Column Buckling Test

Topics: Buckling, Column, Compressive stress Pages: 10 (2175 words) Published: July 6, 2015
﻿Higher Certificate in Civil Engineering
Subject: Structural Analysis I - Laboratory Report
Laboratory Venue: HKIVE (Tsing Yi), Room CL02
Date & Time: 15 October 2001, 19:00 to 20:15

Experiment No. 1: Column Buckling Test

Objective:

1. To study the effect of support conditions on the load, carrying capacity of a slender column. 2. To compare the experimental buckling loads Pcr of test specimens with those predicted by the Euler equation.

Apparatus:

1. SM 105 strut apparatus (Issuing Voucher: 0203141 & Inventory Ledger: CN/s/01/10), 2. Aluminum bar specimen (20 x 3 x 600 mm approximate),
3. Measuring ruler,
4. Venier caliper.

Theory:

A long thin homogeneous column, axially loaded, suffers no deflection as the load is gradually applied until a critical load (the collapsing or buckling load P) is reached. At this load, instability occurs and the column buckles into a curve. The curve of Fig. 2 is not the arc of a circle, and Euler found (with the aid of the calculus) that the buckling load P gets less as the slenderness of the column increases. Euler’s formula is not used for design, since (except for very long columns) it gives a value of the collapsing load which is much higher than the actual collapsing load of practical columns, but it still forms part of modern column formulae. The values of permissible compressive stresses for struts are the product of the grade stress and modification factors appropriate to given conditions of services. It should be noted that the slenderness ratio the length of the column was qualified by the term ‘effective’. For the purpose of calculating the slenderness ratio of columns, an effective length should be assumed. This effective length can be defined as that length of the column, which is subject to buckling. The reason why the effective length of a column may be less or greater than the actual length in a building or structure is as follows. The safe compressive stress for a column depends not only on actual length and cross-sectional dimensions of the column but also on the manner in which the ends of the column are restrained or fixed. The Table A has been derived for one conditions of end fixing (both ends pinned or hinged).

Table AEffective length of column
Type of ‘fixity’
Effective length of column

BS 5950, BS 5268
BS 8110
1) Effectively held in position and restrained in direction at both ends. 0.7L
0.75L
2) Effectively held in position at...

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