Samsul,

You don't score brownie points by quoting from a book, think about the question.

The fact is that the average pipe span (usually in chart form in individual companies) is based on the criteria I outlined, not frequency response. Span limits are based on an assumption of end conditions, usually around midway between fixed and pinned end. This is because the real spans may see either condition, depending on support and geometry.The aim is to cover all situations. Frequency response of a pipe span is greatly affected by end conditions, particuarly rotational stiffness and this would only be properly reflected in a Caesar dynamic analysis or similar.