751.1 Preliminary Design

Forms

751.1.1 Overview

751.1.1.1 Introduction

The Preliminary Design of a structure begins with the district submitting a Bridge Survey indicating their need for a structure, and ends with the completion of the Substructure Layout or TS&L submittal (type, size and location). This article is intended to be a guide for those individuals assigned the task of performing the Preliminary Design or “laying out” of a structure.

The types of structures can be broken into five categories:

1.) Bridge over Water

2.) Bridge over Roadway or Railroad

3.) Box Culvert over Water

4.) Retaining Wall (CIP walls taller than 5 ft., MSE walls adjacent to bridge end bents)

5.) Rehabilitation or Modification of Existing Structure

In addition to the following information, the Preliminary Design shall consider hydraulic issues where applicable.

751.1.1.2 Bridge Survey Processing and Bridge Numbering

The Preliminary Design process starts with the receipt of the Bridge Survey. The following is a list of steps that are taken by the Bridge Survey Processor.

Assign a Bridge Number to the Structure

The Bridge Division assigns bridge numbers in Bloodhound to all new, rehabilitated or modified structures (i.e., bridges, box culverts (see EPG 750.7.4.3 Summary of Responsibilities), CIP retaining walls over 5 ft. tall and MSE walls adjacent to bridge end bents).

Enter the Bridge Number, survey received date and feature crossed in the Bloodhound database.

New Structures:

New structures are numbered in ascending order using the next available bridge number. Numbering for new structures (except timber structures) start at A0001 thru A9999 and will be followed by B1000 thru B9999. (Note: B0001 thru B0581 were used for the Safe and Sound Bridge Replacement Program.)

New timber bridges are numbered in the same manner using the letter “T” instead of the letter “A”.

Temporary Structures:

Temporary bridges use the same number as the new bridge with the letter “T” added to the end (i.e., the temporary bridge for A8650 would be A8650T).

Rehabilitated or Modified Structures (Except when rehabilitation is only for structural steel coating):

Single Structures (Includes twin structures with individual bridge numbers):

Structures without a suffix letter on the existing bridge number will be numbered using the existing bridge number and a suffix number added that corresponds to the number of rehabilitations or modifications to the structure (i.e., bridge number A0455 becomes A04551 upon its first rehabilitation or modification and A04552 upon its second).

Single Structures with the Suffix “R”:

Structures that have the suffix “R” on the bridge number are usually bridges that have been rehabilitated or modified in the past, but in some cases bridges were given the suffix “R” to denote it as a replacement for a bridge with the same number. Review the existing bridge plans to determine if the “R” was for a rehabilitation or replacement. Structures that have been previously rehabilitated should replace the “R” with a suffix number corresponding to the total number of rehabilitations to the structure (i.e., bridge number A0444R would become A04442 (second rehab. or mod.), bridge number A0055R2 would become A00553 (third rehab. or mod.), etc.). For structures where the “R” denotes it as a replacement, the suffix number corresponds to the number of rehabilitations or modifications and the “R” is dropped (i.e., bridge number L0428R becomes L04281 for the first rehabilitation). If the “R” suffix was removed in a previous rehabilitation, the next suffix number is used regardless if the original structure was a rehabilitation or replacement.

Twin Structures with the Same Bridge Number:

Twin structures with the same bridge number will use a different suffix number for each structure. The numbering is similar to a single structure with the lower suffix number being used on the eastbound or southbound structure and the next suffix number being used on the westbound or northbound structure (i.e., bridge number A0144 would become A01441 for the eastbound bridge and A01442 for the westbound bridge. A future rehabilitation would become A01443 for the eastbound bridge and A01444 for the westbound bridge). Twin bridges with an “R” suffix on the bridge number would receive the suffix numbers using the same rules, but with the same consideration given to the “R” as it is for a single structure.

Structural Steel Coating (Use when all bridge pay items are related to structural steel coatings):

Rehabilitations that consist only of structural steel coatings use the existing bridge number plus the suffix “-Paint” (i.e., bridge number A2100 would become A2100-Paint and bridge number A150010 (multiple rehabilitations) would become A150010-Paint). A future rehabilitation consisting of only structural steel coatings would use the suffix “-Paint2” only if no other rehabilitations have been completed since the previous coating rehabilitation.

Removal of Existing Bridge Structures:

When a bridge structure is removed and not replaced by a new bridge structure or is removed under a separate contract, the suffix “-Remove” should be added to the latest bridge number (i.e., bridge number T0415 would become T0415-Remove and bridge number K01651 would become K01651-Remove).

Re-using Bridge Numbers:

Bridge numbers that were assigned to new structures that were never built are only reused if the proposed structure is at the same crossing location that the bridge number was originally assigned to.

Bridge numbers that were assigned to rehabilitate or modify structures where the work was not completed may reuse the previous bridge number by adding the suffix “-#2” to the bridge number (i.e., bridge number A6545 had plans developed for deck repairs and was assigned the bridge number A65451, but the work was never completed. At a later date, bridge A6545 is set up to be redecked; the bridge number assigned to the redeck would be A65451-#2). This suffix is only recorded in Bloodhound for tracking purposes and is not shown as part of the bridge number on file folders or final plans.

Create Job Folders

Check to see if a Correspondence File has been created. If the Correspondence File has been created, record the Bridge Number(s) in Bloodhound and make a Preliminary Design File for each structure received. If the Correspondence File has not been created, make a Correspondence File, an outer folder and a Preliminary Design File for each structure received. Here is the information for each type of folder/file:

Folder Type		Required Information on Folder
Outer (pink label)		County, Route and Job No.
Correspondence		County, Route and Job No.
Preliminary Design		County, Route, Bridge No., Location and Job No.

Also, be sure to notify by email the Structural Resource Manager and the appropriate Structural Project Manager or Structural Liaison Engineer, if known, when a new Correspondence File is created. The email subject line should include the Job No., County, Route and Bridge No. Include the name of the Bridge Division contact in the email, either the Structural Project Manager or the Structural Liaison Engineer.

Calculate Drainage Information

For structures over streams or waterways, calculate the drainage area and length of stream. Generate a drainage summary and include this information along with a map showing the drainage area for the structure and the area surrounding it in the Preliminary Design folder. If the drainage area is less than 1.5 sq. miles, consult the Structural Resource Manager to determine if preliminary design by the Bridge Division is necessary. The accuracy of the drainage area should be to the nearest 0.1 sq. mile for drainage areas less than 10 sq. miles and to the nearest 1 sq. mile for drainage areas greater than or equal to 10 sq. miles. When another stream intersects the subject stream near the downstream side of the proposed structure, create a separate drainage summary for the intersecting stream and include it in the Preliminary Design folder.

Process Electronic Files

When the electronic files listed in EPG 747.1.2 Bridge Survey Submittals are received, verify that the drawing scales are correct and that the necessary reference files are included. Also, review all Bridge Survey Sheets and the Bridge Survey Checklist for accuracy and completeness. The Bridge Survey Processor may have to work with the district to correct any discrepancies and/or omissions.

Add the newly assigned bridge number to the files and place a hard copy in the layout folder.

Final Step for Bridge Survey Processor

Once all of these steps are completed, the Bridge Survey Processor should deliver the Correspondence File, outer folder and the Preliminary Design Folder(s) to the Structural Resource Manager. An acknowledgement email is sent to the district contact(s) informing them that the Bridge Division has received the Bridge Survey. The email subject line should include the Job No., County and Route. Include the Bridge No(s). and the name of the Bridge Division contact in the email.

Once the survey is found to be complete and accurate, the Survey Complete date should be entered into Bloodhound. This date should match the Surv Rec date if no changes were made. If the survey is not complete or contains inaccuracies as submitted, we need to work with the district to fill in the blanks. If the omissions affect the timeline for completing the preliminary design, the Survey Complete date should reflect the date when we have all the information needed for the preliminary design to move forward without delay. If there is a delay in the bridge division review of the survey, this time should not count against the district in the survey complete date. The Bridge Survey Processor should work closely with the preliminary designer and SPM to determine the proper Survey Complete date in this case. For example, a bridge survey is received on 9/16/2016. Initial review by the bridge survey processor shows a complete survey. The job sits for five weeks while a preliminary resource comes available. Review by the preliminary designer shows a profile grade that is unusable and the preliminary design cannot progress until the grade situation is corrected. It takes four weeks for the grade to get worked out. The Survey Complete date should be four weeks after the Surv Rec date (10/14/2016). The district would not be penalized for our five week delay in reviewing the survey. This date is important because it will help us track when bridge surveys are turned in relative to when they are complete and when the project is due to Design.

751.1.1.3 Beginning Preliminary Design

The Preliminary Designer should meet with the Structural Project Manager to go over the Correspondence and Preliminary Design files to see if anything out of the ordinary has come up at Core Team Meetings prior to that date. It is important to include any correspondence or calculations used in the laying out of the structure in the bound portion of the Preliminary Design Folder.

The Preliminary Designer should then examine the Bridge Survey closely for any errors or omissions. Consult EPG 747 Bridge Reports and Layouts. Pay special attention to the scales used. Make sure the district's submittal includes photographs and details of staging and/or bypasses, if applicable. Verify that the proposed roadway width meets the NBI criteria for minimum bridge roadway width to avoid building a deficient bridge. Contact the district to resolve any discrepancies or questions.

A visit to the bridge site by the Preliminary Designer may be warranted to help determine Manning’s “n” values, examine adjacent properties, etc. If you decide to make this trip, advise the Structural Project Manager and the district contact since they may also want to attend.

Vertical Alignment and Bridge Deck Drainage

Laying out a bridge should consider deck drainage concerns for bridges on flat grades and sagging vertical curves and other vertical alignment issues as given in EPG 230.2 Vertical Alignment and EPG 230.2.10 Bridge Considerations.

751.1.1.4 Coordination, Permits, and Approvals

The interests of other agencies must be considered in the evaluation of a proposed stream-crossing system; cooperation and coordination with these agencies must be undertaken. Coordination with the State Emergency Management Agency (SEMA), the U.S. Coast Guard, the U.S. Army Corps of Engineers, and the Department of Natural Resources is required.

Required permits include:

U.S. Coast Guard permits for construction of bridges over navigable waterways.
Section 404 permits for fills within waterways of the United States from the U.S. Army Corps of Engineers.
Section 401 Water Quality Certification permits from the Missouri Department of Natural Resources.
Floodplain development permits for work in special flood hazard areas from the State Emergency Management Agency (SEMA).

Section 404 and Section 401 permits are obtained by the Design Division. U.S. Coast Guard permits are obtained by the Bridge Division. The Bridge Division will obtain floodplain development permits for projects that include structures in a regulated floodplain. The Design Division will obtain floodplain development permits for other projects involving roadway fill in a regulated floodplain.

Copies of approved U.S. Coast Guard permits and floodplain development permit/applications are sent to the district, with a copy to the Design Division.

See MoDOT and the Environment for more information on the required permits.

751.1.1.5 New Regular Bridge Design Schedule (Nonseismic) (Nonrailway Crossing)

751.1.2 Bridges/Boxes

751.1.2.1 End Slopes/Spill Fills

The end slopes are determined by the Construction and Materials Division and are supplied to the Bridge Division by way of the Preliminary Geotechnical Report. If this report is not in the Correspondence file, contact the district to get a copy of it. The Bridge Division has made a commitment to the districts that we will have the bridge plans, specials and estimate completed 12 months after the date the Bridge Survey and Preliminary Geotechnical Report are received. The "12 month clock" does not start ticking until both the Bridge Survey and the Preliminary Geotechnical Report are in the Bridge Division.

When laying out a skewed structure, adjust the end slope for the skew angle. On higher skews, this will have a significant effect on the lengths of the spans. Often the slope of the spill fills will be steeper than the roadway side slopes. On a skewed structure, this makes it necessary to "warp" the slopes.

Whenever there will be a berm under any of the spans, its elevation should be such that there is a minimum of 4 feet clear between the ground line and the bottom of the girder as shown below.

File:751.1 Prelim Design Berm Elevation.gif (*) Specify berm elevation or 4'-0" minimum clearance. BERM ELEVATION

If a rock cut is encountered in the spill slope, a slope of 1:1 may be used to the top of the rock.

751.1.2.2 Wing Lengths

The purpose of wings is to contain and stabilize the abutment fill as the roadway transitions to the bridge. For stream crossings in particular, the wings also protect the abutment during extreme hydraulic events.

The lengths of the wings at the end bents are to be determined prior to the issuance of the Bridge Memorandum. There are two reasons for this. First, the district will use these lengths to determine the placement of their guardrail (bridge anchor section). Second, if the lengths of the wings exceed 22 ft., they will have to be broken into a stub wing and a detached wing wall. If this happens, then you will need to include this extra cost in your Preliminary Cost Estimate and request soundings for the wall. The request for soundings for the wall should include a request for the determination of the allowable bearing of the soil (if in cut - assume piling if it is in fill) and the angle of internal friction for the material retained by the detached wing wall. Also include the bottom of wing footing elevation.

Unequal Wing Lengths

Wing lengths at each end of a bridge could be unequal because of several factors: grade of roadway under, superelevation of bridge, skew of the bridge, and/or other ramps/roads/slopes adjacent to the bridge structure, e.g., stream access roads or unusual geomorphic conditions.

Set/determine the wing lengths using the control points, as shown in Embankment at Bridge Ends, which may be used for both grade separations and stream crossings. This is done after the end bent location is determined. If estimated wing lengths are within 3 ft., they should be made equal and based on the longer wing length. Make sure no slope is steeper than that recommended in the geotechnical preliminary report. Slightly flatter slopes are acceptable. The contractor will warp the slopes to fit the wing tip locations.

Equal wing lengths are preferable at stream crossings to mitigate scour, improve erosion control and improve/mitigate parallel water flow along wing and side embankment. Also, since wing lengths are reported to districts for use in estimating rock slope protection limits, unequal lengths (especially on the upstream side) could mistakenly lead to the unfavorable condition of allowing for less than adequate rock side slope protection.

Judgement is required since no two estimated wing lengths at a bridge end will be exactly equal. More often equal wing lengths are used.

On divided highway bridges with high skews and shallow end slopes, the wing lengths on the median side of the bridge may be less than the other side due to the difference in sideslope between the median and the outside.

751.1.2.3 Live Load Determination

The live load requirements for a structure shall be HL-93

On box culverts, the actual live load applied to the structure is dependent upon the amount of fill on top of the box; however, see Structural Project Manager for the live load that goes on the Bridge Memorandum.

751.1.2.4 Skew Angle

Determining the most appropriate skew angle for the structure involves some judgement. On bridges over streams, pick the angle that will allow floodwater to pass through the bridge opening with the least amount of interference from intermediate bent columns. Another consideration on meandering streams is to avoid a skew which will cause the spill fill – side slope transition from blocking the stream. Often a trip to the field may be justified just for determining the angle (you can even ask the district to stake some different skews for you to observe in the field).

On stream crossings, avoid skews between zero and five degrees and try to use five degree increments. On grade separations, often the skew must be accurate to the nearest second to maintain minimum horizontal clearances.

Keep all bents on a bridge parallel whenever possible and avoid skews over 55 degrees. Also keep in mind that the higher the skew, the higher the Preliminary Cost Estimate due to the beam caps and wings being longer.

751.1.2.5 Bridge Width

For bridge width requirements, see EPG 231.8 Bridge Width.

751.1.2.6 Vertical and Horizontal Clearances

751.1.2.6.1 Grade Separations

Minimum Design Clearances for New Bridges
Facility Under Bridge	Vertical Clearance under Superstructure¹	Horizontal Clearance
Interstate and Principal Arterial Routes	16’-6” over roadway including auxiliary lanes and shoulders	Clear zone clearances from the edge of the traveled way (includes shoulders and auxiliary lanes) are obtained from the District Design Division. The vertical clearance is required for the full width of the clear zone. Barrier is required if unable to locate obstacles outside clear zone (columns, beams, walls, coping, 3:1 [1V:3H] slopes or steeper). If a barrier is required the minimum distance to the barrier shall be specified on the Bridge Memorandum as the horizontal clearance otherwise the clear zone clearance shall be used.
Other State Routes with Volumes ≥ 1700 vpd	16’-6” over roadway including auxiliary lanes and shoulders
Other State Routes with Volumes < 1700 vpd	15’-6” over the roadway including auxiliary lanes and shoulders²
Other Streets and Roads	14’-6” (15’-6” commercial zones) over the roadway including auxiliary lanes and shoulders²
Railroads	23’-0” inside 18’-0” opening or as required by railroad (23’-4” for UPRR, 23’-6” for BNSF)³	14’-0” and 22’-0” from centerline^4,5 (25’-0” eliminates collision walls)
¹ Roadway vertical clearances are based upon AASHTO minimums with an additional 6 inches to accommodate future resurfacing of the roadway. An additional 1 ft. is required for pedestrian overpass facilities over roadways. Vertical clearances shown are also applicable when the facility under the bridge is being carried by a bridge. ² To provide continuity of travel for taller vehicles exceptions can be made both rural and urban for any routes connecting to the systems where taller vehicles are allowed but not to exceed 16.5 feet. ³ Clearance is measured from the top of rails (from top of high rail on superelevated track). The required 18-ft. opening centered on the track shall be increased on each side of centerline 1.5 inches per each degree of curvature for any track crossed. ⁴ Fourteen feet is a preferred minimum. The absolute minimum is 9 ft. from the centerline plus 1.5 inches per each degree of any track curvature. ⁵ The minimum clearance of 22 ft. to be provided on one side of the track(s) is for off-track maintenance. If it is not obvious on which side of the track(s) this clearance is provided, a decision should be obtained from railroad's local representative. Assistance from Multimodal Operations may be required in some situations.

Clearance over Traffic During Construction (New and Existing Structures)
Roadways: Consult with the structural project manager or the structural liaison engineer and the district contact for minimum allowable vertical and horizontal clearance. Vertically this is usually 12 to 18 inches below the final minimum vertical clearance. Horizontally this is usually a minimum number of lanes or minimum size of opening required during the project while specifying the locality of the opening (e.g. centered on existing lanes, two 12-ft. lanes minimum in each direction, etc.). These clearances shall be specified on the Bridge Memorandum to be used in the note required on the final plans. For note see EPG 751.50 A3. All Structures.
Railroads: If feasible, 15 ft. horizontally from centerline of track and 21.5 ft. vertically from tops of tracks (from top of high rail on superelevated track). If either of these clearances is not feasible then obtain acceptable clearances from the railroad projects manager. For the detail required on the final plans showing minimum clearances during construction over railroads, see EPG 751.5.2.1.2.7 Features Crossed.

Deficient Vertical Clearances on Interstates
Refer to EPG 131.1.7 Deficient Vertical Clearances on Interstates for information about coordinating minimum vertical clearance for grade separation structures with the Defense Department.