The novel UHPC connections succeeded in resisting
all cyclic structural loads to which they were subjected
throughout the testing program. No damage was observed
within the UHPC composite connection or in the adjoining
steel connectors throughout the duration of this testing.
During the final phase of cyclic testing, the cyclic horizontal
shear stress in the field-cast UHPC haunch was 168 psi
(1.16 MPa), indicating that a minimum shear plane within
the composite connection can carry this stress.
During the static testing to failure, the UHPC test specimen
carried a peak applied shear load of 498 kip (2215 kN),
which corresponds to a horizontal shear per unit length of
12.0 kip/in. (2.10 kN/mm). At this load, the prestressed
concrete girder began to fail in a combination of horizontal
and vertical shear in the web and top flange of the girder.
Horizontal shear distress was also observed in the precast
concrete deck elements adjacent to the haunch. No damage
was observed within the UHPC connection or in the discrete
steel elements (that is, reinforcing bar or studs). The
peak horizontal shear stress on the otherwise unreinforced
field-cast UHPC haunch was 789 psi (5.44 MPa) along the
minimum shear plane.
The conventional connection specimen also survived the
full set of cyclic load applications. However, as cyclic
testing progressed, it was apparent that the connection
between the emulated steel girder top flange and
the haunch was degrading. The conventional specimen
began to show increasing horizontal movement along
the haunch interface per applied load compared with
the UHPC specimen. This increasing movement can be
attributed to progressive deterioration of the composite
connection along the interface. The deterioration continued
to increase as the cycling progressed. Regardless, the
overall performance of the conventional specimen met
the design requirements.
The conventional test specimen carried a peak applied
shear load of 445 kip (1980 kN), which corresponds
to a horizontal shear per unit length of 10.45 kip/in.
(1.829 kN/mm). At this load, the composite connection at
the emulated steel girder–to–haunch interface failed, with
nearly all of the studs in the shear span detaching from
the steel plate at their bases. By the end of the test, 10 of
the studs had completely detached and 23 had partially
detached during cyclic loading, leaving fewer studs to
carry the horizontal shear during the static loading.
Both specimens exceeded the AASHTO LRFD specifications
ultimate design capacities for the critical horizontal
shear interfaces. In the UHPC specimen, the applied
horizontal shear at failure exceeded the design capacity
of the steel crossing the emulated steel girder/haunch
interface by 66% and of the steel crossing the haunch and
deck interface by 240%. In the conventional specimen,
the applied horizontal shear at failure exceeded the design
capacity of the steel crossing the emulated steel girder
and haunch interface by 45%.