GB2149832A - Stirrup basket - Google Patents

Abstract

A stirrup basket for reinforcing a concrete beam comprises longitudinal wires (1) and transverse stirrups (2, 4), the ends of which are bent into loops (6). The ends of the loops are welded to longitudinal tie wires (5) and the loops are bent outwards from the side planes of the basket. <IMAGE>

Description

SPECIFICATION Stirrup basket The invention refers to a stirrup basket, hereinafter referred to as of the kind described, which may be inserted in beams for reinforced or prestressed concrete supporting structures and which is formed from longitudinal and cross wires connected, preferably welded, together.

Stirrup baskets of this kind have been proposed in the West German Utility Model No.

1 9461 35. The stirrup baskets according to this earlier proposal exhibit, near the two ends of the crosswires forming shear stirrups, in each case two parallel rods crossing the stirrup wires perpendicularly and, in the build-in state, running parallel with the axis of the beam, the duty of which is to anchor the stirrups in the concrete.

An anchoring of this kind is indeed effective but not economic because the wires serving exclusively for the anchoring, yet continuous over the whole length of the reinforced beam, require a fairly large expenditure of material of which only a very small part is utilized.

It has to be appreciated that simple rectangular beams occur relatively seldom in concrete construction. In by far the majority of cases a beam forms, together with the slab supported by it, one unit so that a so called slab beam having a T-shaped cross-section results. In the case of slab beams of that kind the slab reinforcement, which usually consists of welded reinforcing grids, must be connected to the reinforcement of the beam. It then has to be taken into consideration that, in the region of the connection of the slab to the beam, two layers of reinforcement lying one above the other are necessary inside the slab, i.e., one layer of reinforcement arranged at the underside of the slab, which extends, say, between an edge support, for example, a wall, and the slab beam parallel with such support, or else between two adjacent slab beams.This reinforcement has to take up the tensile stresses occuring at the underside of the slab. Further, another upper reinforcement has to be provided in the direct region of the beam which has to take up the negative moments occuring across the beam and the tensile stresses resulting from these moments at the upper face of the slab.

In the connection of these layers of reinforcement to the reinforcement of the beam the materially wasteful anchoring rods running, according to the earlier proposal, in parallel with the axis of the beam are an obstacle.

The invention is to solve the problem of creating a stirrup basket having an anchoring of the reinforcing stirrups, which is more economical of material than that described above and furthermore is also still more effective in that in the region of the greatest shear stresses, that is, in that region in which the beam is connected to the slab, it enables a greater cross-sectional area of steel to be made available for taking up the shear.

In accordance with the invention, a stirrup basket of the kind described is characterised in that the two ends of the crosswires forming shear stirrups are bent back in the direction of the longitudinal wires into loops, the ends of the loops on each side of the stirrup basket are welded to a tie wire running parallel with the longitudinal wires of the stirrup basket, and the loops are bent sharply out of the planes of the sidefaces of the stirrup basket.

Preferably the loops are bent outwards perpendicular to the sidefaces of the stirrup basket.

This preferred construction in accordance with the invention will now be described in greater detail with reference to the accompanying drawing.

In the drawing there may be seen longitudinal wires 1 running in the direction of a beam in which the basket will be incorporated. The wires 1 are connected rigidly, preferably by welding, to crosswires 2 running perpendicular to them.

The longitudinal wires 1 continue over the whole length of the beam and form a basic reinforcement of the beam. In certain cases still further wires may be provided running parallel with the longitudinal wires 1, which are not continuous from one support of the beam to the other, but concentrated in the centre of the beam form a strengthening of the reinforcement graduated approximately to the trend of the moments. These wires may further be completed by added rods which are spliced to the stirrup basket, into final beam reinforcement exactly adapted to the trend of the moments.

Further, at or adjacent to the points of bend of the crosswires 2, still further longitudinal wires 3 may be provided, which likewise may be considered to be part of the longitudinal reinforcement of the beam, and secure the bottom edges of the beam against breaking off.

In the production of the stirrup basket the crosswires 2 are first of all bent up sharply on both sides into the shape of a U so that they form vertical arms 4 which near to their upper ends are connected together on each side by at least one tie wire 5.

The end portions of the crosswires standing up above the tie wire 5 are, in the plane which is defined by the arms 4 and which forms sideface of the stirrup basket, bent back in the direction of the longitudinal wires in the shape of a loop up to the tie wires 5, and the loops 6 are then bent sharply perpendicular to their plane. The bent back ends 7 of the loops 6 are likewise welded to the tie wires 5.

The distance "a", between that point, at which the loops are bent sharply outwards, and the tie wire 5, to which the ends of the roots of the loops are welded, should preferably amount to about 1 scum, so that the tie wire 5 as a rule comes to lie below the concrete slab. Through this measure it is achieved that the portions of the arms of the loops running parallel to the top of the beam form a stirrup in double shear for taking up the maximum shear stresses in the connection between the beam and the slab.

The loops 6 form not only an excellent support for the upper reinforcement of the slab above the beam, but furthermore anchor the shear stirrup 2 securely in the concrete of the slab.

The pitch of the stirrups along the stirrup basket may be equal all the way along, or it may, in known manner, be made to differ in such a way that the stirrups near the ends of the beam lie closer together than in the middle region of the beam.

Claims (5)

1. A stirrup basket for insertion in beams for reinforced or prestressed concrete supporting structures and which is formed from longitudinal and crosswires welded together, characterized in that the two ends of the crosswires forming shear stirrups are bent back in the direction of the longitudinal wires into loops, the ends of the loops on each side of the stirrup basket are welded to a tiewire running parallel with the longitudinal wires of the stirrup basket, and the loops are bent sharply out of the planes of the sidefaces of the stirrup basket.

2. A stirrup basket according to claim 1, characterized in that the loops are bent outwards perpendicular to the sidefaces of the stirrup basket.

3. A stirrup basket according to claim 1 or claim 2, characterized in that the distance between the points of bend of the loops and the tie wire amounts to substantially 1 5 cm.

4. A stirrup basket according to any one of the preceding claims, characterized in that the crosswires forming stirrups along the longitudinal wires are arranged at shorter pitch at the ends of the stirrup basket than in the middle range of the stirrup basket.

5. A stirrup basket, substantially as described with reference to the accompanying drawings.