Wall Support and Anchors. - The usual method of building in the outer ends of the joists in ordinary brick buildings is to cut the end of the joists to a bevel and let the lower edge rest from 4 to 5 inches on the wall, as shown in Fig. 38, and every fourth or fifth joist is tied to the wall by iron anchors to prevent the wall falling outward or the joists from pulling away from it. The object in splaying the end of the joist is to permit the joist to fall, in case of a fire, without lifting the brick above or throwing the wall. In very cheap work the ends of the joists are often left square, but this should never be permitted. The anchors should be made long enough to extend within 4 inches of the outside of the wall, and should always be spiked to the side of the joist near the bottom, as shown in the figure. The nearer the anchor is placed to the top of the joist the greater will be its tendency to pull in the wall in case the joist falls.
Various forms of anchors are used for securing the joists to the wall, that shown at a, Fig. 39, being the most common and about as good as any. The anchor shown at b answers equally as well, but costs a very little more. Anchors like a and b are spiked to the sides of the floor joist and built into the wall, as shown in Fig. 38.
If the wall is a side or rear wall, where the appearance is not of much consequence, it is better to have the anchor pass clear through the wall, with a plate on the outside, as such an anchor gets a much better hold on the wall than is possible when it is built into the middle of the wall. The cheapest form of anchor for this purpose is that shown at c, which has a thin plate of iron doweled and upset on the outer end. This style of anchor may also be used for building into the middle of the wall.
For anchoring the ends of girders, or where a particularly strong anchor is desired, the form shown at d is undoubtedly the best. This anchor is made from a ¾-inch bolt, flattened out for spiking to the joist and provided with a cast iron star washer. It possesses the advantage of having a nut on the outer end, which can be tightened up if desired after the wall is built.
For anchoring walls that are parallel to the joists the anchor must be spiked to the top of the joist, and should either be long enough to reach over two joist, or a piece of 1¼-inch board should be let into the top of three or four joists and the anchor spiked to it.
After the floor joists are set in place and the anchors spiked to them, the brick masons fill between the ends of the joists and around the anchors with brickwork.
55- While this method of supporting and tying the ends of the joists gives ample strength for ordinary floor construction, it has two serious objections, viz., no ventilation is provided around the end of the joist and the method of anchoring is apt to destroy the wall in case of fire.
The lack of ventilation is liable to cause dry rot in the wood, especially if it is not well seasoned. Theoretically, therefore, an air space should be left around the end of the joist, but this is rather difficult to do, especially if the wall is not furred. The only practical device for securing ventilation around the joist (when built into the wall) that the author is acquainted with is the Goetz Box Anchor, shown in Fig. 40. This holds the joist in position and at the same time affords an air space, as shown in plan, Fig. 41.
The second objection given above may also be avoided by using these anchors. The boxes have a lug cast on the bottom, as shown in the figure, and a corresponding notch is cut in the bottom of the joist, so that when the joist is in place it is securely fastened to the box, and, the latter being dovetailed into the wall, affords a sufficient anchor. Large beams or girders may be further secured by anchoring the box to the wall by a bolt passed through a hole in the back, as in Fig. 41. Should the joist fall, in case of fire, it releases itself from the box without pulling the wall.
Another device for permitting the joists to fall without injury to the wall is the wall hanger, of which one type (the Duplex) is shown in Fig. 42. By the use of wall hangers the joists are hung from the wall without entering it. The bracket shown on the back of the hanger is built into the wall, and a lug on the bottom of the hanger holds the joist; every fourth or fifth hanger is also bolted to the walL These hangers possess the advantage that they do not weaken the wall at the floor levels, and in case the joists fall there is little danger of the wall falling also. There is also no danger of dry rot.
Wall hangers are especially desirable for party and partition walls, as where joists enter the wall on both sides they greatly weaken the wall, while when hung in hangers the wall is as strong at the floor level as elsewhere. (See Fig. 43.) As a rule, the box anchor or wall hanger is only used in large brick buildings, and particularly mercantile buildings.
The importance of anchoring the floors to the walls, and thus preventing the latter from being thrown outward, either from settlement in the foundation or from pressure exerted against the inside of the wall, cannot be overestimated and should never be overlooked.
When the first tier of joist is not more than 3 feet above the ground it is not necessary that they be tied to the wall, except in storage buildings or where the first story is over 15 feet high, but all other floors and all flat roofs should be securely anchored to all outside walls, sides as well as ends, at least once in every six feet.
In some localities the outer ends of the floor joists are supported on ledges corbeled out on the inside of the wall. For a description of this method of support the reader is referred to Part I., page 220.