As a part of an experimental program investigating the effects of a variable axial load on the seismic behavior of bridge piers, six scaled re inforced concrete bridge columns with circular sections were tested at the Structural Laboratory of the University of Southern California (USC). The primary experimental parameters were the axial load and loading pattern. The loading program included a combination of a constant, proportionally or nonproportionally variable axial load and a monotonic or cyclic lateral displacement. The objectives were to study the effects of different loads and the displacem ent paths for both the axial and lateral loading directions, to provide the benchmark data for dynamic and large- scale tests, and to evaluate existing material models and analytical methods.
The effects of the axial load and loading pattern were observed to be significant in the flexural strength capacity, the failure pattern, and the ductility and deformation of the columns. The plastic hinge formation was significantly different in the case of a variable axial load, requiring a modification of the existing plastic hinge models. The conventional analytical methods underestimated the flexural strength for high compressive axial loads in a monotonic analysis. Based on the experimental observations, several models for steel and c oncrete stress-strain behavior and two plastic hinge methods were developed and then employed in a computer program developed to address the analytical needs of the research.
Chapters 1 to 5 cover the preparation and phases of the experimental studies. Problem areas, research objectives, previous research on the subject, the development of experimental methods, the method developed and implemented in this research, the experimental program, and results are discussed. Chapters 6 to 9 discuss different material models and various analytical methods, and the models and methods developed in the research. The main features of USC_RC, the application developed to address the analytical needs of this research, are discussed, and the experimental results are compared with the analytical evaluations.
The experimental and analytical studies a nd conclusions are summarized in Chapter 10. Test results are included in terms of different graphs in Appendix 1. The computer code written in FORTRAN 95 and used in the aforesaid application is included as Appendix 2. Appendix 3 explains the simple multispring model developed to simulate a circular reinforced concrete section for a nonlinear degrading hysteretic moment-curvature analysis.
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