Numbers numbers numbers!

Amy Kordosky our super engineer in San Francisco delivered this intense 173 page document of numbers! This is the start of our FEM Finite Element Analysis which will help us determine the appropriate steel sizes and thicknesses, number of ground screws, strength of wire rope required, and many other details of the design. Different kinds of loading, and wind testing is also applied. Overall it means the structure won’t fall down or collapse when Mayan Warrior pulls up to play next to it.

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  1. Columns: Members 1-7, sized as 5” diameter tubes, 3/8” thick. Material is A500 Grade B steel (Fy=42ksi)

    1. Max compression: In member 1 (middle column): 31 kip (compression)

    2. Max moment: In member 2: 0.35 kip*ft

    3. Member capacity: Compression = 38 kip, Moment = ~25 kip*ft

Demand-to-capacity ratio = 31/38+.35/25 = 0.83 (< 1.0, okay)

  1. Wires: Members 8-113, sized at 3/8” diameter. Material is A416 Grade 270 (Fy=270ksi)

    1. Layout: Currently have 3 wires connecting each rock to the columns and/or ground. Also, I have each rock connected to its neighboring rock with a wire (I did this for stability in the model. I don’t think we will need to connect every rock, but I do think connecting some to each other might be helpful. I still need to explore what wires are really needed, and plan to do this once I get the accurate model coordinates from Amihay. A fair amount of wires are currently shown to take no load, meaning they would be in compression, and not helping the structure).

    2. Max axial force: In member 10: 3.6 kip (tension)

    3. Member capacity: Tension = 28 kip

Demand-to-capacity ratio = 3.6/28 = 0.13 (< 1.0, okay – can downsize diameter or get weaker wire if loads stay this low with different wire configuration)

  1. Loads: 

    1. Dead load = self weight of materials + weight of rocks (assumed 1200 lbs.)

    2. Live load = weight of humans (assumed 500 lbs. on each rock)

    3. Wind load = 7.5 psf pressure, equates to ~ 47lbs. on each rock and 3.75plf along each column

  1. Base Reactions:

    1. Max Compression: 31 kips (joint 1- base of center column) 

    2. Max tension: 2.2 kips (joint 12)

    3. Max shear: 2.1 (joint 6)

Ben Langholz