scope:

INTRODUCTION TO STANDARD DESIGNS AND DETAILS

The development of the Standard Designs and Details (SDD) has been undertaken 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 on-going management and maintenance of the network. 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.

The use of the SDDs is promoted from the highest level within Network Rail. Alternatives to the SDDs will only be considered where it can be demonstrated that a SDD cannot be used and must be agreed with Network Rail's professional head of civil engineering. Failure to use a SDD may lead to project authority being withheld.

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 Forms A/B or Forms 001/002/003 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 provide 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. · Acceptable deformations.

· Structure gauge requirements: The underbridges have been designed to cater for a range of positions of the structure gauge allowing their wide use.

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

· Resistance to "bridge bash": The bridges have been designed minimise the risk of catastrophic failure in the event of a "bridge bash".

· Resistance to derailment: The bridges have been designed to cater for the codified derailment loads, as well as protecting the structure whilst mitigating damage to the surrounding structures

These functional requirements are requirements of Network Rail standard NR/L3/CIV/020. Issue 1 of this standard has been used and the requirements therein met in designing the standard U-type details.

A library of standard designs and details for a range of half through underbridges forms meeting these requirements 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.

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