STRUCTURAL MEMBER FOR BRIDGES AND FLOORS

Abstract: The invention pertains to a structural member (3) for bridges, floors, and the like which comprises at least one longitudinal girder of trapezoidal, V-shaped or U-shaped or rectangular cross section (3) with a concrete slab (6) provided thereon, wherein the longitudinal girder is made of synthetic material and at least the side parallel to the concrete slab is reinforced with parallel fibres having an embedded modulus of elasticity of more than 50 GPa. The structural member appreciably simplifies the construction of bridges and floors and has a low weight.

Description: STRUCTURAL MEMBER FOR BRIDGES AND FLOORS The invention pertains to a structural member for bridges, floors, and the like which comprises at least one longitudinal girder of trapezoidal, V-shaped or U- shaped or rectangular cross-section with a concrete slab provided thereon. Such a structural member is known from Netherlands laid-open patent application 7115625, which describes a prefabricated structural member composed of a steel sheet with a concrete slab provided thereon, while a reinforcement structure, also made of steel, is provided on the bottom side of the steel plate. The longitudinal girders in the above structure are very heavy, complicating transportation and placement. The high weight of the longitudinal girders will also have to be taken into account when designing the land abutments and piers supporting the bridge. Moreover, a great many operations are required on site before the structure is ready. The invention has for its object to obviate these drawbacks and achieves its aim as follows: the longitudinal girder of the structural member mentioned in the opening paragraph is made of synthetic material and at least the side parallel to the concrete slab is reinforced with parallel fibres having an embedded modulus of elasticity of more than 50 GPa. The fibres preferably have an embedded modulus of elasticity of more than 75 GPa, or even of more than 100 GPa. Also, it is preferred for a large share of the fibres in the side parallel to the slab (preferably more than 60 wt.%, or even more than 80 wt.%) to extend longitudinally and across the full length of the longitudinal girder or a substantial portion thereof. Conventional upper limits of said modulus are 400 Gpa and 250 Gpa, depending on the material. In addition to fibres extending in the longitudinal direction, fibres which extend in other directions, e.g., crosswise, can be embedded in the matrix to increase, say, the torsional stiffness or the transverse stiffness of the longitudinal girder. Also, places subject to greater load, such as the centre of the longitudinal girder, can be reinforced with additional fibres. For that matter, it should be noted that within the framework of the invention the term "fibres" comprises, int. al., filaments and bundles of filaments. The structural member according to the invention is made of synthetic material, giving it a comparatively low weight and hence making it easy to handle. The position of the fibres (in the side of the longitudinal girder which is parallel to the slab, which is also the side furthest removed from the slab) ensures that the high stiffness and the high tensile strength of these fibres will be made the most of. It should be noted that in the case of longitudinal girders having a V-shaped cross-section or a U-shaped one (with a round underside) the fibres are to be found at the bottom of the cross-section, i.e., in and around the point (of the V) or the curve. As is clear from the last paragraph, it is essential for the fibres to be far removed from the slab. When more than one longitudinal girder is employed, a slab extending right across the width of the longitudinal girders can be selected. Alternatively, of course, each longitudinal girder can be provided with a separate slab. Concrete is known to be especially suitable for absorbing pressure forces. Use of the structural member according to the invention in a bridge or a floor gives a just about ideal structure, one with a material especially suitable for absorbing pressure forces in those places where pressure forces develop, and likewise with a material especially suitable for absorbing tensile forces there where tensile forces develop. It is preferred to use an additional sheet made of synthetic material onto which a layer, or slab, of concrete is later applied on site. Since the sheet bonded to the longitudinal girders is also made of synthetic material, the weight of the structural member is not increased needlessly, and, what is more, very simple and inexpensive techniques can be used to make the connection between the sheet and the longitudinal girder or longitudinal girders. One very suitable example of a technique for uniting the longitudinal girder and the sheet is glueing them together. For that matter, glueing the sheet to the longitudinal girder or longitudinal girders will be further simplified when the two parts are made of the same or' a similar synthetic material. When the sheet is provided with a raised edge all round, the "tray" thus formed can be pumped full of concrete once it has been put in position on site. In that case there is no need for separate manufacture and/or transportation and lifting of the concrete sheet, thus reducing the number of operations and, correspondingly, the cost and the risk of defects or damage. The use of fibre-reinforced synthetic material allows both the designer and the contractor a lot of scope. For, synthetic material is easy to shape and process. The longitudinal girders, the sheet, and, optionally, other components can be made into more or less complex modules (cut to length), which, thanks to their low weight, can be transported to the site at the desired time on a conventional trailer. The low weight of the module also makes for simpler and safer lifting. All this simplifies the construction of, say, a bridge or a building significantly. A further advantage of the structural member according to the invention is that it can be employed in more light-weight objects such as footbridges and cycle bridges. Mostly, tropical hardwood is used to build such bridges, but the use of this type of wood is considered to cause serious damage to the environment. Such use can be avoided by employing the structural member according to the invention. The other sides of the longitudinal girder or longitudinal girders are preferably reinforced with a fabric or non-woven web of fibres. When the ends and picks both are at an angle of 30° to 60° to the longitudinal axis of the longitudinal girder, the shearing forces occurring in the other sides are very well absorbed. Highly suitable for use in the structural member according to the invention are fibres made up wholly or for the most part of poly(p-phenylene terephthalamide), glass or carbon. Such fibres have the required high modulus of elasticity and high strength and are pre-eminently suited to be used in composites. The structural member according to the invention can be used, e.g., in a bridge such as a footbridge or a cycle bridge, in other words, in an object where the structural member is visible to a great extent. In that case a box can be provided around the longitudinal girder or longitudinal girders, which box may be made, e.g., of synthetic material and like the longitudinal girder or longitudinal girders be glued to the sheet. Furthermore, the box can be reinforced with fibres, e.g., in the side furthest removed from the sheet. In that case the box not only has a "cosmetic" effect, it will also contribute to the strength and the (torsional) stiffness of the final structure. The invention further pertains to a bridge and a building provided with a structural member according to the invention. In such objects advantageous use can be made of the member's easy handling, low weight, and lack of restrictions where shaping is concerned. The invention also pertains to a process for manufacturing a bridge or a floor in which the ends of a structural member according to the invention are each placed or fastened on a support, such that the sheet is on the upper side, and in which a layer of concrete is pumped onto the sheet. As the concrete at first does not contribute to the load bearing capacity of the structure, it may be preferable, depending on the (expected) sagging of the structural member under the weight of the wet concrete, to provide temporary support for the structural member. In order to ensure tight bonding between the concrete and the structural member, the latter can be provided with dowels or anchors. In this way, after the concrete has been poured and has hardened, there will come to be good collaboration between the structural member and the concrete slab. The connection can also be made by roughening the structural member's synthetic material, i.e., the sheet on top of which the concrete is to be provided, e.g., by smearing it with epoxy resin and then covering it with sand. If so desired, the concrete can be reinforced. The process illustrates how easy it becomes to construct, say, a bridge using the structural member according to the invention. Once the supports, such as the land abutments and/or the piers, have been put in place, a module made up of a number of longitudinal girders and a covering plate or sheet can be arranged. Once the module has been anchored in place, a layer of concrete is pumped onto the covering plate, and this in effect completes the bridge. Optionally, a handrail can be provided (for which the arrangements can already be made on the module), as well as a layer of asphalt. It should be noted that US 4,079,476 discloses a footbridge made of synthetic material and reinforced with fibreglass. The footbridge has a U-shaped section, and both its sides are reinforced, int. al., with a fibreglass fabric. The floor near the sides is reinforced with parallel fibreglass filaments, as is the handrail, which is part of the sides. At certain intervals along the length of the footbridge members have been provided for extra support. Also, a so-called "torque box" is installed underneath the floor to increase the footbridge's torsional stiffness. The footbridge from US 4,079,476 is not suited for bearing greater loads such as an ambulance, and fails to combine the favourable properties of tension-resistant fibres on the one hand and a pressure-resistant material on the other in a single structure. FR 26835559 describes a footbridge comprising a caisson of U-shaped cross- section. The bottom of the caisson takes the form of a tension member composed of a light filler with fibres wrapped around it. The fibres are impregnated with resin. At the open side of the fibre a sheet is attached which is also made of a light filler with impregnated fibres provided thereon. The filler used for both the tension member and the sheet preferably is balsa. While this bridge as such is suitable for carrying pedestrians and cyclists, the different parts of the bridge, in particular the surface, are highly susceptible to point concentrated loads. A more substantial drawback is that the bridge will collapse under heavier loads, e.g., the weight of an ambulance. The invention will be illustrated below with reference to an example depicted in the drawings. Fig. 1 shows a side elevation of part of a cycle bridge according to the invention. Fig. 2 shows a cross-section of a cycle bridge according to the invention. EXAMPLE On a land abutment 1 and a pier 2 a structural member was mounted. The structural member was composed of two longitudinal girders 3 (length 10 m), which were glued to a sheet 4 (surface area 10 x 2.5 m). The longitudinal girders 3 were made of unsaturated polyester resin based on isophthalic acid and reinforced with fibres of Twaron type 1055 161 Ofl 000 (poly(para-phenylene terephthalamide) having a modulus of elasticity of 120 GPa (measured in accordance with DIN 65356/ DIN 65382). In the side parallel to the sheet 4, the bottom side, the fibres were embedded in the synthetic matrix unidirectionally in the longitudinal direction of the longitudinal girder 3 (90% of the total weight of fibres in the bottom) and in its transverse direction (10% of the total weight of fibres in the bottom). In the two other sides of the longitudinal girder 3, i.e., the sides, a fabric of the same fibres was embedded, such that the ends and picks both were at an angle of 45° to the longitudinal axis of the longitudinal girder 3. The fabrics extended up to 5 centimeters in the bottom side. The bottom side of each of the longitudinal girders 3 had a width of 40 cm, the two sides had a height of 60 cm. The sides were at an angle (α) to the bottom side of 95°. On the sheet 4 dowels were provided (not shown). The sheet 4 had raised edges 5, and the tray thus formed was pumped full of concrete 6. Hardening of the concrete 6 left the longitudinal girders 3 and the sheet 4 bonded to the concrete 6 by means of the dowels. Also, an anchorage 7 was provided in the concrete 6 to secure a connection with the pier 2. A box 8 was provided around the longitudinal girders 3, hiding them from view. Between the box 8 and the pier 2 supporting blocks 9 were mounted. The box 8 was also made of the aforementioned, fibre-reinforced polyester resin.

Claims: Claims 1. A structural member for bridges, floors, and the like which comprises at least one longitudinal girder of trapezoidal, V-shaped or U-shaped or rectangular cross-section with a concrete slab provided thereon, characterised in that the longitudinal girder is made of synthetic material, and at least the side parallel to the concrete slab is reinforced with parallel fibres having an embedded modulus of elasticity of more than 50 GPa. 2. A structural member according to claim 1 , characterised in that more than 60 wt.% of the fibres in the side parallel to the sheet extend in the longitudinal direction of the longitudinal girder. 3. A structural member according to either of the preceding claims, characterised in that between the concrete slab and the longitudinal girder a sheet of synthetic material is provided which extends across the width of the longitudinal girder. 4. A structural member according to claim 3, characterised in that the sheet is provided with a raised edge all around. 5. A structural member according to any one of the preceding claims, characterised in that the other sides are reinforced with a fabric or non¬ woven web of fibres. 6. A structural member according to claim 5, characterised in that the ends and picks both are at an angle of 30° to 60° to the longitudinal axis of the longitudinal girder. 7. A structural member according to any one of the preceding claims, characterised in that the fibres are made up wholly or for the most part of poly(p-phenylene terephthalamide), glass or carbon. 8. A structural member according to any one of claims 3-7, characterised in that the longitudinal girder and the sheet are glued together. 9. A structural member according to any one of the preceding claims, characterised in that a box is provided around the longitudinal girder or longitudinal girders. 10. A structural member according to any one of the preceding claims, characterised in that the box is fixed to the sheet. 11. A bridge provided with a structural member according to any one of the preceding claims. 12. A building provided with a structural member according to any one of claims 1-10.

Inventors: DALMOLEN LAMBERTUS GERRIT PETE, ROB ALPHONSUS JOANNES, ZWART WALTHER HENDRIK, DALMOLEN, LAMBERTUS, GERRIT, PETER, ROB, ALPHONSUS, JOANNES, ZWART, WALTHER, HENDRIK
Applicants: AKZO NOBEL NV, DALMOLEN LAMBERTUS GERRIT PETE, GRONTMIJ ADVIES & TECHNIEK BV, POLYMARIN BV, ROB ALPHONSUS JOANNES, ZWART WALTHER HENDRIK, AKZO NOBEL N.V., DALMOLEN, LAMBERTUS, GERRIT, PETER, GRONTMIJ ADVIES & TECHNIEK B.V., POLYMARIN B.V., ROB, ALPHONSUS, JOANNES, ZWART, WALTHER, HENDRIK
Application year: 1996
Main classification: E01D2
IPC codes: E01D2, E04B5, E04C3