2.2. Specimens and instrumentation
The preparation of all 48 specimens followed a standard
procedure, which has been described elsewhere [16]. The FRP
jackets were all formed via the wet lay-up process and all had
hoop fibres only. For each batch of concrete, 2 or 3 control
specimens of the same size were also tested, from which
the average values of the compressive strength of unconfined
concrete f 0
co and the corresponding axial strain "co were found.
For each control specimen, two longitudinal strain gauges,
with a gauge length of 120 mm covering the mid-height region,
were placed at 180 apart to measure the axial strains. Two
other strain gauges, with a gauge length of 60 mm, were
placed at 180 apart to measure the hoop strains. For each
FRP–confined specimen, either six or eight unidirectional strain
gauges, with a gauge length of 20 mm, were installed at midheight
to measure the hoop strains and another 2 strain gauges
of the same type were installed at mid-height to measure the
axial strains. In addition, axial strains were also measured by