Hi Swift Arrow...glad you found this place too…
I'm going to go through your post by the question you’ve asked and do the best I can with responding to each…...
First, I don’t wish to sound too critical at all, and I apologize if I sound that way even a little bit, but there is a lot about that frame that is not really “best practice” or even good design if we are speaking of a traditional timber frame…(nothing against your Uncle at all…So again, my apologies)...As validation, I have been designing natural architecture and historical architecture for a long time…I’ve been a working Timberwright for over 40 years and teaching the craft for the last 20 plus…I’ve also been working with the same team of PE (professional engineers) that specialize in timber framing only for almost 30 years when a project needs to have one…
In the current design the 2’ oblique “elbow brace does not add any great rigidity to the frame and because of its small size actually are creating a fulcrum effect to the joinery intersection they are near…This is a common sign that someone is putting braces into a wall diaphragm for either aesthetics or “they think” that the wall needs them…You will note that the oldest timber frames in the world are found in China, Korea, and Japan (not Europe)...virtually none of these have oblique bracing in their wall systems with Japan having the oldest and tallest without them, and it is subjected to earthquakes on a regular basis…The reason they don’t is…” oblique braces”...do fail and it is a catastrophic failure when it happens because most only work in compression rather than as a strut that works in both. To achieve that with a brace it must be “let in”...which is typically a “dovetailed brace”
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>“...I just got off the phone with our building inspector who I called to ask about the required anchors, and learned that there is no prescription for timber framed structures and I need to have the design calculations done…”
You do not have to share, of course, your exact locations, but a general location would be interesting because I have never heard of “outbuildings”... especially ones that are being replaced and “grandfathered in” and even need any kind of permitting at all…That is suspicious and I have dealt with many building departments around the country…They do make mistakes…
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>“...So my question here: how do I go about this? I'm an engineer, but not a professional engineer, so I can't stamp drawings. I can do the calculations however was unable to find a clear reference for strength and formulae in the IBC. I'd honestly love to do it myself as a PE stamp isn't required in my town…”
If you're looking for a basic book get both:...” ADVANCED TIMBER FRAMING: Joinery, Design & Construction of Timber Frame Roof Systems,”...by Steve Chappell
You can also join the Timber Framers Guild and reach out to the...Timber Frame Engineering Council (TFEC.)
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>“... I'm familiar with CAD and could use this if it would do the trick, what is the general recommendation here?...”
Most of the frames that we have remaining from history (and there are thousands of them) would not meet…MODERN…engineering standards (i.e. the numbers game, politics, insurance, etc)...yet these structures from bridges to multi steroid Cathedrals have stood for almost 2000 years and are still in serviceable condition…so there is no real trick at all…The modern PE often overthinks and/or tries to apply conditions and understanding that really isn't needed..., especially when dealing with the statistics of what a give "something" is theoretically supposed to be or support...And that's common from someone that has worked with one of the best Timber Framing Engineers in the world for over 30 years...As they say, don't overthink it until someone makes you do so...That's why when I...have to...I ask for their help...
If you don’t need a PE Stamp…do a good design…post it here for feedback…learn how to lay it out properly…cut your joints…put it together…done…LOL!!!...
Almost ten years ago, someone like you reached out that wished to learn more about traditional timber framing and folk architecture…Josh and I have been friends ever since…His videos outline what someone can do with just hand tools and a little bit of effort…Most projects take him between 1 to 3 months to complete…”Mr. Chickadee”...I think you will enjoy watching them…
Good luck with your project and by all means ask more questions if you have them…