Buckling

A. Introduction

All designated members are required to satisfy specific strength, deflection and stability requirements in order to ensure the safety of building occupants. Generally, mathematical analysis of a structure’s deflection and strength will assume that the members are always in stable equilibrium. In fact, some members may be subjected to compressive loadings, and if these members are long and slender, the loading may be large enough to cause the member to deflect laterally or sideway.

Specifically, long slender members subjected to an axial compressive force are known as “column”; while a “strut” is a component member which is designed to resist longitudinal compression. The lateral deflection that occurs is called “buckling”. Buckling of a component may lead to a sudden and dramatic failure of a structure. Hence, the design of columns has to be carried out meticulously. The maximum axial loads that a column can support when it is on the verge of buckling is called “critical buckling load”. Any additional loading will cause it to buckle and deflect laterally as shown in Figure 1.

B. Objective

To investigate the buckling behaviour of pin-ended struts.

C. Apparatus

1. Strut machine (Model SM105):

To measure the horizontal deflection at the mid-point of specimen by applying axial load to the specimen.

2. Micrometer:

To measure the breadth and the thickness of specimen.

3. Metre rule:

To measure the length of specimen.

D. Theory

The buckling behavior of a pin-ended strut is similar to the column. The strut is assumed to be ideal in this experiment based upon the assumptions of:

• The strut is initially perfectly straight before loading and the load is applied axially on the strut.

• Strut is made up of homogeneous, perfectly elastic and isotropic materials which does obey Hooke’s Law.

• The cross sectional area of the strut is uniform throughout its length.

• The length of strut is very large as...