| Summary: | 碩士 === 國立臺灣科技大學 === 營建工程系 === 101 === Abstract (Displacement-Based Design for Precast Segmental Concrete Columns)
Precast concrete bridge construction has been proved to be an efficient solution in accelerating bridge construction and minimizing traffic disruption. However, due to concerns with the seismic performance of such type of construction, its application in seismic regions is limited. This research presents results of the development method to predict the real behavior of precast segmental post-tensioned concrete bridge columns for use in seismic regions. The developed bridge columns adopted unbonded post-tensioning systems to decrease prestress loss due to strong seismic events. In addition, to increase hysteretic energy dissipation, mild steel energy dissipation bars (ED bars) which are continuous across the segment joints are added to the columns. Moreover, The ED bars are additionally unbonded at the critical joint to avoid premature fracture.
The improved method adopted from Displacement Based Design (DBD) has been developed to achieve the good understanding about the behavior of the precast segmental concrete column. The modification in the damping theory corresponding to the equivalent viscous damping of the hysteretic behavior of the precast has been reexamined. A simplified analytical model for static pushover analysis proposed by Ou et al. (2010) has been adopted to predict the capacity and the yield displacement of the column. In addition, a stiffness degrading hysteretic model for response-history analysis which has been proposed by Ou et al (2007) is conducted to examine the seismic performance of the proposed columns with different design parameters.
Design recommendations for the proposed segmental bridge column are presented, and are illustrated by a design example.
Abstract (Splitting Bond Behavior of No. 14 Bars Grouted in Steel Corrugated Ducts)
Recently, many applications in the construction engineering have been growing rapidly. The latest development research was conducted is about joint connection performance. Because amount of uncertainty in this application, it is quite interesting to conduct the experiment related to joint connection behavior. The use of a few large-diameter reinforcing bars for the construction of precast concrete bridge bents allows simplified construction by reducing the number of alignments to be made in the field. These bars are grouted into ducts in some connection application in the precast concrete bridge construction. In the proposed precast concrete substructure system, the grouted bars carry tensile forces across the joint connection. This joint is the yielding element in the structural system, and it is crucial to the performance of the structure that the bars yield before other failure mechanisms, including bond failure, occur. Use large bar-diameter bar in the connection can provide benefits with reducing the depth of the embedded length of the connection which commonly require and restricted by American Association of State Highway and Transportation Officials (AASHTO) bridge code in bridge application system. Designers and contractors prefer this type of precast connection over other types because the volume of grout that is required to complete the connection is minimized.
For this project, 17 splitting tests were conducted to determine the bond characteristics and development length of large-diameter bars grouted into ducts. The main test parameters that influence connection performance are identified. The bars tested in size #14. Splitting tests conducted with embedment lengths of at least seven, nine and eleven bar diameters. The splitting failure was expected to be the failure mode, when consider applying thin cover depth in the connection. The tests and subsequent analysis showed that the bond of these grouted connections is significantly better than the bond of bars cast directly into concrete. Furthermore, amount of number transverse reinforcement bar in the embedded length also contribute to increase the bond capacity. The development lengths needed to fully anchor the bar are therefore within the available depth requirement.
Results from seventeen large scale beam-end tests are reported, and the effects of the studied parameters on connection behavior are evaluated. A simple phenomenological bond-slip model is presented that can be used to estimate the observed behavior. The development of the anchorage design provisions considers the stress in the connectors at service load levels. Observed splitting modes of failure are precluded by incorporating adequate levels of safety in the development of the design recommendations.
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