Advancements in Resilient Timber Design
Hello everyone. I hope y’all are doing well. I’m looking forward to Christmas and I hope you are too. Just in case I decide to not do a post before Christmas I just want to wish y’all a Merry Christmas. Today I want to talk about some advancements in timber design taking place in the multi-family residential building industry in California.
In California, residential structures can be vulnerable to seismic loads – especially if there is an open floor plan on the bottom. Engineering professor John van de Lint from Colorado State University has been leading a team of researchers in that specific area of study as it pertains to first floor garages. He has previously completed similar research with Simpson Strong Tie in 2009 in regards to natural disasters and it led to the consideration of timber for mid-rise structures with high seismic loads. According to Lint, “Earthquakes are particularly damaging to buildings with open spaces at street level because they collapse – the first-floor parking makes the building structurally weak and soft…There are tens of thousands of these multi-family buildings throughout California and much of the U.S., making this a serious safety issue.” The team has tested several concepts for earthquake retrofitting on structures designed to replicate common California architectural practices.
A common characteristic among all the models they tested is a timber frame structure with an open structure on the first floor and a purely timber structure on the upper floors. Some of the retrofits followed the FEMA P-807 guideline because that is the current retrofit requirement in California. This law requires that buildings with a soft story be retrofitted within the next several years. One of the retrofits tested is cross laminated timber. In this test, the shear walls are constructed with cross laminated timber and the floor diaphram is reinforced using plywood and attached to the shear walls using Simpson Strong Tie straps and clips. The test was successful up to 50% Maximum Credible Earthquake (MCE).
The article also mentions some innovations for dealing with harsher environments. In locations with more humidity and rain, protection from the elements can be a critical issue for timber frames. Huber Engineered Woods has developed a material called ZIP System R Sheathing for the construction of walls where protecting the structure against the elements is critical. This is currently the first product of it’s kind to be approved by the International Building Code. This sheathing provides protection against bulk water, thermal, air and moisture resistance while being strong and durable. The sheathing also provides increased energy efficiency for HVAC systems. This system has advantages over regular plywood or oriented strand board in harsher climates because an additional layer of house wrap and hurricane clips is not required.
Both of these improvements may seem a bit generic at first. In fact, the more I think about the descriptions above, the more I think of an advertisement pamphlet you might get from a timber supplier. However, it is my opinion that these are significant advancements for the future of timber usage. These two situations above are textbook reasons for the usage of a material other than timber for taller buildings in these seismic or weather critical locations. With the proper implementation of these advancements in the future, the use of timber can be expanded to a larger variety of locations. The only major drawbacks I see are the increased cost of using the materials and the necessity for contractors with experience implementing these designs.
Do you see these products changing the use of timber on a larger scale? If so, how and why? If not, what is the critical issue that has to be overcome? Thanks for your time and have a good week!
Zweig, Christina, “Resiliant Wood: New Wood Products Help Cope with Nature’s Challenges”, Structural Engineer Magazine, November, 2013, http://goo.gl/NoJT9Z