The dome had been constructed some 2 weeks prior. The mega hubs were all production ABS models made to specifications. The dome was fastened together using 2 ½” 8/32 Oval Head stainless steel machine bolts and matching nuts.
The platform was built of ¾” marine plywood 2’X 4’ dimension. Holes were drilled in the four corners and ½” eyebolts were secured with matching nuts. Chains were attached to the four eyebolts with stainless steel S-hooks and connected to a heavy duty carabiner, which itself was connected to a ratcheting come along with a nylon strap.
The platform assembly weighed 31 lbs. The nylon strap was wrapped over a hexagonal hub two dimensions out from the top center.
Once the platform was secured, paper boxes weighing 52 lbs. Each box was successively added to the platforms. First, 4 boxes were placed on the platform, then 6 boxes, then 7, 8 and 9.
8 cases – 447 lbs.
9 cases – 499 lbs.
After a few minutes at 9 cases of paper, the hub failed. In removing it from the structure, it was observed that the failures occurred at the bolt holes, where the steel bolts deformed the holes in an outward direction until two of the hub arms failed.
Test Results: The 6-arm mega hubs connectors can safely withstand a point load of 450 lbs. and will fail at around 500 lbs.
Ashok Chand Mathur
November 29, 2022
Next time you conduct a point load test, can you conduct a similar test at the Center of a strut?
When does it fail compared to Fea predicted failure of a strut?