Ransome Bar

We ask for probes on a regular basis, usually to find out what something useful about unknown hidden structure. On a recent project we asked for probes through a cellar slab. Our instructions were to remove the concrete while leaving the rebar in place, so the final probes looked like this:

The rebar that was exposed is square in cross-section, and twisted along its length. This style is known as Ransome Bar after its inventor, Ernest Ransome.

The twist was Ransome’s method of solving a basic problem of reinforced-concrete construction: how do you get the rebar and concrete to act together? When there is tension in the bars, they tend to slip relative to the surrounding concrete, destroying the composite action that is the basis of the combined material. The general solution to this problem has been to use “deformed” bars, where some kind of geometric irregularity is used to provide the bond between the steel and concrete.

Ransome was one of the first designers and builders in the Untied States to successfully create large reinforced-concrete buildings and his bar was popular for more than 30 years, into the 1910s. Interestingly, Ransome bar fell out of use because it was too good. The helical twist produced far more bond strength than is needed and cost more than other methods of creating deformation. So we don’t see new Ransome bar but when we find it in old buildings we know that we don’t need to worry about bond strength.