Structural design


Detailed structural bridge design drawings

Detailed bridge structural design drawings are prepared subsequent to, and elaborate upon, the general arrangement drawings. The detailed structural design drawings show aspects and details required to fabricate the structure, materials specifications and dimensions, connection and hardware details, weld details, etc.. Detailed material and fabrication specifications in the form of drawing notes are also required.

In combination, the general arrangement drawings and the structural design drawings provide all information necessary to fabricate and install a bridge meeting all requirements and specification in a safe manner.

A Professional Engineer registered to practice in the province of British Columbia shall design all bridge components.

Non-standard bridge components

Non-standard systems or products that are not approved by the Ministry must follow a specific process before they can be used on an FSR bridge. Learn more about using non-standard materials.


Superstructures

Superstructures shall be one of the following types:

  • Steel girder with concrete deck
  • Steel girder with timber deck
  • Concrete slab girder or box girder
  • Treated glulam girder and timber deck
  • All-steel-portable bridge
  • Timber portable bridge
  • One of the Ministry-approved proprietary concrete types

The following information is provided to help guide the choice of superstructure type for typical single-lane, simply supported, permanent single-span bridges.

For spans 12 m or less, concrete slab structures are typically the most economical. They are particularly conducive where there are alignment issues such as skews or where extra roadway width is required to accommodate vehicle tracking on curves. Precast concrete slabs are heavy, and as such are expensive to ship and difficult to install in some situations. The equipment that will be used to lift and install them shall be considered when selecting component size in the design phase.

For spans between 12 m and 18 m, non-composite concrete decks on steel girders may be most economical. They can be set up to allow for bolted deck connections, providing for bridge removal and reuse elsewhere.  Alternatively, if a bridge in this span range will not be moved for its lifespan, a composite concrete deck on steel girders may be most economical in the long term, since the maintenance of deck joints between concrete deck panels for non-composite bridges can be problematic.

For spans greater than 18 m, composite concrete decks on steel girders are typically the most economical. Concrete composite deck panel installation is labour-intensive, time-consuming, and involves grouting that requires attention to quality control.  Bridges with composite deck panels are not easy to dismantle, if they are required to be moved to a new location.

For some crossing sites an economical solution may be a timber deck on steel girder superstructure; or an all-steel-portable superstructure.  Generally, all-steel-portable superstructures are more expensive than other options.  All-steel-portables are recommended only where they are being utilized for temporary situations.

Fatigue design shall be undertaken in accordance with the following:


Fatigue stress range

fsr < FSR where:
fsr = the calculated stress range at the detail due to the passage of the design traffic load; and
FSR = Fatigue stress range resistance


Number of design cycles

500,000 for spans > 12 m; and
1,000,000 for spans ≤ 12 m

 

Design standards for bridge superstructure deflection are provided in the Supplement to CHBDC Section 3.4.4 Serviceability Limit States.

 

Bridge spans in excess of 8 m shall be cambered for 115% of the design dead load deflection. For spans 8 m or less, the degree of camber is left to the designer’s judgement, unless otherwise specified in Ministry standards.

Standard steel I-girder transverse spacing for several deck widths is:

Deck Width mm (ft) Standard Girder Spacing (mm)

4267 mm (14’)

3000

4876 mm (16’)

3600

5486 mm (18’)

4200

Steel I-girder bolted splices. Provide bolted I-girder splices on all steel I-girders procured through a design/fabricate contract when girders have an overall length >24.384 m (80’) unless otherwise directed by the Ministry bridge engineer.

For design/fabricate/install contracts, bolted steel I-girder splices shall be provided at the discretion of the structural design engineer.

Diaphragms between steel I-girders. Diaphragms shall be provided between steel I-girders at bearing locations and at interior locations with a maximum spacing of 8 m between diaphragms.

Composite bridge plan bracing between steel I-girders. For composite bridges procured through a design/fabricate contract:

When overall girder length ≤ 24.384 m:

  • Provide at least one plan brace for erection purposes when there is no bolted girder splice;
  • Provide at least one plan brace for erection purposes at each bridge end

When overall girder length > 24.384 m: Provide continuous plan bracing.

For composite bridges procured through a design/fabricate/install contract:

Plan bracing shall be at the discretion of the detailed design engineer who shall consider the method of erection.

The following table specifies standard deck edge thickness for square precast concrete deck panels. Variations may be required for skewed or flared deck panels. 

 
Traffic Loading Deck Width mm (ft) Deck Edge Thickness mm

BCL-625

4268 (14’)

175

 

4876 (16’)

175

 

5486 (18’)

200

LOH, L-100

4268 (14’)

200

 

4876 (16’)

200

 

5486 (18’)

225

HOH, L-150, L-165

4876 (16’)

225

 

5486 (18’)

250

The preferred length of concrete deck panels is 3048 mm (10’). Notwithstanding, deck panel lengths should conform to the following: 

 

Item

Length (mm)

Minimum deck panel length

1524

Maximum internal deck panel length

3048

Maximum end deck panel length (deck over ballast wall)

3300

  • Maximum spacing between stud groups = 1200 mm c/c
  • Design of stud groups placed in pockets shall take account of reduced effective strength for stud spacings less than 4 diameters
  • The detailed design engineer shall determine the number and location of stud groups based on the detailed minimum and maximum spacing requirements

The Ministry of Forests, Lands, Natural Resource Operations and Rural Development (FLNRORD) Supplement to CHBDC is to be read and utilized in conjunction with the CSA S6 Canadian Highway Bridge Design Code (CHBDC).

Link to: Supplement to CHBDC (CSA S6)

Design vehicle configuration and design traffic loads: See Supplement to CHBDC (CSAS6), section 3.8, Live Loads

 

Standard superstructure drawings

The Ministry has developed standard drawings for bridges and bridge components which provide component configurations, dimensions and design details that should be used by engineers when preparing detailed structural designs for FSR bridges. Some of the standard drawings are already structurally detailed, and require limited, or no, additional engineering design.

Some of the standard drawings include detailed notes which provide specifications that shall be followed in relation to issues such as design, materials, fabrication, transportation, installation, quality assurance and quality control.

Proprietary bridge component conceptual drawings that have been approved by the Ministry are also included.  In order to obtain Ministry approval, proponents with proprietary systems must demonstrate and provide proof to the Ministry that their components meet stringent requirements for structural integrity, serviceability and durability.

Variations from the standard design requirements may be acceptable in certain special situations. All such variations shall be documented and require approval from the Ministry prior to use.

See a list of Ministry standard drawings


Substructures

Abutments shall have one of the following foundation types. The Ministry has standard drawings for most of these abutment types.

Piles. Piled abutment foundations can be used for all stream crossings where practical.  In soils where there is potential for scour, pile tips shall penetrate at least 4.5 m below the maximum design scour depth.

The design engineer shall specify the required pile capacity and minimum penetration for piles.

Pad and post.” “Pad and Post” abutment foundations are composed of steel pipe columns supported on precast concrete spread footings. These can be used where the footings are placed below the maximum design scour elevation. Cross bracing is required if the pipe height exceeds 1 metre.

All buried steel shall be protected against corrosion using Xymax Mono Guard™ or a similar Ministry pre-approved equivalent, applied in accordance with the manufacturer’s specifications (accelerator to be used as recommended by the manufacturer for specific humidity and temperature conditions).

Spread footings. Spread footing abutment foundations can be used where they are located below the maximum design scour elevation.  Spread footings may include cast in place or precast materials, and may be combined with abutment walls such as in the case of the Ministry standard “Inverted T” abutment.

Bin walls. Bin wall abutment foundations can be used where they are located below the maximum design scour elevation.

Precast interlocking concrete blocks. Precast interlocking concrete block abutment foundations can be used for temporary or permanent bridges with spans that do not exceed 20 m. They require a continuous treated timber or concrete sill to be located on top of the blocks.  The manufacture of precast concrete unreinforced interlocking blocks shall meet the requirements of the Ministry’s bridge component concrete standard.

See drawings STD-EC-050-11 to 13 for precast interlocking concrete block abutment concepts.

The base of the blocks shall be located below the maximum design scour elevation.

If foundation soils expected or encountered at a bridge site give rise to concerns about differential settlement of the abutment over the design life of the bridge, a spread footing shall be used below the base of the blocks to eliminate the possibility of differential settlement between individual blocks.

  • Ballast walls shall be composed of concrete, treated timber or an alternative permanent material pre-approved by the Ministry.
  • Welded connections for precast concrete ballast walls shall not be buried in soil, unless they are designed and protected to match the lifespan durability of the precast ballast wall components.
  • Pile caps shall be used for all multiple span bridges, and for single span bridges where the span length exceeds 30 m.
  • Steel pile caps shall be fully accessible for inspection and maintenance.
  • Concrete pile caps are to be specified for all permanent bridges with spans greater than 30 m.
  • Concrete pile caps shall be used to support prestressed concrete I-girders.

Pipe piles located in the wetted perimeter shall be filled with concrete, sand or gravel, or otherwise protected, if there is a reasonable likelihood for damage from floating large woody debris impacts.

All bridges subject to potentially damaging ice loads shall be designed to accommodate the ice loads without damage to the structure unless otherwise directed by the Ministry.. For piers potentially subject to ice loads, see supplement to CHBDC (CSAS6), Section 3.12.1.

 

Standard substructure drawings

Ministry standard drawings are available for a variety of different substructure components. Substructure standard drawings are provided including the following components:

  • Ballast walls;
  • Substructures for steel bridges;
  • Substructures for concrete bridges;
  • Cap details;
  • Modular concrete block abutments; and
  • Precast concrete “Inverted T” abutments for concrete slab bridges.

See list of Ministry standard substructure component drawings