Precast Concrete Barriers

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MOT / UBC Testing of Bridge Barrier Anchorages

precast concrete barriers in British Columbia.doc page i of 142

Developing and Testing of Precast Concrete

Bridge Barrier Anchorages to meet the

Requirements for PL-2 Barrier Systems of

the Canadian Highway Bridge Design Codeat

University of British Columbia, UBC

Prepared by K. Bleitgen

Edited by S. F. Stiemer


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precast concrete barriers in British Columbia.doc page ii of 142

Conceptual formulation

The objectives of the research and testing will be as follows:

Research and testing of the precast concrete bridge barriers shall result in developingand testing anchorages that meet the requirements for PL2 barrier systems as given by

the Canadian Highway Bridge Design Code (CHBDC).

The scope of the research and testing for the precast concrete bridge barriers will include thefollowing:

1. Review Canadian Highway Bridge Design Code (CHBDC) requirements for bridgebarriers

2. Literature review of background to CHBDC requirements of bridge barriers and otherbackground regarding bridge barriers and bridge testing

3. Review the effect of having inter-connection between adjacent precast concrete barriers

4. Compare British Columbia Ministry of Transportation (BC MoT) anchorage details forprecast concrete bridge barriers to details by other jurisdictions / suppliers

5. Review the effect of type of bridge on the anchorage capacity:- Barrier anchored to concrete slab- Barrier anchored to box girder flange

6. Carry out site visits to existing bridges to see the existing BC MoT precast concrete boltdown barrier system in service

7. Carry out visits to the fabrication plants where the precast concrete barriers are fabricatedand liaise with the fabricators regarding fabrication issues


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precast concrete barriers in British Columbia.doc page iii of 142

Abstract

In this report, an introduction into precast concrete bridge barriers which are used in the

Province of British Columbia in Canada is given with an emphasis on bolt-down barriers.

Concrete barriers appear to be simple and uncomplicated, but in reality, they are sophisticated

safety devices.

Barriers are developed to delineate the superstructures edge to reduce the consequences of

vehicles leaving the roadway or humans leaving the sidewalk. The shape of a barrier as well asthe type of anchorage are the most important features in the design of a barrier. The design can

be done either with a crash test or an analysis method, i.e. the yield line analysis and strengthdesign method or finite element analysis.

Due to constantly updated design provisions established in Codes in order to improve theperformance of barriers, considerable amounts of research and development of new design

methods have been carried out. The basics of the design requirements of barriers have changed

dramatically in the last twenty years. Since most nowadays used precast concrete bridge barriersare developed based on the 1988 Code, the need of an up-to-date design became necessary.

Therefore, the Ministry of Transportation of British Columbia started a series of research

projects to satisfy that need.

This report is the first research report which will be followed soon by further projects and

gives an introduction into bolt-down precast concrete bridge barriers. It gives an overview on

applicable Codes, their precursor as well as relevant literature of other jurisdictions. Finally themost common barriers and their superstructures as well as comparable ones from other

jurisdictions are presented.


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List of Contents

Conceptual formulation ii

Abstract iii

List of Contents ivList of Tables v

List of Figures vi1. Introduction 1

2. The hierarchy and application area of applicable Codes 32.1 In Canada 3

2.2 In the United States of America 3

3. Review of the Canadian Highway Bridge Design Code (CHBDC) requirements forbridge barriers 5

3.1 Traffic barrier 5

3.1.1 Performance Level 6

3.1.2 Crash test requirements 73.1.3 Anchorages 8

3.2 Pedestrian barrier 9

3.3 Bicycle barrier 103.4 Combination barrier 11

4. Literature review of background to CHBDC requirements of bridge barriers and other

background regarding bridge barriers and barrier testing 124.1 The precursor of the Canadian Highway Bridge Design Code 12

4.1.1 Review of CAN/CSA-S6-88 requirements of bridge barriers 12

4.1.2 Comments on changes between CAN/CSA-S6-88 and CAN/CSA-S6-00 13

4.1.3 Review of OHBDC-91-01 requirements of bridge barriers 13

4.1.4 Comments on changes between OHBDC-91-01 and CAN/CSA-S6-00 154.1.5 General comment on the changes of the CHBDC to the precursor 16

4.2 Other background literature regarding the CHBDC 164.2.1 AASHTO LRFD Bridge Design Specifications, Section 13, Railings, from 1997 17

4.2.2 AASHTO LRFD Bridge Design Specifications, Section 13, Railings, 2004:

Important changes from the 2nd

to the 3rd

Edition 194.2.3 Appendix A of AASHTO LRFD Bridge Design Specifications, 1997 21

4.2.4 Appendix A of AASHTO LRFD Bridge Design Specifications, 2004: Important

changes from the 2nd

to the 3rd

Edition 29

4.2.5 NCHRP Report 350: Recommended Procedures for the Safety PerformanceEvaluation of Highway Features 29

4.3 Other literature regarding bridge barriers and barrier testing 304.3.1 Basics of Concrete Barriers 304.3.2 Review of the Washington State Bridge Design Manual 31

4.3.3 Comment on the Washington State Bridge Design Manual 34

5. Literature review of BC MoT's design literature regarding requirements of precastconcrete bridge barriers 35

6. Review the effect of having inter-connection between adjacent precast concrete barriers 37

6.1 The hook and eye connection 37


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6.2 The pin and loop connection 39

6.3 The inter-connection effect between adjacent precast barriers 417. Compare British Columbia Ministry of Transportation (BC MoT) anchorage details for

precast concrete bridge barriers to details by other jurisdictions 42

7.1 Anchor details of the MoT of British Columbia 42

7.1.1 The 810 mm high precast concrete bridge parapet 427.1.2 The 865 mm high precast concrete bridge parapet 45

7.1.3 The 875 mm high precast concrete bridge parapet 47

7.2 Anchorage details of precast concrete bridge barriers of other Canadian Provinces andTerritories than British Columbia 50

7.2.1 Anchorage details McKenzie Creek Hwy 6, used by the Ministry of

Transportation Ontario (MTO) 1991 507.3 United States of America anchorage details 54

7.4 Comparison of the anchorage details 57

7.4.1 Comparison of the BC MoT bolt-down precast concrete bridge barriers with theMcKenzie precast bridge barrier 58

7.4.2 Comparison of the BC MoT bolt-down precast concrete bridge barriers with theL.B. Foster NJ-Shape precast bridge railing 58

8. Review the effect of type of bridge (concrete slab vs. box girder) on the anchorage capacity 608.1 The anchor capacity of barriers anchored to concrete slabs 62

8.1.1 The Misinchinka Bridge, # 6819 62

8.1.2 The Hudgens Bridge, # 7476 648.1.3 The Twan Creek Bridge, # 8023 66

8.2 The anchor capacity of barriers anchored to box girder flange 67

8.2.1 The Standard Precast Concrete Bridge, # 2965 678.2.2 The Elkins Bridge Precast Concrete Parapets, #7780 69

9. Carry out site visits to existing bridges to see the existing BC MoT precast concrete boltdown barrier system in service 71

9.1 Detailed information of the construction of the Birkenhead Causeway Bridge No. 8024 71

9.2 Site visit: Birkenhead Causeway Bridge No. 8024 7310. Precast concrete barrier fabrication plants in British Columbia 76

Conclusions 80

References 81

Appendix 83

List of TablesTable 1 Traffic barrier loads, from Figure 3.8.8.1, CAN/CSA-S6-00 .......................................... 9Table 2 Bridge railing Performance Levels and crash test criteria from Table 13.7.2.1,

AASHTO LRFD Bridge Design Specifications, 1997 .............................................. 18Table 3 Bridge railing Testing Levels and crash test criteria, from Figure 13.7.2-1, AASHTO

LRFD Bridge Design Specifications 2004................................................................. 20

Table 4 Design forces for traffic railings, from Table A13.2-1, AASHTO LRFD Bridge Design

Specifications, 2004 ................................................................................................... 29Table 5 Vehicle impact loading on traffic barrier by WSDOT, WSBDM, Section 10.2.4,

Design Criteria ........................................................................................................... 33


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Table 6 List of precast concrete bridge barriers from Section 941, Standard Specifications for

Highway Construction, BC MoT ............................................................................... 36Table 7 Standard precast concrete bolt-down systems used by the BC MoT............................ 60

Table 8 Precast concrete bolt-down system used by the MoT Ontario ..................................... 60

Table 9 Precast concrete bolt-down systems used by the US. DoT, FHWA............................. 60

Table 10 List of fabricators of precast concrete bridge barriers within British Columbia ........ 76

List of FiguresFigure 1 Sketch of the hierarchy of the Codes concerning traffic barriers in the USA............... 4Figure 2 Application of traffic design loads to traffic barriers, from Figure 12.5.2.4, CAN/CSA-

S6-00 ............................................................................................................................ 9

Figure 3 The application of pedestrian and bicycle design loads to barriers, from Figure12.5.3.2, CAN/CSA-S6-00 .......................................................................................... 10

Figure 4 Application of pedestrian loads for pedestrian railings, from Figure 5-4.5.2.3,

OHBDC-91-01 ........................................................................................................... 14

Figure 5 Application of pedestrian loads for bicycle railings and combination barriers, fromFigure 5-4.5.2.3, OHBDC-91-01................................................................................ 15

Figure 6 Pedestrian railing loads, from Figure 13.8.2.1, AASHTO LRFD Bridge Design

Specifications ............................................................................................................. 18Figure 7 Bicycle Railing Loads, from Figure 13.9.3.1, AASHTO LRFD Bridge Design

Specifications ............................................................................................................. 19

Figure 8 Geometrical definitions of two typical traffic railings, from Figure A13.1.1-1,AASHTO LRFD Bridge Design Specifications ........................................................ 21

Figure 9 Post setback criteria, from Figure A13.1.1-3, AASHTO LRFD Bridge Design

Specifications ............................................................................................................. 22

Figure 10 Nomenclature for traffic railing equations, from Figure CA13.2.1, AASHTO LRFD

Bridge Design Specifications, 1997........................................................................... 23Figure 11 Design forces for traffic railings, from Table A13.2-1, AASHTO LRFD Bridge

Design Specifications, 1997....................................................................................... 24Figure 12 Railing design forces, from Figure A13.2-1, AASHTO LRFD Bridge Design

Specifications ............................................................................................................. 24

Figure 13 Yield Line Analysis of concrete parapet walls for impact within wall segment andnear end of wall segment, part 1 of Table A13.3.1-1/2, AASHTO LRFD Bridge

Design Specifications................................................................................................. 25

Figure 14 Yield Line Analysis of concrete parapet walls for impact within wall segment, part 2

of Table A13.3.1-1, AASHTO LRFD Bridge Design Specifications........................ 26Figure 15 Possible failure modes for post-and-beam railings, from Table A13.3.2-1, AASHTO

LRFD Bridge Design Specifications.......................................................................... 26Figure 16 Combination concrete wall and metal rail evaluation-impact at (1) mid-span of rail

and (2) at a post, from Table A13.3.3-1/ 2, AASHTO LRFD Bridge Design

Specifications ............................................................................................................. 28

Figure 17 Detail drawing of the F-shape and Single Slope barrier, WSDoT, Figure 10.2.3-2 . 32Figure 18 Hooks and eyes, from Standard Specifications for Highway Construction 2006,

SP941-04.01.01 .......................................................................................................... 37

Figure 19 Eye of the BC MoT's precast concrete bridge barrier, from drawing 7780-5........... 38


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Figure 20 Hook and eye end section of a barrier in 3D, standard median barrier 810 mm, from

drawing SP941-02.01.08 and 09, BC MoT................................................................ 38Figure 21 Plan view on the end of a hook and eye unit, standard median barrier 810 mm, from

drawing SP941-02.01.03 and 04, BC MoT................................................................ 38

Figure 22 Connection detail (plan view) of the hook (left) and eye (right) system, standard

median barrier 810 mm, drawing SP941-02.01.03, BC MoT.................................... 39Figure 23 Plan view of the pin and loop system, from drawing C-8d, Standard Drawings,

WSDoT ...................................................................................................................... 39

Figure 24 The pin in detail, from drawing C-8d, Standard Drawings, WSDoT........................ 40Figure 25 Top and side view of the whole barrier, showing the anchors for the pin and loop

system, from drawing C-8d, Standard Drawings, WSDoT........................................ 40

Figure 26 View on the end of the barrier, from drawing C-8d, Standard Drawings, WSDoT.. 41Figure 27 810 mm high precast concrete bridge barrier, from drawing 8023-22, BC MoT ..... 42

Figure 28 Typical section through the 810 mm high precast concrete bridge barrier, from

drawing 8023-22, BC MoT ........................................................................................ 43Figure 29 Bolt sleeve detail of the 810 mm high precast concrete bridge barrier, from drawing

8023-22, BC MoT ...................................................................................................... 44Figure 30 Bolt detail of the 810 mm high precast concrete bridge barrier, from drawing 8023-

22, BC MoT ............................................................................................................... 44Figure 31 865 mm high precast concrete bridge barrier, from drawing 8023-22, BC MoT ..... 45

Figure 32 Typical section through the 865 mm precast parapet, from drawing 2965-4, BC MoT45

Figure 33 Blockout and bolt sleeve detail of the 865 mm high barrier, from drawing 2965-4,BC MoT ..................................................................................................................... 46

Figure 34 Bolt sleeve detail of the 865 mm high barrier, from drawing 2965-4, BC MoT....... 46

Figure 35 One possible anchor bolt of the 865 mm high precast concrete bridge parapet, fromdrawing 2965-23, BC MoT ........................................................................................ 47

Figure 36 875 mm high precast concrete bridge barrier, from drawing 8023-22, BC MoT ..... 47Figure 37 Typical section through the 875 mm high precast concrete bridge barrier, from

drawing 7476-12, BC MoT ........................................................................................ 48

Figure 38 Bolt sleeve detail of the 875 mm high precast concrete bridge barrier, from drawing7476-12, BC MoT ...................................................................................................... 49

Figure 39 Blockout and bolt sleeve detail of the 875 mm high barrier, from drawing 7476-12,

BC MoT ..................................................................................................................... 49

Figure 40 Cut through barrier, anchor type 1, used by the Ministry of Transportation, Ontario51Figure 41 Cut through barrier, anchor type 2, used by the Ministry of Transportation, Ontario51

Figure 42 Anchor details: type 1 and type 2, used by the Ministry of Transportation, Ontario 52

Figure 43 Step I to III of the construction sequence of the McKenzie Creek Barrier, used by theMinistry of Transportation, Ontario........................................................................... 53

Figure 44 Step IV and VII of the construction sequence of the McKenzie Creek Barrier, used

by the Ministry of Transportation, Ontario................................................................ 54Figure 45 Section through L.B. Foster NJ-Shape barrier, from Bridge Rail Guide 2005, FHWA55

Figure 46 Bolt detail of the L.B. Foster NJ-Shape barrier, from Bridge Rail Guide 2005,

FHWA........................................................................................................................ 56Figure 47 Barrier end detail of the L.B. Foster NJ-Shape barrier, from Bridge Rail Guide 2005,

FHWA........................................................................................................................ 57


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Figure 48 Failure modes for anchors under tension and shear load, from CSA A23.3-04, Figure

D.1 and D.2 ................................................................................................................ 61Figure 49 Plan and elevation view of the Misinchinka Bridge, from drawing 6819-9, BC MoT62

Figure 50 Parapet anchor insert of the Misinchinka Bridge, from drawing 6819-8, BC MoT.. 63

Figure 51 Misinchinka Bridge after the installation of the anchor bolt, from drawing 6819-10,

BC MoT ..................................................................................................................... 63Figure 52 Plan and elevation view of the Hudgens bridge, from drawing 7476-12, BC MoT.. 65

Figure 53 Section through exterior bridge deck, from drawing 7476-12, BC MoT.................. 65

Figure 54 Detail drawing of the nut in the panel deck, from drawing 7476-12, BC MoT........ 65Figure 55 The Hudgens precast concrete bridge barrier # 7476 after the installation of the

anchor bolt, from drawing 7476-12, BC MoT ........................................................... 66

Figure 56 Detail of the precast concrete deck bridge, from drawing 8023-21, BC MoT.......... 66Figure 57 Parapet connection to deck at Twin Creek bridge, from drawing 8023-22, BC MoT67

Figure 58 Plan and elevation view of the standard precast parapet MK P1, from drawing 2965-

4, BC MoT ................................................................................................................. 68Figure 59 Section through exterior stringer MK 700/16/E, from drawing 2965-23, BC MoT . 68

Figure 60 Standard precast concrete bridge after installation of the anchor bolt, from dwg.2965-6, BC MoT ........................................................................................................ 69

Figure 61 Elkins bridge after the installation of the anchor bolt, from drawing 7780-6, BC MoT70Figure 62 Section through the Birkenhead Causeway Bridge barrier, from dwg. 8024-9, BC

MoT............................................................................................................................ 71

Figure 63 Plan and elevation view of the Birkenhead Causeway Bridge barrier, from dwg.8024-9, BC MoT ........................................................................................................ 72

Figure 64 Cut through box stringer of the Birkenhead Causeway Bridge, from dwg. 8024-9,

BC MoT ..................................................................................................................... 72Figure 65 After placing the Birkenhead Causeway Bridge barrier, from dwg. 8024-9, BC MoT73

Figure 66 Filled precast concrete barrier forms at the plant of Eagle West Truck & Crane ..... 77Figure 67 Hook bars used for the connection of adjacent barriers at the plant of Eagle West

Truck & Crane............................................................................................................ 77

Figure 68 Eye bar(s) used for the connection of adjacent barriers at the plant of Eagle WestTruck & Crane............................................................................................................ 78

Figure 69 Precast concrete barriers after 3 days at the plant of Eagle West Truck & Crane .... 78

Figure 70 Side and end view of a precast concrete bridge barrier at the plant of Eagle West

Truck & Crane............................................................................................................ 79Figure 71 Side and end view of the precast concrete bridge barrier anchor at Eagle West Truck

& Crane ...................................................................................................................... 79


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1. Introduction

The objective of this report is to give an introduction into precast concrete reinforced

bridge barriers and in particular into bolt-down precast barriers used in British Columbia in

Canada.

Barrier design provisions established in codes are constantly updated in order to improve the

performance of barriers to help to restrain errant vehicles from leaving the roadway or humans

from leaving the sidewalk. Considerable amounts of research and development of new structuralsystems is being carried out. However, there are still many barrier design requirements that

remain challenging.

The 2000 edition of the Canadian Highway Bridge Design Code (CHBDC), as well as the

third edition of the American Association of State Highway and Transportation Officials

(AASHTO), Load and Resistance Factor Design (LRFD), Barrier Design Specifications and

National Cooperative Highway Research Program (NCHRP), Report 350: RecommendedProcedures for the Safety Performance Evaluation of Highway Features, contain significant

changes compared to previous editions regarding barrier design requirements. The main feature

of these standards is the requirement for crash-testing in order to establish a specified level towhich a traffic barrier will perform (Performance Level, Testing Level).

Due to the fact that many Codes and Guidelines which deal with barriers are conflictedbetween the each other, the second chapter gives a short introduction into relevant Codes

showing their hierarchy and application area. In the third chapter, a summary of the section that

deals with barriers in the Canadian Highway Bridge Design Code (CHBDC) is presented.

Many of the nowadays used precast concrete bridge barriers are designed before 2000, based onthe Canadian Highway Bridge Design Code (CHBDC) from 1988. Due to this high importance,

the precursor of the Canadian Highway Bridge Design Code (CHBDC) published in 2000 as wellas their background, are introduced in Chapter 4.1. Afterwards a general introduction into

concrete barriers is given. It explains the reason for the shape of a barrier and gives some

historical background concerning the development of barriers (Chapter 4.2). Then, the mainrelated literatures to the Canadian Highway Bridge Design Code (CHBDC) as the AASHTO

LRFD Bridge Design Specifications and theNCHRP Report 350: Recommended Procedures for

the Safety Performance Evaluation of Highway Features are presented.To make a comparison of the applicable Codes regarding barriers used in British Columbia, the

state Washington in the United States is chosen due to similar conditions. Therefore a summary

of the Washington State Bridge Design Manual as well as a comment on the differences is given.

Then, in Chapter 5, the design and production requirements of precast concrete barriers in British

Columbia which are given by the Ministry of Transportation of BC are explained. These design

provisions give all necessary information for the production of barriers and are therefore relevantfor fabrication plants. One visit to a fabrication plant was done and is presented in Chapter 10.


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Since precast concrete reinforced barriers have to be delivered to the bridge site, they can only be

produced in small pieces. Thus, the connection between two adjacent barriers produces an inter-connection effect which can influence the design and is therefore analysed in Chapter 6.

The main purpose of the research series is to get a proof for used precast concrete bridge barrier

how they perform and in which level (Performance Level or Testing Level) they can becategorized. Therefore, the three main precast concrete bridge barriers which are used in British

Columbia are analysed in the beginning of Chapter 7. Since crash tests are really expensive and

time intensive, the Ministry of Transportation wants to design the barriers either with showingthere are similar to proofed barriers and thus crashworthy or with analysis methods. Due to that

comparable precast concrete bridge barriers of other jurisdictions are presented. Finally, acomparison between the barriers used in British Columbia and the barriers of other jurisdictions

is done.

The Ministry of Transportation of British Columbia uses the aforementioned three barrier types

in combination with different superstructures which results in five different models. Precast

concrete bridge barriers are combined either with a twin box stringer or a concrete panel decksuperstructure. Since different bolt systems are used for different superstructure types, anchorage

capacities are determined when the necessary information was present.

Finally, in Chapter 9, the results of a site visit to an existing bridge which is built with the bolt-down precast concrete bridge barriers are presented after the bridge itself is explained.


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2. The hierarchy and application area of applicableCodes

This short introduction is supposed to give an overview of existing Codes and explains the

hierarchy of the Codes as well as its area of application. Since the first part of this research report

consists of a literature review of existing Codes dealing with traffic barriers this overview ofapplicable Codes should help to understand the coherences between the different Codes and its

countries. It is important to understand the Code's hierarchy and its appropriate application

because there occur conflicts between the structural design literatures. In general the nationalcode provides a general design method whereas the state code deals with specifications.

2.1 In Canada

In Canada the National Code which deals with bridge barriers is the Canadian Highway

Bridge Design Code published by the Canadian Standards Association (CSA) for highway bridge

design. As a subdivision, each state of Canada is having additional specifications and standards

establishing detailed requirements, consistent with current nationwide practices, which apply tocommon highway bridges. For example in British Columbia, the British Columbia Ministry of

Transportation (BC MoT) published the Standard Specifications for Highway Construction 2006

as well as the Design Standards, Bridge Standards and Procedures, which have to be applied inBritish Columbia.

But nevertheless the system is not as clear as it seems, because some Codes give

references to relevant literature of other jurisdictions. For example, concerning crash testrequirements, the Canadian Highway Bridge Design Code refers to theAmerican Association of

State Highway and Transportation Officials (AASHTO), Guide Specifications of Bridge Railings.

And in addition, the AASHTO Guide Specifications of Bridge Railings refers further to the

National Cooperative Highway Research Program (NCHRP), Report 350: RecommendedProcedures for the Safety Performance Evaluation of Highway Features.

2.2 In the United States of America

Since most comparisons are done with the United States of America, the hierarchy and the

application areas of the Codes of the United States of America concerning bridge barriers are

explained as well. The American Association of State Highway and Transportation Officials(AASHTO) Load and Resistant Factor Design (LRFD) Bridge Design Specifications is intended

to serve as the National Standard for use in the development of the Department's own structural

specifications.

Since the United States of America are quite big and consists of many states, the next

lower level consists of three subdivisions which are (1) the Western Federal Lands HighwayDivision, (2) the Central Federal Lands Highway Division, and (3) the Eastern Federal Lands

Highway Division. Each division has a different Project Development and Design Manual.


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The next level under these three subdivisions are the states itself. A sketch of the

hierarchy of the Codes in the United States of America is given in the beneath figure.

AASHTO LRFD BridgeDesign Specifications

USA

-COUNTRY

Western Federal Central Federal Eastern Federal

Lands Highway Lands Highway Lands Highway

Division (WFLHD) Division (CFLHD) Division (EFLHD)

FEDERAL

SUBDIVISION

Alaska California Maryland

Washington Nevada Kentucky

Oregon Utah Virginia

Idaho Arizona Mississippi

Montana Wyoming TennesseeWyoming Colorado Virginia

... ...

STA

TE-

LEVEL

Figure 1 Sketch of the hierarchy of the Codes concerning traffic barriers in the United States of America


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3. Review of the Canadian Highway Bridge DesignCode (CHBDC) requirements for bridge barriers

The Canadian Highway Bridge Design Code CAN/CSA-S6-00 is prepared by the Canadian

Standards Association (CSA) for highway bridge design in Canada and was published in

December 2000. The requirements for the design of barriers are specified in section 12. Barrierson bridges receiving salt are exposed to a highly corrosive environment. To ensure long-term

performance, these barriers must either be made from materials that can withstand this

environment or be protected by an adequate protective coating.

The barriers are divided into four different types of barriers according to their function:

Traffic barrier; Pedestrian barrier; Bicycle barrier; and

Combination barrier.

In the appraisal of a barrier the specific regulations, which will be mentioned in the following

subsections, are not the only factors to consider. There also exist some general factors which

should not be underestimated. These factors are durability, ease of repair, snow accumulation on

and snow removal from deck, visibility through or over barrier, deck drainage, future wearingsurfaces, and aesthetics. Damaged barriers need to be repaired quickly with minimal disruption to

traffic. Traffic barriers should be designed with features such as anchorages that are unlikely to

be damaged or cause damage to the bridge deck during an accident and modular constructionusing prefabricated sections that allow damaged sections to be repaired quickly.

3.1 Traffic barr ier

Traffic barriers should be provided on both sides of highway bridges to delineate the

superstructure edge and therefore to reduce the consequences of vehicles leaving the roadway

upon the occurrence of an accident. Crash tests are used to determine barrier adequacy in

reducing the consequences of vehicles leaving the roadway. If a barrier has the same details asthose of an existing traffic barrier the adequacy can be determined from an evaluation of the

existing barrier's performance when struck by vehicles.

The adequacy of a traffic barrier in reducing the consequences of a vehicle leaving the roadway is

based on the level of protection provided to the occupants of the vehicle, to other vehicles on theroadway and to people and property beneath the bridge. This protection is provided by retainingthe vehicle and its cargo on the bridge, by smoothly redirecting the vehicle away from the barrier

and by limiting the rebound of the vehicle back into traffic.


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3.1.1 Performance Level

Traffic barrier requirements vary from bridge site to bridge site and are based on the expected

frequency and consequences of vehicle accidents at a bridge site. This procedure assumes that thefrequencies and consequences of vehicle accidents at bridge sites are a function of many

variables. The ranking system, used in CAN/CSA S6-00 to determine the site conditions of abridge site, are named Performance Level (PL) and are defined as the following (CAN/CSA-S6-00, Section 12.2 Definitions):

Performance Level 1 (PL-1): The performance level for traffic barriers on bridges wherethe expected frequency and consequences of vehicles leaving the roadway are similar tothat expected on low traffic volume roads. Crash test requirements require crash testing

with a small automobile and a pickup truck in accordance with the AASHTO (American

Association of State Highway and Transportation Officials) Guide Specifications for

Bridge Railings.

Performance Level 2 (PL-2): The performance level for traffic barriers on bridges wherethe expected frequency and consequences of vehicles leaving the roadway are similar tothat expected on high to moderate traffic volume highways. Crash test requirements

require crash testing with a small automobile, a pickup truck, and a single unit truck in

accordance with theAASHTO Guide Specifications for Bridge Railings.

Performance Level 3 (PL-3): The performance level for traffic barriers on bridges wherethe expected frequency and consequences of vehicles leaving the roadway are similar to

that expected on high traffic volume highways with high percentage of trucks. Crash test

requirements require crash testing with a small automobile, a pickup truck, and a tractor-trailer truck in accordance with theAASHTO Guide Specifications for Bridge Railings.

Alternative Performance Levels, as mentioned in Section 12.5.2.1.1 in CAN/CSA-S6-00, have tobe approved by the Regularity Authority for the bridge and defined by specifying their crash test

requirements. These levels shall be considered along with Performance Level 1, 2, or 3 when

determining the optimum performance level which is the one with the least costs.

The optimal level of traffic barrier performance at a bridge site is assumed to be the level giving

the least costs where costs includes the costs of supplying and maintaining a traffic barrier as wellas the costs of the accidents expected with the use of the traffic barrier. The assumed accident

rates, accident severities and traffic barrier costs used by a computer-based Benefit-Cost Analysis

Program (BCAP) in determine optimal levels of traffic barrier performance as well as the

engineering judgement used to adjust these optimal levels for use in the Codes are given inAASHTO (1989).

The Performance Levels are determined with the barrier exposure index (Be) which isbased on the estimated average annual daily traffic for the first year after construction (AADT1).

Other influencing parameters, as the type of the highway, the curvature of the highway, the grade

of the highway and the height of the superstructure as well as the type of substructure, areconsidered in the barrier exposure index.


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The barrier exposure index is defined as:1 h c g s

e

(AADT ) K K K K B =

1000

Where:

AADT1 10,000 vehicles per day per traffic lane per vehicle speeds 80km/h or greater

Kh = highway type factor, see CAN/CSA-S6-00, Table 12.5.2.1.2 (a)

Kc = highway curvature factor, see CAN/CSA-S6-00, Table 12.5.2.1.2 (b)

Kg = highway grade factor, see CAN/CSA-S6-00, Table 12.5.2.1.2 (c)

Ks = superstructure height factor, see CAN/CSA-S6-00, Table 12.5.2.1.2 (d)

With the design speed and the percentage of trucks as well as the barrier exposure index thePerformance Level can be determined with tables given under CAN/CSA-S6-00 Section

12.5.2.1.3. There exist three different tables for three different barrier clearances in the CanadianHighway bridge design Code:

Table 12.5.2.1.3 (a) for Barrier Clearance 2.25m

Table 12.5.2.1.3 (b) for 2.25m < Barrier Clearance 3.75m

Table 12.5.2.1.3 (c) for Barrier Clearance > 3.75m

Due to the Performance Level a minimum barrier height can be determined with Table 12.5.2.2

from CAN/CSA-S6-00. The minimum barrier heights for PL 1, 2, and 3 traffic barriers are 0.68 m,

0.80 m, and 1.05 m respectively. Traffic barrier height requirements are intended to prevent

impacting vehicles from vaulting or rolling over a barrier. The higher the center of gravity of the

impacting vehicle, the greater the required traffic barrier height needed to contain it.

And the geometry of the roadway face of a traffic barrier as well as the transition into theroadway face of the approach roadway traffic barrier shall have a smooth and continuous

alignment, as laid out in Section 12.5.2.2 in CAN/CSA-S6-00. Where a traffic barrier is located

between the roadway and a sidewalk or bikeway, the sidewalk or bikeway face of the barriershould have a minimum height of 0.60 m measured from the surface of the sidewalk or bikeway.

3.1.2 Crash test requirements

With the defined Performance Level the crash test requirements which should be inaccordance with the crash test requirements ofAASHTO Guide Specifications for Bridge Railingsare defined, as mentioned in Section 12.5.2.3 in CAN/CSA-S6-00. Those crash test requirements

shall be satisfied along the entire length of a traffic barrier, including at any changes in barrier

type, shape, alignment, or strength that may affect the barrier performance. Alternative

Performance Levels shall meet the crash test requirements of the optimum Performance Level orof a more severe Performance Level as considered.


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Under Section 12.5.2.3.2 CAN/CSA-S6-00, the crash test requirements for traffic barrier

transitions are defined. They should meet the crash test requirements used for appraising theapproach roadway traffic barrier, provided that it has been crash tested to requirements that test

its geometry, strength, and behaviour to an equivalent or more severe level. These requirements

are normally in accordance with Test Designation 30 ofNCHRP 230: Recommended Procedures

for the Safety Performance Evaluation of Highway Appurtenances (Michie 1981) which requirescrash testing with a 2040 kg automobile travelling 96 km/h and striking the transition at an

impact angle pf 25.

The crash test requirements for longitudinal barrier Test Levels 2, 4, and 5 of National

Cooperative Highway Research Program (NCHRP) Report 350:Recommended Procedures forthe Safety Performance Evaluation of Highway Features shall be taken as meeting the crash test

requirements for Performance Level 1, 2, and 3 respectively.

According to Section 12.5.2.3.4 in CAN/CSA-S6-00, any changes in details effecting the

geometry, strength, or behaviour of the traffic barrier or traffic barrier transition that meets the

aforementioned requirements can be demonstrated to not adversely affect barrier-vehicleinteraction.

3.1.3 Anchorages

The performance of the traffic barrier anchorage during crash testing is the basis for its

capability. In case no significant damage occurs in the anchorage or deck during crash testing, the

anchorage is considered to be acceptable.

If there are no crash testing results for the anchorage available, the anchorage and deck shall be

designed to resist the maximum bending, shear and punching loads that can be transmitted tothem by the traffic barrier. The loads should be applied as the following:


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Figure 2 Application of traffic design loads to traffic barriers, from Figure 12.5.2.4, CAN/CSA-S6-00

But the loads have to be greater than those resulting from the loads defined in Section 3.8.8,Barrier Loads, in CAN/CSA-S6-00. The transverse, longitudinal, and vertical loads should be

applied simultaneously and are specified as the following:

Table 1 Traffic barrier loads, from Figure 3.8.8.1, CAN/CSA-S6-00

3.2 Pedestr ian barr ier

Pedestrian barriers should be provided on both sides of pedestrian bridges and on the

outside edges of highway bridge sidewalks separated from the roadway by a traffic barrier.Pedestrian barriers should be in accordance with the minimum height requirements which are

given in Table 12.5.2.2 in CAN/CSA-S6-00, as aforementioned in chapter 3.1 Traffic barrier.

Openings in pedestrian barriers should not exceed 150 mm in the least direction, or be coveredwith chain link mesh with a minimum wire diameter of 3.5 mm and openings smaller than 50 mm

by 50 mm.


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The design loading for pedestrian barrier are given in Section 3.8.8,Barrier Loads, in CAN/CSA-

S6-00 (see Table 1 Traffic barrier loads, from Figure 3.8.8.1, CAN/CSA-S6-00). These loadsshould be applied as shown in the beneath figure (the design load application for pedestrians and

bicycle are the same). When designing posts of post and railing barriers only one railing should

be loaded at a time.

Figure 3 The application of pedestrian and bicycle design loads to barriers, from Figure 12.5.3.2,CAN/CSA-S6-00

3.3 Bicycle barrier

Bicycle barriers should be provided on both sides of bicycle bridges and on the outside

edges of highway bridge bikeways where the bikeway is separated from the roadway by a traffic

barrier. Bicycle barriers should also conform the minimum height requirements which are given

in Table 12.5.2.2 in CAN/CSA-S6-00, as aforementioned in chapter 3.1 Traffic barrier. Openingsin bicycle barriers for the lower 1050 mm should be smaller than 150 mm in the least direction,

or be covered with chain link mesh with a minimum wire diameter of 3.5 mm and openings

smaller than 50 mm by 50 mm.

The design loading for bicycle barrier are given in Section 3.8.8 in CAN/CSA-S6-00, BarrierLoads. Since the design load application for pedestrians and bicycle are the same, the loadsshould be applied as shown in Figure 3 The application of pedestrian and bicycle design loads

to barriers, from Figure 12.5.3.2,

CAN/CSA-S6-00. When designing posts of post and railing barriers only one railing should beloaded at a time.


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3.4 Combination barrier

Combination barriers shall be provided on the outside edges of bridge sidewalks and

bikeways not separated from the traffic lanes by traffic barrier. They should meet the

requirements mentioned in chapter 3.1 Traffic barrier, 3.2 Pedestrian barrier, and 3.3 Bicycle

barrier except in respect of geometry and the openings. In combination barriers opening shall besmaller than 150 mm in the least direction for the lower 600 mm of the barrier and 380 mm in the

least direction above the lower 600 mm of the barrier.


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4. Literature review of background to CHBDCrequirements of bridge barriers and other backgroundregarding bridge barriers and barrier testing

4.1 The precursor of the Canadian Highway Bridge Design Code

The CAN/CSA-S6-00 Canadian Highway Bridge Design Code amalgamates andsupersedes both, CAN/CSA-S6-88Design of Highway Bridges and the OHBDC-91-01 Ontario

Highway Bridge Design Code, third edition, becoming the standard National Code used in

Canada. CAN/CSA-S6-88Design of Highway Bridges is prepared by the Canadian Standards

Association (CSA) for highway bridge design in Canada and the OHBDC-91-01 Ontario

Highway Bridge Design Code was published by the Ontario Ministry of Transportation,

Downsview, Ontario.

Therefore, reviews of the CAN/CSA-S6-88Design of Highway Bridges as well as the

OHBDC-91-01 Ontario Highway Bridge Design Code are presented and in addition the main

changes of the precursor compared to the CAN/CSA-S6-00 Canadian Highway Bridge DesignCode are outlined.

4.1.1 Review of CAN/CSA-S6-88 requirements of bridge barriers

In Section 4.4 of the CAN/CSA-S6-88 Design of Highway Bridges barriers named

roadway railings are defined. The type of barrier is due to its function defined as traffic railing,

sidewalk railing, bicycle railing, and combination railing. The different types of railings whichshould be illustrative only are shown in Figure 3, CAN/CSA-S6-88, with its dimensions and

design loads. All bridges should have a railing on each side.

Roadway railings are covered in Section 4.4.2. The first subsection, Section 4.4.2.1, deals

with the geometry and defines that the rail on the traffic side should have a smooth and

continuous face of rail. The next section deals with joints and says that provisions should bemade where expansion joints interrupt the continuous railings to transfer the loads. The endings

of railings should be treated with caution and are covered in Section 4.4.2.3.

Concerning the design of traffic railings, Section 4.4.2.4 outlines a height of minimum 700 mm,

except that parapets with sloping traffic faces are used which demands a minimum height of800 mm. The height is measured from the top of the roadway, the top of future overlay, or the top

of the curb to the top of the upper rail members.

The lower element of a roadway or combination railing should consists of a parapet projecting atleast 600 mm above the reference surface, or a participating curb (Section 4.4.2.5). The next

section defines the maximum opening below the lower rail, or between succeeding rails to a

maximum of 380 mm.


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The height of sidewalk and bicycle railings should be as indicated in Figure 3, CAN/CSA-

S6-88. Beside that, sidewalk railings should have a maximum opening of 150 mm in leastdimension (Section 4.4.3, CAN/CSA-S6-88). Concerning combination railings, governed in

Section 4.4.4 ofCAN/CSA-S6-88, the minimum height of combination railings is 1000 mm.

The design of the roadway railings, parapets, and posts, as laid out in Section 5.2.10.4 inCAN/CSA-S6-88, should be done with transverse loads given for some railing types (see Figure 3,

CAN/CSA-S6-88). Sidewalk, bicycle, and combination railings should be designed for transverse

and vertical loads on each longitudinal member, simultaneously (see Section 5.2.10.4.2 to5.2.10.4.4, CAN/CSA-S6-88).

4.1.2 Comments on changes between CAN/CSA-S6-88 and CAN/CSA-S6-00

The requirements on the geometry of the barriers has only little changes. But the

definition of the height of a barrier as well as the design requirements underlie many changes.

Traffic railings are not differentiated due to different site conditions of a bridge site whichis done with the Performance Level in the new Code, CAN/CSA-S6-00. Under Section 4.4.2.4 ofCAN/CSA-S6-88 a minimum height of the roadway railing is defined by 700 mm which is

comparable with the height of PL-1 given in CAN/CSA-S6-00. But on the other side, CAN/CSA-

S6-88gives a minimum opening of 380 mm for traffic barriers which does not exists any more inCAN/CSA-S6-00.

Another point which is new in CAN/CSA-S6-00 are the anchorages of the roadway railings

and their design. Since the aspect of failure became a bigger role in the design, because of thechanges of the power of cars, traffic barriers and their design changed. They should nowadays

also provide a reduction of the consequences of a vehicle leaving the roadway due to the

occurrence of an accident.

The requirements on the geometry of pedestrian, bicycle, and combination barriers has

changed only little too. CAN/CSA-S6-00 describes the requirements on the geometry moredetailed and more separated due to its function. The requirements on the design of pedestrian,

bicycle, and combination barriers are no more as detailed as they were before, but therefore crash

test requirements are defined.

In the end it can be said that CAN/CSA-S6-88 gives a great flexibility in the design of

roadway railings. For some cases the design loads are given but it is mentioned that they are only

illustrative. Therefore a definition of the design of other types of railings is missing. Crash teststo determine the effectiveness in reducing the consequences of vehicles leaving the roadway upon

the occurrence of an accident are not considered at all.

4.1.3 Review of OHBDC-91-01 requirements of bridge barriers

In Section 5 of the OHBDC-91-01, third edition, barriers and highway appurtenances are

defined. In general, barriers are design at superstructure sides or edges and are supposed to helpto restrain errant vehicles from leaving the roadway as mentioned in Section 5-4.1,

OHBDC-91-01. Barriers are differentiated due to their location and function in traffic,


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combination, pedestrian, and bicycle barriers. The barrier alignment, as defined in Section

5-4.1.3, OHBDC-91-01,Barrier Geometry, should be continuous and smoothly transitioned. Theexpansion joints that allow for bridge flexure and thermal movements should be designed in

detail for all barrier types. The minimum barrier heights are defined in Table 5-4.1.3.2, OHBDC-

91-01 and come up to 0.70 m, 0.80 m, and 1.05 m for PL 1, 2, and 3 traffic barriers respectively.

In Section 5-4.2, OHBDC-91-01, superstructure side barriers are defined. Within that section it is

mentioned that traffic barriers should conform to the relevant Performance Levels PL-1, PL-2, or

PL-3 in accordance with the crash testing procedures of the AASHTO Guide Specifications for

Bridge Railings, 1989.

The Performance Level selection, defined in Section 5-4.3, OHBDC-91-01, is based on the

barrier exposure index, BI. And the barrier exposure index is based on the first year annual daily

traffic (ADTi) and corrected by factors concerning the highway type, curvature, grade, and theheight of superstructure. With a calculated barrier exposure index the Performance Level can be

determined together with the design speed, percentage of trucks using the highway, and the

barrier clearance (see Tables 5-4.3.2.2(a) to (c), OHBDC-91-01).

The barrier appraisal due to traffic barrier acceptance and selection are defined in Section

5-4.4.2, OHBDC-91-01. Traffic and combination barriers which conform the geometry and

strength of the prototypes that have been tested and appraised in accordance with AASHTO Guide

Specification for Bridge Railings, 1989, are accepted directly. Barrier transitions should be crash

tested and approved in accordance with NCHRP Report 230:Recommended Procedures for theSafety Performance Evaluation of Highway Appurtenances, to be accepted. Barriers and barriertransitions, which do not meet the conditions as defined in the aforementioned paragraph, but

have similar geometry to that of a specific barrier that has been crash tested, may be used if three

conditions which are mentioned in Section 5-4.4.2.2 (a) to (c), OHBDC-91-01, are met.

Pedestrian and bicycle barriers have more detailed definitions about spacing between

barriers and openings of the barriers themselves in the sections 5-4.5.2, and 5-4.5.3, OHBDC-91-01, respectively. The design loads should be applied as shown in the following figure:

Figure 4 Application of pedestrian loads for pedestrian railings, from Figure 5-4.5.2.3, OHBDC-91-01


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Figure 5 Application of pedestrian loads for bicycle railings and combination barriers,

from Figure 5-4.5.2.3, OHBDC-91-01

4.1.4 Comments on changes between OHBDC-91-01 and CAN/CSA-S6-00

The OHBDC-91-01 was definitely the basis for the development of CAN/CSA-S6-00.There are only little changes in the contents as well as in the sequence.

The requirements on the geometry have almost no changes. The minimum heights of the

barriers are approximately the same in the OHBDC-91-01 and CAN/CSA-S6-00. But there aresome changes in the values which are used in the determination of the Performance Level. The

correcting factors, to calculate the Performance Level, are in average higher in OHBDC-91-01,

but the range is still the same. But besides that, the tables which result to the Performance Levelare based on higher values of the barrier exposure index (BI). And, in the end, it can be said that

the Performance Level results in both Codes, the OHBDC-91-01 and CAN/CSA-S6-00, in average

in the same Levels, although the values used for the determination are different.

Another point that is different in CAN/CSA-S6-00 is that it accepts alternative

Performance Levels whereas the OHBDC-91-01 only accepts the Performance Levels PL-1, PL-

2, and PL-3.

The design of the traffic barriers is based on some prototypes and there geometry inOHBDC-91-01. Crash testing can be waived for barriers that have a successful in-serviceperformance record which makes the design very fast. But nevertheless OHBDC-91-01 does not


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mention any requirements for the traffic barrier anchorages which are the basis in helping to

restrain errant vehicles from leaving the roadway.

The design of pedestrian and bicycle barriers, as well as combination barriers is very

similar in the OHBDC-91-01and the CAN/CSA-S6-00.

4.1.5 General comment on the changes of the CHBDC to the precursor

Finally, it can be said that Section 12 of CAN/CSA-S6-00 Canadian Highway Bridge

Design Code, Barriers and Highway Accessory Supports, is based on OHBDC-91-01 Ontario

Highway Bridge Design Code, third edition. The composition of the twelfths Section ofCAN/CSA-S6-00 is more or less the same than in the OHBDC-91-01. But Section 12 ofCAN/CSA-S6-00 carriers forward the crash testing requirements for barriers that appeared in

OHBDC-91-01. And crash testing may be waived for barriers that have a successful in-service

performance record. Section 12 ofCAN/CSA-S6-00 also propels forward the aspect of alternative

Performance Levels.

4.2 Other background literature regarding the CHBDC

Concerning the design of the barriers the CAN/CSA-S6-00 Canadian Highway Bridge

Design Code as well as the precursor refer several times to theAASHTO (American Association

of State Highway Transportation Officials) Guide Specifications for Bridge Railings.

In 1989AASHTO published Guide Specifications for Bridge Railings, which contains the

recommendations and procedures to evaluate bridge railings by full-scale vehicle crash testing. In

2004, the 3rd

Edition and therefore the newest AASHTO LRFD (Load and Resistant FactorDesign) Bridge Design Specifications was published and deals in section 13 with bridge railings.

This section describes three bridge-railing Performance Levels and associated crash tests and

performance requirements plus guidance for determining the appropriate railing Performance

Level for a given bridge site.

Concerning full-size crash tests the CHBDCas well as theAASHTO refers toReport 350:Recommended Procedures for the Safety Performance Evaluation of Highway Features. Thisreport was published by the NCHRP (National Cooperative Highway Research Program) in 1993.

It presents a uniform guideline for crash testing of both, permanent and temporarily highwaysafety features and recommended evaluation criteria to assess test results.

Due to the importance ofAASHTO LRFD Bridge Design Specifications and NCHRP

Report 350: Recommended Procedures for the Safety Performance Evaluation of Highway

Features even in Canada, the guides itself as well as their backgrounds are presented.


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4.2.1 AASHTO LRFD Bridge Design Specifications, Section 13, Railings,from 1997

In section 13 ofAASHTO LRFD Bridge Design Specifications railings which should be

provided along the edges of structures for protection of traffic and pedestrians are defined. The

guideline indicates the application of four types of rails including which are: (1) traffic railing,(2) pedestrian railing, (3) bicycle railing and (4) combination railing. A traffic railing is used

when a bridge is for the exclusive use of highway traffic whereas a combination barrier is used on

low-speed highways in conjunction with a raised curb and sidewalk and on high-speed highwayswhere the pedestrian or bicycle path should have both, an outboard pedestrian or bicycle railing,

respectively, and an inboard combination railing.

4.2.1.1 Traffic railings

In general, the primary purpose of traffic railings is to contain and redirect vehicles using

the structure and that means that they should be crashworthy, which means a system is

successfully crash-tested). When choosing traffic railings the following aspects should beconsidered:

Protection of the occupants of a vehicle in collision with the railing; Protection of other vehicles near the collision; Protection of persons and property on roadways and other areas underneath the structure; Possible future rail upgrading; Railing cost-effectiveness; and Appearance and freedom of view from passing vehicles.

An approach guardrail system, including a transition from the guardrail system to the rigid bridge

railing system, should be provided at the beginning and end of all bridge railings in high speedrural areas.

Depending on the chosen performance level the corresponding testing criteria as theweight of the vehicles, speed, and angle of impact are defined and can be found in the following

table:


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Table 2 Bridge railing Performance Levels and crash test criteria from Table 13.7.2.1,

AASHTO LRFD Bridge Design Specifications, 1997

Concerning the design, a crashworthy railing system, which is a system that is crashtested and afterwards accepted, may be used without further analysis provided that the proposed

installation features are the same. New railing systems may be used, provided that acceptable

performance is demonstrated through full-scale crash tests which can be tested with the NCHRPReport 350: Recommended Procedures for the Safety Performance Evaluation of HighwayFeatures) or that crash test specimens for a railing system is designed to resist the applied loads

in accordance with Appendix A of AASHTO LRFD Bridge Design Specifications (see chapter4.2.3 Appendix A of AASHTO LRFD Bridge Design Specifications). The minimum edge

thickness for concrete deck overhangs should be 8 inches for concrete deck overhangs, either

supporting a deck-mounted post system or supporting concrete parapets or barriers, and 12 inches

for a side-mounted post system.

The height of concrete railings should be at least 32 inches for PL-2 and 42 inches for

PL-3. For future overlay considerations the bottom 3-inches lip of the safety shape should not be

increased. The minimum height for a concrete parapet with a vertical face is 27 inches whichapplies also to combined concrete and metal railings. The geometry of the railing should provide

a smooth and continuous face of rail on the traffic side.

4.2.1.2 Pedestrian railings

The pedestrian railing should be at least 42 inches high measured from the top of the

walkway. And the clear opening applied to the lower 27 inches should be less than 6 inchesbetween rail elements and above the 27 inches less than 15 inches between rail elements.

The design live loading for pedestrian railing should be w = 0.05 KLF, both transverselyand vertically, acting simultaneously on each longitudinal element. The application of the loads is

shown in the beneath picture.

Figure 6 Pedestrian railing loads, from Figure 13.8.2.1, AASHTO LRFD Bridge Design Specifications


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4.2.1.3 Bicycle railings

The bicycle railing should be at least 54 inches high, measured from the top of the riding

surface. The height of the upper and lower zones of bicycle railing should be at least 27 inches.

The design live loading for bicycle railing should be w = 0.05 KLF, both transversely andvertically, acting simultaneously on each longitudinal element for rail heights under 54 inches. If

the rail is higher than 54 inches, the designer has to determine the design loads himself. The

application of the loads is shown in the beneath picture.

Figure 7 Bicycle Railing Loads, from Figure 13.9.3.1, AASHTO LRFD Bridge Design Specifications

4.2.1.4 Combination railings

The requirements of either the pedestrian or the bicycle railings, whichever is applicable,

should be used for the design of the combination railing.

4.2.2 AASHTO LRFD Bridge Design Specifications, Section 13, Railings,2004: Important changes from the 2nd to the 3rd Edition

The important changes from the second to the third edition ofAASHTO LRFD BridgeDesign Specifications are mainly in the traffic railing chapter.


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The testing criteria are no more chosen due to a selected Performance Level, they are

chosen due to a selected Testing Level. It is the responsibility of the user agency to determinewhich of the test levels is the most appropriate for the bridge site. The Testing Levels are defined

as the following:

Testing Level 1 (TL-1) taken to be generally acceptable for work zones with low postedspeeds and very low volume, low speed local streets:

Testing Level 2 (TL-2) taken to be generally acceptable for work zones and most localand collector roads with favourable site conditions as well as where a small number ofheavy vehicles is expected and posted speeds are reduced;

Testing Level 3 (TL-3) taken to be generally acceptable for a wide range of high-speedarterial highways with very low mixtures of heavy vehicles and with favourable siteconditions

Testing Level 4 (TL-4) taken to be generally acceptable for the majority of applicationson high speed highways, freeways, expressways, and Interstate highways with a mixtureof trucks and heavy vehicles;

Testing Level 5 (TL-5) taken to be generally acceptable for the same applications as TL-4 and where large trucks make up a significant portion of the average daily traffic or when

unfavourable site conditions justify a higher level of rail resistance; and

Testing Level 6 (TL-6) taken to be generally acceptable for applications where tanker-type trucks or similar high center of gravity vehicles are anticipated, particularly along

with unfavourable site conditions.

The testing criteria such as vehicle weights, vehicle speeds, and angles of impact are given in the

following table for a chosen Testing Level:

Table 3 Bridge railing Testing Levels and crash test criteria, from Figure 13.7.2-1, AASHTO LRFD Bridge

Design Specifications 2004


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The height of concrete railings should be at least 27 inches for TL-3, 32 inches for

TL-4, 42 inches for TL-5, and 90 inches for TL-6. For future overlay considerations the bottom3-inches lip of the safety shape should not be increased. The minimum height for a concrete

parapet with a vertical face is 27 inches which applies also to combined concrete and metal

railings. The geometry of the railing should provide a smooth and continuous face of rail on the

traffic side.

4.2.3 Appendix A of AASHTO LRFD Bridge Design Specifications, 1997

In Appendix A the design of barriers and the specimens are explained in detail. The

geometry and anchorages are explained first in chapter A13.1. Then, in chapter A13.2 traffic

railing design forces and in chapter A13.3 design procedures for railing test specimens, dividedinto concrete railings, post-and-beam railings, combination concrete parapet and metal rail, and

wood barriers, are defined. The last chapter in the appendix, A13.4, deals with deck overhang

design.

4.2.3.1 Geometry and Anchorages

Traffic railings have a defined setback distance S which recognizes the tendency for

various shape posts to snag wheels. The implication of the various definitions of the setback

distance S is that all other things being equal the space between a rail and the face of arectangular post will be greater than the distance between a rail and the face of a circular post.

Figure 8 Geometrical definitions of two typical traffic railings, from Figure A13.1.1-1,

AASHTO LRFD Bridge Design Specifications

For post railings, the combination of ratio of rail contact width to height (A/H) and the post

setback distance S, should be within or above the shaded area of the following figure:


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Figure 9 Post setback criteria, from Figure A13.1.1-3, AASHTO LRFD Bridge Design Specifications

The reinforcing steel for concrete barriers should have a sufficient embedment length

which is defined in Section 5 in AASHTO LRFD Bridge Design Specifications to develop thenecessary yield strength.

4.2.3.2 Traffic Railing Design Forces

The railing design forces and geometric criteria that are used for developing test

specimens for a crash test program are defined in this chapter.

The effective height of the vehicle rollover force, He, should be taken as: et

WBH = G -

2F

Where:

G = Height of vehicle center of gravity above bridge deck (FT)

W = Weight of vehicle corresponding to the required Performance Level (KIP)

B = Out-to-out wheel spacing on an axle (FT)

Ft = Transverse force corresponding to the required Performance Level (KIP)


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Figure 10 Nomenclature for traffic railing equations, from Figure CA13.2.1,AASHTO LRFD Bridge Design Specifications, 1997

And the railings should be proportioned so that:

tR F , for which iR= R

eY H , for which

i i(R Y )Y=

R

Where:

Ri = Resistance of the rail (KIP)

Yi = Distance from bridge deck to the ith

rail (FT)

The transverse and longitudinal loads have to be applied in conjunction with vertical loads

as given in the figure below. All the forces should be applied to the longitudinal rail elements.

The distribution of longitudinal loads to posts should be consistent with the continuity of railelements and the transverse loads with the assumed failure mechanism of the railing system.


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Figure 11 Design forces for traffic railings, from Table A13.2-1,


To understand the application of the design loads better they are presented, for example, on a

metal bridge railing which can be seen in the beneath figure.

Figure 12 Railing design forces, from Figure A13.2-1,


4.2.3.3 Design Procedures for Railing Test Specimens

A design procedure for reinforced concrete and prestressed concrete railing or parapet testspecimens is the yield line analysis and strength design. The yield line analysis includes the

ultimate flexural capacity of the concrete component. Stirrups or ties should be able to resist the

shear and the diagonal forces if present. In the yield line analysis it is assumed that the yield line

failure occurs only in the parapet and does not extend to the deck. That means that the decks needa sufficient resistance to force the yield line failure pattern to remain within the parapet.


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The nominal railing resistance to transverse load, RW, can be determined using the yield

line approach as the following:

For impacts within a wall segment:2

c cW b w

c t

M L2R = 8M +8M H+

2L -L H

where the critical wall length is:

2

t t b wC

c

L L 8H(M +M H)L = +

2 2 M

For impacts at the end of wall or joint:2

c cW b w

c t

M L2R = M +M H+

2L -L H

where the critical wall length is:

2

t t b wC

c

L L M +M HL = + H2 2 M

Where:

Rw = Total transverse resistance of the railing (KIP)

Lt = Longitudinal length of distribution of impact force Ft (FT)

Mb = Additional flexural resistance of beam in addition to Mw, if any, at top of wall (KFT)

Mw = Flexural resistance of the wall (KFT/FT)

H = Height of the barrier (FT)

Mc = Flexural resistance of cantilevered wall (KFT/FT)

The yield line analysis is explained in the following figures. The first figure shows the

explanation of the lengths for a wall segment and for a near the end of wall segment. The secondfigure shows the where and in which direction the moments occur.

Figure 13 Yield Line Analysis of concrete parapet walls for impact within wall segment and near end of wall

segment, part 1 of Table A13.3.1-1/2, AASHTO LRFD Bridge Design Specifications


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Figure 14 Yield Line Analysis of concrete parapet walls for impact within wall segment,

part 2 of Table A13.3.1-1, AASHTO LRFD Bridge Design Specifications

For a combination concrete parapet with metal rail, the resistance of each part has to be

determined first, separately. The resistance of the concrete parapet should be determined as

explained in the paragraph before with the yield line analysis. The nominal resistance R of themetal railing is the result of possible yield failure modes for post-and-beam railings. The basis of

the failure modes are shown in the figures on the next page.

Figure 15 Possible failure modes for post-and-beam railings, from Table A13.3.2-1,



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The critical wall nominal resistance, R, for the metal railing should be the least value determined

by the following two equations for various numbers of railing spans N:

For failure modes involving an odd number of railing spans N:

p p

t

16M + (N-1)(N+1)P LR =2NL-L

For failure modes involving an even number of railing spans N:

2

p p

t

16M + N P LR =

2NL-L

Where:

R = Total ultimate resistance, i.e. nominal resistance, of the railing (KIP)

Mp = Inelastic or yield line resistance of all of the rails contributing to a plastic hinge (KFT)

N = Number of railing spans (-)

Pp = Ultimate transverse load resistance of a single post located Y above the deck (KIP)

L = Post spacing or single-span (FT)

Lt = Longitudinal length of distribution of impact force Ft (FT)

The flexural strength of the combination rail, R , should be determined over one span, RR,

and over two spans, R'R. The resistance of the post on the wall, PP, shall be determined includingthe resistance of the anchor bolts or post.

The resistance of the combination parapet with rail is the lesser resistance determined for

the two failure modes, impact at mid-span and impact at post, respectively. The failure modes are

shown in a figure after the equations on the next page.

Where the impact is at mid-span:

The combined resultant strength is: R WR = R + R

and the effective height is: R R W WR H + R H

Y =R

Where the impact is at a post:

The combined resultant strength is: P R WR = P + R' + R'


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and the effective height is: P R R R W WP H + R' H + R' H

Y =R

for which W W P R WW

R H - P HR' =

H

Where:

R = Flexural strength of the combination rail (KIP)

RR = Ultimate capacity of rail over one span (KIP)

RW = Ultimate capacity of wall (KIP)

Y = The effective height (FT)

HR = Height of wall (FT)

HW = Height of rail (FT)

PP = Resistance of the post on the wall (KIP)

R'R = Ultimate transverse resistance of rail over two spans (KIP)

R'W = Capacity of wall, reduced to resist post load (KIP)

Figure 16 Combination concrete wall and metal rail evaluation-impact at (1) mid-span of rail and (2) at a

post, from Table A13.3.3-1/ 2, AASHTO LRFD Bridge Design Specifications


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4.2.4 Appendix A of AASHTO LRFD Bridge Design Specifications, 2004:Important changes from the 2nd to the 3rd Edition

The important changes from the second to the third edition ofAASHTO LRFD Bridge

Design Specifications are only in the chapter Traffic Railing Design Forces. The table giving the

design forces for traffic railings changed due to the change from performance Levels to TestingLevels. The new table is the following:

Table 4 Design forces for traffic railings, from Table A13.2-1,


4.2.5 NCHRP Report 350: Recommended Procedures for the SafetyPerformance Evaluation of Highway Features

Report 350: Recommended Procedures for the Safety Performance Evaluation of

Highway Features was published by the National Cooperative Highway Research Program

(NCHRP) in 1993 and is an all-metric document. This report replaced NCHRPReport 230:Recommended Procedures for the Safety Performance Evaluation of Highway Appurtenances,

which was published in 1981.

In Report 350: Recommended Procedures for the Safety Performance Evaluation of

Highway Features recommended procedures for evaluating the safety performance of various

highway safety features are contained. The features covered by these procedures include (1)longitudinal barriers such as bridge rails, guardrails, median barriers, transitions, and terminals;

(2) crash cushions; (3) breakaway or yielding supports for signs and luminaries; (4) breakaway

utility poles; (5) truck-mounted attenuators; and (6) work zone traffic control devices.

The approach of the report was to normalize test conditions. And therefore the testparameters as the testing facility, the test article, and the test vehicle are defined. Report 350

includes six different Test Levels (TL-1 through TL-6) for various classes of roadside safetyfeatures, and a number of optional test levels to provide the basis for safety evaluations to support

more or less stringent performance criteria. Although this document does not include objective

criteria for relating a test level to a specific roadway type, the lower test levels generally areintended for use on roadways with lower service levels and certain types of work zones, whereas

the higher test levels are intended for use on higher-service-level roadways.


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For vehicle crash tests, specific impact conditions such as vehicle mass, speed, approach

angle, and point on safety feature to be hit are presented. The test matrices including standardtests as well as the standard test vehicle types are described. To evaluate the crash test

performance, three primary appraisal factors as structural adequacy, occupant risk, and after-

collision vehicle trajectory are presented. Depending on the safety feature's function, it should

contain, redirect, and permit controlled penetration of the impacting vehicle, or permit acontrolled stop in a predictable manner to satisfy structural adequacy requirements.

In addition the report reflects a critical review of methods and technologies for safety-

performance evaluation, such as surrogate test vehicles and computer simulations, andincorporates state-of-the-art methods in the procedures. In-service evaluation of extensively

modified roadside safety features are used with the purpose of appraising actual performance

during a broad range of collision, environmental, operational, and maintenance situations fortypical site and traffic conditions.

4.3 Other literature regarding bridge barriers and barrier testing

There exist many literatures dealing with bridge barriers and their testing. A summary of

the paper "Basics of Concrete Barriers" published by Charles F. McDevitt is given to get ageneral introduction to barriers and their shapes.

And to get a comparison to the Codes used in the Province of British Columbia to another

country, the state of Washington in the United States of America has been chosen. Washingtonstate is the neighbour state of British Columbia which means that they deal with the same climate

conditions. And in addition, many of the barriers and anchors used in British Columbia are

compared to the United States of America. Hence, the Washington State Bridge Design Manual

which is the bridge design code of the state Washington in the United States of America, ispresented and a comment on the Manual is given.

4.3.1 Basics of Concrete Barriers

The basic principles of concrete barriers are not generally known and easy to understandand therefore this chapter gives a short introduction explaining the reasons for the shape of a

barrier. Concrete barriers appear to be simple and uncomplicated, but in reality they aresophisticated safety devices. This chapter represents a summary of the paper "Basics of Concrete

Barriers" published by Charles F. McDevitt who is a structural engineer in the Federal Highway

Administration's Office of Safety Research and Development at the Turner-Fairbank HighwayResearch Center in McLean.

The most well-known barrier in the United States of America is the New Jersey Concrete

Safety Shape Barrier, also called NJ-shape or Jersey barrier. Since some problems occurred in the1970's, a parametric study with systematically varying the parameters of various configurations

that were labelled A through F was done. The result was that configuration F performed distinctly

better than the NJ-shape. The results of these computer simulations were confirmed by a series offull-scale crash tests and configuration F became known as the F-shape barrier. The slope of the


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F-shape and the NJ-shape barrier are the same, but the major difference is the distance from the

ground to the slope break point. This distance is 255 mm for the F-shape barrier which is 75 mmlower than the NJ-shape one. The lower slope break point significantly reduced the lifting of the

vehicle and greatly improved the performance of the concrete barrier.

The key design parameter for a safety shape profile is the distance from the ground to theslope break point because this determines how much the suspension will be compressed. For

example for the NJ-shape barrier, this distance is 330 mm (13 inches). The front bumper impactsthe upper sloped face and slides upwards. This interaction initiates lifting of the vehicle. When a

concrete safety shape lifts a vehicle, some of the kinetic energy of the vehicle is converted topotential energy. This potential energy is turned back into kinetic energy as the vehicle returns to

the ground. If the bumper is relatively weak, the front end starts to crush before any uplift occurs.

Then, as the vehicle becomes more nearly parallel with the barrier, the wheel contacts the lowerslope face. Most of the additional lift of the vehicle is caused by the lower sloped face

compressing the front suspension. However, wheel side-scrubbing forces provide some additional

lift, particularly if the barrier face is rough. Therefore, exposed aggregate and other rough surface

finishes should be avoided. Drainage openings in the face of the reveal do not have a significanteffect on an impacting vehicle.

Vertical concrete parapets do not have the energy management feature as described in theparagraph before. But crash tests have demonstrated that they can perform acceptable as traffic

barriers. All of the energy absorption in an impact with a rigid vertical parapet is due to crushing

of the vehicle. Bumpers usually do not slide up vertical concrete parapets and lift the vehicle, soall four wheels tend to stay on the ground. This minimizes the potential for vehicle rollover.

Finally, it can be said that each of these barrier types fills a niche and helps meet the needsof highway agencies that select, design, and locate traffic barriers. In terms of safety

performance, the 1070 mm (42 inches) high F-shape is currently the best technology in the

United States of America. The F-shape profile is clearly superior to the NJ-shape and is gradually

being used by more jurisdictions for both portable concrete barriers and permanent barriers.

4.3.2 Review of the Washington State Bridge Design Manual

The Washington State Bridge Design Manual (WSBDM) M 23-50 was published by the

Was

Precast Concrete Barriers

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