Concrete springboard dive platform design

[DETstru]

I'm working on a project that includes a new dive platform for two springboards. Similar to the lower platform on the left and right of the large platform in this photo (

http://goo.gl/Ttglx3)

but with two columns instead of one. Also attached is a sketch of the platform (

http://goo.gl/2NLbCS).

I was previously made aware of the design loads and had no trouble with the initial concrete concept but now I'm being asked to verify the fundamental frequency of the platform. See the attached image from a design standard that was recently given to me by the "facility certification" consultant (

http://goo.gl/LeUKJ1).

[I don't know what to call the guy, he's basically are there to make sure the facility meets the national regulations for competition]

Does anyone know of references or methodology to do this by hand? I'm only in the DD phase of this project. If I have to tell them I can't do the design and have to defer to someone else I'm ok with that.

Thanks

 

[KootK]

I'd just tell them it will be fine as I'm certain that it will be. Your setup looks pretty stiff. When it comes time to submit "proof" you'll have a nice excuse to spend a couple of hours messing with an FEM model.

Alternately, you can approximate the thing as a simple propped beam and use methods similar to these: Link

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[DETstru]

Thanks KootK but the pdf doesn't seem to load.

I was a little surprised they wanted calcs because to me, this is one of those situations where it works "by inspection."

 

[KootK]

Well, I can understand asking for calcs eventually. Please try the attachment.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[TLHS]

Are they worried that the springiness of the concrete might significantly affect the bounciness of the board? I'm guessing this requirements is more to cover aluminum, steel or wood supports which will have less mass and more flexibility. See if you can get the exact criteria that you have to meet. Maybe you can prove that you're several orders of magnitude over the requirements without an in depth check.

 

[TLHS]

Presumably they want a high frequency in the support (low period). In that case, a single degree of freedom with your mass concentrated at the top would be a conservative check. You could do some hand checks of that case pretty easily and see if you're well within the bounds (you probably are). Just apply point loads in the various directions to work out spring stiffnesses and it's a one line calc to figure out the period of the system.

However, it depends on what they're looking for exactly. There are a bunch of different modes that could effect things. I'm guessing the critical cases to look at are vertical, horizontal and the moment case where you have a spring stiffness that resists moment at the base of the board. I'd have to think about how you apply the structure mass to that one to work out a conservative natural frequency. I haven't done rotational dynamics in a while.

 

[DETstru]

@TLHS
Yes, the requirement is to ensure the supporting structure doesn't alter the "feel" of the standardized springboards that are used for competition. These structures are almost exclusively made of concrete and there are some pretty unique designs at the large international venues. Check out this interesting design from the London Olympics:

https://goo.gl/VBXHn8

@KootK
Thanks, that attachment worked. Oddly it only loads on Internet Explorer (not on Chrome).
Though I haven't gone through it in detail it appears it has what I need to put a complete (looking anyway) set of calcs together. I was trying to rustle up a document like this from my old dynamics class years ago but it still eludes me. I'm sure I'll find it tomorrow morning after I no longer need it...
Based on the what I've seen for these types of structures I have no doubt that mine will meet the requirements so it's just a matter of appeasing the client's consultant. Thanks for the help.

 

[BUGGAR]

I presume these are prestressed concrete? What will you use for your rigidity values?
This looks pretty sophisticated.

 

[DETstru]

BUGGAR, it's all cast-in-place.