Hi, I'm thinking about building a timber frame carport & my questions are: what are some good ways of dealing with exposing timber to weather? How does the open nature of the structure affect load calculating? Is it possible to build bents on other than hard level surfaces? Thanks!

Stern,
there are many commercial products for sealing/staining your timbers to protect them from the weather. talk to your local paint store for guidance. the same products would be used for log homes too.
what is you plan for the base of your carport, gravel or cement ? it would seem to me that this surface would be fairly level. while you are digging to establish the sub base you can also dig the holes for your post footers. using a csrdboard cylinder or pyramid form pour your reinforced post bases to extend above your average snow level. the map tells me you are at pretty high altitude so I suspect you have some significant snowfall. each of these pier tops would be at the same altitude so your posts bottoms will be in the same horizontal plane.
your uneven ground problem just vanished.
yoo can assemble your timberframe bents or wall sections on any temporary cribbing and raise them from there.
good luck, work safe
deralte

I am not an Engineer, so I am simply stating an opinion here.

It would seem to me that the open sides of your carport would improve the 'windload' effects because of the reduction in exposed surface area. On the other hand, the structure will not have the same strength because the siding or sheathing is missing. So figure to use bigger wood in there someplace to allow the joinery to strengthen the frame .

Just an opinion...

Thanks for the responses. Not a lot of snow where I am because it's high desert, lots of snow in the mountains above though (and a lot of wind). I was envisioning exactly what you describe, with sonotube piers above-grade and level.

With open sided structures uplift due to wind is an additional factor to be considered. Not only will the wind try to pull the roof off from above, it also wants to push it off from below. How much is dictated by your building code, local design wind velocity and type of exposure.
Good luck with your project.

Stern,
The responses talking about wind load causing a parachute or umbrella uplift are dead on.
Don't depend on $1.39 hurrican clips, they just keep the pieces together after the wind moves the roof someplace else.
You need really good connections between your post bottoms and their piers. If you lag screw the principle rafters to the top plate you help make the lift problem go away. (assuming good joinery between the plate and the posts). By all means include braces in each wall plane so racking is not a factor. Slightly oversize the timbers will add weight and stability. A pitch steeper than 6/12 has better down force characteristics than a common "garage" roof at a shallow pitch.If you enclose the gable end above the end wall plate be sure to put vents on each end at the peak to reduce the lift effect.

Stern

Re: Exposed timber

Detailed correctly the only members with serious rot potential are the posts
You may want to consider using a rot resistant wood (eg. west red cedar) for the posts. Cedar is suitable for posts (because they are in compression) but is not the best for spans.

Put gutters on the building! Brown rot fungus spores are in the soil and find their way to the building thru ground splash.

As mentioned use a sealer or paint to protect the wood. For purely practical purposes paint is a better protectant but it may not be the look you want. I would do this no mater what type of wood you use (but then I live in wood rot land)In fact I am remodeling my own house including some faceted porch posts (cedar) and plan on painting the lower 30" (above the 12" plinths)white and leaving the posts natural above that

Avoid details that extend other members beyond the roof covering or provide flashings to cover.

For any horizontal members that are exposed, make a drip cut to stop water traveling further into the structure.

Re: bracing

Emmett is quite right about bracing but there is an additional factor with carports in that the braces on the entry side can intrude into the entry space. This can be solved with hardware at post top and/or bottom or...braces in plane with the entry bent could run outside to an extended plate.
And look cool besides

Ultimately if you are not sure, you should run your lateral and uplift concerns by an engineer before building. If you are getting a permit (???) you probably won’t have a choice

And don't forget to have fun...

J.E.B.

Addendum

First let me say duhh!
When I read "protect from weather" my conditioned response was to read it as "protect from moisture"
But....you are in New Mexico, lots of sun, wind and way dry
That being the case, UV and drying are more your problems. Much of what I posted still apply but I would add that any clear finishes should contain a UV protectant and or use paint as opaque surfaces are the best UV protection
And take care to seal all end grain as this where most of the drying will occur. Actually it will all dry eventually but what you want is for the members to dry as evenly as possible along their length.

Ahem....

Thank you for all these great responses. I bumped into an engineer I know after I posted this and he also mentioned uplift. Turns out he has an interest in timber framing having recently worked on a historic national park timber lodge restoration/repair, so I will be picking his brain further. Again, thanks! -Stern