Friday, February 18, 2011

A bridge to nowhere.

Those filthy politicians are doing it all the time and desiring to get into politics someday I thought that I might join in the fun. What fun you might ask, well, building a nearly useless bridge of course.
In my attempt to throw money at everything that either moves or is nailed down I just purchased a large pile of lumber which should be delivered sometime next Friday. While other people may enjoy the idea of hauling 30 sheets of 3/4" plywood up and down the muddy embankment that is the front yard, I do not. It was my original intent to build a small "normal" front porch, followed by a bridge to the sidewalk, however, I am not planning on building the porch for a while. Now is a good time for building a bridge that I can cut to size when the time comes. I doubt that I will be able to do so, but if I can convince the Inspector to buy off on only having a bridge than I will opt to not build the porch and recover the structure with plank instead of plywood.

The construction is simple enough. Four sixteen foot 2x8's, some solid cross bracing, covered with a couple of sheets 3/4" treated plywood. For the supports I took some 4x4's and made a center support. The two ends are supported one on the ground and the other sitting on the old cast cement stairs. There are a couple of additional pcs bracing to keep the whole structure very stable. Before commencing on such an endeavor I would recommend conversing with your local building inspector. I did not in this case as I have a occupancy permit out and do not intend on leaving the bridge in its current configuration as a final design.
One thing that is a good idea on anything that will be subjected to dynamic loads is to build in some overkill. In this case I like to refer to an easy to use span chart as the start of my design, such as this one from AWC. Noting 2x6 16" OC, exterior and the species I am using: I could span greater than 8 ft with a 50Live,15dead load. So using 2x8 ft is reasonable overkill. The whole of the structure floats and is not connected to the house, for this reason it is important to have the supports well braced as shown. Also side loaded movement is minimized by using plywood and having a small cross brace on the center support. I should mention that all the lumber I am using on this bridge is coming from my culled lumber pile which I purchased about 6 months ago, mainly 2x4 and 2x8 ish treated lumber in the 16 plus foot range usually having a twist or split at an end. I purchased the whole of the pile for under $200 and have been using it ever since. I am thankful that God has helped me in finding some good sale items as I as yet have not found a corporate sponsor.
I will likely throw on some basic rails after getting the lumber inside. If I am able to make it permanent I will likely be forced into using footings for the support, but we shall cross that bridge when it arrives.

No comments:

Post a Comment