Chapter 4: Design & Construction of Bridges & Major Culverts

Last Update: Dec 20, 2021

This chapter describes key activities and practices related to addressing safety, environmental , structural and professional responsibility issues in the design and construction of bridges, major culverts and retaining structures on Forest Service roads (FSRs). The topics covered include:

professional responsibilities and considerations;
design requirements and considerations;
types of structures;
site data and survey requirements;
estimating design discharge for streams;
construction drawings and specifications;
construction materials, quality assurance, and fabrication; and
statement of general conformance and construction documentation.

4.0.1 Definitions

Coordinating Registered Professional (CRP), Professional of Record (POR) and specialists are defined in the Guidelines for Professional Services in the Forest Sector - Crossings V.3.0.
Bridge means a temporary or permanent crossing structure carrying a road above a stream or other opening and includes a log stringer/gravel deck structure with i) a span length equal to or greater than 6 m or ii) an abutment height of 4m or greater.
Major culvert means a culvert i) having a pipe diameter of 2,000 mm or greater; ii) a pipe arch with a span greater than 2,130 mm; iii) an open bottom arch having a span greater than 2,130 mm, iv) has a design discharge of 6 m3/sec or greater. or v) is a log stringer/gravel deck structure (log culvert) with a span less than 6 m and a design discharge of 6 m3/s or greater.
Retaining structure means any retaining structure greater than 1.5 m high.
Portable bridge superstructure is a bridge superstructure that is designed and fabricated, in accordance with the Forest Service Bridge Design and Construction Manual, for ease of movement and installation.
Permanent materials: steel, concrete or treated wood.
Temporary materials: untreated logs or untreated timbers.
Permanent bridge is a bridge that has its stringers or girders and abutments comprised of permanent materials (even though it may have an untreated timber deck or untreated timber sills bearing on an abutment comprised of permanent materials). Rail car structures are an exception to the foregoing and will be considered a temporary bridge regardless of the abutment type.
Temporary bridge is a bridge that has its stringers or girders, or abutments, comprised of temporary materials.

The Ministry Bridge Guidelines, Standards and Specifications website provides further discussion on planning, design, and construction of forest road bridges.

Note: Log / wood box culverts, defined as those with gravel decks, spans less than 6m and abutment heights less than 4m, are covered in Chapter 3: Road Survey & Design and Chapter 5: Road Construction of this manual.