CAPITULO II: ADQUISICION DE SISMICA TERRESTRE
2.2 Diseño final del programa sísmico 2D/3D
2.2.7 Métodos de adquisición 3D
2.2.7.3 Sparse
Some state legislatures have outlawed the short-handled hoe for farm workers because it is too hard on backs to bend over low all day long, but no one has considered outlawing the short-handled hammer for carpenters. It is hard on backs to bend over and frame all day long. The long-handled hammer does help, but you still have to reach down to hold the nail so it can be set and driven. There is no way to frame efficiently standing upright. Part of being a good carpenter is learning how to take care of your body. Learn to lift with your legs instead of your back. Exercise to keep strong, soak in a hot bath regularly and get a good massage occasionally to loosen up tight muscles. Many lower-back injuries happen on those cold mornings when the body is still tight. Few carpenters will do calisthenics out on the job, but there is no reason why you can't do some stretching at home before leaving for work.
with the bolts. The bottom plate will usually nail on faster than the top, because all the studs are on edge and more or less in position. Now's the time to nail the corner and channel studs together with three 1 6ds on each side. Drive the first one 2 ft. from the bottom and then two more about every 2 ft.
Intersecting or butt walls are built after the exte rior walls have been raised. These frame just like the through walls. A minor difference is that if you nail the end stud back from the end of the top plate about % in. (see the photo at right) it will allow the top plate of the butt wall to join freely with the top plate of the through wall once they are raised. The top plates of raised walls must fit together tightly no gaps are allowed.
Nail the top of the end stud on a butt wall about
Y4
in. from the edge of the top plate to ensure that the top plates of adjoining walls will fit tightly together.Rake walls
Building rake walls requires that the top ends of the studs be cut at the roof-pitch angle. During the lay out stage, a full-size rake-wall layout was marked out on the floor (see pp. 69-70) . Using straight stock, scatter studs that are a little overlong at every lay out on the bottom plate. Then nail the studs, along with all headers, sills and cripples, trimmers and king studs, to the bottom plate just as on a regular wall. Position top cripples on top of the headers. Framers prefer not to nail the top cripples to the header until they are marked to length and cut.
Set the top plate on edge on the chalkline and mark the stud layout on it.
Next, straighten up the bottom plate and hold it in place just below the chalkline by tacking it to the floor with a few 8d nails. Then bring up the top plate, lay it across the studs and position them on the same layout as the bottom plate, ready for marking.
The next step is to snap a chalkline on the studs directly over the roof-pitch line marked on the floor. Before cutting the studs, grab a longer piece of plate stock. A new top plate has to be cut because it runs at an angle and is longer than the original plate. Lay it on edge directly on the chalkline and mark it for length. Now, with the plate still on edge across the studs, take a pencil and mark the stud location so that the studs can be nailed in once everything is cut.
If the plans call for a ridge beam at the top of a rake wall to carry the rafters, it will sit on a post, of ten bolted or nailed to it using a metal post cap. The length of the post was determined during layout (see p. 70), and it can be cut and installed now.
Now it's time to cut the studs to length. Set the saw to the correct degree for the roof pitch (for ex ample, 18Yz° for a 4-in- 1 2 pitch), pick up the studs one by one and make the cuts. Saw tables tip only one way. If the cut angle runs in the opposite di rection from the tilt of your saw, cut the stud to length square and then tilt the whole saw over and make the angle cut. Finally, nail the cripples to the header, then nail the top plate on the cripples and wall studs.
Once the rake-wall studs and cripples have been marked to length, they can be cut in place.
Double top plate
The next step is to nail the double top plate to the top plate. The double top plate ties all the walls to gether and makes the entire building structurally stronger. Traditionally, carpenters would nail on the double plate after the walls were raised, working off ladders. But this method is very inefficient; double top plates can be nailed on much more quickly and easily while the wall is still lying on the floor.
Begin by scattering the plates right on top of the wall, near the top plates. This way no measuring tape will be needed to cut the plates to length. Try to use long ( 1 6-ft. to 20-ft.) and reasonably straight stock. On through walls, hold the double top plate back from the ends the width of the framing stock (e.g., 3Yz in. on 2x4 walls). Do the same at all chan nels. When the doubles are cut for the intersecting
walls, they will be cut long and then lap over these gaps to help tie the walls together.
Where walls of different heights intersect, there is no need to leave cutouts in the double top plate. They will have to be connected later by metal plate straps (see p. 1 1 5). On rake walls, the double top plate hangs over on the low end about 3 in. so that it can lap and tie into the wall it butts. At the top end, let it run long and cut it when the ridge beam is set on the post.
Most building codes require that double top plates lap over joints in the top plate by at least 4 ft. There are times when this isn't possible, either be cause the plate stock isn't long enough or the inter secting walls are too close together. In such cases, nail an 1 8-in. metal plate strap with four 1 6d nail holes in each end over the joint in the top plate.