A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering, School of Engineering and Technology

Thesis (M.Eng.) - Asian Institute of Technology, 2005

With the recent development of performance based design and assessment of structures, the nonlinear static pushover analysis has become a potential tool to be utilized; while it remained to be unused for many years due to inaccuracy of the results in some cases. The adaptive forced-based pushover analysis, which was proposed few years ago, can be utilized as an alternative method which can automatically adapt higher modes and period elongation effects in lateral loading patterns. The combination of one-dimensional discrete element, fiber section and uniaxial nonlinear material model is utilized for reinforced concrete member modeling. In addition to the existing nonlinear beam elements of XFINAS package, a new nonlinear frame element, namely NLFrame1, has been derived and implemented in this study. Fiber section and uniaxial nonlinear material models are utilized to achieve reliably accurate results in nonlinear material problem. The automatic coordinate generation for both circular and rectangular sections has been further implemented. Nonlinear material models of concrete and steel reinforcements under monotonic and cyclic loading conditions incorporated in this research have been collected from many different sources. The adaptive force-based pushover analysis, nonlinear frame element, fiber section, and material model have been added as an additional performance to the current XFINAS student beam version. Verification examples are given to test all the algorithms of buckling analysis, large displacement of geometrically nonlinear static and dynamic analysis, and static and dynamic analysis with both geometric and material nonlinearities. The results considering the material nonlinearity showed an acceptable outcome of NLFrame1 element compared to the existing nonlinear beam elements. For nonlinear material and geometric verification, a series of concrete columns under monotonic and quasi-static loading has been modeled and the solutions have been compared with experimental results. According to the parametric study for nonlinear material and geometric problem, a sufficient number of elements is a more important factor compared to the size of the fibers. It is observed that for a sufficient number of elements, increasing the fiber-sizes doesnt change the results significantly. Minimum of four elements was the starting point for getting reasonable results while 10% fiber-sized from its section dimension is recommended to be used for general purposes. At the end, a preliminary 6-storey regular reinforced concrete building has been utilized. It was aimed to demonstrate the overall implemented performance of adaptive pushover analysis, nonlinear frame element, fiber section, nonlinear monotonic concrete and steel models. For further study, a full set of dynamic applications may be utilized through the use of the implemented cyclic reinforced concrete model.