210. cyclic performance characterization of large diameter reinforcing steel bars and mechanical couplers

Department: Structural Engineering
Faculty Advisor(s): Jose I. Restrepo

Primary Student
Name: David Elias Duck Rodriguez
Email: dduck@ucsd.edu
Phone: 858-534-5685
Grad Year: 2017

Current design requirements for bridge columns in the State of California rely on the ductility provided at specific regions of the columns to withstand rare but strong intensity earthquakes. Such ductility is achieved through the development of plastic hinges which are capacity designed to ensure the column is able to develop and maintain the inelastic deformations assumed in the design. Experimental work on bridge columns funded by Caltrans over the past two decades has shown that such design requirements are satisfactory and that the deformation capacity of the columns may ultimately be limited by fracture of the longitudinal reinforcement after buckling. Most experimental work, however, has been limited to the use of small-diameter bars given the current limited use of large-diameter bars as longitudinal reinforcement in columns in the state. The limited use is due in part to the difficulty in testing the bars under large amplitude strain cyclic reversals. While previous attempts have failed at characterizing the response of these bars, through the innovative design of a project-specific loading frame, the ambient temperature low-cycle fatigue life of large diameter bars has proven successful by the current research effort. A key element in the success of the experimental work is due to the use of a sulfur-based concrete, as part of the loading apparatus, in order to apply the required cyclic loads. Furthermore, issues with the rigidity of the loading frame and strain measurements experienced by previous attempts have been resolved. While the collected data can be used, and compared with the current deterministic fatigue models, a more physical approach in determining the fatigue life of the bars is proposed. The proposed model is not restricted, like most current models, to the use of constant amplitude cyclic loading to determine the fatigue life of the bars. Furthermore, the accumulation of damage to the bars, related to the formation and propagation of micro-cracks in the buckled bar during cyclic loading is captured by the proposed model. The successful characterization of the fatigue life of continuous and mechanically spliced large diameter bars can ultimately lead to their widespread use as longitudinal reinforcement in bridge columns in the state as well as to accelerate bridge construction, through the use of precast systems.

Industry Application Area(s)
Civil/Structural Engineering | Materials | Earthquake Engineering

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