Table 1.1 Highway classes
2.3 Design for durability
2.3.1 Design concept
The design shall ensure that the structure will be able to maintain its level of serviceability during its design life. The designer shall consider the environmental conditions that exist at the site or are likely to exist during the design life of the structure and shall assess their significance in relation to the possible mechanisms of deterioration in the structure. Structural site investigation shall include testing of soils, groundwater, local runoff water, atmospheric pollution levels, and, when applicable, drainage system discharge (to detect corrosive substances). When a structure is being designed for a new facility, environmental conditions shall be predicted from comparable existing facilities.
The requirements for durability protection and the planned replacement of components shall be identified and shown on the Plans.
2.3.2 Durability requirements
2.3.2.1 General
The structural form, materials, and details shall be suitable for the design loads and environmental conditions that will be experienced during the design life of the structure.
October 2011
Note: See also Clause 2.3.3.
2.3.2.3 Structural details
Members shall be designed to reduce the impact of environmental factors. Preference shall be given to structural details that provide free air circulation for all above-ground components.
Members shall be detailed to minimize exposed surface area and avoid pockets, crevices, recesses, re-entrant corners, and locations that collect and retain water, debris, and moisture.
2.3.2.4 Bearing seats
Bearing seats shall be designed so that contact with de-icing salts, salt-laden water runoff, leakage, and debris is prevented. The surfaces around and between bearing seats shall be sloped so that they are self-draining away from the bearings. Level areas for jacking of the superstructure for bearing replacement shall be provided.
2.3.2.5 Bridge joints
2.3.2.5.1 Expansion and/or fixed joints in decks
Wherever practical, expansion and/or fixed joints in decks shall be avoided or placed in the approach pavements. Where expansion joints cannot be avoided, they shall be detailed to prevent damage to components of the structure from water, de-icing salts, chemicals, and roadway debris.
End floor beams and end diaphragms under expansion joints shall be arranged to permit coating and future maintenance of surfaces that are exposed to surface runoff.
The end diaphragms of box girders shall be detailed to prevent ingress of water into the boxes.
The end diaphragms of slab-on-girder bridges shall be detailed to prevent water from expansion joints travelling along girders.
2.3.2.5.2 Joints in abutments, retaining walls, and buried structures
Expansion and construction joints in abutments, retaining walls, and buried structures shall be sealed at the surface that is in contact with the backfill to prevent damage to components of the structure from water, de-icing salts, and chemicals.2.3.2.6 Drainage
The longitudinal and transverse slopes on bridge decks and the number and location of deck drains shall be in accordance with Section 1.
Downspouts for deck drains shall be located in such a way that runoff water is discharged away from any part of the bridge. Downspouts shall extend at least 150 mm below adjacent members. Wherever practical, deck drains shall not pass through the box girders.
Box girders shall be made watertight at their ends and adequately drained so as to reduce the potential for moisture entrapment and accelerated corrosion.
Pockets and depressions that could retain water shall have effective drain holes or an alternative means of drainage.
Measures shall be taken to prevent erosion from the discharge of drainage water.
2.3.2.7 Utilities
All permanent iron and steel utility supports, fittings, and accessories shall be coated or galvanized. Utility supports shall be designed to prevent stray electrical currents between the structure and the utility supports.
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(Replaces p. 35, November 2006)October 2011
be designed to prevent the entry of birds and other animals.
2.3.2.9 Access
Access for maintenance and inspection shall be provided for all components of the structure.
2.3.2.10 Construction
The quality of the materials, placement procedures, and construction details shall be specified on the Plans. The testing and acceptance methods required at the site for quality assurance of materials and
construction shall be specified on the Plans.
2.3.2.11 Inspection and maintenance
The design of bridges and other structural components shall be predicated on routine inspection and maintenance procedures being instituted.
2.3.3 Structural materials
The designer shall review the environmental conditions and deterioration mechanisms for the material used and shall apply the following durability requirements to achieve the design life of the structure: (a) for concrete: Clause 8.11;
(b) for wood: Clause 9.17;
(c) for steel, including steel components of bearings, expansion joints, light poles, overhead sign supports, soil-steel structures, deck drains, and railings: Clause 10.6;
(d) for fibre-reinforced structures: Clause 16.4 and Annexes A16.1 and A16.2; (e) for aluminum: Clause 2.1; and
(f) for other materials: Clauses 2.5 to 2.10.
2.4 Aluminum
2.4.1
Deterioration mechanisms
The deterioration mechanisms to be considered for aluminum components shall include, but not be limited to, corrosion. More information can be found in Clause 17.6.
2.4.2 Detailing for durability
2.4.2.1 Connections
Aluminum components shall be connected by welding, by stainless steel bolts, or by high-strength steel bolts galvanized in accordance with CAN/CSA-G164.
In hot and very humid conditions, the surface between the galvanized bolt and the aluminum shall be coated with paint or bitumastic materials.
2.4.2.2 Inert separators
Inert separators shall be provided where aluminum components are in contact with other metals (except stainless steel) or concrete.
(Replaces p. 36, November 2006)
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November 2006
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2.6 Polytetrafluoroethylene (PTFE)
PTFE surfaces in contact with stainless steel shall be free of dirt to prevent excessive friction.