When it comes to constructing pavements, roadways and other rigid slabs, reinforcement is just as important as it is for foundations or vertical concrete panels, and the potential risks from getting it wrong are just as serious as for any other form of construction. That’s why tie bars are used in construction projects of this kind, mitigating against a wide variety of construction problems, and keeping road and pavement users safe. In this article, we take a look at exactly what tie bars are in construction, how they are used, and the way in which spacing for tie bars is calculated.
What is a tie bar?
A tie bar is simply a form of concrete reinforcement. Usually made of epoxy-coated steel, tie bars have deformations marked into them like other rebar products, and they come in different diameters, for use in a wide variety of concrete projects. They are positioned at the mid-depth point of a concrete slab, to join longitudinal sections together, or at an edge joint to join a slab to a curb or shoulder.
Benefits of using tie bars in construction
Properly positioned and spaced tie bars help prevent lane separation, differential settlement of adjacent slabs and transverse cracking. Obviously, all of these issues are of serious concern in the construction of roadways, pavements and other surfaces that are designed to handle either pedestrian or vehicular traffic, since the potential for serious accidents or injury is significant. Overall lifetime repairs are also lessened by using tie bars, leading to lower lifecycle costs.
As well as minimising lane separation, settlement and transverse cracking, tie bars also help to support the reinforcement mat across the entire slab, providing continuity and consistency.
What is the difference between tie bars and dowel bars?
When talking about roadway or pavement construction, you’ll often hear the phrase ‘tie bar’ mentioned alongside ‘dowel bars’, so it’s important to recognise the difference between the two terms. The key point to grasp here is that tie bars do not have a load-transfer capacity or function, whereas dowel bars are specifically used for load transfer. Tie bars are used to ‘tie together’ longitudinal joints, to prevent separation of lanes, whereas dowel bars are used between transverse joints to allow load transfer and intentional movement.
How are the dimensions and spacing of tie bars designed?
Like all concrete reinforcement products, tie bars are covered by specific British standards, to ensure they are manufactured in a consistent way, and that they are fit for purpose. Diameters are 15mm, 20mm, 26.5mm and 32mm, and bars are generally supplied in 6m lengths, although a bespoke cutting service is also available. In order to calculate the correct spacing and placement of tie bars, the length of the slab is used, along with the thickness of the slab. It should be stressed that tie bars do not have any load-transfer function within a construction element, and should never be relied upon for that purpose. Generally speaking, the larger the diameter of the tie bar steel, the bigger the distance between tie bars can be, given the same depth of poured concrete.
Bending Tie Bars
It was at one time common practice to bend the tie bars that were protruding from one lane of a concrete pavement or roadway, until they were needed in the construction of the next lane, when they would be straightened ready for the next concrete pour. This practice is no longer recommended, as it could lead to weakening of the steel tie bars, and a reduced lifespan or even structural problems within the road surface or pavement.
To summarise, tie bars perform a vital role in the construction of roadways and pavements, bringing stability, longevity and reliability to a project. It might be tempting to cut costs by not installing tie bars correctly, or at all, but the price potentially paid further down the line, in terms of costly repairs, makes this a very risky strategy indeed.
Contact us today to discuss your pavement and roadway projects, and to find out just how cost-effective tie bars can be, when implemented in the right way.