US2151267A - Truss girder and method of producing the same - Google Patents

Description

March 2l, 1939. u. FlNsTx-:RWALDER TRUSS GIRDER AND METHOD 0F PRODUCING THE SAME Filed June l0, 1937 JZ'ornays Patented Mar. 21, 1939 UNITED STATES.

Ulrich Finsterwalder, eriimwilmerldorf,

Germany Application June 10, 1937, Serial No. 147,580 In Germany March 13, 1936 (Cl. 'I2-110) 9 Claims.

As compared with metal plate girders truss girders offer the advantage that the bending moments and transverse stresses set up by the loads are very elciently taken up, useless dead weight being avoided. For this reason this construction is predominantly used by the designer of iron structures.

In ferro-concrete construction the truss girder has not been universally adopted. This is due 10 to the importance of the subsidiary stresses which result from alteration in length of the bars of the truss girder and the tendency towards bending at the nodal points, or joint regions. While the alterations in length of the bars are of the same l5 order in the cases of iron structures and ferrol concrete structures, the bending stresses due to prevention of angular turning movements at the joints are more diicult to deal with; that is, they require a larger share of the permissible stress.

This depends both on the circumstance that the bars of the ferro-concrete are less slender, and

that the relations of modulus cf elasticity and permissible stress are less favourable.

Further, in a ferro-concrete truss girder there is the difficulty of anchoring the iron properly in the compressed concrete, as the alteration in the bar stresses proceeds in jumps and partly in zones of pure tension.

'I'he invention contributes substantially to the overcoming of the said drawbacks and contemplates the production of truss girders consisting of ferro-concrete in the following manner:

The compression bars of the structure are constructed of ferro-concrete in a well known manner. The tension bars are, however, first produced in simple iron construction, preferably as bundles of round rods. After all or some oi. the tension bars have been anchored at joints provided i'n the ferro-concrete, the truss girder is 4 loaded, for example by freeing the scaifolding, and only then the tension bars are sheathed with concrete and thereby the truss girder converted into a ferro-concrete structure.

In consequence of the smaller strength of the individual round rods the angular turning movements at the joints, which are called for when the structure is subjected to stress, can proceed j without serious subsidiary stresses. Further, the result is obtained that the iron elements are given a preliminary extension relatively to the concrete. It is thus possible to use iron elements of high values, which involves economical advantages, and, further, the structure as such is improved by the diminution of the stresses of the concrete. Further details and features of .the invention chorages i and f the concrete is under compres- PATENT OFFICE are set forth in the following description and indicated in the accompanying drawing illustrating two forms of truss girder produced by the method of the invention.

Fig. l is a diagrammatic elevation of a complete girder.

Fig. 2 is a fragmentary longitudinal section of the girder according to Fig. l.

Fig. 3 is a section at right angles to Fig. 2.

Fig. 4 is an elevation, showing the same section as Fig. 2, at another stage in the erection.

Figs. 5 and 6 are a longitudinal section and a transverse section, respectively, of a second embodiment, in the form of an arched covering.

'I'he truss girder illustrated in Fig. 1 is borne by two supports. It consists of parallel straps, hereinafter called chords a and b, vertical struts c and diagonal stays d. a and c are under compression; b and d are subject to tension.

The diagonals d have an iron reinforcement, designated e; the reinforcement provided in the lower chcrd b is designated h and h' in Fig. 2. The reinforcement e of the diagcnals d is anchored at the joints by means of plates f and g, as shown in Fig. 2.

The anchorages of the reinforcementof the bars b are eiected at the nodal points k by means of similarly formed plates i. Between the ansion so that the diiferential stresses are ordinarily balanced at the joints.

'I'he truss girder is produced by rst forming the compression bars in ferro-concrete. The stays are initially formed of iron only. This preliminary stage in the production of the truss girder is illustrated in Fig..4. In this condition the compression bars a and c as well as the joints k are already sheathed with concrete. Of the bars indicated also in this figure by b and d only the iron skeleton is diagrammatically indicated in the drawing. Fig. 4 is intended also to show that the structure is already under stress. which may be produced by loading. Preferably the stress is set up by simple removal of the shuttering or scaffolding of the structure. Only when the structure is suitably loaded are the bundles of iron rods forming the tension bars b and d sheathed in concrete.

In the structure shown in Figs. 5 and 6 a plu- 5o rality of truss'girders are disposed adjacent to one another, the upper chords a being formed at the same time as roof arches, for example, so as collectively to form a roof for a shed. In other respects the method of production of the several 53 girders is the same'as in the arrangement shown in Figs. 1 to 4.

'I'he application of the inventionto truss girders which are formed as marginal beams of root arches affords important advantages as the new truss girders weigh approximately only half as much as the so-called plate girders usual in this connection.

As ,the marginal girder in a structure of wide span weighsapproximately as much as the covering which is omitted, a reduction in weight -of the marginal girder leads to a considerable increase in the possible span width of the truss girder. Moreover, in this instance the already mentioned other structural and economic ad vantages are realized.

I claim:

`.1. A method of producing a ferro-concrete truss girder comprising first forming a girder structure consisting of compression bars of ferroconcrete and tension bars of iron only, then loading the structure, and then sheathing the tension bars with concrete.

2. A method of producing a ferro-concrete truss girder comprising first forming a girder structure consisting of compression bars of ferroconcrete and tension bars each comprising a bundle of rods of round iron, then loading the structure, and then sheathing said rods with concrete. i

3. A ferro-concrete truss girder comprising an upper chord of ferro concrete in compression, a lower chord comprising metallic bars under tension, vertical struts of ferro concrete, and diagonal stays comprising metallic bars interposed between said straps, and transverse metallic anchor plates secured to said metallic bars in the lower chord and adjacent the ends of said bars in the diagonal stays, said bars and plates being sheathed with concrete for anchoring said' bars and stays at the joints of the girder.

4. A ferro-concrete truss girder comprising an upper cho'rd of arched cross-section, lower chords comprising bars under tension, vertical struts and diagonal bars interposed between said upper chord and said lower chords, and iron anchor plates, sheathed with concrete, anchoring said bars at the joints of the girder.

5. A method of Y producing a ferro-concrete truss girder comprising first formingl a girder structure consisting` of a horizontal upper chord and vertical struts of ferro-concrete, said upper chord and struts being normally under compres- 2,151,267 A c i stays of iron bars only throughout the panels thereof, the iron bars of said lower chord and stays extending through and being anchored beyond the joints of the ferro-concrete members. then loading the structure, and then sheathing the panels of the lower strap and diagonal stays with concrete.

6. A ferro-concrete truss girder as claimed in claim 3, the end of portions of said bars extending through the joints of said girder, said anchor plates being substantially at the ends of said bars whereby to compress the materials at said joints between said plates.

'7. A ferro-concrete truss girder as claimed in claim 3, said iron bars in said lower chord and said diagonal stays extending at least partly through the joints of the girder.

8. A ferro-concrete truss girder comprising an upper chord of arched cross-section, lower chords comprising bars of iron under tension, vertical ferro-concrete struts between said lower chords and the lower edges of said upper chord, diagonal tension bars of iron interposed between said struts, the iron bars in said lower chords being sheathed in concrete at the joints below said vertical struts, the lower ends of said diagonal bars extending through said joint, and iron anchor plates secured to the ends of said tension 'neath twovof said struts, iron anchor plates attached at each end of each of said bundles'and extending transverselyv thereto, diagonal` tension barsextending fromsaid upper chord to said lower chord between said vertical struts, said tension bars comprising bundles of iron rods, each oi said bundles being anchored at its upper ends by a transverse iron plate imbedded in said upper chord, and extending'through the region in said upper chord above one of said struts and extending through the region in said lower, chord beneath one of said struts, and secured to one oi' the rst-mentioned anchor plates, said lower chord and said diagonal tension bars being sheathed in concrete.

ULRICH FINS'IERWALDER.

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