Teardrops n Tiny Travel Trailers

QueticoBill wrote:I'd suspect the 3/4" ply sides would provide all the vertical support necessary, but would worry about any lateral movement (strong wind even) and if there was any risk of the walls "folding". May not be. Its just if walls are not vertical and load is pushing them to lean at all.

My concern is the wood and lag bolts holding the weight of the rooftop tent and two or three people.

Is there a way to run a regular bolt through that blocking? It'd be much stronger. I assume the block is glued and screwed?

Tony

I haven't installed the roof so I could run a bolt through.

tony.latham wrote:My big concern would be the zero-dark-thirty trip down that ladder. I'm talking night terrors.

My concern is the wood and lag bolts holding the weight of the rooftop tent and two or three people.

Is there a way to run a regular bolt through that blocking? It'd be much stronger. I assume the block is glued and screwed?

Tony

• I'm also looking to add extra bracing to my 3/4" walls, both for making a roof rack support, later on, and an inner brace/weight support for the interior (I need to make an overhead lift "trapeze", since I have trouble getting out of bed- can't roll out!) My roof is bolted/glued directly on top of the walls, and needed no spars to support it, as it is well-supported all-around, and is of small overall size. I want to retrofit a 4x4 spar/beam , glued to the roof with PL Premium, and using long lag bolts to affix it to the walls. I'll cut it to 46.5" long (wall-to-wall dimensions), carving out a 2" wide center space (so it will fit over my central light bar on the ceiling), and using eye-bolts to tie my lift rope to (soft, braided 3/8" marine rope). Of course, painted to match the decor! You might consider something similar, though it might be better to lower the beam's height (as low as you could), to make a stronger bracing structure.

• 

  BRACING PROPOSAL.png (23.83 KiB) Viewed 2381 times

• My modification? to come

• 

  trapeze-bed lift proposal.png (245.97 KiB) Viewed 2381 times

Aguyfromohio wrote:

QueticoBill wrote:I'd suspect the 3/4" ply sides would provide all the vertical support necessary, but would worry about any lateral movement (strong wind even) and if there was any risk of the walls "folding". May not be. Its just if walls are not vertical and load is pushing them to lean at all.

I think you have that exactly correct. Back in statics classes we called it "buckling".
Like any column, the side walls are tremendously strong in pure compression.
The trouble starts when a bit of sideways movement sets in.


It's hard to quantify, that what the class was teaching us, Euler's formula and all that.

If the coach is solidly braced at the front and back bulkheads, with a strong corner connection at top and bottom to make a stiff box, it might be OK.
When there's two adults in the tent and one hornet flies in, things could get bouncing around pretty badly.

QueticoBill wrote:I worry about the gust of wind more than the hornet or some nocturnal activity.

djohnsonnv wrote:An erected RTT will add additional lateral wind loading. Lateral resistance isn't hard to overcome with a rigid skin and bulkheads. This is demonstrated by the cheap IKEA/Walmart bookcases. These bookcases will fall right over without backing yet becomes fairly sturdy when a thin sheet is applied to the back. IMO a solid skin will provide better resistance than blocking or bracing.

Also buckling wouldn't come into play. Buckling is a failure that occurs when the supporting member is overcome by the internal stresses. This occurs when very thin members have very large spans. I would elaborate further but also had a hard time staying awake during structural analysis.

KCStudly wrote:I'm with Tony. The typical TD box with good construction, bulkheads and cabinetry is probably going to be more than rigid enough. It's those pesky lag bolts that worry me. Not the first time, probably not the fifth time, but into soft wood, probably won't last forever before wallowing out.

Not an apples to apples comparison, but case in point, the pumpkin chunkin rules were updated a few years back to disallow lag bolts. Too many wooden catapults were falling apart when their lag bolt joints wiggled apart.

Through bolts with washers or T-nuts won't pull out.

• You're very aware of the different forces involved in the simple stresses a RTT would place on fasteners, compared to the violent actions of a punkin-chunker (trebuchet, for instance); the RTT lies flat on the trailer roof, with the most prevalent forces pushing directly downward on one wall, while possible lifting up on the other wall (mainly shearing forces), while the trebuchet will be torquing the supporting framework in a twisting manner, while storing/releasing energy. Unless the RTT is going to be storing/releasing tremendous energy, I don't see how deeply inserted lag bolts (say, 1/2" diameter, inserted at least 4" into the crossing 4x4 bracing/support beam), would be subjected to any such twist. It has already been determined that the usual monocoque box structure of a TD or TTT (especially of 3/4" plywood walls, like mine has) is quite resistant to torque or twist. The RTT platform on top could not impart as much force as the chunker, for sure. Here's a table illustrating the pull-out force needed to defeat the lag bolt in a non-twisting structure (the shear strength would not be a factor, but anyway, the shear strength of a 1/2" lag bolt is far in excess of the downward/upward stresses-there are none, really- imparted from the walls to beam interface).

• 

  Lag-screw pull-out strength chart.PNG (82.58 KiB) Viewed 2274 times

  1/2" lag x 4" insertion depth = 1748 lbs force needed to pull-out of Southern Pine
• The usual 4x4 I encounter around my home is Southern Pine, which I plan to glue and lag-bolt to use as a spar/bridge beam for my lifting "trapeze". I now for sure, from experience how strongly the PL Premium will hold, and the lag bolts will just be for insurance against adhesive failure (with my luck, I can just see a 4x4 crashing on my head).