14 Concrete Box Culverts Structures

14-1

COLORADO DEPARTMENT OF TRANSPORTATION

STAFF BRIDGE

BRIDGE RATING MANUAL

Section: 14

Effective: April 1, 2011

Supersedes: New

SECTION 14 – CONCRETE BOX CULVERTS

14-1 INTRODUCTION TO RATING CONCRETE BOX CULVERTS

This section covers the rating of cast-in-place (CIP) concrete and pre-

cast box culverts. This section does not cover flexible culverts or

corrugated metal pipes. All concrete box culverts are to be rated using

the policies and guidelines of the Bridge Rating Manual, Section 1 and

Subsections 14-2 and 14-3.

The rating of flexible culverts will be discussed in subsequent sections

and is not presented here.

When there are no plans available for the concrete box culverts being

rated, the requirements in Subsection 8-4 will be used.

The types of rigid culverts covered by this section are:

CBC - Concrete Box Culvert

PCBC - Concrete Box Culvert, Pre-Cast

The types of culverts not covered by this section are:

AAC - Aluminum Arch Culvert

CAC - Concrete Arch Culvert

RCPC - Reinforced Concrete Pipe Culvert

RAC - Rubber Arch Culvert

SAC - Steel Arch Culvert

TBC - Timber Box Culvert

TTC - Timber Culvert

14-2

April 1, 2011 Section 14 of 35

14-2 POLICIES AND GUIDELINES FOR RATING CONCRETE BOX CULVERTS

I. General

A. After October 1, 2010 Load and Resistance Factor Rating Method

(LRFR) shall be used for all re-rating and new ratings of

culverts designed with Load and Resistance Factor Design (LRFD).

Load Factor Rating Method (LFR) shall be used for rating culverts

that were designed with Load Factor Design (LFD) or Allowable

Stress Design (ASD).

B. All major concrete box culverts (i.e. length of 20’ or greater

between inside faces of outside walls) shall be rated by the

BRASS-CULVERT program or one acceptable to the CDOT Bridge

Branch. Programs other than BRASS-CULVERT must be approved in

advance by the Staff Bridge Rating Engineer.

C. Inventory and operating rating levels shall be performed for the

HS20-44 and Alternate Military Vehicle loading when LFR method is

used and the HL93 loading when LRFR method is used. Also, an

operating rating shall be performed for the Colorado Permit

Vehicle.

Note: For LFR live load distribution factors refer to “The

AASHTO Standard Specifications”, “The AASHTO Manual for

Bridge Evaluation”, and the “Brass-Culvert User’s Manual”.

For LRFR live load distribution factors refer to “The

AASHTO LRFD Specifications”, “The AASHTO Manual for Bridge

Evaluation”, and “The Brass-Culvert User’s Manual”.

D. When the depth of the fill exceeds 8.0 feet and exceeds the clear

span for a single-cell culvert or exceeds the distance between

interior faces of the outer walls for a multiple-cell culvert,

live load analysis is not required. When the fill height is

greater than 5.0 feet and less than 8.0 feet and the CBC shows no

signs of distress, CDOT will generally consider the structure to

have negligible live load and no live load analysis will be

required. A rating summary sheet is required for culverts meeting

these criteria. Both the inventory and operating rating shall be

coded as 99.9. The permit vehicle rating shall be left blank and

the color code shall be coded as white. The controlling depth of

fill shall be recorded on the Rating Summary Sheet with the

notation “live load is negligible”.

II. Calculations

A. A set of calculations, separate from computer output, shall be

submitted with each rating package. These calculations shall

include derivations for dead loads and any other calculations or

assumptions used for rating.

14-3


B. Dead Loads

1. The final sum of all the individual weight components for

dead load calculations may be rounded up to the next 5

pounds.

2. Dead loads include fill, curbs, sidewalks, railing, etc.

C. Use the minimum design yield strength value Fy and the minimum

compressive strength of concrete F'c from plans.

14-3 RATING REPORTING AND PACKAGING REQUIREMENTS

I. Rating Reporting/Package Requirements

A. A copy of the Brass-Culvert schematic drawing or sketch showing

the elevation and applied loads shall be included with the rating

package.

B. The rater and checker shall complete the rating documentation

(i.e. the rating QA checklist) as described in Section 1 of the

Bridge Rating Manual. Any variation from the original design

assumptions shall be added to the Rating Summary Sheet as

applicable. The rating package requirements shall be per Section

1-13 of the Bridge Rating Manual and as amended herein.

II. Consultant Requirements

A. Consultant designed projects – Before finalizing the rating

package and when BRASS-CULVERT is used as the analysis tool, the

Rater shall verify with the Staff Bridge that the version number

of the program being used is identical to CDOT’S version number.

Data files created using a lower version of the program shall be

rejected.

B. When the rating is finalized, the rater shall save the input and

output files in “*.cus” and “*.out” format respectively. The file

name shall include the structure number of the rated CBC (i.e.,

O-14-BY.cus and O-14-BY.out). The rating package including input

and output files, Rating Summary Sheet and necessary computations

in pdf shall be transmitted electronically to Staff Bridge for

archiving.

14-4 CONCRETE BOX CULVERT RATING EXAMPLES

Two examples are presented in this section. First, Structure X-01-X is a

3-cell culvert with 3 feet of fill. The structure has a 3 inch asphalt

roadway. Loading includes a 1000 lbs. point load at the mid-span of each

of the three cells and a 25 plf load across the structure to account for

the rail dead load. The second structure, X-02-X, is a single-cell

culvert with a skew of 10 degrees. The culvert has 6 feet of fill. It

also carries a 4 inch asphalt roadway and a 23 plf rail load. Each of the

two examples are rated using a HS20-44 truck and lane live load, Colorado

Permit Vehicle and an Alternate Military Vehicle.

14-4


To perform a rating, input the following tabs. When this is completed,

select the Execution button on the toolbar. The output file is viewed by

selecting the output button on the toolbar. A graphical output is also

available for review.

From the main toolbar, click on File and open an existing file or click

on new and enter the following general information. The rater can also

use the button toolbar as shown below or click on the tabs directly. The

button toolbar includes the following buttons: Job Description, Analysis

Control, Design Control, Output Control, Material Properties, Box

Geometry, Skew, Haunches, Concrete Cover, Reinforcing Review, Dead Loads

and Live Loads.

BRASS-CULVERT Program Input Tab, Job Description, Example 1 – Structure No. X-01-X

Enter the title, structure ID, agency, units and a brief description of

the structure.

14-5


BRASS-CULVERT Program Input Tab, Analysis Control, Example 1 – Structure No. X-01-X

Using the same techniques, enter the following Analysis Controls

including structure type, floor system continuity, design method, load

factors and design controls.

Note: If rebar is exposed and corrosion is incorporated in the rating, in

the Reinforcing Input Method, select the Diameter option and enter the

reduced values in the Reinforcing Review tab.

BRASS-CULVERT Program Input Tab, Design Control, Example 1 – Structure No. X-01-X

Skip This Input Tab. Not applicable, Tab is for Design Review.

14-6


BRASS-CULVERT Program Input Tab, Output Control, Example 1 – Structure No. X-01-X

Select the output options desired.

14-7


BRASS-CULVERT Program Input Tab, Material Properties, Example 1 – Structure No. X-01-X

When plans are available, use the minimum concrete strength and yield

strength values given in the plans. If plan values are not known, values

given in Section 1 of the Bridge Rating Manual for the applicable year of

construction may be followed.

14-8


BRASS-CULVERT Program Input Tab, Box Geometry, Example 1 – Structure No. X-01-X

Enter in the culvert geometry and dimensions as indicated below.

14-9


BRASS-CULVERT Program Input Tab, Skew, Example 1 – Structure No. X-01-X

Enter the culvert skew angle if applicable. The skew angle is measured

relative to a line perpendicular to the centerline of the roadway.

14-10


BRASS-CULVERT Program Input Tab, Haunches, Example 1 – Structure No. X-01-X

To add haunches put in the appropriate dimensions and check the

Haunch(es) Exist box. Make sure to check the Consider haunches in

analysis in the Analysis Control tab.

14-11


BRASS-CULVERT Program Input Tab, Concrete Cover, Example 1 – Structure No. X-01-X

Enter in concrete cover as specified in the plans.

14-12


BRASS-CULVERT Program Input Tab, Reinforcing Review, Example 1 – Structure No. X-01-X

Enter the appropriate bar sizes and spacing. If the condition of the

rebar indicates that full strength should not be used, the bar diameter

should be reduced where appropriate, See the Analysis Control tab.

14-13


BRASS-CULVERT Program Input Tab, Dead Loads, Example 1 – Structure No. X-01-X

Enter the dead load and Pressure parameters as indicated below.

14-14


BRASS-CULVERT Program Input Tab, Live Loads, Example 1 – Structure No. X-01-X

Enter in the appropriate live load vehicles. For this example and the

typical LFR rating, use the HS20-44 truck, lane live load, Alternate

Military Vehicle and the Colorado Permit Vehicle.

14-15


BRASS-CULVERT Program Schematic, Example 1 – Structure No. X-01-X

After completing all the input tabs, the schematic gives a graphical

representation of the culvert dimensions and loads.

Click the execute button in the toolbar.

14-16


BRASS-CULVERT Program Graphics, Example 1 – Structure No. X-01-X

After Brass-Culvert has been executed press the graphics button for

moment, shear and axial force diagrams.

14-17


SUMMARY OF RESULTS AND CALCULATIONS FOR CONCRETE BOX CULVERTS

The results of the LFD rating analysis are as follows.

PAGE 70

DATE 01/25/2010

BRASS-CULVERT Version 2.2.8

Example 1

** LOAD RATING SUMMARY **

*INVENTORY RATING*

LOAD NO. 1: AASHTO HS20-44 (MS 18) TRUCK (US)

TOTAL VEHICLE WT. : 36.000 (TONS)

CONTROLLING MEMBER : 2

CONTROLLING POINT : 1

RATING FACTOR : 2.011

LOAD RATING : 72.411 (TONS)

LOAD NO. 2: AASHTO HS20-44 (MS 18) LANE (US)






LOAD NO. 3: Colorado Permit Vehicle






LOAD NO. 4: AASHTO ALTERNATE MILITARY LOADING (US)






*OPERATING RATING*







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14-19


Fill out the Rating Summary Sheet using policies and guidelines in the

Bridge Rating Manual, Section 1.

14-20


BRASS-CULVERT Program Input Tab, Job Description, Example 2 – Structure No. X-02-X

Enter the title, structure ID, agency, units and a brief description of

the structure.

14-21


BRASS-CULVERT Program Input Tab, Analysis Control, Example 2 – Structure No. X-02-X

Using the same techniques, enter the following Analysis Controls

including structure type, floor system continuity, design method, load

factors and design controls.

Note: If rebar is exposed and corrosion is incorporated in the rating, in

the Reinforcing Input Method, select the Diameter option and enter the

reduced values in the Reinforcing Review tab.

BRASS-CULVERT Program Input Tab, Design Control, Example 2 – Structure No. X-02-X

Skip This Input Tab. Not applicable, Tab is for Design Review.

14-22


BRASS-CULVERT Program Input Tab, Output Control, Example 2 – Structure No. X-02-X

Select the output options desired.

14-23


BRASS-CULVERT Program Input Tab, Material Properties, Example 2 – Structure No. X-02-X

When plans are available, use the minimum concrete strength and yield

strength values given in the plans. If plan values are not known, values

given in Section 1 of the Bridge Rating Manual for the applicable year of

construction may be followed.

14-24


BRASS-CULVERT Program Input Tab, Box Geometry, Example 2 – Structure No. X-02-X

Enter in the culvert geometry and dimensions as indicated below

14-25


BRASS-CULVERT Program Input Tab, Skew, Example 2 – Structure No. X-02-X

Enter the culvert skew angle if applicable. The skew angle is measured

relative to a line perpendicular to the centerline of the roadway.

14-26


BRASS-CULVERT Program Input Tab, Haunches, Example 2 – Structure No. X-02-X

To add haunches put in the appropriate dimensions and check the

Haunch(es) Exist box. Make sure to check the Consider haunches in

analysis in the Analysis Control tab.

14-27


BRASS-CULVERT Program Input Tab, Concrete Cover, Example 2 – Structure No. X-02-X

Enter in concrete cover as specified in the plans.

14-28


BRASS-CULVERT Program Input Tab, Reinforcing Review, Example 2 – Structure No. X-02-X

Enter the appropriate bar sizes and spacing. If the condition of the

rebar indicates that full strength should not be used, the bar diameter

should be reduced where appropriate, See the Analysis Control tab.

14-29


BRASS-CULVERT Program Input Tab, Dead Loads, Example 2 – Structure No. X-02-X

Enter the dead load and Pressure parameters as indicated below.

14-30


BRASS-CULVERT Program Input Tab, Live Loads, Example 2 – Structure No. X-02-X

Enter in the appropriate live load vehicles. For this example and the

typical LFR rating, use the HS20-44 truck, lane live load, Alternate

Military Vehicle and the Colorado Permit Vehicle.

14-31



After completing all the input tabs, the schematic gives a graphical

representation of the culver dimensions and loads.

Click the execute button in the toolbar.

14-32



After Brass-Culvert has been executed press the graphics button for

moment, shear and axial force diagrams

14-33


SUMMARY OF RESULTS AND CALCULATIONS FOR CONCRETE BOX CULVERTS

The results of the LFD rating analysis are as follows.

PAGE 52

DATE 01/25/2010

BRASS-CULVERT Version 2.2.8

Example 2

** LOAD RATING SUMMARY **

*INVENTORY RATING*

























*OPERATING RATING*







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14-35


Fill out the Rating Summary Sheet using the policies and guidelines in

the Bridge Rating Manual, Section 1.

14 Concrete Box Culverts Structures

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