A routine method for measuring bond stress, steel strain and slip in reinforced concrete beams at service loads

This paper presents a technique designed to give routine measurements of the average bond stress, average steel strain and total slip of a reinforcing bar relative to its surrounding concrete, between cracks in the constant moment region of concrete beams at their service loads. Tests were conducted on double pull-out concrete prisms reinforced with steel bars that had been fitted with transverse anchor bars at their centre. The major variables considered in the study that generally influence bond stress were type and size of bar, concrete strength and loading history. The method provides data to establish a relationship between the average bond stress, maximum steel stress and the total slip of the reinforcing bar. Equations have been derived on the basis of a linear distribution of the strain in the steel bar for the computation of average bond stress and average steel strain that are required for a rational calculation of crack width and deflections of structural concrete members.