Effective Length of Truss Members in Compression as per IS 800:2007

Introduction
In the design of truss members joined by welding, it is necessary to consider the effective length of the member in compression. The effective length depends on the degree of end restraint provided to the member. The Indian Standard IS 800:2007 provides guidelines for determining the effective length of truss members.

Definition
The effective length of a compression member is the distance between the points of zero moments in the member. It represents the distance within which the member can buckle laterally without any significant increase in the axial compressive load.

Factors Affecting Effective Length
The effective length of a truss member in compression is influenced by the following factors:

1. End Restraint: The degree of end restraint provided to the member affects its effective length. The end restraint can be classified into three categories:

- Fully Restrained: When the member is adequately restrained against rotation at both ends, it is considered fully restrained. In such cases, the effective length is taken as the distance between the points of zero moments.

- Partially Restrained: When the member is partially restrained against rotation at one or both ends, it is considered partially restrained. In such cases, the effective length is taken as the distance between the points of zero moments, subject to certain limitations specified in IS 800:2007.

- Unrestrained: When the member is not restrained against rotation at either end, it is considered unrestrained. In such cases, the effective length is taken as the distance between the points of zero moments, with a reduction factor applied to account for lateral buckling.

2. Member Geometry: The geometry of the member, such as its length, cross-sectional properties, and boundary conditions, also affects the effective length. Longer members with slender cross-sections are more prone to lateral buckling and may have larger effective lengths.

3. Loading Conditions: The applied load pattern and boundary conditions also influence the effective length. Different loading conditions may result in different effective lengths for the same member.

Determination of Effective Length
To determine the effective length of a truss member in compression, the following steps can be followed:

1. Identify the end restraint condition of the member - fully restrained, partially restrained, or unrestrained.

2. Based on the end restraint condition, determine the effective length using the guidelines provided in IS 800:2007. For fully restrained members, the effective length is simply the distance between the points of zero moments. For partially restrained members, there are specific limitations and factors to consider.

3. Apply the determined effective length in the design calculations for the member to ensure its stability and adequacy.

Conclusion
The effective length of truss members in compression, joined by welding, is an important factor to consider in their design. It depends on the degree of end restraint provided to the member, which can be fully restrained, partially restrained, or unrestrained. By determining the effective length accurately, the stability and adequacy of the truss members can be ensured, leading to safe and efficient structural designs.