Dowel bars and Tie bars, both are used in reinforced concrete structure for different purposes. Let us discuss both of them one by one.
What is Dowel bars?
A dowel is simply a cylindrical rod, which is made up of metal, wood, or plastic. A dowel bar is generally made up of short round mild steel bars used to provide the mechanical connection between more than one slab connected to the bars without resisting the horizontal movement at the joint of the bar.
It can also be defined as the steel reinforcement bars which are extended up to some particular length in a framed structure for future construction of the concrete.
Usually, the round steel bars are provided in the concrete structure to transfer the load uniformly throughout the structure to resist the joint movement.
Applications of dowel bars
The application of dowel bars are as follows:
- It is used to connect the old and the new concrete structure
- It is used to connect the column at the level of the slab to connect the next column and next slab
- It is used to improve the performance of pavement joints. It reduces the effect of load on the pavement joints.
- It is used to reduce the corner cracks. The erosion of the concrete in the corner of the structure is generally reduced by the use of the dowel bars.
- Since it connects two slabs, which may be new and the old slab, it is used to transfer the load from one slab to the others.
Advantage
- Since it transfers the load from one slab to the others, it improves the load-carrying capacity of the slab.
- Since it improves the performance of the pavement joints and also reduces the effect of load in the pavement joints, it increases the life span of the pavement.
- It reduces the deflection and the stress in the concrete.
- The extension of the structure is easy if the dowel is provided.
Specification and Installation of dowel bars
The thickness of the pavement determines the size of dowel bars required. The dowel bars are usually of 32 to 38 mm diameter, 460mm long, and spaced at a distance of 305mm apart from each other.
The dowel bars are either coated or made up of stainless steel to protect it from corrosion. Dowel bars always inserted in the mid-depth of the slab. They are placed across the transverse joint of the concrete pavement to allow the movement.
The expansion and the contraction of the adjacent slab are adjacent thus the dowel transfers the load. The bars are placed parallelly to the centerline of the slab.
The main problem during the installation during the dowel bars is that the bars are poorly adjusted and the concrete is poorly compacted.
What is Tie bars?
The deformed rebars or the connector used for holding the rigid slab in contact to make up the aggregate interlock between the slab is known as the tie bar.
It doesn’t transfer the load but sometimes minimum load transfer is available. It is used to decline the transverse cracking. It also avoids the segregation and differential deflection of lanes.
Application
The application of the tie bars are as follows:
- It is used to decline the transverse cracking.
- Tie bars are used in holding the faces of rigid slabs in contact to keep the concrete aggregate interlocked.
- It is used in the plain jointed concrete pavement to connect two lanes and helps to avoid the separation and differential deflection of the lanes.
Advantages
- It connects two lanes.
- It reduces cracking.
- It avoids separation and differential deflection.
- It avoids high stress and high deflection.
Specification and Installation of tie bars
The size of the tie bars depends upon the thickness of the concrete surface and width of the slab. The diameter of the tie bars is generally of 12-16 mm made up of TOR steel bars.
The length of the bar varies from 550-640 mm in size. Tie bars are inserted after one lane is paved by hand or by using a tie bar installer at a time.
The tie bar is installed at the mid-depth of the slab and bent back till the adjacent lane is prepared and to be paved. The tie bar is inserted at the slab edge when slip form pavers are used which makes it a longitudinal joint.
Differences between Dowel bars and Tie bars
The difference between Dowel bars and Tie bars are as follows:
| S.N | Dowel bar | Tie bar |
|---|---|---|
| 1 | It is placed around traverse joint at the mid-depth of the slab | It is placed around longitudinal joints at the mid-depth of the slab |
| 2 | The load is transfer from one slab to another and also joints are prevented from opening | Lanes are prevented from separation and differential deflection |
| 3 | They are of round, smooth, epoxy coated steel bars. | They are of deformed epoxy coated steel. |
| 4 | They can reduce joint fault and corner cracks | They can reduce transverse crack |
| 5 | Dowel bars are made up of mild steel | Tie bar are generally made up of steel |
| 6 | The diameter of the dowel bars is larger in size ranging from 30-38 mm | The diameter of the tie beam is smaller in size ranging from 10-12mm. |
| 7 | Its spacing depends only upon the thickness of the pavement. The thickness of the dowel bars varies within 300-310 mm | The spacing of the tie bars depends both upon the thickness of the pavement and the width of the slab. The thickness varies within 550-640 mm. |
| 8 | It is load transferring device from one slab to the others | It is non load transferring device. |
| 9 | While installation of the dowel bars, its main problem is it being poorly adjusted and the concrete may not be compacted properly. | While installation of the tie bars no problem of adjustment will arise. |
I hope this article remains helpful for you.
Happy Learning – Civil Concept
Contributed by,
Civil Engineer – Shreya Parajuli
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