A span structure such as a bridge

Abstract: A span structure, such as a bridge, consisting mainly of a supporting structure built up from steel sections and a road surface connected therewith and composed of concrete elements. At the location of at least part of the joints (4) between successive concrete elements (3) there are arranged pressure means (7) suitable for applying in the concrete elements (3) compression forces acting in the span direction, transmittable to the supporting structure (1) at the ends (6) of the road surface.

Description: This invention relates to a span structure as well as a method for constructing such a span structure, e.g. a bridge, consisting mainly of a supporting structure built up from steel sections and a road surface connected therewith and composed of concrete elements, said method including the steps of: arranging fluid activated pressure means comprising a pressure vessel at the location of at least part of the joints between successive concrete elements, pressurizing the pressure means by filling with liquid under pressure to generate in the concrete elements compression forces acting in the span direction and transmitted by stops to the supporting structure, filling the joint around the pressurized pressure vessel with hardening and after hardening substantially incompressible material, depressurizing the pressure means after hardening of said material around the pressure vessel, and filling the space occupied by the pressure vessel with substantially incompressible material, such as known from US-A-4,343,123. Constructing a span structure of the above-mentioned general type is known from practice. When the road surface is poured on the site on the supporting structure , shrinkage cracks or other cracks may occur in the course of time owing to the hardening process, resulting in damage to the road surface and symptoms of fatigue. These cracks advance the date of maintenance work and/or shorten the life of the structure. It is known that when using a concrete road surface as a monolithic whole because the concrete parts are under pressure both in transverse and in the span direction, the maintenance costs are substantially lower and the life of the span structure can be prolonged. The compressive stress in the concrete surface in the span direction is usually realized by means of a temporary support of the supporting steel structure ensuring that the supporting structure is bend in the upward direction. Subsequently, the surface is poured on the site in parts in a specific sequence or pre-fabricated concrete elements are placed to form the road surface, after which the joints between and the recesses in the concrete elements serving to connect them with the supporting structure are filled with mortar. After hardening of the road surface or of the mortar in the joints and recesses the temporary supporting structure is removed with the result that the road surface and the joints transverse to the span direction are subjected to pressure by its own weight in the span direction. The compressive stress in the concrete elements transverse to the span direction can be applied in the known manner on the site or in the factory by means of prestressed reinforcement. The laborious erection of an auxiliary supporting structure and the subsequent removal thereof can be left out by using the construction method known from US-A-4,343,123. The compressive forces in the concrete elements are generated by placing hydraulic pressure means of a specific type, so called flat jacks, in a joint between two concrete elements, which are fixedly attached to the supporting construction to form consoles for the hydraulic pressure means. Such a flat jack comprises two parallel pressure plates connected at their perimeter by a channel part with a diameter wider than the maximum distance between the pressure plates. The hydraulic pressure means are placed on a beam of the supporting construction to create a bending moment in said beam. This structure implies that an only locally compressive forces can be generated at a specific part of the edges of the concrete elements bordering the joint and, thus, limits the maximum force to be applied when compared with the above discussed bent-out construction where the edges of two adjacent concrete elements contacting each other over their entire surface. After pressurizing the concrete elements a part of the joint is filled with so called babbit material. After hardening of said material the flat jacks are depressurized and removed, the voids being formed by removing the flat jacks being filled with another substantially incompressible material, such as concrete. The strength of the concrete and the locally acting flat jacks limit the possible compressive forces in the road surface. The combination of relatively low local compressive forces in the road surface and attaching the road surface rigidly to the supporting construction before pressurizing the flat jacks decreases the possibility to compensate the creep of the concrete road surface and the favourable influence on the bending moment in the construction. The object of the invention is to provide a construction method and span structure of the above type in which the road surface can be pressurized in the span direction without requiring an auxiliary structure as a temporary support while retaining the possibility to exert very high compressive forces in the concrete elements with relatively simple and inexpensive means. According to the invention this object is attained by providing stops, which take up the forces in the span direction, applied in the concrete elements, at the ends of the span structure, said stops allowing a horizontal shift of the concrete element between the stop and the pressure vessel with respect to the supporting structure; providing pressure means comprising as pressure vessel (7) a metal tube flattened with smooth flowing forms in cross-section, the long axis of the flattened metal tube, seen in cross-section, being positioned substantially parallel to the main plane of the joint (4) and said metal tube being located completely inside the joint (4), pressuring the whole road surface in the span direction to compensate from the beginning shrinkage and creep effects such that the road surface functions as a monolithic whole; after pressurizing rigidly connecting the concrete elements to the supporting construction; and filling under pressure the flattened metal tube with a hardening and after hardening substantially incompressible mass. By these features the concrete elements are pre-stressed in a uniform way between the local pressure means and the local stops. After achieving this uniformly pre-stressed condition said condition is maintained by filling the joints and connecting the concrete elements between the pressure means and the stops to the supporting construction before depressurising the pressure means. By using a flattened metal tube with flowing forms, which can be relatively cheap made of a one piece tube by simply deforming the tube between two pressing surfaces, said pressure means becomes an integral part of the joint taking an active part in maintaining the compressive forces in the road surface and in reinforcement of the joint against fatigue damage by being filled under pressure. By arranging expandable pressure vessels preferably extending over substantially the length of the joints between the concrete elements the whole road surface can be pressurized in the span direction in such a manner that even after rigidly attaching the road surface to the supporting construction the shrinkage and creep effects otherwise occurring in the span direction are compensated from the beginning across the whole span length as the road surface is equally pre-stressed over its whole length in a sufficient manner, so that the road surface functions as a monolithic whole in a composite construction. The compressive stress applied in the concrete elements in the span direction produces a moment opposite to the weight load, as a result of the eccentric action on the supporting steel structure, so that this supporting structure can be made more slender. The hardening mass can be brought directly into the pressure vessel on condition that the hardening of that mass occurs more slowly than the hardening of the material applied around the pressure vessel in the joint. However, according to a further embodiment of the invention it is preferred that the flattened metal tube is filled under pressure with a hardening mass after depressurizing the pressure means. Depending of the span width of the bridge more than two concrete elements can be present. Then, it is, according to a further embodiment of the invention, preferred, that at least one concrete element is placed between the two concrete elements at the ends of the span structure, which at least one concrete element is provided with pressure means at its opposed ends and is locally firmly connected to the supporting structure, allowing horizontal shift between said local connection and the pressure vessels with respect to the supporting structure. Further, the invention relates to a span structure, such as a bridge, consisting mainly of a supporting structure built up from steel sections and a road surface supported by the supporting construction and composed of at least one concrete element between stops at the end of the road surface, joints being present between at least a concrete element and a stop, pressure means comprising a pressure vessel arranged in a joint and filled with a hardened mass being arranged at the location of at least part of the joints, compression forces acting in the span direction and transmitted to the supporting structure by the stops being present, as known from FR-A-2,218,434. The pressure means in the span structure known from FR-A-2,218,434 consist of Freyssinet jacks composed of two parallel rectangular plates connected at their perimeter by a channel part with a diameter wider than the maximum distance between the pressure plates. These jacks are placed between a single concrete element, shiftable to the supporting construction and forming the road surface, and a console attached to a beam of the steel section, i.e. only a local compressive force on a specific part of the edge of the concrete element can be generated and thus limiting even more the maximum compressive force in the span direction as discussed above with respect to US-A-4,343,123. Moreover, the Freyssinet jacks are to be considered as lost elements which increase the manufacturing costs, especially in view of the specific construction of said jacks and necessitate to differently constructed, costly ends of the supporting construction. When, according to the present invention the road surface is composed of at least two concrete elements rigidly attached to the supporting construction and defining a joint there between and the pressure vessel is located in a joint between two concrete elements and consists of a metal tube having two opposed, in cross-section by deforming flattened surfaces acting as deformable pressure surfaces, the long axis of the flattened metal tube, seen in cross-section, being substantially parallel to the main plane of the joint, very high compressive forces in the span direction can be generated. Although the pressure means, as in the known construction, are to be considered as lost elements the costs are relatively low due to the simple and uncomplicated structure of the flattened metal tube used as pressure vessel and their function as a replacement for an otherwise needed reinforcement in the joint to meet the demands for fatigue resistance. By placing the pressure means in a joint between two concrete elements the whole length of the joint is available for pre-stressing the concrete elements creating the possibility of uniformly dividing the pre-stress forces over the width of the concrete elements. Attaching the concrete elements to the supporting construction after pre-stressing maintains this uniformly pre-stressed condition. The concrete element is provided with a first surface for forming a part of a road surface and an opposed surface suited to be connected with a supporting steel structure suitable for use in a span structure of the above type. Such a concrete element is provided at the second surface with partly poured-in angle irons extending in the span direction to form by the leg of the angle iron projecting from the concrete element a supporting and shifting surface with respect to the supporting steel structure and to connect the concrete element with the supporting steel structure. By this a solid connection between the concrete element and the supporting structure is to be achieved. Further such a concrete element, at at least one edge, comprises a longitudinal recess of a shape corresponding to the flattened metal tube to optimise the pressure contact between the pressure vessel and the concrete element. An embodiment of the span structure according to the invention and of the concrete element employed therein will be explained in more detail with reference to the accompanying drawings in which: Fig. 1 - diagrammetically shows a known span structure; Fig. 2 - diagrammetically shows a span structure according to the invention; Fig. 3 - shows the shape of the pressure vessel arranged between two adjacent concrete elements; Fig. 4 - shows the end of the span structure according to the invention; Fig. 5 - shows the connection between concrete elements and supporting structure during mounting of the span structure; Fig. 6 - shows another embodiment of the connection between the concrete elements; and Fig. 7 - shows a joint between adjacent concrete elements in a ready span structure. Fig. 1 shows the known span structure in a diagrammetic form in which a supporting structure 1 made from steel rests on two supports 2 provided at the ends. The supporting structure 1 will sag by its own weight to a greater or lesser degree, the neutral line 5, depending on the embodiment of the supporting structure, being situated more or less in the middle of the supporting structure 1. Applied to the supporting structure is a concrete road surface consisting of concrete elements 3 and a joint 4 between the concrete elements filled with mortar. The concrete elements 3 are connected with the supporting structure 1 in some way or other. To contribute to the carrying power, the concrete elements must take up pressure in the span direction, which only occurs with increasing load in the vertical direction. Fig. 2 shows the span structure according to the invention in diagrammatic form. This structure differs from that of Fig. 1 by stops 6 provided at the ends of the road surface, which can-take up the forces in the span direction, applied in the concrete elements, and transmit them to the supporting structure 1. Arranged in the joint 4 is a pressure vessel 7 consisting of a flattened metal tube, deformable under internal pressure to generate forces 8 in the span direction. When the pressure vessel 7 is pressurized, the concrete elements 3 are connected with the supporting structure 1 by means of the diagrammatically shown clamp connections 15 allowing horizontal shift. By applying the forces 8 transmitted to the stops 6 by means of the concrete elements 3, a moment opposite to the moment generated by its own weight acts on the supporting structure with the result that the carrying power of the span structure is increased or the same carrying power is obtained with a more slender supporting structure 1. A change of stress has occurred in the supporting steel structure. The forces 8 generated by the pressure vessel 7 apply a tensile stress in the span direction, while the moment produced by those forces 8 because of the eccentric action applies a tensile stress in the upper part of the supporting structure and a compressive stress in the lower part. After providing a solid connection of the concrete elements 3 with the supporting structure 1 by means of diagrammatically shown bolt connections 9, the neutral line 5 of Fig. 2 has shifted in upward direction when compared to Fig. 1. Fig. 3 shows the shape of the pressure vessel 7 placed in the joint 4 between two adjacent concrete elements 3. The pressure vessel 7 consists of a metal tube flattened in cross-section, the long axis of which is parallel to the main plane of the joint 4. By applying in the pressure vessel 7 a pressure of, e.g., 400 bar, considerable forces are generated in the concrete elements 4 which are transmitted via the stops 6 to the supporting structure 1. After the concrete elements 3 have thus been put under compressive stress, the joint 4 is filled with mortar, after the bottom of the joint has first been sealed by means of a rubber element 11. After the mortar in the joint 4 has hardened, the pressure can be let off from the pressure vessel 7, after which the pressure vessel 7 is filled under pressure with a hardening mass which, after hardening, additionally keeps the concrete elements 3 under pressure. Fig. 4 shows the end of the span structure. The supporting structure 1 can be provided at the end with a strengthened flange 12. The concrete elements 3 are provided with poured-in angle irons 13 of which the leg extending into the concrete element 3 is preferably connected with the transverse reinforcement (perpendicular to the plane of the drawing) of the concrete element 3. The leg of the poured-in angle iron 13 projecting from the concrete element is connected by means of a welded or bolt connection 10 with the strengthened flange 12 of the supporting structure 1 to form the stop 6 for transmitting the forces 8 in the span direction, generated in the concrete elements 3, to the supporting structure 1. The steps of mounting the concrete elements 3 and connecting them with the supporting structure 1 will be explained hereinbelow with reference to Fig. 5. Fig. 5 shows a concrete element 3 provided at the bottom with poured-in angle irons 13 resting on the upper flange of the supporting structure 1. Arranged between adjacent concrete elements 3 are pressure vessels 7 filled with a liquid capable of being put under a high pressure of, e.g., 400 bar by means of appropriate means. In the middle between the pressure vessels the concrete element 3 is firmly connected with the supporting structure 1, preferably by means of a bolt connection 14. At the joints 4 the poured-in angle irons 13 are connected with the suporting structure 1 by means of a plate 15 which is fixed in such a manner that shifting of the poured-in angle iron 13 with respect to the supporting structure 1 is possible. By pressurizing the pressure vessel 7 the concrete to the left and the right of the pressure vessels will be put under compressive stress so that the concrete elements are shortened. This compressive stress is transmitted at the ends of the span structure to the supporting steel structure, as a result of which mainly in the upper part thereof a tensile force is generated so that this upper part is lengthened. In view of the described shortening of the concrete 3 and the lengthening of the upper part of the supporting structure 1 the angle irons 13 poured in the concrete shift with respect to the supporting structure 1 (except at the location of the solid fastening bolts 14), after which in the final condition the angle irons 13 are connected with the supporting structure 1 by means of bolts 9. A connection between the concrete elements 3 and the supporting structure 1 may also be effected in a manner different from the one shown in Fig. 5 and described above. This other manner of connecting is shown in Fig. 6. Instead of angle irons 13 extending throughout the length of the concrete element 3, there are only arranged short pieces of angle iron, namely at both ends of the concrete element 3 at the plates 15 allowing shifting and in the middle of the concrete element 3 at the connecting bolts 14. The short angle irons 13 mainly have the function of supporting legs. After fixing the concrete element 3 by connecting the middle angle-iron shaped portions 13 with the upper flange of the supporting structure 1, pressurizing the concrete element by means of the pressure vessels 7, filling the joints 4 with mortar and hardening them, the connection between concrete element 3 and supporting structure 1 is effected by filling the groove 19, arranged on the upper flange of the supporting structure 1, with concrete mortar. The axial confinement between concrete element 3 and supporting structure 1 is obtained by providing the concrete element 3 at the bottom with straps 16 at regular intervals, while dowels 17 projecting into the plane through the horizontal legs of the straps 16 are welded to the upper flange of the supporting structure. Fig. 7 shows a joint between adjacent concrete elements 3 in the final condition. After the liquid in the pressure vessel 7 has been pressurized, the joint 4 is filled with mortar. After hardening of the mortar the pressure in the pressure vessel 7 is let off and the pressure vessel 7 is filled with a mass hardening under pressure for additionally keeping the adjacent concrete elements 3 under compressive stress.

Claims: Method for constructing a span structure, such as a bridge, consisting mainly of a supporting structure built up from steel sections and a road surface connected therewith and composed of concrete elements, said method including the steps of: arranging fluid activated pressure means comprising a pressure vessel (7) at the location of at least part of the joints (4) between successive concrete elements, pressurizing the pressure means by filling with liquid under pressure to generate in the concrete elements (3) compression forces acting in the span direction and transmitted by stops to the supporting structure, filling the joint (4) around the pressurized pressure vessel with hardening and after hardening substantially incompressible material, depressurizing the pressure means after hardening of said material around the pressure vessel, and filling the space occupied by the pressure vessel with substantially incompressible material, characterized by providing stops, which take up the forces in the span direction, applied in the concrete elements, at the ends of the span structure, said stops allowing a horizontal shift of the concrete element between the stop and the pressure vessel with respect to the supporting structure; providing pressure means comprising as pressure vessel (7) a metal tube flattened with smooth flowing forms in cross-section, the long axis of the flattened metal tube, seen in cross-section, being positioned substantially parallel to the main plane of the joint (4) and said metal tube being located completely inside the joint (4), pressuring the whole road surface in the span direction to compensate from the beginning shrinkage and creep effects such that the road surface functions as a monolithic whole; after pressurizing rigidly connecting the concrete elements to the supporting construction; and filling under pressure the flattened metal tube with a hardening and after hardening substantially incompressible mass. Method according to claim 1, characterized in that the flattened metal tube is filled under pressure with a hardening mass after depressurising the pressure means. Method according to claim 1 or 2, characterized in that at least one concrete element is placed between the two concrete elements at the ends of the span structure, which at least one concrete element is provided with pressure means at its opposed ends and is locally firmly connected to the supporting structure, allowing horizontal shift between said local connection and the pressure vessels with respect to the supporting structure. A span structure, such as a bridge, consisting mainly of a supporting structure built up from steel sections and a road surface supported by the supporting construction and composed of at least one concrete element between stops at the end of the road surface, joints being present between at least a concrete element and a stop, pressure means (7) comprising a pressure vessel arranged in a joint and filled with a hardened mass being arranged at the location of at least part of the joints (4), compression forces acting in the span direction and transmitted to the supporting structure (1) by the stops (6) being present, characterized in that the road surface is composed of at least two concrete elements rigidly attached to the supporting construction and defining a joint (4) there between and the pressure vessel (7) is located in a joint (4) between two concrete elements (3) and consists of a metal tube having two opposed, in cross-section by deforming flattened surfaces acting as deformable pressure surfaces, the long axis of the flattened metal tube, seen in cross-section, being substantially parallel to the main plane of the joint (4). A span structure according to claim 3, characterized in that the long axis of the flattened metal tube, seen in cross-section, is approximately 1/3 to 2/3 of the thickness of the concrete elements (3) defining the joint (4).

Inventors: POOT SIMON JACOB, POOT, SIMON JACOB
Applicants: BETON SON BV, IV CONSULT B V, MERCON STEEL STRUCTURES BV, BETON SON B.V., IV CONSULT B.V., MERCON STEEL STRUCTURES B.V.
Application year: 1997
Main classification: E01D2
IPC codes: E04C3, E01D2, E04B5