The very essence of timber framing requires taking timbers and cutting away wood in order to form joinery. These reductions in the timber’s cross-section forces any stress in the timbers to be necked down and concentrated in the smaller areas. Depending on how abrupt the changes in cross-section are, the localized stress at these points can be rise dramatically – sometimes well beyond the allowable capacity of the timber. These stresses can either be from applied loads (weight in the structure) or from internal causes (shrinkage). Wood’s mechanical properties also play a large role – as wood is stronger (or weaker) in various directions.
In this presentation, we will look at the basic mechanics of stress concentrations, primarily as it relates to beams and their associated joinery. Our first line of defense against these stress concentrations is mitigating them with better detailing (scooped vs square reductions on joists for example). However, that isn’t always feasible, so we will also spend some time investigating how to calculate and quantify the nature of the stress concentration on the overall effect of the beam’s capacity. Some time will be spent on how to properly reinforce beams near stress concentrations as well (for both new construction as well as on-site repairs). We will wrap up with a few case studies of what to do, and equally important, what not to do."
About the Speaker: Joe Miller
Joe Miller, PhD, P.E., P.Eng., is a structural engineer specializing in the design and engineering of timber framer structures. As partner with Fire Tower Engineered Timber, he heads up the Michigan office located near the shore of Lake Superior. Catching the timber framing bug early in life when helping restore the familial homestead, Joe gained academic experience through graduate engineering degrees in mortise and tenon joinery as well as key-laminated timber beams. He had hands-on experience working with several timber frame companies, both in the office and in the shop, before working as a consulting engineer, licensed throughout the United States and Canada.
Prior to his current role, he served as the Director of Global Architectural Sales working on international projects designed in one country and built in another. He has held past positions in field sales, operations, training, and management during his 25-year career at Armstrong. Before Armstrong, John estimated and project-managed commercial healthcare, retail, manufacturing, office, and education construction projects in central Pennsylvania for a large regional general contractor.