Local buckling failure

Allowable stresses. The maximum stress is the compressive stress at the tangency of the large knuckle and the cone. Failure would occur in local yielding rather than buckling therefore the allowable stress should be the same as required for cylinders. Thus the allowable circumferential compressive stress should be the lesser of 2SE or Fy. Using a lower allowable stress would require the knuckle radius to be made very large— well above code requirements. See Reference 3. 

The terms buckling and collapse are often used interchangeably. Buckling is defined as localized failure caused by overstress or instability of the wall under compressive loading. Collapse is a general failure of the entire cross section by flattening due to external pressure. 

Figure 15.2 Compression damage of fiber composites through microhuckling. (a) Undulations of buckled fibers (b) kink band local failure schematic and (c) micrograph of kink hand formation in a T800/924C carbon-fiber composite [6].

Spatz, H.-CH., and T. Speck. 1994. Local buckling and other modes of failure in hollow plant stems. Biomimetics 2 149-173. 

The failure mode at aU temperatures is shown in Figure 5.13. A local crashing was observed, which did not change significantly with temperature. As the resin became softer at higher temperatures, the damaged zone was smaller than at lower temperatures. The failure mode at 20 °C was similar to that observed in [21] for similar specimens, where the mode was identified as local buckling. 

Specimen SLCOl/02 did not fail after 90/120 min, when experiments were stopped. The noncooled specimen SLC03, however, failed after 57 min. Post-fire inspection showed delamination cracks at the web-flange junctions and local buckling at the compressed upper face sheet and webs (see Figure 7.7). In order to understand the failure mode, the shear stress at the web-flange junction was calculated as follows ... 

Local buckling (short column failure mode)... 

It was hoped that frame failure would initiate in the connections. However, it appears that initial imperfections (identified in a cross-section dimension survey reported in reference 5 promoted local buckling in the beam compression flange which eventually resulted in cracking of the web-flange junction at mid-span before the moment capacities of the beam-column joints were exhausted. 

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