London Underground Library

Civil Engineering – Bridges and Structures Assessment Standard - Issue A5
 N S1061

Annotation

Purpose

The purpose of this Standard is to set down the requirements for the assessment of bridges and structures assets owned by London Underground, and which are not known to have been designed to loading standards equal to or in excess of current standards, and/or those structures thought to have a reduced loading capacity as a result of deterioration, damage or increased imposed loading

This standard shall not be used for the assessment of structures carrying the public highway. Section 117 of the 1968 Transport Act sets down London Undergrounds duty in respect of bridges carrying the public highways and owned by LU. This duty is

That in constructing or reconstructing a bridge that on completion will belong to LU to ensure that it has the required load bearing capacity

To maintain and improve or strengthen any bridge belonging to LU so that it has the required load bearing capacity

The capacities were not specified in the Act but published later in Statutory Instrument No 1705 entitled Highways England and Wales The Railway Bridges (Load – Bearing Standards)(England and Wales) Order 1972. This Order set two standards, an assessment standard defined in DoT Technical Memorandum BE4 for existing bridges and a design load (HA loading) set down in BS153 for new bridges. In 1984 the DoT issued an assessment code for highway bridges (BD21/84). This has since been revised

Therefore bridges built before 1968 shall first be assessed to BE4 and then reassessed to BD21. Bridges built after 1968 if requiring assessment shall be assessed to BD21

Road bridges which do not carry a public road (Accommodation and Occupation bridges) need only be assessed for 3 tons GVW for bridges built before 1903 and 5 tons GVW for bridges built after 1903 unless there is a specific legal agreement to carry a higher load. Thus BD21/01 shall be used for assessment purposes, but only to determine the structures’ capability of carrying 3 ton or 5 ton GVW. Accommodation and Occupation bridges must always have their safe load capacity prominently displayed on signs at each end of the bridge