scope:

INTRODUCTION TO STANDARD DESIGNS AND DETAILS

The development of the Standard Designs and Details (SDD) has been taken by Network Rail to improve safety, asset reliability and increase efficiency. Their development is linked to Network Rail's overall business objectives, to improve reliability of the railways and reduce the funding requirements for the on-going management and maintenance. The basis of the SDD focuses on two main areas that derive from these issues:

· Ensuring that the design meets Network Rail's requirements

· The design is as successful as the designs of previous railway engineers, who built and maintained bridges that have given good service for approaching 150 years

Network Rail's Requirements

Network Rail's requirements are split between two areas, delivery, and function:

Delivery Requirements

The SDDs have been taken to a stage where Form As and Bs for each aspect covered (underbridge design, ancillaries etc.) have been submitted and approved. This leads to the following benefits:

· A reduction in the design development timescales and costs.

· Minimising contractor and sub-contractor costs associated with uncertainties in detailing requirements.

· Streamlining the technical approval process for commonly used designs and details

Functional Requirements

The SDD have been designed to ensure satisfactory performance of the asset under both normal operations and abnormal operations (both planned and unplanned). A further consideration has been Network Rail's requirement to reduce the volume of maintenance and management costs through the adoption of good practice. This leads to a number of key design drivers including:

· Failure modes: Critical failure modes should give warning, and alternative load paths should be provided for potential local failures.

· No hidden details: All main structural elements should be visible from at least one side.

· Robustness: It is desirable for elements of the structure to have a degree of robustness so that they are not damaged by unforeseen events disproportionate to the cause.

· Capability to support load.

· Safe working environment: The bridges have been designed to minimise the risk to people on or about the bridge.

These functional requirements are requirements of draft Network Rail standard NR/L2/CIV/020. Draft 012 of this standard has been used and the requirements therein met in designing the details for the underbridge ancillary items.

A library of standard designs and details for ancillary items to be used in conjunction with half through underbridges has been produced. This document contains guidance on the use of these standard drawings, including advice on the following:

· The elements and options contained within the suite of standard designs and details.

· Instruction on configuring a design using the standard designs and details

· Specific design restrictions and design assumptions

· Installation guidance

· Safety/CDM/environmental issues

· Safe by Design Principles (SbD)

The library will be maintained and distributed by Network Rail to its stakeholders and key external suppliers for adoption across the network at a national level