Similar to architects, most engineers are not familiar with or educated in timber frame construction. So they use conventional engineering concepts to design connections. Bolts, lags, steel knife plates and bucket hangers are typically part of these connections. The results of these designs is post & beam construction.
Post & beam is a general term for building with heavy timbers. More specifically, timber framing is a type of post & beam construction implementing a traditional method of building using wooden joinery held together with pegs and wedges. More commonly referred to as mortise & tenon, timber framing joinery also incorporates dove tails, splines, shear blocks, half-laps, housings, beam pockets…etc. This type of construction has been around for thousands of years, with many structures still standing today. The oldest structure I found was a Buddhist temple in Tibet built in the 7th century – so over 1300 years old!
I consider timber frame engineering as “special engineering”. The National Design Specification (NDS) for Wood Construction developed by the American Wood Council is a compilation of standardized design requirements and material design values used by engineers when engineering with wood. So why is it acceptable for timber frame engineers to “break” some of these rules?
To some extent, timber framing is based on empirical design, which is design based on observation & experimentation. Do you think that whoever designed that Buddhist Temple had the NDS book? Or formulas to calculate loads and forces? Or testing equipment to establish material capacities? Obviously not – they observed what had worked before or they experimented until they got it to work with many failures along the way.