Tie beam

“ The strength of a beam 40" × 0"·5 × 1" is four times as great as the strength of 40" × 0"·5 × 0"·5, though the quantity of wood is only twice as great in one as in the other. In general we may state that if a beam were bisected by a longitudinal cut, the strength of the beam would be halved when the cut was horizontal, and unaltered when the cut was vertical; thus, for example, two beams of experiment No. 4, placed one on the top of the other, would break with about 40 lbs., whereas if the same rods were in one piece, the breaking load would be nearly 80 lbs. ”

“ The marking-gage, Fig. 211, consists of a head or block sliding on a beam or bar, to which it is fixed by means of a set-screw. On the face of the head is a brass shoe to keep the face from wearing. Projecting thru the beam is a steel spur or point, which should be filed to a flat, sharp edge, a little rounded and sharpened on the edge toward which the gage is to be moved, Fig. 212. It should project about 1⁄8" from the beam. If the spur be at all out of place, as it is likely to be, the graduations on a beam will be unreliable. ”

“ As the beam increased in diameter, one revolution meant a greater length of twist wound on, and the strap had to be moved along the cone drums to diminish the number of revolutions of the beam per minute, and thus keep the speed of the sheet of warp constant.
Numerous presses are used to get a hard beam with a greater number of cuts on it. Although, when extremely hard, the weaving is more difficult, the advantage of fewer gaitings of beams in the shop, doffings at the size frame, and less waste is adequate compensation. ”

“ To keep the beam truly in its place, which is very necessary, as all the bearings are flat, the recesses for the ends of the studs are formed so as to draw the beam without strain into its true position every time that it is thrown out of gear by the sliding frame. The end knife-edges are adjusted and tightly jammed into exact position by means of wedge pieces and set screws, and the beam is furnished with delicate adjusting weights at its top. ”

“ Hence if we take a common joist and cut away all but an upper and lower flange, leaving just web enough between to hold them firmly together, we will have the I-beam which among rectangular supports is strongest and stiffest, weight for weight. In producing it the engineer has bared within the joist the skeleton which confers rigidity, stripping off all useless and burdensome clothing. An I-beam made of rubber when laid flatwise over supports at its ends will sag much; when laid edgewise it will sag but little, clearly showing how due form and disposal confer stiffness on a structure. ”

“ A.--The web of a cast-iron beam or girder serves merely to connect the upper and lower edges or flanges rigidly together, so as to enable the extending and compressing strains to be counteracted in an effectual manner by the metal of those flanges. It is only necessary, therefore, to make the flanges of sufficient strength to resist effectually the crushing and tensile strains to which they are exposed, and to make the web of the beam of sufficient strength to prevent a distortion of its shape from taking place. ”

“ The thickness of the brass does not exceed 0·02 of an inch, but by means of circular rings driven into the cones at intervals they are rendered almost inflexible. Across the middle of the beam passes a cylinder of steel, the lower side of which is formed into an edge, having an angle of about thirty degrees, which, being hardened and well polished, constitutes the fulcrum, and rests upon the agate planes for the length of about 0·05 of an inch. ”

“ Other beams ran lengthwise of the body, placed straight, obliquely, diagonally, and in every direction calculated to strengthen and stiffen, and all bound together with rods and bars and bolts. One great beam, reaching from rear part through the body to centre of his forehead, is calculated to sustain fully a ton’s weight, if at any time his great head should need such support. ”

“ The side of the beam, supposing it square, was found by multiplying the diameter of the cylinder by the length of the stroke, and extracting the cube root of the quotient, which will be the depth or thickness of the beam. This rule allows a beam 16 feet long to bend 1/8th of an inch, and a beam 32 feet long to bend 1/4 of an inch. For cast iron beams the square of the diameter of the cylinder, multiplied by the length between the centres, is equal to the square of the depth, multiplied by the thickness. ”

“ A light beam, A B, having two square inches of pith, C, at one end, is balanced on a very fine fibre of glass, D D', stretched horizontally in a tube; one end of the fibre being connected with a torsion handle, E, passing through the tube, and indicating angular movements on a graduated circle. The beam is cemented to the torsion fibre, and the whole is inclosed in glass, and connected with the mercury pump by a spiral tube, F, and exhausted as perfectly as possible. G is a spiral spring, to keep the fibre in a uniform state of tension, H is a piece of cocoon silk. ”

“ The method of measuring deflection of large beams can be used for small sizes, but because of the shortness of the span and consequent slight deformation in the latter, it is hardly accurate enough for good work. The special deflectometer shown in Fig. 31 allows closer reading, as it magnifies the deflection ten times. It rests on two small nails driven in the beam on the neutral plane and vertically above the supports. The fine wire on the wheel at the base of the indicator is attached to another small nail driven in the beam on the neutral plane midway between the end nails. ”

“ In ordinary, trade balances a triangular piece of hard steel, with a finely-ground edge, is driven through a triangular hole in the beam and jammed tight. This forms the knife-edge, and the scale-pans arc hung from the two projecting ends of the piece of steel. Similarly the two projecting ends of the central piece of steel which forms the fulcrum take bearing on two checks of the stand, between which the beam sways. It is clear that errors will arise if the pieces of steel are not truly perpendicular to the plane of the beam, and the adjustment of great accuracy would be very tedious. ”

“ In taping the warps on the beams, it is customary in some mills to run the threads over a small steel flanged pulley about one and one-half inches wide, which will keep each thread in its proper position and make the tape absolutely straight and flat as it leads to the beam. A perfect fabric is largely dependent upon how well the warps have been made, but it must not be forgotten that a good warp may be spoiled by a poor beam. ”

“ When the weight reaches 140 lbs. the deflection at first indicated is 2"·37; but gradually the cross lines are seen to descend in the field of the telescope, showing that the beam is yielding and finally it breaks across. This experiment teaches us that a beam is at first deflected by an amount proportional to the weight it supports; but that when two-thirds of the breaking weight is reached, the beam is deflected more rapidly.
366. It is a question of the utmost importance to ascertain the greatest load a beam can sustain without injury to its strength. ”

“ The top of the cage contains a square hole into which one end of the test specimen may be clamped, the crosshead containing a similar clamp for the other end, in making tension tests.
For testing long beams a special form of machine with an extended platform is used. (See Fig. 29.)
The weighing platform rests upon knife edges carried by primary levers of the weighing apparatus, the fulcrum being on the bed of the machine, and any pressure upon it is directly transmitted through a series of levers to the weighing beam. This beam is adjusted by means of a poise running on a screw. ”

“ By a screw bolt and nut properly adjusted above the top of the standard and acting along its side, assisted, if need require, by a wedge for tightening and loosening, the beam may be raised and lowered; and the mould-board, with its cutting edge, enabled to make a furrow of greater or smaller depth, as the ploughman may desire, and a latch and key fixed to the beam, and capable of being turned into notches, grooves, or depressions on one edge or narrow side of the standard, serves to keep the beam from settling or [Pg 31] descending. ”

“ Each end of the beam is sprung obliquely upwards and towards the middle, so as to form a spring through which a pushing screw passes, which serves to vary the distance of the point of support from the fulcrum, and, at the same time, by its oblique action to raise or depress it, so as to furnish a means of bringing the points of support and the fulcrum into a right line. ”

“ When the beam is deflected out of its horizontal position and the wire thereby twisted, the resistance to twisting increases with the arc of rotation. To counteract this resistance and to render the beam sensitive to a very slight excess of load at either end, a poise, D, is attached to the beam by a standard, C, which poise carries the center of gravity of the structure above the axis of rotation. This high center of gravity tends to make the beam "top heavy," or in unstable equilibrium. ”

“ The beam-engine, in its adaptation to the conditions under which it was designed to work—namely, a piston speed of 220 feet per minute and a pressure of one or two atmospheres—was as nearly perfect as any work of human skill ever was or will be; but we wonder why the outraged ghost does not haunt the men who cling to the material form they have inherited, when the conditions which it was designed to meet have been all outgrown, who have used up his factor of safety, and now stand among their trembling and breaking structures, deprecating everything which these will not endure. ”

“ A A A, is the frame of the loom, consisting of four upright posts, with caps and cross rails to bind them together. The posts are about six feet high. C C, the cloth-beam, is a wooden cylinder, six inches or thereby in diameter, of sufficient length to traverse the loom, with iron gudgeons in the two ends, which work in bushes in the side frame. On one end of this beam is a ratchet wheel, with a tooth to keep it from turning round backwards by the tension of the web. ”

“ Now, the strength of a beam varies as the square of the depth of the beam, and it is obvious that in the case of a circular steel tube the material is evenly distributed about the neutral axis, and therefore its strength in both horizontal and vertical directions is equal ”

“ Thus, if a beam which is one foot broad and one foot deep support a given weight, then a beam of the same depth and two feet broad will support double the weight; but if a beam be one foot broad and two feet deep it will support four times as much as a beam one foot broad and one foot deep. If a beam one foot square support a given weight, then a beam two feet square will support eight times as much. Also a cylinder of two inches in diameter will support eight times as much as a cylinder one inch in diameter. The appended table gives data bearing on the subject. ”

“ A steel bar placed below the middle of the beam furnishes the useful tensile resistance. But it was found that certain diagonal cracks developed in the beam toward the respective ends of the beam, and it was sought to prevent these by minor auxiliary rods attached to the main reinforcing bar. ”

“ The leading characteristics of such machines are, first, a convenient platform nicely balanced on knife edges of steel levers, and second, a graduated horizontal beam, a sliding weight thereon connected by an upright rod at one end to the beam, and at its opposite end to the balance frame beneath the platform. ”

“ A.--Yes, and for all beams. Engine beams should be made deeper at the middle than they are now made; the web should be lightened by holes pierced in it, and round the edge of the beam there should be a malleable iron hoop or strap securely attached to the flanges by riveting or otherwise. The flanges at the edges of engine beams are invariably made too small. ”

“ The spools used on the carriers are specially designed, and have a series of notches on the upper end, into which a stop will drop upon the breaking of any of the different covering threads, automatically stopping the machine.
The rubber is carried on a beam such as is used in weaving. These beams are grooved on either side for receiving friction cords or belts, on which are hung weights so as to govern the let-off of the beams and keep the rubber at a high tension. ”

“ A pillar supporting a weight is under compression. At c the weight tends to bend the beam. The upper part is under tension, the lower part under compression. This is known as beam action, and depends on whether the beam is supported at one end, as shown, or on both ends. ”

“ Paragraph 18 - If the supports, when the beam sits on pegs in the wall, are not one tefach wide and three long, some say that they must be strong enough to support the beam and a half brick and some say that they only need to be strong enough to support the beam. ”

“ They are designated by the numeral 27 in Plate 54, and are shown in detail in Plate 58 as of a very deep I-beam section, having very narrow flanges top and bottom, the web of the I-beam furnishing the strength in a vertical direction, while sufficient stiffness laterally was obtained from the flanges, assisted by the brace tubes, which acted as struts between the bed plates and the main tubes of the transverse frame. ”