Shear Behavior of Prestressed Beams with Steel Fiber Self-Compacting Concrete

Abstract eng:
Seven prestressed concrete (PC) I-beams were designed to study the effects of steel fibers on the casting procedure, the control of end region cracking, and the increase in shear strength and ductility of beams. Three types of concrete were used in the seven specimens. One beam was cast using normal concrete to serve as the control specimen. While three of the remaining beams were cast using normal concrete reinforced with steel fibers, the others were cast with self-compacting fiber reinforced concrete (SCFRC). Strain gauges and temperature loggers were attached to the rebars in the beams to continuously measure the strains and temperatures respectively during the casting, curing and prestressing stages. It was observed that fibers effectively reduced the tensile strains due to thermal loading in the concrete matrix. Fibers contributed substantially towards enhancing the tensile strength and also prevented stress concentration in the end zones of PC beams. Concentration of stresses in the early stages of the beams often leads to development of cracks in the end regions. However, fibers were found to be more effective with regard to their performance in the end regions of beams with SCFRC than the ones with traditional fiber reinforced concrete (TFRC). After the fabrication of the beams they were subjected to concentrated vertical loads up to their maximum shear or moment capacity using four MTS actuators. During the load tests Linear Voltage Displacement Transducers (LVDTs) were used to measure displacements at several critical points on the web in the end zone of the beams. Several LVDTs were also placed under the beams at the points of loading to measure the actual total and net displacements of the beams. Strain gauges installed on the rebars inside the beams (used previously in the early-age measurements) were also used to monitor the rebar strains during the load tests. From the load tests it was observed that the load carrying capacities of the beams with self-compacting concrete were similar to the one with normal concrete. The shear capacities of the beams were observed to significantly increase due to the addition of steel fibers in concrete. Replacement of shear reinforcing bars with steel fibers also increased the ductility and energy dissipation capacity of the structure. Hence, prestressed beams with steel fiber self-compacting concrete are very appropriate to resist earthquake loading.

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