IRON STRAPS WITH WOOD.

447

IRON STRAP FOR FOOT OF KING-POST, STRUTS, AND TIK-URAM —SCALE, h INCH TO THE FOOT.

D TIE-BEAM-3CAIK. i

INCH TO THE FOOT.

tlie foot of tlie rafter c with the tie-beam b b, fig. 825 —a being the strap,and e the eye-bolt.

1594. The following re-marks from the article “Car-pentry,” Encyclopedia Bri-tannica , on the use of ironstraps, may he useful. “ Whenit is necessary to employ ironstraps for strengthening ajoint, considerable attentionis necessary that we mayplace them properly. Thefirst thing to be determinedis the direction of the strain.

We must then resolve this strain into a strain parallel to each piece, andanother perpendicular to it. Then tlie strap which is to be made fast to anyof the pieces must he so fixed that it shall resist in the direction parallelto the piece. Frequently this cannot he done, but we must come as nearto it as we can. In such cases we must suppose that the assemblageyields a little to the pressures which act on it. We must examine whatchange of shape a small yielding will produce. The strap that we observemost generally ill-placed is that which connects the foot of the rafter withthe beam. It only hinds down the rafter, but does not act against its hori-zontal thrust. It should be placed farther back on the beam, with a boltthrough it, which will allow it to turn round. It should embrace the rafteralmost horizontally, near the foot, and should be notched square with theback of the rafter. We are of opinion that straps with eye-bolts in the veryangles, and allow free motion round them, are of all the most perfect. Abranched strap, such as may at once bind the king-post and the two braceswhich abut on its foot, -will be more serviceable if it have a joint. Whena roof rvarps, these braced straps frequently break the tenons, by affordinga fulcrum in one of their bolts. An attentive and judicious artist will con-sider how the beams will act upon such occasions, and will avoid giving riseto these strains by levers. A skilful carpenter never employs many straps,considering them as auxiliaries foreign to his art, and subject to imperfectionsin workmanship -which he cannot discern or amend.”

1595. In fig. 824 we show a branched strap a joining the king-post c and the

struts cl d. The strap may be fixed by keys driven through at the upper part,or an eye may be Fig . g2 .

given to the strap,and a bolt passedthrough it.

1596. In fig. 826we give a form ofstrap for head ofking - post a, andstruts b c ; fig. 827shows a strap forjoining collar beam rR0N 9TRiPa, and principal b c.

1597. Fig. 828

gives a form of strap for straining-beam a, queen-post 5, and strut c.

? FOR HEAD OF KINO-POST ANDBRACES-SCALE, J INCH TO THE FOOT.

IRON STRAP POR COLLAR AND RAFTER-SCALE,

£ INCH TO THE FOOT.