# Generally columns which are the short wide

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Chapter 32 / Exercise 32-21
Fundamentals of Analytical Chemistry
Skoog/West
Expert Verified
Generally, columns which are the short wide compressive members tend to fail by the material crushing and struts are the long thin compressive members that tends to fail by buckling. When a strut buckles, it will no longer be carrying any load and will simply continue to displace, ie, it will continue to buckle, its stiffness will become zero and will be useless as a structural member. 2.0 Background/ Theory The aim for this experiment is to investigate the effect of length of the strut of different end connections as the struts are loaded until they buckle. The 3 different type of connections used in the experiment are pinned-pinned connections, pinned-fixed connections and fixed-fixed connections. The buckling load is measured and can also be predicted using the Euler bucking formulae. P E = π 2 EI L 2 According to the equation, buckling load depends on the Young’s modulus(E), second moment of area (I) and the length of the strut(m). The relationship can be seen that buckling load is the greatest (buckling less like to happen) if the strut is made of strong material, has a large section geometry and is short in length. The slenderness ratio which is the ratio of the length of the strut to its radius of gyration( l/k) is critical to the use of the Euler formulae. This means higher slenderness is undesirable as it is more susceptible to buckling and the element can take a lower load. Hence for struts with a l/k ratio of less than 125, the Euler formulae becomes inaccurate and should be taken account into any design work. In this experiment, the struts provided have an l/k ratio between 520 and 870 to clearly show the buckling load and deflected shape of the struts. The practice struts with the ratio of more than 200 are of little use in real structures.
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Chapter 32 / Exercise 32-21
Fundamentals of Analytical Chemistry
Skoog/West
Expert Verified
3.0 Experimental Procedure 3.1 Experiment 1: Buckling Load of a Pinned-End Strut 1. The bottom chuck is fitted on the machine and the top chuck is removed from the machine. The shortest strut, number 1, is selected and its cross section is measured with the Vernier provided. The second moment of area, I, is then calculated 2. The position of the sliding crosshead is then adjusted to accept the strut by using the thumbnuts to lock off the slider. We would then ensure that there is maximum amount of travel available on the handwheel thread to compress the strut. The locking screws are then tightened. 3. The handwheel is backed off carefully to ensure that the strut is rested on the notch is resting on the notch but not transmitting any load. The force meter would then be rezeroed by using the front panel control. 4. Load is carefully placed on the strut. If the strut begins to buckle to the left, “flick” the strut to the right and vice versa. This step would help reduce any errors associated with the straightness of the strut. After this, the handwheel is turned until there is no further increase in the load. For this, the handwheel might peak and then drop as it settles into the notches.