Sills are used in all trussed partitions as a fixing for the lower ends of the posts and studs, while they tie in the braces, and in partitions supporting floors they perform the further function of binder to the lower floor joists.

Posts are used as intermediate supports for the head, intertie, and sill, and they should be arranged, as far as the position of the doorways will permit, at regular intervals along the partition. In no case should the horizontal members of a partition receive support between the external walls save that provided by the posts or braces. When a partition rests at either end upon the main walls of a building it should not receive intermediate support from a cross wall, as the slightest inequality in settlement of the supports would cause unsightly cracks in the plaster.

Shoulders are formed upon the posts for the reception of the ends of the braces.

Posts are stub tenoned and securely strapped with iron straps to the head, intertie, and sill, as they are usually subjected to a tensile stress; for which reason iron bolts are sometimes used in place of posts, as shown in Fig. 276.

Braces

The function performed by the braces is to transmit the load to the walls.

Braces should be connected to the heads, interties, and sills by means of bridle or abutment joints, as shown in Fig. 277, and to posts by tenoning them into the shoulder. When two struts occur on either side of a tension rod they are tenoned into the horizontal member and butted against a straining piece, as at A in Fig. 270.

Braces generally do their work best when inclined at an angle of about 45 degrees, so that in designing partitions the braces should be inclined as nearly at this angle as possible; but should it be necessary to incline a brace very obliquely it should be made stouter than usual, and if long should be strutted at its middle from a post.

Studs

In trussed partitions the studs are stub tenoned into the heads, interties, and sills, but are simply cut to the required splay and nailed to the braces, as it is undesirable to impair the strength of the latter by cutting mortises in them.

Sizes Of Timbers

It is impossible to lay down any fixed rule for the sizes of timbers in partitions, save that they should be proportioned to the load and to the conditions of the particular case. The following list of sizes, together with the notes appended thereto, will serve as a guide to the selection of timbers of suitable dimensions: -

Heads .......

4

x

7

inches to

4

x

9

inches

Door heads ....

4

x

3

"

4

x

4

"

Interties ......

4

x

7

"

4

x

9

"

Sills .........

4

x

7

"

4

x

9

"

Posts .........

4

x

4

"

4

x

6

"

Braces .......

4

x

4

"

4

x

9

"

Studs .........

4

x

2

"

The above sizes are suitable for spans up to about 20 feet, and may be decreased or increased with the span, bearing in mind the following facts: - (a) Heads, interties, and sills need not be increased to any considerable extent as the span increases, as their size depends chiefly upon the spacing of the posts or tension rods, which as a rule are increased in number with the span.

Partitions 539

Fig. 278.

Braces increase in size according to their length, and where several braces occur transmitting the loads across successive spans to the abutments, those nearest the abutments are made larger than those nearer the centre of the span, as the former are more heavily loaded than the latter.

As it is desirable to keep the faces of all the timbers in one plane for the convenience of plastering upon them, the studs and door heads vary only in width, and need rarely be increased in depth with the increasing span.

When timbers exceed 3 inches in width on face their edges should be splayed, or wood fillets should be nailed in the direction of their length before the laths are fixed, so as to form a key for the plaster. The plaster should not be applied to partitions until they have been up for some time, so that all settlements may have ceased, and to enable defective joints to be repaired. This is not so essential if the members have been cut for some weeks and stored under cover • before fixing. Wire netting or other forms of metal grids are sometimes used in place of laths, over which they possess the advantage of being more rapidly fixed.

Brick And Bricknogged Partitions

Brickwork 4 1/2 or even 3 inches thick is used for partitioning rooms when a solid support is available along its whole length. Partitions 3 inches thick are formed by laying the bricks on edge.

Thin brick partitions should not be used for walls over 10 feet high, as they are lacking in transverse strength, and bricknogged partitions are used in their place. These consist of 4 by 3-inch quarters, framed similarly to common partitions, but with the studs at intervals of 2 feet 3 inches, 3 feet, or other suitable brick dimension, and with the spaces between the studs filled up with brickwork, as shown in Fig. 278. Fillets of wood from 4 by § inch to 4 by 3/4 inch, called bonding fillets or bond timbers, 4 1/2 by 3 inches, are nailed horizontally between the studs at intervals of from 1 to 2 feet to prevent injury from vibration or shocks. The joints of the brickwork are raked out to form a key for the plaster.

Partitions are sometimes nogged with concrete composed of four parts of coke breeze to one of Portland cement, the sides of the studs having nails driven into them with the heads projecting 1 1/2 inch to form a key for the concrete.

Nogged partitions possess the advantage of being more sound and vermin proof, and more fire-resisting than timber partitions.

Block Partitions

Numerous forms of partitions are on the market at the present day, made in the form of interlocking slabs of concrete, which can be built up rapidly in situ, vertical holes being formed in them for the insertion of bars of iron for giving them greater transverse strength. Some of these, like the "Acton" partition slabs illustrated in Fig. 279, have a rough texture to form a key for a finishing coat of plaster, while others are made with a smooth surface.

Partitions 540

Fig. 279.

Hollow spaces are left within some forms of partition blocks, which may be connected with a room and the outer atmosphere for ventilating purposes.