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Deck Forming-Overhang Bucks, Rails & Parapets

Presenter: Wayne Nolde, P.E.

Staunton District Southern Area Construction Engineer

Learning Objectives

By the end of this lesson participants will better understand:

• Specifications and plan details associated with overhangs, rails, and parapets.

• Means and methods contractors use to construct deck overhangs, rails, and parapets, and potential issues associated with the work.

• Their role in inspection of these items of work and where to focus their inspection efforts to ensure quality and the lowest possible life cycle costs.

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Forming Overhangs- Applicable Specifications

Section 404.03 – Procedures

(a) Forms

• Devices for supporting forms of any type shall not be welded to steel beams or girders unless specified on the plans.

• Metal ties or anchorages within the form shall be constructed to permit their removal to a depth of at least one inch from the face of the concrete without damage to the concrete.

• Forms shall be maintained at a temperature that will not adversely affect curing of concrete.

• Bridge deck slabs shall be constructed in a manner so that the thickness of the finished slab shall not be less than the thickness shown on the plans or more than the thickness plus ½ inch.

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Forming Overhangs - Applicable Specifications

404.03(a) Forms: The contractor shall submit calculations and layout details of the overhang supports and formwork, including fabrication and erection details, to the Engineer for review in accordance with Section 105.10. Overhang formwork details shall be signed and sealed by a Professional Engineer, holding a valid license to practice engineering in the Commonwealth of Virginia.

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Deck Overhang Bucks

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Deck Overhang Forms

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Deck Forming at a Staged Construction Joint

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Deck Overhang Forming Key Inspection Points

• Verify that the overhang is being installed in accordance with the signed and sealed details submitted by the contractor and reviewed by the Department.

• Verify that the depth of concrete will be in accordance with the limits in the specifications.

• Verify that the method of heating the concrete in the overhang is comparable to the method used to heat the concrete in the interior bays when temperatures are expected to fall below 50 degrees during the curing period.

• Verify that the contractor has run the screed across the overhangs several times to seat the formwork prior to checking the cover over the reinforcing steel and the deck of the overhang.

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Applicable Specifications –Bridge Railings and Parapets

Section 410 - Railings and Parapets

• 410.02 –Materials:

(a) Concrete for extruded (slipformed) parapets is different than used for CIP parapets; Slump may be less than 2”, air content shall be greater than or equal to 4%, and aggregate size shall be no less than No. 7.

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Applicable Specifications –Bridge Railings and Parapets

Section 410 - Railings and Parapets

• 410.03-Procedures:

(a) Post alignment: Posts shall be perpendicular to the profile grade and plumb in the transverse direction regardless of the cross slope.

(b) Metal Railings: Grounding conductors for metal railings shall pass through bridge parapets and backwalls in a 1” conduit or raceway to a point 4-8” below the finished grade and shall be attached to a grounding electrode(s) with a minimum of 8 foot contact with soil.

The Contractor shall test the grounding system and provide documentation to the Engineer.

Aluminum railing components that are in contact with concrete shall be coated with an approved aluminum-impregnated caulking compound.

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Applicable Specifications –Bridge Railings and Parapets

Section 410 - Railings and Parapets

• 410.03-Procedures:

(c) Falsework shall be released before constructing concrete parapets.

Concrete parapets shall be constructed within an allowable tolerance of +/- ½ inch for overall depth and width, +/- ¼ inch for the width of the upper portion of the barrier, and +/- ¼ inch in 10 feet for horizontal alignment.

The 3 inch dimension from the deck surface to the bottom of the sloped portion of the inside face is the most critical in the ability of the parapet to redirect an errant vehicle. This should be carefully monitored so that it is not increased unless absolutely necessary. Camber in prestressed members creates a rolling deck surface that will put the same rolling surface in the top of the parapet if there is no overlay on the prestressed members. Use caution when raising the parapets at the piers to improve the visual appearance of the parapet.

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Applicable Specifications –Bridge Railings and Parapets

Section 410 - Railings and Parapets

• 410.03-Procedures:

(c) The use of the extrusion method requires the Engineer’s approval.

The contractor shall submit the details of his extrusion equipment and methods for approval. The extrusion machine shall be operated in such a manner that a minimum of hand finishing will be required to produce a dense homogeneous finish, free from voids and honeycomb.

The contractor is responsible for the extra cost of widening the deck and substructure modifications to accommodate the extrusion machine.

Deflection and expansion joints shall be grooved immediately after the extrusion process and any saw cutting shall be done the same day the concrete is placed.

The Contractor’s means and methods must include provisions to keep concrete from falling over the side of the bridge to the ground or river below. The best way is to leave the overhang forms in place.

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Applicable Specifications –Bridge Railings and Parapets

Section 410 - Railings and Parapets

• 410.03-Procedures:

The engineer may require the Contractor to discontinue the extrusion method if the Contractor’s methods and means do not produce satisfactory results commensurate with cast-in-place construction until such time as the Contractor can modify or alter the means of extrusion to satisfactorily address the Engineer’s concerns. If such modifications do not satisfactorily remedy the concern of the Engineer, he may withdraw approval to continue construction of railing, parapet, or median barrier by the extrusion method.

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Bridge Deck Overhang Details

• In the past contractors could set the form for the bottom of the overhang even with the bottom of the top flange of the exterior steel girder and slope it up to the proposed elevation at the outside edge of the overhang. This practice lead to a variable depth overhang and is no longer allowed.

• The location of the reinforcing steel in the deck which extends up into the railing or parapet is critical and should be verified carefully. Should the contractor use the same height bar supports for the bottom mat of reinforcing steel in the overhang as he uses in the interior bays?

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Bridge Railings-What is Wrong in This Picture?

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Bridge Railings and Parapets Key Inspection Points

• Plan ahead for conduits in backwalls for grounding conductors for railings.

• Verify alignment and reinforcing steel cover and placement.

• Verify anchor bolt placement for railings are inside the reinforcing steel cage.

• Plan ahead for backwall and deck modifications for extruded parapets including adjustments to the backwall reinforcing steel or wingblocks.

• If the wingblocks extend above the top of the bridge deck they mayinterfere with the slipform machine. The contractor may have to leave a portion of the wingblocks off until after the parapet has been slipformed. The orientation of his construction joints should be perpendicular to the top surface of the wingblock and should be at least 6” from the closest edge of the concrete so that no feather edges are produced.

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Bridge Railings and Parapets Key Inspection Points

• Ensure submittals are made and approved for extruded parapets.

Additional longitudinal diagonal parapet reinforcing steel will have to be added at contractor's expense to prevent racking of reinforcing during the slip-forming process. The contractor should submit his plans for the additional reinforcing for review by the Structure and Bridge Section before ordering the materials.

• Verify dimensions for parapets, especially extruded parapets.

• Make sure open joints line up with grooves in the parapet and both are square with the parapet. The forming system must be rigid and the concrete must be poured equally on both sides of the joint to prevent the bulkhead from being pushed out of position during the pour. For slipformed parapets make sure the open joints and grooves line up with the breaks in the longitudinal steel.

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Bridge Railings and Parapets Key Inspection Points

• Verify the reinforcing steel placement for the railings or parapets before the deck is poured. Extra depth of the overhang can effect the location of the RV0502 bars. They need to be 2 inches from the center of the bar to the face of the parapet at its intersection with the deck surface to function as designed.

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Bridge Railings

Kansas Corral Rail is the “preferred” railing systems for bridges over water except where high numbers of trucks or high speed is involved. It may or may not include a curb and it may be 27" or 32" high, depending on the level of service required for a particular project. Common problems to watch for during construction of these railings include shy cover on reinforcing steel in posts and interference between screed wheel covers and vertical reinforcing in the posts. Rails with curbs require additional pours for the curbs since it is almost impossible to pour the curbs, posts, and rails all at the same time without creating honeycomb in the curbs.

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Kansas Corral Railing Steel Reinforcement

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Kansas Corral Railing Forms

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Terminal Wall Reinforcing Steel22

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Completed Section of Kansas Corral Rail

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Route 11 Bridge Phase 1 with Railing

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Kansas Corral Railing with Curb

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Modified BR27C Railing

Other rail systems that are used include the Modified BR27C, which includes tubular steel rails on steel posts mounted on vertical concrete walls. They often have architectural treatment and concrete surface coloring to create the appearance of rock walls while maximizing the view of the river from a vehicle on the bridge.

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Modified BR27C Railing

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Modified Illinois Rail System on Goshen Truss

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Modified Illinois Rail System on Glue Laminated Wooden Curb

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Guardrail Mounted to the Truss Members

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Guardrail Mounted on Posts Attached to the Bridge Curb

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Guardrail Transitions at the End of the Bridge

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Texas Cathedral Rail

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Symmetrical and Asymmetrical Thrie Rail Systems

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Thrie Rail Attachment to the Bridge Deck

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