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ii

Mn/DOT B RIDGE OFFICE

LRFD Bridge Design Manual

Minnesota Department of Transportation3485 Hadley Avenue North Mail Stop 610

Oakdale, MN 55128-3307Phone: (651) 747-2100 Fax: (651) 747-2108

JULY 2003 OCTOBER 2003 JANUARY 2004 APRIL 2004 OCTOBER 2004DECEMBER 2004 FEBRUARY 2005 MARCH 2005 NOVEMBER 2005


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OCTOBER 2004 LRFD BRIDGE DESIGN i

TABLE OF CONTENTS

1. INTRODUCTION..................................................................................... 1-11.1 Overview Of Manual 5-392 ...............................................................1-1

1.1.1 Chronology Of Manual 5-392 ...................................................1-11.1.2 Material Contained In Manual 5-392 .........................................1-11.1.3 Updates To Manual 5-392 .......................................................1-21.1.4 Format Of Manual References .................................................. 1-2

1.2 General Bridge Information ..............................................................1-21.2.1 Bridge Office .........................................................................1-21.2.2 Highway Systems...................................................................1-81.2.3 Bridge Numbers.....................................................................1-81.2.4 Limit States To Consider In Design ......................................... 1-101.2.5 Ductility, Redundancy, Operational Importance ........................ 1-10

1.3 Procedures................................................................................... 1-101.3.1 Checking Of Mn/DOT Prepared Bridge Plans............................. 1-101.3.2 Checking Of Consultant Prepared Bridge Plans ......................... 1-121.3.3 Schedule For Processing Construction Lettings ......................... 1-151.3.4 Bridge Project Tracking System.............................................. 1-161.3.5 Approval Process For Standards ............................................. 1-18

2. GENERAL DESIGN AND LOCATION FEATURES........................................ 2-12.1 Geometrics ....................................................................................2-1

2.1.1 Bridge Geometrics..................................................................2-12.1.2 Bridge Deck Requirements ......................................................2-22.1.3 Bridge Undercrossing Geometrics .............................................2-72.1.4 Geometric Details ................................................................ 2-152.1.5 Bridge Railings .................................................................... 2-27

2.2 Bridge Aesthetics .......................................................................... 2-272.3 Preliminary Bridge Plans ................................................................ 2-27

2.3.1 General .............................................................................. 2-272.3.2 Bridge Type Selection ........................................................... 2-37


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OCTOBER 2004 LRFD BRIDGE DESIGN ii

2.4 Final Bridge Plans and Special Provisions.......................................... 2-422.4.1 Final Design Instructions ....................................................... 2-44

2.4.1.1 Superstructure ................................................................ 2-442.4.1.1.1 Framing Plan ..................................................... 2-442.4.1.1.2 Concrete Wearing Course .................................... 2-452.4.1.1.3 Diaphragms and Cross-frames ............................. 2-45

2.4.1.2 Pedestrian Bridges........................................................... 2-462.4.1.3 Temporary Bridges and Widenings ..................................... 2-482.4.1.4 Bridge Approaches........................................................... 2-492.4.1.5 Survey........................................................................... 2-502.4.1.6 Utilities .......................................................................... 2-502.4.1.7 Precedence of Construction Documents............................... 2-512.4.1.8 Design Calculation Requirements ....................................... 2-51

2.4.2 Final Plans .......................................................................... 2-522.4.2.1 Drafting Standards .......................................................... 2-532.4.2.2 Drafting Guidelines .......................................................... 2-532.4.2.3 General Plan and Elevation ............................................... 2-552.4.2.4 Bridge Layout and Staking Plan ......................................... 2-602.4.2.5 Standard Abbreviations .................................................... 2-632.4.2.6 Inclusion of Standard Bridge Details in Plan Sets.................. 2-632.4.2.7 Use of Bridge Standard Plans ............................................ 2-632.4.2.8 Standard Plan Notes ........................................................ 2-632.4.2.9 Quantity Notes and Pay Items ........................................... 2-64

2.4.3 Revised Sheets .................................................................... 2-652.5 Reconstruction Guidelines and Details .............................................. 2-66

2.5.1 Superstructure .................................................................... 2-662.5.1.1 Railings.......................................................................... 2-662.5.1.2 Wearing Course............................................................... 2-682.5.1.3 Expansion/Fixed Joints ..................................................... 2-68

2.5.2 Substructure ....................................................................... 2-802.5.2.1 Abutments...................................................................... 2-802.5.2.2 Piers.............................................................................. 2-80

2.5.3 Pavement ........................................................................... 2-80


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OCTOBER 2004 LRFD BRIDGE DESIGN iii

2.6 Construction Requirements............................................................. 2-86Appendix 2-A: Bridge Type Numbers ....................................................... 2-87

Appendix 2-B: Bridge Special Provisions................................................... 2-88

Appendix 2-C: Standard Abbreviations..................................................... 2-92

Appendix 2-D: Bridge Details Part I (B-Details) ......................................... 2-94

Appendix 2-E: Bridge Details Part II ........................................................ 2-96

Appendix 2-F: Bridge Standard Plans: Culverts ......................................... 2-98

Appendix 2-G: Bridge Standard Plans: Retaining Walls ............................... 2-99

Appendix 2-H: Standard Plan Notes....................................................... 2-100

Appendix 2-I: Standard Summary Of Quantities Notes ............................. 2-109

Appendix 2-J: Bridge Pay Items ............................................................ 2-111

Appendix 2-K: Conversion From Inches To Decimals Of A Foot .................. 2-115

3. LOADS AND LOAD FACTORS .................................................................. 3-13.1 Load Factors And Combinations ........................................................3-13.2 Load Modifiers ................................................................................ 3-33.3 Permanent Loads (Dead And Earth)...................................................3-33.4 Live Loads .....................................................................................3-4

3.4.1 HL-93 Live Load, LL................................................................3-43.4.2 Multiple Presence Factor, MPF .................................................. 3-43.4.3 Dynamic Load Allowance, IM ...................................................3-43.4.4 Pedestrian Live Load, PL .........................................................3-43.4.5 Braking Force, BR ..................................................................3-53.4.6 Centrifugal Force, CE .............................................................. 3-53.4.7 Live Load Application To Buried Structures ................................3-53.4.8 Live Load Surcharge, LS..........................................................3-5

3.5 Water Loads, WA ............................................................................3-53.6 Wind Loads, WS..............................................................................3-53.7 Wind on Live Load, WL ....................................................................3-63.8 Earthquake Effects, EQ ....................................................................3-63.9 Ice Load, IC ................................................................................... 3-63.10 Earth Pressure, EV, EH, Or ES...........................................................3-63.11 Temperature, Shrinkage, Creep, Settlement, TU, SH, CR And SE ...........3-7


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OCTOBER 2004 LRFD BRIDGE DESIGN vi

5.7.2 Prestressed I-Beam Design Example....................................... 5-715.7.3 Three-Span Haunched Post-Tensioned Concrete Slab

Design Example ................................................................. 5-101

6. STEEL STRUCTURES............................................................................... 6-16.1 Materials .......................................................................................6-16.2 General Dimensions And Details ........................................................6-36.3 General Design Philosophy ...............................................................6-7

6.3.1 Shear Connectors ..................................................................6-96.3.2 Fatigue................................................................................. 6-96.3.3 Deflections............................................................................6-96.3.4 Camber .............................................................................. 6-10

6.4 Rolled Beams ............................................................................... 6-136.5 Plate Girders ................................................................................ 6-13

6.5.1 High Performance Steel Girders.............................................. 6-146.6 Curved Girders ............................................................................. 6-146.7 Box Or Tub Girders ....................................................................... 6-156.8 Bolted Connections And Splices....................................................... 6-156.9 Two-Span Plate Girder Design Example............................................ 6-16

7. RESERVED

8. WOOD STRUCTURES.............................................................................. 8-18.1 Materials .......................................................................................8-1

8.1.1 Wood Products ......................................................................8-18.1.2 Fasteners And Hardware .........................................................8-28.1.3 Wood Preservatives ................................................................8-2

8.2 Timber Bridge Decks ....................................................................... 8-38.2.1 General ................................................................................ 8-38.2.2 Geometry .............................................................................8-58.2.3 Design/Analysis .....................................................................8-58.2.4 Detailing...............................................................................8-68.2.5 Camber/Deflections................................................................ 8-6


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DECEMBER 2004 LRFD BRIDGE DESIGN vii

8.3 Timber Pile Caps.............................................................................8-68.3.1 Geometry .............................................................................8-78.3.2 Design/Analysis .....................................................................8-78.3.3 Detailing...............................................................................8-78.3.4 Camber/Deflections................................................................8-7

8.4 Additional References ......................................................................8-78.5 Design Examples ............................................................................8-8

8.5.1 Longitudinally Laminated Timber Deck Design Example ............... 8-88.5.2 Design Example: Timber Pile Cap ........................................... 8-26

9. DECKS AND DECK SYSTEMS................................................................... 9-19.1 General .........................................................................................9-1

9.1.1 Deck Drainage.......................................................................9-29.2 Concrete Deck on Beams ................................................................. 9-2

9.2.1 Deck Design and Detailing.......................................................9-49.3 Reinforced Concrete Deck Design Example ....................................... 9-17

10. FOUNDATIONS .................................................................................... 10-110.1 Determination of Foundation Type and Capacity ................................ 10-1

10.1.1 Foundation Report................................................................ 10-110.1.2 Foundation Recommendations ............................................... 10-1

10.2 Piles............................................................................................ 10-310.3 Drilled Shafts ............................................................................... 10-510.4 Footings ...................................................................................... 10-8

10.4.1 General .............................................................................. 10-810.4.2 Footing Supported on Piling or Drilled Shafts............................ 10-910.4.3 Spread Footings................................................................. 10-10

10.5 Pile Bent Piers and Abutments ...................................................... 10-1110.6 Evaluation of Existing Pile Foundations when Exposed by Scour ......... 10-1110.7 Structure Excavation and Backfill .................................................. 10-13


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OCTOBER 2004 LRFD BRIDGE DESIGN viii

Appendix 10-A: Sample Bridge Construction Unit Recommendations

(Future Content) .......................................................... 10-14

11. ABUTMENTS, PIERS, AND WALLS ....................................................... 11-111.1 Abutments ................................................................................... 11-1

11.1.1 Integral or Contraction Abutments.......................................... 11-311.1.2 Parapet Abutments............................................................... 11-6

11.1.2.1 Low Abutments ............................................................... 11-911.1.2.2 High Abutments .............................................................. 11-9

11.1.3 Wingwalls ......................................................................... 11-1211.1.4 Approach Panels ................................................................ 11-20

11.2 Piers ......................................................................................... 11-2111.2.1 Geometrics ....................................................................... 11-2111.2.2 Columns ........................................................................... 11-2111.2.3 Cap.................................................................................. 11-2111.2.4 Crash Walls....................................................................... 11-2211.2.5 Design and Reinforcement................................................... 11-2311.2.6 Miscellaneous .................................................................... 11-24

11.2.6.1 Pile Bent ...................................................................... 11-2511.3 Retaining Walls........................................................................... 11-25

11.3.1 Cantilever Retaining Walls ................................................... 11-2511.3.2 Counterfort Retaining Walls ................................................. 11-2511.3.3 Anchored Walls.................................................................. 11-2611.3.4 Mechanically Stabilized Earth Walls....................................... 11-2611.3.5 Prefabricated Modular Walls................................................. 11-2811.3.6 Timber Noise Walls on Retaining Walls .................................. 11-2811.3.7 Cantilevered Sheet Pile Walls ............................................... 11-2811.3.8 Design Charts of Cantilevered Sheet Pile Soil Retention

Walls for Temporary Applications.......................................... 11-29

11.4 Design Examples ........................................................................ 11-3911.4.1 High Parapet Abutment Design Example................................ 11-3911.4.2 Retaining Wall Design Example ............................................ 11-7111.4.3 Three-Column Pier Design Example ...................................... 11-93


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OCTOBER 2004 LRFD BRIDGE DESIGN ix

12. BURIED STRUCTURES.......................................................................... 12-112.1 Geotechnical Properties ................................................................. 12-112.2 Box Culverts ................................................................................ 12-2

12.2.1 Precast ............................................................................... 12-212.2.2 Cast-In-Place ...................................................................... 12-4

12.3 Design Guidance........................................................................... 12-412.4 Arch Or 3-Sided Structure Design Data ............................................ 12-612.5 Design Criteria for Long-Span Corrugated Steel Structures ............... 12-1412.6 10' x 10' Precast Concrete Box Culvert Design Example.................... 12-18

13. RAILINGS ........................................................................................... 13-113.1 Materials ..................................................................................... 13-113.2 Design Requirements..................................................................... 13-1

13.2.1 Traffic Railing ..................................................................... 13-813.2.2 Pedestrian/Bicycle Railing...................................................... 13-913.2.3 Combination Railing ........................................................... 13-1013.2.4 Protective Screening........................................................... 13-1013.2.5 Architectural/Ornamental Railings ........................................ 13-11

13.3 Design Examples ........................................................................ 13-1213.3.1 F Rail Design Example ..................................................... 13-1213.3.2 Adhesive Anchor Design Example ......................................... 13-27

14. JOINTS AND BEARINGS ...................................................................... 14-114.1 Bridge Movements and Fixity .......................................................... 14-114.2 Expansion Joints .......................................................................... 14-2

14.2.1 Thermal Movements ............................................................. 14-214.2.2 Expansion Joint Opening ....................................................... 14-214.2.3 Expansion Joint Detailing ...................................................... 14-314.2.4 Modular Expansion Joints ...................................................... 14-3

14.3 Bearings ...................................................................................... 14-414.3.1 Loads and Movements .......................................................... 14-414.3.2 Bearing Details .................................................................... 14-414.3.3 Elastomeric Bearings ............................................................ 14-5


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JULY 2003 LRFD BRIDGE DESIGN 1-1

This section contains general information about the manual along with a

general description of the Bridge Office and its procedures. It also

includes guidance on use of the ductility, redundancy, and operational

importance factors given in LRFD 1.3.3 through 1.3.5.

Mn/DOT utilizes a decimal numbering system to classify documents. The

5 before the hyphen represents a publication related to engineering

functions. The 300 series of documents is assigned to the Bridge

Office; the 90 series indicates that this is a Manual. The last digit 2

specifies that the subject matter of the document is Design.

The original bridge design manual, numbered 5-392, provided guidance

for the design of highway structures in Minnesota in accordance with

allowable stress design methods. Subsequently, it has received periodic

updates as design methods have changed. This version of the Bridge

Design Manual contains significant changes. It presents Mn/DOTs design

practices in conformance with a new design methodology, Load and

Resistance Factor Design (LRFD), and also contains fifteen

comprehensive design examples.

Use of this manual does not relieve the design engineer of responsibility

for the design of a bridge or structural component. Although Bridge

Office policy is presented here for numerous situations, content of the

manual is not intended to be exhaustive. Therefore, use of this manual

must be tempered with sound engineering judgement.

After the introductory material provided in this section, the manual

contains material arranged around the following section headings. To

simplify locating material, section numbers correspond to those used in

the LRFD specifications:

1. Introduction

2. General Design and Location Features

3. Loads and Load Factors

4. Structural Analysis and Evaluation5. Concrete Structures

6. Steel Structures

7. Reserved

8. Wood Structures

9. Decks and Deck Systems

10. Foundations

11. Abutments, Piers, and Walls

12. Buried Structures

1 .

I N T RODUCT I O N

1 . 1 O v e r v ie w o f

M a n u a l 5 - 3 9 2

1 . 1 .1 Ch r o n o l o g y

o f M a n u a l 5 - 3 9 2

1 . 1 . 2 M a t e r i a l

Co n t a i n e d i n

M a n u a l 5 - 3 9 2


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13. Railings

14. Joints and Bearings

Memos

This manual will be updated multiple times each year as procedures are

updated and new information becomes available. Current files for each

section of the manual are available on the Bridge Office Web site

[http://www.dot.state.mn.us/bridge/].

Each section of the manual contains general information at the start of

the section. Design examples (if appropriate) are located at the end of

each section. The general content is divided into subsections that are

identified with numerical section labels in the left margin. Labels for

design example subsections are identified with alphanumeric labels in the

left hand margin. The left hand margin also contains references to LRFD

Design Specification Articles, Equations, and Tables. These references

are enclosed in square brackets.

Within the body of the text, references to other sections of this manual

are directly cited (e.g. Section 10.1). References to the LRFD

Specifications within the main body of the text contain a prefix of: LRFD.

A bridge is defined under Minnesota Rule 8810.8000 as a structure

having an opening measured horizontally along the center of the roadway

of ten feet or more between undercopings of abutments, between spring

line of arches, or between extreme ends of openings for multiple boxes.

Bridge also includes multiple pipes where the clear distance between

openings is less than half of the smaller contiguous opening.

In accordance with Minnesota Statute 15.06 Subd. 6, the Commissioner

of Transportation has delegated approval authority for State Preliminary

Bridge Plans, and State, County and City Final Bridge Plans to the State

Bridge Engineer. Plans for all bridge construction or reconstructionprojects located on the Trunk Highway System, and plans on County or

City highways funded fully or in part by state funds shall be approved by

the State Bridge Engineer.

The Bridge Office is responsible for conducting all bridge and structural

design activities and for providing direction, advice, and services for all

1 . 1 . 3 U p d a t e s t o

M a n u a l 5 - 3 9 2

1 . 2 G en e r a l B r i d g e

I n f o r m a t i on

1 . 2 . 1 B r i d g e O f f i ce

1 . 1 . 4 Fo rm a t o f

M a n u a l R e fe r e n c e s


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bridge construction and maintenance activities. The responsibilities

include:

Providing overall administrative and technical direction for the

office.

Reviewing and approving all preliminary and final bridge plans

prepared by the office and consultants.

Representing the Department in bridge design, construction and

maintenance matters with other agencies.

The office is under the direction of the State Bridge Engineer. It is

composed of sections and units as shown on the organizational chart

(Figure 1.2.1.1). Each of these subdivisions with their principal functions

is listed as follows:

A. Bridge Design Section

Responsible for the design, plans, and special provisions activities for

bridges, and miscellaneous transportation structures.

1. Design Unit

a. Designs and drafts bridge plans.

b. Reviews bridge plans prepared by consulting engineers.

c. Prepares special provisions for bridge plans.

d. Designs and drafts plans for miscellaneous highway structures.

e. Provides technical assistance, designs, and plans for special

bridge and structural problems.

2. Bridge Standards and Research Unit

a. Provides design aids and standards for the office and for

consultants, counties, and cities.

b. Coordinates the development and users of computer programs

with data processing systems.

c. Supports computer users throughout the office and manages

the local area network.

d. Provides oversight for research projects, which involve the

Office of Bridges and Structures.

3. Design/Build Unit

a. Provides oversight of design/build projects.4. LRFD Implementation

a. Maintains LRFD Bridge Design Manual.

b. Provides support to office and consulting engineers concerning

LRFD issues.

B. Bridge Planning Section

Responsible for program, cost estimates, preliminary bridge plan

activities for Trunk Highways and review of state aid bridges.


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1. Bridge Agreements and Estimates Unit

a. Selects and negotiates with consulting engineers and

administers engineering agreements for the preparation of

bridge plans.

b. Provides liaison between the office and the consulting engineer

retained to prepare bridge plans.

c. Coordinates public and private utility requirements for bridges.

d. Prepares preliminary, comparative and final cost estimates.

e. Maintains and provides current program and plan status

records.

2. Preliminary Plans

a. Conducts preliminary studies from layouts and develops

preliminary bridge plans.

b. Provides liaison with district and central office road design

through the design stage.

c. Obtains required permits from other agencies for bridges.

3. State Aid Bridge Unit

a. Reviews bridge plans and special provisions for county and

municipal state aid projects.

b. Provides technical assistance to counties and municipalities,

when requested, for nonparticipating projects.

C. Bridge Construction and Maintenance Section

Responsible for bridge construction and maintenance specifications,

and bridge construction and maintenance advisory service activities to

the office and to the job site.

1. Construction and Maintenance Unit; North, Metro and South

Regions

a. Provides construction and maintenance advisory service to

bridge construction and maintenance engineers in the field.

b. Writes bridge construction and maintenance specifications,

manuals and bulletins.

c. Writes and maintains the file of current special provisions for

bridge construction and maintenance.

d. Performs preliminary, periodic and final review of bridge

construction and maintenance projects and makesrecommendations.

e. Reviews bridge plans and special provisions prior to lettings

and makes recommendations.

f. Aids municipal and county engineers with bridge construction

and maintenance problems, upon request.

g. Provides foundation design including selection of pile type,

length, design load, and foundation preparation.


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h. Reviews bridge improvement projects and prepares

recommendations for scope of work.

2. Bridge Ratings Unit

a. Makes bridge ratings and load postings analysis for existing

bridges and maintains the records.

b. Reviews and approves special load permit requests.

3. Structural Metals Inspection Unit

a. Provides inspection services for structural metals, fabrication

and assembly to ensure conformity with plans and

specifications.

4. Fabrication Methods Unit

a. Reviews and approves structural metals shop drawings

submitted by fabricators.

b. Provides fabrication advisory service to designers, fabricators

and field construction and maintenance personnel.

c. Provides overhead sign design services to the Office of Traffic

Engineering, including the design of bridge-mounted sign

trusses.

5. Bridge Management Unit

a. Maintains inventory and inspection data for the 19,600 bridges

in Minnesota. Works with all agencies to make certain

appropriate data is collected.

b. Responsible for implementing bridge management systems to

provide information on bridges for maintenance, repair,

rehabilitation and replacement.

6. Bridge Inspection Unit

a. Provides expert assistance to the Districts in organizing and

conducting inspections of complex bridges, special features,

and fracture critical bridges.

b. Conducts quality assurance inspections of all agencies

responsible for bridge inspections in Minnesota.

c. Reviews, recommends and provides bridge inspection training

for District, county, and municipal bridge inspectors.

D. Hydraulic Engineering Section

Responsible for providing statewide hydraulic engineering servicesthat include design, construction and maintenance activities. In

addition, the section provides leadership in the development and

implementation of hydraulic automation technology, establishes policy

pertaining to hydrology and hydraulics, prepares design aids, provides

client training, participates in research projects, and represents the

department on state and national committees.

1. Bridge Design Hydraulics Unit


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a. Provides bridge and culvert waterway designs for trunk

highway, county, city and township projects.

b. Analyzes and evaluates inplace bridges for scour.

c. Provides technical assistance to counties and municipalities

upon request.

d. Provides training in hydrology and hydraulics.

2. Road Design Hydraulics Unit

a. Evaluates and codes all bridges over water for scour.

b. Provides technical assistance to Districts on all aspects of

drainage design.

c. Reviews and cost prorates storm drains on the municipal and

county state aid system.

d. Coordinates the review of new products and development of

specifications and policies pertaining to their use.

3. Hydraulics Automation Unit

a. Provides leadership and technical direction for managing the

statewide hydraulic automation effort.

b. Develops and implements the means to integrate the hydraulic

design process with the road design process.

c. Develops, implements, and supports a hydraulic information

system to facilitate the sharing of hydraulic data among all

users and stakeholders.

e. Provides statewide training and support in the implementation

and use of hydraulic automation techniques.


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2. Since about 1950, a five-digit number has been assigned to each

bridge as it was constructed. The first two digits coincide with the

county number (01-87) in which the bridge is located (99 refers to

temporary bridges). The last three digits are assigned consecutively

using the following guidelines:

a. 001-499 are used for regular trunk highway bridges.

b. 500-699 are used for county bridges.

c. 700-999 are used for interstate bridges (any bridge on or

over the interstate system).

3. In 1991, additional numbers were required for bridges on the state

aid system in Hennepin County and for interstate bridges in Hennepin

County. To allocate more numbers for bridges on the local system an

alpha character is used as the third character of the bridge number.

For example, the next bridge number after Bridge No. 27699 will be

Bridge No. 27A00. Note that this happens only after 500 and 600

series have been exhausted.

To allocate more numbers on the Interstate road system, the 400

series of numbers will be used along with the 700, 800, 900's

presently used. For a bridge number XXYZZ, the following now

applies:

XX = county number (99 = Temporary Bridge)

Y = 0, 1, 2, 3, or R, T, U (for Trunk Highway Bridges)

Y = 4, 7, 8, 9, or V, or W (for Interstate Bridges)

Y = X and Y (Trunk Highway or Interstate Culverts)

Y = 5 or 6 or A through H (for non-trunk highway Bridges)

Y = J through N, and P, Q (for non-trunk highway Culverts)

ZZ = Sequence number (00 through 99)

4. In cases of twin bridges, a westbound or southbound lane bridge is

generally assigned a lower number than an eastbound or northbound

lane bridge.

All bridge numbers are assigned by the Bridge Office (phone 651-747-2122). A complete listing of all numbered bridges is available in

computer printout form entitled Minnesota Trunk Highway Bridge Log-

Statewide Listing.


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Bridge designs shall typically consider Strength, Service, Extreme Event,

and Fatigue limit states. The limit state checks will vary with the

component under consideration. Not all elements will require

consideration of all limit states. For example, the fatigue limit state need

not be considered for fully prestressed pretensioned elements.

For most structures and structural elements the load modifiers for

ductility, redundancy, and operational importance shall be 1.00.

Exceptions are noted below:

1. The ductility factor shall be 1.05 for prestressed concrete through-

girder pedestrian bridges when they are over-reinforced.

2. The importance factor shall be 1.05 for a bridge which satisfies any

one of the following three criteria: 1) it is a major river crossing, 2)

its ADT is greater than or equal to 40,000, or 3) it is a new mainline

interstate bridge.

3. The importance factor shall be 0.95 for bridges with an ADT less than

500.

This section covers the Bridge Office procedures for checking of bridge

plans, scheduling of projects, and revising or creating standards.

The general practice of most engineering offices is to require that designs

they produce be checked before they are reviewed and certified by the

Engineer in Responsible Charge. Although this practice has always

been required for structures designed for Mn/DOT, it is recognized that

the quality of the checking process often varies according to time

restraints, confidence in the designer, and the instructions given to the

checker. Therefore, in order to maintain a consistent design checking

process the following guidance is given for routine bridge designs.

For more complex or unusual designs, the checker is advised to discuss

additional requirements with the design unit leader. Also, the checking

process described is not meant to apply to the check or review functionsrequired for Mn/DOT review of consultant plans (see Section 1.3.2.) or

for construction false work reviews. (See the Bridge Construction

Manual.)

Three types of design checking will apply:

a. An independent analysis of the completed design.

b. A check of original design computations for mathematical accuracy,

application of code, and accepted engineering practice, and

1 . 2 .5 D u c t i l i t y ,

R e d u n d a n c y ,

O p e r a t i o n a l

I m p o r t a n c e

[ 1 . 3 . 3 ]

[ 1 . 3 . 4 ]

[ 1 . 3 . 5 ]

1 . 3 P r o c e d u r e s

1 . 3 .1 Ch e c k i n g o f

M n / DO T Pr e p a r e d

B r i d g e P l a n s

1 . 2 . 4 L im i t S t a t e s

t o Co n s i d e r i n

De s i g n


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c. A review of drafted details for constructibility, and accepted

engineering practice.

Generally, an independent analysis to confirm the adequacy of the

complete design is preferred. Significant differences should be discussed

and resolved before the plan is certified. The separate set of calculations

should be included with the design file as a record of the completed

design check.

When circumstances prevent a complete independent analysis, as a

minimum, an independent analysis shall be completed for the following:

a. Live and dead loads

b. Critical beam lines

c. A pier cap

d. A pier footing

e. Main reinforcement for high abutments

f. An abutment footing

However, for the elements not independently analyzed, the original

computations should be checked for mathematical accuracy of original

design computations, applications of code, and accepted engineering

practice. Checked computations should be initialed by the checker, and

the independent analysis should be included in the design file.

When doing a separate analysis, the checker may make simplifying

assumptions to streamline the checking process. However, when major

differences are found, results must be discussed and resolved with the

designer. For instance, for normal piers, piling might be analyzed for

dead and live loads only if lateral loads appear to have been reasonably

applied in the original computations or the AISC Beam Diagram and

Formula Tables may be used to approximate pier cap moment and

shear.

Whether the check is a completely independent analysis or a minimal

analysis combined with a computations check, some details, such as the

reinforcing details in a wall corner, also require review by the checker.Often referencing old bridge plans with similar details allows the checker

to compare the current design to details that have performed well in the

past.


25/757


Consultant prepared bridge plans are created by private engineering

firms through contracts with the Department. The finished plans are

complete to the extent that they can be used for construction.

Since these plans receive final approval of the State Bridge Engineer,

there must be assurance that the plans are geometrically accurate and

buildable; structural design is adequate and design codes have been

correctly applied; proper direction is given to the construction contractor;

and all construction costs are accounted for. Plan errors may cause

costly construction delays or safety may be compromised by an

inadequate design.

To keep consultant plan reviews consistent and timely, a procedure was

developed as a guide that assigns priority to specific items in the plans.

The overall review includes a Thorough Check and Cursory Review of

various items. The distinction between Thorough Check and Cursory

Review is as follows:

Thorough Check refers to performing complete mathematical

computations in order to identify discrepancies in the plans, or

conducting careful comparisons of known data and standards of the

Project with values given in the plan.

Cursory Review refers to a comparative analysis for agreement with

standard practice and consistency with similar structures, all with

application of engineering judgment. Mathematical analysis is not

required, but may be deemed necessary to identify the extent of a

discrepancy.

The review procedure is listed on the CONSULTANT BRIDGE PLAN

REVIEW form following this section. Headings on this list are defined as

follows:

PARTIAL PLAN: In order to assure that the consultant is proceeding in

the right direction, an early submittal of the plan is required. This

submittal usually consists of the General Plan and Elevation sheetshowing the overall geometry of the structure and the proposed beam

type and spacing; the Bridge Layout Sheet; the Framing Plan sheet; and

the Bridge Survey sheets. Errors and inconsistencies found in this phase

can be corrected before the entire plan is completed. For example, a

framing plan, including the proposed beams, must be assured as

workable on the partial plan before the consultant gets deep into the

design of the remainder of the bridge.

1 . 3 . 2 Ch e c k i n g o f

C o n s u l t a n t

P r e p a r e d B r i d g e

P l a n s


26/757


FINAL PLAN: A final plan should be complete in all areas to the extent

that it can be certified by the designer, although a certification signature

is not required for this phase.

THOROUGH CHECK: Items indicated for checking on the consultants

partial plan must be correct. Given geometry must fit the roadway

layout. Most of this information can be checked using data from the

approved preliminary plan. Approval of the partial plan will indicate that

Mn/DOT is satisfied with the geometry and proposed structure, and the

consultant may proceed with further development of the plan. For the

final plan, obvious drafting and numerical errors should be marked to

point out the errors to the consultant, however, the reviewer should not

provide corrections to errors in the consultants numerical computations.

Checking on the final plan should be thorough to eliminate possible errors

that may occur, such as the pay items in the Schedule of Quantities.

Plan notes and pay items can be difficult for a consultant to anticipate

because of frequent changes by Mn/DOT. Pay items must be correct

because these are carried throughout the entire accounting system for

the Project. Plan (P) quantities must also be correctly indicated.

CURSORY REVIEW: Normally, a cursory review would not require

numerical calculations. This type of review can be conducted by reading

and observing the contents of the plan in order to assure the

completeness of the work. The reviewer should be observant to

recognize what looks right and what doesnt look right. Obvious errors or

inconsistencies on any parts of the plan should be marked for correction.

Although structural design is usually the major focus of any plan, most

consultants are well versed in design procedures and should need only

minimal assistance from our office. A comparison of the consultants

calculations with the plan details should be performed to assure that the

plans reflect their design and that the applicable codes are followed. An

independent design by our office is time consuming and is not

recommended unless there is a reasonable doubt as to the adequacy of

the consultants design.

NO REVIEW: A thorough review of these items would be time-consuming

and may not produce corrections that are vital to construction; therefore,

it is recommended that little or no time be spent on the listed items.

Numerous errors can occur in the Bills of Reinforcement and quantity

values. However, checking this information is also time-consuming,

hence the burden of providing correct data should be placed on the

consultant.


27/757


CONSULTANT BRIDGE PLAN REVIEW

Br. No. ________ RTE ____ DATE: PARTIAL PLAN REC'D. _____ DATE FINAL PLAN REC'D. ______

DESIGN GROUP _______________________ CONSULTANT ______________________________

No. OF SHEETS IN PLAN ______ DESCRIBE COMPLEXITY_________________________________EST. REVIEW TIME BY DESIGN GROUP ________(hrs.) ACTUAL REVIEW TIME __________(hrs)

PARTIAL PLAN FINAL PLAN

THOROUGH CHECK THOROUGH CHECK

Horizontal and vertical clearances Pay items and plan quantities

Stations and elevations on survey line Project numbers

Deck and seat elevations at working points Design data block & Rating on GP&E sheet

Deck cross-section dimensions Job number

Working line location and data Certification block

Coordinates at working points and key stations Standard plan notes

Substructure locations by station Concrete mix numbers

Framing Plan Construction joint locations

Conformance to preliminary plan Prestressed beam design if inadequate design is suspected

Design loads Bridge seat elevations at working points

Utilities on bridge

Existing major utilities near bridge

CURSORY REVIEWSteel beam splice locations and diaphragm spacing; flangeplate thickness increments (enough to save 800+ # ofsteel)Abutment and Pier design to be checked againstconsultants calculations

Conformance to foundation recommendations.Pile loads and earth pressures. Check against consultantscalculations.

CURSORY REVIEW Rebar series increments (min. 3)

Proposed precast beams [per 5-393.509(2)] Interior beam seat elevations

Precast conformance to industry standards Bottom-of-footing elevations (for adequate cover)

Proposed steel beam sections Railing lengths and metal post spacing (check for fit)

Use of B-details and standard plan sheets

Conformance to aesthetic requirements

Notes General, construction, reference, etc.

Quantity items on tabulations

Precast beam design (Check against consultantscalculations)

NO CHECK OR REVIEW REQUIRED

Diagonals on Layout sheet

Figures in Bills of Reinforcement

Bar shapes and dimensions

Rebar placement dimensions

Bar marks on details against listed bars

Quantity values (including total of tabulations)


28/757


To meet the Department s schedule requirements for construction

lettings, the following schedule for processing bridge plans, special

provisions and estimates must be followed. This schedule applies to all

projects: Federal Aid, State Funds and Maintenance. In general,

processing of bridge plans, special provisions and estimates for lettings

shall be given priority over all other work, and every effort must be made

to complete the processing in advance of the times shown, which are

deadlines.

SCHEDULE AND REMARKSDEADLINE TIME BEFORE

LETTING DATE

Federal Project State Project

Bridge plans complete to the extent thatprocessing can be completed on schedule.

14 Weeks(Friday)

12 Weeks(Friday)

Preliminary bridge pay items andquantities for estimate (to Estimating Unit

Design Services)

13 Weeks(Friday)

11 Weeks(Friday)

Bridge plan and special provisions review

Complete (by Bridge Construction Unit)13 Weeks

(Friday)11 Weeks

(Friday)

Bridge special provisions complete, otherInformation or material for inclusion in

Roadway Special Provisions complete (toSpecial Provisions & Final Processing Unit

Design Services)

12 Weeks

(Friday)10 Weeks

(Friday)

Bridge plans complete, approved and

dated (to Office Management Unit)12 Weeks

(Friday)10 Weeks

(Friday)

Final bridge pay items and quantities forestimate (to estimating Unit - Design

Services)

12 Weeks(Friday)

10 Weeks(Friday)

Final computer runs for bridge estimate during 9th week during 8th week

Office copy and final bridge plans (Bridgeplans to Special & Final Processing Unit -

Design Services for submittal to FHWA)

8 1/2 weeks

(Tuesday)7 weeks

(Friday)

Federal Project to FHWA 7 1/2 weeks(Tuesday)

7 weeks

(Friday)

Preliminary advertisement 6 1/2 weeks

(Tuesday)

6 weeks

(Friday)Final advertisement 5 1/2 weeks

(Tuesday)5 weeks(Friday)

Sale of plans and proposals 5 weeks (Friday) 5 weeks(Friday)

Last date for mailing letter addendums bySpecial Provisions & Final Processing Unit

Design Services

10 days(Wednesday)

10 days(Wednesday)

1 . 3 . 3 S ch e d u l e f o r

P r o c e s s i n g

C o n s t r u c t i o n

L e t t i n g s


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Completing a bridge design project for contract letting is a multiple step

process that involves input from a variety of work units and personnel.

To follow the process of these projects, the following major milestones

shown in Tables 1.3.4.1 and 1.3.4.2 are tracked in the Bridge Program

and Project Management System (PPMS). The project typically begins in

the Preliminary Plan Unit, continues through a Bridge Final Design Unit,

and is completed with the Engineer s Estimate. The progress and

activities completed on active bridge projects are updated monthly.

Table 1.3.4.1 PPMS Activities for Mn/DOT Prepared Bridge Plans

PPMS

ACTIVITY NO.

COMPLETED

ACTIVITY

% PROJECT

COMPLETED

0012

0020

00220023

0025

0030

0031

0035

0040

0045

0050

0076

0080

0085

0090

Program Estimate

Bridge Survey

Bridge HydraulicsBridge Grades (Packet)

Bridge Foundations

Bridge Construction Foundation Review

Bridge Aesthetics Recommendation

Bridge Preliminary Plan

District Letter & Prelim. Bridge Estimate

Bridge FHWA Approval

Final Bridge Plan

Designed:

Drawn:

Checked:

Bridge Plan Specifications

Bridge Plan Review by Bridge Construction

Bridge Plan Signed

Bridge Engineer s Estimate

0 %

5 %

6 %8 %

13 %

14 %

14 %

15 %

20 %

20 %

20 - 40 %

40 - 65 %

65 - 85 %

90 %

90 %

95 %

100 %

1 . 3 . 4 B r i d g e

P r o j e c t T r a c k i n g

S y s t em


30/757


Table 1.3.4.2 PPMS Activities for Consultant Prepared Bridge Plans

PPMSACTIVITY NO.

COMPLETEDACTIVITY

% PROJECTCOMPLETED

0012

0019

002000220023

0025

00300031

00350040

00450060

0062

00640066

00680070

00750076

0080

00850090

Program Estimate

Bridge Consultant Pre Design Start

Bridge SurveyBridge HydraulicsBridge Grades (Packet)

Bridge Foundations

Bridge Construction Foundation ReviewBridge Aesthetics Recommendation

Preliminary PlanDistrict Letter & Bridge Prelim. Estimate

Bridge FHWA ApprovalBridge Consultant Start

Consultant Partial Plan Delivery

Mn/DOT Review Partial PlanConsultant Final Plan Delivery

Mn/DOT Review Final PlanConsultant Final Plan In

Tracing BackcheckBridge Plan Specifications

Bridge Plan Review by Bridge Construction

Bridge Plan Signed

Engineer s Estimate

0 %

3 %

5 %6 %8 %

13 %

14 %14 %

15 %20 %

20 %20 %

25 %

30 %30 - 80 %

85 %88 %

88 %90 %

90 %

100 %100 %


31/757


1 . 3 . 5 A p p r o v a l

P r o c e s s f o r

S t a n d a r d s

NEED FOR NEW ORREVISED STANDARD

INPUT FROM S.S.R.C.INPUT FROM BRIDGEDESIGN ENGINEER

INPUT FROM

CONSULTANTS,INDUSTRY, ANDOTHER Mn/DOT

OFFICES

INPUT FROM BRIDGESTANDARDSENGINEER

INPUT FROM BRIDGEDESIGN UNITS

R. & D. COMMITTEEFOR POLICY AND APPROVAL

TO MAKE CHANGES TOSTANDARD OR DEVELOP

A NEW STANDARD

IDEA IS SCRAPPED NO

NE WSTANDARD

DEVELOPED BYSTANDARDS

UNIT, DESIGNUNIT OR

CONSULTANT

S.S.R.C., WITHSTANDARDSUNIT, MAKESCHANGES TOSTANDARD

STANDARDGOES TOR. & D.

COMMITTEE FORAPPROVAL

THE WORDM OD IFI ED A ND AREVISION DATE IS

ADDED TOSTANDARD.

STANDARD IS MADEAVAILABLE.

COMMENTS RESOLVED ANDCHANGES MADE .

STANDARD IS SENT TOSTATE BRIDGE ENGINEER

FOR APPROVAL. A COPY ISSENT TO THE STANDARDS

UNIT.

YELLOWROUTING

SHEET ISDEVELOPED BYBRIDGE

STANDARDSENGINEER

REVISED

STANDARDAFFECTS ONLYBRIDGEOFFICE

NO

YE S

MODIFY

ACCEPT

APPROVALDATE AND

SIGNATUREADDED TO

STANDARD.

TRANSMITTAL LETTERDEVELOPED BY

BRIDGE STANDARDSENGINEER AND

SIGNED BY STATEBRIDGE ENGINEER.

TRANSMITTAL LETTERAND STANDARD SENTTO PRINTER. COPIES

ENTERED INTOSTANDARDS UNIT

FILE.

ARCHIVE OLDSTANDARD

WITHBACKGROUNDOF CHANGES

MANUAL INSERTSRECEIVED BY USERS

FOR PLACEMENTINTO MANUALS.

STANDARD IS SENT OUT ONYELLOW TO OTHER OFFICES

WITHIN Mn/DOT AND TO BRIDGEOFFICE PERSONNEL. THE WORD

M OD IF IED A ND RE VI SIO N DA TEIS REMOVED BEFORE

DISTRIBUTION.

CHANGESREQUESTED BYBRIDGE OFFICE

AND OTHEROFFICES ARE

MADE .

MINOREDITORIALCHANGESMADE TO

STANDARD

NO

REVISIONDATE IS MORE

THAN ONEYEAR OLD

YE S

MODIFY

YE S


32/757

APRIL 2004 LRFD BRIDGE DESIGN 2-1

2 . GENERAL

DESI GN AND

LOCAT I ON

FEATURES

2 . 1 Ge om e t r i c s

2 . 1 . 1 B r i d g e

G eom e t r i c s

The design of a bridge typically takes place in two major phases of work:

preliminary design and final design. During preliminary design, the

structure type, the foundation type, the aesthetics, and the primary

geometry for the bridge are determined. During final design, specific

details for all of the elements of the bridge are developed and presented

in the plan set. These details include material descriptions, quantities,

and geometric information. Final plan sets are typically assembled in an

order that roughly follows the order of construction: from the ground up.

This section of the manual contains a large amount of information useful

for the preparation and assembly of plans for a project. To facilitate the

production of plans and standardize the content of bridge plan sets,

special provisions, B-Details, standard plans, standard plan notes, and

standard pay items have been prepared by the Bridge Office. Appendices

to Section 2 identify the material available.

As the name of the section implies, content for this section is general in

nature. Guidance for the design of specific structural elements (e.g.

decks, retaining walls, etc.) is provided elsewhere in the manual.

Definitions

For discussion of bridge geometrics in this section, roadways are

classified as Mainline Highways, Ramps, Local Roads, and Local Streets.

Each of these four groups is further classified under either Urban or Rural

Design.

The following definitions apply:

Mainline Highways Roadways that carry through traffic lanes for

freeways, expressways, and primary and secondary highways.

Local Roads Rural roads off the trunk highway system.

Local Streets Urban roads off the state trunk highway system.

Ramps Segments of roadway connecting two or more legs at an

interchange.

Urban Design Roadways with curbs on the right and/or left sides.

Rural Design Roadways without curbs. Median Width The distance between the edges of opposing through

traffic lanes.

Auxiliary Lane A lane adjoining a through traffic lane for a purpose

supplementary to through traffic movement such as truck climbing,

weaving, speed change or turning.


33/757


34/757


Functions of the shoulder include:

Recovery area to regain control of a vehicle.

Emergency parking area for stalled vehicles and escape route for

stranded motorists.

Passageway for bicycles and occasional pedestrians.

Passageway for emergency vehicles.

Parking area for bridge maintenance and inspection vehicle (snooper).

Temporary traffic lane during deck repairs or overlay construction.

Area for deck drainage and snow storage.

Accommodates passing of wide oversize loads, especially farm

machinery.

On two-lane highways, the shoulders provide an escape area to avoid

a head-on collision with an oncoming passing vehicle.

The following shoulder widths for both rural and urban design apply to

trunk highway bridges. In addition, these standards apply to bridges on

local roads at a trunk highway freeway interchange. For local roads and

streets, the bridge roadway widths are given in the State Aid Manual,

Section 5-892.210 and the State Aid Operations Rules, Chapter 8820.

Exceptionally long bridges or bridges with a high cost per square foot

should be evaluated on an individual basis and modifications to these

standards are allowed based on judgment. In addition to these values,

the bridge roadway width shall meet the additional requirements for sight

distance and sharp curvature as specified in Part 3 below.

1) Rural Designa) Two-Lane Rural Design

Shoulder widths are given in the table on Figure 2.1.4.1 and are

dependent on the functional classification of the roadway and

traffic volumes.

b) Four-Lane Rural Design

i) Right Shoulder 12'-0"

ii) Left Shoulder 6'-0"

c) Six- or Eight-Lane Rural Divided Highway


ii) Left Shoulder 12'-0"The full inside shoulder allows disabled vehicles in the left lane

to stop on the inside shoulder rather than try to cross two or

three lanes of traffic to get to the outside shoulder.

d) Mainline Rural Bridge with Auxiliary Lane


e) Mainline Rural Bridge with Entrance or Exit Ramps



35/757

MARCH 2005 LRFD BRIDGE DESIGN 2-4

f) Rural Bridges with Turn Lanes

i) Right Turn Lane

(1)Right shoulder 6'-0"

ii) Left Turn Lanes

(1)Adjacent to a barrier railing: 4'-0" minimum shoulder, 6'-0"

desirable.

g) Rural Ramp Bridges (one 16'-0" lane, one-way)


ii) Left Shoulder 4'-0"

On ramp bridges the dimension from edge of lane to gutter is

reduced to prevent the appearance of a two-lane bridge on a

one-lane ramp. The roadway width is 26'-0", which allows

traffic to pass a stalled vehicle. With a 16'-0" lane the outside

2'-0" could, in effect, be considered as part of the shoulder for

a 12'-0" lane.

2) Urban Design (Approach Curbs)

For urban designs the bridge gutter lines shall be aligned with the

curb line on the approaching roadway with the following exceptions:

a) On four-lane divided highways where there are no median curbs,

the left shoulder shall be 6'-0".

b) On six- and eight-lane divided highways where there are no

median curbs, the left shoulder shall be 10'-0" minimum.

c) On one-lane urban ramps (16'-0" approach roadway), both right

and left shoulders shall be 4'-0" (provides a 24'-0" roadway).

d) Where an auxiliary lane, ramp, or taper extends onto a mainlinebridge, the right shoulder shall be 6'-0".

e) The minimum distance to a barrier railing is 6'-0" desired, 4'-0"

minimum.

Urban shoulder widths will vary according to functional class, traffic

volumes, scope of work, and quality of pavement surface. Typical

values are shown in the Road Design Manual, Tables 4-4.01A,

4-4.01B, and 4-4.01C. Provide a 2'-0" reaction distance to a raised

island type median or sidewalk curb where vehicle speeds are 40 mph

and under. For design speeds 45 mph and higher, provide a 4'-0"reaction distance.

3) Bus Shoulders

Where the right shoulder has been designated as a bus shoulder a

12'-0" width shall be provided across bridges. See Road Design

Manual 4-4.03 and Table 4-4.03A.


36/757


4) Additional Width Criteria

a) Where a ramp (loop) bridge is on a radius of 190'-0" or less, or

when the volume of trucks is 10% or greater, the effective traffic

lane is increased from 16'-0" to 18'-0" in width to accommodate

truck turning movements. Increase the width of the ramp bridge

accordingly.

b) For curved bridges longer than 100 feet, check the horizontal

stopping sight distance and increase the inside shoulder width up

to a maximum of 10'-0". See Road Design Manual, Chapter 3 for

calculation of this distance. The 2001 edition of the AASHTO

book, A Policy on Geometric Design of Highways and Streets,

changed the height of object from 6" (muffler) to 2'-0" (tail light).

Table 2.1.2.1 gives widths required for a continuously curving

bridge for various design speeds and curvature, and applies only

where the line of sight is blocked by the railing.

Table 3.1.2.1

Shoulder Width Requirements for Curved Bridges

SHOULDER WIDTH FOR DEGREE OF

CURVATURE LISTEDDESIGN

SPEED6 FT. 8 FT. 10 FT.

70 mph to 0o 45 > 0o 45 to 1o > 1o

60 mph to 1o 15 > 1o 15 to 2o > 2o

50 mph to 2o 30 > 2o 30 to 3o 15 > 3o 15

40 mph to 5o 30 > 5o 30 to 7o > 7o

c) For bridges on tapers, the taper should begin or end at a pier or

an abutment, or continue across the entire length of the bridge.

Extra width to eliminate or simplify a taper or curvature is

permissible where justified by simplified design and construction.

Cross Slopes on Bridges

1) The cross slope on bridge traffic lanes is the same as the approaching

roadway lanes, normally 0.02 ft./ft. The shoulder cross slope on the

bridge may continue at 0.02 ft./ft. or, if better drainage is desired,

may be 0.005 ft./ft. greater than the adjacent lane, with a maximum

cross slope of 0.04 ft./ft. When the bridge deck is superelevated, the

shoulders shall have the same slopes as the adjacent bridge traffic

lanes.

Keep superelevation transitions off bridges. In instances where they

are unavoidable, it is preferable for ease of deck pouring to maintain


37/757


a straight line across the deck at all locations (allows a straight screed

between paving rails placed at both sides of the deck.)

2) Ramp cross slopes shall be uniform between the bridge curbs with a

slope of 0.02 ft./ft. to the right unless superelevated.

Bridge Median

On divided highways with a separate bridge for each roadway, the

openings between bridges must be a minimum of 8'-0" wide if access for

bridge inspection vehicles (snoopers) is required.

Longitudinal joints along the median of bridges should be used only for

bridge roadways wider than about 100 feet or for other special cases. By

eliminating this joint on bridges with medians, simpler detailing and

simpler construction can be used.

Bridge Sidewalks and Bikeways

Bridge sidewalks of 6'-0" minimum widths are to be provided where

justified by pedestrian traffic. When bicycle traffic is expected, the width

should be 8'-0" minimum and 10'-0" desirable. Where an off road

bikeway is to be carried across a bridge, the full width of the approach

bikeway may be continued across the bridge up to a maximum width of

12'-0". Widths beyond 12'-0" are considered excessive. When the

shoulders of the bikeway cannot be carried over bridges, provide lead-in

guardrail.

The curb height for sidewalks adjacent to the roadway is 8". When the

design speed on the street is over 40 mph, a concrete barrier is required

between the roadway and the sidewalk (or bikeway). In addition, a

pedestrian (or bikeway) railing is required on the outside.

When a barrier is provided between the traffic lanes and the sidewalk,

use the bridge slab for the walkway (i.e., do not require an additional

pour for sidewalk). Advise the road plans designer to provide for any

necessary sidewalk ramping off the bridge.

Sidewalks and bikeways shall have a minimum cross slope of 0.01 ft./ft.

Protective Rails at Bridge Approaches

The ends of bridge railings must be protected from being impacted

(except on low speed roads such as city streets). For design speeds over

40 mph, a crash tested guardrail transition (normally plate beam

guardrail) is required.


38/757


2 . 1 . 3 B r i d g e

U n d e r c r o s s i n g

G eom e t r i c s

Refer to State-Aid Operation Rules, Chapter 8820 for guardrail

requirements on local bridges.

General Criteria for Lateral Clearance

Bridge undercrossing geometrics must rationalize safety requirements

with costs and physical controls such as span length and permissible

depth of structure. The following guidelines apply in establishing these

geometrics:

1) Safety

Piers, abutments, side slopes and back slopes steeper than 1:3, and

guardrails can all be hazards to an out of control vehicle. It is

desirable at all bridge undercrossings to provide a clear zone recovery

area beside the roadway that is free from these hazards. This clear

zone is given in the Road Design Manual, Section 4-6.0 and is a

function of the roadway curvature, design speed, ADT, and ground

slope. For the area under bridges a practical maximum clear zone of

30 feet may be used as permitted in the 2002 AASHTO Roadside

Design Guide, Table 3.1 based on consistent use and satisfactory

performance. Eliminate side piers from the roadside area wherever

possible. The desirable bridge undercrossing will satisfy the above

safety criteria.

For those locations where it is totally impractical to provide a full clear

zone recovery area at an undercrossing (as at some railroadunderpasses and in certain urban situations), lesser side clearances

are permitted. Where the full recovery areas must be infringed upon,

the greatest side clearances that circumstances will permit shall be

used. A side clearance of 20 feet is not as desirable as 30 feet but is

still better than the absolute minimum clearance. Minimum lateral

clearances are specified under the section for Lateral Clearance for

Mainline Highways.

Where drainage must be carried along the roadway passing under a

bridge, either a culvert must be provided at the approach fill or theditch section must be carried through at the toe of the bridge

approach fill. The use of a culvert will often permit more desirable

bridge geometrics, but the culvert openings can also introduce a

roadside hazard. A determination regarding drainage (need for

culverts, size of a culvert, and assessment of possible hazard) will be

a controlling factor in deciding geometrics of the bridge for the site.


39/757


2) Economics

Prestressed concrete beam spans (in length up to about 145 feet) are

normally the most economical type of construction for grade

separations. In addition, there will usually be greater economy in

constructing grade separations using two long spans rather than

constructing four shorter spans, provided that a concrete

superstructure can be used.

3) Aesthetics

The use of longer spans will necessitate a deeper superstructure and

higher approach fills. Consideration must be given to the effect of the

depth of structure on the overall appearance and design of the

undercrossing.

For rough calculations during preliminary planning, the depth of

highway bridge superstructures can be assumed to be about 1/20 of

the length of the longest span. (Depth of superstructure refers to the

dimension from top of slab to bottom of beam.) Contact the

Preliminary Bridge Plans Engineer for the exact dimensions to be used

in final planning. Contact the Preliminary Bridge Plans Engineer for

depth of structure on railroad bridges.

Lateral Clearance for Mainline Highways

1) The desirable lateral clearance right and left from the edge of through

traffic lanes to any hazard (as described above) is the full clear zone.

30'-0" may be used as a practical maximum. Side piers shall beeliminated entirely wherever feasible.

2) The details for rural design provide for selection of geometrics that

carry the ditch section through the bridge (Alternate B), and also

geometrics that have a filled ditch (Alternate A). (See Figures 2.1.4.1

and 2.1.4.3.) Alternate A permits a shorter bridge superstructure and

thereby improves the economics and the chance of eliminating side

piers and is used almost exclusively. However, Alternate A can only

be used where ditch culverts will be deleted or used without

introducing a significant safety hazard.

3) Where the roadway ditch section (rural design) is modified at the

bridge (Alternate A), a longitudinal transition from the ditch section to

the 0.04 ft./ft. side slope under the bridge must be provided. Use a

maximum longitudinal slope of 1:20.

4) For an auxiliary lane, the clear zone must be maintained from both

the through traffic lane and the auxiliary lane.


40/757


5) For ramps and tapers adjacent to the mainline highway, the clear

zone must be maintained from both the through lane and the taper.

A reduced design speed, usually 50 mph, is assumed for the taper.

6) Minimum Lateral Clearances

The following paragraphs list those instances where less than

desirable geometrics can be considered and describes the minimum

values that will apply. Where geometrics less than desirable are to be

used, approval of the State Bridge Engineer and State Design

Engineer must be obtained. For plate beam guardrail with standard

6'-3" post spacing, a minimum of 3'-0" is required between the face

of the guardrail and the face of the pier or abutment to allow room for

the guardrail to deflect. (See Road Design Manual10-7.02.01.)

a) Through Traffic Lanes Right Side

For urban design, the lateral clearance on the right measured

from the edge of the through lane shall be not less than 10'-0"

width for an approaching shoulder plus the minimum width of

approaching berm. This will result in minimum dimension of

16'-0" from the edge of a lane to face of substructure unit.

For auxiliary lanes, tapers, and ramps along urban mainline

highways, the minimum lateral clearance from the edge of a lane

to face of pier or abutment on the right is 10'-0". This provides

room to construct the standard 6'-0" ramp shoulder plus providing

an additional 4'-0" of space for guardrail. However, in no eventshall the distance from the edge of a through lane to the face of a

pier be less than 16'-0".

For rural design, the lateral clearance on the right may be reduced

from the full clear zone distance at railroad overpasses. At these

locations the minimum clearance on the right shall be as described

above for urban designs.

b) Through Traffic Lanes Left Side of Divided Highways

i) Urban Highways with Continuous Median BarriersThe minimum clearances at continuous median barriers are

based on the use of a concrete barrier between the roadways.

(See Std. Plate 8322.)

For urban design, four-lane divided roadways, the minimum

clearance on the left will be based on providing an 8'-0" wide

shoulder from the edge of a through lane to median gutter line

away from the bridge. The 8'-0" wide shoulder may be


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infringed upon as necessary to carry the median barrier

around a bridge pier. At normal grade separations, using 3'-0"

thick piers, the 8'-0" shoulder may be reduced to 6'-2" at the

pier. (See Figure 2.1.4.11.)

For urban design, six- and eight-lane divided roadways, the

minimum clearance on the left is based on providing a

10'-0" minimum wide shoulder from the edge of a through

lane to median gutter line outside of the bridge. As described

above for four-lane divided roadways, this dimension may be

infringed upon as necessary to carry the median barrier

around a bridge pier. This may result in reducing the shoulder

width from 10'-0" to 8'-2" at normal grade separations

(assuming 3'-0" thick pier). (See Figure 2.1.4.11.)

ii) Urban Highways without Continuous Median Barriers

The warrant requiring a median barrier is based on the median

width and the ADT. (See Road Design Manual.) At those

locations where the clear distance to a center pier is less than

the clear zone distance from the edge of a lane, but where a

continuous barrier will not be provided, a plate beam barrier

will normally be required at the pier.

The pier with plate beam guardrail protection can be used only

in medians that are 18'-6" or wider for four-lane divided

highways, and 22'-6" or wider for six- and eight-lane dividedhighways. (Dimensions are from the edge of lane to edge of

lane.) Piers on high speed roadways should not be placed in

medians narrower than 18'-6" (four- lane) or 22'-6" (six- or

eight-lane).

The face of the plate beam will be located 2'-0" from the face

of the pier. At normal grade separations (with 3'-0" pier

thickness) this will result in a dimension of 5'-6" from the edge

of lane to face of the guardrail on four-lane divided roads, and

a dimension of 7'-6" from the edge of lane to face of theguardrail on six- and eight-lane divided roads.

iii) Rail Overpasses Using Rural Design

For rural design, the median width (edge of lane to edge of

lane) for roadways passing under railroads may be considered

for a reduction. Where a reduced width is used, the distance

from the edge of lane to face of pier should be not less than

20'-0".


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Lateral Clearances for Ramps

When rural or urban ramps pass under a bridge independently, piers

should be eliminated and the approaching typical section should be

carried through the bridge. On extremely skewed bridges where piers

are necessary, place the face of pier 2'-0" further from roadway than toe

of back slope. (See Figure 2.1.4.8.)

Lateral Clearances for Local Roads

Lateral clearances for local roads are dependent on ADT. The applicable

values are shown on Figure 2.1.4.9.

Lateral Clearance for Local Streets

Locate the face of piers or abutments on or beyond the property line.

This will provide for the ultimate development of the section by local

authorities. A minimum distance of 6'-0" from the face of a curb to the

face of pier or abutment must be provided.

Lateral Clearance for Railroads

Lateral clearances at railroads are to be determined as follows:

1) The statutory clearances diagram shown on Figure 2.1.4.10

represents the absolute minimums that must be adhered to. For

design, a minimum horizontal clearance of 9'-0" to a pier or abutment

is to be used (8'-6" legal).

2) Side piers are placed 4'-0" in from the back slope control point (18'-0"

clear to the centerline of track for a cut section without amaintenance road). This puts the face of pier 2'-0" outside the

bottom of a 3'-0" deep ditch with a 1:2 slope and allows the railroad

to periodically clean the ditch with track-mounted equipment.

3) Mn/DOT and FHWA have agreed to the horizontal clearances shown in

Figure 2.1.4.10 (25'-0" minimum clearance to pier, 30'-6" to back

slope control point) for mainline BNRR tracks at sites meeting the

following conditions:

a) When the standard will not increase the cost of the structure by

more than $50,000.b) When sufficient vertical clearance exists between the tracks and

inplace or proposed roadway profile to accommodate the structure

depth necessary for the longer spans typically required by the

standard.

If these conditions cannot be met, submit a letter to the Railroad

Administration Section along with the signed Preliminary Bridge Plan


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stating the reasons the standard cannot be met including an estimate

of the increased cost if applicable.

4) Back slopes shall be 1:2 and pass through the back slope control

point shown on Figure 2.1.4.10 for the applicable case. The

dimension to the back slope control point indicates the maximum

extent of federal participation in the construction and must not be

exceeded.

5) The Preliminary Bridge Plans Engineer will contact the Railroad

Administration Section of the Office of Railroads and Waterways to

determine the need for provisions for a maintenance road for track

maintenance equipment. If the Railroad Administration Section

determines that the need is justified, the dimension to the back slope

control point can be increased up to 8'-0".

Waterway Sections Under Bridge Crossing Streams

The Waterway Analysis (hydraulics report) gives information on the

required stream cross section under the bridge including waterway area

and low member elevation. Potential flood damage, both upstream and

downstream, and permitting agencies requirements must be considered.

Vertical Clearance for Underpasses

Table 2.1.3.1 lists the minimum vertical clearance requirements for trunk

highway underpasses.

Table 2.1.3.1

Vertical Clearance for Underpasses

TYPE OF STRUCTUREDESIGN VERTICAL

CLEARANCES

Trunk Highway Under Roadway Bridge 16'-4"

Trunk Highway Under Railroad Bridge 16'-4"

Railroad Under Trunk Highway Bridge 23'-0" *

Trunk Highway Under Pedestrian Bridge 17'-4"

Trunk Highway Under Sign Bridge 17'-4"

Portal Clearances on Truss or Arch 20'-0"

* Critical vertical clearance point offset 8'-6" from centerline of track, statutoryminimum vertical clearance is 22'-0".

For trunk highway bridges over local streets and roads, the minimum

vertical clearance is 16'-4" for rural-suburban designs and 14'-6" for


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Vertical Clearance over Waterways

1) Non-Navigable Waterways

A 3'-0" minimum clearance between the 50-year flood stage and low

point on the bridge superstructure is recommended. This amount of

clearance is desired to provide for larger floods and also for the

passage of ice and/or debris. If this amount of clearance is not

attainable due to constraints relating to structure depth, roadway

grades or other factors, reduced clearance may be allowed. The

Preliminary Bridge Plans Engineer, after consultation with the

Hydraulics Section and the Mn/DOT District Office, will determine the

required clearance.

2) Navigable Waterways

a) Waterways that require a construction permit from Coast Guard

(generally considered to be waterways for commercial shipping):

The Mississippi River downstream from I-694 in Fridley

The Minnesota River downstream from Chaska

The St. Croix River downstream from Taylors Falls

The St. Louis River downstream from Oliver, Wisconsin.

Guide vertical clearances published by the Coast Guard are:

Mississippi River:

52'-0" above 2% flowline or 60'-0" above normal pool,

whichever is greater, for the portion downstream of the

Burlington Northern Railroad Bridge near the University of

Minnesota (mile point 853.0). 4'-0" above river stage of 40,000 c.f.s. for the river portion

upstream (mile point 853.0 to 857.6).

Minnesota River:

55'-0" above normal pool from mouth to I-35W bridge

(mile point 10.8).

30.8 feet above 1881 high water from I-35W bridge to

Chaska.

St. Croix River:

52'-0" above 2% flowline or 60'-0" above normal pool from

mouth to Stillwater. St. Louis River:

The Bong Bridge over the St. Louis River Bay in Duluth has

a vertical clearance of 120'-0".

The Preliminary Bridge Plans Engineer shall be consulted when

establishing navigation clearances.


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F ig u r e 2 . 1 . 4 .1

G eom e t r i c s

2 - L a n e H ig h w a y ( R u r a l )


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F ig u r e 2 . 1 . 4 .5

D e s ir a b l e G eom e t r i c s

6 - L a n e D iv i d e d H i g h w a y ( R u r a l)


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F ig u r e 2 . 1 . 4 .6


6 - L a n e D iv i d e d H ig h w a y ( U r b a n )

(Details for 8-Lane Divided Highway Are Similar)


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F ig u r e 2 . 1 . 4 .7


6 " R a is e d I s l a n d , Tu r n L a n e s , a n d S id e w a l k s ( U r b a n )


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F ig u r e 2 . 1 . 4 .8


R am p s ( R u r a l a n d U r b a n )


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F ig u r e 2 . 1 . 4 .9

L o c a l R o a d s

( R u r a l )


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F ig u r e 2 . 1 . 4 . 1 0

Ra i lr o a d Cl e a r a n c e s


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2 . 1 . 5 B r i d g e

Ra i l i n g s

2 . 2 B r i d g e

A e s t h e t i c s

2 . 3 P r e l i m i n a r y

B r i d g e P l a n s

2 . 3 . 1 Ge n e r a l

See Section 13 of this manual for the policy on design of bridge railings

for Mn/DOT projects.

The aesthetic design process is initiated early in a bridge projects life.

The Preliminary Bridge Plans Engineer will determine which of three

levels of aesthetic attention is appropriate for the bridge.

Level A is intended for bridges with major cultural or aesthetic

significance.

Level B is used for mid-level structures, including highway corridors.

Level C is used for routine bridges.

Maximum levels of Mn/DOT participation in aesthetic costs are given in

the Mn/DOT Policy Manual, Chapter 6, 6-41. For Level A the maximum is

15% but not to exceed $3 million per bridge; for Level B the maximum is

7% but not to exceed $300,000 per bridge; for Level C the maximum is

5% but not to exceed $200,000 per bridge.

The Preliminary Bridge Plans Engineer along with the District Project

Manager coordinates the implementation of the aesthetic design process

as it relates to bridges. Other people, offices