Technical Field

The present invention applies to a bridge structure for road bridges including a beam composed of two types of concrete parts laid alternatively with p re-stressing rods placed in a cable in their centre allowing for continuous changes of the p re- stressing force according to the external load intensity. The beam may also be adapted to the needed width.

Prior Art

In the past bridges were constructed of beams KA 73 for the spans of 9, 12, 15 and 18 m and beams I 73 for the spans of 21 , 24, 27 and 30 m. This was true until 992, as long as the Type Documents prepared by Dopravoprojekt Bratislava applied. These beams were built in most of the bridges constructed in our country. Most of these prefabricates were "KA" or "I" shaped (Fig.1).

In about 1992 new types of the prefabricates began to be used and have been used until now. They are small-span beams, IMP, lengths 3, 6-9 m, reinforced concrete beams, Amos, with maximum length of 16 m, K-T beam length 15-32m (Fig. 2a) of cable concrete, VSTI beam length 9-35 m (Fig. 2b) of cable concrete and T-93 beams, intended to replace the original "KA" and T beams and similar to MK-T beams. For larger span bridges there are Petra beam lengths 24-30 m (Fig. 2c) which may experimentally be used for about 40 m span too. They are also beams made of cable concrete and consisting of parts which are on-site pre-stressed. All bridges assembled of these prefabricates are provided with a coupled reinforced concrete slab, usually 0.25 m thick, connecting the beams crosswise and distributing the load among them.

The to-date shapes of the prefabricates were required to be arranged without hollows where water might accumulate. The pre-stressed reinforcement was usually laid in cable channels in parabolic routes for the pre-stressing force to act against external loads. The pre-stressing effect adapted to the bend momentum progress and its calculation considered also the prop and wall thickness for the reason of crosswise forces resulting from the pre-stressing.

The ends of the beams were provided with anchors, ideally in even distribution along the beam height for the pre-stressing to be effected and to assure action of the summary forces of the cable as close as possible to the cross section centre of gravity for the reason of even distribution of the pressure from the individual cables across the cross-section.

The disadvantages of the beams were in that after the beam assembly the end crosswise members had to be concreted for better load distribution among the beams. This was a wet process of connection of the old concrete with the new concrete, which is inconvenient and relatively labour-intensive in the formwork and the concrete laying stages. These beams were hard to connect with the substructure into an integrated bridge with a construction without bearings with low maintenance demand. The forces in the pre-stressing cables had to correspond to the wall thickness. In most cases the builders used more cables with lower pre-stressing force per cable, which required more anchoring material.

Invention Essence

The above mentioned drawbacks are resolved by a bridge structure including a beam for road bridge construction according to the present invention, consisting of at least one row of nine parts in the row, including five parts of full cross section and trapezoidal shape extending downwards and four parts of lightened cross section forming a bottom-open trapezoidal frame also extending downwards. This beam is symmetrical around its centre with the individual parts arranged symmetrically from the centre towards the sides. The beam includes one end piece on each end in the length of 1.5 m; followed in the direction towards the centre with one open trapezoidal part with the bottom opening in the length of 5.88 m, and then a full cross section trapezoid in the length of 0.5 m and finally an open trapezoidal frame again, bottom open, in the length of 5.88 m. The centre of the beam is made of one full cross section trapezoid in the length of 0.5 m. The full cross section parts in the length of 0.5 m perform the role of a deviator (brace) in the beam. AH parts of the beam are provided with a lengthwise edge on the outside along both side walls forming an at least 0.3 m projection at their bottom. All beam part heights are identical, maximum 1.10 m, and their total width is 1.44 m. the lengthwise projection on the beam part sides can be used for changes of the beam height within a certain range, depending on the projection height. The form adaptation within the help of the fill can result in reduced height of the beam.

The opening in the centre of the full-cross-section parts is used for laying a cable comprising rods additionally p re-stressed in the full-cross-section parts with cohesion and loose in the open frame parts, where they are provided with anti- corrosion surface protection. Both end parts of the full cross section are provided with anchors where the pre-stressed rods of the cable pass through. The pre-stressing may be performed either on one or on both ends of the beam. The end parts of the beam rest in the bridge supports. The full part of the beam in the length of 1.5 m better transfers shear stresses increasing in the direction towards the supports.

The sidewise beam assembly creates the cross-section of the bridge load- bearing structure in the width required by the respective road type. All rows of the beam are connected by crosswise pre-stressing on the end parts. Instead of the so- far laid reinforced concrete end cross pieces this invention suggests two variants of the crosswise joining of the beams in their end pieces. The end parts of the full cross section are provided with a steel strip below the projection in the same height across the part width for fixation of the connecting steel sheets across the beam width with each sheet covering the connection of two neighbouring parts of the beam. This assures crosswise connection of the neighbouring beam rows. The openings in the neighbouring full-cross-section parts under the projection may also be used for laying a steel pipe across the hole width. The lengthwise projections of the full cross section beam parts catch crosswise forces of crosswise pre-stressing.

The beam parts are made of plain or high-standard concrete, provided in inside structural concrete reinforcement along the wall inside, usually of material 10425 or 10505.

The structural concrete reinforcement is placed along the beam length according to the construction principles defined by the Euro Code and extended according to the calculation if needed. The main load-bearing element of the reinforcement is represented by high-strength ropes Lp 15.8 mm, normal or annealed or stabilised and passing lengthwise through all beam parts in the needed numbers found by load-bearing capacity and applicability calculations. The number of the ropes and their placement along the beam length may be changed with regard to the external load intensity. The anchors placed on the end parts of the beams (beam faces) are passed though with pre-stressed ropes in the numbers specified by the calculation. The pre-stressing force acting against the external load may be adapted according to the beam stress calculation.

After the beam assembly to the supports the beam surface is covered with a reinforced concrete coupled joint-less slab, 0.25 m thick, reinforced with lengthwise ribs surrounding the beam on the sides or filling the space between the beams where there are more of them sidewise. This increases the overall stiffness of the bridge structure. The designed beam shows a compact frame-like shape with adjustable width. Another advantage is the option of operative adjustment of the pre-stressing force according to the external load intensity, or simple implementation of the structure as fully pre-stressed, partly pre-stressed or as pre-stressed reinforced concrete.

Drawing Description

Fig. 1 : Schematic drawing of prior art beams: a) KA-beam b) I-beam

Fig. 2: Schematic drawing of prior art beams: a) MKT-beam b) VST!-beam c)

PETRA-beam

Fig. 3: Lengthwise section of the beam with arrangement of the two part types with passing cable and the cable anchoring.

Fig. 4: Crosswise section A-A according to Fig. 3 through the end part of the beam with full cross section of trapezoidal shape, an opening for lengthwise cable laying, an anchor and a hole for the steel pipe placement across the part width.

Fig. 5: Crosswise section Β-Ε according to Fig. 3 through the open-frame beam part in trapezoidal shape with loose cable position marking.

Fig. 6: Crosswise section C-C according to Fig. 3 through the full cross section beam part of trapezoidal shape performing the role of a deviator and with marked opening of the lengthwise cable laying.

Fig. 7: Lengthwise section of the end part of the beam with full cross section with a hole for the pipe laying and marked rope position and support location.

Fig. 8: Crosswise section of the end parts of the full cross section for road S1 1 , 5/80 consisting of nine beams, a pedestrian space and a reflective strip with marked crosswise connections of the neighbouring beam parts with anchored strip steel and welded connecting sheets.

Fig. 9: Crosswise section of the end parts of the full cross section for road S11 , 5/80 consisting of nine beams, a pedestrian space and a reflective strip with marked pipe location for crosswise pre-stressing.

Fig. 10: Crosswise section of the lightened beam parts for road S11 , 5/80 consisting of nine beams with a reinforced concrete slab, a pedestrian space and a reflective strip.

The invention is further described through embodiment examples, by no means limiting other embodiment options within the scope of the claims for patent protection. Examples of invention embodiments

Embodiment 1

The load-bearing structure of a bridge for road S11.5 /80, providing a pedestrian space on the right side 16 and a lengthwise reflective strip on the left side 17 (Fig. 8, 0) consists of nine beams i according to the present invention placed sidewise and provided with an interlocked reinforced concrete slab 14 with reinforcing ribs 15 filling the space between the beams JL

Each beam 1 consists of nine parts 2, 3, 4 arranged sidewise and consisting of five parts 2, 4 with full cross section and trapezoidal shape extending downwards and four parts 3 lightened and forming a bottom-open frame of trapezoidal shape extending downwards (Fig. 5). The beam 1 is symmetrical around its centre where the individual part types 2, 3, 4 are arranged symmetrically from the centre to the sides. The beam i comprises one end piece 4 (Fig. 4) on each end in the length of 1.5 m, followed on each end in the direction towards the centre with one open trapezoidal frame part, bottom-open 3 in the length of 5.88 m (Fig. 5), this part 3 being further followed with one trapezoidal full cross section part 2 in the length of 0.5 m (Fig. 6) and with another part 3 forming an open frame on the bottom in the length of 5:88 m and in trapezoidal shape. The centre of the beam 1 comprises one part 2 with full cross section and trapezoidal shape in the length of 0.5 m. Parts 2 with the full cross section and lengthy 05 m are used in beam I as a deviator (brace). All parts 2, 3, 4 of beam 1 are provided with a lengthwise edge 5 forming a projection 0.3 m high along the bottom edge of both side walls on their outside. The lengthwise projections in beam 1 with the full cross section catch crosswise forces from the p re- stressing. All parts 2. 3, 4 of beam I are 1.00 m high and in total 1.44 m wide. The opening 8 in the centre of parts 2 and 4 hides a cable laid lengthwise through all parts 2, 3 and 4 The cable consists of ten high-strength ropes 6, 7 type LP 15.8 mm, with additional pre-stressing and cohesion in parts 2 with the full cross section (6) and in parts 3 forming the open frame laid loose with surface protection against corrosion (7) (Fig. 3). Both end parts 4 of the full cross section are provided with anchors 9, through which the pre-stressed ropes 6 of the cable pass. The pre- stressing is performed on both ends of the beam ±. The end parts 4 of the full cross section are supported from the bottom with a strut 10 (Fig. 7). The full end parts 4 of beam I in the length of 1.5 m between transfer the shear stress increasing in the direction towards the struts.

The assembled nine beams 1 sidewise were crosswise connected in their end pieces 4. The end parts 4 of the full cross section are provided with a steel strip 11 below the projection in the same height across the part width. The strip size is 200/300 and the length is 1.40 m. The strips JM are part of the end pieces 4 of beam 1, laid in the beam 1 formwork before the beam concrete laying. The assembled beams 1 are connected with steel sheets 12 size 150/30 mm and length 1.4 m welded to the strips 1_1 for each sheet 12 to cover a joint of two neighbouring parts 4 of beam 1. This assures crosswise connection of the neighbouring rows of beam 1 Beam 1 is provided with a reinforced concrete coupled slab 14 reinforced with lengthwise ribs 15 filling the space between parts 2, 3, 4 of the neighbouring rows of the beam ±.

Embodiment 2

In beam i of bridge structure for road S11.5 /80 according to embodiment 1 the crosswise pre-stressing is implemented with a steel pipe in the neighbouring end parts 4 of full cross-section in the area below the projection placed in a hole 13 along the beam 1 width (Fig. 9). The pipe is laid in before the beam i concrete laying and its position and profile is identical in all beams 1. After assembly of beams 1 crosswise pre-stressing reinforcement is passed through all pipes and the pre- stressing is implemented by anchors laid in concrete on the external dent of the edge beams 1 and a pres-stressing device. The pre-stressing is implemented in the end parts 4 of beam i, and with it the beams 1 are not only connected but also pressed together by the acting pre-stressing force (crosswise pre-stressing). Industrial Applications

This beam can be used in a wide range of applications with different crosswise arrangements for roads with pavements, with reflective strips, and for motorway bridges. A certain reinforcement of the beam frame section and a suitable composition of the number of the beams for crosswise arrangement is expected to allow for development of a beam for railway bridge application.