EP0666940B1

EP0666940B1 - composite bridge structure consisting of steel girders carrying a deck made of steel case profiles and concrete

Info

Publication number: EP0666940B1
Application number: EP93924264A
Authority: EP
Inventors: Anders GRANSTRÖM; Nils-Gustav Svensson
Original assignee: Granstrom Anders; SVENSSON NILS GUSTAV; SVENSSON Nils-Gustav
Current assignee: GRANSTROEM, ANDERS; SVENSSON, NILS-GUSTAV
Priority date: 1992-10-29
Filing date: 1993-10-26
Publication date: 1999-06-23
Anticipated expiration: 2013-10-26
Also published as: DK0666940T3; SE9203192L; NO951564L; SE501583C2; NO305445B1; NO951564D0; FI109715B; FI952002A0; SE9203192D0; EP0666940A1; DE69325460D1; FI952002A; WO1994010385A1; DE69325460T2; ATE181579T1

Abstract

This invention is a new method to achieve composite action between girders (3) and a concrete slab (1), as well as within the slab itself. The load transmission within the slab (1) is improved by the invention in the following way. The inferior capacity of the concrete to carry transverse forces is repaired by the composite load carrying capacity of the profile's edge flanges (9), upwards inclined top flanges (10) and upwards extended top parts (11). Due to this fact the slab may be made thinner than usual. Shear forces between steel (2) and concrete (17) are effectively transmitted by mechanical contact between the vertical edges (16) of the cuts (12) and the reinforcing bars (13). Due to the fact that the bottom flange of the case profile (8) is capable of resisting the entire tensile force in the cross section, maximum moment carrying capacity is obtained, whereupon main reinforcement may be omitted.

Description

This invention concerns a structure to achieve composite action between girders and a concrete slab, as well as within the slab itself. The invention may be used for car-, railroad-, bicycle- and pedestrian bridges or similar structures.

Technical field

A bridge, small, average or great, is usually composed of two parallel main girders, extended from one abutment to another, directly or via a number of intermediate supports. The girders carry a bridge deck for the relevant traffic, its load being transmitted to ground via the girders and the bridge supports. The bridge deck, connected to the bridge girders, consists of structures made of timber, steel or concrete or a combination of these materials, and it is usually covered by a surfacing of bitumen or concrete. A concrete bridge deck is usually fabricated in a mould, which may be prefabricated or built in situ, fixed directly to the main girders. Usually traditional scaffolding is used for small and medium sized bridges, and prefabricated scaffolding for large bridges. The scaffolding may either extend along the complete length of the bridge, or be built for each new section of the bridge slab which is to be produced. Suitable connectors may then be cast into the slab on this occasion. Reinforcing bars have to be accurately fixed before casting, both inside the mould and around connectors welded to the girders. By these means the concrete slab can accomodate shear forces and take part in composite action with the bridge girders. This method to achieve composite action between bridge deck and bridge girders makes production steps cost consuming, time consuming, and dangerous.

State of the art

The most common way to transmit shear forces and to make a bridge slab and bridge girders act in composite action is to weld, bolt or shoot shear connectors to the plane top side of the bridge girders, which may be made of steel or concrete. I conjunction with these shear connectors, which may be either welded studs, threaded bolts, steel loops, or other adequate connectors (see Fig 1), reinforcing bars are being mounted, the meaning of these are to prevent concrete cracking due to the extremely concentrated forces from the shear connectors. Reinforcement is also used to distribute the compressive forces from the connectors to the width of the concrete slab. All this reinforcement naturally leads to costs that preferably should be limited. The welding and testing of the studs is time consuming and costly as well, and it has to be done indoors for quality reasons. When moving the scaffolding and working with it and when casting the concrete the numerous shear connectors are generally disturbing, which also lead to time losses and increased cost. The use of welded studs in conjunction with severe fatigue loading is not generally accepted due to the extremely concentrated forces in the concrete.
The traditional way of carrying the load to the main girders is to let reinforcing bars in the concrete slab carry the tensile forces of the bending moment. The slab is generally too thin to allow shear reinforcement to be used. In order to carry transverse forces from wheel loads and other loads, it must therefore be made extensively thick. An alternative way of carrying tensile forces from bending moments is to use lost scaffolding made of corrugated steel sheet, with intrusions or extrusions supposed to grip to the bottom surface of the concrete slab. This method is not generally accepted, and is not used for road bridges.
One traditional way of making girder bridges is to design the slab with reinforcement that rigidly connects the slab to massive concrete girders. Another common way is to use steel girders, e.g. I-girders where the top flange is connected to a flexible web below. The former construction is complicated and cost consuming to build. The latter leads to extensive temperature movements at non-consistent weather conditions, and requires bracing and care at execution.

The aim and most important characteristics of the invention

The aim of the invention is to provide an overall solution to the actual problem. The invention is a new way to combine structural elements from other applications with purely new designed elements in order to manage both load transmission from the girders to the slab and load transmission within the slab itself. With the invention, speed, economi, and safety in execution of the job are achieved.
Composite action between girders and slab in this construction is not ensured by studs, cleavage reinforcement, nor shear reinforcement, but by a special type of bolted connection, which in a first step transforms the shear forces from the girders to the steel case profiles, which are placed on top of the girders, extending from one girder to another and cantilevering beyond the girders as well. In a second step, the case profiles are capable of distributing the shear forces to a greater width of the slab due to their great stiffness in the plane of the slab. In the beam-to-case shear connection is used a special thread-forming bolt with a hardened end. In combination with a spacer plate which is also a remaining fixture for the bolts, or in combination with other spacers, an extremely high fatigue resistance of the connection is obtained, which consequently is well fit to transfer fatigue loads. The case profile is designed with a substantially plane bottom flange, edge flanges extending from the bottom flange on both sides almost perpendicularly upwards and inwards or vertically upwards, then inwards and upwards inclined and preferably symmetrically extended top flanges, which are terminated by vertical upwards extended top parts with cuts, open at the top, for reinforcing bars. The inwards and upwards inclined flanges constitute support for the jig that is used for drilling through both the case profile and the girder flange. The plane bottom flange makes it possible to mount the required number of special bolts. The shape of the case profile, and the fact that it is pressed against the adjacent profile by a special tool, makes it possible both to transmit contact force between the case profiles and to transmit force from the bottom corner of the case by means of multiaxial pressure in the concrete. Space between the bottom of the case profile and the girder may be closed by an adhesive or an elastic sealant in string form or as a coating.
The load transmission within the slab is improved by the invention in the following way. The inferior capacity of the concrete to carry transverse forces is replaced by the composite load carrying capacity of the profile's edge flanges, upwards inclined top flanges and upwards extended top parts. Due to this fact, the slab may be made thinner than usual. Shear forces between steel and concrete are effectively transmitted by mechanical contact between the vertical edges of the cuts and the reinforcing bars. The profile's elongated shape in the vertical direction makes the forces to be transmitted at the approximate level where the resultant compressive force of the concrete is situated. The thickness of the case profile is so great that all tensile reinforcement at the bottom of the slab in the transverse direction of the bridge is substituted by the bottom flange of the case profile itself. Due to the fact that the bottom flange of the case profile is capable of resisting the entire tensile force in the cross section, maximum moment carrying capacity is obtained. Even with bending moment of the opposite sign, maximum load carrying capacity is obtained, due to the fact that the bottom flange of the case profile itself can carry the compressive force of the moment. The inwards and upwards inclined flanges of the profile, in combination with the reduced amount of reinforcement, make a safer concrete casting possible and lead to a slab of better quality. Consequently the slab gets a superior resistance to large concentrated forces by its extremely good capacity to carry both moment and transverse force at a given plate thickness.
SE, A, 468 484 also shows a bridge structure composed of steel girders placed on two or more supports. On top of them there is a deck made of steel case profiles and concrete poured in- and onto the profiles to form a concrete slab.
The structure is designed in such a way that only limited composite action is obtained between the steel girders and the concrete slab, such as braking and acceleration forces can be transmitted by shear connectors from the concrete slab to the girders.
In cross section each case profile is made of steel plate and has a central top flange, connected by tilted webs to surrounding bottom flanges with edge flanges extending almost perpendicularly upwards. The edge flanges then stretch horisontally in the same direction and upwards, thus generating extended top flanges, terminated by vertical upwards extended top parts with cuts, open at the top, for reinforcing bars.
The cited document mainly differs from the invention in that in the invention composite action is obtained between the steel girders and the concrete slab - whereas in the cited document little space is left for shear connectors at the bottom flanges. making full composite action impossible. Furthermore, in the invention, the case profiles have a higher depth, and the inwards and upwards extended top flanges are situated at the approximate level in the slab where the resultant compressive force is situated.
Due to the shape of the edge beam in the invention and the fact that concrete and bolts in the slab are protected by the hermetical bottom and the impermeable sealing layer on top of the slab, the concrete, bolts, and reinforcement are well protected from all sides against thawing salt, soaking, and carbonating.
Where concrete-filled girders with two adjacent webs are being used, the advantage of the concrete-beam-bridge to compensate temperature changes is obtained, which often leads to simpler and cheaper abutments, bearings and joints. At the same time a construction with good torsion resistance and stability is obtained, with or without concrete filling. The advantages of the steel-girder-bridge; low weight and a high level of prefabrication are also obtained. According to the invention, the special bolted connection, in combination with the dimensions and the shape of the case profiles, leads to complete composite action between girders and slab in the longitudinal direction of the bridge, whereupon the connection may be designed so flexible that it can carry horizontal forces and moments from the girders without harmful constraint in the case profiles and bolts.

List of illustrations

Figure 1: shows a bridge deck and its composition
Figure 2: shows a bolted connection of a case profile to a main girder, including a spacer plate, and a reinforcing bar put in a cut of the profile.
Figure 3: shows the thread-forming bolt with the hardened end and an example of a spacer.
Figure 4: shows a special tool used to press the case profiles together at execution.
Figure 5: shows a steel girder with I-section. In the top flange is a blind hole made.
Figure 6: shows a steel girder with two webs. In the top flange are through holes made.
Figure 7: shows how the shear from the bolts is transmitted by local concrete stress to the slab.
Figure 8: shows how the edge beam is connected to the case profiles by self-tapping screws.
Figure 9: shows how the shear in the web of the case profile, without adhesion can build necessary compressive bending stress in the concrete slab.
Figure 10: shows how horizontal forces act on the concrete slab at composite action with the main girders.
Figure 11: shows how the internal lever arm of the slab is greater than in a conventional concrete slab with tensile stress at the bottom.
Figure 12: shows how the internal lever arm of the slab is greater than in a conventional concrete slab with compressive stress at the bottom.
Figure 13: shows that the deck by a certain arrangement of the bolts is elastically restrained by the girders in a controlled fashion, since the cross section of the case profile may be elastically deformed.
Figure 14: shows an example of sealing between a case profile and a girder.

Description of applications

A cross section of a bridge may look like Fig 1. On top of the bridge girders (3) is a concrete slab (1) cast. The concrete (17) is cast in case profiles (2) transverse to the girders (3) and bolted to these. The case profiles (2), cantilevering from the girders are terminated by an edge beam (Fig 8). On top of the slab is an impermeable sealing layer (19) situated.
In order to achieve composite action between the girders (3) and the slab (1) case profiles made of steel (2) are bolted to the girders (3). The profiles (2) are designed with a substantially plane bottom flange (8), edge flanges (9) extending from the bottom flange on both sides almost perpendicularly upwards and inwards or vertically upwards, then inwards and upwards inclined and preferably symmetrically extended top flanges (10), which are terminated by vertical upwards extended top parts (11) with cuts (12), open at the top, for reinforcing bars (13).
When a number of case profiles (2) have been put onto the girders (3) they are bolted in place by the connection in Fig 2. In order to obtain the required mounting contact pressure between the flanges (9) of the profiles (2) a special tool, Fig 4(14) is used. Bolt holes are drilled in one operation through the bottom flange (8) of the profiles (2) and the top flange of the girder (3) according to Figs 5, 6, and 7. After that, thread-forming bolts (4) with a hardened end (5) are fastened by the use of pneumatic or electric screwdrivers through the case profile and the top flange. Between the bolt head and the bottom flange of the profile (8) a spacer is mounted, on the picture shown as a template (6), the meaning of which is to accurately fix the bolts (4) in order to get the right flexibility. The profile (2) distributes the forces to the width of the bridge and transmit the forces to the slab (Fig 10) by contact pressure (Fig 7). Alternative spacers (7) may be used. Space between the bottom of the profile and the top of the girder may be closed by an adhesive or an elastic sealant (Fig 14).
When the profiles (2) are mounted to the girders (3), and the edge beams are mounted to the profiles with self-tapping screws (Fig 8) the reinforcement is put into the punched cuts (12) of the profiles (2). The task of the reinforcement (13) is, according to Fig 9, both to secure composite action between the concrete (17) and the steel profiles (2), and to be reinforcement in the longitudinal direction of the bridge. When the profiles (2) are mounted and the reinforcement job is finished the deck is poured with concrete (17). Finally a sealing layer (19) of wearing concrete or bitumen is applied.
Without restrictions, a few suggestions concerning material and dimensions should also be mentioned. The case profile (2) is made of steel plate in the thickness range 4 to 7 mm. The total depth of the profile (2) may be 110 to 130 mm, the depth from the symmetric inclined flange (10) to the bottom flange is 80 to 100 mm and the total width of of the profile is 400 to 450 mm. The punched cuts (12) in the finishing top part of the profile are spaced 50 mm apart. The edges of the cuts are vertical and horizontal. The bolt in quality 10.9 is metric M12 - M16.
This structure may also be used for structures, such as parking decks and floor structures for heavy trucks.

Claims

Bridge structure or similar structure, composed of steel girders (3) placed on two or more supports, on top of it a deck made of steel case profiles (2), and concrete (17) poured in- and onto the profiles (2) forming a concrete slab (1), the structure being designed in such a way that composite action is obtained between the steel girders (3) and the concrete slab (1); composite action being defined as the ability of the concrete slab to accomodate over its entire width in a cross section a total compressive force as great as the tensile force the girders can carry, the structure being provided with high strength bolts (4) for transmitting this force from the girders (3) to the concrete slab (1); whereas composite action is also obtained between the case profiles (2) and the concrete slab (1) itself in the transverse direction, and the slab (1) is also able to carry great concentrated loads, without making the load carrying capacity of the case profiles at casting inferior, whereas each case profile (2) in a cross section has a horizontal bottom flange (8), edge flanges (9) extending from the bottom flange (8) on both sides almost perpendicularly upwards, then top flanges (10), which are terminated by vertical upwards extended top parts (11) whith cuts (12), open at the top, for reinforcing bars (13) characterized in that said top flanges (10) extend inwards and upwards inclined, said case profiles being made of steel plate with 4-7 mm thickness, in order to achieve such a great stiffness that they can transmit the forces further to the concrete (17) and that they can transmit shear force for composite action by mechanical contact to the reinforcement bars (13), said profiles having a total depth of 110-130 mm, whereas the distance between the bottom flanges and the inwards and upwards extended top flanges is 80-100 mm in order to transmit shear force for composite action at the approximate level in the slab where the resultant compressive force is situated, and that the case profiles are 400-450 mm wide in order to be able to distribute the shear forces from the girder to a great width of the structure.
Structure according to claim 1, characterized in that the top of the steel girder (3) is substancially in contact with the substantially plane bottom flanges (8) of the case profiles which are connected to the steel girders (3) with at least high strength bolts (3) M12 grade 10.9, in order to make the bolted connection capable of transmitting the shear forces required for composite action between the steel girders (3) and the concrete slab (1).
Structure according to claim 2, characterized in that the bolts (4) are fitted with spacers (6,7) and are thread-forming in accurately designed holes, in order to get good fatigue characteristics for the connection.
Structure according to claim 3, characterized in that the spacers consist of templates which accurately fix the location of the bolts (4).
Structure according to any of the claims 2 to 4, characterized in that the bolt holes end in a closed space, protected from atmospheric exposure.
Structure according to claim 5, characterized in that the closed space is filled with concrete.
Structure according to any of the claims 1 to 4, characterized in that the bolt holes are blind holes.
Structure according to any of the former claims, characterized in that the case profiles (2) are being pressed against each other by a special tool (14) in order to provide load transmission in the concrete slab at the level of the bottom flange of the case profiles (8).