751.40 LFD Widening and Repair

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Contents

751.40.1 General

751.40.1.1 Widening and Repair of Existing Structures

The Federal Highway Administration and the States have established a goal that the LRFD standards be used on all new bridge designs after October 2007. For modification to existing structures and with the approval of the Structural Project Manager or Structural Liaison Engineer, the LRFD Specifications or the specifications which were used for the original design, may be used by the designer.

751.40.1.2 Steel HP Pile Maintenance and Repair

Maintenance/Repair Guidelines

Piles are primary structural members and are compressively loaded all the time which makes it important to safely inspect, maintain and repair them if necessary. Pile inspection will require an assessment of pile performance by looking for pile deterioration and measuring pile section loss in order to determine the level of pile maintenance/repair required. The following schedule may be used for selecting the level of maintenance/repair required:

Pile Percent Section Loss Method* Level
0% through 25% Clean and recoat existing piles Maintenance
>25% through 40% Encasement of deteriorated section Maintenance
>40% through 75% or holes in any element or local buckling of any element Plating ** of deteriorated section OR replacement *** of section (splicing), AND encasement of the repaired section Repair
>75% Contact the Bridge Division Repair
* Method may also include cleaning and recoating all exposed piles, and cleaning and recoating all remaining exposed pile sections after encasement and/or repair.
** Plating can be for both flanges only, web only or both flanges and web. Overall symmetry of the pile cross-section shall be maintained when plating.
*** Based on additional factors other than just the percent of pile section loss, a replacement pile section (splicing) may be considered. Minimizing or eliminating traffic loading, adding falsework or just having support conditions such as integral bents (where both the pile cap beam and the superstructure concrete diaphragm are connected by more than just dowel bars – see bridge plans) can help to determine the method of repair. A replacement pile section can be coated or galvanized. See Structural Project Manager.

Estimating Pile Percent Section Loss in the Field

Quantifying pile section loss can be inexact. To encourage uniform application of the maintenance/repair guidelines, the following procedure is recommended:

1. Pile section loss should be determined using a thickness meter.
2. Remove deteriorated material and clean pile for measurement.
3. At any point along a pile (cross-section) where there are three elements to be considered independently, e.g. two flanges and a web.
4. Estimate the actual cross-section area of each element at its most deteriorated point along the length of pile. Using the thickness meter, measure the thickness at several points along a horizontal line across the element. From this data, estimate the actual cross-section area of each element.
5. The fraction of section remaining (PSR) is the actual cross-section area of each element at its most deteriorated point along the length of pile divided by the original area of same element.
6. Percent section loss is 100(1 – PSR) for each element.
7. The greatest PSR dictates the maintenance/repair method.
8. Examine continuity at flange/web intersections. Section loss along these intersections along the length of pile of more than 6 linear inches should be repaired using encasement as either the only method or part of plating/replacing repair method regardless of a low percent section loss.
9. Interference from cross bracing at pile sections to be repaired will need special consideration not detailed on the standard drawings.
Bridge Standard Drawings
Steel HP Pile Maintenance and Repair Reinforcement


Additional types of maintenance and repairs may be considered which include but are not limited to:

  • Zinc tape coating
  • FRP strengthening
  • Corrosion inhibitor

751.40.2 Typical Sections of Concrete Repairs

751.40.2.1 Resurfacing

751.40 Resurfacing Plan.gif
PLAN


751.40 Resurfacing Section Thru Roadway.gif
SECTION THRU ROADWAY


Place the following notes on plans.

The existing Asphaltic Concrete surface shall be removed to a uniform grade line (*) below the existing control grade line as noted.
Resurface with (*) Asphaltic Concrete.
(*) Depth of Asphaltic Concrete as specified in the Bridge Memorandum.

751.40.2.2 Special Repair Zones

The following order of repair zones shall be used for the deck repair on continuous concrete structures.

Hydro Demolition Projects (Case 1 and 2)

Conventional deck repair required in the areas designated as special repair zones shall be completed before demolition in alphabetical sequence beginning with Zone A. Zones with the same letter designation may be repaired at the same time.

Any deck repair in areas not designated as a special repair zone shall be completed after hydro demolition. Case 1 is primarily monolithic deck repair after hydro demolition. Case 2 is primarily conventional deck repair after hydro demolition.

Note:

- Case 1 shall not be used for polyester polymer and low slump concrete wearing surfaces (too stiff for monolithic repairs).
- Conventional deck repair is required with void tube replacement after hydro demolition with both Case 1 and Case 2.
- If an excessive number of zones are required at any bent, see the Structural Project Manager or Structural Liaison Engineer.
- Consider combining zones if the length of a zone in the longitudinal direction of the bridge is less than 24 inches.
751.40.2.2 ABCD.jpg
(1) Development Length.
See EPG 751.50 Standard Detailing Notes for appropriate notes.

Non-Hydro Demolition Projects

Any deck repair in areas not designated as a special repair zone shall be completed prior to work in Zone A. Zones with the same letter designation may be repaired at the same time.

Note:

- If an excessive number of zones are required at any bent, see the Structural Project Manager or Structural Liaison Engineer.
- Consider combining zones if the length of a zone in the longitudinal direction of the bridge is less than 24 inches.
751.40.2.2 ABC.jpg
(1) Development Length.
See EPG 751.50 Standard Detailing Notes for appropriate notes.

751.40.2.3 Substructure Repair

751.40.2.3.1 Formed and Unformed Repair Areas

751.40.2.3.1.1.jpg

Fig. 751.40.2.3.1.1, Elevation of Int. Bent


751.40.2.3.1.2.jpg
Fig. 751.40.2.3.1.2, Section through End Bent

751.40.2.3.2 Bent Cap Shear Strengthening using FRP Wrap

Bridge Standard Drawings
Fiber Reinforced Polymer (FRP) Wrap


Fiber Reinforced Polymer (FRP) wrap may be used for Bent Cap Shear Strengthening.

When to strengthen: When increased shear loading on an existing bent cap is required and a structural analysis shows insufficient bent cap shear resistance, bent cap shear strengthening is an option. An example of when strengthening a bent cap may be required: removing existing girder hinges and making girders continuous will draw significantly more force to the adjacent bent. An example of when strengthening a bent cap is not required: redecking a bridge where analysis shows that the existing bent cap cannot meet capacity for an HS20 truck loading, and the new deck is similar to the old deck and the existing beam is in good shape.

How to strengthen: Using FRP systems for shear strengthening follows from the guidelines set forth in NCHRP Report 678, Design of FRP System for Strengthening Concrete Girders in Shear. The method of strengthening, using either discrete strips or continuous sheets, is made optional for the contractor in accordance with NCHRP Report 678. A Bridge Standard Drawing and Bridge Special Provision have been prepared for including this work on jobs. They can be revised to specify a preferred method of strengthening if desired, strips or continuous sheet.

What condition of existing bent cap required for strengthening: If a cap is in poor shape where replacement should be considered, FRP should not be used. Otherwise, the cap beam can be repaired before applying FRP. Perform a minimum load check using (1.1DL + 0.75(LL+I))* on the existing cap beam to prevent catastrophic failure of the beam if the FRP fails (ACI 440.2R, Guide for the Design and Construction of Externally Bonded FRP, Sections 9.2 and 9.3.3). If the factored shear resistance of the cap beam is insufficient for meeting the factored minimum load check, then FRP strengthening should not be used.

* ACI 440.2R – Guide for the Design and Construction of Externally Bonded FRP

Design force (net shear strength loading): Strengthening a bent cap requires determining the net factored shear loading that the cap beam must carry in excess of its unstrengthened factored shear capacity, or resistance. The FRP system is then designed by the manufacturer to meet this net factored shear load, or design force. The design force for a bent cap strengthening is calculated considering AASHTO LFD where the factored load is the standard Load Factor Group I load case. To determine design force that the FRP must carry alone, the factored strength of the bent cap, which is 0.85 x nominal strength according to LFD design, is subtracted out to give the net factored shear load that the FRP must resist by itself. NCHRP Report 678 is referenced in the special provisions as guidelines for the contractor and the manufacturer to follow. The report and its examples use AAHTO LRFD. Regardless, the load factor case is given and it is left to the manufacturer to provide for a satisfactory factor of safety based on their FRP system.

Other References:

751.40.2.3 references.jpg

751.40.2.4 Deck Repair and Filled Joints

Bridge Deck, Repair
Report 2002
See also: Research Publications
Bridge Standard Drawings
Deck Repair and Wearing Surfaces

751.40.2.5 Temporary Traffic Control Device

Show Barrier as per district recommendation. Typically Barrier is shown when structure is on interstate and/or the rail is being removed. Otherwise, show the dimension lines with 2'-0" dimension.

751.40.2.5.jpg
(* If this dimension is less than 3 feet, the temporary concrete traffic barrier shall be attached with tie-down straps, with the approval of the Structural Project Manager or Structural Liaison Engineer. Where lateral deflection cannot be tolerated, the temporary concrete traffic barrier shall be attached with the bolt through deck detail (to be used only on existing decks). See EPG 617.1 Temporary Traffic Barriers and EPG 751.1.2.12 Temporary Barriers.
(** Where slab removal represents small and discontinuous openings in the deck along the bridge length (i.e. expansion device replacement) use of either a flat steel plate, a 22 ½” temporary traffic control device or a temporary concrete traffic barrier may be more appropriate. Consult with the Structural Project Manager or Structural Liaison Engineer.

751.40.3 Dimensions

751.40.3.1 Wearing Surfaces

Replacement of Typical Expansion Joint Systems (Strip Seal Shown, Other Systems Similar)

751.40.3.1 wearing surfaces.jpg

When concrete is removed and armor is replaced, see EPG 751.13 Expansion Joint Systems for the appropriate expansion joint system details and EPG 751.50 H5 for the appropriate notes.