Structural behaviour of reinforced concrete beams strengthened by epoxy bonded steel plates.

The development of synthetic adhesives based on epoxy
resins has opened new possibilities for bonding structural
materials together.
The present work was concerned with the use of epoxy
resins to strengthen reinforced concrete beams by externally
bonded steel plates.
It was found in the first part that the assessment of
the properties of the epoxy adhesive is of paramount importance
as they varied considerably with the thickness of the test
specimen and the rate of loading.
The adhesive proved to offer a bond stronger than
concrete in shear and resulted in a composite action between
the beams and steel plates.
Preloading the beams prior to strengthening them did
not have any adverse effect on their behaviour. The added
strength from the plates was fully exploited even in beams
which were held under a preload of 70% of their ultimate
strength while being strengthened.
Stopping the plate in the shear span, short of the
support, created a critical section where premature bond
failure occurred beyond a certain plate thickness. Failure was
caused by the combination of high peeling and bond stresses
present in the region where the plate was stopped. These
stresses were due to the transfer of tensile forces from the
plate to the bars in that region and were higher with thicker
plates. Bonding steel plates on the tension face of the beams
increased their shear capacity by 9 to 15%. This may have been
due to dowelling action from the plates which had a greater
contact area with concrete than an equivalent amount of
internal steel bars. The use of externally bonded steel as
shear reinforcement was effective but requires further
investigation. The external web strips failed prematurely as
compared to equivalent stirrups.
The long term deformations in plated beams were
highly affected by the conditions of their environment but
despite 47 month exposure no visual deterioration of the
concrete-epoxy-steel joint was observed.