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.
Longitudinal and Transverse Joints in Pavement
Fig. 1: Longitudinal and Transverse Joints in Pavement
Influence of Tie Bars on Pavement Behavior
Fig. 2: Influence of Tie Bars on Pavement Behavior

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 Bars placed in Longitudinal Joints of Pavement
Fig. 3: Tie Bars placed in Longitudinal Joints of Pavement
Bent Tie Bars
Fig. 4: Bent Tie Bars

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
Lane Separation Due to Inadequate Tie Bars
Fig. 5: Lane Separation Due to Inadequate Tie Bars
Vertical Position Problem
Fig. 6: Vertical Position Problem

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, mmDistance to Free Edge, mmDistance to Free Edge, mmDistance to Free Edge, mmDistance 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, mmDistance to Free Edge, mmDistance to Free Edge, mmDistance 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.