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From: kas@hpcvia.CV.HP.COM (ken_scofield)
Newsgroups: rec.skydiving
Subject: Re: BASE and Bungee
Message-ID: <42640007@hpcvia.CV.HP.COM>
Date: 15 Apr 91 15:40:51 GMT
References: <2756.28075041@ehsnet.fidonet.org>
Organization: Hewlett-Packard Co., Corvallis, Oregon
Lines: 103

From: SKYDIVE@f15.n233.z1.FIDONET.ORG (SKYDIVE)
Subject: BASE and Bungee
Message-ID: <2756.28075041@ehsnet.fidonet.org>

>   This is just a mental excercise, and I am asking if 
> any structural engineers or architects out there would 
> like to help me. 

  I'm not an architect, but as a mechanical engineer, I can give some
  generalizations...

>   I am just dreaming about building a special purpose 
> platform dedicated to bungee jumping, and BASE jumping 
> (jumping with a parachute). Here's a very rough sketch. 
>     
>        /-I-\             I-\           ^
>       /  I  \            I  \          |
>      /   I   \           I   \         |
>     /    I    \          I    \        | 500-600'
>    /     I     \         I     \       |
>   /a     I     a\        I     b\      V
>    
>      front view          side view
>    
>    All I have so far, is a 3 legged structure, with a 
> platform on top, and the platform is 500' to 600' off 
> the ground, and capable of holding 2,000 lbs of people 

  Compared to the weight of the structure itself, this load is peanuts.
  Your main concern will be to make the structure sufficiently strong to
  support its own weight.  I suspect each leg would weigh several tons,
  so a few hundred extra pounds per leg is negligible.

> and equipment.  The 2 front legs are in the vertical 
> plane, with the 3rd back leg at a sharper angle. This 
> would give 180 degrees of freedom for parachute (BASE) 
> jumpers. The platform would have a railing. 
>    I envision the platform being 10' wide by 6' deep. 
>    To make the structure safe for parachute jumping, 
> there shouldn't be any guy wires.  All 3 legs would 
> consist of 3 or 4 bars or angle beams with cross-
> bracing.  Sorry, I don't know the technical terms. One 
> leg would have steps with hand railings on both sides 
> for access to the platform. 
>    I don't know what angle "a" should be.  I am 
> guessing somewhere between 60 and 45 degrees. I'm 
> hoping 60 degrees would do. I also have no idea what 
> angle "b" should be for the 3rd leg (that leg is in a 
> plane perpendicular to the plane of the front 2 legs.) 
> I'm guessing 45 degrees. 

  In general, you want all of the angles to be as large as possible (i.e.,
  approaching 90 degrees.  In fact, just about the only force you are
  designing for, other than the structure's own weight, is wind loading.
  Anything that is several hundred feet tall is going to have substantial
  "sail" area.  (To over-simplify a bit, in a perfectly calm environment, the
  ideal solution to your problem would be a giant flagpole, not a tripod.)
  It's impossible to give you the "best" angles to use without actually
  doing the complete design, because the design determines the amount of
  wind drag which will occur, which in turn affects the angles needed.
  But, using the Seattle Space Needle as an example, it's obvious that the
  angles can be near-vertical.

  Perhaps a bigger issue is how much lateral movement a bungee jumper would
  experience due to wind.  While near-vertical legs would be sufficient to
  support the structure, a rebounding bungee jumper in a crosswind might
  end up colliding with a leg.  Something to think about.

>    We would also need to take lightning protection
> devices into account.

  A) Anyone on the tower in a lightning storm deserves what they get... ;-)
  B) With a sufficient ground rod attached, lightning isn't going to hurt
     the tower.

>    Would anyone like to help me on this dream project
> with some figures for dimensions, angles, kind of
> steel to use, how deep to sink the cement footings and 
> estimates for cost of materials and labor.  Like I 
> said, this is just a dream project. But with people 
> paying up to $90 for a bungee jump, and lots of base 
> jumpers looking for legal jumps, this project just 
> "might" become reality some day.  

  The real answer to these questions is this:  You're going to have to get
  permits to build something like this, especially if it will be open to 
  the public.  The powers that hand out such building permits will demand
  that you have card-carrying engineers design the structure -- at no small
  expense.  Any "free" advice you get from me or anyone else is worth what
  you paid for it.  (Sorry if I'm raining on your parade, but nothing is
  ever as simple as we'd like it to be.)

> * Origin: The Drop Zone, Dave Appel, 1:231/30.30 (Quick 1:231/30.30)
>--  
>SKYDIVE - via FidoNet node 1:233/13    (ehsnet.fidonet.org)

                 Ken Scofield           C-9355  SSI #453890085
      ^          Hewlett-Packard, ICO   Phone:  (503)750-2426
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