Behaviour of continuous beams during repair breakout.

The main cause of deterioration of reinforced concrete is chloride-induced corrosion of reinforcement. Repairs may require that contaminated concrete around the reinforcement be broken out and replaced. The pattern of strains will change when bond is lost and if the beam carries load during the repair process, the pattern of strains will differ from those in the “as new” condition. This study aims to develop analytical procedures to represent structural behaviour and to assess the circumstances in which changes in behaviour are significant.
Previous research on patch repairs has largely focussed on simply supported beams. This paper will examine the effect of the patch repair process on the structural behaviour of two-span beams, concentrating on beams in the “weakened” state. In a statically indeterminate structure, breakout of concrete over a portion of a span causes loss of section stiffness in that region and a consequent transfer of moment to other parts of the structure. Concrete breakout at one location may therefore cause overstressing of the structure at another location. The rate at which this moment transfer takes place and the parameters which affect it are examined.
The testing programme embraced a range of parameters including the length and position of breakout. Various top and bottom reinforcement areas were chosen to investigate the influence of the exposed steel area and the difference between the elastic and plastic bending moment diagrams for the “fully bonded” specimen.