by Asad Esmaeily, A.M.ASCE; Steven D. Hart; and`Brandy Gaitan
In this paper, the authors, Sakai and Kawashima, propose a “comprehensive . . . model . . . that takes into account the effect of repeated unloading and reloading and partial loading.” This model was evaluated by conducting several tests on concrete cylinders confined by carbon-fiber-reinforced polymer CFRP material.
Three standard 150 mm300 mm 6 in.12 in. concrete cylinders were cast and cured for 28 days in a moist curing room. Two strain gauges with a length of 50 mm 2 in. were placed
longitudinally on the central part of the specimens on opposite sides. The unconfined compressive strength of the specimens was 40.7 MPa 5.9 ksi at the time of testing. Confinement was provided by two layers of CFRP attached by an epoxy adhesive, which is different from conventional confinement by steel as used in the authors’ original research. Testing was conducted by using a closed loop servocontrolled material testing system with a maximum capacity of 667 kN 150 kips. Since the envelope for CFRP confined concrete does not have the descending branch after a peak point as observed for conventionally reinforced cases, all specimens were initially loaded to 614 kN 138 kips at a rate of 62 kN 14 kips per minute to achieve sufficient plastic strain for a reasonable evaluation of the unloading/reloading paths.
There was a creep-hold of 108 min at 133 kN30 kip load level for one of the specimens. At the load level of 614 kN 138 k, the specimen with a creep-hold was subjected to three complete unloading and reloading cycles at a rate of 124 kN 28 kips per minute, the next specimen had similar cycles but at a rate of 186 kN 42 kips per minute, and the last one was loaded monotonically to 614 kN 150 kips to establish the envelope curve.
Learn more about Discussion of “Unloading and Reloading Stress-Strain Model for Confined Concrete” by Junichi Sakai and Kazuhiko Kawashima, you can download here
In this paper, the authors, Sakai and Kawashima, propose a “comprehensive . . . model . . . that takes into account the effect of repeated unloading and reloading and partial loading.” This model was evaluated by conducting several tests on concrete cylinders confined by carbon-fiber-reinforced polymer CFRP material.
Three standard 150 mm300 mm 6 in.12 in. concrete cylinders were cast and cured for 28 days in a moist curing room. Two strain gauges with a length of 50 mm 2 in. were placed
longitudinally on the central part of the specimens on opposite sides. The unconfined compressive strength of the specimens was 40.7 MPa 5.9 ksi at the time of testing. Confinement was provided by two layers of CFRP attached by an epoxy adhesive, which is different from conventional confinement by steel as used in the authors’ original research. Testing was conducted by using a closed loop servocontrolled material testing system with a maximum capacity of 667 kN 150 kips. Since the envelope for CFRP confined concrete does not have the descending branch after a peak point as observed for conventionally reinforced cases, all specimens were initially loaded to 614 kN 138 kips at a rate of 62 kN 14 kips per minute to achieve sufficient plastic strain for a reasonable evaluation of the unloading/reloading paths.
There was a creep-hold of 108 min at 133 kN30 kip load level for one of the specimens. At the load level of 614 kN 138 k, the specimen with a creep-hold was subjected to three complete unloading and reloading cycles at a rate of 124 kN 28 kips per minute, the next specimen had similar cycles but at a rate of 186 kN 42 kips per minute, and the last one was loaded monotonically to 614 kN 150 kips to establish the envelope curve.
Learn more about Discussion of “Unloading and Reloading Stress-Strain Model for Confined Concrete” by Junichi Sakai and Kazuhiko Kawashima, you can download here
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