A funny coincidence happened this evening. My husband and I were
walking down the main street of our old mining town in the mountains,
and I suddenly noticed a pergola recently constructed in a small park
out of 8x8 timbers! The vertical posts were old 8x8's, with 8x8 cross
posts on top. The vertical posts were fastened to cross beams by
custom-made, thick, steel connecting plates. The design was very
similar to what you are describing, though the entire structure was
shorter and did not branch out into a Y.
Your design sounds interesting and unique. I have compiled a number
of resources that cover various aspects of pergola construction which
should help you figure out the basics. While they are not specific to
your "Y" design, they all offer valuable information for the methods
used to build pergolas of different types. Almost every design I have
seen connects the post with a lengthwise cross beam - however, just
ignore that aspect if you will not be considering that type of design.
I still have not figured out whether you are planning to put any beams
or lattice work on the top of the structure, but if so, you can see
how that is accomplished in some of the following plans.
While most designs offer different dimensions for the cross beams, a
6x6 can certainly be supported by two 6x6 vertical posts. Note that
most of the articles recommend placing the vertical post in a 3' hole
filled with cement.
There are some edge-cut designs for the end of the crossbeams in the
following articles, as well as different methods of fastening the
elements. Since I don't know how fancy you want to make your pergola,
I thought you might want to look them over.
One consideration for fasteners is a to use a couple of long lag bolts
down through the top beam into the vertical post. Another
consideration might be Simpson column caps for 6x6's, which are a very
common connector that can be found at Home Depot or large hardware
Again, since your design is very simple (with no lengthwise
attachments and apparently no lattice work or structure on the top to
connect the individual components of the pergola), the following
articles will simply provide you with some basic construction
information. Or, in the event that you see something else you like,
you might decide to alter your design a bit.
PERGOLAS - CONSTRUCTION AND DESIGN
"Pergola Construction." Paving Expert.com
A basic design and structural plan for a pergola. Shows a nice
design element for a cross member. Since you will not be joining the
structure lengthwise along the path, just ignore that feature.
"The first step in construction is to erect the posts that will carry
the pergola. The posts need to be concreted into the ground to a depth
of at least 450mm..."
(Alternatively, my contractor husband suggested a 3'depth for 6x6
beams, which would mean that you must purchase 12' beams to
accommodate the buried depth, if you want 9' posts above ground.)
* The article measures in millimeters, so here is a handy conversion
tool if you need one:
Step by Step Construction - Pergola
Scroll down page to Pergola.
From Ron Hazelton.com
Click on tabs for Overview, What You Need and Instructions. Noted that
this site also recommends digging a 3' hole for post placement. Note
also that they use 6x6's for the posts and 2x10's for the beams, but
6x6 beams should be fine.
"A Pergola, Perhaps," by Cliff Caron Building and Remodeling (2002)
If you are using lumber posts, plan on placing them in holes at least
3 feet deep and fill with concrete to guarantee a strong footing.
Brace the posts for plumb until set.
"Pretty Pergola," From the book, Home Landscaping
Building the Structure
Plans from GardenStructure.com
* You might want to look at the "Adaptable Design" Pergola. (Skim
through all pages)
Making a Pergola
From Design Lifestyle Gardening
Click through 6 pages, which includes materials, design and construction.
Making a Pergola
2 pages of simple instructions that can be modified to your own design.
Build Your Own Pergola
Short article with some advice.
Building Overhead Structures, Pergolas and Arbors
Home Improver Guide 8 - TIMBER PERGOLAS
Cedar Pergola Details
Pergola pictures from Fine House.net
A crude pergola made of logs
A simple Pergola
"Australian Deck and Pergola Construction Manual," by Staines, Allan
"Better Homes and Gardens mini workbook series "Building Pergolas."
I hope this information is helpful. If you have any further
questions, please don't hesitate to ask. I will be happy to help if I
Google Search Strategy
constructing a pergola
simpson nail plates
simpson column caps