McKee, Codi David (2018-05). Analysis of Experimental Behavior of Pretensioned Concrete Bent Caps Using Motion Capture Systems. Master's Thesis. Thesis uri icon

abstract

  • Precast, pretensioned concrete (PSC) bent caps allow for accelerated bridge construction while reducing, or eliminating, cracks typically seen in reinforced concrete (RC) bent caps. When cracks do form in PSC caps, they occur at internal discontinuities such as those created by emulative cap-to-column connections and interior voids for weight reduction. To assess the behavior of PSC bent caps, an experimental test program was conducted of six full-scale bent cap sub-assemblages. This thesis focuses on the behavior of the specimens with interior voids and monitoring of initial cracking using an Optotrak Certus motion capture system. Visual observations of the tests indicate that interior voids significantly decrease the cracking shear strength of the caps. Void detailing did not appear to have a significant impact on the onset of shear cracking, but did impact the orientation and extent of shear cracking at design loads. Beyond design loads, differences in the behavior were negligible. Failure occurred in the negative bending region with spalling of concrete in the compression zone for the specimens with varied void details. A more abrupt failure occurred in the bent cap with a voided overhang due to additional spalling of concrete along a compression strut along the overhang interior void. The Optotrak Certus system provided displacement data for a dense grid-like array of light-emitting diodes (LEDs). LED displacements were validated using traditional instrumentation and treated as nodal displacements in a mesh of four-node isoparametric quadrilateral elements to establish strains. Regions of concentrated principal tensile strains indicated the regions and orientation of observed cracks, indicating the promise of motion capture systems as a tool for assessing the development of cracking in PSC members.
  • Precast, pretensioned concrete (PSC) bent caps allow for accelerated bridge construction while reducing, or eliminating, cracks typically seen in reinforced concrete (RC) bent caps. When cracks do form in PSC caps, they occur at internal discontinuities such as those created by emulative cap-to-column connections and interior voids for weight reduction. To assess the behavior of PSC bent caps, an experimental test program was conducted of six full-scale bent cap sub-assemblages. This thesis focuses on the behavior of the specimens with interior voids and monitoring of initial cracking using an Optotrak Certus motion capture system.

    Visual observations of the tests indicate that interior voids significantly decrease the cracking shear strength of the caps. Void detailing did not appear to have a significant impact on the onset of shear cracking, but did impact the orientation and extent of shear cracking at design loads. Beyond design loads, differences in the behavior were negligible. Failure occurred in the negative bending region with spalling of concrete in the compression zone for the specimens with varied void details. A more abrupt failure occurred in the bent cap with a voided overhang due to additional spalling of concrete along a compression strut along the overhang interior void.

    The Optotrak Certus system provided displacement data for a dense grid-like array of light-emitting diodes (LEDs). LED displacements were validated using traditional instrumentation and treated as nodal displacements in a mesh of four-node isoparametric quadrilateral elements to establish strains. Regions of concentrated principal tensile strains indicated the regions and orientation of observed cracks, indicating the promise of motion capture systems as a tool for assessing the development of cracking in PSC members.

publication date

  • May 2018