US2898757A - Method of constructing reinforced concrete bridge - Google Patents

Description

Aug. 11, 1959 I U.FINSTERWALDER 5 2,898,757

memon 0F CONSTRUCTING REINFORCED CONCRETE BRIDGE;

Original Filed April 11, 1949 v 3 Sheets-Sheet 1 iifi'flf-flulbdj jfi I. 7. i 7. 5%?

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In venfar dlforng s Aug. 11, 1959 u. FINSTERWALDER 2,898,757

METHOD OF CONSTRUCTING REINFORCED CONCRETE BRIDGE 3 Sheets-Sheet 2 Original Filed April 11, 1949 t In ven for y 73' J MW+M4E Aug. 11, 1959 u. FINSTERWALDER 2,398,757

METHOD OF CONSTRUCTING REINFORCED CONCRETE BRIDGE Original Filed April 11, 1949 3 Sheets-Sheet 3 In vnfor nitude as the specific pressure prevailing in the thrustbeams of the frame-work. To this end, the re-enforcing bars consisting of a material having a high tensile strength are prevented from entering into a bonding relationship to the surrounding concrete either by coating the reenforcing bars by a plastic or by forming the concrete beam with longitudinal bores or cavities accommodating the re-enforcing bars in spaced relationship to the concrete permitting of a free relative longitudinal displacement. After the concrete has set, the re-enforcing bars extending through the beam are subjected to a powerful bias by use of known implements, the reactionary force of the tension set up in the re-enforcing bars serving to compress the surrounding concrete lengthwise. Subsequently, a bond may be produced between the steel bars and the surrounding concrete element of the thrust-beams by filling up the bores or cavities with cement.

Important advantages in various regards are attained by the present invention.

Owing to the provision of a gap in the center, the bending torques approach zero with decreasing distance from the gap permitting of a particularly light design of the adjacent zones of the adjoining trusses as is desirable on account of their large distance from the pillars, whereas a maximum bending torque resulting from the own weight of the bridge and largely fluctuating torques from the traffic load would result within this zone, were the truss a continuous one. The use of a truss of the described design permits of taking up the torque prevailing at any point with the largest vertical dimension of the truss 7 available at such point. This again entails the admissability of an extremely light design of the beams over a large range of the truss. While it is true that the bending torques prevailing in the truss within the zone above the pillars will exceed those set up in a continuous beam of the customary design, this consequence is more than off-set by the afore-stated advantage regarding the bending torques produced. The savings in weight of the large middle span result in a surprising increase of the span possible with a given vertical dimension of the bridge above the pillars, such increase amounting to about 30%. With a given span the present invention makes it possible to reduce the dimensions of the bridge thus resulting in savings of concrete and steel enhancing the efiiciency. The reduction of the materials required is not purchased at the cost of complicated and expensive construction implements and building methods for producing the beams. Regarding the difficulties involved, the new construction methods do not differ from those ordinarily used in the normal re-enforced concrete construction art.

The elimination of a scaffold supported by the ground offers great advantages in the construction of bridges of large span, particularly in such cases in which such scaffolds are hampering navigation on rivers or are endangered by floods and ice. The novel method of constructing the trusses section by section progressively simplifies the process substantially resulting in a cost reduction. This holds true for both species of the novel constructing method in which one and the same scaffold and the same concrete forms supported by the finished truss sections are used requiring a minimum of capital investment for the constructing implements.

The second species of the constructing method as above described entails the advantageous possibility of adjusting the bias set up in re-enforcing bars, as the work proceeds, to meet the requirements arising in the course of the completion of the truss. Such adjustments take care of the fact that the distribution of the forces set up in the beams changes with the progress of the work, since in the finished truss such distribution is quite different from Another object of the present invention is a displaceable 4 scaffold comprising steel beams imposed on the finished joints of the upper chord and projecting therefrom a distance corresponding to one section, such scaffold being so dimensioned as required to support the concrete forms and the load to be taken up in the assembly of one truss section.

Further objects and features of the present invention and the manner in which the same may be performed as well as the advantages attained by the invention will appear from a detailed description of two preferred embodiments of the invention described hereinafter with reference to the accompanying drawings.

In the drawings Fig. 1 is an elevation of the novel bridge comprising three spans;

Fig. 2 is a partial vertical cross-section through a cantilever truss forming part of the bridge said crosssection being taken within the middle span at a distance from a pillar of about one quarter of the span and shown on an enlarged scale;

Fig. 3 is a partial view of Fig. 1 on an enlarged scale showing the central joint of the two cantilever trusses;

Fig. 4 is an elevation of one section of the truss in a semi-finished condition in which the re-enforcing bars of the tension-beams are not yet provided with a mantle of concrete;

Fig. 5 is a longitudinal section of the same truss section as shown in Fig. 4 in a finished condition showing the position of the re-enforcing bars and the interconnection of the same;

Fig. 6 is a partial longitudinal section through a modi' fied cantilever truss illustrating the second species of the building method;

Fig. 7 is a cross-section taken through the truss shown in Fig. 6 on an enlarged scale;

Fig. 8 is a partial elevation of a semi-finished centilever truss under construction showing the novel displaceable scaffold and concrete form used to successively construct one section after the other;

Fig. 9 is an end view from the right of Fig. 8.

The bridge shown in its entirety in Fig. l embodying the present invention extends over three spans A, B and C at a ratio of 1:2: 1. It comprises two cantilever trusses carried by and projecting equal distances from the two pillars 2 and 3. The adjacent ends of the cantilever arms 5 and 6 are separated by a gap 1. The cantilever arms 4 and 7 constituting the spans A and C are supported on embankment rests or foundations 8 and 9 by customary supporting means such as roller bearings and counterweights or other means not shown in detail adapted to transfer forces in a vertical direction.

Each of the two cantilever trusses of identical design comprises an upper chord in form of a plate of re-enforced concrete constituting the road bed, a lower chord of re-enforced concrete preferably in form of a plate, vertical beams between the two chords and diagonal beams adapted to take up tensional forces.

With this arrangement the own weight of the structure produces negative bending torques only in each of the trusses over their entire lengths, whereas the traffic load produces negative torques only in the middle span, i.e. in the cantilever arms 5 and 6 and positive torques in the outer spans i.e. in the cantilever arms 4 and 7. Such positive torques, however, are small compared with the negative torque caused by the weight of the structure and may surpass the same only in the immediate proximity to the embankment rests 8 and 9. In Figs. 2, 3, 4 and 5 details of the structure are shown to illustrate the cantilever truss composed of thrust-beams built up in accordance with the standard practice of re-enforced concrete construction and of tension-beams built in accordance with the standard steel construction practice. Fig. 2 illustrating a cross-section through the middle span taken ata distance of about one quarter of the span from the pillar, shows the lower chord 10 constituted by a standard plate of rec-enforced concrete' and; the; upper chord 11 reenforced by bundles; of steelbars 12 in cross-section. These bundles take up a spaceof about half of thecrosssection of' the upper chord the latter forming 11G road bed. Moreover, Fig. 2'shows a vertical thrust beam which, in the present embodimennis constituted by a plurality of posts or columns 13 ofre-enforced concrete. The diagonal tension-beams 14 shown in Figs. 4 and 5 are not visible in" Fig; 2 as they are hidden from view by thezposts. 131-.

Fig. 3 shows the joint between the two cantilever trusses with a gap 1 provided therebetween in the middle of the span B and with a vertical link 15 of known design for the transfer of vertical forces only.

Fig. 4 shows a section of the frame-work truss in a semi-finished condition in which the vertical beams 13 and the lower chord section 10, all subject to thrust, have been completely formed of re-enforced concrete, the scaffolding and the concrete forms having been removed, iwhereas the re-enforcing bars 12 of the upper chord 11 and the re-enforcing bars of the diagonal beams 14, all subject to tension under the weight of the semifinished truss-sections, have not yet been provided with a mantle of cement. It will be appreciated that owing to the removal of the scaifolding the thrust beams and 13 as well as the tension- bars 12 and 14 are placed under load.

Now the concrete forms are brought into position as will be described later for the purpose of mantling the tension- bars 12 and 14 with concrete. Fig. 5 shows the finished structure in section illustrating the re-enforcing bars embedded in concrete.

In a modified process the number of re-enforcing bars placed in position in a slack condition for the upper chord sections is limited to the figure required to carry the weight of the bridge. After assembly of the bridge in the condition shown in Fig. 4, additional bars or cables sheathed with sheet metal or a plastic coat adapted to carry the final load are inserted in the concrete form for the upper chord and are then embedded in the concrete. After the latter has set, the additional re-enforcing bars or cables are subjected to a bias of such a degree that the resulting pressure set up in the surrounding concrete is sufficient to prevent any tension from being exerted on the concrete of the upper chord section under the influence of the biggest possible load of the finished bridge.

This process has the advantage that the road bed Will have an increased density and that cracks are prevented from forming under load. Another advantage is the reduction of the number of sleeve joints and other connecting elements required to connect the tension-bars of adjoining upper chord sections. Each of the biassed tension-bars is anchored at its two ends only, that is to say at two points and not at any beam junction.

The tension-bars may be arranged and distributed in various manners. They may be arranged in a bundle located in a special zone or they may be distributed over the entire width of the upper chord section. The hollow space between each of the biassed tension-bars or cables and the surrounding sheathing may be filled up with cement.

In building up a bridge constituted by cantilever trusses as shown in Figs. 1 to 5 the following method may be employed:

First two sections of the truss above each of the two pillars 2 and 3 are constructed in accordance with the standard practice using the customary scafiolding and concrete forms except for the tension-beams which are left in semi-finished condition as shown in Fig. 4. Then the auxiliary scaffold shown in Figs. 8 and 9 is brought into position for the purpose of constructing the adjoining sections progressively. This scaffold consists of a plurality of beams 17 arranged parallel to each other at: a suitable distance and distributed oven the entire width of the bridgetresting.onthelast; twoibeamvjunce tions. 18 and projecting: beyonditheendsection; a. distance corresponding to. the length. of one section. as shown in Fig. 8. From such beams the concrete forms. 19 are suspended: by. means of suspending elementsv 20:

With the aid of this. scaffoldz'the lower-chord. section 21 and the vertical posts 22 positioned thereon. are formed of re;enfor,cedf concrete the diagonal tension-bars 23 and theuppen chord re-enforcing' bars 24: are assem bled. The section 21 is formed adjoiningihe previously finished section abutting against the latter at the joint 26. The tension- bars 23 and 24 are connected by means of connecting sleeves 27 and 28 with those of the preceding truss section. Care must be taken to postpone the mantling of the diagonal tension-bars 23 and of the bars 24 of the upper chord with concrete until the entire cantilever arm has been built up in the described manner up to its end.

The other species of the novel method of constructing the cantilever trusses will now be described hereinafter with reference to Figs. 6 and 7.

Fig. 6 illustrates one section of the cantilever truss differing from that illustrated in Figs. 1 to 5 by the provision of thrust-beams as diagonal braces 30 in lieu of the diagonal tension-beams shown in the first described embodiment. The road bed plate 32 constituting the upper chord 31 of the truss as well as the vertical posts 33 are biassed in a special manner. Only part of the reenforcing bars 34 of the upper chord are anchored at each beam junction while the rest of the re-enforcing bars 35 extends the whole length of the bridge. Whenever a truss section has been finished and its concrete has set, the short tension-bars of the upper chord are put under tension. In order to prevent the tension bars from entering into a bonding relationship with the surrounding concrete and to thus render a subsequent tensioning possible after the concrete has set, the re-enforcing bars to be subjected to a bias are either coated with a plastic or inserted in hollows or cavities or bores provided in the concrete.

Fig. 7 shows clearly that the tension-bars 34 are anchored at the beam-joints whereas the tension-bars 35 are running clear through the entire length of the bridge. With this mode of construction the truss may be progressively built up section by section with the aid of the auxiliary scaffold shown in Figs. 8 and 9 with slight modifications to suit the requirements.

The term re-enforcing bars used in the claims following hereinafter is to be construed as including wires, rods, solid bars, cables or the like. While my invention has been described herein-above with reference to specific embodiments thereof I wish it to be clearly understood that my invention is in no way limited to the specific features of such embodiments but is capable of numerous modifications within the scope of the appended claims.

What I claim is:

1. A method of constructing a reinforced concrete cantilever truss bridge comprising constructing a center pier, simultaneously constructing truss panels from opposite sides of said pier by placing first short upper chord reinforcing rods, said rods being anchored to the center pier and extending one panel length and second upper chord reinforcing rods extending over a plurality of panel lengths, and vertical post reinforcing rods, these being tension members, then pouring concrete and forming the lower compression chord and compression diagonal strut and encasing in concrete the upper chord and vertical strut rods with said first short upper chord rods left unbonded to the concrete, tensio-ning said first short upper chord rods after the concrete has set to compress the upper chord, and then progressively repeating in the same manner the erection of adjoining panels until mid-span is reached with the weight of each panel being constructed and the construction equipment being supported by the preceding completed panel and thereb; tensioning References Cited in the file of this patent said upper chord and vertical strut rods.

2. A method as in claim 1, further comprising connect- UNITED STATES PATENTS ing the first short bars ofone panel to similar bars in an 21151367 Flnsterwalder 1939 adjoining PaneL 5 2,414,011 Blllner Jan. 7, 1947 3. A method as in claim 2, further comprising bonding FOREIGN PATENTS saici first short bars after they are tensioned to the en- 196,575 France of 1889 casing concrete. 1 a

4. A method as in claim 1, further comprising con- OTHER REFERENCES structiqg i pp and lower chords as slabs extending 10 Civil Engineering Publication, March 1941, pages 1so the entire width of the bridge. 1S3.

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