Investigation into the residual strength of reworked reinforcement bars in reinforced concrete structures

Abstract

Reinforced concrete is a major material of construction in this country. A key component of this material is steel reinforcing bars. Sometimes these bars are bent wrongly, straightened and re-bent, resulting in the altering of their original characteristics. Some of such steel has been known to be used whereas some has been condemned as unfit for reinforcing purposes.

This dissertation reports on investigation into the residual properties of reworked steel including yield strength, ultimate strength, modulus of elasticity and ductility. Comparison of these has been done against those of normal reinforcement bars using stress strain plots resulting from tensile tests. A comparison of the behavior of reworked steel as opposed to that of normal steel bars in reinforced concrete has also been done using bending tests on reinforced concrete testbeams built some using normal and others reworked bottom reinforcement bars.

In these tests, load-deflection relationship, beam side strains and ultimate load were investigated. From the investigations residual crookedness and cracking during the rework were found to cause reduction of yield and ultimate strength of the reworked bars by up to 3 %. Reworkingwas also found to reduce ductility. The reduction was however small and the reworked bars were found to still meet the codes' requirement for minimum elongation. More than half the number of reworked bars tested broke away from the reworked region, an observation suspected to be the result of work hardening on the region of the rework.

Further work could be done with a large enough number of samples to satisfy statistical requirements, and to vary the number and amount of rework to establish a relationship between property change and number / amount of rework. This can then be used to suggest modifications on the current design formulae and to look into the practicality of having a design based on serviceability and checked at the ultimate limit state, since it has been established that the reworked bars might be good within the serviceability limit.