Composite Sleeper Index (CSI) requirement for bridge sleepers For wooden sleepers used over bridge girders, what is the minimum Composite Sleeper Index (CSI) typically specified to ensure adequate strength and durability?

Introduction / Context:
The Composite Sleeper Index (CSI) is a numerical index that combines key properties of timber (like strength, durability, and resistance to decay) to rate suitability. On bridges, sleepers face concentrated loads, vibration, and exposure; thus, a higher CSI is mandated for safety and longevity.

Given Data / Assumptions:

• Application: timber sleepers over bridge girders.
• We seek the minimum CSI threshold typically specified.
• Bridge environments impose more severe loading and exposure than plain track.

Concept / Approach:
Higher CSI sleepers perform better under repetitive impact and variable moisture conditions prevalent on bridges. A minimum CSI of about 1455 is commonly stipulated to ensure that only high-quality timber species are used for bridge sleeper applications.

Step-by-Step Solution:
Recognize increased demands on bridge sleepers: impact, limited ballast, exposure.Apply the index threshold commonly used for bridge service.Select CSI ≥ 1455 as the minimum requirement.

Verification / Alternative check:
Procurement and design guides list higher CSI requirements for bridge sleepers than for ordinary track, with 1455 cited as a typical minimum.

Why Other Options Are Wrong:
1355, 1255, 1155: Suitable for lesser-duty applications; inadequate for bridge loading and exposure.None of these: Incorrect because a recognized minimum exists for bridges.

Common Pitfalls:

• Selecting sleepers fit for plain track but not bridge duty, leading to premature failures.
• Overlooking treatment and seasoning, which also affect long-term performance.

Final Answer:
1455