What is Tie Bar in Construction? Functions, and Design Specifications

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Tie Bars are deformed steel bars, deformed epoxy coated steels, or connectors that are used to hold faces of rigid slabs in contact, as per AASHTO, 1993. Not only are they used to decline transverse cracking but also avoid separation and differential deflection of lanes.

Moreover, tie bars are not designed to act as a load transfer device and not advised to be employed as a load transfer means, but they might offer some minimal amount of load transfer. Additionally, they need to be protected from corrosion.

Lastly, they are commonly utilized at longitudinal joints or between an edge joint and a curb or shoulder. Typically, tie bars are 12.5mm or 16mm in diameter and between 0.6 and 1.0 m long.

Tie Bar Functions

1. Tie bars used for holding faces of rigid slabs in contact to keep aggregate interlock. They are also used in plain jointed concrete pavement to connect two lanes.
2. They are used to reduce transverse cracking.
3. Tie bars avoid separation and differential deflection in lanes.
4. They are not designed to work as a load transfer device.

Tie Bar Placement

Tie bars are installed or inserted by hand or using a tie bar inserter attachment (in case of slipform pavement only) after one lane is paved at a time.

They are placed at mid-depth slab and bent back till the adjacent lane is prepared to be paved. When slipform pavers are used, tie bars are inserted on the slab edges that would become longitudinal joints.

Tie Bar Installation Problems

1. Bars are missing.
2. Poorly adjusted equipment.
3. Concrete around bars is poorly consolidated.
4. Too stiff mix, often caused by mix delays.
5. Tie bar misplacement

Tie Bar Spacing

Table 1 and Table 2 are used to determine spacing of tie bars for bar diameter of 12.5mm and 16mm, respectively.

Table 1 Spacing of Tie bars for Steel Yield Strength of 280MPa and Bar Diameter of 12.5mm

Concrete Thickness, mm	Distance to Free Edge, mm	Distance to Free Edge, mm	Distance to Free Edge, mm	Distance to Free Edge, mm
-	3000	3600	4800	7200
225	650	550	400	275
250	600	500	400	250
275	550	450	350	225
300	500	400	325	225

Table 2 Spacing of Tie bars for Steel Yield Strength of 280MPa and Bar Diameter of 16mm

Concrete Thickness, mm	Distance to Free Edge, mm	Distance to Free Edge, mm	Distance to Free Edge, mm	Distance to Free Edge, mm
-	3000	3600	4800	7200
225	1050	875	650	425
250	950	775	600	400
275	850	725	525	350
300	775	650	500	325

Advantages

1. Tie bars improve the performance of pavement joints substantially.
2. They increase the initial cost but reduce life cycle cost.