Amsler Universal Testing Machine Lab Report

An Amsler universal testing machine with a loading capacity of 300kN was used to load specimens in compression. The test set-up is shown in Fig. 2. Pin ended support conditions using ball bearing supports were used for all the specimens as described by Liu and Hui [7]. Each support consisted of two 10mm parallel plates with 30mm diameter stainless steel ball seated between them on sockets suitably milled into the plates as shown in Fig. 3. The geometric centres of both top and bottom loading plates were marked and aligned with the steel ball and the centre of the loading head. Vertical deformations and mid-height lateral deflections of each specimen were measured using three dial gauges.
Table 1 Test specimen details and results
3 Ball bearing support flexural buckling failure. S500-1A and S500-1B are identical specimens. These specimens were tested under similar loading conditions to verify repeatability of test procedures. Failure loads obtained with these specimens where 125kN and 122kN with a variation of 8%, which is considered to be within permissible limits. Therefore the test set-up and procedure were considered to be reliable.
5.1 Effect of eccentricity The effect of eccentricity on the load carrying capacity of single angles was studied with the help of normalised load P/Py vs e/x0 curves for specimens S500 and S1100 under compression causing both major axis and minor axis bending as shown in Fig. 4. The ultimate load was normalised with yield strength of specimens, Py and eccentricity was normalised with x0, the distance of centroid of the angle cross section from shear centre. Fig. 4 shows that specimens subjected to minor axis bending failed at considerably lower load than those subjected to major axis bending. Rate of reduction of ultimate load is more pronounced in the case of minor axis bending. For example, the rate of reduction of ultimate load for S500 specimen, when e/xo increases from 0 to 2.8, is 5.7% and 56% for the specimen subjected to major axis bending and minor axis bending respectively. The corresponding rate of reduction of strength for S1100 specimens are 6.15% and 23.8% respectively. At larger eccentricity ratios (from 1.4 to 2.1), the curves become flatter
5(a) indicates that there is a critical eccentricity associated with each slenderness ratio. Critical eccentricity points are shown with colourless markers. Critical eccentricity is the eccentricity limit within which there is no much reduction in the ultimate capacity of specimen. The approximate values of critical eccentricities for specimens S500 and S800 are 0.3xo and 0.75xo. For S1100 specimens no critical eccentricity was identified as the effect of eccentricity diminishes at higher eccentricities. There is no such critical eccentricity seen in the case of specimens subjected to minor axis bending. The above findings have also been reported by Liu and Hui [7] based on their experimental work.

(a) S500 specimen

(a) Major axis bending

5.3 Failure modes
The observed failure modes for the tested specimens were flexural buckling and torsional-flexural buckling. Specimens subjected to concentric loading, eccentric loading with small eccentricities and minor axis bending failed in flexural buckling mode. Specimens subjected to major axis bending failed in torsional-flexural buckling mode.
The two failure modes obtained are shown in Fig. 6. S1100-6 specimen was subjected to minor axis bending and failed in flexural buckling mode. S1100-4 specimen subjected to major axis bending with eccentricity equal to 15mm, failed in torsional-flexural buckling mode. Load vs mid height lateral deflection curves were made use of in the determination of failure