The main things to know
- The size, position and spacing of steel come from the engineer’s drawings.
- Steel needs suitable supports to keep it in place during the pour.
- More bars do not automatically mean a better structure.
- Changes must be agreed before concrete hides the work.
The position matters as much as the amount
Concrete and steel work together. Concrete is good at carrying compression, which is a squeezing force. Steel helps where the structure experiences tension, a pulling force.
The bars are placed where the design needs them. Moving them to make room for a pipe can change how that part of the building works. The team needs to resolve clashes with the engineer, not simply push the steel aside.
Does the delivered steel match the drawings?
The drawings specify the bar sizes, types, numbers and arrangement. Ask who will check the delivery and the installed steel against them.
If a particular size is unavailable, the engineer should agree any substitution. Buying a different size or adding extra bars without a check can create problems with spacing and concrete placement.
Why steel must not sit against the edge
The concrete around the bars helps protect them. The distance between the steel and the outside face of the concrete is called cover.
Spacers and supports hold the bars in position so the required cover is maintained. The amount depends on the design and exposure. It should not be guessed or copied from another part of the building.
Where one bar meets another
Bars sometimes overlap or connect so forces can pass from one to the next. You may hear an overlap called a lap. Its length and position are part of the design.
Ask the team to check these connections before pouring. A short overlap that looks tidy is not necessarily adequate, and joints cannot be moved wherever they are easiest to assemble.
What are the smaller loops of steel for?
The loops around the main bars in beams or columns are often called links or stirrups. They have a structural role as well as helping hold the cage together.
Their size, spacing and shape need to match the drawings. They are not packing material that can be omitted when the team is short of steel.
Things to flag before concrete arrives
- Bars resting on the ground or pressed against the mould.
- Loose supports that allow steel to move when people work around it.
- Bars cut, bent or moved to fit pipes without agreement.
- Changes in bar size or spacing that have not been checked.
- Connections that differ from the drawings.
- Steel too congested for the concrete to be placed properly.
Flagging a concern does not mean you have to diagnose or fix it. Ask the responsible person to check and record the answer.
Who signs off the work before the pour?
Agree the inspection arrangements before pour day. The required checks should cover steel, cover, openings and supports, using the current drawings.
Photographs are useful records, particularly for an owner abroad. Ask for labelled pictures and the inspection outcome. A photograph is not a substitute for the inspection itself.
Leave changes to the design team
Your role is to ask whether the work has been checked and whether changes have been agreed. The engineer remains responsible for deciding the steel your building needs.
Further reading
Questions we get asked
- What is concrete cover?
- It is the distance between the steel and the outside surface of the concrete. It helps protect the steel and is specified in the design.
- How much cover is needed?
- Use the engineer’s drawings. The requirement varies with the part of the building and its conditions.
- Can the builder use loose stones as spacers?
- Ask for spacers that meet the specification and hold the steel reliably in position. Improvised loose packing should be checked before pouring.
- How long should bars overlap?
- The engineer specifies the length and location. There is no general overlap length that suits every bar and situation.
- Why do balconies need particular care?
- Some balconies project beyond their supports. Their steel position, connections and loading are critical and must follow the design.
- Is rust on steel always a problem?
- Surface appearance alone is not enough to decide. The responsible professional should assess the condition and any loss of material before use.
Written by
Eng. Samson Gitonga
Civil & Structural Engineer
Samson Gitonga is TimberStone’s civil and structural engineer. Based in Nanyuki, he helps clients understand how the ground, the building plans and the materials come together to create a safe, practical structure.
- Registered Civil & Structural Engineer, Engineers Board of Kenya
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