A tie bar is a steel bar, usually deformed reinforcement, that prevents unwanted movement between parts of the same structure. It is cast across a joint and holds the two adjoining elements together.
Tie bar versus dowel
This is the distinction that goes wrong most often on site:
| Tie bar | Dowel | |
|---|---|---|
| Surface | Deformed (ribbed) reinforcement | Smooth, often coated or sleeved |
| Purpose | Keep the joint closed, transfer tension | Transfer load, allow movement |
| Movement | Prevents displacement | Lets the joint open and close freely |
| Where | Longitudinal joints, connections meant to stay tight | Expansion and contraction joints |
In short: a tie bar connects, a dowel guides. Put a deformed bar into an expansion joint by mistake and the joint cannot do its job — the concrete will simply crack somewhere else.
Applications
- Concrete pavements — tie bars sit beneath the longitudinal joints of concrete roads and industrial floors. They hold adjacent slabs together so the joint does not open up with temperature changes. The centre section often has a plastic coating to protect against corrosion.
- Concrete floors and walls — tie bars connect a newly cast section to one that has already hardened, for example at a construction joint or where a wall meets a foundation.
- Precast elements — tie bars connect units so they act together.
Points to watch
- Position — parallel to the surface and central in the load-bearing layer. Set too high or too low, the bar acts as a lever and the concrete cracks.
- Cover — the concrete cover determines whether the bar corrodes. Insufficient cover is the leading cause of concrete damage around tie bars.
- Material — reinforcement must comply with the applicable standard for reinforcing steel; ordinary structural steel is not a substitute.
- Sound transmission in housing — tie bars between elements of different dwellings carry structure-borne sound. Keep the number and diameter as low as the structure allows.
Related terms
- Reinforcing steel
- Reinforcement
- Dowel
- Expansion joint
- Contraction joint
- Concrete floor
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