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    was 240 GPa and 0.176 mm, respectively. Fifty millimetres
    wide strips were used in all the strengthened specimens.
    Two different number of layers and strip spacings of
    0.75D and 0.50D were investigated, D being the full depth
    of the beam. The spacings were chosen as they were the
    minimum spacing required for shear in the Australian Con-
    crete Code, and it was expected in future that existing
    structures would be strengthened for both actions.
    A 150 mm overlapping length of strip was applied in the
    longitudinal fibre direction.
    The test setup is shown in Fig. 2. One end of the speci-
    men was fixed by a steel collar to an anchored base so no
    longitudinal, vertical, transverse and rotational movements
    were allowed. On the other end, the specimen was sup-
    ported by a spherical seat on linear bearings that allowed
    the loaded end to twist freely and elongate/shorten. Torque
    was applied on the 1.8 m test zone through the lever arm by
    a single 250 kN capacity hydraulic actuator.
    Load cells were placed under the spherical seat and the
    hydraulic actuator to measure applied torque. LVDTs and
    inclinometers were used to determine the exact amount of
    extension/shortening and twist respectively. Strain gauges
    placed on steel reinforcement and CFRP strips at specific
    locations were used to determine the strain distribution.
    Photogrammetry was also used to capture the deforma-
    tions of the beams under torsion.2.2. Experimental results
    The torque-twist curves for all six tested beams are
    shown in Fig. 3. The pre- and post-cracking stiffness, crack-
    ing and ultimate torque capacity of both solid and box-sec-
    tion RC beams are closely related to the amount of CFRP
    applied (Table 2). Up to a 40% and 78% increase in crack-
    ing and ultimate strengths from FH050D2 is observed. For
    the solid RC beams, an increase of 8% and 49% of crackingand ultimate strengths were recorded for FS050D2. The
    presence of the CFRP strips inhibited these cracks from
    propagating and widening compared to the control beams.
    The steel reinforcement was found to have yielded at peak
    load for all the beams. Further detailed discussion on the
    strains measured in the reinforcement can be found in
    Hii and Al-Mahaidi [2].
    Generally, the failure mechanism observed is similar for
    all the strengthened beams. At higher load levels, cracking
    propagated along the CFRP strips (Fig. 4b). This indicates
    partial debonding. However, immediate failure through
    debonding of the CFRP reinforcement did not occur due
    to the use of full hoop strips providing the necessary
    anchorage and support to the debonded portions. Review
    of the high-speed video recordings show that at failure,
    rupture of the CFRP strips first occurred at the corners,followed by peeling away with a thin layer of concrete still
    bonded to the laminate (Fig. 4a). It is observed in the
    strengthened beams that the succession of CFRP ruptures
    occurred at the corners of the beams, and not necessarily at
    locations intersecting the spiral cracks.
    3. Close-range photogrammetry measurements
    The investigation was conducted with the aid of photo-
    grammetry, which is the process of obtaining precise mea-
    surements about physical objects by means of photography
    [7]. Reflective targets were placed on the test zone in each
    beam, on both the concrete surface and the CFRP strips
    as shown in Fig. 5. During testing, loading of specimens
    was paused at certain intervals to allow photogrammetry
    surveys to be taken. By taking photos from different loca-
    tions, the data was automatically processed on a computer
    workstation to obtain the precise location of each target.
    The statistical accuracy of the photogrammetry survey
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