New Design – Standard SL and SLW Bridge Design Guidelines

Overview

Once a Standard SL Bridge or a Standard SLW Bridge has been identified as appropriate for a given site (satisfies the Standard SL/SLW Bridge Requirements), the site specific design may proceed.

The following Standard Bridge Design drawings are available:

• Standard SL Bridge girders: S-1723 to S-1749
• Standard SLW Bridge girders: S-1816 to S-1837
• Standard SL and SLW Bridges with Steel Substructures: S-1753 to S-1756
• Standard SL and SLW Bridges with High Backwall Steel Abutments: S-1793 to S-1796
• Standard SL and SLW Bridges with Cast-in-Place Concrete Substructures: S-1762 to S-1764
• Standard SL and SLW Bridges with Precast Substructures: S-1765 to S-1770

The framework for Standard SL and SLW Bridges has been designed to accommodate various site specific requirements by incorporating designated lettered variables in the standard drawing set. The Consultant can use these variables to tailor suit the standard bridge framework to their site. The Consultant shall clearly define all these variables on the site specific P drawings.

The following is a summary of the Standard SL and SLW Bridge verification requirements and the site specific design requirements.

Verification of design assumptions

The Standard SL/SLW Bridge designs were developed based on various assumptions and limiting criteria. The Consultant shall verify that the site specific conditions are within these limitations and assumptions before the standard design can be employed.

The Consultant shall refer to the standard drawings and familiarize themselves with these criteria (Commentary 1).

Structure related geometry

Much flexibility has been designed into the Standard SL/SLW Bridge designs. This is achieved through the use of lettered variables.

Standard values for these lettered variables have been tabulated on the standard substructure drawings. The Consultant need only choose and then subsequently define, on the site specific drawings, the standard value being incorporated into their project.

Variables include girder span lengths, number of spans, skew, and roadway width (Commentary 2).

Foundations

Abutment piles

The standard design incorporates driven steel HP Pile sections with the weak axis orientated perpendicular to the abutment. Refer to S-1755, S-1762, S-1765, or S-1794.

The Consultant is responsible for determining the approximate pile tip elevations, based on site specific geotechnical information and providing this information along with pile spacing on the site specific drawings (Commentary 3).

Pier piles

The standard design incorporates driven steel piles for multi span girder bridges with piers. Refer to S-1754, S-1762, and S-1765 for information.

The Consultant is responsible for determining the approximate pile tip elevations, based on site specific geotechnical information, and providing this information along with pile spacing on the site specific drawings (Commentary 3).

Abutments

The Standard SL/SLW Bridge designs incorporate the following abutment features:

• standard abutment designs in structural steel, cast in place concrete, and precast concrete are provided
• skews of 0, 15, 30 and 45 degrees
• abutment widths to facilitate clear roadway widths between 8940 and 15020 mm
• steel backwall abutments:
  • maximum abutment height shall be 2500 mm from top of streambed to underside of girder
• steel spill-through abutments:
  • maximum abutment height shall be 800 mm from top of fill to underside of girder
• cast-in-place or precast concrete:
  • maximum abutment height shall be 600 mm from top of fill to underside of girder

The Consultant shall select the appropriate skew, clear roadway width and associated abutment geometry from the standard framework and clearly label on the site specific drawings (Commentary 4).

It should be noted that the standard SLW girders have been detailed for use with the standard SL girder steel substructures. Because the standard SLW design incorporates a corbel at the end of the girder for approach slab support, the backwall cannot extend behind the girders as it does for SL girders. As such the backwall must be trimmed on each side of the exterior SLW girder.

A vertical plate, bent to accommodate the bridge skew, is bolted to each end of the steel abutment cap to provide support to the free edge of the trimmed backwall. See drawing S-1756 or S-1795 for detail.

Piers

Similar to the abutments, the Standard SL/SLW Bridge designs incorporate the following features:

• standard pier designs in structural steel, cast-in-place concrete, and precast concrete are provided
  • pier heights are limited to 5500 mm as measured from top of streambed to underside of girder
• skews of 0, 15, 30, and 45 degrees
• pier widths to facilitate clear roadway widths between 8940 and 15020 mm

The Consultant shall select the appropriate skew, clear roadway width and associated pier geometry from the standard framework and clearly label on the site specific drawings (Commentary 5).

Bearings

Standard SL/SLW Bridge designs incorporate continuous neoprene bearing pads under the girders and secure the superstructure to the substructure with galvanized dowels. No bearing design is required from the Consultant when using the standard design framework.

However, care shall be taken to ensure the appropriate dowel size and location is shown based on the abutment geometry (spill-through versus backwall type).

Girders

Standard SL/SLW precast concrete girders are 510 deep and are available in 6, 8, 10, 12, and 14 m lengths. In addition, standard SL precast concrete girders are available in 20 ft (6.1 m), 28 ft (8.53 m), 30 ft (9.14 m), 33 ft (10.06 m), 35 ft (10.67 m), 38 ft (11.58 m), 40 ft (12.19 m) and 42 ft (12.8 m) lengths.

Tables summarizing the available span arrangements (summarized based on pile loads) can be found on drawings S-1753, S-1763, and S-1767. Standard SL/SLW girder bridges are limited to 3 spans and a maximum bridge length of 42 m in order to limit thermal movement at the bridge ends. The Consultant shall clearly identify the length of each span on the site specific drawings (Commentary 6).

Wearing surface

Standard SL Bridge designs are intended for use on local roads with a gravel wearing surface. In this scenario, the girder top acts as the wearing surface. For paved roadways or roadways that are expected to receive a paved surface, the Standard SLW Bridge designs shall be utilized. The wearing surface and appropriate girder type shall be clearly identified on the site specific drawings (Commentary 7).

Bridgerail

Standard SL/SLW Bridge designs support a Performance Level 1 bridgerail. Standard SL Bridge designs utilize standard PL-1 Thriebeam Bridgerail without a curb. Refer to standard drawing S-1652 for information. For Standard SLW Bridge designs, standard drawing S-1797 provides information on standard PL-1 Thriebeam Bridgerail with 75mm high exposed curb.

The Consultant shall clearly identify the bridgerail post locations and approach rail transitions on the site specific drawings (Commentary 8).

Approach slab

• Standard SL Bridge designs do not incorporate an approach slab due to the gravel wearing surface
• Standard SLW Bridge designs incorporate a 200 mm thick by 3000 mm long cast in place concrete approach slab. Reinforcing for the approach slab is included in the Standard SLW Bridge design details. The Consultant shall provide a barlist detailing the approach slab reinforcing based on the site specific bridge width and skew
• contrary to major bridges, Standard SL/SLW Bridge designs do not incorporate concrete collectors or drain troughs at the bridge ends due to the relatively short bridge length

Commentaries

1 – Standard SL/SLW Bridge Design – Verification

The Standard SL and SLW Bridge designs are based on specific design criteria and assumptions. Design criteria related to the standard SL and SLW girder designs can be found on standard drawings S-1749 and S-1836, respectively.

Substructure related design assumptions are separated by substructure material type. Information on steel substructures can be found on S-1753, cast-in-place concrete substructures on S-1762, precast concrete substructures on S-1765, and steel substructures with high backwalls on S-1793.

The Consultant shall familiarize themselves with the limitations and requirements listed on these drawings to ensure the appropriate use of standard designs.

Site specific criteria found to be in non-conformance with that listed in the standard design framework requires the Consultant to perform an engineering assessment to verify whether the standard design is in fact suitable for implementation at their site. If it is found that the standard designs cannot be used, the Consultant shall perform a site specific design in accordance with the requirements laid out for major bridges.

2 – Standard SL/SLW Bridge Design – Structure Geometry

The Standard SL and SLW Bridge designs accommodate several geometric variables. The Consultant shall select the geometric variables within this framework that best suit the site specific requirements.

• Bridge width: Select a standard bridge width appropriate for the approach roadway geometry. Bridge widths shall be at least as wide as the approaching roadway. The standard drawings define the various geometric variables in tabular form based on the bridge width selected. See S-1754 and S-1755 for information on steel substructures, S-1764 for cast-in-place concrete substructures, S-1768 for precast concrete substructures and S-1795 for steel substructures with high backwall. Bridge width, number of girders, and the other variables associated with the bridge width shall be clearly identified on the site specific drawings.
• Determine skew parameters: Standard designs include skews of 0, 15, 30, and 45 degrees. The Consultant shall choose the most appropriate skew value within the standard design framework and identify this on the site specific drawings.
• Bridge Length and span configurations: In general, Standard SL and SLW Bridge designs accommodate bridge lengths from 6 m to 42 m. The 42 m bridge length limitation is based on three 14 m spans. Standard designs include 6, 8, 10, 12 and 14 m spans. Standard imperial span lengths are also available for superstructure replacement projects utilizing existing substructures with imperial span lengths. The standard imperial designs include 20 ft (6.1 m), 28 ft (8.53 m), 30 ft (9.14 m), 33 ft (10.06 m), 35 ft (10.67 m), 38 ft (11.58 m), 40 ft (12.19 m) and 42 ft (12.8 m) spans.
• Roadway Cross section: The standard design assumes bridge symmetry about the centreline crown. A 2% cross fall from crown to gutter is provided for drainage purposes. Designs requiring alternative cross falls or non symmetric cross sections about the centreline of crown will require site specific design.

3 – Standard SL/SLW Bridge – Pile Design

The Standard SL and SLW Bridge designs incorporate driven steel piles at both the abutments and pier(s). The Consultant shall verify that the site specific loading conditions and required geotechnical resistances satisfy the requirements/limitations of the standard design.

 See S-1753, S-1762, S-1765, and S-1793. These requirements/limitations include:

• Earth pressure: The Standard SL and SLW Bridge designs incorporate pinned integral abutments. In order not to overstress the abutment piles in a combination of bending and axial load, limiting assumptions are assumed in the standard design. When actual site conditions result in more severe load effects or less effective resistance, the standard design shall require engineering verification.
• Required bearing capacity: Pile load bearing requirements are outlined on the standard drawings for various span combinations.
• Pier pile length above streambed where the pipe acts as a pier shaft. Maximum unbraced pipe lengths and associated lateral bracing requirements are provided on the standard drawings. The Consultant shall ensure that the site specific bridge geometry is within the prescribed unbraced lengths and the maximum pier height (including the effects of scour) limits of the standard design.
• Ice forces on pier bents: The site specific ice forces shall be within the limits assumed and listed in the standard drawings.

If the conditions of the standard design are satisfied, the standard foundation can be employed. The Consultant shall determine the approximate pile tip elevations and include them on the site specific drawings along with the standard number of piles and standard pile spacing designated for the bridge width and skew selected.

Refer to the following standard drawings for information:

• S-1754 and S-1755 for steel substructures
• S-1764 for cast-in-place concrete substructures
• S-1768 for precast concrete substructures

4 – Standard SL/SLW Bridge Design – Abutments

The Consultant is responsible for defining all of the variable abutment information, designated with letters, as shown on the standard drawings specific to the abutment type and material (steel or concrete) chosen.

Tables have been assembled to define these variables according to bridge width and skew. The site specific drawings shall include an abutment layout similar to that shown on the standard drawings except with the individual letters replaced with the appropriate numbered values selected from the tables listed on S-1755, S-1764, S-1768 or S-1795.

The appropriate dowel size and location based on the abutment geometry selected, shall also be shown on the site specific abutment drawings. Some abutment details for Standard SLW Bridge abutments are provided on S-1837. Abutment seats shall be sloped to match the longitudinal gradeline.

Standard abutment designs are included in three material types namely: structural steel, cast in place concrete, and precast concrete. Abutments constructed from structural steel include both spill through and backwall type geometries.

Bridge skews in excess of 30 degrees, a cast in place concrete abutment seat should be utilized due to the additional geometric complexities inherent with higher skew crossings.

Refer to S-1753 to S-1756 for steel substructures, S-1762 to S-1764 for cast in place concrete substructures, and S-1765 to S-1770 precast concrete substructures. Information regarding High backwall structural steel abutments can be found on standard drawings S-1793 to S-1796.

5 – Standard SL/SLW Bridge Design – Piers

The Consultant is responsible for defining all of the variable pier information, designated with letters, as shown on the standard drawings specific to the pier material (steel, or concrete) chosen. Tables have been assembled to define these variables according to bridge width and skew.

The site specific drawings shall include a pier layout similar to that shown on the standard drawings except with the individual letters replaced with the appropriate numbered values selected from the tables listed on S-1754, S-1764, or S-1768.

The Consultant should be aware that some specialized pier details for use on Standard SLW Bridges are provided as part of the Standard SLW Bridge drawing set. Refer to S-1837 for details. Pier caps shall be sloped to match the longitudinal gradeline.

Standard pier designs are included in three material types namely: structural steel, cast in place concrete, and precast concrete. Bridge skews in excess of 30 degrees, a cast in place concrete pier cap should be utilized due to the additional geometric complexities inherent with higher skew crossings.

Refer to S-1753 to S-1756 for steel substructures, S-1762 to S-1764 for cast-in-place concrete substructures, and S-1765 to S-1770 precast concrete substructures.

The Consultant shall ensure that pier pile bracing is located within the elevation limitations set out by the standard design, with the site specific bracing elevation indicated on the site specific drawings. Refer to S-1754, S-1762, and S-1765.

6 – Standard SL/SLW Bridge Design – Girders

The Consultant shall identify the number of girders, span length(s), and span combination chosen from those included in the standard design and identify this information on the site specific drawings.

The Consultant is also responsible for providing the bridgerail post spacing, within the limits of the standard bridgerail design, for use in placing the anchorage assemblies during fabrication of the exterior girders and indicating this information on the site specific girder drawings.

Standard SL girders are provided with imperial spans for use on superstructure replacement projects where the existing substructure elements on being maintained and the existing spans are imperial.

7 – Standard SL/SLW Bridge Design – Deck

Bridges located on paved local roadways require the use of the Standard SLW Bridge designs and shall be waterproofed and paved.

Those bridges that are not paved during construction but are expected to be paved in the future shall also incorporate the Standard SLW Bridge designs for future waterproofing and ACP installation. Refer to AT Best Practice Guideline 3 (BPG 3) for information regarding concrete bridge deck protection.

For bridges that are located on local roads with gravel surfacing and not exposed to de-icing chemicals, the Standard SL Bridge designs should be utilized.

The Consultant shall ensure that the chosen girder type (SL versus SLW) is clearly identified on the site specific drawings.

8 – Standard SL/SLW Bridge Design – Bridgerail and Transitions

The Consultant shall include all bridgerail post locations along the girder length on the site specific drawings to ensure proper placement for the anchorage assemblies during girder fabrication.

Standard bridgerail transitions are used on both the Standard SL and SLW Bridge designs. Refer to S-1652 and S-1797 for Standard SL and SLW Bridge designs, respectively.

In instances where a Standard SLW Bridge design is used in an interim unpaved condition, a temporary steel rub rail shall be installed to protect the 165 mm exposed curb height. The rub rail shall be removed when the waterproofing and ACP wearing surface are added to the bridge. See S-1837 for details.