beamcolumnpergola
I'm planning to replace some rotten beams on a free-standing pergola. What is the best way to attach them to the top of the existing columns? The columns are hollow squares made of 3/4" boards with a flat cap (made of a 1/2" board with flashing). The beams are 1 1/2" thick. I can't tell how they're currently attached – maybe just toed in, which doesn't seem very sturdy to me. I'm thinking of using Simpson Z-Max hurricane ties, but is there a better way that will look nicer?
It's impossible to suggest a proper structure without much more detail about the existing deck structure. A solution is very likely available, I just can't say what it is. Here's some structural issues that must be addressed to be successful.
The weight of the added structure must be properly transfered into the deck structure. Plus some live load for accumulated snow or simply added safety factor. The weight cannot overload any existing structure or joints, nor the foundation system.
The added structure must resist lateral loads from wind and possibly seismic factors without racking. The railing posts could be adequate, depending on how they tie into the rest of the structure. If not, employ knee braces at every post to resist lateral loads.
You are basically building a parachute. All connections must be tied together so that this thing cannot possibly be blown away in a wind storm. Ties must be employed to transfer uplift loads from the roof all the way down into the foundation. If the existing deck connections do not provide this, they must be reinforced.
You can easily span 12' with a 2x12 for a pergola as long as your load is not crazy. What is going on top of the 2x12's? 2x2's? I would set my posts on 12' centers and cantilever 4' on each side. I would also sandwich a 2x12 on each side of the post. There actually is enough information in your question but there are many online beam span charts. Here is one. Hope it helps. Make sure there is no earth to wood contact on your posts and you will enjoy your pergola for decades. http://www.decks.com/deckbuilding/beam_span_chart_table
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