Plataforma de procesamiento Seismic Unix (SU )
4.4. Edici´ on por reporte de observador
4.5.3. Controles de calidad a la geometr´ıa asignada
Frame carpentry requires carrying a lot of lumber. Because of its size and moisture
content, much of it is heavy. Experienced carpenters have been known to identify only three types of lumber - redwood, deadwood and leadwood. Wet 2x 12s fall into the latter
category. Learn to lift with your legs and arms and not with your back.
People just starting in the trade most often carry lumber in their hands held down at their
waist. If you have to do this for any length of time it is likely to cause undue strain on the lower back. Boards are most easily carried on the shoulder. It's a trick that's easily learned: Grab a joist at the balance point, and in one fluid motion lift it and flip it so that it lands gently on your shoulder. The weight of the joist is now directly on the body frame.
Joist stock can be heavy. Experienced framers learn how to lift joists with their legs and carry them on their shoulders.
Scattering joists
Having to carry all the joist stock around the foun dation or second floor will make you, and your back, really appreciate a well-placed lumber drop (see p. 26) or a forklift. Carrying joists a long dis tance can wear you out fast. Check the plans to de termine what lengths of j oist are needed for each span. Longer ones will be needed for cantilevers that
hang out over the building line. Don't worry about joists that are a little long; they will be cut to size later. Keep an eye open for joists that are badly bowed or twisted or have large knots in them. These can be set aside to be cut up and used for blocks or short joists later on.
If you are scattering joists for a second floor, don't rest too many up against a wall - their weight
can push it out of plumb or alignment. Instead, put one end of the joist up on a wall, then, standing on a short stool, a work bench or a bucket, place the opposite end on the parallel wall.
Cutting and rolling joists
With the joists scattered and any necessary rims and beams in place, it's time to cut and "roll" the joists. (Rolling means nothing more than setting them on edge and nailing them on.) As a general rule, lapped joists should lap at least 4 in. If they lap more than 12 in., cut off the excess and use it for blocking. Cut ting joists to length is easy to do, because once they are in place, the building itself does the measuring. Just eyeball and cut.
Joists that butt beams are rolled on edge with the crowns up and dropped into the hangers. Secure them first with a 1 6d toenail driven through the joist into the beam. Along with the hanger nails, this toenail should prevent the joists from moving in the hanger and causing floor squeaks later on.
When joisting a second floor, joists that extend from a beam to an outside wall are often cut to length after they have been rolled in place. If the cut
is flush with the outside, sight down the joist and begin the cut straight up from the wall. Cut until the saw table hits the top plate, reach down, pick up the joist a bit and finish the cut. If the cut is
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in. back from the edge to leave room for a rim joist, sight down and hold the left side of the saw table (on a worm-drive saw) back about Yz in. from the in side of the wall and make the cut. On a 2x4 wall, this will leave the joist bearing 2 in. on the wall withBiz
in. for the rim joist. It takes a little practice to make this cut accurately, but once you have it down you will be surprised at how much it will speed up joisting. Just remember, when working on a second floor, watch for fellow workers below.An easy way to roll the joists is to stand on the flat joists, reach down and grab one and sight down it to check the crown, that is, the bow along the edge of a joist. Crowns should be placed pointing up because when the joists are sheathed and begin bearing a load they tend to straighten out; or at least they won't sag. When joisting over girders that are close together, this practice doesn't matter so much because the joists will be held straight by the girders once they are nailed in pOSition.
Floor joists should be installed with the crown up.
Once all the joists have been scattered, they can be secured to the rim joist with 7 6d nails.
To secure joists to a rim, line them up with the layout and drive two 1 6d nails through the rim, di rectly into the end of each joist. Nails can be driven with a hammer or with a nailer. Drive one nail high and one low to help keep the floor jOists upright and stable. Learn to set up a rhythm when you work, a sort of dance. With practice, your body will begin moving comfortably from joist to joist. Keep your eye open for any special layout, such as for a can tilever or for a stairwell. There's no reason to nail in joists where they aren't needed. Before long you should be able to look back and see a "sea of joists./I It feels good to see all you've accomplished.
Cutting and nailing blocks
In an earthquake, unblocked joists can roll over flat. Blocking helps prevent any joist rotation and adds strength and stability to the entire floor. Blocking is usually required between lapped joists over a girder or wall, and some codes require all joists (lapped or not) to be blocked over all bearing points. If the blocks are cut accurately, they will automatically space the joists correctly. On the standard floor with joists spaced 16 in. o.c., the blocks that go between single joists are 14Yz in. long. Blocks between lapped joists are 13 in. long (see the drawing on p. 43).
Before you cut any blocks, however, check to see how thick your joist stock is running. You might find that it's a bit thicker or thinner than 1Yz in., in which case you would need to adjust the size of your blocks accordingly.
The preferred tool for cutting blocks is the radial arm saw. Once it is set up, a lot of blocks can be cut in a short time. But you can also cut blocks quickly with a circular saw. This is a good time to use up some 2x scraps. If you're cutting blocks with a cir cular saw, you can lay them out quickly with a fram ing square. Assuming that you are cutting 1 4Y2-in. blocks, align the end of the 2x with the 14Y2-in. mark on the blade of the square. Then draw a line across the 2x using the inside of the tongue of the square as your guide. Using this method, you can mark hundreds of blocks in very little time. When it's time to cut them, hold the sawblade to the right
Blocks can be marked to length quickly using a framing square.
of the line ("leave the line") to ensure that each block will be the same length.
The blocks can now be scattered near to where they will be nailed on. You can lay pieces of 1x6 across the tops of the joists to give you a surface on which to set the blocks.
As a standard practice, when nailing blocks be tween lapped joists, nail them flush with one side or the other of the girder or wall. This will make it easier to add extra joists later that may be needed to support walls above (for more on this, see p. 5 1) .
Be careful to start correctly. You want to make sure that the joists maintain the same on-center lay out at the blocks as they do at the rim joist. After nailing in a few blocks, use your measuring tape to check for accuracy. Begin nailing in blocks by set ting the first one on edge, flush with one side of the girder or wall. Drive a 1 6d toenail through the top of the block into the joist. Draw the next joist up to the block and drive two more 1 6d nails through the joist into the block. Then pull the lapped joist up against the first joist and nail these two together, again with two 1 6ds. Secure this joist to the girder
Nail all the blocks and joists in one direction, then turn around and nail from the other side.
or wall with another 1 6d toenail angling down through the joist. Then grab another block and re peat the process. Once you reach the end, turn around and drive a 1 6d toenail through the back side of every joist into the girder or wall. Always nail all the joists and blocks in one direction before turn ing around. Every joist should be toenailed to its support on both sides. Never put a nail in the top of a joist because this could cause you to dull a saw blade when cutting floor sheathing.
Finally, each joist needs to be secured to the sill or wall plate at the rim. Do this by walking one way, driving a 1 6d toenail through each jOist into the sill or plate. When you reach the end, turn around and repeat the process on the other side of each joist. Do the same over every girder or interior wall. Before nailing to these intermediate supports, check that the joists are running straight from the rim to the lap blocks.
Special length blocks ("specials") may be needed in some locations, for example, between the rim joist and the last lapped joist. Usually these can be cut by laying a piece of joist stock flat across the space it will fill, butting the end against the adjacent joist, sighting down and cutting.