Truss

“ If we build thus, the two ends, A B, are firmly fixed and can not in any way yield to the load that may come upon them. If we now construct an ordinary framed truss, of either the Howe, Pratt, or any other type, and instead of putting this truss upon two piers or abutments we simply hang it between the two ends of the cantilever spans, A B, which are projecting over the river, the weight of this truss will be sustained by the tie-rods from the king-posts, or in the case of the cantilever that run over the tower and are anchored down upon the other side. ”

“ A panel is one of any number of equal parts into which the truss of a bridge is divided by means of the posts or rods. This second truss is called the queen-post truss; here also the full black lines are in compression and the dotted lines are in tension. As you will notice in this truss, which is also the case in the flanged girder, the top part of the truss and the top flange are always in compression; so the lower chord is always in tension, as the lower flange in the flanged girders. ”

“ If a load be placed over any panel point, it causes that portion of the truss to sink, and produces an elevation of the corresponding panel point at the other end of the truss—thus producing a distortion, which change of form is resisted by proper counterbraces. The strain to which this timber is subjected is caused by the moving load on one panel only—and requires only scantling of the size of the middle braces. ”

“ There are six vertical trusses which inclose the five ways into which the roadway is divided. The top chords of the two outer trusses are 912 feet above the roadway, those of the other four are 16 feet. Each truss has a slip-joint in the middle of each span to allow for expansion and contraction of the structure from heat and cold. For a hundred feet out from the towers these trusses are said to be able to support themselves, not adding their weight to the strain on the cables. ”

“ I claim, 1st, The within described novel construction of a truss for a wall building machine, the same consisting in the pyramidal framing, A B B, the horizontal timbers, D D, uprights. E F, holding-down bolts G J, and inclined braces, I H, combined and arranged substantially as and for the purpose herein set forth.
2d, Also in such truss firmly securing the timbers, D D, to the pyramidal framing, A B B, by enlarging and bolting, or equivalent fastenings, at the points of contact, in addition to the truss work before described, substantially as and for the purpose herein specified. ”

“ In Fig. 118 is shown a method that is sometimes used in the construction of trusses. A truss is that part of a roof which supports the purlines, rafters and sheathing. A roof is the covering or upper enclosure of a building with the frame work by which it is supported. It may be of almost any shape. A light roof is usually of moderate span, without trusses, the rafters being supported by the walls or partitions of the building. A heavy roof is employed for wider spans, [Pg 96] and the rafters are then supported by the purlines and trusses. ”

“ The thrust must be resisted either by the massiveness of the abutments or by the opposition to it of counter-thrusts from other arches or vaults. Roman builders used the first, Gothic builders the second of these means of resistance. The truss is a framework so composed of several pieces of wood or metal that each shall best resist the particular strain, whether of tension or compression, to which it is subjected, the whole forming a compound beam or arch. It is especially applicable to very wide spans, and is the most characteristic feature of modern construction. ”

“ The beam or girder. 2. The framed truss. 3. The arch. 4. The suspension bridge.
The most ordinary form which we see in this country, and the one most generally used for the purpose of railway bridges, is the framed truss, and that is the one the development of which it is our purpose to show.
The one point to be carefully studied in all bridge construction is economy—that is, to get as much strength with as little material as possible; in other words, the maximum amount of strength with the minimum amount of material. ”

“ The wrought-iron girders, or trusses, are partly forty-eight and partly seventy-two feet long, to span the avenues of those respective widths; the principle of the construction is the same in each. The top rail (if it may be so called) of the truss is formed with two pieces of iron placed back to back , and the bottom rail with two flat bars , the total depth being three feet ”

“ A truss is a rectangular block cut out of the solid stack, usually about 3 ft. long and 2 ft. wide, and of a thickness sufficient to give a weight of 56 ℔: thirty-six of these constitute a “load” of 18 cwt.—the unit of sale in many markets. A truss is generally bound with two bands of twisted straw, but if it has to undergo much handling it is compressed in a hay-press and tied with two string bands. In some districts a baler is used: a square box with a compressible lid. The hay is tumbled in loose, the lid forced down by a leverage arrangement and the bale tied by three strings. ”

“ These are in no sense Gothic, but are here given to more clearly explain the principles of roof construction. The common rafters (c.r.) bearing the covering are of light timber, tending to bend under the weight; to prevent this purlins (P.) , stout beams, are placed at suitable intervals, and these are carried at their ends by the roof trusses. The tie-beam (t.b) is the chief beam of the truss. The principal rafters (p.r.) are framed into it and into the heads of the King and Queen posts. In the Queen-post-truss the collar unites the Queen posts; struts and cross-braces complete the structure. ”

“ Thus, the Fink truss consists of king-post trusses; the Pratt truss (fig. 63) and the Whipple truss (fig. 64) of queen-post trusses alternately upright and inverted.
Fig. 62.
A combination bridge is built partly of timber, partly of steel, the compression members being generally of timber and the tension members of steel. On the Pacific coast, where excellent timber is obtainable and steel works are distant, combination bridges are still largely used (Ottewell, Trans. Am. Soc. C.E. xxvii. p. 467) . The combination bridge at Roseburgh, Oregon, is a cantilever bridge. ”

“ A frame used to support a weight is often called a truss; the stresses on the various members of a truss can be computed for any given load with greater accuracy than the intensity of stress on the various parts of a continuous structure such as a tubular girder, or the rib of an arch. Many assumptions are made in treating of the flexure of a continuous structure which are not strictly true; no assumption is made in determining the stresses on a frame except that the joints are flexible, and that the frame shall be so stiff as not sensibly to alter in form under the load. ”

“ Fig. 120.
[Pg 100] The line E, D, on the diagram represents a tie-rod, which by the construction of this truss would naturally tend to stiffen the structure by supporting the center of the tie-beam.
Wire, nuts, and washers are supplied (where the student makes a whole model) to make the tie-strut.
The student in writing out notes will make two sketches of trusses he may have observed on shop visits. The buildings visited almost all have trussed roofs, either wood or iron. ”

“ The essential feature of these buildings is a steel-roof truss supported on steel columns, the columns being braced both to the truss and longitudinally of the building. It is usually the purpose in the design of such buildings to neglect everything but the necessary stability and the first cost. The steelwork, consequently, is of the lightest possible construction, usually designed for a unit fiber stress of from 18,000 to 20,000 pounds, and the covering of the sides of the building, together with window details, etc., is made only sufficiently good to keep out the weather. ”

“ The Cluthe Automatic Massaging Truss is so utterly unlike anything else for rupture—so much more than just a truss—that sometimes we feel we should have adopted some other name.
11 For the country is full of worthless trusses; and so many people have tried truss after truss without being in any way benefited that they think that nothing called a truss can do any good. Although when people get an inferior article of some other kind—like clothing or shoes—they don't condemn everything similar. ”

“ It is more usual to have the tie rods of the horizontal diagonal bracing, and the braces themselves, meet in a point about midway of a Truss panel on the centre line, nearly, of the chord. This will generally give a half panel of diagonal bracing near each end of the truss—and it is very usual to have the diagonals foot at their intersection there against a cross timber interposed between the trusses, while the tie rod prevents any spreading. ”

“ On taking the field, two trusses of 36 pounds each to every five men, at the end of eight days to be refreshed by one truss, and at the end of eight days more to be refreshed again by the same quantity. At the end of twenty-four days the whole to be removed, and an entire new bedding to be given, and refreshed as before, viz. two trusses for every five men. ”

“ While I was always skeptical as to a permanent cure of rupture by means of a truss the fact remains that after following your advice and instruction, I have been going about without a truss, doing all kinds of work same as I did prior to becoming ruptured. I cheerfully recommend your truss to one and all afflicted with rupture. Only the patient himself knows from experience how he has to suffer. ”

“ When putting a truss together in its proper position, on the abutments, 'false works' must first be erected to support the parts until they are so joined together as to forma complete self-sustaining truss. The bottom chords are first laid as level as possible on the false works, then the top chords are raised on temporary supports, sustained by those of the lower chord, and are placed a few inches higher at first than their proper position, in order that the web members may be slipped into place. ”

“ Plate X., Fig. 4, is a trussed rafter roof requiring no purlins nor principal—each common rafter is a truss. This kind of roof is suitable{68} only to small spans; its weakest part is from a. to b.
In the roof-truss, or principal, the Gothic architects objected to the tie-beam as an obstruction to the sense of loftiness, so desirable in the church interior, and therefore invented the hammer-beam principal (Plate X., Fig. 7) , which resembles a Queen-post-truss, having a collar and King post. The hammer-beams (h.b.) are substitutes for the tie-beam. ”

“ The raising and fixing of the extra-strong roof-trusses crossing the main avenue near the side of the transept required particular care, from their great weight; the heaviest being, as we have before mentioned, no less than eight tons. These trusses were the first that were fixed across the central avenue, and about 150 men were engaged in the hoisting of each one. They are secured to the columns by four strong bolts passing through the end-standards. ”

“ The verticals are of wood, and the diagonals foot on steps formed by enlarging the ends of the verticals. The counters are in two lengths, and are adjusted by wedges at the points where they intersect the braces. The bridge is in two spans, and has a double track, and consequently three trusses. There are two timber arches to each truss, and the truss is supported on them by connecting them to the verticals by short cross pieces notched into the posts, and resting on the upper surface of the arches. ”

“ Large timbers 12 x 12, or thereabouts, are laid on the bridge seats of the abutments to support the ends of the trusses, one of these should be directly under each of the extreme panel points. A panel point is the intersection of the centre line of a brace produced, with the centre line of a chord. The rise of a truss is the vertical distance between the centre lines of the upper and lower chords. ”

“ The truss bridges which have been mentioned as types of the modern railway bridge are erected by the use of false works of timber, placed generally upon piling or other suitable foundation, between the piers or abutments, and made of sufficient strength to carry each span of the permanent structure until it is completed and all its parts connected, or, as is technically said, until the span is swung. ”

“ The trusses for a span of seventy-two feet are cambered or bent upwards about ten inches, which both adds to their strength and improves the appearance. The form and arrangement of these roof-trusses may be clearly traced in several of the views of the interior which are presented to the reader. The weight, when completed, of each of the trusses of seventy-two feet span is about thirty-five cwt., and of those of forty-eight feet span about thirteen cwt. ”

“ But the introduction of an iron goose-neck, centering and securing the yard well free of the mast, very much supersedes the use of trusses.
TRUSS-HOOPS. Synonymous with clasp-hoops for masts or spars; they [701] are open iron hoops, so made that their ends, being let into each other, may be well fastened by means of iron wedges or forelock keys.
TRUSS-PARREL. That part of a rope-truss which goes round the yard.
TRUSS-PENDANT. That part of a rope-truss into which the truss-tackle blocks are seized. ”