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increased the beam moment strength in the region adjacent to the column face, and thus lead to
spreading of the beam inelastic deformations away from the column face, as shown in Fig. 5c. In
addition, the external steel plates controlled the opening of the gap at the beam-column interface,
reducing pinching in the load vs. displacement hysteretic loops compared to Specimen 1 The strength
of Specimen 3 was governed by the beam moment strength, which was increased due to the use of
steel FRC. For all drift levels, no decay in strength was measured and only little decay hi stiffness
during repeated cycles at the same drift level was observed. Specimen 2, which had the same details as
Specimen 3 but with standard holes in the external steel plates for connection with the beam throughbolts,
exhibited a response somewhat between those of Specimens 1 and 3 due to slip of the external
plates that did not control the opening of the gap at the column face as effectively as the plates with
tight holes used in Specimen 3.
Specimen 4 had no longitudinal beam bars, and thus the steel reinforcement was provided by the
embedded steel truss. The moment connection in this specimen was achieved entirely through external
steel rods as shown in Fig 4. Specimen 4 showed a load vs. displacement response characterized by
full hysteretic loops (Fig. 5d). The strength of this specimen was governed by yielding of the truss
chords, which occurred in the region adjacent to the embedded steel tubes connecting the steel truss
with the external steel rods. In Specimen 4, tlexural cracking concentrated at this location and at large
drift levels a significant opening of a single crack was observed in the FRC beam. Severe local
buckling of the truss chords was observed at 5% drift, leading to a significant decay in the specimen
strength.
Energy Dissipation Capacity
The energy dissipation capacity exhibited by the test specimens was evaluated by comparing the area
of the hysteretic loop corresponding to the last cycle at a particular drift level with that of an equivalent
elasto-plastic system with a stiffness corresponding to the initial stiffness of the specimen and the
strength measured during the first cycle at the story drift level of interest. Fig. 6 shows the energy ratio
(specimen vs. equivalent elasto-plastic system) for the four test specimens. As can be seen, Specimen 1
exhibited poor energy dissipation capacity with energy ratios below 12% for displacement levels larger
than 1.0% drift. On the other hand, Specimen 4, with external steel rods, exhibited energy ratios as
high as 47%. Specimens 2 and 3 exhibited energy ratios of approximately 15% and between 19-25% at
story drifts larger than 2%, respectively.
Beam Rotations
Rotations in the FRC beams were measured with linear potentiometers over a length of 22 in. from the
column face (1.1 x beam depth). In Specimen 1, beam rotations primarily concentrated at the beamcolumn
interface due to significant slip of the beam longitudinal reinforcing bars. In Specimen 2, due
to the use of standard holes in the external steel plates, the opening of the gap at the beam column
interface was not adequately controlled, and thus beam rotations consisted of both concentrated
rotations at the beam end and in the beam region adjacent to the column face. However, in Specimen 3
with a combination of internal beam bars and external steel plates with tight holes, significant rotations
were measured in the region adjacent to the through-bolts due to relocation of the plastic hinge region
and an adequate control of the opening of the gap at the beam-column interface. In this specimen,
rotations in excess of 4% were measured over approximately one depth from the column face. In
Specimen 4, beam rotations concentrated primarily in the beam region connected to the external steel