

where t is the time in days after application ofload or prestress, and,

k = 1 - e-0.w (3-18)fIn regions designated as earthquake zones,structures should be designed to resist seismicmotions by considering the relationship of the siteto active faults, the seismic response of the soils atthe site, and the dynamic response characteristicsof the total structure in accordance with the latestedition of AASHTO Standard Specifications forHighway Bridges."3.11 Certain local jurisdictionshave Zone 4 high seismic risk requirements foranalysis and design. For structures in this zone, adynamic analysis is recommended.

3.5.2 -Derailment Load, DRDerailment may occur when the vehicle

steering mechanism fails to respond on curves orwhen the wheels jump the rails at too large apull-apart gap, which may be the result of a breakin a continuously welded rail. Derailment may alsobe caused by intervehicle collision. For the designof the top slab and the barrier wall of theguideway, both the vertical and horizontalderailment loads may be considered to act si-multaneously.

The force effects caused by a single derailedstandard vehicle should be considered in the de-sign of the guideway structure components. Theseeffects, whether local or global, should in-cludeflexure, shear, torsion, axial tension orcompression, and punching shear through thedeck. The derailed vehicle should be assumed tocome to rest as close to the barrier wall asphysically possible to produce the largest forceeffect. In the design of the deck slab, a dynamicload allowance of 1.0 should be included in thewheel loads.

The magnitude and line of action of a hori-zontal derailment load on a barrier wall is afunction of a number of variables. These includethe distance of the tracks from the barrier wall,the vehicle weight and speed at derailment, theflexibility of the wall, and the frictional resistancebetween the vehicle and the wall. In lieu of adetailed analysis, the barrier wall should bedesigned to resist a lateral force equivalent to 50percent of a standard vehicle weight distributedover a length of 15 ft (5 m) along the wall andacting at the axle height. This force is equivalentto a deceleration rate of 0.5 g.

Collision forces between vehicles result fromthe derailment of a vehicle and its subsequentresting position against the guideway sidewall.

NCRE358.1R-22 MANUAL OF CO

This eccentric load on the guideway causes tor-sional effects, which should be accounted for inthe design. The magnitude and eccentricity of thisvertical collision load is a function of the distanceof the guideway center line from the side wall, theaxle width and the relative position of the centerlines of the car body and the truck after thecollision.

3.5.3 -Broken Rail Forces, BRForces on the guideway support elements due

to a broken rail are discussed in Section 3.4.3,under Rail-Structure Interaction.

3.5.4 - Collision Load, CLPiers or other guideway support elements that

are situated less than 10 ft (3 m) from the edge ofan adjacent street or highway should be designedto withstand a horizontal static force of 225 kips(