monsoon99-
I built an arbor a while back, and there are lots of good designs and pictures you can find with just a little Google searching. A couple of sites I found that helped me think about styles are: www.finehouse.net, www.baldwinpergolas.com, www.trellisstructures.com, www.gardenstructure.com, and www.brattleworks.com. There are others, but that should get you started.

However, I do have a concern, which is that steel brackets are not engineered to support freestanding structures like you are wanting to build. Such structures have a tendency to lean and even collapse over time due to various loads, including wind loading because they exert such highly leveraged forces on the brackets at the base. Unless you have adequate cross-bracing at the corners, you may have problems, particularly if you need to get a permit to build. If you look at the specs for those kinds of brackets they typically say that they are not intended to be used for freestanding structures like fences and carports. I'm not telling you not to do this. I'm simply saying to take this problem into consideration when you design the structure so you aren't unhappy in ten years when wind, rain, and the forces exerted by the grape vines start to cause it to twist and lean.

Thanks for your response Kudzu9. I am really concerned about your point regarding the brackets. Why would the hardscape contractor suggest these brackets if they are not meant for an arbor. Specially considering the dimensions I have, I can see how it could be a problem over time. Is there anything we can do to bolster the structure (other than the cross bracing at the corners). Any suggestions on the dimensions and material of the 4 posts to make sure they hold up this structure? Thanks.

Kudzu9: Follow up question: When you say cross-bracing at the corners, are you talking about the base where the bracket are or on the top corners of the pergola?

I would appreciate your input about the height of this structure as well. Thanks.

Normally, for the strongest free-standing structure like that, you want the 4 corner posts anchored in concrete. However, since that is not an option now, you can still make it sturdy by putting in corner braces at the top...these can be decorative and look just like you planned it in the first place! I've given you a link below to a style of pergola with corner bracing that looks very nice. Obviously, there are many styles that work equally well. However, using braces also argues for making the arbor a little higher so the leg of each brace is above head height. I made my pergola/arbor about 9-1/2' tall since I didn't want to feel closed in. If you went for something like 8'-9', any corner bracing or gussets should be well out of the way.

I would also say, for a structure of the size you are planning, that 6 X 6 posts would look the most pleasing. You probably have brackets that are made for 4 X 4's, but you can always notch out the base of a 6 X 6 so that it fits the smaller bracket. Just think of the brackets as being good for holding the structure in place and the braces/gussets as keeping it from leaning.

Some of those links I gave you before have dimensions, so you should just browse through and see what feels right for you. Good luck. I think you'll be fine if you just put in the effort to make the corners rigid.

P.S.: Regarding the contractor recommending the brackets: many people use brackets for these types of applications because it's easy and seems to make sense...until you think about the long-term consequences.

Here is a link that might be useful: Pergola

Thanks for your input Kudzu9. Your suggestions make perfect sense and I feel more comfortable going forward. I appreciate you taking the time to respond.