7.4 Reinforcement cages
This subclause applies to reinforcement cages inserted into cast in situ concrete diaphragm walls, where reinforcement is required by the design.
The reinforcement within a panel may comprise one or more cages within the panel length.
The design of the reinforcement cage(s) shall be made in accordance with ENV 1992. The design shall provide not only adequate strength for the final wall, but also adequate strength and stiffness during construction, in particular for the handling and concreting phases. It shall also allow the fresh concrete to flow easily around each of its components.
The vertical length of a reinforcement cage shall be such that the distance between its base and the bottom of the excavation is at least 0,2 m.
The reinforcement cage shall include:
- vertical reinforcement, usually arranged in either one or two layers on each face of the wall;
- horizontal reinforcement in the form of links, stirrups or other suitable shapes;
- suspension and lifting bars; and when necessary:
- special reinforcement for anchors, props or other structural elements connected with the diaphragm wall;
- bracing bars to improve the stiffness of the cage for the handling operations;
- formwork for recesses or tubes for anchors, services,...;
- vertical tubes for grouting, dowel bars, control tests, etc.
In the case of welding, only electric welding is permitted, provided that the steel quality is suitable.
Tack welding is permitted for all types of steel for assembly purposes, provided that the mechanical properties of the bars are not affected.
7.4.2 Vertical reinforcement
The minimum diameter of the bars shall be 12 mm and there shall be a minimum of 3 bars per meter on each side of the cage.
The horizontal clear space between single bars or groups of bars, parallel to the wall face, shall be at least 100 mm. This figure can be reduced to 80 mm for the lap length or in the case of heavily reinforced panels, provided the maximum size of the aggregates does not exceed 20 mm.
When the cage is made up of several elements in the vertical direction, the junction between bars shall be made either by overlapping or by couplers. When overlapping is used, slippage during handling shall be prevented by tack welding or other suitable means.
7.4.3 Horizontal reinforcement
The horizontal reinforcement shall be arranged in such a way as to prevent movement of the vertical bars and to provide adequate space for the concreting pipe(s).
The vertical clear space between bars shall be at least 200 mm. This figure can be reduced to 150 mm provided the maximum size of the aggregates does not exceed 20 mm.
The horizontal clear space between transverse bars shall be at least 150 mm. A minimum spacing of 200 mm is recommended to ensure free flow of concrete.
7.4.4 Multiple cages and joints
The minimum clear distance between two cages in the same panel shall be 200 mm.
The minimum clear distance between the ends of the cages and panel joints shall be 100 mm and shall take into account the verticality tolerances, the shape of the joints and the possible use of water stops. In the case of curved joints, the cage shall not enter into the concave portion of the joint. This does not apply to the case of diaphragm walls with continuous horizontal reinforcement across the joints.
7.5 Recesses and perforations
All formwork for recesses and tubes shall be securely attached to the reinforcement cage in order to prevent any movement during concreting.
Recesses and perforations shall be of limited size and shaped in such a way as to minimize interference with the free flow of the concrete.
Recesses for slabs shall not exceed the length of the reinforcement cage in each panel. It is recommended that the recesses do not extend behind the first layers of reinforcement.
Normally perforations for anchors are formed with a tube not exceeding 300 mm in diameter, in order to facilitate the free flow of the concrete. Special precautions may be necessary when perforations greater than 300 mm in diameter are required.
7.6 Concrete cover
The design concrete cover is defined as the distance between the outside of the reinforcement cage and the design position of the face of the panel.
In order to ensure that the concrete flows freely and that the physical concrete cover complies with ENV 1992, the design cover shall be at least 75 mm.
Except in the case of very soft soils, this value can be decreased to 60 mm in the case of non-aggressive ground or temporary walls.
Spacers shall be provided to ensure that the correct concrete cover is maintained.
The spacers can be either vertical tubes, or individual units (pads, rollers,...). The size of the individual units shall be adapted to the ground conditions.
For permanent structures, spacers shall be made of a non-metallic material, which is at least equivalent to concrete with respect to durability, unless they are removed during concreting.
|1 Wall thickness
2 Horizontal length of reinforcement cage
3 Cage width
4 Length of panel
5 Platform level
6 Casting level
8 Cut off level
9 Vertical length of reinforcement cage
10 Reinforcement cage
11 Depth of excavation
- P Primary
- S Secondary
- 1 Starter
- 2 Intermediate
- 3 Closure