Sunday, June 04, 2006

timber sizing

i've spent the last few days sizing the timbers for the timber frame. i've not done structural work since architecture school, so a good day was spent reviewing old notes and books to refresh my memory. i also had to find the current allowable stresses for timber since they've changed from when i was in school.

i actually enjoy doing structural calculations. i feel good understanding what's actually happening in a piece of wood and why it needs to be a certain shape in order to work. it helps inform design.

my friend andrea, a timber frame designer who has been helping me with this project, sent a spreadsheet with the sizing calculations nicely programmed which saves a great deal of time. doing the calculations by hand is interesting, too, and helped me understand the theory behind the sizing, but it is time consuming.

the upshot of my structural work has been an adjustment to the design. what i had planned for originally required timbers i felt were too large for us to handle. i'd prefer not to have to hire a crane to lift our work. so, i spaced the elements of frame closer so that each was carrying less load and could be made smaller. we will have to carve more joints as a result. other factors contributed too: the recommended values for snow loads (the major load on our building) have increased about 40%. so, while my house built in the 1830s has 7x7 beams spanning 13 feet (the cat makes the floor bounce), our building will have 8x14 beams spanning about the same distance (and you could probably drive a truck onto the roof with barely a jiggle).


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