scope:

The guidance in this document may be used for the assessment of all underbridges and culverts required to be assessed under RT/CE/S/035, and is applicable for permissible speeds up to a maximum of 125mph for passenger traffic, and 75mph for freight traffic.

Recommendations for the assessment of underbridges constructed from steel, wrought iron, cast iron, concrete, timber, or composite steel/concrete construction are provided. Recommendations for masonry arches, substructures, bearings, and bridges with spans less than 2.0 metres constructed from natural rock are also included. Limit state principles are used for underbridges of steel, wrought iron, concrete and steel/concrete composite construction. Permissible stresses or allowable loads are used for other materials and forms of construction.

Where appropriate, guidance on the use of simple and more rigorous methods of analysis is given. Unusual forms of construction such as cable stayed, moveable or combined road/rail bridges are not specifically covered, but the principles outlined may be applied in checking the elements of such structures.

Requirements for the assessment of superstructures and supports under accidental loading conditions are excluded from this document, although the effects of consequential damage may be assessed using the Section appropriate to the material of construction of the bridge.

Purpose

The purpose of this document is to provide recommendations for applicable standards and analytical methods which may be used to determine the load carrying capacity of existing Network Rail underbridges. The load carrying capacity is determined in the context of the performance requirements of an underbridge. The requirements are that the bridge meets safety and serviceability criteria whilst regularly carrying rail traffic up to a level of traffic load and speed in accordance with operational system requirements.