Tie Bar
A tie bar is a deformed steel bar across a joint in concrete pavement that holds the two slab faces in close contact. Item P-501 of FAA AC 150/5370-10H specifies tie bars as deformed steel bars to ASTM A615.
What a tie bar does
A tie bar does not carry wheel load across the joint. AC 150/5320-6G says that tie bars “do not act as load transfer devices”. They “prevent opening of the joint, facilitating load transfer by aggregate interlock”.
A dowel bar does the other job. The FAA says dowels provide load transfer across the joint and prevent relative vertical displacement of adjacent panel ends. Item P-501 specifies dowels as plain bars with a bond-breaker, so the slabs can slide on them.
Where the FAA uses tie bars
AC 150/5320-6G section 3.16.10.1 tells the designer to tie a longitudinal contraction joint in a panel up to 9 inches (225 mm) thick. The joint must lie within 20 feet (6 m) of a free edge. Table 3-5 calls this a hinged contraction joint, type B. Thicker panels use a doweled contraction joint, type C, at the same locations. In construction joints of runway and taxiway panels thinner than 9 inches, the AC replaces every third dowel with a tie bar (type E1).
The AC gives two bar sizes:
| Panel thickness | Bar | Length | Spacing |
|---|---|---|---|
| 6 in (150 mm) or less | No. 4 | 20 in (510 mm) | 36 in (900 mm) |
| Above 6 in (150 mm) | No. 5 | 30 in (762 mm) | 30 in (762 mm) |
The AC tells designers not to use tie bars to make continuous tied joints longer than 75 feet (23 m).
Placement
Item P-501 asks for tie bars at right angles to the slab centerline. They lie parallel to the pavement surface, in the middle of the slab depth, at the spacing on the plans. Crews may not paint or grease them, or enclose them in sleeves. At a longitudinal construction joint, a bar that reaches into the unpaved lane may be bent against the form. The plans can instead specify threaded or other assembled bars. After coordination with the FAA, the Engineer can require extra corrosion protection. P-501 names chromium bars to ASTM A1035 and stainless steel bars to ASTM A955.
Tie bars in inspection and repair
Tie bars lie at mid-depth, so a surface or drone survey does not see them. It sees what happens at the joint above them. The PAVER manual for concrete airfields defines joint seal damage and settlement or faulting, a difference of elevation at a joint. It has no distress type for tie bars. This page gives no joint-opening limit for tie bar failure, because no opened FAA source states one.
Tie bars matter again in a slab repair. AC 150/5380-6C covers dowels or tie bars along the edge of a full depth repair. The crew either saves them by sawing just beyond their ends, or cuts and replaces them.
Frequently Asked Questions
- What does a tie bar do?
- A tie bar keeps the faces of two concrete slabs in close contact at a joint. The FAA says tie bars do not act as load transfer devices. They prevent the joint from opening, so load passes across the joint by aggregate interlock.
- How is a tie bar different from a dowel bar?
- A tie bar holds the joint closed, and a dowel bar carries load across it. FAA Item P-501 specifies tie bars as deformed steel bars and dowel bars as plain steel bars with a bond-breaker coating. The FAA says dowels provide load transfer and prevent vertical displacement between adjacent panel ends.
- Where does the FAA use tie bars in airport pavement?
- The FAA uses tie bars in a longitudinal contraction joint when the panel is up to 9 inches (225 mm) thick. The joint must lie within 20 feet (6 m) of a free edge. AC 150/5320-6G also uses them in some construction joints of thin runway and taxiway panels. Thicker panels use dowels at the same joints.
- Can a drone survey see tie bars?
- No. Tie bars sit in the middle of the slab depth, so a surface survey cannot see them. A survey can rate distresses that show at joints, such as joint seal damage and faulting. The PAVER manual for concrete airfields defines both.
References
- faa-ac-150-5320-6g
- AC 150/5320-6G, Airport Pavement Design and Evaluation FAA
- faa-ac-150-5370-10h
- AC 150/5370-10H, Standard Specifications for Construction of Airports, Item P-501 Cement Concrete Pavement FAA
- faa-ac-150-5380-6c
- AC 150/5380-6C, Guidelines and Procedures for Maintenance of Airport Pavements FAA
- faa-paver-concrete
- PAVER Distress Identification Manual, Concrete Surfaced Airfields FAA, from the PAVER system
This is a reference entry. TarmacView provides drone inspection services and doesn't sell the equipment or materials described in this glossary.
