Temporary Hanging frame for picture frame - How To?

I am not too sure where to post this? MOD’S - please move if better elsewhere - thanks.
I have made a large oak “picture frame” or “photo booth” for a wedding (to match other wedding things I have made for this couple) which needs to be hung from a frame that is self supported and easily assembled by unknown staff of unknown intelligence and at an unknown wedding venue. The picture frame is made form 3/4 inch oak, to be hung from pine handrail by chain.

The attached image shows the concept.

Attachment 341236

The posts are 2m /79” tall and the top horizontal beam is the same wide.
I do not know the formula/ratio to work out how long/wide/heavy the base needs to be in order to accommodate this, i.e.: to stop the poles falling over. I intend to have the poles (handrail) slip into pre cut holes in laminated MDF by 12.5 cm/5”. The wedding venue will not allow sinking poles into lawn or to hang the frame anywhere, hence the need for this base - but how long/wide/heavy do I make it - any help in this calculation is gratefully received as it is a long time ago since I studied physics!

Thanks and kind regards, John

Will they allow spikes in the lawn? With 4 holes drilled at steep angles and spikes driven thru you would get good stability even if the surface area of the mdf is not enough. I have no scientific calculation, but would go with at least 18" front and back.

Your objective is to prevent the center of mass of the assembly from ever moving outside the rectangle shape of the base. If there was no chance of anyone bumping it, and no chance of wind blowing against it, it would be simple. But obviously you have to allow for bumping and wind and it is further complicated because the frame is on chains and will swing out if the stand it bumped, thus moving the center of mass out and encouraging it to topple.

Just guessing from your sketch, I'd say the center of mass as drawn is in the center left to right and near the top, up and down. If you made the base twice as heavy as all the rest of it, it would move the center of mass down to maybe 1/4 of the way up, say .5 meter from the ground. If the base was .5 meter front to back, you would have to tilt the assembly past 30 degrees before it would topple. (ignoring the swinging frame). That would probably be the minimum I would consider, and making it heavier or wider would improve the margin of safety.

If you can get by with long outriggers on the base without them being trip hazards, that would do a lot to make it really stable. Problem with that would be if the ground was uneven.

If you can make the base hollow and add ballast that would help a lot....concrete blocks or even gallon jugs of water would add a lot of weight.

And as Joe mentioned, a few spikes would also add a lot of safety margin.

Hi Joe & Paul,
Thanks very much for your input. I have gone around in circles on this design, the last thing I need is a lawsuit because of overconsumption of intoxicating fluids and subsequent leaning on a post :0 This is where the old Public Liability insurance could come into play!
Kind Regards,
John

I'm no engineer, but I would build , for the base, a small deck made out of kiln-dried cedar or cypress to keep the weight down. Then they could stand on it, & unless really drunk, people would notice that more so than just outriggers. It would be lighter than a 4x6 pallet ......

Hi Joe, Paul & Roger,

Just a note to say thanks for your advice. The project is now delivered and the customers pleased with it. I do not have any images at hand, but will get some up as soon as I can in case it is of use to anyone else.
Thanks again!