Detailing of Reinforcement in Concrete Structures: A reinforced concrete column is a structural members designed to carry compressive loads, composed of concrete with an embeddedsteel frame to provide reinforcement. For design purposes, the columns are separated into two categories: short columns and slender columns.
3.1Detailing rules that conform to BS EN 1992-1-1, Euro code 2:
3.1.1 Design and detailing notes Concrete grade. Concrete grades less than 28/35 MPa (cylinder strength
/cube strength) are not normally used. Care should be taken to ensure that the design strength of concrete required in a column does not exceed1.4 times that in the slab or beam intersecting with it unless special measures are taken to resist the bursting forces.
3.1.2 Reinforcement guidelines by BS EN 1992-1-1, Euro code 2
i. Bar diameter:
Recommended minimum bar diameter is 16mm for very small section columns. Minimum number of bars for rectangular columns is 4. Minimum number of bars for circular columns is 6 for very small diameter columns, and the minimum of 4 for less than 200mm.
ii. Maximum area of main reinforcement:
Maximum area of reinforcement should not exceed 0.04Ac unless it can be shown that any resulting congestion of reinforcement does not hinder the ease of construction. At laps the maximum area of reinforcement should not exceed 0.08Ac. Mechanical splices should be considered where congestion becomes a problem.
The size of link should be the greater of a quarter the maximum size of longitudinal bar and 8mm (for very small diameter columns, less than 200mm, the minimum of 6mm may apply).Bundled main bars may be represented by a single bar for the purpose of calculating link size and spacing. This single bar has an equivalent size to give it the same cross section area as the bundle.
An overall enclosing link is required together with additional restraining links for alternate main bars or bundle of bars. Provided that all other main bars in the compression zone are within 150mmof a restrained bar no other links are required .Otherwise additional links should be added to satisfy this requirement. Additional links are not required for circular columns.
bars. These effects may be ignored if the change in direction is 1 in 12or less.
v. Moment connection between beam and edge column:
Wherever possible U-bars which can be placed within the depth of beam should be used. These are fixed in position and concreted with the beam, and thus do not require precise fixing when the column is being concreted. L-bars which penetrate down into the column should be used when the distance ‘A’ (see
Figure ) is less than the anchorage length for that bar diameter. These bars must be fixed accurately at the top of the column lift which is a difficult and unattractive site task. A standard radius to the bend may normally be used provided a bar of the same size or greater is placed inside the corner normal to it. A non-standard bend may be required if a corner bar is not present. If so, a thorough check should be carried out tonsure that the reinforcement fits and will perform as intended. The critical effective depth may not be obvious, and various locations may need to be assessed.
Special care should be taken by the Designer and Detailer to make sure that this reinforcement does not conflict with any beam reinforcement passing through the column in the other direction.
vi. Shear capacity of column:
The maximum tensile reinforcement in the beam or that part required for the moment connection to the column is also controlled by the shear capacity of the column. Where there is no edge beam intersecting at approximately the same level as the joint, transverse column reinforcement should be provided within the depth of the beam (See Figure ). This may be in the form of links or horizontal U-bar extending into the beam. Unless specified by the Designer the spacing should be as for the links in the column.
vii. Starter bars:
It is important to recognize at the design stage the implications of theconstruction sequence and the level of foundation on the length ofstarter bars, e.g.
If the foundation reinforcement is placed at a depth lower than specified the consequent lap of the first lift of column bars is likely to be too short. For this reason the length of starter bars from pad footings and pile caps is specified longer than required.
Design information for detailing should include:
3.1.3 Presentation of working drawings:
Nominal cover to all reinforcement specified by designer (Normally: Internal 35, External 40).
This detail is used where the column is concentric and of the same dimensions as the story below. Nominal cover to all reinforcement specified by designer (Normally: Internal 35, External 40)
Detail ‘A’ applies when slab depth is not less than:
–200usingᴓ20 size of column bars
–250usingᴓ25 size of column bars
–300usingᴓ32 size of column bars
Otherwise Detail ‘B’ applies
For single story buildings or where splice bars have been used at the floor below
Top detail | Detailing of Reinforcement in Concrete Structures
This detail is used for single story buildings and where splice bars have been used at the floor below.
Circular columns Helical binders are used unless circular links are specified by designer.