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Specimen 1
Specimen 1 represented an interior beam-column subassembly with beams framing into the column
from two opposite sides (Fig. 1). As mentioned above, a 20 in. square beam and an octagonal shape
column with a side length of 8.25 in. were used in this specimen. The column was constructed prior to
the beam to simulate the existing columns of the structure. The FRC beam had steel hooked fibers with
a volumetric fraction of 1% and the beam reinforcement consisted of 4 #5 top and bottom longitudinal
bars, #3 closed stirrups, and a steel truss embedded in FRC (Fig. 2). In this specimen moment transfer
in the connection region was achieved by passing the longitudinal beam bars through holes drilled in
the RC column, which were later epoxy injected. The chords of the steel truss were connected to a steel
plate with slotted holes that was in turn bolted to the column (Fig. 2), and thus the truss was not
expected to contribute to moment strength in the beam plastic hinge region adjacent to the column
face. The truss, however, was designed to resist the shear force demand in the plastic hinge in addition
to supporting the permanent steel forms during the concrete casting process.
The original column design in Specimen 1 included 12 #5 longitudinal rebars representing a steel ratio
of 1.1%. However, because core drilling of the column would be performed in this retrofit scheme,
four bars were eliminated to account for possible cutting of longitudinal reinforcement during the
drilling process. The column transverse reinforcement consisted of a #3 spiral with a 4 in. pitch. The
spiral reinforcement was cut at different locations in the joint region to simulate possible cutting during
column core drilling. To maintain adequate concrete confinement after cutting of the column
transverse reinforcement, the column was wrapped with glass fiber sheets in the connection region.
Specimen 2
Specimen 2 was similar to Specimen 1. Moment transfer in the connection region was achieved by
passing the beam longitudinal reinforcement through holes drilled in the RC columns, as for Specimen
1, in combination with external steel plates (Fig. 3). The purpose of these external plates was to control
the opening of gap at the beam-column interface, as well as to increase the beam moment strength in
the region adjacent to the column, forcing the plastic hinge to form away from the column face.
Connection between the FRC beam and the external reinforcement was achieved through a 1.25 in.
steel rod that was embedded in the beam section (Fig. 3). Standard holes were drilled in the steel plates
to connect them to the beam through-bolts. To decrease the moment capacity in the relocated plastic
hinge region so as to maintain a shear demand comparable to that in Specimen 1, the beam longitudinal
reinforcement was reduced to 2#5 and 2#4 top and bottom rebars.
Specimen 3
This specimen represented an exterior beam-column subassembly and used a moment connection
consisting of internal beam rebars and external steel plates, as in Specimen 2. A beam stub was used in
the opposite (back) side of the column for anchorage of the beam longitudinal reinforcing bars.
Because the use of hooks at the bar ends would pose construction difficulties, the beam longitudinal
bars were terminated with a mechanical anchor. In Specimen 3, 2 in. through-bolts were used for
transfer of forces between the FRC beam and the external reinforcement. In addition, tight holes were
used in the external steel plates to avoid any slip that would lead to "pinching" in the load vs.
displacement hysteretic response (Fig. 3). With regard to beam transverse reinforcement, #3 stirrups
were used only adjacent to the through-bolts and reinforcement mechanical anchors. No transverse